large null in theater room...help - Page 4 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #31 of 49 Old 02-25-16, 02:58 PM
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Hello,

Just one question.

What is bad with a null?

Basically the human ear works differently than the microphone that is used for measurements.

The microphone just records sound levels when such measurements are being made , independent of the time structure of the sound.
It does not distinguish between the first wavefront and reflection that arrive at the same time as the most recent wavefront but originated with a different wavefront much earlier.

The microphone just sums up the sound pressures and thus also detects when those sounds cancel reach others out (nulls)

The ear does does distinguish between the first wavefront and reflections because it analyzes the time structure of arriving sound patterns.

That's why our ears are also not really sensitive to comb filter effects.

A null is just a position, the direct sound, the first wavefront is not being disturbed by room resonances.
One can still hear the respective frequencies very well. Just try it out with sine waves with the respective frequencies.

I would rather be worried about the resonances that increase the sound level at certain frequencies.

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post #32 of 49 Old 02-25-16, 03:08 PM
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Re: large null in theater room...help

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One can still hear the respective frequencies very well. Just try it out with sine waves with the respective frequencies.


Cheers
Babak
Nope. Not true. I've tried this many times before I had REW. Manually implemented sine waves, and an spl meter can show in real time which frequencies are cancelled, or exaggerated by the room. Time doesn't alter this. The LP position, or wave propagation location does. That's why moving speakers/subs, or the LP alters the effect.



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post #33 of 49 Old 02-25-16, 03:35 PM
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Well, an SPL meter is also a microphone and does not resemble the human hearing.they both only measure sound pressure.

It doesn't make sense to conclude an audible effect based on a measurement with devices and methods that work completely different than the human auditive system.

The question is if it's really a null (of a room mode) or some cancellation at that frequency (a low frequency comb filter effect).

If it is a real null, than great!
Put the speakers or subs right on the null. There they can't excite any room resonances at the respective frequencies.
Also put the listening position onto a null. The resonances with the respective frequencies will have the least sound pressure and hence the least audible effect there.
That's also in line with recommendations by Floyd Toole.

Of it is a comb filter effect at a low frequency - just forget them.
The human ear is not sensitive to comb filter effects (proven in studies).
A comb filter effect is just something that looks ugly on a measurement graph because - yes microphones vs ears.

What else can that null be that needs treatment?
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post #34 of 49 Old 02-25-16, 04:04 PM
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Re: large null in theater room...help

I guess it depends on what the null is from.(I think that's also what you're saying). Fwiw, when manually running and measuring tones, my ears heard the differences in level. If a null is created by the room, the only help is relocating equipment or LP. If a null is a phase issue then that can be addressed. I also still say nulls need to be addressed whether there created by the room, or equipment. Do I understand you to mean that nulls from phase, or comb filtering are just measurement anomalies that should be left alone, as the ears are not effected the same way a mic is?


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post #35 of 49 Old 02-28-16, 05:00 PM Thread Starter
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Re: large null in theater room...help

Well here is my waterfall. what now?
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post #36 of 49 Old 03-01-16, 11:30 AM
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Quote:
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I guess it depends on what the null is from.(I think that's also what you're saying).
That's right

Quote:
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Fwiw, when manually running and measuring tones, my ears heard the differences in level.
Of course.
Can you tell whether that is because the respective frequencies are reduced or those frequencies are at normal level an others around them are increased in level due to resonances?

Here one should also keep in mind that due to the loudness cuves of the human ear we perceive low frequency sound with a lower loudness anyway.


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If a null is created by the room, the only help is relocating equipment or LP. If a null is a phase issue then that can be addressed. I also still say nulls need to be addressed whether there created by the room, or equipment.
Of course fluctuations in the frequency response need to be addressed.
I personally would rather focus on the peaks and resonances rather than the nulls and dips.


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Do I understand you to mean that nulls from phase, or comb filtering are just measurement anomalies that should be left alone, as the ears are not effected the same way a mic is?
Yes and no.

I wouldn't say that they are abnormalities because they can be clearly measured - repeatedly and consistently.

And yes, the ears are not effected the same way as a microphone is that one users for measurements.

Cheers from Vienna
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post #37 of 49 Old 03-01-16, 11:32 AM
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Well here is my waterfall. what now?
Do you also have a RT 60 or RT30 measurement?

The decay times at certain frequencies would tell more.

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post #38 of 49 Old 03-01-16, 02:19 PM
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Re: large null in theater room...help

It looks like you are about a foot off the from wall. Spin them 180 degrees & measure again. That will effectively change the null ~2 feet. If still bad can you then move them out 1 more foot from the front wall.
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post #39 of 49 Old 03-01-16, 06:00 PM Thread Starter
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Right now they are 6' off the front wall. Both subs are pointing inward toward the center of the room. I can spin them 90' and have them face toward to back of the room.

I will post rt30 and rt60 later today.
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post #40 of 49 Old 03-01-16, 10:45 PM
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Re: large null in theater room...help

BC, wish I had something to offer on your waterfall. Looks like extra ringing between 35 and 55hz. Traps? That's all's i got...


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