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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
 
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#52 ·

Quote:
Originally Posted by Digital_Chris /forum/post/21820412


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

Your procedure is right. Get the low frequencies under control first.

Didn't find mention of room size/listening and speaker position.

Draw us a floor plan and take some pictures!

And take Fottos and Arnys advice - source some cheap 'pink' insulation to fill up all your corners temporarily, play with your listening position forward-backward to get out of major nulls. When modal freq. is under control, THEN look at what can be done with imaging/intelligibility/coloration, guided by ETC graphs of listening positions you wish to optimize. You don't need 120dB range for ETC display, we need to see where and with what gain the reflections are impeding the listening position - about 30-50dB.
 
#53 ·
Unfortunately, I don't have the room upfront to add bass traps, I mentioned that earlier in the thread but I understand how it could have gotten missed. The room is on the small side as well so I don't have the room to start placing thick traps of 705 around the room. I'm just trying to work with what I got, not asking for perfection (just so you guys don't get the wrong idea of this thread)


My room dimensions are roughly 18' x 10.5' x 7'.


LCR speakers are horn designed econowaves and are flush mounted into the front wall. Subs are infinite baffle design in a line array across the front wall also. First row of seats is just under 10' from speakers and rear seats are about 14' from front wall. There are 2 rows of 3 seats. You can brows photos here


Bass traps are about 4" off the ground and just about a foot from the ceiling. They were built that way to match the height of my designed wall panels.










Here is a shot of one of the front corners, no room for traps unfortunately...




When I think of more details, I will add them
 
#54 ·

Quote:
Originally Posted by Digital_Chris /forum/post/21928176



Here is a shot of one of the front corners, no room for traps unfortunately...




When I think of more details, I will add them

No matter what people say here about using low density fiberglass, the fact is that the same thickness of higher density fiberglass can be more effective at lower frequencies. Adding density works right up until you turn your absorber into a reflector. I've never seen that done with 705.
 
#55 ·

Quote:
Originally Posted by arnyk /forum/post/21929506


No matter what people say here about using low density fiberglass, the fact is that the same thickness of higher density fiberglass can be more effective at lower frequencies. .

this is entirely incorrect.

first of all, gas-flow-resistivity is the key value regarding the porous insulation, NOT density as perpetually propagated so often.


porous insulation is a velocity-based absorber and as such, needs to be placed into areas of relatively high particle velocity in order to be most effective. at low frequencies (long wavelengths), this means very thick traps (or large air-gap spacing from rigid boundary) are required. however, as you make the LF absorbers thicker and thicker, you will want to use a material with lower flow-resistivity.


the acoustical impedance plays a large role and any sudden change will result in a reflection regardless of the material. it would actually be ideal to start with a light fibre with impedance close to that of air, and then slowly increase GFR as the porous insulation approaches the rigid boundary.


if constricted to thin traps, then a denser (higher GFR) material will perform better - but there is little advantage to using thin porous absorbers for LF absorption regardless of material used --- the insulation needs to be placed into areas of high particle velocity to be most effective, period. if this is not an option, or you need attenuation at the lower octaves, then pressure-based resonator traps (VPR, membrane, helmholtz) are available. and since they are pressure-based absorbers, their optimal placement is directly on the boundary where pressure is maximized and velocity approaches zero.


if unwilling to experiment and design your own, there are commercial products available:
http://www.rpginc.com/product_Modex_Broadband.cfm
http://www.rpginc.com/product_Modex_Corner.cfm
http://www.rpginc.com/product_Modex_Edge.cfm
http://www.rpginc.com/product_Modex_Module.cfm
http://www.rpginc.com/product_Modex_Plate.cfm



the transfer function formulas are available and you can experiment with a porous absorber calculator or utilize AFMG SoundFlow (free for 30-day trial).


pink fluffy has a flow-resistivity of ~ 5000rayl/m




and this is before we even get into discussion of modifications to the speed of sound as the pressure-wave is passing through the porous insulation...

Quote:
Originally Posted by arnyk /forum/post/21929506


Adding density works right up until you turn your absorber into a reflector. I've never seen that done with 705.

so then why don't you provide the optimal flow-resistivity and thickness for such an application?


-----------------------------


the user's issue is lack of surface area coverage - plain and simple.
 
#56 ·
Chris,


Ive been dealing with some of the same issues as you. No ability for ANY corner bass traps, more pronounced bass in the second row than the front, and very limited places to put the subs (in your case, only ONE place
) I feel your pain brotha, and I cant stress enough how the proper combination will help you. One thing that might help in running your graphs is to not assum you can tame EVERYTHING with room treatment, you have the BFD and audyssey after your preliminary eqing to also aid in your quest for a flat bass response. Try some filters on the BFD at the 28hz and 60hz peaks to pull those down a shade and see what you think. Dont quit on the room treatment stuff either! Just give some other things a tweak and see where you get. Peaks are better than nulls IMO so go after those and redo your waterfalls and whatnot, see if they clean up a little
Ill be following your thread closely and will continue to post any findings I have in the same search for "better bass up front"
 
#57 ·
Thanks beast, I'm going to take a few more graphs tonight possibly. I popped in the movie hot fuzz last night and was happy with the sound for the most part, but there are definitely some sounds that just sound boomy and its not just the bass, I'm not sure of another way to describe it, maybe I should say it sounds muddy? Either way, it doesn't sound right. It's like some of the sounds are just louder than they should be, louder than the rest of the movie.


There are definitely plenty of parts in that movie and others I have watched too, that the dialogue isn't 100% intelligible either. A lot of the times when it's intelligible, it's because it sounds lower in volume than the rest of the movie. I'm not sure if room treatments would help this because I don't see how they could help in bringing up the volume but it just doesn't sound right.


Also, I popped in the movie Tron this morning to demo to a friend and he sat in the backseat where I knew the bass would be boomier than the rest of the room, so I turned the subs down a tick and had the volume at -15 rather than -10 where I would normally have it, and the bass was just way overpowering, the dialogue and other action sounds were fine, it's just that the bass was way too loud/strong, I don't get it



God, I just want this room to sound awesome and at the same time I feel like I'm never going to get it to that point
 
#58 ·

Quote:
Originally Posted by Digital_Chris /forum/post/21947225


God, I just want this room to sound awesome and at the same time I feel like I'm never going to get it to that point

The issues are pretty straightforward and all focus on one chart:




You have a resonance at ~58 Hz or so at a level of 76 dB. At 20 KHz, your response is down to 37 db for whopping ~40 db variation in response! I don't know what Mic you used and if this is a calibrated setting. But even if we back off and look at the response at 5 Khz, you are at ~54 dB for a very large difference of 22 dB. While some amount of bass boost is desirable, you don't want to have such large differential.


The first fix then is to pull down that peak at 76 db with a parametric EQ. You can stand dropping that by 10 db. If you did that, a lot of boominess will go away and the bass would not overwhelm the rest of the sound as it is doing now. You will lose some of your sub power with that but with four of them in front, I assume you still have sufficient. If you do not, you can increase the gain for the whole region some. There is a list of DSPs people use in REW. Select the "EQ" window and you see them in the drop down list. The few hundred dollars on one of these is well worth the price and a necessary item no matter what acoustic product you put in your room. You will always have fluctuations in the response.


For a much higher-end implementation of this, take a look at this article on low frequency room optimization . As you see there and was noted by the beastaudio above, there are a lot of tools at your disposal and you should not limit things to just acoustic products. Our room is professionally designed including computer modelling and lots of acoustic products yet it still benefited from the techniques in that article.


You have a nice looking room and you will be able to improve it sound a lot relative to where it is now.
 
#59 ·
One more thing: run the graph in 1/12th when optimizing bass. Turn off all other speakers and try to linearize the subs by themselves that way first, not worrying about the crossover region. Then look at both being on and getting a smooth response during the crossover. Make sure your subs have proper output that is clean up to the crossover range. Listen to them playing for example 80 to 100 Hz by themselves to make sure they sound clean. If not, filter that out.
 
#60 ·

Quote:
Originally Posted by amirm /forum/post/21947330


You have a resonance at ~58 Hz or so at a level of 76 dB. At 20 KHz, your response is down to 37 db for whopping ~40 db variation in response! I don't know what Mic you used and if this is a calibrated setting. But even if we back off and look at the response at 5 Khz, you are at ~54 dB for a very large difference of 22 dB. While some amount of bass boost is desirable, you don't want to have such large differential.

I agree, it is odd, I'm not sure why my response drops off dramatically that early. I used the Behringer ECM8000 mic with the generic calibration file from the REW forum. Maybe I can do a sweep with the mic right in front of the speaker(s) to see if it's the speaker or room? Could it be the AVR that is causing the decent?

Quote:
Originally Posted by amirm /forum/post/21947330


The first fix then is to pull down that peak at 76 db with a parametric EQ. You can stand dropping that by 10 db. If you did that, a lot of boominess will go away and the bass would not overwhelm the rest of the sound as it is doing now. You will lose some of your sub power with that but with four of them in front, I assume you still have sufficient. If you do not, you can increase the gain for the whole region some. There is a list of DSPs people use in REW. Select the "EQ" window and you see them in the drop down list. The few hundred dollars on one of these is well worth the price and a necessary item no matter what acoustic product you put in your room. You will always have fluctuations in the response.

I do have a FBD inline between the AVR and the EP4000, the 1124 I believe, so I will be able to tame those peaks. Will that one adjustment of -10db at 58hz make that much of a difference in the overall sound? I got the idea that it will take multiple adjustments and dramatic room treatments to cure most of that boomy bass, hopefully I'm wrong?!

Quote:
Originally Posted by amirm /forum/post/21947330


For a much higher-end implementation of this, take a look at this article on low frequency room optimization . As you see there and was noted by the beastaudio above, there are a lot of tools at your disposal and you should not limit things to just acoustic products. Our room is professionally designed including computer modelling and lots of acoustic products yet it still benefited from the techniques in that article.


You have a nice looking room and you will be able to improve it sound a lot relative to where it is now.

Thanks for the encouragement, I hope you're right. I just can't help but feel that no matter what I do, the room will not change in sound. Dumb thought I know, but until I make a change that I can honestly hear, I will continue to think that way


Quote:
Originally Posted by amirm /forum/post/21947353


One more thing: run the graph in 1/12th when optimizing bass. Turn off all other speakers and try to linearize the subs by themselves that way first, not worrying about the crossover region. Then look at both being on and getting a smooth response during the crossover. Make sure your subs have proper output that is clean up to the crossover range. Listen to them playing for example 80 to 100 Hz by themselves to make sure they sound clean. If not, filter that out.

What do you mean by making sure that my subs have clean proper output and how would I filter the unwanted dirtyness out?


Thanks a lot amirm
 
#61 ·

Quote:
Originally Posted by localhost127 /forum/post/21929600


Quote:
Originally Posted by arnyk /forum/post/0


No matter what people say here about using low density fiberglass, the fact is that the same thickness of higher density fiberglass can be more effective at lower frequencies.

this is entirely incorrect.

That's because you are reading what you want to read, and not what I said.


And by the way, prove by means of actual math or experiments that higher density fiberglass won't help this specific project.


What you've done so far is run the phrase "gas-flow-resistivity" into the ground with a series of non-answer posts.


I never said anything about "gas flow resistivity". I was talking specifically about two different absorbent materials.

Quote:
first of all, gas-flow-resistivity is the key value regarding the porous insulation, NOT density as perpetually propagated so often.

No contest. I've never said otherwise. Your continual harping on this topic and false criticisms serves nobody but perhaps yourself.


I commented on some specific construction details, and in this post a lame attempt is being made to turn construction details into a global statement about how sound absorbers work.


Of course gas-flow-resistivity is of the essence, and no matter how you spin it, I've never said otherwise.


If you'd like to claim that loose fiberglass thermal insulation has more gas-flow-resistivity in the lower audio range than the same material in the form known as Dow Corning 705 please be my guest.


But, when you do that don't just make false claims about my comments, wave your hands, and throw some technical terms around. Actually contribute something. Do you actually know anything but a few catch-phrases and how to make false statements about other people's posts?


Please actually show what the materials being discussed do to system bass response in the application we are discussing.


If you haven't noticed, you've completely lost the OP.
 
#62 ·

Quote:
Originally Posted by arnyk /forum/post/21948612


That's because you are reading what you want to read, and not what I said.

so let's go back and re-read your original statement of which i replied,

"No matter what people say here about using low density fiberglass, the fact is that the same thickness of higher density fiberglass can be more effective at lower frequencies."


you claim "fact" with zero measurements, models, etc of your own. so you expect the onus to be on ME to provide data for YOUR global claims?


and i provided modeling via AFMG SoundFlow that shows how pink fluffy (5000rays/m) loosely filled fiberglass will outperform higher GFR OC703 (and OC705 is even higher GFR) across the LF range.


you've probably been recommending OC705 for years and simply had your world turned upside down upon this "realization" and thus, need to make an attempt to save-face.

Quote:
Originally Posted by arnyk /forum/post/21948612


And by the way, prove by means of actual math or experiments that higher density fiberglass won't help this specific project.

actual math? you mean the transfer function forumulas from Acoustic Absorbers and Diffusers (D'Antonio/Cox)?



i didn't say the higher density fiberglass "won't help" - instead, i gave a more effective solution based on a different material. there is no getting around that porous insulation is a velocity-based absorber and LF content has long frequencies of which means the porous LF absorbers need to be 1) physically large with respect to wavelength, and 2) placed (or spaced away from rigid boundary) into areas of high particle velocity.


are you in contention with either of these two statements?


and from the "actual math", we know that as the traps get thicker and thicker (required for the longer wavelengths), a material with LOWER GFR is more effective across the bandwidth!


you've basically provided a more expensive and less effective solution for broadband LF absorption with respect to OC705 vs pink fluffy porous insulation.


Quote:
Originally Posted by arnyk /forum/post/21948612


What you've done so far is run the phrase "gas-flow-resistivity" into the ground with a series of non-answer posts.

I never said anything about "gas flow resistivity". I was talking specifically about two different absorbent materials.

uhh, and just what is the key value here that dictates the difference between the two material's performance?




Quote:
Originally Posted by arnyk /forum/post/21948612


No contest. I've never said otherwise. Your continual harping on this topic and false criticisms serves nobody but perhaps yourself.


I commented on some specific construction details, and in this post a lame attempt is being made to turn construction details into a global statement about how sound absorbers work.


Of course gas-flow-resistivity is of the essence, and no matter how you spin it, I've never said otherwise.

you've never said otherwise?

have you ever mentioned gas-flow-resistivity in your commentary? i don't see any reference to such correct terminology in your search history.


the only posts where you reference GFR is in response to my or dragonfyr's commentary.


hmm,
http://www.avsforum.com/avs-vb/showp...98&postcount=4


arny - "It's not clear at all what the above all means,"


and please detail to me the "global statements" im making based on "how sound absorbers work". why don't you provide detailed commentary of how sound absorbers work?



Quote:
Originally Posted by arnyk /forum/post/21948612


If you'd like to claim that loose fiberglass thermal insulation has more gas-flow-resistivity in the lower audio range than the same material in the form known as Dow Corning 705 please be my guest.

i don't think you understand what the term means based on this statement.

Quote:
Originally Posted by arnyk /forum/post/21948612


But, when you do that don't just make false claims about my comments, wave your hands, and throw some technical terms around. Actually contribute something. Do you actually know anything but a few catch-phrases and how to make false statements about other people's posts?

yes, attack me for using "technical terms" while we discuss physics and actual acoustical behavior in the real world. is this some sort of default fall-back psychological behavior on this forum? when you are unfamiliar with a topic (or proven wrong on an acoustic misconception), you simply attempt to invalidate the other user by their use of "technical terms"?


face it - you were just called out.

and this is your response? why don't you provide some data, measurements, modeling of your own instead of commentary like this previous post of which has ZERO substance related to the topic.


"actually contribute something" -- yeah, let's see - i detailed to the OP how porous absorption works, where it must be placed in order to be most effective, a cheaper and more effective material to use as a solution, AND i also went into detail about more ideal LF absorbers (pressure-based) and even linked to many different commercial products for sale!! you don't call that "contributing"?


AFMG SoundFlow is free for 30day trial if you wish to experiment; and while you're at it, you may want to investigate REFLEX as well (wonderful tools).
 
#63 ·

Quote:
Originally Posted by localhost127 /forum/post/21948693


so let's go back and re-read your original statement of which i replied,

"No matter what people say here about using low density fiberglass, the fact is that the same thickness of higher density fiberglass can be more effective at lower frequencies."


you claim "fact" with zero measurements, models, etc of your own. so you expect the onus to be on ME to provide data for YOUR global claims?

I didn't make a global claim. I said that " higher density fiberglass can be more effective at lower frequencies"


All I need is one instance where higher density fiberglass is more effective at lower frequencies to have a correct statement.


For your claim that my statement "is entirely incorrect" to be true, you have to prove a global statement.


As far as your alleged Soundflow results go, I just searched for them, and I can't find any comparisons involving 705. Perhaps you have a URL and post number?
 
#65 ·

Quote:
Originally Posted by arnyk /forum/post/21948730


As far as your alleged Soundflow results go, I just searched for them, and I can't find any comparisons involving 705. Perhaps you have a URL and post number?

why don't you simply tell us why you recommend 705 vs any other material - what data are you using to make your recommendations?


you've never used a porous absorber calculator? impedance tube (normal incidence) measurements? AFMG SoundFlow is available for free 30-day trial; why don't you explore and experiment for yourself!


and if you're so familiar with gas-flow-resistivity, then you should already know the approx. GFR values for the relevant materials we are discussing.

i gave a more effective solution based on a different material. there is no getting around that porous insulation is a velocity-based absorber and LF content has long wavelengths of which means the porous LF absorbers need to be 1) physically large with respect to wavelength, and 2) placed (or spaced away from rigid boundary) into areas of high particle velocity.

are you in contention with either of these two statements?
 
#66 ·

Quote:
Originally Posted by localhost127 /forum/post/21948758


why don't you simply tell us why you recommend 705 vs any other material - what data are you using to make your recommendations?

I asked a simple question, namely where your alleged results disproving my simple comment were posted.


Since you don't want to respond to that simple request, but instead appear to to be ready to pick yet another fight, I conclude that the results you claimed don't actually exist.


Please correct me if I am wrong about your inability to back up your own claims about your own results.
 
#67 ·

Quote:
Thanks for the encouragement, I hope you're right. I just can't help but feel that no matter what I do, the room will not change in sound. Dumb thought I know, but until I make a change that I can honestly hear, I will continue to think that way

One major thing to consider, your main listening position is going to be at the quarter wavelength, bad things happen in this area. That is why if you eq to your MLP, other parts of the room are going to sound boomy, vis a vis, the closer you get to the boundaries in the room, the more pronounced the bass is going to be. Since placement of the subs is obviously out of the question perhaps do the crawl test with your RS meter and see how different parts of your room are reacting, not just the two listening positions.


Oh and also, dropping that peak at 58hz is going to make a MAJOR difference. That frequency is smack-dab in the middle of where people perceive the peak in response as being "boomy" try this before all else.
 
#68 ·
Quote:
Originally Posted by arnyk
I asked a simple question, namely where your alleged results disproving my simple comment were posted.


Since you don't want to respond to that simple request, but instead appear to to be ready to pick yet another fight, I conclude that the results you claimed don't actually exist.


Please correct me if I am wrong about your inability to back up your own claims about your own results.
Local, why even try? You are stuck doing actual research into topics whereas others foundation is faith and belief. And inertia from repeating he same misnomers over and over until they become fact.


Its a shame that none of the oft made original "simple comment(s)" are seemingly never substantiated.


Nor are texts such as Acoustic Absorbers and Diffusers ever read or referenced as well that would render this running gag where density is imagined to be a valid determinant of absorptive quality moot.


But one might find it odd as results such as the following have been known for 30+ years with work on such projects as NASA's Ames wind tunnel where even then their conclusions were:

"The conclusions can be summarized as follows:

Sound absorption in the low to mid frequency range can be increased by the use of PF3350 fiberglass (nominal flow resistivity 4100 mks rayls) instead of Owens Corning 703 fiberglass (27,000 mks rayls) and by an increase in lining thickness from 6 inches to 10 inches.


When PF 3350 fiberglass is used, the acoustic absorption coefficients predicted for 10 inches of material are essentially the same as those for 8 inches of material plus a 2-inch air gap."



Don't worry about the part numbers - the operative terms are the GFR values.


...Maybe we should alert them to the ease of referencing density figures rather than GFR values?


Funny how the 'audiophile' community lags so far behind what has known within common acoustics and noise control engineering circles.


But why should anyone expect such notions more often derived from marketing brochures to be substantiated when belief is more important than objective substance?


Ironically, the onus is placed upon the acoustics and engineering circles to prove their assertions that run counter the 'universal truths'(sic) of the hobbyist community sourced in the indisputable urban myths and marketing brochures that supplant legitimate sources.


But whatever you do b'rer fox, Don't throw me into that briar patch where one might actually read Acoustic Absorbers and Diffusors and find out how this stuff actually works!!

 

OC703 vs OC PF3350 Ames Wind Tunnel.pdf 77.677734375k . file
 

Attachments

#69 ·

Quote:
Originally Posted by Digital_Chris /forum/post/21948190


I agree, it is odd, I'm not sure why my response drops off dramatically that early. I used the Behringer ECM8000 mic with the generic calibration file from the REW forum. Maybe I can do a sweep with the mic right in front of the speaker(s) to see if it's the speaker or room? Could it be the AVR that is causing the decent?

First thing to do is calibrate your sound card. REW does this for you. Next, if you can capture the output from the processor and make sure there is no roll off there. If all is calibrated, then maybe you have too much high frequency absorption. What is the nature of the panels on the walls? How thick are they and what are they made of? Are you able to temporarily remove them and remeasure?


Also was the mic on axis from your center speaker? If so, that rules out off-axis response of the speakers being the culprit. BTW, if you can, it would be good to tilt your L&R speakers toward the center seat. Right now you are hearing on-axis for center but off-axis for L+R.

Quote:
I do have a FBD inline between the AVR and the EP4000, the 1124 I believe, so I will be able to tame those peaks. Will that one adjustment of -10db at 58hz make that much of a difference in the overall sound? I got the idea that it will take multiple adjustments and dramatic room treatments to cure most of that boomy bass, hopefully I'm wrong?!

As I described in my article, dramatic room treatment is not necessary to get there. Use the EQ to pull down that 58 Hz and pull that down. You will hear the difference immediately and clearly. Right now, your bass level itself as a whole is much higher and then top of that you have that resonance. Pull one of them down and it should make a big difference in that area. Your bass will become "tight."


Try turning your subs on and off while some music with good bass is playing. All you should hear is the speaker appearing to have better low end extension. If all of a sudden you hear booming, exaggerated bass, then you are not dialed in right.

Quote:
Thanks for the encouragement, I hope you're right. I just can't help but feel that no matter what I do, the room will not change in sound. Dumb thought I know, but until I make a change that I can honestly hear, I will continue to think that way

That's cool. If gives you motivation to try these ideas
.

Quote:
What do you mean by making sure that my subs have clean proper output and how would I filter the unwanted dirtyness out?


Thanks a lot amirm

Just measure them by themselves and notice what the frequency response looks like when they get outside of their comfort zone/crossover frequency. Say you have that set to 80 Hz, measure up to 500 Hz and see what you have. Ideally it would just slope down to nothing. But if all of a sudden you see peaks going up in amplitude as frequencies go up, then put a filter there and pull them down. You never know if there are resonances that set in from your front wall, etc.
 
#70 ·

Quote:
Originally Posted by dragonfyr /forum/post/21949665


But one might find it odd as results such as the following have been known for 30+ years with work on such projects as NASA's Ames wind tunnel where even then their conclusions were:

"The conclusions can be summarized as follows:

Sound absorption in the low to mid frequency range can be increased by the use of PF3350 fiberglass (nominal flow resistivity 4100 mks rayls) instead of Owens Corning 703 fiberglass (27,000 mks rayls) and by an increase in lining thickness from 6 inches to 10 inches.


When PF 3350 fiberglass is used, the acoustic absorption coefficients predicted for 10 inches of material are essentially the same as those for 8 inches of material plus a 2-inch air gap."

great reference - thanks,

Quote:
Originally Posted by dragonfyr /forum/post/21949665


Ironically, the onus is placed upon the acoustics and engineering circles to prove their assertions that run counter the 'universal truths'(sic) of the hobbyist community sourced in the indisputable urban myths and marketing brochures that supplant legitimate sources.
 
#71 ·

Quote:
Originally Posted by localhost127 /forum/post/21948738


and speaking of arny's "global" statements - check out his history here on how he makes assumptions about users he doesn't even know -


arny's comments:
http://www.avsforum.com/avs-vb/showp...5&postcount=15


Since the comment began with "LOL", this is obviously a pathetic effort to make a mountain out of a molehill.



the response:
http://www.avsforum.com/avs-vb/showp...1&postcount=18

"And I have worked more hours with professional SR systems than you have listened to them. Hell, I will bet I have spent more hours actually designing large SR systems than you have spent listening to them."


Given that I'm not exactly a spring chicken, does he really know what he is claiming? Besides, he does not rebut my actual claim directly.


If you are going to fault people who make global assumptions about unknown people, then you need to first work over this dragonfyr guy. ;-)


Your intent with this post is to tell a joke, not make a fool out of yourself, right? ;-)
 
#72 ·

Quote:
Originally Posted by dragonfyr /forum/post/21949665


Local, why even try? You are stuck doing actual research into topics whereas others foundation is faith and belief. And inertia from repeating he same misnomers over and over until they become fact.


Its a shame that none of the oft made original "simple comment(s)" are seemingly never substantiated.


Nor are texts such as Acoustic Absorbers and Diffusers ever read or referenced as well that would render this running gag where density is imagined to be a valid determinant of absorptive quality moot.


But one might find it odd as results such as the following have been known for 30+ years with work on such projects as NASA's Ames wind tunnel where even then their conclusions were:

"The conclusions can be summarized as follows:

Sound absorption in the low to mid frequency range can be increased by the use of PF3350 fiberglass (nominal flow resistivity 4100 mks rayls) instead of Owens Corning 703 fiberglass (27,000 mks rayls) and by an increase in lining thickness from 6 inches to 10 inches.


When PF 3350 fiberglass is used, the acoustic absorption coefficients predicted for 10 inches of material are essentially the same as those for 8 inches of material plus a 2-inch air gap."



Don't worry about the part numbers - the operative terms are the GFR values.


...Maybe we should alert them to the ease of referencing density figures rather than GFR values?


Funny how the 'audiophile' community lags so far behind what has known within common acoustics and noise control engineering circles.


But why should anyone expect such notions more often derived from marketing brochures to be substantiated when belief is more important than objective substance?


Ironically, the onus is placed upon the acoustics and engineering circles to prove their assertions that run counter the 'universal truths'(sic) of the hobbyist community sourced in the indisputable urban myths and marketing brochures that supplant legitimate sources.


But whatever you do b'rer fox, Don't throw me into that briar patch where one might actually read Acoustic Absorbers and Diffusors and find out how this stuff actually works!!

The comparison fails on several grounds.


(1) My comments related to this application and this application only:




Critical points:


(1) This application involves home thermal insulation which has a typical density of 0.4 to 0.6 pounds per cubic foot.


(2) This application applies to an absorber whose average depth appears to be about 5 inches.


(3) This application applies to an absorber that opens up into the space it serves through an apparently acoustically transparent grille cloth.


The Ames research paper exists in several forms, more complete versions of which reveal the following significant differences:


(1) As mentioned above the thickness of the Ames absorber was about twice the depth of the absorber I commented on.


(2) A little research suggests that the PF 3350 material Ames used has a density of about twice - more specifically about 1 pound per cubic foot.


(3) More complete versions of the referenced paper show more details about the Ames wind tunnel application. Please see: http://ntrs.nasa.gov/archive/nasa/ca...1988003624.pdf Figures 1 and 2.


I see no effective comparison between the two applications. The Ames wind tunnel application involved multiple layers with spacing between the layers and was covered by a perforated metal cover, not an acoustically transparent grille cloth.


Nice try guys, but no cigar!
 
#73 ·

Quote:
Originally Posted by arnyk /forum/post/21953065


The comparison fails on several grounds.


(1) My comments related to this application and this application only:




Critical points:


(1) This application involves home thermal insulation which has a typical density of 0.4 to 0.6 pounds per cubic foot.


LOL!!!! Let's see, is that mass comprised of one large strand? Or is that mass comprised of thousands of smaller strands? Mass simple tells you how much of something there is, it tells you NOTHING about how the mass is distributed.

Quote:
Originally Posted by arnyk /forum/post/21953065


(2) This application applies to an absorber whose average depth appears to be about 5 inches.

Let's see. A Superchunk style absorber, being 24 inches on each wall boundary and 34 inches on the face - which is typically covered with a minimum of 6 mill plastic in order to retain specular frequencies above 600 Hz in the room, but which can easily be covered by luann or MDF in order to render is more effectively as a bass only low frequency absorber.


The maximum normal depth of the Superchunk absorber using those dimensions is 17 inches. Ironically, that is less important than the effective width of the material.


The irony is that perforated metal covers can easily be used to extend the mid frequency effectiveness, as is so commonly done in industrial application where resiliency is required.

Quote:
Originally Posted by arnyk /forum/post/21953065


(3) This application applies to an absorber that opens up into the space it serves through an apparently acoustically transparent grille cloth.

First, the presence of a perforated membrane is moot as the configuration would be equal for both the compared PF3350 and the OC703 materials.


And furthermore, if one were knowledgeable about the use of perforated materials and their very mature use in noise abatement, one would know that they are effective as mid-high frequency absorbers. And technically, a cloth is a perforated membrane as well. Again, "acoustically transparent" is a misnomer, as it is only pertinent to the degree that it significantly affects the behavior of sound at frequencies of which we are concerned. It does NOT mean that it is truly acoustically transparent at ALL frequencies. Damned that fisiks stuff.


But as we shall see, the perforated covers were not used for the advantages they can offer in terms of increased mid and high frequency absorption. Instead they were used to address matters of resiliency! And the issue of their negligibly small contributory effects with regard to absorbancy are noted in the conclusion as well.


To quote from the oft ignored Acoustic Absorbers and Diffusers:

"Often porous absorbers are covered by a thin membrane; this might be achieved by wrapping the material in thin plastic or similar. This is done to prevent the absorber being damaged or to stop fibers from the absorber being lost. The effect of the membrane will be to reduce the high frequency absorption."


But in any case, their effects would be the same, regardless of the materials chosen, materials whose own effectiveness was rather radically different - which speaks to the very point of the thread and the critical causal nature of the effect of gas flow resistivity on the issue rather than density - ironically, a measure not mentioned once in the paper.

Quote:
Originally Posted by arnyk /forum/post/21953065


The Ames research paper exists in several forms, more complete versions of which reveal the following significant differences:

Hmmm... I am only aware of it in its complete form. Perhaps that is why some might be aware of the effects of gapping and the effects of the perforated panels that contribute only structural resiliency unlike others commenting on the paper who are obviously unaware of the facts. I might suggest referring only to the complete paper, as apparently much of the substance was missing in alternatively referenced copies whereas the complete paper more than adequately addresses the points raised here.

Quote:
Originally Posted by arnyk /forum/post/21953065


(1) As mentioned above the thickness of the Ames absorber was about twice the depth of the absorber I commented on.

Yes, it was 8 inches with a 2" gap, which, as they observed, performed equivalent to a 10 inch porous absorber. A fact clearly stated in the conclusion.


The maximum effective depth of the Superchunk is 17 inches, and as mentioned, the more critical dimension is the effective width, of which the maximum face is 34 inches.


A point superfluous to the absorptive capacity measure of the porous material itself, assuming it is sufficiently large to be effectively 'seen' by the wavelengths in question. And since 100 Hz is 11.25 feet long, and 1/4 of that equals 2.81 feet or 33.72 inches. And as a material must be at least 1/10 the wavelength to have any effect (p.131 of AA&D 1st ed.), that corresponds to 13.5 inches....


One should note that the lower in frequency that one desires to treat with porous absorption, the larger the treatment must be in order to address the physics of longer wavelengths, right? Too small and the sample is not even effectively 'seen' by the wavelengths in question, and the energy simply diffracts around it as if it were not there. Thus, if the sample is too small it really doesn't matter what material is used. I am assuming that anyone worried about this issue is cognizant that this condition be met...

Quote:
Originally Posted by arnyk /forum/post/21953065


(2) A little research suggests that the PF 3350 material Ames used has a density of about twice - more specifically about 1 pound per cubic foot.

Only someone preoccupied with an inconsequential measure would go to so much trouble to try to extrapolate inconsequential units which are not even addressed in the paper!


They utilized a material whose gas flow resistivity was 4100 mks rayls, as compared to 27,000 mks rayls. Roughly 1/7 the GFR. And the amount of material was sufficient to be 'seen' by the wavelengths at issue.


If one wants to misuse the density figures, so be it. Assuming a linear relationship, if OC703 is ~3 pounds/unit measure, then the PF3350 was roughly .43 pounds/per unit volume. ...As if the density has necessarily anything to do with gas flow resistivity give the differences in mass distribution within the material structure! ...Its that fisiks stuff again...

Quote:
Originally Posted by arnyk /forum/post/21953065


(3) More complete versions of the referenced paper show more details about the Ames wind tunnel application. Please see: http://ntrs.nasa.gov/archive/nasa/ca...1988003624.pdf Figures 1 and 2.


I see no effective comparison between the two applications. The Ames wind tunnel application involved multiple layers with spacing between the layers and was covered by a perforated metal cover, not an acoustically transparent grille cloth.

Multiple layers?

It involved ONE layer of porous material and a 2 inch gap of air. The effects of the perforated membranes is discussed at length in the piece, and you can refer to their conclusion for a well stated synopsis of their relative lack of acoustic pertinence here, whereas it was actually employed for mechanical resiliency.


The fact that no comparison between basic material absorption characteristics and the fact that such a causal comparison is dependent upon gas flow resistivity is quite apparent.


We have already addressed that issue of the gapping (which should be well understood even here on this forum by now) and the effects of perforated material; but apparently some still lack an awareness of such issues as the effects of spacing porous absorptive material from a wall - given its near free lunch effective attributes where the advantage is stated rather clearly in the report.


But rather than explain them once again, here they are in a very neatly summarized form as quoted from the Ames document:



The conclusions can be summarized as follows:


Sound absorption in the low to mid-frequency range can be increased by the use of PF 3350 fiberglass (nominal flow resistivity 4100 mks rayls ) instead of Owens Corning 703 fiberglass (27,000 mks rayls) and by an increase in lining thickness from 6 inches to 10 inches. When PF 3350 fiberglass is used, the acoustic absorption coefficients predicted for 10 inches of material are essentially the same as those for 8 inches of material plus a 2-inch air gap.


The presence of the fiberglass cloth improves the sound absorption of the lining, but there appears to be reasonable latitude in the choice of flow resistance of the choice of the flow resistance of the cloth.


Increasing the thickness of the perforated plate from 22 gauge to 12 gauge, increasing the plate open area from 33% to 40%, or introducing a perforated backing plate has only a small effect on the predicted sound absorption coefficient.


It is recommended that the perforated plate be thicker than 22 gauge for structural reasons.


The installation of a wire mesh screen between the perforated face plate plate and the fiberglass cloth is recommend for erosion protection. The mesh should be sufficiently open that it does not effect acoustic performance of the lining.


Representative characteristics of the wire mesh screen are given in Table 1.





In fact, I would suggest folks take a look at the figure on pages 36-41 and note that the performance of the perforated plate varies only slightly among the various sample changes in the mid-high frequencies. Again, a fact one would easily know if they were familiar with the mature design and use of perforated materials for noise abatement in industry.

AN ANALYSIS OF SOUND ABSORBING LININGS FOR THE INTERIOR OF THE NASA AMES 80x120-FOOT WIND TUNNEL

Quote:
Originally Posted by arnyk /forum/post/21953065


Nice try guys, but no cigar!

Seeing as we do not smoke, a good thing. But I might suggest others lay off smoking stuff until they gain a more complete understanding of the causal relationship between gas flow resistivity and absorption, the behavior of perforated plates for use in noise abatement and control, and jettison the notion of density, which only accounts for how much stuff is available per unit volume but utterly fails to account for the critical factors of how such mass is distributed within said unit volume - unlike gas flow resistivity which via its focus on porosity and tortuosity, and their effects on the acoustical impedance of a material, does.



Do us all a favor, and before trotting out another ill-formed case for density being a determinant causal basis for evaluating the absorptive behavior of porous material, PLEASE read Acoustic Absorbers and Diffusers and learn a bit about the physics of how the material actually works. And then, if one is really brave, they can actually access the various studies and models upon which the prediction and modelling of the materials performance are based.


This topic is done.
 
#74 ·

Quote:
Originally Posted by dragonfyr /forum/post/21954540



Do us all a favor, and before trotting out another ill-formed case for density being a determinant causal basis for evaluating the absorptive behavior of porous material,

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

Quote:
PLEASE read Acoustic Absorbers and Diffusers and learn a bit about the physics of how the material actually works.

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.

Quote:
And then, if one is really brave, they can actually access the various studies and models upon which the prediction and modelling of the materials performance are based.

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

Quote:
This topic is done.

What's done is your credibility.


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


You may feel that you're all the reference you need, but maybe not everybody agrees with you.


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.


Tell me, do your fingertips get frostbit when you wave your hands this fast? ;-)
 
#75 ·
thanks for putting the Science back in AVS, dragon.

Quote:
Originally Posted by arnyk /forum/post/0


If density doesn't matter, why do we put any absorptive material into the absorber at all?
Quote:
Originally Posted by arnyk /forum/post/0


What's done is your credibility.

ignorance preserved. he still doesn't understand the topic of porous insulation, gas-flow-resistivity, complex impedance, etc.


im still waiting on the flow-resistivity values for OC705.


when can we expect any 'science' in your commentary?


there is NO meat in your response to dragon.
 
#76 ·

Quote:
Originally Posted by localhost127 /forum/post/21954764


thanks for putting the Science back in AVS, dragon.

One dirty hand washes the other.



Quote:
ignorance preserved. he still doesn't understand the topic of porous insulation, gas-flow-resistivity, complex impedance, etc.

If either of you you had said something useful and instructive, the results may well be different, were different results reasonable.


What comes through well is that you are very pleased with yourself. Since that seems to be the most important thing to you, well done!
 
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