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post #151 of 179 Old 07-08-2006, 06:24 AM
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The length of the chosen tone-burst is a compromise between being able to measure frequency or time data more accurately. The width of the effective signal spectrum is inversely proportional to the length (T) of the tone-burst. As T tends towards infinity you get an infinitely narrow frequency spike a la JJ's single-tone continuous sine waveSpectraPro/Lab measurements. At T=0, you get a single infinitely short pulse with a spectrum including all possible frequencies.

Using a 10-cycle burst at 20Hz as Linkwitz demonstrates in the link, it gives better frequency-domain accuracy (narrower spectrum) than a 5-cycle burst. However, either way, he would still have had to conduct the measurement out of doors (or in an anechoic chamber) because the first room-reflection in any sensible-sized room would arrive long before the direct tone-burst could be captured completely or even as far as its mid-point. ;)
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post #152 of 179 Old 07-08-2006, 06:39 AM
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I believe he made his measuremenrts 1/2" from the driver to minimize room acoustics. Outside would have been better especially on a sunny day. 72' in the air would have been better still. ;)

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post #153 of 179 Old 07-08-2006, 06:42 AM
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Quote:
Originally Posted by Ed Mullen
I've been chasing my tail a bit on this current review simply because of all the new tests and methods of data presentation we have developed. While the test data exists, I doubt all of it will actually make the final version of the review. I'm pretty conservative about what will actually be added to the review format as new tests/data, simply because I want it to have relevance to previous test data as a comparative tool. The review format has undergone numerous interim revisions, some of which have led me full circle back to the current version. :rolleyes: :(
Looking forward to your next review. I'm sure it will be insightful as always. Like yourself I am curious how well CEA-2010 correlates with historical measurements.

John
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post #154 of 179 Old 07-08-2006, 06:44 AM
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"... The non-linear behavior of a subwoofer increases rapidly as cone excursions become large, because force factor Bl, compliance Cms, and voice coil inductance Le, change with displacement from the resting position. Distortion also changes with frequency, even when the peak-to-peak displacement is held constant. This can be seen by comparing 30 Hz and 20 Hz harmonic distortion measurements of THOR for constant p-p excursion of 0.5" (13 mm).
(All sound pressure levels are relative in these tests. They were measured outdoors with the speaker on the ground. The microphone was at 4" from the plane defined by the driver's rubber surround and on-axis with the dust cap.)"
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post #155 of 179 Old 07-08-2006, 07:41 AM
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Quote:
Originally Posted by craigsub
Charley, Who ever said you needed to blind test 12 subs in a day ? I think blind testing 4 subs at one time, then doing the measurements would be the ideal test.
Hiring the venue for our subwoofer tests and providing refreshments for the participants costs money. Eric pays this out of his own pocket. How many other forum owners do you see actively supporting something like this out of their own pocket? I can think of at least one well known UK-based forum that would NEVER contemplate something like this. The simple fact is that we have to make best use of the day. ;)
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post #156 of 179 Old 07-08-2006, 10:46 AM
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Quote:
Originally Posted by cjwhitehouse
"... The non-linear behavior of a subwoofer increases rapidly as cone excursions become large, because force factor Bl, compliance Cms, and voice coil inductance Le, change with displacement from the resting position. Distortion also changes with frequency, even when the peak-to-peak displacement is held constant. This can be seen by comparing 30 Hz and 20 Hz harmonic distortion measurements of THOR for constant p-p excursion of 0.5" (13 mm).
(All sound pressure levels are relative in these tests. They were measured outdoors with the speaker on the ground. The microphone was at 4" from the plane defined by the driver's rubber surround and on-axis with the dust cap.)"
Thanks for pointing that out. I was thinking about the test on midrange distortion here http://www.linkwitzlab.com/frontiers...udy%20material where he measures "with the microphone in the center of the plane that touches the driver's roll surround". Interesting that he chose to measure the Thor outside 4" from the dust cap. I wonder if his main concern was nearby object. Maybe he needs directions to your parking lot. :)

Regarding high excursion mid-range drivers and distortion he found " if a low frequency signal is present together with the high frequency signal, then the large low frequency voice coil displacements can cause large amounts of intermodulation distortion products near the high frequency signal due to the large low frequency variation of Le(x)."

He observed when comparing a high excursion driver with a low excursion driver that, " there is a huge difference between the distortion estimates and the measured values. The question is why? The mechanical displacements are extremely small and in the order of 30 micron. The displacements that produce the measured distortion are less than 1 mm. Which nonlinear mechanism is causing the distortion? The currents, magnetic fields, forces and accelerations are the same as at low frequencies for constant SPL, only the excursions are drastically reduced."

Great stuff from a leading thinker.

P.S. You are lucky to have such support from Eric though he must be aware of the extra traffic your sub tests bring to AVTalk. :cool:

John
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post #157 of 179 Old 07-08-2006, 12:10 PM
 
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Quote:
Originally Posted by cjwhitehouse
Hiring the venue for our subwoofer tests and providing refreshments for the participants costs money. Eric pays this out of his own pocket. How many other forum owners do you see actively supporting something like this out of their own pocket? I can think of at least one well known UK-based forum that would NEVER contemplate something like this. The simple fact is that we have to make best use of the day. ;)
Charley ... I know you are relatively new on this forum ... and therefore it is not fair to expect you to know all that has happened here over the last couple of years.

There are a certain few people who look down their collective noses at listening tests. Of course, the reason for doing so is listening tests, especially done blind, might disprove statements made, and positions taken. I know Velodyne has taken a lot of abuse from people looking at just the numbers .. these same people who refuse to listen to a subwoofer sure enjoy making performance obversations about the same subwoofer.

The tests I have done have all been entirely at my own expense ... to the tune of well over $10,000 ... considering the price of product vs. the selling price.

I understand and appreciate the investment required.

You think the day is better spent measuring more subs. I think it would be better with fewer subs, and with listening added.

It is your call, and I respect that. :)
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post #158 of 179 Old 07-08-2006, 02:54 PM
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Quote:
Originally Posted by craigsub
Charley ... I know you are relatively new on this forum ... and therefore it is not fair to expect you to know all that has happened here over the last couple of years.
Actually, according to join date, I have been here rather longer than you. :cool:

I do follow what goes on, but usually only say something if the topic interests me sufficiently. ;)
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post #159 of 179 Old 07-08-2006, 02:59 PM
 
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Quote:
Originally Posted by cjwhitehouse
Actually, according to join date, I have been here rather longer than you. :cool:

I do follow what goes on, but usually only say something if the topic interests me sufficiently. ;)
Charley, having seen first hand when you elect to chime in, and when you don't, it is pretty clear what your thought processes must be. As you have never participated in any of my review threads, I gather you found them to be of no interest. That is no surprise ... ;)

The fact that you then elect to get offended about rather benign requests that others conduct listening tests to go along with their measurement sessions is also pretty telling.

You see, Charley, using your own words, you have decided to neglect outright abuse of listening tests we have conducted here, while stepping in to defend other's tests, when the non use of listening tests was questioned.

Again, you have decided your method for testing a subwoofer is the only way to go, and that is your choice.

Your tacit disdain for the listening test is unfortunate, but expected, based on your posts here.
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post #160 of 179 Old 07-09-2006, 04:59 AM
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Quote:
Originally Posted by jakeman
Thanks for pointing that out. I was thinking about the test on midrange distortion here http://www.linkwitzlab.com/frontiers...udy%20material where he measures "with the microphone in the center of the plane that touches the driver's roll surround". Interesting that he chose to measure the Thor outside 4" from the dust cap. I wonder if his main concern was nearby object. Maybe he needs directions to your parking lot. :)

Regarding high excursion mid-range drivers and distortion he found " if a low frequency signal is present together with the high frequency signal, then the large low frequency voice coil displacements can cause large amounts of intermodulation distortion products near the high frequency signal due to the large low frequency variation of Le(x)."

He observed when comparing a high excursion driver with a low excursion driver that, " there is a huge difference between the distortion estimates and the measured values. The question is why? The mechanical displacements are extremely small and in the order of 30 micron. The displacements that produce the measured distortion are less than 1 mm. Which nonlinear mechanism is causing the distortion? The currents, magnetic fields, forces and accelerations are the same as at low frequencies for constant SPL, only the excursions are drastically reduced."

Great stuff from a leading thinker.
In the link you give, he is evaluating small mid-range drivers for possible future inclusion in one of his designs. We know that driver A is a Peerless HDS 134, 850488, 5.25". He doesn't tell us what driver B and C are. You cannot say that any of these have higher excursion than the others without knowing what they actually are. In fact I see no mention of their respective excursions at all.

He then goes on to calculate the theoretical contributions of Le(x), electrical and due to reluctance force generated, to see if they account for the measured distortion at higher frequencies, and comes to the conclusion that while they have some contribution, they are not the primary contributors to the measured results; hence he states that the estimates do not match the measurements. He then goes on to calculate the theoretical Le(i) contribution from flux modulation and comes to the conclusion that this is the dominant contributor to the measured distortion in the case of these particular drivers. He has to make an assumption in this calculation for a parameter value he does not know - it gives a good correlation with driver B but not so good with driver A, indicating that A is rather better than his estimate. His overall conclusion seems reasonable nonetheless.

In the course of this discussion, he does say " if a low frequency signal is present together with the high frequency signal, then the large low frequency voice coil displacements can cause large amounts of intermodulation distortion products near the high frequency signal due to the large low frequency variation of Le(x)." as you state, but one would need to see the actual Le(x) values for a whole lot of drivers, both low and high excursion before you could possibly generalise. For example, there is a considerable difference in Le(x) for drivers A & B but we don't know their respective max excursions so we don't know if there is any correlation.

Quote:
Originally Posted by jakeman
P.S. You are lucky to have such support from Eric though he must be aware of the extra traffic your sub tests bring to AVTalk. :cool:
Yes, but there is also a price to pay in extra bandwidth used for all those graphs. ;)
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post #161 of 179 Old 07-09-2006, 06:46 AM
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The track I was talking about with the reverse bass sweep is Under the Influence on the Surrender album.

(let's see if the link to the amzn sound bite works... if not, you can hear it on amzn or another site with samples.)

The subsequent sweep is even deeper and the bass is hypnotic and enveloping. :D
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post #162 of 179 Old 07-09-2006, 05:49 PM
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Quote:
Originally Posted by cjwhitehouse
In the link you give, he is evaluating small mid-range drivers for possible future inclusion in one of his designs. We know that driver A is a Peerless HDS 134, 850488, 5.25". He doesn't tell us what driver B and C are. You cannot say that any of these have higher excursion than the others without knowing what they actually are. In fact I see no mention of their respective excursions at all.
He does allude to the likelihood that more non-linear behaviour is coming from the drivers with higher excursion all other factors held constant. Indeed one can note throughtout his studies that reoccurring theme. When discussing the Thor subwoofer for example he mentions quite factually that the non-linear behavior of a subwoofer increases rapidly as cone excursions become large, because force factor Bl, compliance Cms, and voice coil inductance Le, change with displacement from the resting position. He goes on to say that distortion also changes with frequency, even when the peak-to-peak displacement is held constant. Though he does not produce the data he is basing his statements on his prior study.

He is making a reasonable assumption based on the fact that the driver has maximum motor force available at small excursion. At longer excursion the voice coil start to leave the gap which results in a unsymmetrical drop in motor force and its attendant non linear distortions and modulations. Some drivers handle this stress better than others but all drivers exhibit the non-linear behaviour to varying degrees.

We can see from Klippel's recent chart on non-linearities that IMD is closely associated with Le(X) from position of the coil in the gap at excursion. Linkwitz could not account for all distortion hence his focus on Li(X) flux modulation which is also an indicator of THD along with IMD. He doesn't mention the efficiency of the drivers but I suppose he was searching for something more efficient than the Peerless but the lack of linearity of drivers A and B was not to his liking.

It's always hard to balance linearity with efficiency in a moving system. That's a reason for my renewed appreciation of servo systems though they can be large power hogs as well.

John
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post #163 of 179 Old 07-10-2006, 05:32 AM
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Like Jack showed with the screen shots from those two subs (which also have a very similar FR): One of them clearly has a more-uniform and lower-amplitude noise profile with less isolated spikes between the tones, particularly in the 35-55 Hz region. Ostensibly, the subjective conclusion for proponents of the SC test is that this subwoofer should be the superior sounding unit. But has that ever been proven in controlled ABX testing?
I was thinking someone might be able to spot at least a vague correlation between the informal impressions posted about those two and any of the suggested "non-Big 5" indicators (SC, IMD, GD, etc.) given the disparate nature of the subjective opinions.

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post #164 of 179 Old 07-10-2006, 07:13 AM
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Quote:
Originally Posted by Jack Gilvey
I was thinking someone might be able to spot at least a vague correlation between the informal impressions posted about those two and any of the suggested "non-Big 5" indicators (SC, IMD, GD, etc.) given the disparate nature of the subjective opinions.
In light of the greater inaudibility of distortion at LF such correlations will be hard to come by. More fruitful would be spotting a correlation of SD and non-linearities at higher frequencies where our ears are more sensitive.

John
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post #165 of 179 Old 07-10-2006, 08:30 AM
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Quote:
Originally Posted by Jack Gilvey
I was thinking someone might be able to spot at least a vague correlation between the informal impressions posted about those two and any of the suggested "non-Big 5" indicators (SC, IMD, GD, etc.) given the disparate nature of the subjective opinions.
Every time I scan through the measurements, with the exception of the Axiom EP600, which I suspect might have had complications in measurement, I see trends which do in fact lend to correlation to common listener descriptions. I'm throwing a question mark at the EP600 since I recall Ilkka having some earlier issues with longer duration test signals and such. One factor I don't see anyone ever discussing is that in the 6 Moons review, there was a note about a curious feedback that was generated when placed near the main speaker. This confirms my suspicion of there likely being some form of current-feedback in the system which accounts for their claims of "keeping the driver linear, etc., etc." You can't have feedback without some loop back to the input. This characteristic, combined with some creative limiting could account for problems in measurement.

So, forgetting the EP600 for a moment, when I look at more usual suspects like say the PB-10 and Hsu VTF3 in 20Hz mode, I do see trends in both the frequency response with increasing level and the spectral contamination measurements. It looks like Ilkka took down the 25-31PC+ measurements with the 12.3 drivers, but those were some interesting comparisons. Even the Plus/2 with the 12.1 vs. 12.3 driver makes some interesting comparisions that clearly show that these are different subwoofers and should sound different. The differences in response make it a bit more work to compare results, but as an example, we can see that the distribution of noise/distortion is different with the 95dB spectral contamination measurement probably being the most interesting as well as the 100dB measurement showing some other interesting things.

Unfortunately you are unlikely to see the "sore thumbs" people want to make analysis easy, but differences are there, and some head scratching with some awareness of how we hear give us some insights.

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post #166 of 179 Old 07-10-2006, 09:41 AM
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Every time I scan through the measurements, with the exception of the Axiom EP600, which I suspect might have had complications in measurement, I see trends which do in fact lend to correlation to common listener descriptions.
Fair enough, we'll leave out the 600 in that case. What would you look for in a SC measurement that would indicate what people commonly call "musicality"? And, to Jakeman's point above, what bandwidth would such a measurement of a subwoofer have to cover to be useful? Ilkka's only go to 200Hz.
Quote:
The differences in response make it a bit more work to compare results, but as an example, we can see that the distribution of noise/distortion is different with the 95dB spectral contamination measurement probably being the most interesting as well as the 100dB measurement showing some other interesting things...Unfortunately you are unlikely to see the "sore thumbs" people want to make analysis easy, but differences are there, and some head scratching with some awareness of how we hear give us some insights.
As always, you have my attention. ;) What might be revealed to make SC a reliable, encompassing indicator of the subjective experience?

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post #167 of 179 Old 07-10-2006, 01:04 PM
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Quote:
Originally Posted by Jack Gilvey
what bandwidth would such a measurement of a subwoofer have to cover to be useful? Ilkka's only go to 200Hz.
I would rephrase to question to: at what point do the non-linearities become insiduous with respect to audibility and sound quality. If we reexamine the CEA guidelines they took into account the problem with noise/distortion at higher frequencies and the masking effect close to the fundamental. They set the lower limit at 8.5 times Fo up to 10,000HZ. Also note that Klippel monitors non-linearities up to 5,000hz. CJ may not believe it but some inferior subs could likely generate noise that high or higher. Anyway you want to slice it we are well in excess of 200hz.

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post #168 of 179 Old 07-10-2006, 06:02 PM
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Quote:
Originally Posted by Jack Gilvey
Fair enough, we'll leave out the 600 in that case. What would you look for in a SC measurement that would indicate what people commonly call "musicality"? And, to Jakeman's point above, what bandwidth would such a measurement of a subwoofer have to cover to be useful? Ilkka's only go to 200Hz.
Having an adequate noise floor above 200Hz and having it reasonably constant for a test make things somewhat more complicated. Frankly you won't know if there is anything to look at above 200Hz until you've tested a sub. The vast majority shouldn't show much up there, but you will probably see some things as you start to reach the linear limits of the sub.

Unfortunately it comes back to the old quandry of measurement that the founders of SynAudCon love to highlight: To devise and perform a proper test of any device, you generally have to know what the answer is going to be before you start. :confused:

Of course if you know the answer then why are you measuring? ;) In the real world we are testing to confirm what we expect or suspect. When things don't make sense with our understanding of the device, we need to alter our test and/or our understanding.

Quote:
Originally Posted by Jack Gilvey
As always, you have my attention. ;) What might be revealed to make SC a reliable, encompassing indicator of the subjective experience?
Someone's going to have to spend a lot of time translating what different areas of the noise spectrum will correspond to and then look at what those various effects sound like. Basically I expect such measurements to be as straight-forward as a set of frequency responses and THD measurements. :rolleyes: (meaning not very clear, but certainly able to paint a general picture)

I don't feel compelled to disect each and every graph there, as others will look at the same data and draw entirely different conclusions. What I would suggest is looking at both the spectral distribution of the "noise" (higher/lower in freq. & where things are sparce), and consider what we know about audibility from both classic research and that which Earl Geddes and Lidia Lee have published on their website. Looking at how the noise changes as level increases can in some cases point to a few possible sources of distortion and their sonic "fingerprint" if you will.

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post #169 of 179 Old 07-10-2006, 06:03 PM
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With all that said in the above post, I should point back to the fact that there is still a LOT more to be told in the frequency response and compression curves that are commonly dismissed when discussing subjective impressions of different subwoofers.

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post #170 of 179 Old 07-10-2006, 09:33 PM
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Just a question about mic placement.

I assume the mic is placed at 2 meters at the other end of the tape measure. Using that assumption, won't Illka's placement of the mic on the PB12+/2 be a disadvantage for that sub? He shows the tape at 90 degrees from the driver, but more than 90 from the ports as he has it at the opposite corner. If you look at the HSU, the mic is placed at 90 from both the driver and the ports.

In this quasi-anechoic environment, wouldn't placing the mic at 90 degrees also be a disadvantage for down firing/rear ported or front/rear subs VS the 0 degree placement for the front/front or sealed subs?

I just find it hard to believe that the sound wave is as strong off center when there is no reinforcement of walls. I also have a problem believing that with a down firing sub that the total SPL is the same in all four directions as it is for a front firing sub when you are right in front of the driver. In room, there are walls to reflect the wave going away from you, but outside, isn't that just wasted energy?

If I am wrong, that would mean that I should hear as much standing behind a speaker as I would standing in front of it.

I know I could have worded this better, but I think you get my meaning.

Randy
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post #171 of 179 Old 07-10-2006, 09:58 PM
 
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Quote:
Originally Posted by ransac
Just a question about mic placement.

I assume the mic is placed at 2 meters at the other end of the tape measure. Using that assumption, won't Illka's placement of the mic on the PB12+/2 be a disadvantage for that sub? He shows the tape at 90 degrees from the driver, but more than 90 from the ports as he has it at the opposite corner. If you look at the HSU, the mic is placed at 90 from both the driver and the ports.

In this quasi-anechoic environment, wouldn't placing the mic at 90 degrees also be a disadvantage for down firing/rear ported or front/rear subs VS the 0 degree placement for the front/front or sealed subs?

I just find it hard to believe that the sound wave is as strong off center when there is no reinforcement of walls. I also have a problem believing that with a down firing sub that the total SPL is the same in all four directions as it is for a front firing sub when you are right in front of the driver. In room, there are walls to reflect the wave going away from you, but outside, isn't that just wasted energy?

If I am wrong, that would mean that I should hear as much standing behind a speaker as I would standing in front of it.

I know I could have worded this better, but I think you get my meaning.
Ransac ... the 20 Hz wave is 56 feet long. Driver direction is not a factor ... especially outside ... the driver acts like a point source.
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post #172 of 179 Old 07-11-2006, 04:37 AM
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Quote:
With all that said in the above post, I should point back to the fact that there is still a LOT more to be told in the frequency response and compression curves that are commonly dismissed when discussing subjective impressions of different subwoofers.
Thanks for both posts...good stuff.

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post #173 of 179 Old 07-16-2006, 04:08 PM
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Originally Posted by vinyl
...I would like Zipman’s comments on each sub’s results discussed HERE once he releases them...
He has started a US hosted forum that very soon will be here Subwoofer Tests.
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post #174 of 179 Old 07-17-2006, 04:31 PM
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Quote:
Originally Posted by bobgpsr
He has started a US hosted forum that very soon will be here Subwoofer Tests.
It is live now and can be accessed by everyone. :)

Bob
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post #175 of 179 Old 07-17-2006, 06:25 PM
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Quote:
He has started a US hosted forum that very soon will be here Subwoofer Tests.
Well thats interesting. :cool:

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post #176 of 179 Old 07-18-2006, 03:33 PM
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Please don't advertise for other forums.

Thanks,

Kyser

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post #177 of 179 Old 07-19-2006, 05:56 AM
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Wow... you guys must really have thing for Ilkka... why not just let him back here?
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post #178 of 179 Old 07-19-2006, 06:41 AM
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Kyser, some forum crossreferencing is inevitable, especially on the web-spanning subwoofer sealed/ported/objective/subjective thread. Strict enforcement of your policy will, in my opinion, result in decreased traffic on AVS. I refer people here, moderately, when the situation warrants -- shall I stop doing so?
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post #179 of 179 Old 07-19-2006, 06:52 AM
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Quote:
Originally Posted by Kysersose
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Please don't advertise for other forums.

Thanks,

Kyser

BOOOOOOOOOOOOOOOOOOOOOOOOOOOOO :confused: :confused:

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