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Post by indranil on Jun 4, 2018 2:39:36 GMT
Hello, I took some measurements earlier today with the current layout of bass traps and found following 1. ETF graph of IR analysis shows substantial improvement when there are traps. The significant source of noise appear to be coming from the opening behind the couch where I have the staircase. This matches with my listening experience, the sound gets less harsh and clear when I have bass traps in front of the openings 2. Although there is no change in the low end in the FR domain but I see an improvement in the waterfall graph. With the bass traps placed in front of the openings the graph shows less ringing even at the lower end like 50 hz-100hz 3. The FR response in 100 hz-200hz got little worse in the new layout. It also shows a little ringing, not a lot. This might be because I have moved a couple of bass traps from the front side walls where the vertical wall meets the ceiling. I have to add more bass traps with plastic membrane, which now works for me, in these areas
I will send you the REW measurements once I save the file from the Windows machine to Mac. Please let me know if these observations make sense... Thanks.
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Post by Hexspa on Jun 4, 2018 2:59:28 GMT
Hello, I took some measurements earlier today with the current layout of bass traps and found following 1. ETF graph of IR analysis shows substantial improvement when there are traps. The significant source of noise appear to be coming from the opening behind the couch where I have the staircase. This matches with my listening experience, the sound gets less harsh and clear when I have bass traps in front of the openings 2. Although there is no change in the low end in the FR domain but I see an improvement in the waterfall graph. With the bass traps placed in front of the openings the graph shows less ringing even at the lower end like 50 hz-100hz 3. The FR response in 100 hz-200hz got little worse in the new layout. It also shows a little ringing, not a lot. This might be because I have moved a couple of bass traps from the front side walls where the vertical wall meets the ceiling. I have to add more bass traps with plastic membrane, which now works for me, in these areas I will send you the REW measurements once I save the file from the Windows machine to Mac. Please let me know if these observations make sense... Thanks. Hey indranil. Thanks for posting. I really appreciate your detail orientation and contribution. Please let me give you my unsolicited advice.
Your room is fine. Forget the graphs. Ethan, and indeed most speaker manufacturers, give priority above 50Hz. The decay target I use is 20dB within 150ms. You seem thereabouts or close throughout your relevant bass range.
So I advise you to pick out two or three specific objectives. You've moved stuff around and have gotten different results, naturally. Please tell me what, exactly, is giving you dissatisfaction?
For what are you aiming, exactly, and how are you presently not achieving it?
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Post by rock on Jun 4, 2018 3:44:44 GMT
Hexspa also has good advice in that measurements can also get us into the weeds so some caution is advised here. The good news is it does seem like you're on the right track in that the problems you hear are solved by adding traps were you suspect the problem is...Carry on!
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Post by Michael Lawrence on Jun 4, 2018 3:58:11 GMT
Indranil- What you really want to look at is the room below the Schroeder frequency (say, 400 Hz), which is the frequency below which modal behavior dominates. Take traces before and after the treatment and you can overlay and compare the results. I use a linear frequency scale because modal phenomena are more readily apparent. For an example of how the data can be illustrative, see my post from last week. the-audio-expert.freeforums.net/thread/445/studio-control-treatment-before-afterWith the single set of traces, it is rather hard to advise. The worst modal ringing is around 40 Hz, but my biggest concern would be the wide, deep null between 70 Hz and 100 Hz. That's a lot of energy missing in the critical bass region. Yes, the deep nulls look scary on a chart but it's the wide ones I'd be more concerned about. EDIT: Your room is actually in very good shape given the size. So overall I wouldn't be terribly concerned.
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Post by indranil on Jun 4, 2018 4:38:47 GMT
@hexpa- Thanks for your feedback. I am trying to address two specific issues. 1. The sound w/o bass traps in my room becomes too hazy which is not too unexpected but when I tried adding bass traps it became shrill and sounded like compressed music which fooled me several months, even years until I experimented with bass traps partially covering the openings. I tried putting bass traps in all possible areas in the room (it is in a relatively poor condition because of my wild experiments...) but none produced the result that I got by arranging a couple of these traps in front of the openings. Music for the first time sounded full bodied, smooth and coming with a noticeable blacker background. However I am not sure if I can or how much I can further improve it by moving to a closed room which I don't have it at the moment. So I am really excited to hear from you folks that the current room although not ideal but not certainly the weakest link in the chain 2. The bass response specially with bass heavy music sounds a little uncontrolled in this room. I don't use a subwoofer in 2 channel music. It feels like there is a peak around the couch from timer to time. A large part of that could be attributed to the placement of my couch which is only 30 inch from the half wall which has the staircase. It is not possible for me to move the couch further into the room. So I wanted to move the bass traps around to get a better bass response or minimize ringing to control the low end such that I can enjoy it
I think I have a good handle on the 1st but the 2nd one still needs further work. Thanks.
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Post by indranil on Jun 4, 2018 4:43:01 GMT
@michael- Thanks for your feedback. I would look at your post showing the trace analysis shortly and get back to you if I have questions. Thanks.
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Post by Hexspa on Jun 4, 2018 23:21:59 GMT
@hexpa- Thanks for your feedback. I am trying to address two specific issues. 1. The sound w/o bass traps in my room becomes too hazy which is not too unexpected but when I tried adding bass traps it became shrill and sounded like compressed music which fooled me several months, even years until I experimented with bass traps partially covering the openings. I tried putting bass traps in all possible areas in the room (it is in a relatively poor condition because of my wild experiments...) but none produced the result that I got by arranging a couple of these traps in front of the openings. Music for the first time sounded full bodied, smooth and coming with a noticeable blacker background. However I am not sure if I can or how much I can further improve it by moving to a closed room which I don't have it at the moment. So I am really excited to hear from you folks that the current room although not ideal but not certainly the weakest link in the chain 2. The bass response specially with bass heavy music sounds a little uncontrolled in this room. I don't use a subwoofer in 2 channel music. It feels like there is a peak around the couch from timer to time. A large part of that could be attributed to the placement of my couch which is only 30 inch from the half wall which has the staircase. It is not possible for me to move the couch further into the room. So I wanted to move the bass traps around to get a better bass response or minimize ringing to control the low end such that I can enjoy it I think I have a good handle on the 1st but the 2nd one still needs further work. Thanks. I've been thinking about your room. First let me give you my 'away from the computer' thoughts then I'll address your current post.
Bass isn't one thing. It's a concept we have of a group of frequencies which behave a certain way within given dimensions. Maybe I need to study physics but this is my understanding.
Your 'uncontrolled low end' is a reality. What you have to do to tame it is identify the contributing dimensions and dampen them with the appropriate thickness of absorption. The only other option is to set up several tuned absorbers but that's not the general advice given on this site.
If you don't know, room modes have areas of maximum and minimum pressure which are the inverse of their velocity points. Our ears hear pressure, hence SPL - sound pressure level. Wherever you're sitting has high pressure at some frequencies and low pressure at others. This contributes to some of the unevenness. The other contributing factor is the decay.
With that in mind, realize that your 'open space' is available for some frequencies to use as modal boundaries. The point I'm making is that you can treat that other room and expect to see a result at your listening position. Whether those dimensions correspond to your problem frequencies is another story but I'll guess probably. The method to determine which boundaries are the primary movers in your modal problems has been documented by others already. Please take the time to find the correlations then all you have left is to decide whether you can manage the solution.
Now on to your most recent post. If you liked the sound "by arranging a couple of these traps in front of the openings" then why not just leave it at that? You probably won't improve your response by moving to a closed room since the energy will have nowhere to escape. Your room is good!
The bottom line here is that, for better performance, you need more absorption. However, if you've already got a desired result then just revert to it and be on with your listening pleasure.
Hopefully this helps.
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Post by Michael Lawrence on Jun 5, 2018 1:14:36 GMT
Bass isn't one thing. It's a concept we have of a group of frequencies which behave a certain way within given dimensions. Maybe I need to study physics but this is my understanding. Spot on. Acousticians have basically two models for sound wave behavior in a space: The high frequencies behave like flashlight beams: they go where you point them. It's a "ray model." They obey Snell's Law: they hit a surface and bounce off at a predictable angle, just like pool balls. The low frequencies behave like water, simply flowing around obstructions, like if you stood in a river. You Drunk people at a concert can stand in front of a speaker and block the high frequencies very easily, but they can stand in front of the subs all they want to no avail. The difference is wavelength. Long wavelengths can more easily bend ("diffract") around obstructions. The question then becomes "at what frequency do we switch from one model to the other?" It depends on the room. We have the wave model in the lows, and the ray model in the highs, with a transition region between. Note that it's a region, not a single frequency, so of course we call it the Schroeder Frequency. There's a lovely diagram here. (PDF link) The Schroeder Frequency depends on the size of the room but it's probably around 300 Hz for the room in question. Take the RT60 in seconds, divide it by the room volume in cubic meters, take the square root of the result, and multiply it by 2000. That's your approximate Schroeder frequency. I believe Schroeder changed the 2000 coefficient after his initial publication. If you want to use cubic feet, use 11,885 for the coefficient instead. Be aware that the concept of RT60 for small rooms is a little sketchy. I say all this to say, yes, Hexspa is right. We have to think of the room differently at 80 Hz and at 4 kHz.
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Post by indranil on Jun 5, 2018 15:29:07 GMT
Hexpa & Michael,
Thanks a lot for taking time to review the REW graphs and provide your feedback on the current issue. Your suggestion of doing additional room analysis makes a total sense but I consider myself a rookie when it comes to jumping into room mode analysis and using the result to determine areas where bass trapping would further smooth out FR/Waterfall graphs. I understood the importance of bass trapping or any audio foundation work for that matter in getting good result from the day I got into this audio hobby but struggled a lot in the implementation part. For example I invested some good amount of money in buying room acoustic products i.e bass traps 7-8 years back but it was not until last year or so that I started putting them in the correct places and got some ROI...What helped me along the way is reading a lot of online articles and slowly understanding the concept which is very abstract for people like me who don't have any background in this domain. Yes, I liked reading Ethan's articles a lot and learnt many important implementation tricks like arranging bass traps at 45 deg at the wall/ceiling corners, using plastic membrane in bass traps to keep the liveliness in the room, etc which I implemented and instantly felt the huge difference. However my experience dealing with a few vendors in this space is not as good but I am not going to rant about it here.
Now coming to the current issue, as I stated before, the placement of bass traps in front of the openings helped a lot to clear the midrange and the room sounds far better than before. But I do see the dips in the frequency range 70hz-100hz and wanted to compare the effort to fix/reduce those dips with the additional benefit. If you guys think that spending time and money to address those two areas is going to significantly improve my listening experience then I would take the plunge, otherwise not. As always I value your opinions.
Thanks.
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Post by Michael Lawrence on Jun 5, 2018 16:26:39 GMT
Indranil-
Understand that a room that size will never be perfectly flat, so don't spend too much time and money trying to make it so. Ethan says that if you're within a 10 dB range below Schroeder you're doing great.
The problem with some of these acoustics companies is that they take advantage of the fact that people don't understand acoustic treatment, and take them for a (financial) ride. In that sense, the best money you can spend is a copy of The Audio Expert and a copy of the Master Handbook of Acoustics. If you read both of those, you'll know more about acoustics than most people in pro audio.
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Post by Hexspa on Jun 7, 2018 19:49:38 GMT
Hexpa & Michael, Thanks a lot for taking time to review the REW graphs and provide your feedback on the current issue. Your suggestion of doing additional room analysis makes a total sense but I consider myself a rookie when it comes to jumping into room mode analysis and using the result to determine areas where bass trapping would further smooth out FR/Waterfall graphs. I understood the importance of bass trapping or any audio foundation work for that matter in getting good result from the day I got into this audio hobby but struggled a lot in the implementation part. For example I invested some good amount of money in buying room acoustic products i.e bass traps 7-8 years back but it was not until last year or so that I started putting them in the correct places and got some ROI...What helped me along the way is reading a lot of online articles and slowly understanding the concept which is very abstract for people like me who don't have any background in this domain. Yes, I liked reading Ethan's articles a lot and learnt many important implementation tricks like arranging bass traps at 45 deg at the wall/ceiling corners, using plastic membrane in bass traps to keep the liveliness in the room, etc which I implemented and instantly felt the huge difference. However my experience dealing with a few vendors in this space is not as good but I am not going to rant about it here. Now coming to the current issue, as I stated before, the placement of bass traps in front of the openings helped a lot to clear the midrange and the room sounds far better than before. But I do see the dips in the frequency range 70hz-100hz and wanted to compare the effort to fix/reduce those dips with the additional benefit. If you guys think that spending time and money to address those two areas is going to significantly improve my listening experience then I would take the plunge, otherwise not. As always I value your opinions. Thanks. I think Ethan will tell you that actual modal response in a room is the result of complex factors. Still you can relate the problem frequencies to the distance between boundaries. At it's most simple you can take 1x 1/2x or 2x a wavelength and see what two, likely parallel, large surfaces relate to that distance. For nulls you need to find odd quarter distances such as 1/4x, 3/4x, and 5/4x the wavelength.
I think that gets tricky though because the modal pressure will change along the wave. You can use this calculator, plug in your dimensions, and begin to see what's going on: amcoustics.com/tools/amroc For what it's worth, I took it's creator up on an offer to edit the article explaining resonances but, at last check, he hasn't published my changes.
Room analysis is a perishable skill. If I had it my way, I'd have forgotten this crap several years ago. For better or worse, I've had to dust off my fact sheet the past few location changes. The take away here is that if I can put my panels in the right spot with high school math then very few people should have trouble doing the same.
Just take it one step at a time. The truth is out there!
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