AVS Forum banner

First run with REW... advice and tips please :)

17K views 145 replies 16 participants last post by  beastaudio 
#1 ·
These are my first few measurements with REW in my HT. No calibration what so ever has been done yet except for level matching speakers. No Aydyssey and no Behringer DSP filters either. I'm sure these graphs won't mean too much yet, but I wanted to post them anyway because it was fun :p


No room treatments have been applied either, superchunk bass traps are waiting to be installed though



This first one is full range from 10hz - 10khz, crossing over to sub at 120hz and speakers set to small...




These next two are subs only, 10hz - 100hz, no tweaks at all, just a baseline run. The first one is front center LP and 2nd is rear center LP...






Marantz SR5005 AVR

Behringer EP4000 amp

Behringer FBD (no filters yet)

(4) FiCar Audio IB3 18's in a line array on front wall

DIY Econowave LCR speakers


Once again, these graphs won't mean much but it's a start. Any tips and tricks you can jot down would be fantastic...


My only questions so far are...


The R-Shack meter feeds a bit of static into the sound card input that I hear through the avr, is this normal?


Should I consider upgrading to a Dayton Omni Mic?


How about the sound card, right now it's a basic USB SoundBlaster sound card.


Also, how do I word this... Right now, I have the sub levels in the AVR set to 0 (neutral) and I turned up the amp gain enough to get 75db out of the subs with test tones (this is when I was level matching speakers). This leaves the amp gains at about 1/3 the way up. For ease of asking the question, lets say the amp could put out 900 watts at full gain, with the amp gain at only 1/3, is the amount of power the amp is able to send to the subs only 300 watts no matter how strong the signal being sent to the amp from the AVR is?


Gosh I hope thats easy to follow
 
See less See more
5
#77 ·

Quote:
Originally Posted by arnyk /forum/post/21954664


If density doesn't matter, why do we put any absorptive material into the absorber at all?

So now the substance of his reply fails to account for the NATURE of the material and instead focuses on the mere existence of material.



Density is a secondary term that has an extremely limited applicability in the realm of absorption. Its use as a derivative factor assumes that all of the structural material characteristics remain constant except for the degree of compression of the material structure. One could just as accurately say that the behavior of materials of similar construction but differing degrees of compression based upon the color of their wrapper, where the red one is more absorbent than the blue one which is more absorbent than the yellow one. But only a fool would mistake such a derivative attribute as exhibiting a casual absorptive nature.


Such a comparison is one of convenience and is NOT portable between materials whose internal structure varies Thus a semi-rigid bond fiberglass cannot be compared to a non bound fiberglass material, nor to another fiberglass material featuring differing porosity or tortuosity or strand orientation (anisotropism). And the critical factors that directly 'cause' the absorptive characteristics are the variance in the porosity (fraction of air volume in the material), material structure (anisotropism or orientation of fibers, tortuosity), both of which contribute to the characteristic known as gas flow resistance.

Quote:
Originally Posted by arnyk /forum/post/21954664


If you made a credible argument, I'd plunk down the $80-160 in a heartbeat. Of course if you knew the topic as well as you seem to claim, you'd be able to cite a relevant online document in a relevant, believable way.

I have a reference library of such materials. And they ALL deal with the material structure and rely on GFR rather than density. The fact is that you refuse to even read an overview of the concepts and now expect me to go and do YOUR work for you.


Its not up to me to convince you. I really don't care what what you fantasize. I merely have to mention the actual basis by which such behavior is gauged.


I have cited a prominent source that synopsizes of the major concepts, which also therein cites many of the pertinent source documents.


Maybe you can find a grade schooler who can help you navigate the scary library sufficient to access the reference desk in order to obtain the book via the inter-libary loan program without having to pay the money that others have had to in order to become more familiar with concepts about which you are obviously not familiar - and whom did not whine that it is others responsibility to read and learn for them.

Quote:
Originally Posted by arnyk /forum/post/21954664


Given how you blew off this one, what's the chance you being able to accomplish what you demand of others?


Clear points were made and you dismissed them all without any reference to any external support other than to drop their names.

LOL! Actually, you are wrong once again as I have made no recent reference to any of the models or to the actual researchers who have done the original research.


I merely referenced a source that does discuss many of the original sources. And I mentioned a few of the variables that are pertinent to their study, of which density is not a significant determinant factor. Get a copy of the book. I am not responsible for you doing your homework.


Quote:
Originally Posted by arnyk /forum/post/21954664


The interesting thing is that with all the smoke and mirrors, dogs and ponies, you never actually provided an apples-to-apples comparison or ran the item we are discussing through any of the software you said would resolve the question.

Yes, I can see where a complete read of the Ames study would confuse one seeing as they reference the behavior and implications of all of the factors you subsequently mischaracterize and dismiss without a single mention of "density".


And I have many advanced software packages that address the acoustical impedance of materials and boundaries as well as enable the actual measurement of absorption as well as diffusion that I had to save and buy based upon MY additional research and learning that I had to perform in order for them to be of use, as they are not substitutes for understanding the basic principles.


And here you sit on your posterior whining that others have not done YOUR due diligence that you now demand of them while absolving yourself of any and all responsibility, the least of which is to even discover the pertinence of a concept.


But its cute to see that you are now reduced to personal attacks devoid of any reference to any acoustical concepts.


You're done.


Ironically (unfortunately) our experience is not unique...
http://groups.google.com/group/rec.a...zkWdXVgvdvw?pl


Its also interesting that even commercial sites have noted this fact as well as the fact that OC has measured and determined that OC703 is a better absorber of LF energy than OC705 for some time as well...
http://www.readyacoustics.com/index....3_4&faqs_id=36


" Chapter 7: Sound Absorption

...

Primary material parameters affecting absorption:

• porosity (fraction of air volume in the material)

• structure factor (orientation of fibers, tortuosity)

• flow resistance"
 
#78 ·
I dont see this argument as helping the OP, and Im not taking sides here at all. Ive enjoyed reading the parts of each response where there is some science to help me learn more about absorbtion techniques, but please dudes, start a new thread on this if you want to continue the banter. With the exception that the OP is ok with the pissing match going on in his thread, otherwise, carry on gents
Oft times it is when two sides oppose, that the most is learned, and that goes for life in general, not just sound absorbtion...
 
#79 ·

Quote:
Originally Posted by dragonfyr /forum/post/21954809


But its cute to see that you are now reduced to personal attacks devoid of any reference to any acoustical concepts.

basic human nature and easily identifiable.


i think the root of the contention is he has likely been recommending oc705 for LF porous absorption for some considerable amount of time. suddenly realizing that the misconception that 'denser is better' is invalid may be a tough pill to swallow! every other acoustical forum has gone through the same teething process regarding such facts.
 
#80 ·

Quote:
Originally Posted by beastaudio /forum/post/21954841


I dont see this argument as helping the OP, and Im not taking sides here at all. Ive enjoyed reading the parts of each response where there is some science to help me learn more about absorbtion techniques, but please dudes, start a new thread on this if you want to continue the banter. With the exception that the OP is ok with the pissing match going on in his thread, otherwise, carry on gents
Oft times it is when two sides oppose, that the most is learned, and that goes for life in general, not just sound absorbtion...

regarding the OP,

he's already been notified his surface coverage is NOT sufficient, period.


and also that since he is limited with respect to real estate of where he can place such absorbers, that he is better off building or procuring pressure-based absorbers that do NOT need to be thick as they are NOT required to be placed into areas of high particle velocity in order to be effective! ...but instead, placed against the boundary where pressure is maximum (and velocity approaches zero).

http://www.avsforum.com/avs-vb/showp...0&postcount=55


i even provided links to commercial pressure-based resonator absorbers for more information on actual products and their actual measured performance.


there is NOTHING else to say to the OP with respect to LF absorption unless he is able to add more surface coverage for his porous, velocity-based absorbers - or to source pressure-based resonator traps.


and there is no "pissing match" or "debate" going on - just the presentation of facts regarding porous insulation, and then the merciless blind contention of said facts via personal attacks lacking any scientific value. eg, "shoot the messenger".
 
#85 ·
Alright guys, this has gotten WAY out of control. To the acoustic guru's that are posting in here, if you need to prove to others in an incredibly lengthy manner (other than me), that they're wrong about something, please keep it in PM's, or in another thread. If I'm wrong/mislead about a statement or an idea, keep your posts friendly and simple, I'm just trying to learn here, to an extent anyway. All of this technical data and "big words that I don't understand" talk is giving me a headache.


On the other hand, I do appreciate the vast amount of knowledge and vocabulary you guys have, honestly, I do, but you need to chill on the incredibly long replies, especially if they don't help me out directly. If you feel other replies are steering me in the wrong direction, you're welcome to offer your advice in a fairly simplistic and Layman's term manner, or even better, feel free to PM me if you are willing to offer advice that can relate to me and my room personally.


Thank you.
 
#86 ·

Quote:
Originally Posted by localhost127 /forum/post/21955151


another post devoid of substance.

you have nothing of scientific value to offer here wrt: the subject of porous absorption.

Just a humble little link that provides tools for designing porous absorbers with perforated fronts via a cookbook technique that many forum participants, perhaps even you, could benefit from:

http://www.iperf.org/pdfdownloads.html


more specifically: http://www.iperf.org/IPRF_DES.pdf
 
#88 ·

Quote:
Originally Posted by Digital_Chris /forum/post/21956924


Alright guys, this has gotten WAY out of control. To the acoustic guru's that are posting in here, if you need to prove to others in an incredibly lengthy manner (other than me), that they're wrong about something, please keep it in PM's, or in another thread. If I'm wrong/mislead about a statement or an idea, keep your posts friendly and simple, I'm just trying to learn here, to an extent anyway. All of this technical data and "big words that I don't understand" talk is giving me a headache.


On the other hand, I do appreciate the vast amount of knowledge and vocabulary you guys have, honestly, I do, but you need to chill on the incredibly long replies, especially if they don't help me out directly. If you feel other replies are steering me in the wrong direction, you're welcome to offer your advice in a fairly simplistic and Layman's term manner, or even better, feel free to PM me if you are willing to offer advice that can relate to me and my room personally.


Thank you.

Ill continue to try and keep it up your alley, regarding your situation by asking if you have tried to pull that one peak down with your BFD yet? I still have a lot of work to do with mine, but at least down to 10hz, Im pretty close to ruler flat and it is just amazing what flat bass sounds like. I try and find my last sweep I ran.
 
#89 ·
Also, here is a link to how I managed to eq out my two XXX 18's. You can see with just a couple filters that I was easily able to get it near flat. Since then I have tweaked a little more and gotten it to sound even better, but im still concerned about the rolloff right before the 10hz line. You easily have the same capability with the BFD


http://www.avsforum.com/avs-vb/showt...2#post21819762
 
#90 ·
Thanks for the link to your graphs. I haven't played around with the BFD yet, I'm going to get myself down there to run a few more graphs for both rows and see how much of a difference there is between the two. I'm afraid that if I EQ for one row, the other row will sound even worse and there will be no compromise



Do you have 1 or 2 rows of seating if your space?


EDIT: Just saw your construction pics, nice color :p Mine is just about the same. How did the wagner sprayer work out? Any streaks? How about overspray, did it cloud up the room while you were painting? I need to re-do my ceiling and was curious is the gun was the way to go
 
#91 ·
Here are a couple graphs I took tonight, the only change was the mic position from front center seat to rear center seat, what a difference!! What do you guys do when you are trying to EQ for multiple rows? Since I'm sure that EQ can't make my response flatter for both rows, what are my next options, some other form of bass trapping?

Front Center Seat



Rear Center Seat



Overlayed

 
#92 ·

Quote:
Originally Posted by Digital_Chris /forum/post/21965463


Here are a couple graphs I took tonight, the only change was the mic position from front center seat to rear center seat, what a difference!! What do you guys do when you are trying to EQ for multiple rows?

Now you know why people look at their situation carefully and don't put all of their eggs in one basket. Room eq is one basket and room acoustics is another. In general the eq basket is cheapest and fastest, but it has strong limitations and you just found one of them.


When a room has large variations among nearby seating positions in the bass range, the usual cause is some kind of standing wave. It might be possible to do something with multiple subwoofers, but the far more straightforward approach is bass-oriented room treatments.


I had a room where the standing waves were so pronounced that if I played a 100 Hz tone, I could walk from seat to seat and hear it almost totally disappear, and then if I moved a few fee it would reappear. Classic standing waves! Treating the back wall of the room with large custom made sound absorbing panels that were composed of 2" thick 705 spaced about 4 inches from the wall pretty well erased them.


Most people who enter the room and sit there for hours never notice the panels visually. Big sonic difference - the overall sound is significantly more pleasant. There was a big audible slap echo off the back wall that also disappeared, no surprise.
 
#93 ·

Quote:
Originally Posted by arnyk /forum/post/21956980


Just a humble little link that provides tools for designing porous absorbers with perforated fronts via a cookbook technique that many forum participants, perhaps even you, could benefit from:

http://www.iperf.org/pdfdownloads.html


more specifically: http://www.iperf.org/IPRF_DES.pdf

im not sure what your links have to do with the respect to the discussion that flow-resistivity is the key value of porous insulation, not density as apparently is still attempted to be propagated...


and AFMG SoundFlow is more than sufficient for perforated panel design and modeling.


and if the goal is a tuned, resonate (pressure-based) absorber - then chapter 6 of AA&D by Cox/D'Antonio is a good place to start - http://www.amazon.com/Acoustic-Absor.../dp/B001Y35IHW
 
#94 ·

Quote:
Originally Posted by Digital_Chris /forum/post/21959222


Thanks for the link to your graphs. I haven't played around with the BFD yet, I'm going to get myself down there to run a few more graphs for both rows and see how much of a difference there is between the two. I'm afraid that if I EQ for one row, the other row will sound even worse and there will be no compromise



Do you have 1 or 2 rows of seating if your space?


EDIT: Just saw your construction pics, nice color :p Mine is just about the same. How did the wagner sprayer work out? Any streaks? How about overspray, did it cloud up the room while you were painting? I need to re-do my ceiling and was curious is the gun was the way to go

Eqing for the main position is obviously more important. arny has a good point that this is a multi-basket deal. Room modes are dominant and your graph is showing that. I tpyically like to eq to the main position as close as I can get, then go back and see what it does to the other seating areas. The way my friends see it, my room sounds better than any commercial theater, and definitely better than any of theirs systems, even when the response looks like mt everest... they dont care, and moreover, cant notice.


Now before you read into that too far, I still would prefer to have a flat response across all seats, but for me, in my odd shaped room, I havent found that to be quite possible. ive gotten close, but not exact. That leaves me with having to make small sacrifices, therefore I tend to eq to the MLP and then tweak to make the rest of the room sound as good as it can.


This was one reason I shied away from a IB type setup as I was quite nervous about doing all that and then the position I chose not being optimal for the room :/


In regards to the wagner sprayer, it was awesome!! It definitely clouds the room up, and youll want to cover all doors, windows, vents, floor with plastic. The overspray wipes off pretty easily after dry, but it was funny, the dust cloud would still work its way into wherever the air was escaping and I had to scrub off the inside of some door panels in spots. all in all, for a bigger space it is totally worth it. and it is super efficient. I only used 2 gallons of paint for my whole room!!


I actually have 3 rows of seating, but I need to update my gallery something aweful, most of what is in that album is not even there anymore!!! stereo rack has moved, new bigger a-t screen, new subs, new speakers, new surrounds, new AVR, (with another on the way), yea I need to update!!!
 
#95 ·

Quote:
Originally Posted by arnyk /forum/post/21966215


Now you know why people look at their situation carefully and don't put all of their eggs in one basket. Room eq is one basket and room acoustics is another. In general the eq basket is cheapest and fastest, but it has strong limitations and you just found one of them.

Well, acoustic treatment has strong limitations too. Please see below.

Quote:
When a room has large variations among nearby seating positions in the bass range, the usual cause is some kind of standing wave. It might be possible to do something with multiple subwoofers, but the far more straightforward approach is bass-oriented room treatments.

It is not just "might be possible" with multiple subs. It absolutely is possible and the most powerful tool we have to cancel/attentuate out some of the modes. From my article on low frequency room optimization: , here is a single sub response across multiple seating positions:




Now this is what happens when you use four subs:




We have almost completely done away with seat to seat variations. The article then goes on and talks about how electronic correction (and not just EQ) flattens the curve for all the seating positions and the overall response. Nothing is as easy to understand and apply than those techniques.


OP does have four subs but unfortunately they are all on the front wall. If they were put in opposing sides and seats places away from the remaining room modes, then he would be most of the way there.

Quote:
I had a room where the standing waves were so pronounced that if I played a 100 Hz tone, I could walk from seat to seat and hear it almost totally disappear, and then if I moved a few fee it would reappear. Classic standing waves! Treating the back wall of the room with large custom made sound absorbing panels that were composed of 2" thick 705 spaced about 4 inches from the wall pretty well erased them.

100 Hz tone? His problems as typically exists, is below that frequency. In his example, it is down to 30 and 50-60 Hz. Your proposed solution doesn't work there, nor does it even work at 100 Hz. Here are the simulated results for the panel you are proposing:



We see that at 100 Hz and below, it has no absorption ability to speak of. So it will do nothing for those resonances. Acoustic products can be helpful in low frequencies but they are challenging to design and use, and can take considerable amount of space. If OP bought just one other sub and put it in the middle of the opposing wall, he would sharply reduce two of the modes length-wise.

Quote:
Most people who enter the room and sit there for hours never notice the panels visually. Big sonic difference - the overall sound is significantly more pleasant. There was a big audible slap echo off the back wall that also disappeared, no surprise.

What you describe is what it does. Reduce room issues at transition frequency and above. Let's take disagreements to this thread: http://www.avsforum.com/avs-vb/showthread.php?t=1407637


My advice to OP is as was given by beastaudio. Go ahead and take out the peak at the main seating position. You are likely more sensitive to it than others sitting in the room. If you can borrow another sub and experiment with, try what I explained above.
 
#96 ·

Quote:
Originally Posted by localhost127 /forum/post/21966298


im not sure what your links have to do with the respect to the discussion that flow-resistivity is the key value of porous insulation, not density as apparently is still attempted to be propagated...


and AFMG SoundFlow is more than sufficient for perforated panel design and modeling.


and if the goal is a tuned, resonate (pressure-based) absorber - then chapter 6 of AA&D by Cox/D'Antonio is a good place to start - http://www.amazon.com/Acoustic-Absor.../dp/B001Y35IHW

You are both right in a way
. As Mike and OP have asked to not side-track on topics from what OP has asked about, I created a thread and put the response there: http://www.avsforum.com/avs-vb/showthread.php?t=1407637 . Let's take disagreements there.
 
#97 ·
holy crap - all of my parroting and i finally got another user to actually USE SoundFlow!

and to think it was only a week or so ago that some were debating that validity of the modeling inherent in such software!



and why do you guys apply smoothing to your modal region frequency responses?
 
#98 ·

Quote:
Originally Posted by localhost127 /forum/post/21967118


holy crap - all of my parroting and i finally got another user to actually USE SoundFlow!

No, I am not a user. If I had the data for real panels in that configuration handy, I would post that. I happen to have found the SoundFlow simulations posted elsewhere and thought that in a discussion with you, you would accept them better since you cut and past them the same way. Again, let's take debates to the other thread.

Quote:
and why do you guys apply smoothing to your modal region frequency responses?

The problems he has at 1/6th will be there unfiltered. So while you don't want to apply that much smoothing in general (e.g. if you want to know the specific frequency to filter), for the purposes of the discussion, it is still fine.
 
#99 ·

Quote:
Originally Posted by amirm /forum/post/21967196


No, I am not a user. If I had the data for real panels in that configuration handy, I would post that. I happen to have found the SoundFlow simulations posted elsewhere and thought that in a discussion with you, you would accept them better since you cut and past them the same way. Again, let's take debates to the other thread.

oh,

so then your above modeling isn't accurate representation as arnyk was using OC705 and you are at the mercy of whatever the user used that you "borrowed" the photos from. heh. you said: "Your proposed solution doesn't work there, nor does it even work at 100 Hz. Here are the simulated results for the panel you are proposing:" clearly you did not present simulation based on modeling of OC705...


SoundFlow is free for 30-day trial. why don't you model arnyk's proposed solution instead of arguing against it based on data for a different material?



Quote:
Originally Posted by amirm /forum/post/21967196


The problems he has at 1/6th will be there unfiltered. So while you don't want to apply that much smoothing in general (e.g. if you want to know the specific frequency to filter), for the purposes of the discussion, it is still fine.

only apply smoothing in the modal region if you're attempting to hide something.
 
#100 ·

Quote:
Originally Posted by amirm /forum/post/21966981



In his example, it is down to 30 and 50-60 Hz. Your proposed solution doesn't work there, nor does it even work at 100 Hz. Here are the simulated results for the panel you are proposing:

Amir, you appear to be off in fantasy land, again. I made no specific recommendation. I only provided an anecdote about some work I did involving a 100 Hz standing wave.


Your modeling program or your interpretation of its report seems broken because the audible effect of the absorber I mentioned @ 100 Hz was nothing short of dramatic.


Edit: I can't make out your parameters well, but the material and density may be incorrect. I ran my own choice of models with density of about 25% of what 705 actually is, and obtained results very much like yours.


However, the effect of the anecdote's absorbers at 50 Hz and below leaves a lot to be desired.


Edit: With the proper material and density, my model predicts poor performance below 50 Hz as well.
 
#101 ·

Quote:
Originally Posted by localhost127 /forum/post/21967339


SoundFlow is free for 30-day trial. why don't you model arnyk's proposed solution instead of arguing against it based on data for a different material?

I suspect that Amir tried to model my absorber, but he may have screwed up the data entry.


That might be an err unnh.. Rookie Mistake. ;-)


Careful workers run their models with test cases for which solutions are published and see how they agree.


I found a modeling program that doesn't have a time limit on it and ran my absorber. Its results agree with my real world observations. Also agrees with published specs for common materials.


I ran it with sound absorbing material that has about 25% the absorbency of 705 and got something very similar to what Amir posted.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top