Speaker boundary interference

Thanks M,
I was experimenting earlier and it seems that against the wall I have far too much bass throttling the mids and highs; my speakers are rear ported Tapco S8's.
The sweet spot (so far) in my nearly cube shaped room is with them about one foot away from the front wall. I'm right at the beginning stages and haven't applied any treatment yet except some quarter inch Auralex foam that I had laying around behind the speakers. The plan currently is to build a bunch of 5'' thick absorbers with rockwool to dampen reflections and hopefully tame the bass a little. (No spare cash for proper traps right now.)
Anyway - life story over, sorry if you were dropping off while reading that!

Thanks for the link. As I mentioned on YouTube: I just posted a comment at that video. I'll try to be kind, but Dennis is a sort of laughing stock among acoustic professionals. I've seen several of his videos and they are full of misinformation. The guy is truly clueless, so please don't follow his advice. If you want to find the best place for your speakers, do that by measuring the response with software like REW as you experiment. The good news is as you add bass traps all of these problems are reduced, including response changes versus position.

Then you asked for more specifics, and I'm glad to oblige. It's true that sound becomes softer with distance due to the inverse square law, so you'd think that being four feet away from a boundary gives half the SBIR interference when only two feet away. But that's only for sound outdoors away from reflecting surfaces. My home studio is 33 feet from front to back, and my speakers are less than a foot from the front wall. Even with the rear wall 33 feet away, for a round trip distance of 66 feet, the peaks and nulls in my room are not that different than those in a smaller room. Plus, in a typical bedroom size home studio, it's not even possible to put the speakers four feet away from every boundary!

More important, the farther you put a speaker from the walls (and floor and ceiling), the lower in frequencies the SBIR peaks and nulls begin. So that makes them more difficult to treat. At one foot away the lowest problem frequency is 283 Hz, but at four feet it's 70 Hz. An SBIR null at 283 Hz is very easy to tame! But a null at 70 Hz requires much thicker bass trapping. Indeed, this is why the main speakers in a million dollar control room are built directly into the wall. That's as close as you can get.

Not to pick on Dennis too much, but he really is a fountain of misinformation. Just a few other observations from this and one of his other videos:

This video is about SBIR but he mistakenly calls it SBIE. Then he claims that loudspeakers have such a small amount of distortion it's inaudible, which of course is ridiculous. Then he shows even more confusion by claiming that amplifiers amplify loudspeaker distortion. Say what? Then he says putting a speaker against the wall is the worst place, when in fact it's often the best place. If Dennis had spent even half an hour experimenting and measuring with SBIR he'd realize he's completely wrong. So that's one video. I just watched this other video, and I feel confident saying that pretty much every single statement he makes is just wrong:

www.youtube.com/watch?v=WdlriyxsvPc

Hi M,

I'm sure it doesn't but the effect is of the bass overwhelming much of the soundstage I'm used to hearing in the mids and high's of the song I am using to test my speaker placement; It sounds muddy and over compressed basically. I'll try and wrap my head around R.E.W and get a more accurate idea of what is going on in my room and I'll post up a photo when it's done.
Cheers!
Save

Thanks M

Hi Ethan,

I'm Arif a newcomer in here , saying hallo from jakarta Indonesia. I'm glad to see your own forum.
I already made membrane traps for low, mid and high frequency. Still not finished yet, but I still dont understand how to manage Speaker Boundaries Interference especially at 70Hz. I can't even put my speaker close to rear wall, because my enclossure has rear port and when i try to put speaker close to wall behind speaker, mid and high instrument became unclear, I think because of wood panel behind and beside the speaker.

very poor kickdrums in my room. I calculate my room size, speaker placement, seat position with REW, and the result is like my rta. drop 15db at 75hz.
Already think to try any option like hemholtz, very thick absorber, but still can't decide is that enough?

please help me Ethan.
thank you

-Yes Hexspa, my room has 12' length. If I made absorber with air space behind , I thought my room will be narrow. But its nice to try gapping four 4' rigid panel behind speakers. thank you.