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post #181 of 194 Old 07-09-2012, 07:38 AM
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Originally Posted by LTD02 View Post

i'm not back pedaling at all.
at this point it is clear that you just don't understand the argument bosso.

it doesn't matter what combination of drivers you use--the yellow lines represent the full extremes of drivers used from the re-xxx to the jbl 2242h. anybody can take an 8 cubic foot enclosure and keep adding drivers and see the same effect.
it doesn't matter how you stack them, how many you use, what the compliance is, etc., you can't get any additional efficiency/sensitivity out of an enclosure in the low bass. the enclosure size sets the limit.
the argument in the o.p. was that the re-xxx in an 8 cubic footer provides no more efficiency/sensitivity than any other combination of drivers and it has been confirmed.
to throw out that would be to throw out the empirical work of thiele and small, hoffman, and others. if you can do that, well, that would be ground breaking. until then, i suppose that i will stick with the guys and their work.
it is case closed.


Let's have a look...
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Originally Posted by LTD02 View Post

It has been a little quiet around here since the re-design, so I figured that we might light it up a bit.
Let's talk about efficiency vs. depth.
Traditional thinking is that high sensitivity drives have no low end and low end drivers dominate bottom end sensitivity.
By forfeiting the top end, the triple X drives win the low end right?
NOPE!
I'll go ahead and nuke a hole in this theory and say that it is upside down...low sensitivity drives don't have any high end.
For example, here is the re-xxx in 8 cubic ft against another set of drivers in the same sealed enclosure, 8 cubic feet. I'm not saying which, but if you poke around a bit you can find them.
The re-xxx has no sensitivity advantage anywhere.
From 60hz up, they just suck 10X the power for a given spl.
As for maximum spl, the re plops out around 42mm +/-, so dual 18's with +/- 20 will be pretty much the same but at much less power.
HONK!
482
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edit: you have mentioned craig chase a couple of times. i don't know what his arguments were and i'm not attempting to defend them in any way.

So, we have the RE XXX-18 in 8 cubes vs 2 unnamed 18s in the same 8 cubes with 1000W? Are you saying this is a coincidental comparison? Right. rolleyes.gif

I understand your sensitivity blurb. I couldn't possibly understand it more clearly. I'm pointing out that that's not what your OP suggests at all and that, when designing a HT sealed subwoofer system, your sensitivity point is all but irrelevant. What matters is results. Your suggestion is that results are equal regardless of the driver used. I haven't seen a single example of results using this or that driver that even remotely suggests your premise is valid.

I endorse the SM because Seaton knows what he's doing and accomplished a lot with a little. But, that's not the same as accomplishing more with a lot. There is a difference, your argument notwithstanding. Period.

I think it's great that people believe sidechain limiting is harmless, transparent and necessary, or that shelf filtering at cross adds headroom or that short throw drivers are better than the XXX, UXL, LMS, MX drivers for 'x' reason. Just makes it easier to build a better system than they can. But, this is DIY. My career here is about to end, so I'm impatient... Put up or shut up. wink.gif
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post #182 of 194 Old 07-09-2012, 08:33 AM
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Originally Posted by J_Palmer_Cass View Post

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Originally Posted by bossobass View Post

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Originally Posted by maxmercy View Post

I am doing some measuring this weekend, I'll give it a whirl. Maybe not 110dB, but I'll compare a single tone to LFE pink noise at the same SPL and post the results.
JSS

Josh and Ilkka have done this test. Not exactly pink noise, but you'll get a very similar result. Here's 10 tones that equal 110dB:

Nxxxpppspectralcontamination110db.jpg




Every time you double the number of individual sine wave frequencies (all with identical signal level) you gain 6 dB of signal level.

Pink noise and white noise (full or bandwidth limited) are different animals.

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Originally Posted by J_Palmer_Cass View Post

Every time you double the number of individual sine wave frequencies (all with identical signal level) you gain 6 dB of signal level.

Why is that not reflected in the posted graph?

Because electrical signal summation is ~3dB/doubling or 10dB/10x... which does bear out in the graph.

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post #183 of 194 Old 07-09-2012, 08:57 AM
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Originally Posted by bossobass View Post


I understand your sensitivity blurb. I couldn't possibly understand it more clearly. I'm pointing out that that's not what your OP suggests at all and that, when designing a HT sealed subwoofer system, your sensitivity point is all but irrelevant. What matters is results. Your suggestion is that results are equal regardless of the driver used. I haven't seen a single example of results using this or that driver that even remotely suggests your premise is valid.

This should be a very obvious point to anyone planning/designing a sealed subwoofer. Box size plays the dominant role in how much power it will take to reach a given output level down low. DCR and suspension differences can easily leave 3dB in sensitivity between different drivers down low, but no matter the optimization, there's a direct relationship defining a ceiling for box size and power required down low.

At the same time a sealed box only produces sound from the displacement of the woofer, and there's no way around the fact that you need a specific amount of air displacement for a specific SPL output. It won't matter if it's 48 6.5" woofers or a single 21" beast. If the air displacement is the same, the SPL produced is the same.

The "results" are the intersection of the two. Lots of sensitivity from a big box may save a few $$$ on amplification, but if the displacement capability isn't there, the tiny box requiring 4kW might still get louder. The corollary is of course true where a 21" woofer with +/- 60mm p-p crammed in a shoebox is of no more value if you don't have safe power to reach more than +/-10mm.

Again this should be clear to those who have done any tinkering with models and kept an eye on the load impedance. Given the original post, it isn't as clear as we might have assumed.
Quote:
I endorse the SM because Seaton knows what he's doing and accomplished a lot with a little. But, that's not the same as accomplishing more with a lot. There is a difference, your argument notwithstanding. Period.

Thanks again. Bigger is fun as well. The real question probably circles back to if a stack of subs optimized to be able to function well using 1-2 units gives up much to an assembly intended to operate as a group.
Quote:
I think it's great that people believe sidechain limiting is harmless, transparent and necessary, or that shelf filtering at cross adds headroom or that short throw drivers are better than the XXX, UXL, LMS, MX drivers for 'x' reason. Just makes it easier to build a better system than they can. But, this is DIY. My career here is about to end, so I'm impatient... Put up or shut up. wink.gif

More big and awesome offerings make for more excitement about what is really possible beyond the Velodyne and JLs of the world. At least with your long business experience you should have a sustainable effort which so many others have failed to achieve, especially the suppliers to and those coming from the DIY world.

Mark Seaton
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post #184 of 194 Old 07-09-2012, 12:03 PM
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It seems like the conversation is going in cricles and jumping across a variety of subjects as usual. Sensitivity, maximum output, limiters, test signals versus complex real content, etc. I'm going to repeat a lot of things previously mentioned here.

Sensitivity in the deep bass is largely (but not totally) determined by box volume. HIL etc. I don't think anyone is arguing against that. I don't remember anyone being confused about this either so I'm not sure why it was brought up to begin with?

However I would like to point out that there can be some differences as I noted in some measurements posted earlier in the thread so I am quoting that post below because sensitivity was brought up again. There can be differences of 3 to 4 dB or more and this is not seen in WinISD or other modeling programs and the reason is partly because the data used for the simulations is incomplete and missing the complex inductance which is a major component in the final performance that can impact the response shape, efficiency and sensitivity in a big way which in turn affects the amount of power or voltage to driver excursion relationship. I've posted about this before and that is why I keep bringing it up. A lot of people consider inductance relatively unimportant for sub drivers operated <100Hz. After seeing how the real world result differs radically from the model due to the inductance being unnaccounted for in high inductance drivers, I consider that missing information pretty important. Albeit for a slightly different reason than the classic view on it. So yes at the end of the day there can be sensitivity and efficiency differences. Don't forget about varying impedance that makes it very difficult to match power input into 2 differing systems at any particular frequency too. This doesn't mean that HIL isn't true, it just means that it is a bit more complex than X size driver in X size volume will always have X sensitivity at X deep bass frequency such as something like WinISD shows. The programs that model this behavior are rare, but the worst part is that you simply can't get the information needed to do so on most large bass drivers anyway. Essentially you have to use something that has already been vetted by someone else, or use your best judgment and pick a driver and then test these things yourself. I put much less stock in simulation bench racing now than I did a few years ago.

Sensitivity is great but it is only one parameter. Deep bass is usually the first region of response to run out of headroom. Deep bass requires high displacement for high output especially using sealed enclosures. This is why there has been an explosion in long xmax drivers over the last decade and a half. Even the pro audio high efficiency drivers are recognizing the need for increased displacement and are sacrificing sensitivity and efficiency to some extent for power handling and xmax. In general the more sensitive the driver the lighter the moving mass and higher the motor strength. Both of which usually mean a shorter xmax or greatly increased cost. Longer stroke usually means a heavier moving assembly and reduced peak motor strength so efficiency goes down. It's a sliding scale. In the middle is a good region of overlap where you can get a reasonable amount of both or optimize for a certain application.

The above factors all reinforce the point that Bosso and also Mark are making that yes...There is quite a bit more to doing it right than stuffing any old driver in a sealed box and strapping an amp to it. A system as used typically involves the speaker, enclosure, amplifier, equalization, front end electronics, speakers being integrated with the subwoofer system and the room.
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post #185 of 194 Old 07-09-2012, 02:13 PM
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Originally Posted by Ricci View Post

There can be differences of 3 to 4 dB or more and this is not seen in WinISD or other modeling programs and the reason is partly because the data used for the simulations is incomplete and missing the complex inductance which is a major component in the final performance that can impact the response shape, efficiency and sensitivity in a big way which in turn affects the amount of power or voltage to driver excursion relationship. I've posted about this before and that is why I keep bringing it up. A lot of people consider inductance relatively unimportant for sub drivers operated <100Hz. After seeing how the real world result differs radically from the model due to the inductance being unnaccounted for in high inductance drivers, I consider that missing information pretty important. Albeit for a slightly different reason than the classic view on it. So yes at the end of the day there can be sensitivity and efficiency differences. Don't forget about varying impedance that makes it very difficult to match power input into 2 differing systems at any particular frequency too. This doesn't mean that HIL isn't true, it just means that it is a bit more complex than X size driver in X size volume will always have X sensitivity at X deep bass frequency such as something like WinISD shows. The programs that model this behavior are rare, but the worst part is that you simply can't get the information needed to do so on most large bass drivers anyway. Essentially you have to use something that has already been vetted by someone else, or use your best judgment and pick a driver and then test these things yourself. I put much less stock in simulation bench racing now than I did a few years ago.

Yay! I'm in this exclusive group. cool.gif Yeah, that's what I like about Unibox. It can do that. *ssssnniiiiifffffffff*

But yeah, most manufactures are sketchy about details and stuff. We know the drill. I don't have to buy it though.


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post #186 of 194 Old 07-09-2012, 03:13 PM
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Originally Posted by Ricci View Post

Sensitivity in the deep bass is largely (but not totally) determined by box volume. HIL etc.

Of course you're aware of this, but sensitivity is not the same as efficiency, and HIL speaks to the latter.

I was also thinking how I and others tend to ignore a few dB in efficiency and say HIL holds true.

But 2 dB is a 33% difference in efficiency, and would be considered huge in most any other field of endeavor.

And while not a significant difference in SPL, it would make a quite significant difference in VC temp.

Noah
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post #187 of 194 Old 07-09-2012, 03:44 PM
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Originally Posted by noah katz View Post

Of course you're aware of this, but sensitivity is not the same as efficiency, and HIL speaks to the latter.
I was also thinking how I and others tend to ignore a few dB in efficiency and say HIL holds true.
But 2 dB is a 33% difference in efficiency, and would be considered huge in most any other field of endeavor.
And while not a significant difference in SPL, it would make a quite significant difference in VC temp.

Yep...Hence the second chart posted which is actual 1w applied power and not voltage sensitivity. Agreed on the rest as well. smile.gif


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post #188 of 194 Old 07-09-2012, 07:57 PM - Thread Starter
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"So, we have the RE XXX-18 in 8 cubes vs 2 unnamed 18s in the same 8 cubes with 1000W? Are you saying this is a coincidental comparison? Right."

lol. i see what you are insinuating now. no, it is not a craig chase design. i used 1 watt, not 1000.

the 18's in the model are bms 18n860, which are a pro audio driver with a relatively long throw. they cost somewhere around $710 each.

edit: updated the price. http://www.assistanceaudio.com/assistance_audio_bms_cones.html
neo has been all over the map in the past year, so the price might be +/-.

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post #189 of 194 Old 07-09-2012, 08:54 PM - Thread Starter
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"I couldn't possibly understand it more clearly. I'm pointing out that that's not what your OP suggests at all."

then go read it again. what you are looking at in the picture is the dual high sensitivity 18 approach has the same sensitivity in the low end as the heavier longer throw driver.

as a result both will require the same power to create the low end bass spl. that part of the sensitivity is set by the size of the enclosure. at the top end however, the dual 18 has much higher sensitivity, so when the two systems are eq'd the same, the dual 18 design will pull less power.

then i observed that with about the same swept volume of the two designs, the two systems will have about same total output, but that was not the main point. most folks are aware of that already.

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post #190 of 194 Old 07-09-2012, 09:10 PM
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Im a pretty big noob and i dont think ive ever seen anyone state that high efficiency drivers are bad for low frequencies because they have worse efficiency... i dont think your OP is as mindblowing as you think it is.

id say the much more common understanding is "if you want low in a sealed box you need lots of excursion" and its well understood that pro sound drivers give up throw for better efficiency in the 30hz-40hz and higher area.

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post #191 of 194 Old 07-09-2012, 09:57 PM - Thread Starter
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omega, the way that hoffman's iron law manifests itself in practice on many posts is that for small sealed enclosures, you will need lots of power, no matter which driver you choose. why? because sensitivity on the low end is not dictated by the driver in the limit. it is a function of the cabinet size only. that is not intuitive to most folks.

i've read quite a few posts around here and if i were to have taken a poll that went something like, "hey guys, in an 8 cubic foot enclosure, what will get more spl at 20hz for a watt, an re-xxx or two pro audio drivers?" most everybody would have voted for the re-xxx. in that sense, i think it is an interesting observation, if not quite 'mind blowing'.

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post #192 of 194 Old 07-10-2012, 04:31 AM
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Originally Posted by LTD02 View Post

i've read quite a few posts around here and if i were to have taken a poll that went something like, "hey guys, in an 8 cubic foot enclosure, what will get more spl at 20hz for a watt, an re-xxx or two pro audio drivers?" most everybody would have voted for the re-xxx. in that sense, i think it is an interesting observation, if not quite 'mind blowing'.

How do they compare in a 25 cubic foot encloure, all other conoditions as described?
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post #193 of 194 Old 07-10-2012, 05:51 AM
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Originally Posted by LTD02 View Post

omega, the way that hoffman's iron law manifests itself in practice on many posts is that for small sealed enclosures, you will need lots of power, no matter which driver you choose. why? because sensitivity on the low end is not dictated by the driver in the limit. it is a function of the cabinet size only. that is not intuitive to most folks.
i've read quite a few posts around here and if i were to have taken a poll that went something like, "hey guys, in an 8 cubic foot enclosure, what will get more spl at 20hz for a watt, an re-xxx or two pro audio drivers?" most everybody would have voted for the re-xxx. in that sense, i think it is an interesting observation, if not quite 'mind blowing'.

That is the problem with the original post and this thread. I'd guess that most if not all of the posters who replied to your post were completely aware of that fact. It has some significance but not to point where you would be better off with dual small sealed BMS's over dual small sealed XXX's if you are shooting for deep bass. Sensitivity matters, but comparing at 1w is only a small component in designing a system.

Maybe the uninitiated who pops on asking how he can reach 10hz @ 120db with a car audio 10" woofer doesn't understand this, but the vets on this board do.
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post #194 of 194 Old 07-10-2012, 06:45 AM
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Originally Posted by Mark Seaton View Post

Because electrical signal summation is ~3dB/doubling or 10dB/10x... which does bear out in the graph.



It all depends on what sine wave summation you are talking about.

You change the RMS value by 3 dB with each doubling of a sine wave, and you change the PEAK value of the combined signal by 6 dB with each doubling of a sine wave. The change in PEAK value will clip the amplifier.
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