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post #151 of 354 Old 08-10-2012, 12:50 PM
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Dave good post #147.
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post #152 of 354 Old 08-10-2012, 03:34 PM
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Quote:
Originally Posted by Ricci View Post

Dave good post #147.

Back atcha on #150. cool.gif

I've become adept at normalizing graphs and overlaying traces for direct comparison. I decided to use your DataBass data to compare the 18" ported JBL to the 18" sealed UXL.

provsht.jpg

Unfortunately, we don't have the THD data for the UXL, but I'll bet my bottom buck the UXL was cleaner at 40 Hz comparing both subs 115dB sine sweep.

In complete agreement with what you said, left naked it would be a no-brainer to tell them apart, and zero doubt, this is what the majority have compared. EQ'd and level matched to the same FR and playback level, not gonna happen.

It would be a simple matter to apply a 4th order HPF at 20 Hz to the sealed UXL and pull the JBLs top end down to match the UXL and have a listen. I would like to be a part of a blind listening test between these 2 subs and I'll bring bettin' dough with me.

I'll bet that when EQ'd to same FR and level, no one will tell the difference with music. The reason I'll wager $$ is I've done this test myself using my EVX-180As vs all sorts of sealed subs.

Typically, the HT enthusiast will double up on the 18s for ULF displacement. In that case, the multiple HT 18s will display certainly inaudible THD at 40 Hz. The ported pro sound sub (they're all ported because the drivers are designed for a ported box) will give unavoidably audible 2HD with the low E string of a bass guitar (40 Hz fundamental) which the majority will prefer over the more accurate presentation every time.

With movie soundtracks and the HT subs optimized for the room and maximum extension, it's no contest.
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post #153 of 354 Old 08-10-2012, 03:37 PM
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Bosso,

Bring your REW rig and I'll host. only exception is ive got the 4648 cabs and the XXX18's with the dcx2496, and sms-1 to eq out if we need them both, or just one.

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post #154 of 354 Old 08-10-2012, 03:48 PM
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I'd make a drive for that...
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post #155 of 354 Old 08-10-2012, 03:56 PM
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Me too ...but I require wings. frown.gif

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post #156 of 354 Old 08-10-2012, 07:38 PM
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Originally Posted by beastaudio View Post

Bosso,
Bring your REW rig and I'll host. only exception is ive got the 4648 cabs and the XXX18's with the dcx2496, and sms-1 to eq out if we need them both, or just one.

Hmmm, I might could bring more than the REW rig. cool.gif
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post #157 of 354 Old 08-10-2012, 08:15 PM
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Wow, these parties involved, that'd be one not to miss.

I always envisioned a big, well sorted out mash up such as this in a rental hall, lending itself to being a bit more load in/load out friendly. Also, any effort toward diminishing the room from the equation is a step in the right direction. Perhaps a full exploration of multi-sub location room response smoothing, etc., issue mitigating,.... would warrant such a space, ....that's akin to re-engineering the wheel eek.gif so maybe a different event altogether.

Best of luck gentlemen, cross country road trip for sure.

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post #158 of 354 Old 08-10-2012, 09:23 PM
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Quote:
Originally Posted by Ricci View Post

"What is the point of matching the responses to be the same when they are so different to begin with? That is the whole point!". I have the same target goals for my system regardless of what drivers are used. The trip to get there may be quite different but the end destination should be the same.

Hi there,

Ive performed too a big bunch of tests with diffrent subs. We have listening outside room, so that there is no room-effect which compromises a real lot.
And we have used on time FIR filtering to perfectly equal the responses of all subs. What we have not tried until now, to measure and correct the rectangular shape of the signal, that would be pretty nice to see, but that kind of stuff is not easy to apply at all.
But still, even with flatened response to nearly the same FR and controlled by amps which have the required stability for massive drivers like the RE for example (amps like AA V6001+), the differences where significant.

there is no doubt, that it is hard to compare subs to each other, as long there is a difference in response, and because of the human listening experience, a subwoofer with much deepere response (and without eq a RE XXX has definitly a much deeper FR as a "low mass" driver, will sound more "fat", or on the other hand, a light driver will sound naturally more "precise".
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post #159 of 354 Old 08-11-2012, 02:14 AM
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"below 1/2 wavelength of longest room dimension, there isnt any wave. The air pressure is rising in the whole room at the same time (not instantaneous, but faster than you described)

Thats the problem I have using my double bass array with 2by2 subs each side of the room. Below the first mode of my room @25Hz I encountered the problem, that the active bass absorption at the rear wall didnt work below 25Hz."

poison nuke, after *much* additional reading this evening, it seems that you are correct.

from what i have been able to gather, below about the 1/2 wavelenth region, air transitions from behaving like a compressible fluid, where sound moves at the speed of 340 m/s roughly, to a region where the air behaves more like a non-compressible fluid and the speed of sound increases to extremely high levels...almost infinite for a practical first order approximation (edit: that is an overshoot, but something like 10X faster).

that would be consistent with your results and why the dba fails in that region.

below the transition frequency, the pressure is rising and falling everywhere in the room almost simultaneously. as a result, there are no modes, no reflections, and the whole system is behaving (almost) according to the ideal gas law pv=nrt.

this also would explain why there is no 12db/oct rolloff, as the driver is effectively coupled to all the air in the room and is simply pressurizing it and depressurizing it everywhere at once and explains why it is called pressure vessel gain.

it also explains how a room can be pressurized even with a window open. the speed of sound is moving so much faster in the room than in the window, the window cannot vent the pressure.

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post #160 of 354 Old 08-11-2012, 07:47 AM
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Quote:
Originally Posted by Poison Nuke View Post

there is no doubt, that it is hard to compare subs to each other, as long there is a difference in response, and because of the human listening experience, a subwoofer with much deepere response (and without eq a RE XXX has definitly a much deeper FR as a "low mass" driver, will sound more "fat", or on the other hand, a light driver will sound naturally more "precise".

This is the simple truth of the matter. Lower frequencies = longer waves = longer decay time. This will always led to comments that the sound is 'slower', 'warmer', 'muddier', etc.

Someone recently posted 2 youtube vids of subs playing music. His comment was something like "this vid has tight bass, that vid has muddy bass'. Of course, they were 2 different songs with completely different spectral content.

Here are the spectrographs of the 2 vids, so maybe you can guess which was 'tight' and which was 'muddy'.

tightvsmuddy-b.jpg

The problem is that the 2 vids were used to suggest that the subs used were the cause of the muddy vs tight presentations and this fallacy will persist if no one intervenes with the facts. Pro sound drivers are designed for ported boxes tuned in the 30s Hz. They have lots of top end and harmonic distortion and no bottom end. HT subs are designed for maximum displacement. 5 Hz wave length is 200 ms, 40 Hz wavelength is 25 ms, etc.
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post #161 of 354 Old 08-11-2012, 09:05 AM
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"This is the simple truth of the matter. Lower frequencies = longer waves = longer decay time. This will always led to comments that the sound is 'slower', 'warmer', 'muddier', etc."

that doesn't seem consistent with the bag end elf subs. they employ pro audio drivers, are eq'd flat to 8hz or something like that, yet are subjectively described as extremely tight/fast/whatever term you want to apply.

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post #162 of 354 Old 08-11-2012, 09:58 AM
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Quote:
Originally Posted by LTD02 View Post

yet are subjectively described as extremely tight/fast/whatever term you want to apply.

I realize most everyone participating is aware, but for those un-aware those subjective characterizations, are predominantly a function of the time domain. The time domain encompassing both the acoustic environment in which the system is utilized, and the overall top to bottom system coherency and signal (time) alignment.

A kick drum beater hit is a good example. Once EQ'd to the desired contemporary flavor (boom, smack, click), it can easily contain a multi-octave, very wide spectral content.

Outdoors, a system with an overwhelmingly large amount of displacement capability at low distortion levels, aligned coherently, possesses all the subjective snap, speed, tightness, and signal tracking transient ability that one can imagine. Additionally, more realistically indoors, a well damped environment, whereas the LF decay characteristics aren't problematic, will lend itself toward that same goal. To elicit the coveted "speed" or transient ability, the material, in this case a kick drum, must be well delineated. How? Spectrally align all the components of the material in time, and assure the environment decay doesn't linger and recontribute thus smearing the material in time.

What's attainable outdoors (no LF decay issues), over a large scale state of the art PA is stunningly powerful and amazing. Typically, that's what the client wants. Now bring that indoors, the same fully coherent rig begins to encounter the nasty decay issues of the rooms interaction. Even the best rooms, this smears detail. And in bad rooms, it can turn to mush unless you're overwhelmingly within the near-field.

An interesting yet brief story; the local casino has a center bar, open stage and PA without any wall boundaries for hundreds of feet in any direction. The acoustic observations I've made in there are really quite interesting because they're so well defined. LF lobing is clearly heard as one moves around. without the usual boundaries, it's really fascinating how well defined the polar pattern of the LF is as one moves about. Clearly, either co-located subs, or a time aligned/controlled array would be in order. Each FOH guy I talk to really isn't interested sadly. It's a shame, because the sound attainable in there is extremely high quality. Apathy....oh well. So far, only one visit was I entirely impressed by the acoustic effort put forth.

----

WRT the PVG and boundary discussion, I don't understand/lost track as to what was initially being disagreed upon. I thought PVG/boundary gain is essentially well understood. confused.gif

Quite interesting none the less, it's made me re-evaluate the manner in which I view it, which is always good...but I don't think I change my viewpoint.

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post #163 of 354 Old 08-11-2012, 10:23 AM
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"I realize most everyone participating is aware, but for those un-aware those subjective characterizations, are predominantly a function of the time domain."

that is kind of what i was thinking, but it is still unresolved. bosso says it is all frequency domain and harmonic distortion. i don't agree with that. mark argues subs are linear systems, so through the fourier analysis, they are the same thing, but he never plays all his cards. i don't agree with the linear system theory. ricci argues that once you are linear, the response into the higher frequencies is what matters most. i agree that is a big part, but not the full effect. there is still energy storage to deal with and some other messy effects such a intermodulation distortion.

"WRT the PVG and boundary discussion, I don't understand/lost track as to what was initially being disagreed upon. I thought PVG/boundary gain is essentially well understood."

bosso made the bold claim that there was no way a sealed sub could pressurize a room period.

initially, i was thinking that the pressurization may have been from an illusion, where there was still a wave, but it was so large, that the pressure could be positive everywhere in the room.

comments from poison nuke sent me to really try to figure out what the heck is going on. after reading several very technical papers that made my head hurt, it appears that there is no longer a wave as you go below the critical frequency. the subwoofer excites the entire room pretty much at the same time and the speed of sound actually increases in this region dramatically. the literature refers to these two regions as a compressible fluid zone (where speed of sound is 340 m/s and waves travel and reflect as we think and interact with the room by creating modes), and below this region an incompressible fluid zone (the speed of sound transmission goes up dramatically and the room literally couples to the sub and in turn compresses and decompresses everywhere almost instantly as a result, among other things, the 12db/oct rolloff of a sealed sub outdoors goes away). what makes it so darn confusing is that air is a compressible fluid behaving like an incompressible one below the critical frequency.

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post #164 of 354 Old 08-11-2012, 01:17 PM
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I think best way to resolve that question would be a comparing measurment of two equalized subwoofers in free field with square wave signal and then overlay the results. Because a square wave conmsists of has all frequencies, the resulting wave should show exactly the driver can follow any signal
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post #165 of 354 Old 08-11-2012, 01:21 PM
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with a typical 80hz or so low pass filter, most of the square wave will just be filtered away, no?

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post #166 of 354 Old 08-11-2012, 01:43 PM
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Quote:
Originally Posted by LTD02 View Post

with a typical 80hz or so low pass filter, most of the square wave will just be filtered away, no?
Pretty much all of it. If you don't low pass you'll see the harmonic content, but seeing the differences between two subs outside their usual pass band is of limited value, if any.

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post #167 of 354 Old 08-11-2012, 01:53 PM
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"Pretty much all of it. If you don't low pass you'll see the harmonic content, but seeing the differences between two subs outside their usual pass band is of limited value, if any."

?

harmonics don't get filtered away with an electronic low pass, just the base frequencies above the low pass, unless it is an acoustic low pass, as in a bandpass sub, no? or do the two work the same?

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post #168 of 354 Old 08-11-2012, 01:54 PM
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Originally Posted by FOH View Post

----
WRT the PVG and boundary discussion, I don't understand/lost track as to what was initially being disagreed upon. I thought PVG/boundary gain is essentially well understood. confused.gif
Quite interesting none the less, it's made me re-evaluate the manner in which I view it, which is always good...but I don't think I change my viewpoint.

From an article written in 1997:
Quote:
According to one rationale, this phenomenon occurs because the car cabin is so small compared to the wavelengths where wave acoustics begin; the speaker thus energizes the interior as though it were a pressure pot. In other words, the speaker cone motion actually changes the size of the cabin.

Another theory holds that the driver will be close to all the boundaries, even the opposite corner, so boundary reinforcement is the primary force operating here.

So, I obviously didn't coin the term 'pressure pot', but I have added a bit to the description of the boundary gain definition and I have dubbed the phenomenon 'progressive constructive interferences' because it better describes the mechanism and it can be distilled to an equal letter acronym (PVG vs PCI).
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post #169 of 354 Old 08-11-2012, 02:07 PM
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Originally Posted by LTD02 View Post

harmonics don't get filtered away with an electronic low pass
Sure they do. If there's a 160Hz signal in there the filter doesn't know if it's a 160Hz fundamental, an 80Hz second harmonic, a 40Hz fourth harmonic or 20 Hz eighth harmonic, nor does it care, it will attenuate it in all cases.

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post #170 of 354 Old 08-11-2012, 02:25 PM
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"So, I obviously didn't coin the term 'pressure pot', but I have added a bit to the description of the boundary gain definition and I have dubbed the phenomenon 'progressive constructive interferences' because it better describes the mechanism..."

lol. not even close.

http://www.win.tue.nl/~sjoerdr/papers/boek.pdf

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post #171 of 354 Old 08-11-2012, 02:50 PM
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"Sure they do..."

that seems right bfm. my bad. dr. g. was talking about the benefit of using an acoustic vs. electronic crossover some time ago. i believe his assertion at the time was that the acoustic (bandpass) method worked better for minimizing harmonic distortions out of band, but i don't remember his argument.

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post #172 of 354 Old 08-11-2012, 03:48 PM
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"Sure they do..."
that seems right bfm. my bad. dr. g. was talking about the benefit of using an acoustic vs. electronic crossover some time ago. i believe his assertion at the time was that the acoustic (bandpass) method worked better for minimizing harmonic distortions out of band, but i don't remember his argument.
Dr. G is correct to some extent, as a crossover can't filter out HD created by the driver. BP cabs, folded horns in particular, do.

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post #173 of 354 Old 08-11-2012, 03:49 PM
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Sure they do. If there's a 160Hz signal in there the filter doesn't know if it's a 160Hz fundamental, an 80Hz second harmonic, a 40Hz fourth harmonic or 20 Hz eighth harmonic, nor does it care, it will attenuate it in all cases.

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"Sure they do..."
that seems right bfm. my bad. dr. g. was talking about the benefit of using an acoustic vs. electronic crossover some time ago. i believe his assertion at the time was that the acoustic (bandpass) method worked better for minimizing harmonic distortions out of band, but i don't remember his argument.

Yeah, and these are the people who want to convince me sound moves at the speed of light below the Star Trek mode. ^^^ rolleyes.gif
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post #174 of 354 Old 08-11-2012, 04:34 PM
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Yeah, and these are the people who want to convince me sound moves at the speed of light below the Star Trek mode. ^^^ rolleyes.gif

i like that analogy as the sound goes into something of warp speed below the critical frequency. :-)

did you get a chance to read the paper that i linked up for you in #170?

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"...a crossover can't filter out HD created by the driver..."

now i am confused. isn't that what i said back in #169.

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post #176 of 354 Old 08-11-2012, 05:03 PM
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Hmmm, I might could bring more than the REW rig. cool.gif

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Wow, these parties involved, that'd be one not to miss.
I always envisioned a big, well sorted out mash up such as this in a rental hall, lending itself to being a bit more load in/load out friendly. Also, any effort toward diminishing the room from the equation is a step in the right direction. Perhaps a full exploration of multi-sub location room response smoothing, etc., issue mitigating,.... would warrant such a space, ....that's akin to re-engineering the wheel eek.gif so maybe a different event altogether.
Best of luck gentlemen, cross country road trip for sure.

I would totally fly out for something even resembling this. eek.gif

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post #177 of 354 Old 08-11-2012, 05:23 PM
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it would be impossible to control though scott.

2 feet between listeners would result in a different frequency response, so then we'd be back to that and all the results would be dismissed as worthless.

this is why jbl created the 'speaker swapper' or whatever the heck it is called in their test facility.

that way each listener, one at a time, would get the same comparo at the same listening position.

i'm not sure where their lab is. maybe you could coordinate with them if you want an actual scientific controlled test.

perhaps some sort of outdoor test could come close? eq match and level match every pair of subs under test...sounds too time consuming, unless the pairs were configured before the gtg.

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post #178 of 354 Old 08-11-2012, 06:26 PM
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"...a crossover can't filter out HD created by the driver..."
now i am confused. isn't that what i said back in #169.
Both the crossover and a BP filter harmonics. The combination of the two will filter more effectively than one or the other alone.

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post #179 of 354 Old 08-11-2012, 07:29 PM
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did you get a chance to read the paper that i linked up for you in #170?

Yeah, all 300 pages. rolleyes.gif

Point me to a relevant chapter.
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Originally Posted by LTD02 View Post

"below 1/2 wavelength of longest room dimension, there isnt any wave. The air pressure is rising in the whole room at the same time (not instantaneous, but faster than you described)
Thats the problem I have using my double bass array with 2by2 subs each side of the room. Below the first mode of my room @25Hz I encountered the problem, that the active bass absorption at the rear wall didnt work below 25Hz."
poison nuke, after *much* additional reading this evening, it seems that you are correct.
from what i have been able to gather, below about the 1/2 wavelenth region, air transitions from behaving like a compressible fluid, where sound moves at the speed of 340 m/s roughly, to a region where the air behaves more like a non-compressible fluid and the speed of sound increases to extremely high levels...almost infinite for a practical first order approximation (edit: that is an overshoot, but something like 10X faster).
that would be consistent with your results and why the dba fails in that region.
below the transition frequency, the pressure is rising and falling everywhere in the room almost simultaneously. as a result, there are no modes, no reflections, and the whole system is behaving (almost) according to the ideal gas law pv=nrt.
this also would explain why there is no 12db/oct rolloff, as the driver is effectively coupled to all the air in the room and is simply pressurizing it and depressurizing it everywhere at once and explains why it is called pressure vessel gain.
it also explains how a room can be pressurized even with a window open. the speed of sound is moving so much faster in the room than in the window, the window cannot vent the pressure.

Two subs, separately placed in the same room. Both are fed the same input separately, then at the same time. Explain how the PVG region sees a significant drop in SPL in the summing at the microphone in the context of your latest theory:

Bothjpg.jpg
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post #180 of 354 Old 08-11-2012, 07:39 PM
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Quote:
Originally Posted by LTD02 View Post

it would be impossible to control though scott.
2 feet between listeners would result in a different frequency response, so then we'd be back to that and all the results would be dismissed as worthless.
this is why jbl created the 'speaker swapper' or whatever the heck it is called in their test facility.
that way each listener, one at a time, would get the same comparo at the same listening position.
i'm not sure where their lab is. maybe you could coordinate with them if you want an actual scientific controlled test.
perhaps some sort of outdoor test could come close? eq match and level match every pair of subs under test...sounds too time consuming, unless the pairs were configured before the gtg.

We only need one pair of subs, a real one and a pro sound one. One listener at a time sitting in the same seat. This is a simple test and the results are absolutely predictable. To do this with a well thought out methodology, spectrographs and accurate measurement hardware has never been done with forum members.

Quote:
Originally Posted by Scott Simonian View Post

I would totally fly out for something even resembling this. eek.gif

Giving it some serious thought. Long overdue, actually.

Would be too awesome to meet the Mighty Scott Simonian as well. cool.gif
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