artto Posted November 11, 2003 Share Posted November 11, 2003 Rick, thats not too bad, as far as the middle & upper frequencies go. Notice that the amplitude levels have dropped significantly in the corner areas where your new traps are placed. However, also notice that the SPL at the center seat center row has not changed. If the bass traps were actually working properly at the low end, we should have seen an increase in SPL at this location. This would be due to a reduction in the SPL of low frequency standing waves in the corner areas which typically causes a cancellation, or reduction, in SPL (in the low frequencies) at this location. Since we are not seeing an increase in SPL here, the low frequency cancellations are still taking place. And therefore, the so-called bass traps are primarily absorbing upper & middle frequencies, and possibly some (very little) upper bass. Id be willing to bet that they are not very effective below 200-300Hz. You really need to get down into the critical 75-300Hz range. Let me ask you this. When you watch the response of the SPL meter at one of the rear corners, what does the peak level seem to be responding to the most? The bass range? Or does it seem to respond somewhat equally to (for instance) lead vocals, bass, & other sounds? Quote Link to comment Share on other sites More sharing options...
artto Posted November 11, 2003 Share Posted November 11, 2003 ---------------- On 11/11/2003 9:58:49 AM DrWho wrote: yay, thx for the numbers i was trying to find this out for myself, but is it safe to assume that doubling the thickness would also double the results? (how bout tripling the thickness to double the results?) i ask because im interested in using this design, but need it to do a lot more (like on the magnitude of 12db?...i will be doing other room treatments too). ---------------- No. It doesnt quite work like that. Even though sound frequencies double (or halve) in wavelength as the frequency halves or doubles, the sound pressure levels are logarithmic (exponential) in nature which basically means that a 3dB increase is a doubling of acoustic power. And dont forget we are dealing with a three-dimensional wavefront. So there are tangential and other angular aspects to sound absorption & diffusion of room modes. Also the thickness of the absorbers we are dealing with is only a small portion of the wavelength at lower frequencies. This is why its important to treat the entire corner, because then, youre at least using an absorption/diffusion device that is, say, 8 tall. So (for instance) even though it may only be 1 deep & wide, the 8 portion of this component is going to determine the effective low frequency cut-off, which is one-half the wavelength of..guess. 75Hz! (the critical 75-300Hz range, just like I mentioned in my previous post). This is why its very difficult to get much effective bass trapping below 75Hz. Either the absorption device must be (MUCH) thicker, and/or (MUCH) taller, and/or (much) wider. I have a 16 section of corner bass trapping across the rear wall/ceiling horizontal corner behind the seating area. Its angled. Its 1 deep from corner to the outside edges. So while this absorption, technically speaking, has some effectiveness all the way down to 35Hz (16 is one-half of 32 which is the wavelength of 35Hz), it is not located in the vertical corners where the most bass pressure (standing waves) build-up occurs. And it is only 1 wide (effective in this aspect from 550Hz up). But it is located in the second most important corner type, the horizontal. And its located in the rear of the room directly behind & above the listeners where it can most effective(yes I have vertical corner trapping too). Remember, we are trying to treat all frequencies evenly. This becomes increasingly difficult as the room size gets smaller, and as the room proportions increasingly move away from ideal. Quote Link to comment Share on other sites More sharing options...
m00n Posted November 11, 2003 Author Share Posted November 11, 2003 artto, I don't have any idea on what frequencies as I never did any analysis on certian frequencies. What I have used and only used has been the pink noise test from the avia DVD. You very well may be correct, but at least I can say one thing, these are making a difference in some regards and the room does sound better. I have noticed that that the bass is not as boomy. Quote Link to comment Share on other sites More sharing options...
artto Posted November 11, 2003 Share Posted November 11, 2003 ---------------- On 11/11/2003 1:56:30 PM m00n wrote: artto, I don't have any idea on what frequencies as I never did any analysis on certian frequencies. What I have used and only used has been the pink noise test from the avia DVD. ---------------- Rick, you dont want to be using individual frequencies (such as sine waves) to tune the room anyway. Pink noise should have equal energy per octave (as opposed to equal energy per frequency as in white noise). In other words, its energy is equal to 1/f, which describes a -3dB/octave response. This means that each octave of increasing frequency should contain half the power of the preceding one. Pink noise is arguably the better source for tuning a room. But white noise can tell you a lot too. With either white or pink noise source you should be already producing noise that contains all audible frequencies. So it doesnt really matter that you dont have any idea on what frequencies or that you never did any analysis on certain frequencies. Youre doing an analysis on ALL frequencies by the very virtue that you are using pink noise. If you want to do an analysis of what individual frequencies or frequency bands look like at various locations in the room, you will need to use a real-time frequency analyzer. Right now, we're just trying to get a general, relative, idea of what's going on. Now check that meter again, and make note of when the meter is hitting peaks. Is this during a bass note? Or can you see consistently see similar peaks on vocals that are wailing (for instance)? Are any true peaks present on higher frequency sounds such as vocals or a cymbal crash? As the room approaches getting closer to ideal, you wont see the bass range dominating the SPL meter as much. The meter will peak & subside more generally with the overall sound. One frequency range or type of instrument (like bass guitar or kick drum) will not be responsible for almost always peaking the meter. Its easiest to observe this in the rear of the room, especially up against the back wall, and particularly in the rear vertical corners where the bass piles up. Quote Link to comment Share on other sites More sharing options...
m00n Posted November 11, 2003 Author Share Posted November 11, 2003 Nevermind Quote Link to comment Share on other sites More sharing options...
Rockets Posted November 12, 2003 Share Posted November 12, 2003 I have a dumb question. Why can't you remove the corners? Bridge a piece of drywall between say the walls and ceiling (or wall to wall). Would this not kill the standing waves produced by the 90* corners? Just asking... Not that this may factor in, but I could't believe the difference carpeting makes. One of the control rooms at work used to be all hard surfaces and the room was loud as hell. The installation of carpet on the floor and walls made an unbelievable change. Quote Link to comment Share on other sites More sharing options...
artto Posted November 13, 2003 Share Posted November 13, 2003 Rockets, Ricks room is only 10.5 wide. And there are doors to the room at both rear corners. And on top of that, it still boils down to a scale or size issue regarding absorption or diffusion since the wavelengths are long at the low frequency range were trying to treat. If you thought carpet made a big change, you have heard nothing yet. Carpet isnt really all that good at sound absorption. It works well in a relatively narrow frequency range. Its sound absorption coefficient isnt really all that effective until the frequency gets higher. It does absolutely nothing for the bass range which is what Im helping Rick with at the moment. Quote Link to comment Share on other sites More sharing options...
Rockets Posted November 13, 2003 Share Posted November 13, 2003 Arto, let me begin by saying you ARE the master. I was only looking at this from a fly on the wall, common sense point of view. Albiet probably too late, and maybe I should have stayed on the wall... I DON'T profess to know what you know about acoustics. Rather, I'm listening to where the corners are the 'source' of the problem, and I'm thinking "take the damn things out!". The easiest way (to me) would be to bridge a 12" to 18" piece of drywall (fill the cavity if need be) between the wall/ceiling junction, and any other non-exit corners. If you REALLY wanted to get creative, you could wet the drywall and bend it to a convex shape in the corners. Obviously you can't do the doors, but that's only two out of 8 or more 90* angle's in the room. Or at least he could still treat the four or more high gain "corner reflectors" (maybe this only works in microwaves) in the room (including above the doors). Either way $2 per corner for drywall is CHEAP! (IF it works) , and it doen't eat up that much real estate. If I'm getting ahead of your suggestions, I apologize...I'll just go back to that spot on the far left wall.... sorry... BTW, I agree that carpet is 'nothing' compared to what can be done. It just that I was so blown away as to how such a simple, and cheap change made SUCH a difference. FWW, I've been playing around with the foam (similar to neoprene) that's commonly used as a floor runner to reduce foot/leg fatigue, and how much it absorbs sound. Pretty good stuff actually. Excuse me...I hear the wall calling......... Quote Link to comment Share on other sites More sharing options...
artto Posted November 14, 2003 Share Posted November 14, 2003 Rockets, myself & many others have already been through many alternative solutions for Rick. He has chosen this particular path & wanted minimal modifications to the room itself at this point. There is another thread, I think its buried into the 180day section now, where Rick shows more details of the room. I agree there are many better alternatives. But everyone has their own set of compromises. And this route is the compromise Rick has chosen. As far as treating the corners with convex shapes goes, you dont even need to wet & bend drywall. You can more easily achieve the same thing with 1/8 to 1/4 Masonite fiberboard, the same thing I used for the diffusion panels in my room. I dont mean to sound insulting, but, how did you come to the conclusion that neoprene is a good sound absorber? Are you talking about something more like blocking shock transmission/impact resistance, or actually absorbing air-born sound? I cant see its usefulness as a foam air-born sound absorber. Acoustic foam is a completely different animal. Its antithesis actually. And if were talking about blocking sound transmission or increasing impact resistance, there are far superior materials engineered specifically for that purpose. I wish these materials were more readily available & relatively inexpensive when I built my room. Quote Link to comment Share on other sites More sharing options...
Rockets Posted November 14, 2003 Share Posted November 14, 2003 Arto, I'm not insulted about your question on neoprene. I wish I could tell you exactly where on the net I read about it. I do know that I was looking at acoustical foam vendors. I think that PE even sells a multilayered acoustical treament now that has, what appears to me, to be neoprene or a close cousin of it as one of the layers. All I can tell you is it worked for me. As far as Ricks room, I'm not trying to tell you how to do your job. Sorry I joined in in the middle of the conversation...I'll just go back to the spot on the wall now... Quote Link to comment Share on other sites More sharing options...
artto Posted November 14, 2003 Share Posted November 14, 2003 The main point Im trying to make is that in acoustic applications there are many materials that work. The real question is how well? What frequencies does it absorb/reflect? And to what extent? Ive been through using all the hanging curtains & piles of carpet remnants as acoustic treatments. Thats were most of us start. And certainly (in most cases) some treatment is better than no treatment at all. So please forgive me if at times I tend to sound arrogant & biased towards certain products/techniques. My room was initially completed around 1982. Its now in the process of its fourth major upgrade/renovation. Same speakers. Same amplification. (this is not to say that I havent had any other components in the system) But I do I have a reference point. And I guess thats also why I know that if you start with the room, and its acoustics, that this is the only way to really hear what is going on, both with your components, and the recording. For live music, look at what we do to build auditoriums. These are very complex structures. Extraordinary measures taken to isolate vibration & make the place quiet. The interior surfaces are complex. It is essentially a building within a building. It makes me laugh to see so many people screwing around with this cap, or that cap. Spending hundreds, if not thousands of $ on a speaker cable, when their listening environment is so crude (sorry). Dont get me wrong. I do think there is something to the synergy argument. Getting the right components together. But youll never really hear how good it really is unless your auditorium is decent. By the way Rocket.Welcome to the Forum. And dont stay stuck on that wall. Were all here to share the info, ideas, learn. And besides. If you stay on the side of the wall youll spoil the room symmetry of the high frequency acoustics! Quote Link to comment Share on other sites More sharing options...
DrWho Posted November 14, 2003 Share Posted November 14, 2003 lol perhaps i should move to the opposite wall then? i hope niether one of us is significantly fatter than the other outta curiousity though...where has artto acquired all this info? Quote Link to comment Share on other sites More sharing options...
artto Posted November 14, 2003 Share Posted November 14, 2003 ---------------- On 11/14/2003 7:23:14 PM DrWho wrote: outta curiousity though...where has artto acquired all this info? ---------------- LOL. Didn't know I would be asked for a resume'. For what it's worth............. artto is an architect. artto also plays music professionally (part time). And artto also does some pro recording of live concerts, does the mastering & CD production. I must admit that my main area of practice as an architect has more to do with land-use issues. Grading & drainage. Land planning. Site design. Urban design. City planning. On the other hand, I started apprenticing with a building architect while I was still in H.S. And worked with an (electrical) engineering firm before I went to the big U. Because of my music interests, & as an architect, I have interests in sound & its production or reproduction. I have studied both interior and landscape acoustics. My graduating major was in landscape architecture (big mistake) with minors in architecture & civil engineering. I admit, I do have a significant advantage when it comes to accessing info on building systems & acoustics. And how to apply them. Just here to share the info and hopefully yuall can avoid some of my mistakes. And hopefully benefit from the things Ive found works best, and why, and apply it TO YOUR situation. Quote Link to comment Share on other sites More sharing options...
DrWho Posted November 14, 2003 Share Posted November 14, 2003 lol, i was hoping for a website or a book or something to read...cuz i got plenty of questions, but at the same time i don't wanna bog you down lol, to think i was askin for a resume Quote Link to comment Share on other sites More sharing options...
formica Posted November 15, 2003 Share Posted November 15, 2003 ---------------- As far as treating the corners with convex shapes goes, you dont even need to wet & bend drywall. You can more easily achieve the same thing with 1/8 to 1/4 Masonite fiberboard, the same thing I used for the diffusion panels in my room. ---------------- Just curious about the objective of eliminating corners... would this be to control (randomise) mid to high frequency reflections? It just seems that low frequency modes would remain primarily unchanged in frequency and magnitude give the parallel surfaces are the defining factors, and they would be simply displaced (location) ? ---------------- It makes me laugh to see so many people screwing around with this cap, or that cap. Spending hundreds, if not thousands of $ on a speaker cable, when their listening environment is so crude (sorry). ---------------- Couldn't agree more with you.... esp on some of the other "audio" forums you've got guys arguing about which esoteric wire sounds better... while one is listening in his concrete block dorm room and the other in his perfect cubic library with no furniture other than a Corbusier chair. I look forward to the day where I can dedicate a room and apply proper treatment myself, as I'm guilty of not following what I believe in. ---------------- So please forgive me if at times I tend to sound arrogant & biased towards certain products/techniques. ---------------- Really?? Sorry about that, you have to admit that it was too easy a shot... Rob Quote Link to comment Share on other sites More sharing options...
Rockets Posted November 15, 2003 Share Posted November 15, 2003 Formica, I can't give you the "definitive" answer, but I do know that corner reflectors are used for the calibration of microwave signals. Why? Becaue of their high GAIN and ability to return the signal directly to its source. Now do a little creative thinking here or extrapolation...and think about your ceiling and floor corners. Depending upon your wall height you may have several 8 to 10 foot or more corner reflectors built in. Due to this size you can cover a broad spectrum of 1/4, 1/2 or full wavelengths. Anyway, to me, the best way to kill this is by eliminating the 90* angles. You'll never totally eliminate the return, but you can significantly reduce the gain, and directivity by changing the angle of attack the sound waves have to bounce from. Sticking a small, 1 foot to 18" flat triangle in the ceiling corners should, by itself, knock the hell out the gain...though I haven't taken the time to prove it... Try creating a containment bag and filling the corner with "spray foam" LOL!! Sorry...... A change of 3 db here, another 3db from floor carpeting, and another from...well you get the picture! Of course, this is only my opinion...and that's all I have to say about that. Quote Link to comment Share on other sites More sharing options...
artto Posted November 15, 2003 Share Posted November 15, 2003 Dr., I wish I could list everything for you. Maybe I should post a bibliography on my thread. Much of what I learned came from my professional reference text books. While I was in college I also hung at the music & engineering department libraries where I copied/collected a lot things from professional journals. Even the hi-fi slicks have articles on acoustics occasionally. Another source of technical info is the Klipsch Dope From Hope newsletters and the Klipsch Audio Papers. I did a compilation of these for Forum members earlier this year. Forum member justin16TX converted these to PDF format & its available from his website soundwise.org. Rockets on the right track in that using non-parallel room surfaces is the best way to reduce/eliminate standing wave & cancellation problems. The objective is not so much to eliminate corners as it is to eliminate parallel surfaces. It might be helpful to think of a trihedral room corner as the most severe representation of a concave surface. Concave surfaces tend to focus, concentrate, the sound to one area (pressure build-up, ie: standing wave) We use non-parallel surfaces (including convex polycylindrical) to control (randomize) not only mid to high frequency reflections, but even more importantly, low frequency reflections. As the frequency gets higher, the wavelengths get shorter & shorter, the mode spacing gets closer & closer, to the point where it is basically a continuum (a good thing. this is what we want to achieve in the bass range too). Its the bass range (which is nearly half of the entire octave range of music), with its long wavelengths, that experiences the most problems, especially as the room size decreases. And the unfortunate fact is that for the most part, the majority of us live in domestic environments that are rectangular with mostly parallel surfaces. Perhaps the biggest mistake we all make in the beginning is thinking that the sound in one area of the room doesnt, literally, affect the quality of sound in another area of the room. For instance, if you stand in the rear room corner, does the bass sound very heavy, or bloated? Or just plain louder or over weighted compared to the other frequency ranges or your favorite listening position? Well, this pressure build-up has ramifications. In other parts of the room. And its effects are often quite the opposite. A reduction (cancellation) of certain bass frequencies creating a very lumpy low-end response, and reducing detail & definition, and low bass extension. And we havent even gotten into the subjects of reverberation time or acoustic overload yet! Quote Link to comment Share on other sites More sharing options...
m00n Posted November 22, 2003 Author Share Posted November 22, 2003 ---------------- On 11/11/2003 2:40:22 PM artto wrote: Now check that meter again, and make note of when the meter is hitting peaks. Is this during a bass note? Or can you see consistently see similar peaks on vocals that are wailing (for instance)? Are any true peaks present on higher frequency sounds such as vocals or a cymbal crash? ---------------- Do you have any suggestions as to what I should listen to music wise? Crunchy rock, smooth new age, pop? Hard bass hitting club music? Or just a mix? What do we hope to get out of these findings? Are you going to give suggestions or are you simply trying and get a picture of what is going on in the room, then move on and deal with it's imperfections? Non the less, I am not sure what else I can do to fix any imperfections in them. If I could afford some professional absorbers I would buy them . One thing I would like to keep in mind is that my original goal which was to improve the sound quality of my theater. Even if these traps are not absorbing below 200hz (which we don't know for sure) they are helping. Quote Link to comment Share on other sites More sharing options...
artto Posted November 24, 2003 Share Posted November 24, 2003 Music wise what Im looking for is something that has some decent low-end slam, like Hard bass hitting club music but that also has something like vocals that really whale, or loud guitar parts, so we can compare average and peak SPL in middle frequency ranges to the bass. Even a drum solo would be fine. I dont want to bias you so Im not going to tell you what the result should be ahead of time. At this point, Im just trying to get an idea of how effective your bass traps are. Im sure they are helping to some degree. Im just trying to get an idea of how much & how far down. After thinking about this for a while, I think the best place to start with the next (diffusion) part of the equation would be to use the ceiling. Yeah, I know its already vaulted, which certainly helps, but the room is so narrow Id hate to close it in even more by applying acoustical materials to it. Perhaps more bass traps in the front corners & more absorption/diffusion there too. And dont forget we can treat the horizontal corners with bass trapping also. Quote Link to comment Share on other sites More sharing options...
artto Posted November 24, 2003 Share Posted November 24, 2003 Another thought: After looking at the drawing of your room again, you have plenty of space in the front of the room to put up a pair of polycylindrical Masonite panels like I use. Hang the screen in front of them. Stuff the area behind the panels with fiberglass. Fiberglass is kind of expensive, so that part can be postponed. In the meantime you still get the benefits of superior diffusion across at least one wall (which will affect all the other walls too). A 4'x8' (or 4'x12') sheet of 1/4" smooth-sided (one side) tempered Masonite should set you back $5, 10 at most. The large curved panels help to break up standing waves. They are very efficient at mid range & high frequency diffusion. And they absorb more bass then treble (actually more of a true 'bass trap' than the Sonex/Auralex stuff) even without the fiberglass. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.