Dual subwoofers of different sizes [Text View]

sivadselim

10-26-08, 02:34 PM

No way, if you place them properly.Please read the explanation of why it is problematic in the thread I linked to in Post#13, above. Without EQ, unless you are very lucky and your room somehow solves the problem, there is no getting around it. The issue is pretty obvious. It's not rocket science. I do not understand why people have such a problem grasping it.

I don't have a laptop yet to do any measurements.
But I have used down loaded test tones with a spl meter to see what the difference in db increase there is between 1,2 and 3 subs. Maybe crude but it still gives me an idea. I know how loud the subs go with 1,2 and 3 subs playing in over all spl.You can find many measurement of the Pb10 and you can look at the Epik thread pg13 post #389 and someone charted ther Plus/2 and there Valor. My meter shows the Valor going as loud as 2 Pb10 in the low end with test tone. Yes it may not be accurate but I doubt I'm being cheater with a sealed Valor on the low end. My point is I wouldn't use 3 if it wasn't better for HT. The 3 play alot louder than 2. Different subs yes sound good yes. Sure 3 or 2 Valors would probably be better but that wasn't an option at the time. And I can truly belive 2 Pb10 and one Valor would sound better than 3 Pb10. So ime similar subs work in my room collated. So what different subs have you compared to know it won't possibly work? I agree a Vrp1000 won't mix well with a Pb13 ultra.Based upon this response, I would be led to say that you do not really understand the issue. Have you read the posts of craig john's and mine at the link I am referencing or not? And if so, is the issue apparent to you or not?

You still have not explained how you calibrate your 3 subs. Ideally, the goal would be for each individual sub to contribute equally to the overall output. Collocated like that it may not be so important, but I would still be interested to know how you decided to split the duty across the 3 subs and what your logic or rationale was.

goneten

10-26-08, 03:06 PM

The NS12 is a good driver, very linear and very clean, but obviously they don't have nearly the output potential of a 33mm xmax 18.

Due to the fact that both subwoofers have vastly different output capabilities (and FR curves), how would you maintain less distortion and greater output across the range without causing phase issues and/or causing distress to the weaker subwoofer as output increases ?

BUT, they do a fantastic job of smoothing the overall room response from 40-120Hz even without extra EQ.

How do you calibrate two subwoofers with two completely different LF curves and output capabilities without causing phase anomalies and/or bottoming of the weaker subwoofer at increasing output levels ? How would you calibrate as to maintain a linear progression in both output and frequency response ?

I have pen and paper at the ready.

Regards,

Ironmike86

10-26-08, 03:26 PM

Please read the explanation of why it is problematic in the thread I linked to in Post#13, above. Without EQ, unless you are very lucky and your room somehow solves the problem, there is no getting around it. The issue is pretty obvious. It's not rocket science. I do not understand why people have such a problem grasping it.

Based upon this response, I would be led to say that you do not really understand the issue. Have you read the posts of craig john's and mine at the link I am referencing or not? And if so, is the issue apparent to you or not?

You still have not explained how you calibrate your 3 subs. Ideally, the goal would be for each individual sub to contribute equally to the overall output. Collocated like that it may not be so important, but I would still be interested to know how you decided to split the duty across the 3 subs and what your logic was.

I read the link. Yes I understand it's not hard. For me it's pure spl for HT. I have 2 Pb10 identical. Adding the Valor gives me alot more spl collated than running the 2. I've checked it with downloaded test tone on a cd like I said previously. Playing the single Valor which I do for music is nice doesn't need to go as loud. But for HT it good but keeping my Pb10 and letting them run makes the spl loud like I like. probably a little hot but that what I like more over head. The lower frequency is similar. Yes maybe without eq there maybe some loss in the upper region but I can't tell. probably with eq I can make it sound better . All 3 identical sub would sound better if the were Valors. I doubt 3 Pb10 would sound as good. But for Ht I maybe losing some of the Valor capabilities? But playing it by itself isn't as good. I only can calibrate with a spl meter and test tones like I said before. I'm just posting if you have 2 different subs that are similar all you can do is try. Sure the same is probably better but this post make it seem like it would never work. When I buy a lap top or some sort of eq and I can graph then I can see. But many ppl do it show graphs and have good results. Unless you have killer hearing and can tell every sound like some ppl who say they do. Most ppl I know can't tell the difference with there ears. So imo that's what counts. Especially when I use the test tone and they measure similar. But they are collated both subs are good @20hz. Maybe losing in the upper frequency in the Valor but I can't tell. A single Valor doesn't give enough spl for me.2 Pb10 doesn't give enough spl 3 subs do. Not the spl but I don't want them to bottom out or hear the ports so I can run the a little hot 3-4 db with low volume. Pretty easy. The best thing would have been buy a big killer sub but I have space issues and the Valor /Pb10 is as wide as I can go. Until I diy some 18"

sivadselim

10-26-08, 04:14 PM

I read the link. Yes I understand it's not hard.

I'm just posting if you have 2 different subs that are similar all you can do is try. Sure the same is probably better but this post make it seem like it would never work.I'm not alluding to your particular situation, but what would be the point of someone adding a dissimilar sub that could go 5Hz lower than what they currently owned if those extra 5Hz were never properly utilized and were always being produced at a lower output level than they should be relative to what their level would be were the more capable subwoofer used alone? There wouldn't be. It'd be much better to simply use the more capable subwoofer, alone, and hear those extra 5Hz correctly, at the proper output level.

Just because you have 2 subs on hand doesn't mean that you should use them. In almost all cases the extra output that a lesser sub would provide can easily be achieved by simply increasing the output of the more capable sub, used alone, by 3 to 6 dB. This, very obviously, would also raise the volume of that extra 5Hz on the bottom end by 3 to 6dB relative to the level it would have been were both subs used together. That extra 5Hz was one of the main reasons a more capable sub was purchased in the first place. Why pay for it and then, not use it? One single, more capable sub is better than one more capable sub paired with a lesser sub. It's a no-brainer.

Unless you have EQ (or are very, very lucky), there is no way to adjust both subs' levels so that your response is flat beyond the low-end capability of the lesser sub and on down through to the low-end capability of the more capable sub. There just isn't. It's impossible. You can't break the laws of physics.

Ironmike86

10-27-08, 12:36 AM

Unless you have EQ (or are very, very lucky), there is no way to adjust both subs' levels so that your response is flat beyond the low-end capability of the lesser sub and on down through to the low-end capability of the more capable sub. There just isn't. It's impossible. You can't break the laws of physics.

Can't break any laws sure. But with 2 Pb10 they bottom out / port chuff in movies with alot of bass. The single Valor runs out of gas. All three gives me the bass I want.Calibrated a little hot.2-3db. Increasing a sub by 6db how do you do that? When I went from one Pb10 then added another collated I gained 6db. So how do you increase one sub to output 6db more?Unless you have an eq that can do this? Both subs have similar frequency in the low range. I dunno why it's so hard to feel it's not possible to mix subs collated. Like I said if it didn't sound better I wouldn't do it. Sure a Ultra Pb13 one of those probably be better than my 3 subs. But it wouldn't fit in my space.

Down

10-27-08, 09:11 AM

I'm not alluding to your particular situation, but what would be the point of someone adding a dissimilar sub that could go 5Hz lower than what they currently owned if those extra 5Hz were never properly utilized and were always being produced at a lower output level than they should be relative to what their level would be were the more capable subwoofer used alone? There wouldn't be. It'd be much better to simply use the more capable subwoofer, alone, and hear those extra 5Hz correctly, at the proper output level.

Just because you have 2 subs on hand doesn't mean that you should use them. In almost all cases the extra output that a lesser sub would provide can easily be achieved by simply increasing the output of the more capable sub, used alone, by 3 to 6 dB. This, very obviously, would also raise the volume of that extra 5Hz on the bottom end by 3 to 6dB relative to the level it would have been were both subs used together. That extra 5Hz was one of the main reasons a more capable sub was purchased in the first place. Why pay for it and then, not use it? One single, more capable sub is better than one more capable sub paired with a lesser sub. It's a no-brainer.

Unless you have EQ (or are very, very lucky), there is no way to adjust both subs' levels so that your response is flat beyond the low-end capability of the lesser sub and on down through to the low-end capability of the more capable sub. There just isn't. It's impossible. You can't break the laws of physics.

Not to derail the thread, but since it's certainly related AND in you I have someone well versed, apparently, in the trade offs of this scenario, I'd appreciate your opinion on something.

I've been contemplating mixing subs, as I currently have an older PB10-ISD and will be purchasing a Knight or MFW-15 in the next couple weeks. I know this a loaded question that would probably require measurements that I don't have, so forgive me.

Would losing the extra extension of the new sub be an acceptable trade off given the leveling of freq. response? Assuming no more tweaking than running MCACC and setting levels with an SPL meter?

craig john

10-27-08, 12:15 PM

Would losing the extra extension of the new sub be an acceptable trade off given the leveling of freq. response?
Honestly, only you can answer that question. If you are going to spend the money to get a subwoofer with more output and deeper extension, are you willing to waste it by mating it with a lesser sub that will hold it back? Not only will you lose the lower extension, but you'll lose the maximum output capability, (i.e., the better sub will never be able to play louder than the lesser sub because the lesser sub will distort and possibly be damaged.)

One would need to know how much FR improvement would be realized with the two subs before making a value judgment about the benefits.

Craig

Down

10-27-08, 12:45 PM

Honestly, only you can answer that question. If you are going to spend the money to get a subwoofer with more output and deeper extension, are you willing to waste it by mating it with a lesser sub that will hold it back? Not only will you lose the lower extension, but you'll lose the maximum output capability, (i.e., the better sub will never be able to play louder than the lesser sub because the lesser sub will distort and possibly be damaged.)

One would need to know how much FR improvement would be realized with the two subs before making a value judgment about the benefits.

Craig

Thanks for the response.

I'd figured that was the case, however, since people are always asking subjective, "unanswerable" questions around here, I figured I should go ahead and give it a try.

:D

sourbeef

10-27-08, 02:27 PM

Honestly, only you can answer that question. If you are going to spend the money to get a subwoofer with more output and deeper extension, are you willing to waste it by mating it with a lesser sub that will hold it back? Not only will you lose the lower extension, but you'll lose the maximum output capability, (i.e., the better sub will never be able to play louder than the lesser sub because the lesser sub will distort and possibly be damaged.)

One would need to know how much FR improvement would be realized with the two subs before making a value judgment about the benefits.

Craig

This is my dilemna. I am still comtemplating a second sub, the PC-13 Ultra. I already have a SB-12plus. I was thinking about running them both, but more and more I read it seems like it would be better to run just the Ultra, if I get one.

sivadselim

10-27-08, 03:22 PM

Increasing a sub by 6db how do you do that? When I went from one Pb10 then added another collated I gained 6db. So how do you increase one sub to output 6db more? Unless you have an eq that can do this?That's sort of a silly question, isn't it? You use its volume knob to turn it's volume up 6dB or you turn the subwoofer level trim in the receiver up by 6dB. I don't mean to be an ass, but you are demonstrating that you do not understand the explanation. And I'd really like you to understand it. When 2 subs are calibrated properly, each one's output will be less than it would be were it used alone and properly calibrated. If collocation of 2 subs created a 6dB increase in output, and the 2 subs are calibrated, if you turn one sub off, in order to get back to being calibrated properly, you would have to increase the output of the other single sub by 6dB. It's pretty simple.

You never explained how you calibrate your 3 subwoofers.

Both subs have similar frequency in the low range. I dunno why it's so hard to feel it's not possible to mix subs collated. Like I said if it didn't sound better I wouldn't do it. Sure a Ultra Pb13 one of those probably be better than my 3 subs. But it wouldn't fit in my space.I do not know how different their low-end -3dB point might be. What is the Valor's low-end -3dB point? I suspect it is higher than the 20Hz that SVS claims for the PB10. Perhaps 5Hz higher. One thing I DO know is that the PB-10 is ported and the Valor is sealed, so they most likely also have different roll-off profiles.

Again, I am not trying to be an ass or argue. I want you to understand this. From my and craig john's explanation in that other thread, to my most recent, very straightforward example/explanation, it should be understandable. But I will give one more simple example/explanation:

Let's suppose Joe has 2 subs. One goes down to 20Hz. The other goes down to 25Hz. He collocates them. First of all, how does Joe calibrate the 2 subs properly? Ideally, he wants each sub to contribute equally (half) to the overall output. So, he turns one on and he calibrates it to 75dB with the usual method. Then he turns that sub off and he turns the other sub on. He calibrates it to 75dB by the usual method. So, since he has calibrated each sub individually to the same exact level, if he runs them simultaneously, each one should now, more or less, contribute equally to the combined output, right?

Now, without changing anything, he turns them both on and he measures their combined output with his calibration tone. It is 81dB. OK, so the output gained by running the two subs collocated is indeed the 6dB (81dB - 75dB = 6dB) that is often cited. So, how does he get back to the point where the subs are calibrated to 75dB and each one is still contributing equally to the combined output? Well, this is easy. All he has to do is decrease the receiver's subwoofer level trim by 6dB. So he does this. Now he once again measures the two subwoofer's combined output with his calibration tone. No surprise, it is now back to 75dB. Everything is cool. He has now calibrated his 2 subs correctly.

Now, if he turns the sub that can go down to 25Hz off, and without changing anything, measures the 20Hz sub's output with his calibration tone, what will it be? It should be 69dB, right? 75dB - 6dB = 69dB. How does he get it back to 75dB? Simplest way is to just turn his receiver's subwoofer level trim back up the 6dB that he had lowered it, right? Now, the 20Hz sub by itself is 6dB louder and is back to being calibrated to 75dB. But look what just happened. In turning the 20Hz subwoofer up that 6dB he gained 6dB in output in the 20Hz to 25Hz range that he didn't have. So, calibrated properly, when he uses the 20Hz sub alone, the range of frequencies between 20Hz and 25Hz is actually 6dB louder than it is when he uses both subs together. WOW! That's quite a difference for those lowest frequencies that Joe considers so important. So, which option is best. Use both subs together or use the 20Hz sub alone? The answer is pretty obvious to me.

There is nothing that Joe can do to allow him to utilize both subs and adjust for this difference over that 5Hz range without EQ.

So, that is why I keep saying that utilizing 2 differing subs is problematic. Using the more capable (meaning it can go lower) sub alone is actually better than using both. You keep saying "try it", but no matter how hard you try, you will not be able to take full advantage of the better sub's superior low end capability when used in conjunction with the lesser sub.

Which brings me back to the question: How do YOU calibrate your 3 subs? Whether you do it properly, as I described above (except you would do it for 3 instead of 2), or you just adjust them by ear, you have no idea what is REALLY happening to your very lowest frequencies.

sivadselim

10-27-08, 03:36 PM

Would losing the extra extension of the new sub be an acceptable trade off given the leveling of freq. response? Assuming no more tweaking than running MCACC and setting levels with an SPL meter?MCACC aside, not utilizing the greater extension of the more capable sub to its fullest would be sort of silly, no? If you are asking if it would be worth it to even the room's FR, if MCACC includes EQ, it is sort of a moot point. It should do that for you, shouldn't it? Whether you use one OR 2 subs.

With 2 subs, if MCACC does include EQ, then it should compensate for the difference in FR between the 2 subs and adjust, as best it can, the overall FR to be flat all the way down to where the lowest sub rolls off. I do not know the details of how MCACC works, exactly, but there is a specific way to calibrate 2 subs such that they contribute as equally as possible to the combined output, both before and after you run MCACC. Even though the EQ is applied to the combined subwoofer output, there is a chance that after EQ, the subs are no longer contributing equally to the combined output and there is a way to compensate for this difference.

But when you add EQ to the picture, everything changes. Whether you would want to use 2 different, but EQ'd, subs would probably depend upon, as craig john pointed out, their relative capability as well as how much output you need. If using both significantly decreases the stress on either, then it might not be a bad idea.

sivadselim

10-27-08, 03:51 PM

This is my dilemna. I am still comtemplating a second sub, the PC-13 Ultra. I already have a SB-12plus. I was thinking about running them both, but more and more I read it seems like it would be better to run just the Ultra, if I get one.Is it your "dilemna"? Do you have MCACC/Audyssey/AutoEQ or whatever your manufacturer calls it or not?

If you understand the issue, and you do not have EQ capability, then the answer is obvious, especially when it is between those 2 subs. The PB13 can go significantly lower and is capable of significantly more output than the SB12+. As much as it hurts to not use Rosie, it would very most likely be best to use the PB13 alone. Now, if you were very, very, very lucky, you might find that your room and where you placed the subs actually accentuates those very frequencies such that it provides a flat FR when they are calibrated. The only way you could figure this out is to measure the FR.

But I gave another good example of a real situation (a 25Hz sub and a 20Hz sub) just above here that illustrates exactly what you may encounter with those 2 subs.

There was someone here over the weekend that was looking for a good deal on a small, nice looking sub. I mentioned that you may have one for sale. :D Search on "sourbeef" and you can find the thread. May want to PM him if you are serious about getting the PB13.

Down

10-27-08, 04:00 PM

MCACC aside, not utilizing the greater extension of the more capable sub to its fullest would be sort of silly, no? If you are asking if it would be worth it to even the room's FR, if MCACC includes EQ, it is sort of a moot point. It should do that for you, shouldn't it? Whether you use one OR 2 subs.

With 2 subs, if MCACC does include EQ, then it should compensate for the difference in FR between the 2 subs and adjust, as best it can, the overall FR to be flat all the way down to where the lowest sub rolls off. I do not know the details of how MCACC works, exactly, but there is a specific way to calibrate 2 subs such that they contribute as equally as possible to the combined output, both before and after you run MCACC. Even though the EQ is applied to the combined subwoofer output, there is a chance that after EQ, the subs are no longer contributing equally to the combined output and there is a way to compensate for this difference.

But when you add EQ to the picture, everything changes. Whether you would want to use 2 different, but EQ'd, subs would probably depend upon, as craig john pointed out, their relative capability as well as how much output you need. If using both significantly decreases the stress on either, then it might not be a bad idea.

I was under the impression that the MCACC left a whole lot to be desired in EQing subs.

Looks like it's back to the books for me.

Thanks!

sivadselim

10-27-08, 04:04 PM

I was under the impression that the MCACC left a whole lot to be desired in EQing subs.

Looks like it's back to the books for me.You may be correct. You probably know more about that than I do, actually. I really do not know anything about it, specifically. I just assumed it calibrated and EQ'd (yes, as best it can). I do not know how good a job any of the auto EQ programs do at the low end (or anywhere, for that matter). I "think" that I know that they are only able to apply a very limited number of specific filters.

Gov

10-27-08, 04:32 PM

MCACC does NOT EQ a sub. What it does do is, phase, standing wave and reverb

goneten

10-27-08, 05:01 PM

How does MCACC "do standing wave" ? Are you trying to say that MCACC eliminates standing waves ?

Regards,

Ironmike86

10-27-08, 10:17 PM

That's sort of a silly question, isn't it? You use its volume knob to turn it's volume up 6dB or you turn the subwoofer level trim in the receiver up by 6dB. I don't mean to be an ass, but you are demonstrating that you do not understand the explanation. And I'd really like you to understand it. When 2 subs are calibrated subwoofers.

Are you even reading my post? I calibrate with a spl meter using downloaded test tones for comparison. I use test tone for calibration with my meter. 20 hrz with the valor and Pb10 hit close to the same in spl. When I calibrate 1 Pb10 the gain is 1/2 to reach 75db on -10 with my receiver with the osd @0.When 2 are calibrated I put the osd to -6. So by taking one away you don't increase 6db that easily. I would need to turn the gain up way to far and increase the volume on my receiver so it won't be as clean. I know how to calibrate with a spl meter. I just don't have an eq to graph. Sure the spl meter I have may not be that accurate but you are post like I'm doing everything by ear. What 2 subs have you played together and did you have problems? Like I said many times for Ht it sound good because the Valor keeps up in the low. Look at all the graph available online. The Valor probably goes lower than the Pb10. I'm probably losing in the mid with the Valor but it's the low I'm trying to produce in Spl. Regardless it sound better to my ears calibrated with a spl meter with downloaded test tones. I played them all different ways. Here's a graph of the Valor from the Epik thread.
http://www.avsforum.com/avs-vb/attachment.php?attachmentid=90297&d=1190569784
Like I said before the Valor by itself doesn't give me enough spl. 2 P10 bottom out @ the spl I want. The 3 have enough overhead. My plan is to diy some 18" then I will have enough. If I don't diy I probably will add another Valor because it's a good sub. And sell the Pb10's. A Valor goes just as low as a Pb10 easily and louder. Remember you are comparing a 15" sealed to a 10" ported subs. The 15" has more double the surface area and a bigger box.This imo make a big difference than just comparing a ported and sealed sub. I believe these subs are pretty close on the lowed for HT. But I wouldn't use a PbUltra13 and a Sb12 unless the 12 was going to be use like a MBM only for the mid range. Alot of ppl mix subs and have good results or the MBM wouldn't sell so well.

DS-21

10-28-08, 01:14 AM

Please read the explanation of why it is problematic in the thread I linked to in Post#13, above.

I just went back and read the "explanation." It is utterly without merit, and belies a fundamental misunderstanding of the purpose of subwoofers in an audio system designed for high fidelity. (In fairness, others' purposes may just be to make pointless, plotless special effects Hollywood special effects spectaculars boom louder. In which case, a different type of system design may be more appropriate.

In a thoughtfully designed audio system intended to reproduce music with high fidelity, multiple subwoofers are not employed to get lots more output, though a little higher overall output is a happy byproduct. A primary sub, which should be as capable as possible, goes in a corner, where it benefits from maximal loading from the room. The other subs, placed randomly around the room (in my current situation, one along the front wall outside the left speaker, one about 42" from the back wall up against the left arm of the couch. Yes, a high-mounted sub would be better, but my 12" Dual Concentric mains are above the room's centerline, so they contribute substantially above ~40Hz or so) play at a much lower level, and only really serve to smooth out the response of the primary subwoofer.

Without EQ, unless you are very lucky and your room somehow solves the problem, there is no getting around it. The issue is pretty obvious. It's not rocket science. I do not understand why people have such a problem grasping it.

People should have problems grasping "issues" that don't exist. Here is what can happen with thoughtful placement and no EQ. Three subs, mains run in LFE+Main mode (no high-pass on the mains).
http://img393.imageshack.us/img393/244/sms1frgraphwebsizeod6.jpg

(Note: those subs were ported. The new ones are much more capable in that bottom octave. I'm pretty sure my current sealed Maelstrom-X has about 3x the extreme LF output of the Tannoy B475 that was the primary sub then, and the Aura NS12's are at least equal to the JBL 2235H's that were the filler subs.)

You still have not explained how you calibrate your 3 subs.

I use Dr. Geddes' procedure, more or less, as explained here. (http://www.diyaudio.com/forums/showthread.php?postid=1619786#post1619786) The SMS-1 speeds up the process quote a bit.

Ideally, the goal would be for each individual sub to contribute equally to the overall output.

Quite the opposite, as explained above.

Ironmike86

10-28-08, 09:38 PM

In fairness, others' purposes may just be to make pointless, plotless special effects Hollywood special effects spectaculars boom louder. In which case, a different type of system design may be more appropriate.
Hey that sounds like me :) Wish I had a Sms-1

bachusTheOld

10-28-08, 10:37 PM

DS-21: Yes.

And:

Regarding the issue of phase nodes etc it seems to me that as soon as you put one sub in a room with walls you've already spilled that can of worms all over the floor.

http://farm4.static.flickr.com/3154/2983255958_6c6f1b6fc7_o.jpg

sivadselim

10-31-08, 01:53 PM

In a thoughtfully designed audio system intended to reproduce music with high fidelity, multiple subwoofers are not employed to get lots more output, though a little higher overall output is a happy byproduct.Of course multiple subs are not employed to get more output. Multiple subs should be calibrated to the exact same combined SPL level that would be employed were only a single sub used.

People should have problems grasping "issues" that don't exist.

I use Dr. Geddes' procedure, more or less, as explained here. (http://www.diyaudio.com/forums/showthread.php?postid=1619786#post1619786)I don't think you understand the issue. Not as it applies to someone who calibrates their subs' output levels with ONLY an SPL meter.

Quite the opposite, as explained above.For someone who calibrates their subwoofers' output levels with only an SPL meter, equal contribution from each sub to the total perceived output at the listening spot WOULD be the goal. The method I described for calibrating 2 (or more) identical subs with an SPL meter IS the proper method and IS the method that is used most often by someone who is calibrating multiple subs. Start a thread that asks "How do you calibrate 2 identical subwoofers with an SPL meter?" and see what answers you get.

Armed only with an SPL meter and (maybe) a calibration DVD, how would you calibrate 2 identical subs, no matter their location in the room, DS-21?

DS-21

11-01-08, 04:47 PM

Of course multiple subs are not employed to get more output. Multiple subs should be calibrated to the exact same combined SPL level that would be employed were only a single sub used.

You're using the word "output" differently than I am. I mean maximum in-room SPL. You seem to mean relative level.

I don't think you understand the issue. Not as it applies to someone who calibrates their subs' output levels with ONLY an SPL meter.

It applies the same, whether somebody's using the proper tools (sweeps and either decent measurement setup, such as FuzzMeasure Pro or a dedicated subwoofer measurement setup such as that built into the SMS-1) or more primitive stuff.

For someone who calibrates their subwoofers' output levels with only an SPL meter, equal contribution from each sub to the total perceived output at the listening spot WOULD be the goal.

That is a stupid goal. One should do it the same way, setting up the primary sub and using the second one to fill some of the room-caused shortcomings of the primary sub.

Armed only with an SPL meter and (maybe) a calibration DVD, how would you calibrate 2 identical subs, no matter their location in the room, DS-21?

It's not 1995 any more. I see no reason to resort to last millennium primitivism when we have better tools today. Not that an SPL meter and test tones can't be used, but doing it right takes bloody forever.

sivadselim

11-01-08, 06:43 PM

That is a stupid goal. One should do it the same way, setting up the primary sub and using the second one to fill some of the room-caused shortcomings of the primary sub.That is just not true. And it is not at all a "stupid goal". It is the same exact goal utilized when calibrating your individual speakers' levels. With 2 identical subwoofers, there is no primary sub. I do not know ANYONE who would use one of two identical subs to "fill some of the room-caused shortcomings of the primary sub". The method I described to calibrate the SPL of dual, identical subwoofers is the way that almost everyone does it.

Not that an SPL meter and test tones can't be used, but doing it right takes bloody forever.No it doesn't. It is quite simple and takes at most 5 more minutes than it takes to calibrate a single subwoofer with an SPL meter. Each sub is calibrated INDIVIDUALLY to the correct SPL (i.e.75dB), then the COMBINED output of both is decreased in unity back down to the correct SPL (i.e. 75dB). In doing this, both subs will contribute equally (as possible) to the SPL at the listening position no matter where they are located in the room. This is elementary stuff and IS the proper way to calibrate the output level of 2 identical subwoofers with an SPL meter.

Although the relative output of their multiple subs may not be as important when more complex methods are used to calibrate and EQ multiple subwoofers, most people DO attempt to adjust the subs' individual outputs so that they are contributing as equally as possible to the total output.

Look, for example, HERE (http://www.avsforum.com/avs-vb/showpost.php?p=14874774&postcount=68) at how bsoko2 describes how he calibrates his multiple subwoofers. He calibrates his subs to the same individual SPL (75dB), then adjusts their combined output, in unison, to that same 75dB SPL prior to EQ. Then after EQ, he checks to make certain that their combined output is still at 75dB. He has an inline volume control on his LFE line, prior to his 8033, that allows him to adjust the sum total of the subwoofers' output, in unison.

This is how almost anyone with multiple subwoofers would want them calibrated. No one wants one of their subs to be significantly louder than any of their others. They want as even and equal a contribution as possible of each sub to the overall output as measured at the sweet spot. Likewise, most people EQ the sum total of all their subwoofers' output; not each one individually. EQing each sub, individually, to be flat, does not at all assure that when used in unison they will be flat. In fact, it's quite the opposite.

Now, there may be people with more than 2 subs who do things differently, EQ-wise, especially with differing subwoofers, but I know of no one with 2 identical subs who doesn't attempt to adjust them to contribute equally to the overall output at the listening spot.

There ARE a few people who try to utilize multiple subwoofers to even out the room's response such that it is flat when measured at multiple locations around the room, and this probably requires significantly differing output contributions form each sub. But this is not at all the kind of stuff a novice attempts. Not nearly. When someone posts a single graph here in the forums of their room's FR measurement, it is almost always the FR as measured at their sweet spot.

Room effects aside, without EQ, their is no way, with an SPL meter, using the method I described, to calibrate 2 subs with disparate low-end capabilities such that the more capable (can go lower) subwoofer's range of output that is below the low-end roll-off of the less capable subwoofer is calibrated to the correct level. There just isn't. And, room effects aside, even if you had a reasonably quick way to measure your room's response, fiddling with each subs' individual output until you "magically" achieved some ratio of their outputs that would produce a flat response would be an exercise in randomness.

Hypothetically, without EQ, if you had a sub that, individually, at a particular location in your room, measured flat from 120Hz down to 25Hz at your sweet spot, and another that, individually, at another (or the same) location in your room, measured flat from 120Hz down to 20Hz at your sweet spot, and ignoring any interactions of their combined output, explain to me how you would adjust their individual outputs so that their combined output was still flat from 120Hz all the way down to the 20Hz capability of the more capable sub? You can adjust them individually to ANY output level you wish. Forget calibrating their combined SPL. We can do that later, after you achieve a ratio of their outputs that achieves the identical flat FR, all the way down to 20Hz, of the lone, more capable subwoofer. If you think it is possible, you need to think a bit about what I am asking. Because it is not possible.

JBLsound4645

11-01-08, 08:01 PM

You need the JBL 4642 as used as part of the screen speaker or stage speakers at the famous Empire Leicester Square, L Lex C Rex R oh yeah good frequency response and SPL db delivery.

http://www.ltt-versand.de/shop/images/jbl_4642a_563x459.jpg

Yes I know its sub and that is why its also used as stage bass to mid speaker because it pucker! The bass level from these in the Empire with Transformers was priceless!:p:cool::);)

Features
1200 Watts Continuous Pink Noise, 2400 Watts Continuous Program Power Handling
Usable response to 22 Hz (-10 dB, no EQ), flat to 22 Hz (-3 dB) with External EQ
Approved by Lucasfilm, Ltd. for THX® installations

Specs
Low Frequency Driver : (2) 2241H
Frequency Range : 22 Hz - 500 Hz (-10 dB)
Power Capacity (Continuous Pink Noise) : 1200 Watts

Power Capacity (Continuous Program) : 2400 Watts
Sensitivity : 101 dB SPL (1W, 1m, 3.3ft.)
Crossover Frequency : 80-150 Hz recommended
Nominal Impedance : 4 ohms
Width : 48 inch (1219 mm)
Height : 30 inch (762 mm)
Depth : 24 inch (610 mm)
Net Weight : 216 lbs. (98 kg)

JBLsound4645

11-01-08, 08:06 PM

Damn that is big JBL sub!:cool:

http://www.ac2.jp/go/images/061012.jpg

titch--

11-01-08, 08:27 PM

heh

scottod

11-01-08, 11:39 PM

what do you think of vtf-3mkII this in new con but slightly used for about 400.0 good deal y/n

DS-21

11-02-08, 01:09 AM

That is just not true. And it is not at all a "stupid goal". It is the same exact goal utilized when calibrating your individual speakers' levels.

The individual speakers, of course, play different signals from each other. The subs play a summed signal. Not the same thing at all.

With 2 identical subwoofers, there is no primary sub.

Not if you do it badly, that is.

I do not know ANYONE who would use one of two identical subs to "fill some of the room-caused shortcomings of the primary sub". The method I described to calibrate the SPL of dual, identical subwoofers is the way that almost everyone does it.

And "almost everyone" has bad-sounding bass, rather appallingly bad-sounding, really, so what's your point?

And I agree that two subs are suboptimal, but used properly they are better than a single one. Misused as you suggest, a single one may be superior depending on the room.

No it doesn't. It is quite simple and takes at most 5 more minutes than it takes to calibrate a single subwoofer with an SPL meter.

Some of us have higher standards, I suppose. Yes, it is easy to do things half-arsed quickly. But putting some thought into optimizing the results means one's going to spend more time tweaking, plotting, listening, and tweaking some more.

most people DO attempt to adjust the subs' individual outputs so that they are contributing as equally as possible to the total output.

I could not care less what most people do. Most people are ecstatic for mediocrity. I care about leading edge methods that achieve measurably and audibly superior results.

Likewise, most people EQ the sum total of all their subwoofers' output; not each one individually. EQing each sub, individually, to be flat, does not at all assure that when used in unison they will be flat. In fact, it's quite the opposite.

Here we mostly agree. "Mostly" because sometimes individual EQ (e.g. a Linkwitz Transform to extend the LF response of a sealed sub, or an assisted vented alignment) is useful. But, just playing with placement and phase controls, and using subwoofers with wide bandwidth due to their low-inductance, Faraday-ringed motors, one will find that little to no global EQ is even required (maybe a ceiling notch) in a well-designed, well-executed system. I am not interested in systems that meet lesser standards.

But this is not at all the kind of stuff a novice attempts. Not nearly.

But they should. It is not difficult. It is only because novices keep getting bad advice like what I'm responding to that they settle for inferior application of the equipment they've bought.

goneten

11-02-08, 07:49 AM

This is a very interesting discussion.

Regards,

sivadselim

11-02-08, 12:26 PM

This is a very interesting discussion.How do you calibrate (and EQ, if applicable) your 2 subs, goneten?

sivadselim

11-02-08, 12:53 PM

Does that help you?Yes. Thank you very much. Makes perfect sense to me. ;)

SteveMo

11-02-08, 01:11 PM

With that in mind, don't turn up the gain on them, move them together until it is 75dB.

goneten

11-02-08, 01:17 PM

With that in mind, don't turn up the gain on them, move them together until it is 75dB.

Nah.

Regards,

goneten

11-02-08, 01:20 PM

I do the following; increase gain level on single subwoofer until I reach a target output level of 72 dB's then I will turn off the subwoofer. Turn on second subwoofer to reach the same target output level of 72 dB's. The gain levels on both subwoofers will not necessarily be at the same level.

I then turn on both subwoofers and the resulting output increase is 75-76 dB's. Both subwoofers are not co-located but (scientific hint) given the fact that the full benefits of co-location are determined by 1/4 wavelength spacing, or more accurately, reinforced by 1/4 wavelength spacing, I still gain the benefits from 40 hz and below.

Okay, so that was needless pontification on my part, I admit that. Anywho, I then lower the unity gain to 73 dB's using the subwoofer level control in my AVR. Why ? I do this for two reasons. For one, I prefer a flat level. Two, I lower distortion at the same time and improve my dynamics. And because both subwoofers are now operating in unison, I can now equalize my room response to my hearts desire.

What are my thoughts on using dissimilar subwoofers as I know you really want to know what I think about this ? Well, I don't think it is a wise decision as both subwoofers will have a different frequency response curve and output levels will start to become nonlinear as compression starts to set in on the lesser subwoofer.

But the wise man said, "But my sub will fill in the much needed 40 hz range", to which I responded, "you're sacrificing output linearity at the sake of having a smoother frequency response in one particular part of the frequency range and that frequency range that you assume is smooth won't be smooth when output compression sets in due to, well, compression".

Does that help you ? Don't bother trying to watch movies at reference level using one monster subwoofer and one crappy subwoofer because no matter how smooth your frequency response will look, having the VC hit the back plate due to insufficient travel is not going to help you.

"So why don't I just lower the gain level on the crappy subwoofer then ?" the wise man said. "Because it's just a stupid idea, that's why". At the end of the day, using dissimilar subwoofers can result in a smoother frequency response but I don't think the compromises are worth it.

Now no one has explained to me how MCACC "do standing wave" ? When will "gov" explain to me how MCACC "do standing wave" ? I wait with baited breath.

Regards,

craig john

11-03-08, 11:42 AM

When Mark Seaton sets up two *identical* subs, he sets their gains to be identical, whether co-located or separate. This ensures that their "clip points" are the same, and that one sub does not go into compression before the other. While one can then end up with dissimilar measured in-room levels, this setup technique ensures that the full output capacity of both subs is available to the user. This is essentially how I set mine up. I run my JL F112's in "Master/Slave" mode. The gain, phase and other settings are all controlled by the Master. They each have equal input signals to the amps. Their measured in-room levels are dissimilar by about 4 dB.

I don't believe I've ever seen a post by Mark Seaton wherein he details his technique for setting up dissimilar subs. This is probably commentary in and of itself.

Craig

goneten

11-03-08, 11:57 AM

When Mark Seaton sets up two *identical* subs, he sets their gains to be identical, whether co-located or separate.

I have found that this is not true all the time. Placement and positioning can affect output even when the gain levels are exactly the same using pink noise. Dual subwoofers with identical gain settings do not necessarily reflect identical "drive" levels as a result and so the work load will not be split accordingly.

There are, of course, fewer variables when co-locating and less chance of output irregularities due to awkward positioning.

Regards,

sivadselim

11-03-08, 12:17 PM

Dual subwoofers with identical gain settings do not necessarily reflect identical "drive" levels as a result and so the work load will not be split accordingly.Could you elaborate? :confused: The work load would be split equally, no? But, depending upon the room's effects and the subs' relative distances, the contribution of each sub to the overall output perceived at the sweet spot would (or could), of course, be different.

Regards ;)

Mark Seaton

11-03-08, 12:26 PM

I have found that this is not true all the time. Placement and positioning can affect output even when the gain levels are exactly the same using pink noise. Dual subwoofers with identical gain settings do not necessarily reflect identical "drive" levels as a result and so the work load will not be split accordingly.

There are, of course, fewer variables when co-locating and less chance of output irregularities due to awkward positioning.

Regards,

Craig had me quoted correctly. The acoustic output (separate from the interaction with the room) should be set the same unless you have a very good reason and clear benefit. Of course others will have different approaches, but that is my recommendation.

If you consider that different locations in the room will most certainly produce different frequency responses, there is no way to test SPL at the listening position that produces any real "match" of output level.

goneten

11-03-08, 12:38 PM

goneten

11-03-08, 12:39 PM

Sorry, I edited my post and modified it again for additional clarity.

Regards,

Mark Seaton

11-03-08, 12:42 PM

If sub A requires the gain levels be set to 50% to reach 70 dB's at the listening position and sub B with the exact same gain settings reaches 67 dB's, how is the work load split identically ?

If I set the gain levels identically on both subwoofers then I do not get the 3 dB increase using pink noise at the seats. However when I use a gain setting that yields identical levels then I get the full coupling benefit.

If I want the benefits of mutual coupling and I am getting dissimilar levels using identical gain levels at the seats then I'm not sure how that would benefit me.

If the phase, level and frequency are not the same between the two subwoofers then how do I gain full coupling benefits between both subwoofers ?

Please elaborate. :)

Regards,

You can't look at the problem with a noise signal or a single frequency, as the output varies with frequency for every location in the room. It's about acoustic power into the room. You are free to deviate from that, but that's not my recommendation.

Of course the above assumes that the two subwoofers are identical. I have seen cases of old versions of subwoofers having different gains than newer models. In this case, it is best to place the subs in the same location and with the same input signal measure at a very close, fixed distance from each to match the acoustic output. Ideally you would do this in the middle of the room, noting the gain differences and maintaining those once in their respective locations.

goneten

11-03-08, 12:43 PM

Mark Seaton

11-03-08, 12:50 PM

From what I understand about mutual coupling is that in order for you to benefit from it you need to match the levels, phase and frequency. If you deviate from any one of these things then the full coupling benefits are lost.

Please correct me if I'm wrong.

Regards,

You are partially correct. Let's look at 2 stacked subwoofers as an example. In some rooms the upper subwoofer could measure lower with pink noise than the bottom at the listening position when set identically. If you measured both subwoofers 1" from the center of the woofer's cone, you would find the output equal, as they are both producing the same acoustic output. This is what you want, and you would not want to raise the level of the upper subwoofer.

As soon as you do raise the level of the upper subwoofer, now the upper subwoofer is working harder than the lower at the same drive level, and will run out of gas sooner.

goneten

11-03-08, 01:00 PM

As soon as you do raise the level of the upper subwoofer, now the upper subwoofer is working harder than the lower at the same drive level, and will run out of gas sooner.

I understand that. But it seems like in my specific situation the output does differ by 2-2.5 dB's using identical gain settings.

Turning the first subwoofer on (second sub off) requires that I set the gain to 40% to reach 72 dB's but yet in the opposing corner (first sub off) the second subwoofer requires a gain close to 50% to reach the same SPL.

Turning both subwoofers on the net SPL then is 75-76 dB's given that the levels are identical and I would then lower the subwoofer level to reach my required figure at 73 dB's. Any other combination and I don't get the same increases.

Is the procedure that I am using incorrect ?

Regards,

sivadselim

11-03-08, 01:31 PM

If sub A requires the gain levels be set to 50% to reach 70 dB's at the listening position and sub B with the exact same gain settings reaches 67 dB's, how is the work load split identically?Each sub still ends up 'working' the same amount. But because of their relative locations in the room, their individual contribution to the overall output is not equal. Even with their gains set identically, their combined output can still be calibrated in unison. All that matters, using his method, is the final SPL measurement.

goneten

11-03-08, 01:46 PM

But because of their relative locations in the room, their individual contribution to the overall output is not equal.

If the individual contribution of each subwoofer is not equal then the work load is not halved between both, yes ?

All that matters, using his method, is the final SPL measurement.

Perhaps I'm smoking grass here but the final SPL measurement based on two equal gain settings does not infer that both subs are working the same amount if their individual levels end up being different.

If one sub generates 70 dB's at X gain and another produces 73 dB's with X gain in a different location then the latter example will reach compression issues first and both subs will not be driving the load equally at the listening position.

Does that make sense to you ? Unless my thinking cap is not on and it very well might not be. . .

Regards,

Mark Seaton

11-03-08, 02:08 PM

Perhaps I'm smoking grass here but the final SPL measurement based on two equal gain settings does not infer that both subs are working the same amount if their individual levels end up being different.

If one sub generates 70 dB's at X gain and another produces 73 dB's with X gain in a different location then the latter example will reach compression issues first and both subs will not be driving the load equally at the listening position.

Does that make sense to you ? Unless my thinking cap is not on and it very well might not be. . .

Regards,

Maybe this will help tighten that thinking cap. ;)

Let's take a single subwoofer...

First measure it outside at a given drive level... Let's say at this level it produces 75dB @ 2m with pink noise. Now let's pull that driver inside a room while using the exact same input signal and gain setting. At location #1 we measure a pink noise level of 74dB on an SPL meter at the listening position. At location #2 we measure a level of 70dB on an SPL meter at the listening position. The subwoofer is producing the same acoustic output per frequency as it did outdoors, and the input signal required to reach a clip/limiting point is still the same. The different SPL levels are due to the interaction with the room and how efficiently the acoustic power is transmitted to the listening position.

As we know, the frequency will vary greatly with each location, so a big 6-10dB peak at 40Hz from one location will measure much higher in level than another location where the response is flat, or happens to have a dip at this frequency. In both cases, there was no change to the operation of the subwoofer. Again note that this is how all of the studies of multiple subwoofers in a room are calculated.

Sure, if you raise the level of one of the subwoofers you will get more SPL! You're also working that subwoofer harder. ;)

sivadselim

11-03-08, 02:19 PM

If the individual contribution of each subwoofer is not equal then the work load is not halved between both, yes?

Perhaps I'm smoking grass here but the final SPL measurement based on two equal gain settings does not infer that both subs are working the same amount if their individual levels end up being different.

If one sub generates 70 dB's at X gain and another produces 73 dB's with X gain in a different location then the latter example will reach compression issues first and both subs will not be driving the load equally at the listening position.

Does that make sense to you ? Unless my thinking cap is not on and it very well might not be. . .No. The work load IS equally shared when their gains are set identically. The contribution of each of the subs equal amount of work, though, to the overall output is not equal. But they both exert the same amount of work. That's sort of Mark's point. If one of the subs is set to a higher gain, then it can potentially "run out of gas" before the other. Setting their gains identically assures an equal amount of work from each one with any given input signal. It certainly makes calibrating them a bit simpler. Try it. If bass, theoretically, is not localizable, it should work fine.

But I have read so many times to calibrate them such that they contribute equally to the combined output that, certainly, there are some other opinions. In a way, BOTH methods seem logical. Mark's method makes more sense, I suppose, in a large, dedicated HT environment, where the subs may be driven to the point where they may "run out of gas". Based upon the pictures you have posted of your listening room, I do not know if this is really a concern of yours or not. However, his insinuation, above, of how a room peak with one of the subs can skew the results when trying to calibrate them to equal SPL makes perfect sense and sort of makes attempting that prior to EQ a moot point. His method treats the 2 identical subs as a single entity, instead of as individual contributors.

I, for one, am really glad he jumped in here. Definitely food for thought.

Of course, none of this is really relevant to the use of two dissimilar subs.

goneten

11-03-08, 03:45 PM

Sure, if you raise the level of one of the subwoofers you will get more SPL! You're also working that subwoofer harder.

According to the room (not ground plane, outdoors) the output at the seats are the same per each sub but the gain settings differ slightly to reach that output. My main contention is that if I want to gain the benefits of coupling (and I do) using multiple subwoofers then I need both to run at the same level at the seats.

I have measured using the SMS-1 that I do gain more "free" output due to coupling when the levels are matched. When the gain levels are the same but the output is different per each sub at the seats the output increases I get are not equal. In some cases the output actually does down.

Regards,

goneten

11-03-08, 03:55 PM

The contribution of each of the subs equal amount of work, though, to the overall output is not equal. But they both exert the same amount of work.

Outdoors, away from room boundaries and rigid surfaces, what you are saying may be true, but in my room in order for each subwoofer to have equal levels requires slightly different gain settings. That is simply the way it is.

If you have two subwoofers that are co-located and one subwoofer is putting out 70 dB's, the other 73 dB's (independently), the net increase will be irregular due to the levels being irregular.

Set both subwoofers to 73 dB's (same level and phase) and the coupling benefits begin. You then gain a maximum net increase of 6 dB's at the seats in the majority of cases. I stress the importance of having equal levels per sub at the seats.

Regards,

goneten

11-03-08, 04:03 PM

Setting their gains identically assures an equal amount of work from each one with any given input signal. It certainly makes calibrating them a bit simpler. Try it. If bass, theoretically, is not localizable, it should work fine.

I have tried it. My subwoofers are not placed equidistant from each other. If one subwoofer is placed a meter (or two) closer than another then identical gain levels will simply not yield correct results.

Regards,

bsoko2

11-03-08, 04:29 PM

Sounds contradictory. Outdoors, away from room boundaries and rigid surfaces, what you are saying may be true, but in my room in order for each subwoofer to have equal levels requires slightly different gain settings. That is simply the way it is.

If you have two subwoofers that are co-located and one subwoofer is putting out 70 dB's, the other 73 dB's (independently), the net increase will be irregular due to the levels being irregular.

Set both subwoofers to 73 dB's (same level and phase) and the coupling benefits begin. You then gain a maximum net increase of 6 dB's at the seats in the majority of cases. I stress the importance of having equal levels per sub at the seats.

Regards,

Interesting, I'll give it a try tonight.

Bill

sivadselim

11-03-08, 04:37 PM

................but in my room in order for each subwoofer to have equal levels requires slightly different gain settings. That is simply the way it is.But that's not a goal of Mark's.

If you have two subwoofers that are co-located and one subwoofer is putting out 70 dB's, the other 73 dB's (independently), the net increase will be irregular due to the levels being irregular.What do you mean "irregular"? The output will be what it is, whatever it is. How can the net increase be "irregular"? It is an increase. It's not "regular" or "irregular". According to Mark's method, all that matters is the total SPL at the sweet spot. The 2 subs' overall output can be adjusted in "unity" to a specific SPL whether they are contributing equally to the total SPL or not.

Set both subwoofers to 73 dB's (same level and phase) and the coupling benefits begin. You then gain a maximum net increase of 6 dB's at the seats in the majority of cases. I stress the importance of having equal levels per sub at the seats.Yeah, I hear you, but I think Mark's logic makes sense. I don't know what "coupling" is, but you're not looking for more output anyway, are you?

sivadselim

11-03-08, 04:39 PM

I have tried it. My subwoofers are not placed equidistant from each other. If one subwoofer is placed a meter (or two) closer than another then identical gain levels will simply not yield correct results.What is a "correct" result, goneten? :confused: The additive result is what it is. You can calibrate the subs' combined output in unison to whatever level you want.

sivadselim

11-03-08, 04:42 PM

Interesting, I'll give it a try tonight.I thought you DID calibrate your subs to the same individual SPL, bsoko2. At least according to the method you posted it seemed that was what you did.

craig john

11-03-08, 05:46 PM

Set both subwoofers to 73 dB's (same level and phase) and the coupling benefits begin. You then gain a maximum net increase of 6 dB's at the seats in the majority of cases. I stress the importance of having equal levels per sub at the seats.

Regards,
You *may* get a larger increase in the level. What you give up is the maximum output capability of the sub that is set lower. When the higher-set sub reaches it's max output, the lower-set sub will still have headroom available.

I think the biggest difference in the thought process between your technique and Mark's is that you are looking for the highest "coupling" of the two subs, while his primary goal is flat frequency response at the seats. Personally, I prefer the later method, and I think it's more likely to be achieved with subs placed separately than with subs placed for highest coupling. If you are starting out with capable subs, the 3 dB increase in level from the second, non-co-located sub is just a bonus.

Craig

otk

11-03-08, 06:11 PM

a chain is only as strong as it's weakest link :)

craig john

11-03-08, 06:16 PM

a chain is only as strong as it's weakest link :)

:)

otk, you have a system that is a combination of multiple subwoofers and powered woofers with differing LF extension capabilityies How do you determine the levels and calibration settings for your subs?

Craig

otk

11-03-08, 06:30 PM

:)

otk, you have a system that is a combination of multiple subwoofers and powered woofers with differing LF extension capabilityies How do you determine the levels and calibration settings for your subs?

Craig

the subs that are built into my towers are all identical and i calibrate each tower separate with an slp meter

my 6 "LFE" subs are all identical. i calibrate each sub one at a time from the listening position with an spl meter using the level knob on each sub. then i turn them all on and adjust the sub level from the receiver with the spl meter from the listening position

DaGamePimp

11-03-08, 07:34 PM

sivadselim

11-03-08, 08:25 PM

How about dual powered subs where the lesser sub is doing the L&R (mains) bass while the better sub is doing the LFE ?

This should be an acceptable set-up for using 2 different powered subs , yes/no ?

The mains sub is calibrated in with the mains and the LFE sub has its own calibration .

Sound reasonable ?

- JasonThat is definitely a way to completely sidestep any issues if you wanted to use 2 different subwoofers. Depending upon your specific connection options, your front speakers' capabilities, the sub's capability, and your own preference, you would still have a couple of decisions to make. If your processor has pre-outs, do you set your fronts to LARGE, let them run full-range, and utilize the pre-outs for the front channel sub? Or, if you don't have pre-outs and/or your sub has speaker level inputs/outputs and a high-pass, do set your fronts to LARGE and utilize a speaker level connection through the sub or not? The only real difference setup-wise, here, would be the crossover setting used on the front channel sub. You'd have to decide how you wanted to spread that front channel bass across the speakers and the sub which, again, would depend upon your speakers' and sub's capabilities and performance over the range of frequencies between your speakers' low-end roll-off and the sub's high-pass filter.

The only thing I don't like about that arrangement is that most processors reroute the bass from any channels set to SMALL to the subwoofer output which would mean that it would go to the "LFE sub", which doesn't really jibe with that whole scheme (IMO). If I was attempting such a setup, I'd probably set my processor up as having NO SUB and let the processor reroute everything through the front channels. That way I could smear the rerouted bass/LFE gumbo across the front speakers and both of the subs to my liking. Everything would get in on the action. :)

sivadselim

11-03-08, 08:30 PM

the subs that are built into my towers are all identical and i calibrate each tower separate with an slp meter

my 6 "LFE" subs are all identical. i calibrate each sub one at a time from the listening position with an spl meter using the level knob on each sub. then i turn them all on and adjust the sub level from the receiver with the spl meter from the listening positionAre your "LFE subs" identical? If so, try Mark's method of setting them all to one specific gain setting. You would still adjust their overall output to the correct level, in unison, with your receiver.

otk

11-03-08, 09:53 PM

Are your "LFE subs" identical? If so, try Mark's method of setting them all to one specific gain setting. You would still adjust their overall output to the correct level, in unison, with your receiver.

yes, each sub is identical (2 stacks of 3 sealed subs, 1 stack in the front right corner, 1 stack in the front left corner)

i used to run them all at the same exact level for over 10 years then about a month ago did some testing with the SPL meter and noticed that in each stack, the subs closest to the floor had more output

but after just reading mark's comments in this thread, i'll probably go back to running them all at the same level again. i'm glad you asked :)

craig john

11-03-08, 11:49 PM

yes, each sub is identical (2 stacks of 3 sealed subs, 1 stack in the front right corner, 1 stack in the front left corner)
All that, and you *still* get "directional" bass from your surrounds? Wow. :eek::) Maybe you do know sumthin' I don't. I think I would enjoy hearing your system. :):):)

Craig

otk

11-04-08, 12:40 AM

All that, and you *still* get "directional" bass from your surrounds? Wow. :eek::) Maybe you do know sumthin' I don't. I think I would enjoy hearing your system. :):):)

Craig

why do i have the feeling you're being sarcastic again :)

or at the very least facetious :p

goneten

11-04-08, 02:45 AM

I think the biggest difference in the thought process between your technique and Mark's is that you are looking for the highest "coupling" of the two subs, while his primary goal is flat frequency response at the seats.

Correct. That isn't to say that in my room the results of using identical sound pressure levels for each independently set up subwoofer does not result in a smoother FR because the results are still a lot smoother than using just a single subwoofer.

Regards,

goneten

11-04-08, 02:51 AM

But that's not a goal of Mark's.

I know that. My goal is lowest distortion and highest coupling between both subwoofers. I might not need it but I want it and I will get it.

What do you mean "irregular"? The output will be what it is, whatever it is. How can the net increase be "irregular"? It is an increase. It's not "regular" or "irregular".

You obviously have been spending too much time in bass management threads to understand how coupling works and the resulting output increases. :D The difference in dB between any two sound pressure measurements is:

dB = 20 * log (Px/Py) (where Px and Py represent the two pressure levels).

If you double the sound pressure, then Px/Py = 2. Solving for the dB increase = 6.0206 dB. A doubling of the sound pressure equates to a 6 dB increase in sound pressure. But in order to gain this you need to do a few things. You will only see a 6 dB increase when the two sound pressure sources are co-located and are identical in frequency, phase, and individual sound pressure.

It is not a requirement that both subwoofers be together to gain coupling benefits but in order for full mutual coupling to the x-over region you must co-locate unless the crossover chosen is ungodly low. I have not co-located my subwoofers and as a result I don't gain the full benefit up to my crossover point (80 hz) due to the spacing being almost 5 m apart but from 40 hz and below I am seeing a solid 5-6 dB increase due to the 1/4 wavelength spacing that I have mentioned on several occasions.

According to Mark's set up procedure you will not gain these coupling benefits and from my experience (as little as it is). I am not disagreeing with his procedure but mine is different and I feel that I benefit from it.

According to Mark's method, all that matters is the total SPL at the sweet spot. The 2 subs' overall output can be adjusted in "unity" to a specific SPL whether they are contributing equally to the total SPL or not.

Okay, got it. :)

Yeah, I hear you, but I think Mark's logic makes sense. I don't know what "coupling" is, but you're not looking for more output anyway, are you?

I'm always looking for more output. What is most important to me is sufficient headroom for the given application - i.e., room size, distance from the listening position, preferred playback level, etc. I also want a relatively flat response too.

FYI, I recommend the 1/4 wavelength distance for complete acoustic coupling based on my own in-room measurements. I've experimented with side-by-side, stacked, 1/4 wavelength, 1/2 wavelength, opposite corners, front/rear, etc.

What is a "correct" result, goneten?

The correct result for me is not necessarily the correct result for you. I seek maximum output and best dynamics and lowest distortion and my set up procedure mated with my experience allows me to achieve it.

The additive result is what it is.

No, I'm afraid it is not.

You can calibrate the subs' combined output in unison to whatever level you want.

You don't seem to understand the issues here. It's not so much that the overall level is X but that both sound pressure sources are outputting equal output at the seats hence the levels are equal at the seats (provided both subwoofers are operating in phase) and gaining "free" output due to the coupling nature of two subwoofers 1/4 wavelength spaced and set up for equal level and phase. :)

Regards,

craig john

11-04-08, 08:49 AM

why do i have the feeling you're being sarcastic again :)

or at the very least facetious :p
Actually, I've never heard a system comprised of "full-range" speakers at all main speaker positions. And I don't think I've ever said anything negative about this type of system. I've only ever defended Bass Management and re-directed bass.

I also don't think I knew your system had dual columns of sealed subs up front. Is that something new? I thought you had a Supercube. What sealed subs do you have?

I really do think I would enjoy hearing your system. It would be a "learning experience" for me. :)

Craig

goneten

11-04-08, 09:13 AM

I've only ever defended Bass Management and re-directed bass.

You probably don't know this, but sivadselim is our resident bass management fundie on all things large and small. That is his forte. If you have any questions on bass management he will know. :D

Regards,

Mark Seaton

11-04-08, 09:51 AM

I know that. My goal is lowest distortion and highest coupling between both subwoofers. I might not need it but I want it and I will get it.
...

I'm always looking for more output. What is most important to me is sufficient headroom for the given application - i.e., room size, distance from the listening position, preferred playback level, etc. I also want a relatively flat response too.
...

The correct result for me is not necessarily the correct result for you. I seek maximum output and best dynamics and lowest distortion and my set up procedure mated with my experience allows me to achieve it.
...

You don't seem to understand the issues here. It's not so much that the overall level is X but that both sound pressure sources are outputting equal output at the seats hence the levels are equal at the seats (provided both subwoofers are operating in phase) and gaining "free" output due to the coupling nature of two subwoofers 1/4 wavelength spaced and set up for equal level and phase. :)

Regards,

Hi goneten,

I'll take another stab this morning here. :rolleyes:

The crux of the matter is that you are looking at a pink noise measurement to quantify something it is not intended to measure. Of course increasing the level on one sub is likely to make for a louder measurement. The difference is that I'm looking at a frequency response, not a pink noise measurement which is indiscriminate in frequency and weighted toward the upper octave of the subwoofer range.

You can also play with phase knobs to adjust the interaction of the two subwoofers if you don't have independent delay adjustments which are available from something like a DSP-30 or DCX2496. The key here is to be looking at the frequency response, not a gross SPL reading from pink noise. You want the settings that yields the fewest dips in response, and one which overall adds to the output of a single subwoofer, with the possible exception of reducing a peak or two.

A flatter response without any big depressions IS more efficient than a response with a 10dB peak at one frequency and a 15dB dip elsewhere in the response, but the response with a 10dB peak will measure louder with pink noise, especially if its above 40Hz.

goneten

11-04-08, 11:58 AM

The crux of the matter is that you are looking at a pink noise measurement to quantify something it is not intended to measure. Of course increasing the level on one sub is likely to make for a louder measurement.

Mark, I mentioned earlier that I measured my response and I gained a solid 5-6 dB's below 40 hz.

The difference is that I'm looking at a frequency response, not a pink noise measurement which is indiscriminate in frequency and weighted toward the upper octave of the subwoofer range.

I'm not sure where you get the impression that I'm just looking at pink noise to confirm my findings because I'm not. I have measured my room response and I am aware that pink noise measurements are not indicative of real world performance within a room. :rolleyes:

I agree with you on many of your points, make no mistake about it. But the results in my room call for different set up procedures that work best for me. FYI, I think you make great subwoofers. :)

Regards,

kemiza

11-04-08, 12:06 PM

I have a Klipsch RSW 12 and a Velodyne HGS 18 connected to my receiver. The bass is insane!

sivadselim

11-04-08, 03:42 PM

You probably don't know this, but sivadselim is our resident bass management fundie on all things large and small. That is his forte. If you have any questions on bass management he will know. :DEverything I know, I learned from craig john. :D

sivadselim

11-04-08, 03:43 PM

I have a Klipsch RSW 12 and a Velodyne HGS 18 connected to my receiver. The bass is insane!Well, maybe you could comment on the quality of the output of the much maligned RSW subs. ;)

craig john

11-04-08, 04:03 PM

Everything I know, I learned from craig john. :D

I taught him everything he knows...

...but not everything *I* know! :D:D:D

craig john

11-04-08, 04:09 PM

^
Actually, that line came from a heart surgeon I used to work with. He taught residents and when they graduated, he would always use that line. :) (I'm pretty sure he actually *meant* it, but ya gotta know heart surgeons.)

Craig

goneten

11-04-08, 04:26 PM

I taught him everything he knows...

Did you teach him that settings speakers to small can be harmful to them at high levels especially if they are not capable ?

Oops. . .:D

Regards,

sivadselim

11-04-08, 04:35 PM

Did you teach him that settings speakers to small can be harmful to them at high levels especially if they are not capable?Nope, he probably knows that. Setting speakers to LARGE at high levels can be harmful to them, as well. ;)

goneten

11-04-08, 04:38 PM

Nope, he probably knows that. Setting speakers to LARGE at high levels can be harmful to them, as well

Just checking. :)

Regards,

kemiza

11-04-08, 05:41 PM

Well, maybe you could comment on the quality of the output of the much maligned RSW subs. ;)
Ok the RSW 12 is wicked!!!

12" woofer to reproduce the upper bass frequencies
18" driver to recreate the lowest frequencies

craig john

11-05-08, 04:02 PM

dB = 20 * log (Px/Py) (where Px and Py represent the two pressure levels).

If you double the sound pressure, then Px/Py = 2. Solving for the dB increase = 6.0206 dB. A doubling of the sound pressure equates to a 6 dB increase in sound pressure. But in order to gain this you need to do a few things. You will only see a 6 dB increase when the two sound pressure sources are co-located and are identical in frequency, phase, and individual sound pressure.

It is not a requirement that both subwoofers be together to gain coupling benefits but in order for full mutual coupling to the x-over region you must co-locate unless the crossover chosen is ungodly low. I have not co-located my subwoofers and as a result I don't gain the full benefit up to my crossover point (80 hz) due to the spacing being almost 5 m apart but from 40 hz and below I am seeing a solid 5-6 dB increase due to the 1/4 wavelength spacing that I have mentioned on several occasions.
A 40 Hz soundwave has a wavelength of 8.5 meters:

speed of sound at sea level = 340.29 m/s
340.29/40 Hz = 8.5
8.5/4 = 2.125 meters

How are you getting mutual coupling with the 1/4 wavelength theory if your subs are 5 meters apart? They would need to be no more than 2.125 meters apart for 1/4 wavelength coupling at 40 Hz. :confused:

Of course, not everyone agrees that 1/4 wavelength is the distance needed for mutual coupling. Some think that 1/2 wavelength spacing is required. This is from the Genelec website:
When two or more subwoofers (except the 7050B as it does not have a sum output) are positioned close to one another mutual coupling is the fortunate by-product. This is due to the long wavelengths, associated with low frequencies, causing constructive superimposition. For mutual coupling, the subwoofers must be placed within ½ a wavelength of one another (85 Hz upper crossover frequency ½ wavelength is approximately 2 m). For example, two subwoofers give a 6 dB increase in acoustical output at the listening position

Here is another interesting discussion on "coupling" of drivers from the Rane website:
coupling or mutual coupling Loudspeakers. General term describing the combining behavior of two or more drivers reproducing the same frequency. If two or more identical loudspeakers are mounted such that their acoustic centers are close together (i.e., some fraction of a wavelength), their acoustic outputs over some frequency range will combine (couple) and propagate forward as one waveform, thus two smaller drivers behave as one big driver. [This is the simple vague answer, a detailed specific answer requires a great deal more.]

Mark Gander, VP of pro marketing for JBL, puts it this way: "The correct maximum distance that mutual coupling occurs depends on what you want to define as the limit of coupling. For example, is it the maximum approaching +3 dB, or when it reverts to unity gain? It's a gradual transition, so either 1/4 wavelength or 1/2 wavelength separation distance is just a rule of thumb." [Gander sites Lee Henney's Radio Engineering Handbook, 5th ed., Ch. 11 'Loudspeakers and Room Acoustics,' as a useful source that shows the response from groups of pistons at various distances, following the work of Klapman (Klapman, S. J., "Interaction Impedance of a System of Circular Pistons," J. Acoust. Soc. Am., vol. 11, p. 289, 1940.)"

John Murray, Digital Audio Lab Manager, Columbia College Chicago, explains: "Mutual coupling is when multiple drivers produce relatively more output at the low end of their response curve than a single driver. This occurs when the drivers are close enough together to have less than 90 degrees of path length difference for the wavelengths of interest at a given listening position. This phenomena is position-dependant, and is, in fact, what causes the high level portion of lobing. At shorter wavelengths (higher frequencies) and listening positions farther off-axis of the drivers, the phase difference becomes destructive which results in the nulls of lobing. Even with drivers that are touching, mutual coupling over a wide listening area are virtually always below 300-500 Hz.

Chuck McGregor, Technical Services Manager for EAW, says, "It depends." And goes on to explain: "There is no such thing as a correct, maximum source spacing distance for mutual coupling. First one has to define what they consider as mutual coupling (i.e., at what level off-axis does one stop considering the sources as no longer being mutually coupled) and then what is the criteria is for a particular situation, meaning the frequency to which one requires the coupling and the overall angle over which it is needed. Based on this stuff you can figure out the maximum, acceptable driver spacing.

Harry Olson analyzes this (although he does not call it mutual coupling) as a double or doublet source in his book, Acoustical Engineering, section 2.3.

McGregor's personal view: "First, mutual coupling will occur on-axis even if the center-to-center distance of two sources is 100 light years. At 1/2 wavelength separation they cancel completely at 90 degrees off-axis. At 45 degrees off-axis the signal is roughly 6 dB down, i.e. the equivalent of one source. Does this mean their mutual coupling beamwidth is limited to 45 degrees or is it limited at the 6 dB down point? Maybe it is 3 dB down over a lesser angle?"

McGregor offers this as a detailed definition: "Mutual coupling is when the outputs of two or more acoustical sources producing the same signal combine (couple) and propagate forward as one waveform. In this way, two smaller drivers can behave as one larger driver. While any number of sources can mutually couple, for clarity this discussion will focus on two sources.

The amount of coupling directly on axis between two sources producing the same signal will result in a 6 dB increase in level. On-axis, the spacing of these sources has absolutely no effect on this result. However, because the two sources must be physically separated, the coupling decreases off axis as the path lengths from each source to the listener increasingly differ. This is because the two waveforms become increasingly out of phase. For a given source spacing, the higher the frequency is, the more quickly off-axis this occurs. Likewise for a given wavelength (frequency) the wider the source spacing, the more quickly off-axis this occurs. Thus, the amount of mutual coupling at any point off-axis depends on both the source spacing and the wavelength (frequency) of the sound being produced.

What is considered mutual coupling? The broadest definition is that any multiple sources producing the same signal whose outputs acoustically combine to produce an increase in level over that of one of the sources means mutual coupling is taking place.

For audio purposes, changes of 3 dB and 6 dB are often used as typical criteria for acceptable increases or reductions in level. For two sources, a 3 dB decrease from the on-axis coupling of 6 dB occurs when the path length difference from the sources to the listener is 1/4 wavelength. This equals a 90 degree phase shift between the two waveforms. Likewise for two sources, a 6 dB decrease from the on-axis coupling of 6 dB occurs when the path length difference from the sources to the listener is 1/3 of a wavelength. This equals a 120 degree phase shift between the two waveforms. It also results in a level that equals the output of one source, meaning the amount of mutual coupling is effectively equal to zero.

Thus, the best definition for mutual coupling is defined by what is acceptable for any given situation. This can vary from the full, on-axis mutual coupling to the effective absence of mutual coupling, which is where the level decreases to be equal to or less than of one of the sources. Contrary to popular notions, there is no particular driver spacing that results in mutual coupling. Mutual coupling is defined by the level below which mutual coupling is not longer considered mutual coupling. This is an arbitrary level but, in any case, it cannot be below the level of one of the sources. The source spacing and the wavelength (frequency) of the signal then determines the angle over which the combined wavefront falls within the chosen definition of being mutually coupled."
http://www.rane.com/par-c.html

And another one from the ServoDrive manual:
If you are using more than one ServoDrive subwoofer for an application, coupling the subwoofers by placing them next to each other will result in a large increase in efficiency and extended low frequency response. Coupling ServoDrive subwoofers in this manner has the effect of creating a larger, more powerful single sound source equivalent to a much larger subwoofer. Units may be placed at a desired wavelength apart from each
other to effectively create "lobes" of sound where the output would resemble a large figure 8, with little output to the sides, yet projecting a large output to the front and rear.
http://www.servodrive.com/Download_files/Contrabass/ContraBassManual.pdf

Finally, see "Low Frequency Augmentation - Subwoofers" starting on Page 26 of this article from the JBL Pro Sound Systems Design Reference Manual:
http://www.jblpro.com/pub/manuals/pssdm_2.pdf

Craig

goneten

11-05-08, 04:30 PM

How are you getting mutual coupling with the 1/4 wavelength theory if your subs are 5 meters apart? They would need to be no more than 2.125 meters apart for 1/4 wavelength coupling at 40 Hz

Your math appears better than mine. Who knew. :) I must have messed up my actual distance numbers because looking back my subwoofers are not 5 m apart but 3.5 m apart. :D Below 40 hz I am getting solid gains.

Of course, not everyone agrees that 1/4 wavelength is the distance needed for mutual coupling. Some think that 1/2 wavelength spacing is required. This is from the Genelec website:

Sure. The theories mentioned at Genelec are interesting and informative. I won't claim to be more knowledgeable than them but I will say that I have put my theories to test time and again and my hypothesis confirms it. :)

And another one from the ServoDrive manual

Very good material.

Regards,

DS-21

11-05-08, 08:08 PM

craig john

11-05-08, 08:22 PM

Once you've set up the primary sub, why do you care at all about the response of the other subs in isolation? Individual sub response could not be less relevant.
He didn't say *anything* about "response". He said "levels".

Once you've set up the main sub, you're building a system, not playing with a single block. In a system designed to reproduce recorded bass with high fidelity (and I understand other people have different goals with different methodologies being appropriate), the other subs should just be fixing issues caused by placement from the main sub, and raising the overall level just a little bit, nothing else.
You can set your's up any way you like. If you like Earl Geddes's approach, feel free to use it. However, there are other ways to set things up. Personally, I'll use Mark Seaton's and Carl Kennedy's method of using identical subs and setting equal *gains* on the subwoofers. It is the most logical IMO.

The "wise man" is actually a bit of a dunce, it seems. Or bloody ignorant of high fidelity audio.
Why do you need to be so arrogant and condescending?

Craig

sivadselim

11-05-08, 09:14 PM

Once you've set up the primary sub, why do you care at all about the response of the other subs in isolation? Individual sub response could not be less relevant.

Once you've set up the main sub, you're building a system, not playing with a single block. In a system designed to reproduce recorded bass with high fidelity (and I understand other people have different goals with different methodologies being appropriate), the other subs should just be fixing issues caused by placement from the main sub, and raising the overall level just a little bit, nothing else.I don't think this is how anyone wants to use their identical subwoofers. What you are describing may be a way to use dissimilar subs and may actually be a better way than trying to use a lesser sub, full-bore. But designating one of two (or more) identical subs as the primary subwoofer and using the other(s) in a secondary role is probably not acceptable for many here who invest in multiple subwoofers. That is not to say that your (Geddes's) method is wrong; only unpalatable.

I also think it is important to make a distinction here in this discussion between calibration of identical subwoofers versus calibration of dissimilar subwoofers. The (usual) approach and rationale employed in each case is completely different.

We now have in this thread 2 different ways to calibrate the output levels of identical subwoofers, both of which are logical and defensible. One involves (or requires) level matching the subwoofers and the other, instead, involves (or requires) matching their gain. Both approaches, in the end, can result in a "correct" calibration of the subs' overall output.

But neither of those methods is appropriate for calibrating the relative and combined output of 2 dissimilar subwoofers. I would still posit that using dissimilar subwoofers without any EQ capability is extremely problematic, especially for a novice. If you asked me, randomly adjusting both the relative output and locations of two (or more) dissimilar subs with only an SPL meter for guidance is an exercise in frustration and maybe even futility. Even with the ability to measure the FR more simply and accurately with software, randomly adjusting the relative output and the locations of 2 (or more) dissimilar subs and expecting to stumble upon some magical arrangement and relative output ratio that results in both the flattest FR and also properly calibrates their combined SPL seems ambitious, to say the least.

goneten

11-06-08, 02:15 AM

We now have in this thread 2 different ways to calibrate the output levels of identical subwoofers, both of which are logical and defensible. One involves (or requires) level matching the subwoofers and the other, instead, involves (or requires) matching their gain. Both approaches, in the end, can result in a "correct" calibration of the subs' overall output.

Bingo.

Regards,

goneten

11-06-08, 02:26 AM

Individual sub response could not be less relevant.

Oh, okay then, you've changed my mind.

Regards,

DS-21

11-06-08, 01:31 PM

I don't think this is how anyone wants to use their identical subwoofers.

Why not? Do people who buy identical subwoofers not care about high fidelity bass reproduction?

I also think it is important to make a distinction here in this discussion between calibration of identical subwoofers versus calibration of dissimilar subwoofers. The (usual) approach and rationale employed in each case is completely different.

It is a distinction utterly without a difference.

Both approaches, in the end, can result in a "correct" calibration of the subs' overall output.

"Correctly" calibrating the subs' output (i.e. level) is child's play for idiots. What's far more interesting and useful is smoothing out the bass subsystem's frequency response. Especially in the upper bass

If you asked me, randomly adjusting both the relative output and locations of two (or more) dissimilar subs with only an SPL meter for guidance is an exercise in frustration and maybe even futility.

I didn't ask you, because you seem to bizarrely fetishize 20th century tools and notions.

Even with the ability to measure the FR more simply and accurately with software, randomly adjusting the relative output and the locations of 2 (or more) dissimilar subs and expecting to stumble upon some magical arrangement and relative output ratio that results in both the flattest FR and also properly calibrates their combined SPL seems ambitious, to say the least.

Yes, it requires some actual human thought. Either one cares about high fidelity and is willing to make the investment and effort to attain it, or one doesn't. You know what camp I'm in.

sivadselim

11-06-08, 02:22 PM

Why not? Do people who buy identical subwoofers not care about high fidelity bass reproduction?Maybe not. That is not the way I have seen anyone in this subforum claim to be utilizing dual identical subs.

It is a distinction utterly without a difference.Well, we disagree. And most here would disagree. They are fundamentally different situations. But your idea of how to implement dual subs, even when identical, is not the conventional method most here employ. That is not at all to say that the conventional method is correct. Your method may be correct. Everyone else could be doing it incorrectly. Most people are attempting to level match the subs and consider that important. Mark's method, although different, is still very similar. If you feel that strongly about it, you should try and convert everyone here who uses multiple subs. And I'm not being facetious. Conventional wisdom CAN be turned on its head.

"Correctly" calibrating the subs' output (i.e. level) is child's play for idiots. What's far more interesting and useful is smoothing out the bass subsystem's frequency response. Especially in the upper bassI agree that smoothing the response is an important goal, even with a single sub, DS-21. But for the purposes of a discussion of the implementation of dual and different subs, the room must be removed from the equation in order to at least discuss the theoretical result of combining the output of 2 different subs.

So, if you combine the output of a sub that goes down to 30Hz and a sub that goes down to 20Hz in a "perfect room", no matter how you adjust each sub, the output will not be flat down to 20Hz. Disregarding their roll-off for the purposes of discussion, as well, the 2 subs' output will be additive from 30Hz and up, but the 20Hz to 30Hz range will only be reproduced by one of the subs. Increasing the 20Hz sub's output in order to raise that 20Hz to 30Hz region to the proper level will not help anything as that will comcomitantly increase the combined output of the subs form 30Hz and up. You might as well just use the single 20Hz sub.

I realize that you are looking at it from an entirely different point of view. But the way I am approaching it is applicable to the way that most people here are used to discussing the implementation of dual subs.

I didn't ask you, because you seem to bizarrely fetishize 20th century tools and notions.LOL. OK. So, where is the "vibrate button" on my SPL meter.

Yes, it requires some actual human thought. Either one cares about high fidelity and is willing to make the investment and effort to attain it, or one doesn't. You know what camp I'm in.The thought is the easy part.

DS-21

11-06-08, 02:34 PM

If you feel that strongly about it, you should try and convert everyone here who uses multiple subs. And I'm not being facetious. Conventional wisdom CAN be turned on its head.

I wouldn't bother with the discussion if experience hadn't convinced me that there is a far superior way.

I agree that smoothing the response is an important goal, even with a single sub, DS-21. But for the purposes of a discussion of the implementation of dual and different subs, the room must be removed from the equation in order to at least discuss the theoretical result of combining the output of 2 different subs.

But the deleterious effects of the room on frequency response in the bass are IMO the only reason to use multiple subs in the first place. Otherwise, just get one huge one in a coner, or stack a bunch of smaller ones there, to get more SPL. And apply the heroic EQ that will be inevitably required to get a semblance of reasonable response, and that only at one small spot and to the probable detriment of everywhere else in the room. (Colocation is the one case where the conventional method makes sense. Colocation is generally an inefficient use of multiple subs, assuming again that high fidelity reproduction is the goal, as opposed to just making the booms in plotless wonders shake more stuff.)

So, if you combine the output of a sub that goes down to 30Hz and a sub that goes down to 20Hz in a "perfect room", no matter how you adjust each sub, the output will not be flat down to 20Hz. Disregarding their roll-off for the purposes of discussion, as well, the 2 subs' output will be additive from 30Hz and up, but the 20Hz to 30Hz range will only be reproduced by one of the subs.

Not true. We're talking about rolloffs, not brick walls. Their output will still add together. For that matter, so will the bass output of mains properly specified and run full range.

goneten

11-06-08, 02:50 PM

Colocation is generally an inefficient use of multiple subs, assuming again that high fidelity reproduction is the goal, as opposed to just making the booms in plotless wonders shake more stuff.)

What is "inefficient" for you is not "inefficient" for others. If low distortion is of utmost priority then co-location is a very efficient means of achieving that goal.

Regards,

sivadselim

11-06-08, 02:51 PM

I wouldn't bother with the discussion if experience hadn't convinced me that there is a far superior way.I understand.

But the deleterious effects of the room on frequency response in the bass are IMO the only reason to use multiple subs in the first place. Otherwise, just get one huge one in a coner, or stack a bunch of smaller ones there, to get more SPL. And apply the heroic EQ that will be inevitably required to get a semblance of reasonable response, and that only at one small spot and to the probable detriment of everywhere else in the room. (Colocation is the one case where the conventional method makes sense. Colocation is generally an inefficient use of multiple subs, assuming again that high fidelity reproduction is the goal, as opposed to just making the booms in plotless wonders shake more stuff.)I (mostly) agree with all of this. Additional headroom is (apparently) desirable.

But my point is that, for a novice, who does not intend to apply EQ, implementing identical subs, conventionally, is much easier than implementing differing subs, conventionally. As I said, that is not to imply that the conventional methods are necessarily "correct". Your (Geddes's) method may BE best, particularly when one is implementing differing subs. But for a novice, with a limited ability to measure their FR, and no EQ, I think it is asking a lot. It seems that doing what you are describing, armed only with an SPL meter and some 1/6 octave test tones, would require a whole lot of patience. Maybe I am wrong and it would be easier than I am imagining. But I DO understand the payoff, regardless of the effort required.

Not true. We're talking about rolloffs, not brick walls. Their output will still add together. For that matter, so will the bass output of mains properly specified and run full range.I'm not sure what is "not true". I am only saying that for the purposes of understanding the additive output of the 2 hypothetical subs, we can ignore the roll-offs. If you want to consider them, that is fine. One of the subs still has a range of unique and singular output that is lower than the other. And I DO understand how that is irrelevant from your point of view.