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^^Exellent work :)

If you connected them internal for 2ch 2ohm operation, why don’t you just do the series connection on the outside, from the two speaker posts? No need to open hatch and reconfigure the whole thing?

In distorsion graph you need to put the marker somewhere to get numbers, say at tuning or ~ 20hz.
 

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Discussion Starter #142
^^Exellent work :)
Thanks!



If you connected them internal for 2ch 2ohm operation, why don’t you just do the series connection on the outside, from the two speaker posts? No need to open hatch and reconfigure the whole thing?
Superstition? Or at least lack of understanding.
Since I don’t understand why parallel vs series/parallel changes the model so much, I have been sticking to wiring configurations that seem the most “balanced” to me.
Series/parallel: I series the upper and lower driver on each side, then parallel these 8ohm pairs.
Parallel 2ch: I parallel the upper and lower drivers, each side on a channel.

I like your way better for changing up in the driveway though.


In distorsion graph you need to put the marker somewhere to
get numbers, say at tuning or ~ 20hz.

I wasn’t sure what frequency to be interested In, so I left it off.

Chry
Chris
 

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Thanks!

Superstition? Or at least lack of understanding.
Since I don’t understand why parallel vs series/parallel changes the model so much, I have been sticking to wiring configurations that seem the most “balanced” to me.
Series/parallel: I series the upper and lower driver on each side, then parallel these 8ohm pairs.
Parallel 2ch: I parallel the upper and lower drivers, each side on a channel.

I like your way better for changing up in the driveway though.

I wasn’t sure what frequency to be interested In, so I left it off.

Chry
Chris
Yeah, the differences between how you connected it was news to me too ;)
But if you measure it with internal and external series-parallel next time and see if it is the same, you can continue to do it external from here on ;) The easiest would be two external 4pole speakons, and you would be set now matter what :) (for the life of me i can’t understand why you guys don’t use speakons??? They are soooo much easier to deal with )

Well, maybe where 2nd and 3rd harmonics maxes out would be a starting point for distorsion?? Like ~28 or ~45hz.

EDIT: maybe you should try series and parallel them sideways to? Just to see if there is a difference that way too?

Edit2: you say you use one Stewart amp here, but isn’t there two amps on that test cart?
 

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Discussion Starter #144
Yeah, the differences between how you connected it was news to me too ;)

But if you measure it with internal and external series-parallel next time and see if it is the same, you can continue to do it external from here on ;) The easiest would be two external 4pole speakons, and you would be set now matter what :) (for the life of me i can’t understand why you guys don’t use speakons??? They are soooo much easier to deal with )

Yeah, I can give it a shot next time I change it.
The don’t use speakons because they stick out. All my theater speakers are tight to a wall/chair.
This project would make sense with speakons, but I didn’t have any. I always keep a handful of my favorite terminal cups around. I could add another pair for wiring ease, but they’re 6 bucks each. I’ll probably just keep popping the hatch cover.


Well, maybe where 2nd and 3rd harmonics maxes out would be a starting point for distorsion?? Like ~28 or ~45hz.


I can do that tonight. I’m not sure that it’s relevant now that I’ve shown the spl is different.

EDIT: maybe you should try series and parallel them sideways to? Just to see if there is a difference that way too?
I could, not sure what it proves though.



Edit2: you say you use one Stewart amp here, but isn’t there two amps on that test cart?

The second amp is not being used. It was running the full range speakers for music testing.


As of now, my next plan is to verify voltage on the second channel.
If that checks out, I’ll try to get a car amp set up thats capable of 1000w 1ohm. Try a true parallel sweep.
I have one of these sitting on the shelf:
https://www.crutchfield.com/S-SpoRbe0lrly/p_575T1001BD/Rockford-Fosgate-Power-T10001bd.html

This is subject to change with suggestions, of course.

Chris
 

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You think the 2” it sits above the ground significantly changes response at bass wavelengths?
I tend to doubt it would make a measurable difference. After all, if I had the box sitting sideways, much of the port and horn mouth would be much farther from the ground. As are the cones in most direct-radiator designs. Yet, those are still ground-plane measurements.
As you found out it can make a measurable difference but in most cases it would be small enough to ignore.

Also you are nuts for dragging all this gear out in the snow and cold! I was being half sarcastic earlier when I asked if this was fun...It can also be very frustrating and a lot of work!

The cold will tend to slow down the speed of sound, boost the SPL some and stiffen the speaker suspensions compared to normal room temps. Humidity and barometric pressure also will affect the measurements.

I used the multimeter and a 60hz sinewave to set the amp at 100w for a baseline. Using 4ohm nominal impedance, that is 20v.

I ran a set of sweeps, ending at 1000w, the rating of the amp.
Voltages are recorded from DMM, wattages are calculated using the 100w baseline and the change in dB.
Ex. First sweep is -9db, 12.5w.
I use the voltage corresponding to 100w nominal into the nominal impedance because it is well accepted as the standard voltages for sensitivity. I use 10X the voltage in order to get better SNR and also because subs get used harder than any other speaker usually so it's more representative of use than 1w nominal.

Don't worry about labeling things with power or testing at a certain power IMO. I never do. It's voltage that matters. Power is not constant at all and varies with impedance and frequency. Voltage on the other hand is constant from the amplifier. It takes a while to get this stuck in your head, since everything is marketed by power ratings and it's deeply ingrained in most of us. Power still matters of course but it's much more complicated than a single number.

If you want to calculate how much maximum power the speaker is receiving just use the dcr if you don't have an impedance measurement. It's close enough. If you have the impedance curve just use the in bandwidth minimum.

Speaking of which an impedance curve would give a lot of additional information. You already seem to have a good grasp of REW and you seem to have everything you need. Just takes a bit of wire an amp and a resistor if you don't have something like a DATS. You do have to be careful with the level to not fry your soundcard with the amp. This is something that could be done inside at low volume with 1 volt or less into the sub.

I performed another set of sweeps, stopping at 1000w. Voltage was recorded from dmm on one channel, wattage is total calculated.

These don’t look nearly as pretty as the series/parallel, not sure what is going on.
Background noise is much higher in this set. Any time you see random bumps and dips in the measurements that do not repeat in other measurements it is noise. Sometimes it DOES repeat too like a 60Hz ground hum for example, but if it doesn't repeat between measurements that's a dead giveaway.

Lets compare the 1000w sweeps from each set, and see how they match up.

Well, thats not good.
That is a BIG difference. Could be an imbalance in the amp channels, or the amp current limiting a lot more into the impedance minimums when it wasn't fully bridged. This'd be my guess. Other thoughts are some output compression going on due to drivers getting some heat buildup in the coils, mismatched excursion issue, etc but none of this would make that big of a difference.


Now, let’s add in the models on 1000w.

This isn’t getting better.

The more I try to remove variables, the farther off my results are, lol. This is getting frustrating.
I'm with you on this. I can see a bit extra from baffle effects and potentially a bit more from regular old variations in gear and the SPL calibration and another boost from the cold temperature and denser air. Parts of the graph show 6 to 8dB of difference though. That much of a difference is hard to account for.

How far away are you from buildings and other large objects?

Series/Parallel:


Parallel 2ch:


Chris
Remember when MTG90 brought up the 90Hz peak in output and we were discussing it boosting the 2nd and 3rd harmonics? The orange bump at 30Hz is the 3rd harmonic getting boosted by the output at 90Hz and the large driver excursion in this range. The 2nd harmonic of 45Hz is being boosted by 90Hz, it is the red line. As expected.

Distortion is getting pretty high on these measurements. I don't think there's too much left in the tank.
 

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I could, not sure what it proves though.
Couple more things to add.

I checked the wiring combinations in Akabak again and it turns out that not all of the wiring options with drivers in series results in the driver behavior mismatch.
All drivers parallel = Even
All drivers in series = Uneven
2 drivers closest to the closed end in series / 2 other drivers in series and then both groups parallel = Even
Driver pairs wired in series with a closed end driver and further way driver and then in parallel = Uneven
Driver pairs wired diagonally in series and then parallel = Uneven
Directly driving each woofer should = Even

I think this is right. Going from memory here.

Can you take one of the highest output measurements and scale them back by the amount of gain added from the starting level so that it compares at the same level as the starting / quietest curve? This will show how much the response changed and if there is compression happening.

Also can you post a group delay graph from one of the louder measurements but not the loudest? You want it loud to be out of the noise floor as much as possible but not so loud that the speaker is being run ragged.

These are things you can do with the measurements you've already done without taking all this gear out again.

If you feel like it attach or send me a few of the measurements.
 

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For the distortion graphs in REW you can go into controls and check Plot Normalized to Fundamental and make sure Distortion Figures: Percentage and that will graph the distortion on a percentage scale which is much easier to interpret. Also be sure to make the Y axis limits something like 0.01 to 200%.
 

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Discussion Starter #149
Thanks Josh!
Ok, I’ll answer this half first, as it is huge for my testing.

Couple more things to add.



I checked the wiring combinations in Akabak again and it turns out that not all of the wiring options with drivers in series results in the driver behavior mismatch.

All drivers parallel = Even

All drivers in series = Uneven

2 drivers closest to the closed end in series / 2 other drivers in series and then both groups parallel = Even

Driver pairs wired in series with a closed end driver and further way driver and then in parallel = Uneven

Driver pairs wired diagonally in series and then parallel = Uneven

Directly driving each woofer should = Even



I think this is right. Going from memory here.
Can you verify this for me? If so, it really opens this design up to run on 4ohm. I will test to verify.

First, lets make sure we are using the same terminology. I use top referring to how the cabinet sits. Closed end of horn is top.


How I have it wired for series-parallel now: the top driver series to the one directly below it. The two resulting vertical pairs paralleled. I believe you’re saying this is Uneven.

What you’re saying: Top two series, bottom two series, results parallel = Even.

This will allow me to perform tests with the same output from the amp, excellent. Avoids the car amp cluster&@$? I was looking forward to.

Can you take one of the highest output measurements and scale them back by the amount of gain added from the starting level so that it compares at the same level as the starting / quietest curve? This will show how much the response changed and if there is compression happening.
Standard compression sweep stuff, sure. Super easy since I know the db changes. Do you want me to use the 12.5w and 1000w sweeps, or start a little higher to avoid noise issues?



Also can you post a group delay graph from one of the louder measurements but not the loudest? You want it loud to be out of the noise floor as much as possible but not so loud that the speaker is being run ragged.
Sure, I’ll try.
I’ve had issues with trying to use REW delay before. Don’t you need a timing reference to properly measure this? I was trying to use it to integrate sealed and ported in my theater, didn’t work out.



If you feel like it attach or send me a few of the measurements.
Pm me your email and I can send ya whatever data you want. I have all sweeps saved and labeled.

Thanks again,

Chris
 

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GREAT post fellas! I love this site!

Hey Josh,

With freezing temps, stiffer cones and surrounds, would those situation cause the enclosure to move the dolly during testing?
 
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I think this thread has become one of my favourites in a long time :) Awsome work guys 🤓😜
 

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Discussion Starter #152 (Edited)
Also you are nuts for dragging all this gear out in the snow and cold! I was being half sarcastic earlier when I asked if this was fun...It can also be very frustrating and a lot of work!
Gotta deal with the conditions I have. You’d think I’d be smart enough to unload the tools from the amp cart, gotta be an extra 75lbs on there, lol.

I was responding with sarcasm as well. Have to have some fun with the thread. Along with the fun in the cold

The cold will tend to slow down the speed of sound, boost the SPL some and stiffen the speaker suspensions compared to normal room temps. Humidity and barometric pressure also will affect the measurements.
Yup. Again, just working with the conditions I’ve got.


I use the voltage corresponding to 100w nominal into the nominal impedance because it is well accepted as the standard voltages for sensitivity. I use 10X the voltage in order to get better SNR and also because subs get used harder than any other speaker usually so it's more representative of use than 1w nominal.



Don't worry about labeling things with power or testing at a certain power IMO. I never do. It's voltage that matters. Power is not constant at all and varies with impedance and frequency. Voltage on the other hand is constant from the amplifier. It takes a while to get this stuck in your head, since everything is marketed by power ratings and it's deeply ingrained in most of us. Power still matters of course but it's much more complicated than a single number.



If you want to calculate how much maximum power the speaker is receiving just use the dcr if you don't have an impedance measurement. It's close enough. If you have the impedance curve just use the in bandwidth minimum.
Yeah, my power fixation is just the way most people (myself included) think about this stuff. Plus, I know my amp is rated at 1000w, and power doubling every 3db makes the calc really easy.

Ok, back to using Re instead of nominal for power calcs.



Speaking of which an impedance curve would give a lot of additional information. You already seem to have a good grasp of REW and you seem to have everything you need. Just takes a bit of wire an amp and a resistor if you don't have something like a DATS. You do have to be careful with the level to not fry your soundcard with the amp. This is something that could be done inside at low volume with 1 volt or less into the sub.
I was reading on this one the other day, but got sidetracked with other measurements. I’ll have to order some resistors. Wait, does radioshack still sell components? Maybe I can grab some today. Apparently need 1% though.

Rew’s article talks about using diodes to protect sound card when using amp. Necessary? Or just use dmm to check voltage before hooking to soundcard?

Looks like a 33ohm resistor?

Article: https://www.roomeqwizard.com/help/help_en-GB/html/impedancemeasurement.html


Background noise is much higher in this set. Any time you see random bumps and dips in the measurements that do not repeat in other measurements it is noise. Sometimes it DOES repeat too like a 60Hz ground hum for example, but if it doesn't repeat between measurements that's a dead giveaway.
Right, it was getting windier on this set.



That is a BIG difference. Could be an imbalance in the amp channels, or the amp current limiting a lot more into the impedance minimums when it wasn't fully bridged. This'd be my guess. Other thoughts are some output compression going on due to drivers getting some heat buildup in the coils, mismatched excursion issue, etc but none of this would make that big of a difference.
Probably not thermal. The hatch was off between sweep sets in the cold while I rewired. Both sweep sets had an equal number of sweeps, at equal power (roughly)





I'm with you on this. I can see a bit extra from baffle effects and potentially a bit more from regular old variations in gear and the SPL calibration and another boost from the cold temperature and denser air. Parts of the graph show 6 to 8dB of difference though. That much of a difference is hard to account for.



How far away are you from buildings and other large objects?
At least 20ft from shop, there is a tractor on one side and some railroad ties on the other that are a bit closer.
I can push the mic down to the edge of the road and take the sub 10 feet or so farther away.

Pic kinda shows situation:


Tractor is farther away than it appears, about even with test cart and 10ft+ sideways.



Remember when MTG90 brought up the 90Hz peak in output and we were discussing it boosting the 2nd and 3rd harmonics? The orange bump at 30Hz is the 3rd harmonic getting boosted by the output at 90Hz and the large driver excursion in this range. The 2nd harmonic of 45Hz is being boosted by 90Hz, it is the red line. As expected.



Distortion is getting pretty high on these measurements. I don't think there's too much left in the tank.

Yup, I caught the boosted 3rd harmonic. Didn’t think about the second

Yeah, these measurements were at “1000w”, closer to 1200w by Re. So thats the end of this setup by model anyway.

Thanks again,
Chris
 

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Discussion Starter #153
For the distortion graphs in REW you can go into controls and check Plot Normalized to Fundamental and make sure Distortion Figures: Percentage and that will graph the distortion on a percentage scale which is much easier to interpret. Also be sure to make the Y axis limits something like 0.01 to 200%.


Will do, thanks.

Chris
 

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Discussion Starter #154
One additional point on the distortion sweeps I forgot:

During the high level sweeps, including the distortion sweeps, the enclosure rattled against the plywood at certain frequencies. Not sure if/how this affected results

I’ll get an old blanket or towel down in the future.

Chris
 

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ACK! Edited as I can't even get my thoughts out right...


Chris, this is what I had suggested before: wiring the two drivers in series that were both seeing the same pressure gradient within the horn. Their impedance should track closely and so both should be similarly loaded. Now the other two drivers will likely have slightly more or less impedance at a given freq & spl, so there will be different current flowing from the other pair. Therefore (and this is simply from ZERO KNOWLEDGE, simply my hypothesis in thinking on electro-mechanical properties) slight differences in power consumption between upper and lower drivers.


As I type this, it further occurs that the pressure change inducing impedance change is going to either increase or decrease 'mechanical resistance to excursion'. So, for example, a higher pressure in one driver presents a higher load to the amplifier, yes? Using my utter lack of background in acoustical engineering principles, it might seem that this would induce differences in excursions, top-to-bottom... This is where drivers with a second vc (as used in servo drivers) would be interesting, monitoring what is happening mechanically.


So, to be silly for a moment we need a bunch of pressure transducers capable of VERY fast response times, a means of monitoring excursion of each driver, and realtime electrical data for each driver. Then we could really get a handle on it.


Such intellectual ... uh ... 'self-pleasuring' ... is quite appealing to me now. Back as an engineering undergrad, I never had any sort of interest in actually thinking through problems relating to my own interests. Girls & partying was the order of the day! Although I WAS into high end stereo gear, and for a time my roommate had what was probably the finest high end audio system on campus. I just didn't get "research" for the sake of FUN things ... other than perhaps a bit of experimentation in the chemistry lab. It is truly a blessing to have guys like you, RedFive, Ricci, LTD02, and others who like to think AND try stuff out.


At some point I will commit to doing a Quad JBL + 2xSLAPS-M12 box and measuring the results. What I am most interested in is adding mass to the PRs and reporting on the changing frequency response. I would appreciate some guidance when I get to the measuring side of things. I have a Umik and MiniDSP-HD, so I should be able to contribute something.


Okay, back to you guys who actually know what you are talking about, I will cease my speculations :cool:
 

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One additional point on the distortion sweeps I forgot:

During the high level sweeps, including the distortion sweeps, the enclosure rattled against the plywood at certain frequencies. Not sure if/how this affected results

I’ll get an old blanket or towel down in the future.

Chris
I've noticed rattles often present themselves in the data as a narrow spike of a bunch of high order harmonics at the frequency the rattles occurs. I don't really see that in your measurements but it may be just low enough in level to be hiding out of view. Either way eliminating that rattle will give you cleaner data.
 

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Can you verify this for me?
Confirmed.

First, lets make sure we are using the same terminology. I use top referring to how the cabinet sits. Closed end of horn is top.
Correct.

How I have it wired for series-parallel now: the top driver series to the one directly below it. The two resulting vertical pairs paralleled. I believe you’re saying this is Uneven.
Correct. According to Akabak this results in uneven excursion.

What you’re saying: Top two series, bottom two series, results parallel = Even.
Yup. According to Akabak this results in nearly equal excursion.

The reason I find this interesting is I modeled it in the MAUL when I was going to use 21Ipal's and since those are 1 ohm each you are pretty much forced to wire those in series. I may have been able to use them in parallel but I went another direction and never really thought about it further. I think the excursion difference was more exaggerated in that case because the spacing on 21" drivers is much larger. I'd sold my DTS-10's by then and I never investigated with those, but I've heard of a few people killing only one driver out of the cab. I think in the DTS-10 case it may not have been so bad due to a really tight spacing on the drivers. In the case of this 4X12 sub according to the model I'd advise against wiring in ways that cause it but it may be a total nothing burger anyway. I've never seen anybody investigate it really.

Standard compression sweep stuff, sure. Super easy since I know the db changes. Do you want me to use the 12.5w and 1000w sweeps, or start a little higher to avoid noise issues?
The lowest volume would be best but sometimes those are noisy so it's a judgment call.

The way I measure for output compression is I take multiple sweeps at the lowest 2 or 3 output levels. I'll usually do 5 or 6 at the starting level, 3 or 4 at the next highest and 2 or three at the next. I'll average these to get a clearer measurement out of the background noise. It helps particularly below 20Hz. I'll remove any measurements that are clearly "bad" if there are outliers that don't match the general trend of the rest and are contaminated with noise. There isn't enough power at these levels to cause any real heating in the drivers so it doesn't hurt to run a bunch in a row. I usually consider the point where real heating can occur to be at the nominal 100w level. Past that it is single measurements but the level is usually high enough to get a good SNR anyway. Also I'll keep the mic at 2 meters up to the point that it runs out of headroom. This is also for SNR purposes. I'll move back to a further 4 or 8m distance only if required for mic headroom and use the inverse square law to scale it back to match the other measurements from a shorter distance if required. I always use a 1M length measurement in REW or whatever is longest in the software I'm using. This helps out with noise rejection too.

It takes longer to do it like this with the long measurements and many redundant low volume measurements but it is worth it later on. In a quieter environment like a house, or building this is overkill usually but outside with wind, road noise and the like it really helps clean things up.


Sure, I’ll try.
I’ve had issues with trying to use REW delay before. Don’t you need a timing reference to properly measure this? I was trying to use it to integrate sealed and ported in my theater, didn’t work out.
Hmm. I always have a loopback timing reference. You can try to estimate IR delay.
 

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Discussion Starter #158
ACK! Edited as I can't even get my thoughts out right...
Nice timing, you fixed it after I read it, but before I quoted it.

Chris, this is what I had suggested before: wiring the two drivers in series that were both seeing the same pressure gradient within the horn. Their impedance should track closely and so both should be similarly loaded. Now the other two drivers will likely have slightly more or less impedance at a given freq & spl, so there will be different current flowing from the other pair. Therefore (and this is simply from ZERO KNOWLEDGE, simply my hypothesis in thinking on electro-mechanical properties) slight differences in power consumption between upper and lower drivers.
I believe you’re correct here.

My original thinking on the wiring involved making series pairs that would act identically, thus drawing the same power.

I missed a key point though, that all drivers parallel removed the variable distortion problem.
This tells us that having drivers at different points of the horn in parallel is not a problem.

So what happens if we series the drivers at the same point in the path? Since they are experiencing the same acoustic loading, they will act as one driver with twice the impedance.

Then, they can be paralleled without experiencing the variable excursion problem. You end up with the same situation as the narrow 2-driver version discussed earlier. Problem solved, at a nice 4ohm final load.

I do believe drivers at different points in the path will be demonstrating different impedance curves, and therefor absorbing different amounts of power. The difference shouldn’t be enough to put us anywhere near thermal failure, these are robust drivers and relatively low powers.

Looks like we just opened up the “magic square” version of horn design. @Red Five, better get the 3x3 BMD design rolling.


As I type this, it further occurs that the pressure change inducing impedance change is going to either increase or decrease 'mechanical resistance to excursion'. So, for example, a higher pressure in one driver presents a higher load to the amplifier, yes? Using my utter lack of background in acoustical engineering principles, it might seem that this would induce differences in excursions, top-to-bottom... This is where drivers with a second vc (as used in servo drivers) would be interesting, monitoring what is happening mechanically.
Remember, the amp supplies constant voltage at a certain frequency. The acoustic loading if the drivers will affect their impedance curves, causing them to absorb variable amounts of power. This is way above my ability to visualize to get any more specific.

So, to be silly for a moment we need a bunch of pressure transducers capable of VERY fast response times, a means of monitoring excursion of each driver, and realtime electrical data for each driver. Then we could really get a handle on it.
Yup, high speed cameras and scales should work nicely for excursion measurements. Lets go all myth-busters on this one and use a ridiculous amount and cost of equipment to measure a $300 subwoofer

Such intellectual ... uh ... 'self-pleasuring' ... is quite appealing to me now. Back as an engineering undergrad, I never had any sort of interest in actually thinking through problems relating to my own interests. Girls & partying was the order of the day! Although I WAS into high end stereo gear, and for a time my roommate had what was probably the finest high end audio system on campus. I just didn't get "research" for the sake of FUN things ... other than perhaps a bit of experimentation in the chemistry lab. It is truly a blessing to have guys like you, RedFive, Ricci, LTD02, and others who like to think AND try stuff out.
I got tired of partying after my first two years of college. (Really after the first one) I enjoyed audio, but didn’t have the budget to play with it much.
I mostly got into junkyard hotrodding instead. We rented a house with a decent sized detached garage. This caused me to just miss having a 3.5 GPA, but I had plenty more fun in the process. Was pushing 350hp from a NA ford 302 with no aftermarket parts besides valve springs. Was trying to mess with boost, but thats very hard to do without aftermarket controls.

At some point I will commit to doing a Quad JBL + 2xSLAPS-M12 box and measuring the results. What I am most interested in is adding mass to the PRs and reporting on the changing frequency response. I would appreciate some guidance when I get to the measuring side of things. I have a Umik and MiniDSP-HD, so I should be able to contribute something.
This thread has a bit of measurement information, lol. I’ve certainly learned way more than expected.
Feel free to pm me questions, or just start a thread when you get there.


Okay, back to you guys who actually know what you are talking about, I will cease my speculations :cool:
I’m not sure that anyone here “knows what they’re talking about” with multi driver horns, other than Josh anyway. And judging by the variable excursion modeling, even he doesn’t deal with it much. Gotta love playing with abstract designs.

Chris
 

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Discussion Starter #159 (Edited)
The reason I find this interesting is I modeled it in the MAUL when I was going to use 21Ipal's and since those are 1 ohm each you are pretty much forced to wire those in series. I may have been able to use them in parallel but I went another direction and never really thought about it further. I think the excursion difference was more exaggerated in that case because the spacing on 21" drivers is much larger. I'd sold my DTS-10's by then and I never investigated with those, but I've heard of a few people killing only one driver out of the cab. I think in the DTS-10 case it may not have been so bad due to a really tight spacing on the drivers. In the case of this 4X12 sub according to the model I'd advise against wiring in ways that cause it but it may be a total nothing burger anyway. I've never seen anybody investigate it really.
Hey, even you might learn something out of this one, lol.
Time for a NSW6021 MAUL?

I will do my best to investigate by performing sweeps at the corrected wiring and comparing.




The lowest volume would be best but sometimes those are noisy so it's a judgment call.



The way I measure for output compression is I take multiple sweeps at the lowest 2 or 3 output levels. I'll usually do 5 or 6 at the starting level, 3 or 4 at the next highest and 2 or three at the next. I'll average these to get a clearer measurement out of the background noise. It helps particularly below 20Hz. I'll remove any measurements that are clearly "bad" if there are outliers that don't match the general trend of the rest and are contaminated with noise. There isn't enough power at these levels to cause any real heating in the drivers so it doesn't hurt to run a bunch in a row. I usually consider the point where real heating can occur to be at the nominal 100w level. Past that it is single measurements but the level is usually high enough to get a good SNR anyway. Also I'll keep the mic at 2 meters up to the point that it runs out of headroom. This is also for SNR purposes. I'll move back to a further 4 or 8m distance only if required for mic headroom and use the inverse square law to scale it back to match the other measurements from a shorter distance if required. I always use a 1M length measurement in REW or whatever is longest in the software I'm using. This helps out with noise rejection too.



It takes longer to do it like this with the long measurements and many redundant low volume measurements but it is worth it later on. In a quieter environment like a house, or building this is overkill usually but outside with wind, road noise and the like it really helps clean things up.
Ok, will do. Sweeps at 2m until clip, then move back and adjust.







Hmm. I always have a loopback timing reference. You can try to estimate IR delay.
I got lost last time I tried digging in to this one. Then again, I was also looking at rePhase and FIR filters and other things over my head.

Thanks,
Chris
 
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