[denverdoc]

Jim,

In the afterthought department, it occurred to me you might be referring to unsmoothed comb filtering effects all audio systems are subject to--after years of looking at magazize articles that all post near field msmts, or use smoothing, it is a shock to see the raw response in all its glory. These tightly spaced vertical lines in close proximity look like noise and generally should be regarded as such--room treatment may reduce the amplitude somewhat, but they will still be there.  If you have dips with width, then this is a concern! Try posting the msmts if you can, and we'll all have a better idea as to what your describing.
John

[jhenderson010759]

Hi Jim,

Welcome to AudioCircle.  Sorry to hear of your difficulties.  Was Andre able to help at all?

Where are you in So CA?  Are you a member of the LA & Orange Co Audiophile Society?

In any event, hope you can get it "dialed in".  

I may want to "pick your brain" a bit since I (if I ever get my laptop back) will be trying out the DEQX on my system.

I'd like to join - if for no other reason than to observe and learn from the others in the group.  How do I go about joining?  I am located in Ventura County - bit of a drive to OC, but not out of the question.  

I'd be happy to answer anything I can.   While I have used SoundEasy for a while, and I am a DSP engineer, I have but four hours of use time on the PDC.  Probably very little I can offer.

[John Ashman]

Generally the dealer sends in your e-mail address and then DEQX contacts you with an "invitation" e-mail and then you follow the instructions.

[jhenderson010759]

Generally the dealer sends in your e-mail address and then DEQX contacts you with an "invitation" e-mail and then you follow the instructions.

I'm already a member of the deqxbeta group.  I was referring to the LAOC Audiophile Society.

[John Casler]

Jim,

Didn't want to sidetrack the thread too much, so I PM'd you with info.

[jhenderson010759]

Jim,

In the afterthought department, it occurred to me you might be referring to unsmoothed comb filtering effects all audio systems are subject to--after years of looking at magazize articles that all post near field msmts, or use smoothing, it is a shock to see the raw response in all its glory. These tightly spaced vertical lines in close proximity look like noise and generally should be regarded as such--room treatment may reduce the amplitude somewhat, but they will still be there.  If you have dip ...

It's a possibility.  But, I ran slow sine sweeps using SE on this same gear about two months ago, (pre PDC), and I didn't see anything quite this nasty.  

Now that the PDC is in, I'm going to run some MLS tests using SE just as a sanity check.  

Thank you for your suggestions.

[jhenderson010759]

I am tri-amping.  Actually, in PDC parlance, I am "bi-amping with stereo subs".  

Below is the summed response from all speakers at my oxymoronic "sweet spot" [/url]

Actually, I guess I lied in my earlier post.  The null is only -20dB at 170Hz.  Looks like the worst one is at ~280 Hz or so.

I already have wool rugs on the floor and numerous tapestries on the walls.  I was planning on affixing some more SelectBoard to the backs of some more tapestries.  But, I am wondering whether the present damping is responsible for the tail in the response from ~3 to 8 kHz.  

I guess, as I review it now, if I could successfully treat the 170 and 280 Hz nulls and reduce the tailing, it might not be so bad.  

Sounds like I'm just kidding myself.  Sort of like "If we had some ham, we could have some ham and eggs, if we had some eggs."

Jim

[denverdoc]

Jim.

Those are nasty--170 and 280 Hz  hmm, Lets see at 570 Hz you have a foot path length difference to null, 280 would be 2 feet and 170 about 3 and a third ft, if I aint screwing up the mental arithmetic.

Any chance these are basic ole  floor reflections--you have a bunch of quilts or better yet a bare matress you could try on the floor?

John

[John Ashman]

Jim,

     I wouldn't worry about those two little nulls, they're thin enough to largely be unnoticeable.  I'd just worry about flattening the other issues.   Remember too that, if you raise the level of a particular frequency by 10dB, you're using 10 times as much power.  10W becomes 100W. And, if it's an acoustic cancellation, no amount of increase at that frequency will make the null go away.  It's like the equation "100x0" is the same as "1000000 x 0".  If a positive and negative wave collide and create that null, raising the volume of the signal just raises the volume of the cancellation wave.    In any case, it's not THAT bad from the measurements, so, if the acoustics have been handled, I'd just do a FR correction and see what happens there, but don't try to fix the nulls.

[csero]

For all the flat response, correction, perfect impulse response etc. fanatics ( no offense here, I WAS one of you) I'd suggest an easy experiment:

Take your perfect(ly corrected) speakers and play pink noise in both channels, then walk in front of the speakers, parallel to them at the normal listening distance. You can hear huge tonality change in the pink noise as you move. And this is not coming from the room interaction. Actually the more treated the room, the more pronounced this comb filtering - 10-15 dB narrow dips in the most sensitive 1-5k hearing range.

Then think about what have you achieved with the correction.

I don't say that perfect ( or corrected ) transducers are not important, but to do them right is about as important as picking the right nail to build a house. It is important, but the result can be a shack in the woods or a mansion. And with the standard audiophile soutions building even a shack in the woods is a miracle.

Csero

[mac]

Take your perfect(ly corrected) speakers and play pink noise in both channels, then walk in front of the speakers, parallel to them at the normal listening distance...

I've done this and the uniformity in tone is very linear.  This correlates to the widening of the sweet spot at the listening position and the reduction in lobbing, both of which are quite audible.

[goskers]

Jim,

I would be great if you could offer us more details about your room setup and dampening material placements.  The more info for these guys to work with the better.

[csero]

If it is linear, then something is very wrong in the reproduction  Lobing, widening of the sweetspot has nothing to do with it.

[John Ashman]

Fortunately, we don't listen to pink noise and correcting the speaker with tri-amping and steep crossovers improves the sense of interspeaker coherency, so I'm not sure what you're trying to say.  Speakers interact constantly, that's part of how it works.  Driver correction doesn't make it worse, phase/time correction makes it a lot better, at least with real sources, so.........?

[csero]

Fortunately, we don't listen to pink noise

Of course not, as you dont use Mahler 2nd for MLS measurements.

[mac]

If it is linear, then something is very wrong in the reproduction

If you believe that the sound of the noise should change when moving the mic or your ear in front of the speakers I'd be curious to hear your reasoning.

Lobing, widening of the sweetspot has nothing to do with it.

If you say so.    

[jhenderson010759]

For all the flat response, correction, perfect impulse response etc. fanatics ( no offense here, I WAS one of you) I'd suggest an easy experiment:

Take your perfect(ly corrected) speakers and play pink noise in both channels, then walk in front of the speakers, parallel to them at the normal listening distance. You can hear huge tonality change in the pink noise as you move. And this is not coming from the room interaction. Actually the more treated the room, the more pronounced this comb filtering - 10- ...

The "tonality change" is predominantly the result of the off-axis dispersion response of the tweeter.   But, your assertion that room interaction is not responsible seems unfounded.  "Normal" listening distances (as opposed to "near-field") are substantially affected by room acoustics, as evidenced by any near-field vs far field measurement (swept sine, MLS, etc).  What is your basis for this assertion?

[csero]

If you believe that the sound of the noise should change when moving the mic or your ear in front of the speakers I'd be curious to hear your reasoning.

If you play the same signal ( pink noise or centered solo - but pink noise is better, because you are not emotionally connected to the tonalyty,  your brain will not try to ignore the tonality change for the content) from two different distant sound sources, wild comb filtering happens at any point which is not exactly equidistant from the two speakers.
Your two ears are about 6" apart, so they by default can not be equidistant from the two sources, so both hear very different freq response in the midrange which is constantly changing with the slightest head movement. These changes usually contradict the head ear "built in" direction finding comb filtering, confusing the brain about the image, dept and other spatial information, which is available on the record.

[csero]

The "tonality change" is predominantly the result of the off-axis dispersion response of the tweeter.   But, your assertion that room interaction is not responsible seems unfounded.  "Normal" listening distances (as opposed to "near-field") are substantially affected by room acoustics, as evidenced by any near-field vs far field measurement (swept sine, MLS, etc).  What is your basis for this assertion?

What if I can demo you the effect with a constand dispersion and mooth directivity index speaker in an anechoic chamber too?

The room and imperfect speakers are usually just cover it up, but still remain noticeable

[mac]

If you play the same signal ( pink noise or centered solo - but pink noise is better, because you are not emotionally connected to the tonalyty,  your brain will not try to ignore the tonality change for the content) from two different distant sound sources, wild comb filtering happens at any point which is not exactly equidistant from the two speakers.
Your two ears are about 6" apart, so they by default can not be equidistant from the two sources, so both hear very different freq response in the midrang ...

What you're describing is inherient with stereo reproduction even when using two single driver speakers.  What I'm talking about is driver intrgration for a single point-source speakler.  So, assume that you are listening to a single speaker and then explain to me why a change in tonal balance is desirable.