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post #1 of 48 Old 04-19-2012, 08:32 PM - Thread Starter
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Hey everyone. I'm looking for a good resource to learn about room treatment. I have a small room (14x14) and it's pretty lively. Looking to control it a little more but I have no idea where to start. Gear:

Marantz sr5002 receiver, with an XPA-3 on order.
Kef IQ9 floor standing on L/R of 92" screen
Kef iq60c center mounted at ear level
Kef dipoles mounts ear level on side walls, jus behind main listening position
SVS PC-12plus sub in the corner
Two rows of leather theater seats, one on an 8" riser

I've calibrated by hand using the Avia disc and an spl meter.

I notice bass is too boomy in the back row. With music, very "busy" or complicated passages really get muddied, especially at higher SPLs. With movies, dialogue from the center is crisp and clear, but again loud and complicated scenes become a jumble or noise.

Bass traps, acoustic panels, ceiling, walls... I don't know where to start.

Thoughts?

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post #2 of 48 Old 04-19-2012, 08:38 PM
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http://www.ethanwiner.com/acoustics.html is a start.

Nice reference: Everest's Master Handbook of Acoustics

Kal Rubinson

"Music in the Round"
Senior Contributing Editor, Stereophile
http://www.stereophile.com/category/music-round

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post #3 of 48 Old 04-20-2012, 09:03 AM
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Another resource:

http://www.gikacoustics.com/contact_us.html

Contact Bryan Pape:

bryan.p@gikacoustics.com


GREAT folks!
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post #4 of 48 Old 04-20-2012, 10:42 AM
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Quote:
Originally Posted by adamnyholt View Post

Bass traps, acoustic panels, ceiling, walls... I don't know where to start.

Thanks to Kal for linking my Acoustics FAQ. This gives a brief overview that may be easier to digest:

Acoustic Basics

Additional links then branch out for more detail.

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post #5 of 48 Old 04-24-2012, 08:51 AM - Thread Starter
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Wow, Ethan! What a great resource! I read both articles, as well as some others on your company's site. I have a few questions:

1. For making my own bass traps, do I need to go floor to ceiling with them? (I have 8 ft ceilings, so I'd use 2 4x2' panels) Or do I mount just a single panel? If so, how high up?

2. I'm probably going to use mostly 2" panels, because my room is very small. I can't afford to put them too far away from the wall (again, small room), but I could do maybe 2-3 inches. Is that worth it, or should I just put them right against the wall?

3. What do you recommend for my back wall. I have a row of seats on an 8" riser directly against that wall. Should I put panels flat on the back wall, in the corner between wall and ceiling, or both? If I can only do one, which is better?

Right now my plan is bass traps in the corners, 2-3 panels along the major reflection points on the ceiling, 2 panels on each L/R wall (on reflection point) and 2-4 panels on the back wall. I'm going to try to use 4" panels where I can, but I think it will mostly be 2" panels.

I appreciate your feedback! I'll try to sketch up a room diagram today if I can!

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post #6 of 48 Old 04-24-2012, 10:04 AM
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1. The more total corner surface you cover, the better.

2. Bass traps that straddle corners should be at least four inches thick. Absorbers at reflection points can be two inches thick.

3. Sitting right in front of a reflecting wall is about the worst place to be. One solution is absorption on all parts of the wall behind someone's ears. Another choice is diffusion, but that's more complicated (DIY) or expensive (commercial).

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post #7 of 48 Old 04-24-2012, 02:28 PM - Thread Starter
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Thanks, Ethan! Another question. My rear surrounds are dipoles. Will eliminating too much reflection hurt their functionality?

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post #8 of 48 Old 04-24-2012, 03:32 PM
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Hello Ethan, will 4 layers thick (2 inches total) of rigid fiberglass suspended ceiling tiles placed diagonally on a corner with roughly a foot of air behind it be sufficient as a bass trap? (Overall surface dimensions would be 18" x 6 feet)

You mentioned 4 inches is what you want to have as a minimum, but I also remember reading where you said a good gap of air behind a panel in a corner helps a lot as well.
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post #9 of 48 Old 04-24-2012, 03:41 PM
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Re: boomy / muddy bass - first order of business would be experiment with sub and seating positioning; then bass trapping and EQ.
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post #10 of 48 Old 04-25-2012, 12:14 PM
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Quote:
Originally Posted by adamnyholt View Post

My rear surrounds are dipoles. Will eliminating too much reflection hurt their functionality?

I have no direct experience with dipole speakers for surrounds, so all I can say is to experiment. You can use doubled-up bath towels to get a sense of what better absorption will do in various locations.

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post #11 of 48 Old 04-25-2012, 12:15 PM
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Quote:
Originally Posted by TMRaven View Post

will 4 layers thick (2 inches total) of rigid fiberglass suspended ceiling tiles placed diagonally on a corner with roughly a foot of air behind it be sufficient as a bass trap? (Overall surface dimensions would be 18" x 6 feet)

Meh.

Quote:


You mentioned 4 inches is what you want to have as a minimum, but I also remember reading where you said a good gap of air behind a panel in a corner helps a lot as well.

Yes, but that was for four inch material with a four-inch gap. Now that will be effective. Also, 18 inches is kinda narrow for treating corners. Most panels are 24 inches wide, and 36 inches wide is better still when that can fit.

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post #12 of 48 Old 04-30-2012, 01:13 PM - Thread Starter
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Ok Folks,
I can't seem to find any local dealers who sell OC. I have found 2" Johns Mansville that is foil lined and I think 3 lbs/cubit foot. The dealer is having a hard time giving me the exact model. If it is what i think it is, the spec sheet says It says it has an absorption coefficient of .17 at 125 hz, and .63 at 250 (mounted directly against a firm surface). Does this sound right?

Also, Ethan: i can't find 4" board anywhere. Can I double up 2" board? Do I need to glue it using any special material?

Thanks!

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post #13 of 48 Old 05-01-2012, 01:39 PM
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Yes, you can place two 2-inch panels adjacent. No need to glue them either. But if you get the type with a facing, remove it from one of the pieces. You want only one layer, on the side facing the room (for bass traps).

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post #14 of 48 Old 05-02-2012, 06:23 AM
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Quote:
Originally Posted by Ethan Winer View Post

Yes, you can place two 2-inch panels adjacent. No need to glue them either. But if you get the type with a facing, remove it from one of the pieces. You want only one layer, on the side facing the room (for bass traps).

--Ethan



So if you got some with a foul backing, you recommend only removing one of the foil backing liners (assuming you are using 2 panels) and not both? Wouldn't leaving the foul backing on one panel cause the air gap behind the panel to be useless? I thought that the larger the air gap the better, but, if you left the foil liner on the panel, wouldn't that stop all air/sound movement completely?


I am new to this (room acoustics) so please bear with me!
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post #15 of 48 Old 05-02-2012, 08:16 AM
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Quote:
Originally Posted by Ethan Winer View Post

Meh.

Yes, but that was for four inch material with a four-inch gap. Now that will be effective. Also, 18 inches is kinda narrow for treating corners. Most panels are 24 inches wide, and 36 inches wide is better still when that can fit.

--Ethan


So what would be more effective overall, 18inches by 6feet that start at the top of my floorboards or 24 inches by 4 feet that span the middle of my walls? The edges would be tapered down to 1.5 inches where they meet the walls. I'd need to make some kind of consistency with my tv panel.


Also since I'm using 4 inch thick material, layering 8 pieces of ceiling tile seems rather much. Owens courning fiberglass sheets are my best bet?
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post #16 of 48 Old 05-02-2012, 09:46 AM
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Quote:
Originally Posted by TMRaven View Post

So what would be more effective overall, 18inches by 6feet that start at the top of my floorboards or 24 inches by 4 feet that span the middle of my walls? The edges would be tapered down to 1.5 inches where they meet the walls. I'd need to make some kind of consistency with my tv panel.


Also since I'm using 4 inch thick material, layering 8 pieces of ceiling tile seems rather much. Owens courning fiberglass sheets are my best bet?

From a cost benefit, cotton batts

http://www.atsacoustics.com/recycled-cotton-batts.html

may have a lot going for them.

Shipping is signficant in products like this, so I checked the manufacturers web site and found a more local source.

I've heard rumors that Roxul mineral wool products can be SO'd from Lowes.
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post #17 of 48 Old 05-02-2012, 10:24 AM
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Oh wow, with prices like that I don't even know if I should make my own.
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post #18 of 48 Old 05-02-2012, 10:38 AM
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Quote:
Originally Posted by Martycool007 View Post

if you left the foil liner on the panel, wouldn't that stop all air/sound movement completely?

No, waves pass through the paper / foil into the fiberglass behind.

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post #19 of 48 Old 05-02-2012, 10:39 AM
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Quote:
Originally Posted by TMRaven View Post

So what would be more effective overall, 18inches by 6feet that start at the top of my floorboards or 24 inches by 4 feet that span the middle of my walls?

I have no idea. The only way to know for sure is to measure the room each way. But if you can go 24 inches wide, why limit the height to four feet?

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post #20 of 48 Old 05-02-2012, 10:43 AM
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Originally Posted by Ethan Winer View Post

I have no idea. The only way to know for sure is to measure the room each way. But if you can go 24 inches wide, why limit the height to four feet?

--Ethan

Because my couch would get in the way otherwise

Also looking at the measurements from this ATS site in particular, it seems as though 4 feet height is a standard.
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post #21 of 48 Old 05-02-2012, 11:37 AM
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Quote:
Originally Posted by TMRaven View Post

Because my couch would get in the way otherwise

Also looking at the measurements from this ATS site in particular, it seems as though 4 feet height is a standard.

That's probably more for shipping costs, lol.

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post #22 of 48 Old 05-02-2012, 11:50 AM
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Quote:
Originally Posted by arnyk View Post

From a cost benefit, cotton batts

http://www.atsacoustics.com/recycled-cotton-batts.html

may have a lot going for them.

Shipping is signficant in products like this, so I checked the manufacturers web site and found a more local source.

I've heard rumors that Roxul mineral wool products can be SO'd from Lowes.

I got my Johns Manville rigid firberglass locally from this company:
http://spi-co.com/
http://spi-co.com/directory.html

I think the pack of 6 - 2'x4'x2" FPK backed boards ended up costing like $74. They sell Roxul and some others as well.

Bill
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post #23 of 48 Old 05-03-2012, 04:44 AM
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How does a person know whether to use absorption panels or diffusion panels? I am assuming that a person would have to measure their room first, with something such as REW and then what ever the results are, you decide if you need absorbion or diffusion?
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post #24 of 48 Old 05-03-2012, 05:14 AM
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Quote:
Originally Posted by Martycool007 View Post

How does a person know whether to use absorption panels or diffusion panels? I am assuming that a person would have to measure their room first, with something such as REW and then what ever the results are, you decide if you need absorbion or diffusion?

One means of choosing is to look at your budget. Diffusion generally costs a lot more per square foot then absorption.

Also, consider the audio frequency related to the problem you wish to address. Diffuser size is related to wavelengths of the sounds you wish to address.
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post #25 of 48 Old 05-03-2012, 05:56 AM
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Quote:
Originally Posted by arnyk View Post

One means of choosing is to look at your budget. Diffusion generally costs a lot more per square foot then absorption.

Also, consider the audio frequency related to the problem you wish to address. Diffuser size is related to wavelengths of the sounds you wish to address.



What is the correlation from frequency problem(s) to using either diffusion or absorbion? Do you mean like peaks and nulls in certain frequencys? I have never used REW so I am not well versed on what possible problems might occur, but I am in the process of obtaining all of the necessary equipment to get started using REW, so I am trying to learn some of this stuff now. Are there other factors that come in to play, other than peaks and nulls? I have read that the whole RT60/reverb thing is unimportant. This came from a guy whom is an expert in room acoustics.

Sorry for getting off topic!

Is it better to treat with diffusion when dealing with mid to high frequency problems? Ie, 400hz and above?
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post #26 of 48 Old 05-03-2012, 06:12 AM
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Quote:
Originally Posted by Martycool007 View Post

What is the correlation from frequency problem(s) to using either diffusion or absorbion?

Fixing very low frequencies can be expensive and space-consuming either way.

Quote:
Do you mean like peaks and nulls in certain frequencys?

Yes.

Quote:
I have never used REW so I am not well versed on what possible problems might occur, but I am in the process of obtaining all of the necessary equipment to get started using REW, so I am trying to learn some of this stuff now.

You can get an estimate of what low frequency problems you may have simply by playing low frequency swept tones over your system.


Quote:
Are there other factors that come in to play, other than peaks and nulls?

Yes, problems with reflections can cause actual echos. Smooth hard walls often create "slap echos" Walk around your room while clapping your hands and listening for the echoes. If the character of your hand slapping changes quite a bit, you may have these kinds of problems.

Quote:
I have read that the whole RT60/reverb thing is unimportant. This came from a guy whom is an expert in room acoustics.

Small rooms often have such low RT60s that this kind of reverberation is not so much of a problem, while still having slap echoes and dips and peaks in the bass range.


Quote:
Is it better to treat with diffusion when dealing with mid to high frequency problems? Ie, 400hz and above?

Certainly diffusion costs less to apply to be effective at higher frequencies.

A good-sounding room generally has a combination of absorption, diffusion, and reflection. Getting the amounts and combination of these things right is your goal. Diffusion is generally the most expensive to add, but it can be a vital ingredient in the mix.
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post #27 of 48 Old 05-03-2012, 06:59 AM
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Quote:
Originally Posted by Martycool007 View Post

What is the correlation from frequency problem(s) to using either diffusion or absorbion? Do you mean like peaks and nulls in certain frequencys? I have never used REW so I am not well versed on what possible problems might occur, but I am in the process of obtaining all of the necessary equipment to get started using REW, so I am trying to learn some of this stuff now. Are there other factors that come in to play, other than peaks and nulls? I have read that the whole RT60/reverb thing is unimportant. This came from a guy whom is an expert in room acoustics.

Sorry for getting off topic!

Is it better to treat with diffusion when dealing with mid to high frequency problems? Ie, 400hz and above?

yes, rt60 (reverberation time) is irrelevant measurement in Small Acoustical Spaces (SAS) as there is no statistically developed reverberant sound-field at any frequency we are concerned with. what little reverberation exists is above our hearing range and below the ambient noise floor. we do have LF decay and specular room decay, but many incorrectly (sloppily) mis-apply the term 'reverb' to such behavior. measuring rt60 also implies the requirement of an omni-directional source (dodec), of which typical home loudspeakers are NOT satisfactory. it also is to be measured past Dc (critical-distance), of which we do not have in a Small Acoustical Space (See below).

in Large Acoustical Spaces (LAS), there is a developed reverberant sound-field that is homogenous (equal and probable in all directions) - this is frequency dependent based on volume of the acoustical space (thanks to Dr. Manfred Schroeder). there exists also in LAS a 'critical distance' of which the reverberant sound-field becomes louder in gain than the direct signal. in a LAS, the reverberant sound-field becomes the effective noise-floor. also note in LAS, echos are perceived (ignoring gain for simplicity) as a reflection that arrives > 80ms (that's ~89ft of travel!). how large is your home listening room?

this is not the same acoustical behavior we experience in Small Acoustical Spaces - as in SAS we are subject to focused specular energy (reflections) that bounce around the room of which the vector (ingress direction of the signal), magnitude (gain), and time-arrival can all be resolved. the energy is NOT well-mixed and response changes drastically as you move throughout the room. the frequency response at a given point in 3space is determined by the summation (superposition: http://en.wikipedia.org/wiki/Superposition_principle) of the direct and indirect signals. since the indirect signals arrive at later times than the direct signal (due to longer paths of travel and with the speed of sound being a constant within your room's medium), they will sum constructively and destructively with the direct signal producing a comb-filter interference pattern within the frequency response (peaks and nulls; acoustical interference). a comb-filter doesn't exist in the real world but is simply an interference pattern manifested within the frequency-response (important distinction to note).

it is also important to note that REW does not tell you whether you need absorption, diffusion, redirection, etc or anything of that nature. measurement tools do not make these decisions for you but help you understand the actual (measured) acoustical behavior of the space based on source-receiver position and how that changes as you apply treatment in an attempt to achieve the desired response.

understand that there is a modal region of which the acoustical energy has wave properties - where the wavelengths are larger than the room boundaries. a transition region (as a wavelength may be larger than one boundary/axis but not necessarily the other 2) - and then the specular region where the acoustic energy behaves and can be modeled like ray-tracing light (angle of incidence = angle of reflection; geometry exactly like how pool balls bounce around a billiards/pool table). for the modal (LF) region (typically 0-250hz), you can utilize the Waterfall Plot within Room EQ Wizard. this will detail to you the frequency response of the LF region as well as the decay times (displayed as the Z-axis). this will indicate to you how long it takes acoustical energy at those frequencies to decay down. you will usually see high decay times from frequencies relevant to room modes, as those are resonances within the acoustical space as the energy tends to persist. long LF decay times will impart a perceived response at the listening position of the bass notes running together into a muddied mess.

since the specular region (~250-300hz and above) can be modeled like light, this is why you can utilize a mirror to identify 'reflection points' - but the mirror does NOT detail any relevant information to the acoustical energy incident from such a boundary. within Room EQ Wizard, there exists a tool called the Envelope Time Curve (ETC) response, which displays the time-domain behavior and how specular energy impedes the listening position. the frequency response details you Gain vs Frequency, while the ETC displays Gain vs Time, and time can be substituted with Distance since the speed of sound will be a constant. you can think of this like an impulse such as a gun-shot or balloon bursting. the direct signal will arrive first in time due to the direct signal to listening position being a straight vector and thus the shortest path traveled. following the direct signal will be any indirect energy (eg, first-order early reflection paths), followed by the later arriving reflections, and then the remaining energy as it decays until the last of the energy has been fully damped. the longer the reflection path, the longer in time it will take for that energy to reach the listening position (mic).

the ETC allows one to identify ALL of the destructive specular interference, and work backwards to resolve the particular boundary that the energy is incident off of. for example, if you measure a high-gain reflection that arrives 6ms after the direct signal, you know that the reflection path traveled (6ms * 1.126ft/ms) ~ 6.756ft longer than the direct signal. you can then work backwards and identify exactly which boundary this measured high-gain reflection is incident from and apply treatment as necessary. you're essentially identifying the ACTUAL high-gain early arriving reflection paths vs merely all POSSIBLE reflection paths as with a mirror. thus, you're not blindly placing treatment (absorber, diffuser, reflector) but instead placing the treatment at actual problem areas. eg, why would you place a large, expensive diffuser at a reflection point that is not incident of any high-gain reflections? and to the same point, many place absorption panels blindly via the mirror at any and all reflection points, which can quickly lead to a dead room. instead, if your criteria is to attenuate any early arriving high-gain indirect signals then you would place broadband absorption surgically ONLY at the areas incident of high-gain reflections (as measured with the ETC) and limit the amount of broadband absorption within the room.

but the ETC is merely a measuring tool and does not indicate the particular response you wish to achieve. that is your decision. and diffusion is for the specular region and has its own set of design criteria based on a multitude of factors and variables. for a 2ch listening space, you would want 1-Dimensional Reflection Phase Grating diffusers (QRD/PRD) with the wells oriented vertically such that the diffused returns off the rear wall are dispersed in the horizontal plane - which allows the diffused returns to arrive laterally from the rear side-walls for envelopment. bandwidth would be extend as low in frequency as physically possible, as the diffuser needs to be large with respect to wavelength as well as minimum seating distance requirements for Reflection Phase Grating diffusers (near-field vs far-field). so seating distance to rear wall is a factor in design as well.

edit: and reflection phase grating diffusers are absorbers for all intents and purposes -
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post #28 of 48 Old 05-05-2012, 05:51 AM
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Thanks for that wealth of information, Localhost127! Man, that really helped me and was probably the most helpful post I have ever read.

Ok so now I understand that I need to run REW and measure the ETC so that I can see what destructive specular interference I have at my listening position, due to room boundaries or other reflection points. After I take my ETC measurements to identify what the high gain reflections I am dealing with are, then I will work out the math and treat my room with absorbion panels in those particular places, then remeasure and replete.

I will also run a waterfall plot so that I can see what kind of LF decay times I have. Keep in mind that i have never used REW, although i will soon, and I have no idea what the waterfall plot looks like. How do I see, by looking at a waterfall plot, what kind of low frequency decay times I have and where the room modes are at? Also how will this tell me where and how I need to treat my room in order to lower or shorten decay times in the low frequency region?

Are there any other usefull measurement tools in REW besides the ETC, which measures gain vs time, and the waterfall plots, which measure LF decay times? What other factors are important in treating rooms, and, how can they be measured?

Thanks for your help Localhost127! Kudos to you for taking the time to explain all of that!
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post #29 of 48 Old 05-05-2012, 09:42 AM
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Originally Posted by Martycool007 View Post

Thanks for that wealth of information, Localhost127! Man, that really helped me and was probably the most helpful post I have ever read.

Ok so now I understand that I need to run REW and measure the ETC so that I can see what destructive specular interference I have at my listening position, due to room boundaries or other reflection points. After I take my ETC measurements to identify what the high gain reflections I am dealing with are, then I will work out the math and treat my room with absorbion panels in those particular places, then remeasure and replete.

While local's posts does have good acoustic information, his recommendations on a course of action which you are saying you will follow with regards to ETC and acoustic material, is heavily disputed by major industry experts and ordinary posters like me . We have had a long thread on it. Instead of rehashing it, I invite you to read my summary response to his position: http://www.avsforum.com/avs-vb/showt...2#post21937322.

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I will also run a waterfall plot so that I can see what kind of LF decay times I have. Keep in mind that i have never used REW, although i will soon, and I have no idea what the waterfall plot looks like. How do I see, by looking at a waterfall plot, what kind of low frequency decay times I have and where the room modes are at? Also how will this tell me where and how I need to treat my room in order to lower or shorten decay times in the low frequency region?

There is little reason to try to learn all of this. Your ears and brain do not see those waterfalls. Pyschoacoustics comes into play here and without it, you will be fixing measurements and may even make your room worse, not better.

The part of REW you want to pay attention is simple frequency response sweeps especially in low frequencies as described in the above summary post.

Amir
Founder, Madrona Digital
"Insist on Quality Engineering"

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post #30 of 48 Old 05-07-2012, 04:51 PM
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. . .

There is little reason to try to learn all of this. Your ears and brain do not see those waterfalls. Pyschoacoustics comes into play here and without it, you will be fixing measurements and may even make your room worse, not better.

The part of REW you want to pay attention is simple frequency response sweeps especially in low frequencies as described in the above summary post.

I'm sorry to say you are giving false and non-helpful information to the poster and I sure wish you would cease and desist. You fundamentally don't understand what you are talking about and disagree with many industry heavyweights on this.

Go back to your quoted post and stay out of this one, we don't need your type of help here, because you have a distorted viewpoint as a seller of high-end audio equipment. You should read "Sound System Engineering" by Davis and Patronis to get a better education on facts.
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