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post #31 of 57 Old 02-07-2007, 12:26 PM
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Quote:
Originally Posted by Ethan Winer View Post

Terry,

> Above 80 Hz, you are seeing the result of a whole lot of acoustic treatment! <

Obviously! I'm glad to have had such a large influence on you!

???
Most of what I do is design of acoustical treatments. It always has been. I use EQ when I have too -- at frequencies where bass absorbers are not effective.

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So please tell us more about this room. How big, how much treatment, where the treatment is placed, how thick it is, and so forth.

--Ethan

The room is 2300 cubic feet. And no, I will not tell you where and what type of treatment was used. This is my intellectual property, and I do not give it away. It is what I do for a living, the results of working in the acoustics profession for a few decades!

- Terry

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post #32 of 57 Old 02-07-2007, 01:32 PM
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Quote:
Originally Posted by Ethan Winer View Post

.

Actually, the span is 10 dB - each division is 3 dB.

--Ethan

My mistake. I should have said +- 5db.

You have to admit Terry's measurements look better.
I have to wonder how he got those measurements. I also wonder how
the room actually sounds. I've heard a room with mix of Helmholtz
absorbers tuned to the room, and 6-12" broadband absorbers almost
everywhere else. It sounded good. But too dead for my tastes.

I think in the end there is no perfect room, and what sounds
best to the user depends on what they like (i guess that could be called
personal phyco acoustics)

Everything I say here is my opinion. It is not my employers opinion, it is not my wife's opinion, it is not my neighbors opinion, it is My Opinion.
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post #33 of 57 Old 02-08-2007, 01:50 AM
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Originally Posted by bpape View Post

As to whether or not subwoofer range ringing is detrimental, I don't know that a single paper that you cited is enough to get me to ignore 2 second decay times fom 80Hz down.

I should explain more carefully the experiments done in this paper. The authors distinguished between two types of modal EQ. There is the precise parametric inverse filter method, where you have to match and cancel the center frequency, Q, and gain. There is also a non-parametric, less critical method where all you do is equalize the magnitude response to reduce the mode amplitude without trying to match its exact characteristics. You are not going to clean up the modal decay with such a cruder method, because you are not matching and precisely cancelling the resonance.

In the experiments, a synthetic room mode was added, and the the second type of EQ was done on it. At most frequencies, subjects could readily discriminate the EQed synthetic room mode vs. no added mode when the modal decay time was only 0.2 to 0.3 seconds. Sound reasonable? There was no amplitude peak at the modal frequency because it was EQed down, but the pesky decay tail remained. Although softer, this could still be heard.

But several modal frequencies were used, and an interesting thing happened at very low frequencies. To quote the authors:

"Below 100 Hz the value [discrimination threshold] exploded so that at 50 Hz in these listening conditions the subjects could not notice systematically any difference within the given samples even for a synthetic mode decay time of almost two seconds."

More experiments are planned, as these listening tests were done with just single room modes and 8 subjects listening to only four types of sound (speech, bandpass noise, drum hits, and rock music) at a single listening level of 75-80 dB.

I encourage anybody interested in the science of acoustics to read the original literature. Don't take my word for it. Read any paper carefully, and judge for yourself!

- Terry

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post #34 of 57 Old 02-08-2007, 04:58 AM
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Terry, can you tell us approx. how many traps were used in the room where you measured that waterfall plot?
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post #35 of 57 Old 02-08-2007, 02:22 PM
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Quote:
Originally Posted by dknightd View Post

You have to admit Terry's measurements look better.
I have to wonder how he got those measurements.

Terry got those measurements the same way I made the REW measurements below.

Both of the graphs below show the response in my large (34 by 18 by ~10) home recording studio, using identical gate times and all other parameters. One is measured the proper way, and the other was measured using an improper (read: disingenuous) method. This is the very same room, and these are real measurements taken 15 seconds apart. Yet one reflects reality and the other surely does not.

I have no need to hide anything, and I'll be glad to show how I made my studio appear far flatter and tighter than it really is. But first Terry needs to answer Tukkis' question about how many traps there were, and also reveal what speakers they were, where the sub was placed, and where the measuring microphone was in relation to the speakers and sub.

I find it amusing that Terry is now the champion of using "a whole lot of acoustic treatment" after he criticized me many times for telling people that more bass trapping is always better. The only legitimate ETF graph I have ever seen that looks even remotely like what Terry posted was for a home studio control room that was 1/3 filled with rock wool. Not 1/3 of the square footage, but 1/3 of the room's entire volume!

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post #36 of 57 Old 02-08-2007, 09:18 PM
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Quote:
Originally Posted by Tukkis View Post

Terry, can you tell us approx. how many traps were used in the room where you measured that waterfall plot?

I didn't use discrete traps, except for a couple of custom tuned absorbers which had only minor impact. It is all integrated into the overall acoustical treatment, which in this case varied in thickness from 2 inches to nearly 2 feet. But even 2 feet of depth is not enough to thoroughly correct the lowest bass frequencies. That's where parametric EQ is necessary. For this room, an independent set of parametric equalizer channels was used to optimize each sub -- yes, there were multiple subwoofers.

This room had approximately 10% of its volume taken up by acoustical treatment. That is the sort of commitment you have to make when you are serious about achieving high performance home theater acoustics. Barhoram has some great space behind his screen for placing low frequency absorption.

- Terry

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post #37 of 57 Old 08-26-2008, 09:56 AM
 
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Bump.

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post #38 of 57 Old 08-26-2008, 01:07 PM
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Quote:
Originally Posted by Terry Montlick View Post

???
Most of what I do is design of acoustical treatments. It always has been. I use EQ when I have too -- at frequencies where bass absorbers are not effective.


The room is 2300 cubic feet. And no, I will not tell you where and what type of treatment was used. This is my intellectual property, and I do not give it away. It is what I do for a living, the results of working in the acoustics profession for a few decades!

- Terry

So, would it be fair to say that you're here on this forum not so much to share your experience with others in the hope that they will learn from it and be able to improve their system, but instead you're here just to promote your business?
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post #39 of 57 Old 08-26-2008, 01:15 PM
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Quote:
Originally Posted by Peter White View Post

So, would it be fair to say that you're here on this forum not so much to share your experience with others in the hope that they will learn from it and be able to improve their system, but instead you're here just to promote your business?

That's an unfair statement, especially from a new arrival to these forums. Terry has shared his knowledge and experience with us for a long time, including ideas and theory about room acoustics. OTOH, expecting him to provide free the specific services from which he makes living is unreasonable.

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post #40 of 57 Old 08-26-2008, 02:14 PM
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Originally Posted by Kal Rubinson View Post

That's an unfair statement, especially from a new arrival to these forums. Terry has shared his knowledge and experience with us for a long time, including ideas and theory about room acoustics. OTOH, expecting him to provide free the specific services from which he makes living is unreasonable.

It wasn't a statement. It was a question. And the implied relevance of my being a new arrival is childish.

Terry's implied claim that he's using some sort of secret methodology is rather humorous. Perhaps he's using some fantastic new speaker cable he read about in Stereophile? Let's see, you make a plot of all the nulls in the room, feed the data into some secret formula, and the formula tells you where to tie the speaker cable in knots which then cancel all the nulls! ;-)
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post #41 of 57 Old 08-26-2008, 02:31 PM
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Quote:
Originally Posted by Peter White View Post

It wasn't a statement. It was a question. And the implied relevance of my being a new arrival is childish.

It is certainly relevant since, had you been around for a while, you would know more about him.

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post #42 of 57 Old 08-26-2008, 03:01 PM
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Quote:
Originally Posted by Terry Montlick View Post

...More than 12 dB range from 20-200 Hz?....

I read those graphs as about 10dB, but aside from that, I'd ask if those frequencies need to be flat for the perceived tonal qualities. Yes, I prefer something flat above that for voice and music, but for bass, can we distinguish a flat response...without a "golden ear"???
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post #43 of 57 Old 08-26-2008, 03:05 PM
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Terry, Ethan, and a host of others provide general guidance. The amount and specificity of the comments they provide are peculiar to their own, individual, comfort levels. If you find it useful, that's great. If you need more information, then perhaps posting in other areas might garner what you're looking for. IMO, the effort they expend in promoting their own endeavors is next to nil.

"I've found that when you want to know the truth about someone that someone is probably the last person you should ask." - Gregory House
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post #44 of 57 Old 08-26-2008, 03:18 PM
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I am kind of curious if I missed something as this thread is pretty old, and then bumped and then a person responds to a post made over a year ago questioning their posts as advertising. What am I missing here?
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post #45 of 57 Old 08-26-2008, 03:25 PM
 
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Originally Posted by Randybes View Post

I am kind of curious if I missed something. . .[snip]

Nope.

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post #46 of 57 Old 08-26-2008, 03:31 PM
 
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Quote:
Originally Posted by Jim Hef View Post

I read those graphs as about 10dB, but aside from that, I'd ask if those frequencies need to be flat for the perceived tonal qualities.

What is important to understand is that a flat measured response is not the same thing as a perceptually flat response. That probably didn't question your question. Uh. .

A flat measured response will mean that the recorded material is faithfully reproduced but -- not quite. In order for the material to be faithfully reproduced (as in 100% faithfully reproduced) the frequency response would need to measure flat with an identical RT60 time in the bass range as per the mixing engineers requirements.

Good luck with that. A flat response is overrated as it doesn't necessarily mean that it will be perceptually accurate but rather a measurably accurate duplicate of the recorded material.

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post #47 of 57 Old 08-26-2008, 08:58 PM
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Most bizarre thread bump ever.

Mourning the disappearing usage of the -ly suffix. Words being cut-off before they've had a chance to fully form, left incomplete, with their shoelaces untied and their zippers undone. If I quote your post (or post in your thread) without comment, please check your zipper.
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post #48 of 57 Old 08-27-2008, 01:53 AM
 
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I have seen more bizarre thread bumps in my time here but I digress. Perhaps something good can become of it. Or not.

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post #49 of 57 Old 08-27-2008, 09:35 AM
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Thanks for your explanation!
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post #50 of 57 Old 08-27-2008, 11:52 AM
 
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You are most welcome.

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post #51 of 57 Old 08-27-2008, 06:50 PM
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Bumping a thread without explanation after 18 months of inactivity is poor form. and bad boarding.

Mourning the disappearing usage of the -ly suffix. Words being cut-off before they've had a chance to fully form, left incomplete, with their shoelaces untied and their zippers undone. If I quote your post (or post in your thread) without comment, please check your zipper.
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post #52 of 57 Old 08-28-2008, 06:15 AM
 
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Quote:
Originally Posted by CruelInventions View Post

Bumping a thread without explanation after 18 months of inactivity is poor form. and bad boarding.

No offense but your opinion on what constitutes bad form and bad boarding matters very little to me.

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post #53 of 57 Old 09-17-2013, 09:19 AM
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Euh...bump?

Stef
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post #54 of 57 Old 09-17-2013, 12:16 PM
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Second most bizarre thread bump ever. wink.gif

Mourning the disappearing usage of the -ly suffix. Words being cut-off before they've had a chance to fully form, left incomplete, with their shoelaces untied and their zippers undone. If I quote your post (or post in your thread) without comment, please check your zipper.
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post #55 of 57 Old 09-23-2013, 03:17 PM
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Quote:
Originally Posted by CruelInventions View Post

Second most bizarre thread bump ever. wink.gif

Maybe so but thanks-- I had to get a rear subwoofer to get the slam and blending I wanted because the only place to put the front one was on a side wall in an inopportune spot in front of a fireplace and then I saw this:
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Originally Posted by barhoram View Post


I have several left over bags of Roxul Safe N' Sound (mineral wool) from building the theater. Would I be ok stacking them in their plastic bags in the fireplace cutout?? Or would I need to open them up? Should I leave any space on the sides or back of the mineral wool?

Could this be the cheapest way to plug up the hole and possibly do something with it so it doesn't look so bad? Right now it just looks like an unused fireplace with a rear-firing sub sitting in front of it. The way it's set up now is the sub is partially in front of the opening and about a third of it in front of the brick wall surrounding it. It actually doesn't sound bad but...
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post #56 of 57 Old 09-23-2013, 07:47 PM
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It took me a full hour to read through all the posts and was facinated by the charts and tables. The theory is great for all those who sit back and design these things but the nuts and bolts make the difference. Installation begins at the physical mounting point, its position and direction of projection. Then it gets complicated and approaches have to be modified to fit the environment. Then as a last step, the environment can be altered to reduce offending paths or enhance others. Reflections aren't always bad. Each room/chamber/studio is different and there is no hard and fast rules, mostly you have to go by trial and error. YPAO can be a big help, even diagnosing phase faults(some are environmentally created) and adjusting for that listening position. That will get you CLOSE, close enough to get what you want with just a bit more tweaking.
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post #57 of 57 Old 09-24-2013, 02:39 AM
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Quote:
Originally Posted by goneten View Post

Quote:
Originally Posted by Jim Hef View Post

I read those graphs as about 10dB, but aside from that, I'd ask if those frequencies need to be flat for the perceived tonal qualities.


What is important to understand is that a flat measured response is not the same thing as a perceptually flat response. That probably didn't question your question. Uh. .


A flat measured response will mean that the recorded material is faithfully reproduced but -- not quite. In order for the material to be faithfully reproduced (as in 100% faithfully reproduced) the frequency response would need to measure flat with an identical RT60 time in the bass range as per the mixing engineers requirements.


Good luck with that. A flat response is overrated as it doesn't necessarily mean that it will be perceptually accurate but rather a measurably accurate duplicate of the recorded material.

+1

The above are only some of the reasons why a measured flat response can be less than the "final word".

For example, our perception of bass is strongly dependent on level. Basically, lower level, more bass needed for the perception of a good balance. Almost nobody plays their audio system at reference level all the time. Many report maxing out as much as 15 dB lower. This basically means that you'll have to turn up the bass (decidedly nonflat response) for a perceived good spectral balance.

Furthermore, a perception of the same balance as the life performance is contingent on the recording being an accurate reproducer of the live sound. That almost never happens due to the vagaries of recording.
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