Drew in the desert Posted May 17, 2005 Share Posted May 17, 2005 I have attempted to chart my in room frequency response using some test tones I downloaded online. I'm not sure if I even went about the process correctly, so let me explain what I did: As mentioned, I downloaded some test tones online and burned them to cd. I wanted to know how well my crossover of 80Hz worked between my sub and mains. So, I played the test tones from 16Hz to 200Hz in "Stereo" mode. It is obvious from the graph that I have my sub set a bit Hot, but that's how I like it (Red line is compensated SPL for Radio Shack meter). But, what's up with the huge dip at 40Hz? If the crossover is set to 80Hz, shouldn't the sub be going strong through 40Hz? Any ideas? For reference, I have RF-35 mains, SVS2039PC+ sub, Denon AVR4802, crossover set to 80Hz, and all speakers set to "small". The room is 14'x19' with the front array positioned about 1.5' off of the 14' wall. The sub is located in the front left corner of the room, also about 1.5' off the wall. Quote Link to comment Share on other sites More sharing options...
InFlux Posted May 17, 2005 Share Posted May 17, 2005 Just to be clear... what is your Sub's low-pass crossover set at? What is your receiver's crossover set at? 80Hz? Any bass boost being used (ie. loudness type button)? Quote Link to comment Share on other sites More sharing options...
Drew in the desert Posted May 17, 2005 Author Share Posted May 17, 2005 InFlux, the crossover in my receiver is set to 80Hz with the sub crossover disabled. I am not using any kind of tone boost. Quote Link to comment Share on other sites More sharing options...
DrWho Posted May 17, 2005 Share Posted May 17, 2005 Well it appears that you have a room mode at 40 Hz. That means you have a standing wave and your measuring point is sitting in the null of that wave. The only way to cure this problem would be some acoustical treatment that absorbs those frequencies at another place in the room where they are strong, which will then cancel the cancellation that is happening at the listening position. That dip around 70Hz leads me to believe that the phase on your subwoofer isn't set properly, or that there's another standing wave at that frequency. What does the graph look like when you turn off the subwoofer? What does it look like when you turn off the mains? Anyways, +- 5dB is actually pretty good for an in-room response. Btw, what does the graph look like when you read up to 1kHz or so? I think you might have another mode near 160Hz (which would be a harmonic of 40 and 80 Hz), but it's unclear because your chart stops about there. Quote Link to comment Share on other sites More sharing options...
Drew in the desert Posted May 17, 2005 Author Share Posted May 17, 2005 Dr Who, thanks for the response. Unfortunately, I haven't taken any readings above 200Hz. I will have to go back take readings with the sub off and then with the mains off. To be clear, what you are saying about the 40Hz dip is find a a spot in the room where the 40Hz tone is strong and then add a acoustic absorption in that location? Quote Link to comment Share on other sites More sharing options...
InFlux Posted May 17, 2005 Share Posted May 17, 2005 I'm asking, not recommending here... Wouldn't moving the sub AWAY from the corner of the room also potentially help tame the nodes? You could test the response with the sub in different locations or even with varried distances from the corner... I like your approach. You now have a clear baseline to compare any changes against. Please keep posting your results! Quote Link to comment Share on other sites More sharing options...
DrWho Posted May 17, 2005 Share Posted May 17, 2005 ---------------- On 5/17/2005 10:40:14 AM Drew in the desert wrote: To be clear, what you are saying about the 40Hz dip is find a a spot in the room where the 40Hz tone is strong and then add a acoustic absorption in that location? ---------------- More or less. Play some bass heavy music and walk around the room and note how much the sonic signature of the bass changes...especially in the corners. Here's a great article to read to get your feet wet about some of the approaches (there's also lots of info in the architectural forum as well): http://www.ethanwiner.com/acoustics.html Quote Link to comment Share on other sites More sharing options...
DrWho Posted May 17, 2005 Share Posted May 17, 2005 ---------------- On 5/17/2005 10:57:26 AM InFlux wrote: I'm asking, not recommending here... Wouldn't moving the sub AWAY from the corner of the room also potentially help tame the nodes? You could test the response with the sub in different locations or even with varried distances from the corner... I like your approach. You now have a clear baseline to compare any changes against. Please keep posting your results! ---------------- Moving the sub away from the corner actually just changes which frequencies are being affected (almost like sliding the dips to the left and right on the graph). However, as you move the sub closer to the listening position, the direct sound becomes relatively louder than the reflected sound which will then reduce the magnitude of the cancellations (we're takling maybe 3dB here). However, I think it sounds wierd with a subwoofer at your feet (for other reasons besides just frequency response). If you've got the time, I think it's a great idea to plot the responses at all sorts of various positions in the room. To avoid wasting time at bad locations, you might consider listening to music when you move the sub and only measure locations that sound good (keeping in mind that you've grown accustomed to dips around 40 and 80 Hz, which might sound wierd when those frequencies are now louder). Quote Link to comment Share on other sites More sharing options...
InFlux Posted May 17, 2005 Share Posted May 17, 2005 ---------------- http://www.ethanwiner.com/acoustics.html ---------------- Interesting Article! Thanks for the clarification. Quote Link to comment Share on other sites More sharing options...
Drew in the desert Posted May 17, 2005 Author Share Posted May 17, 2005 Good article Dr. Who. The more I think about it, I'm pretty sure I need a bass trap in my left rear corner. I have always noticed extremely heavy bass in that location compared to the rest of the room. Do you know of any quick and easy way to make a temporary bass trap for the corner of a room. I'm thinking that if I can quickly test my response with a generic trap in that corner and have good results, then I can make a more professional looking trap. Maybe there are some items laying around the house that can serve the purpose just to get a feel for how a trap might perform. Quote Link to comment Share on other sites More sharing options...
Beetlejuice Posted May 17, 2005 Share Posted May 17, 2005 Hi Drew Another great source of imformation is Ethan Winers forum. http://www.musicplayer.com//ultimatebb.php?/ubb/forum/f/26.html Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted May 17, 2005 Share Posted May 17, 2005 Good article. Thanks! Here is aother very good article/tutorial with very straightforward plans for Bass traps as well. http://web.archive.org/web/20000816145216/www.headphone.com/EditorialHeadroom/RoomTubes.asp Quote Link to comment Share on other sites More sharing options...
DrWho Posted May 18, 2005 Share Posted May 18, 2005 Here's another forum to look into as well: http://www.johnlsayers.com/phpBB2/viewforum.php?f=3 It's more oriented towards studio design, but the acoustic concepts are all the same. After some hunting around you should find some good info about helmholtz resonators and all that (same concept as the site dragonfyr linked to). The important thing to keep in mind about these kind of treatments is that they aren't broadband, which means you need to use a lot of differently tuned tubes to obtain a broadband solution (notice how many tubes that one guy implemented). As far as common household items, there really isn't anything that would work well at bass frequencies, unless you've got big rolls of insulation laying around. Quote Link to comment Share on other sites More sharing options...
Drew in the desert Posted May 18, 2005 Author Share Posted May 18, 2005 I had a chance to pay around with my setup last night to see if I could remedy the 40Hz dip I have at the listening position. I noticed that if I move the SPL meter only a foot away in either direction, my SPL jumps up to 70-75Hz. The same 40Hz tone is also generating close to 90Hz in the rear left corner of my room (which is where I think a bass trap might help). So, If my listening position measures in at 67Hz and 75Hz only 1 foot behind me, then I should just be able to move my couch back a foot. I think this will at least help the situation a bit. Quote Link to comment Share on other sites More sharing options...
Drew in the desert Posted May 18, 2005 Author Share Posted May 18, 2005 For reference, this is a picture of my front array. Quote Link to comment Share on other sites More sharing options...
Drew in the desert Posted May 18, 2005 Author Share Posted May 18, 2005 And this is a picture of the listening position. The back corner by the surround speaker is where I get the huge bass build up. Quote Link to comment Share on other sites More sharing options...
InFlux Posted May 18, 2005 Share Posted May 18, 2005 ---------------- On 5/18/2005 8:50:49 AM Drew in the desert wrote: I had a chance to pay around with my setup last night to see if I could remedy the 40Hz dip I have at the listening position. I noticed that if I move the SPL meter only a foot away in either direction, my SPL jumps up to 70-75Hz. The same 40Hz tone is also generating close to 90Hz in the rear left corner of my room (which is where I think a bass trap might help). So, If my listening position measures in at 67Hz and 75Hz only 1 foot behind me, then I should just be able to move my couch back a foot. I think this will at least help the situation a bit. ---------------- Very nice setup and room. How do you like those KSP-S6's? The scientific method works again. Are you confusing Hz with dB - either way your point was well made. After seeing how "reflective" your room is, I can fully see Dr. Who's points. I would bet money that you will find a similar phenomenon at higher frequencies if you looked at your full spectrum of sound. There may be some benefits to attempting to get some acoustical treatments on the front and side walls (curtains, acoustical tiles, etc...). People have claimed that their dog can change the acoustics of a room. I added an ottoman (sp?) and I had to adjust my center channel... Quote Link to comment Share on other sites More sharing options...
Drew in the desert Posted May 18, 2005 Author Share Posted May 18, 2005 Ah yes, I meant to say 67Db - 75Db. Quote Link to comment Share on other sites More sharing options...
DrWho Posted May 18, 2005 Share Posted May 18, 2005 Keep in mind though that fixing your 40Hz bump by moving the listening position back will most likely introduce a new trough at some other frequency Looking at your room, you would be a prime candidate for some major room treatment. I'm not sure what your budget is, but you might consider looking at some of these items available over at http://www.musiciansfriend.com: -http://www.musiciansfriend.com/srs7/fg=101/g=home/search/detail/base_pid/422632/ -http://www.musiciansfriend.com/srs7/fg=101/g=home/search/detail/base_pid/421192/ These first 2 are both kits that provide LF treatment as well as MF and HF...A great place to start with these is to put the LENRD's in the corners and then treat all the early reflections. These kits are huge bang for the buck -http://www.musiciansfriend.com/srs7/fg=101/g=home/search/detail/base_pid/421191/ -http://www.musiciansfriend.com/srs7/fg=101/g=home/search/detail/base_pid/422628/ These last two are both specifically LF treatments. The atom 12's will be able to treat lower frequencies (like that 40Hz you're dealing with). The Lenrd system would be the absolute minimum you'd need to start addressing your problems, but I would really consider going with one of the kits because you get more bang for the buck. Total overall cost here will be around $200-$400, but I can guarantee the results will be far more drastic than say the difference between a $50 cd player and a $1000 one. I really am surprised that more people don't go about treating their rooms. Quote Link to comment Share on other sites More sharing options...
Drew in the desert Posted May 20, 2005 Author Share Posted May 20, 2005 I was playing around with my setup again last night and decided to chart my frequency response from several different point around the room. The good news is that I was able to cure the 40Hz dip, but in turn I have created a 40Hz peak in its place. I have permanently relocated my sub to the back wall and overall my in room response is more level. Like I said, I have created at 40Hz peak and also moved the dip to around 25Hz. The dip and peak are not as severe as my original problem, so the sub will remain in this new location. It is obvious to me that if I add a second sub (one in the original location and one in the new location) I should be able to tame both the peaks and nulls. The problem is getting the wife to allow me to do so. Quote Link to comment Share on other sites More sharing options...
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