Listening Position Against Wall

[mikie]

Acoustic treatment newbie here. I've seen several posts advising not to put the listening position against the back wall, but unfortunately that's what I'm stuck with. I could pull the couch out 1 foot or so, but that's about it (WAF). The room is 15 ft wide x 14 ft deep with 8 ft ceiling. About 50/50 between music & movies. The system sounds good with no annoying peaks/dips, but I'm wondering if I'm missing something. No acoustic treatments yet, but I've convinced the little lady to let me try a few absorbers so we could evaluate the acoustic and visual impact. Would bass traps in each rear corner be a good place to start, or should I do something to the rear wall?

[Chrisbee]

Sitting tight up against the back wall tends to reinforce the bass.

Whether this is a good thing is a matter of opinion and depends on you, your system your room. Allow nobody to dictate to you whether it is good or not. If it sounds right it is right.

If you go into a large open-plan building like a noisy factory, workshop, train station or supermarket it can be interesting to lean (casually) against the inside of a boundary wall. Particularly in a corner! You will find yourself bombarded with incredibly deep and loud bass. Solid tyred/tired forklift trucks and tractors can make impressively deep noises on concrete floors. No sub could possibly compete.

Of course you wont get this effect in a normal-sized room but it should help to boost a small sub's output if you are sitting tight against the back wall.

Try some very simple sound traps with the least effort and zero cost. (to see if they have any effect in your room) You could stack stiff, cloth covered cushions or small mattresses up on edge in the corners of your room as an experiment. Or even on edge on the back of your chair or sofa. The idea is to expose the maximum surface area to absorb sound that is bouncing around in your room. Leather-covered cushions won't have much absorbent effect compared with cloth.

Sponge isn't all that absorbent but is still worth trying. A manmade fiber sleeping bag or bed duvet hung up in a corner will absorb the high and mid frequencies much more than the bass unless they are very thick. Spacing off the back wall or corner will help lower the absorption band a little.

At the very least you can convince yourself and your wife that the exercise is worthwhile before you start making or buying proper sound traps.

Don't let any of your experimental traps fall over and break anything or you automatically lose at least a year's WAF housepoints!

[Glenn Kuras]

Hey Mikie welcome to the forums.

Yes you are correct it is never a good thing to be sitting against the back wall. One thing you could do is put some 4" or 6" rigid fiberglass or mineral wool panels directly behind where you sit. This will not make things perfect, but it will help a lot with the bass build up.

Thanks,

Glenn

[bpape]

Sitting up against a wall will certainly provide more bass - but it will never provide a smooth frequency response. Whether you like the effect or not is somewhat a personal preference but the response curve won't be correct.

Rear corners can certainly help. Also, if you can get that 1' behind the couch, an underused, very effective place for absorbtion is on the floor behind the couch straddling the corner. Between that dealing with the height related issues in the rear and the back corners, it should help quite a bit.

Also, you may want to take a look at the REQ forum here on the shack. It is a free tool that will allow you to measure your room response. I think you may be very surprised at your room response. Most untreated rooms, especially ones that are basically square and you're sitting against a wall will have several nulls that are up to 20-25db in depth.

Bryan

[Ethan Winer]

mikie wrote:

I could pull the couch out 1 foot or so, but that's about it (WAF).

You're already in good hands here, but I'll add the graph below to drive home the point that increased bass is not the only problem from sitting so close in front of a reflecting boundary. In this case the response shown was measured 20 inches in front of a standard sheet rock wall. Not a pretty story, eh?

--Ethan

[mikie]

Thanks for the prompt responses. I hope to have measurements via REW this weekend, so expect followup qustions . I'll try to get measurements with/without cushions too. -- Mikie

[mikie]

REW is pretty straight forward - I like it. I'm sure I messed-up something, but I was able to get the attached measurments for my left main . The pink measurements are with no absorbers and with blue measurements are with cushions stacked in 1 corner. I think my sub is active in both, but I disconnected the mic & PC before thinking to check .

The dip at 160 Hz and the peak at 184 Hz are dampened quite a bit. I was surprised that the cushions resulted in such a drop below 80 Hz and that it got all comb filtery - is that normal?. Any thoughts / recommendations?


-- Mikie

[bpape]

Looks to me like below 80 is better. The reason it's lower is that you're minimizing boundary interfacing.

To get a better handle on what's up, you should take a pair of measurements.

- 1 with JUST the sub with the xover in place so we can see what it's doing and move it around a little accordingly to smooth things.

- 1 with BOTH main speakers running full range with NO sub on. You can use a Y cable to feed both L and R channels of the amp to do this. This will allow movement for smoothest untreated and best interface with the sub. Also, treatment of the boundaries behind and beside the speakers to deal with bondary response issues.

Bryan

[brucek]

I think my sub is active in both, but I disconnected the mic & PC before thinking to check

It's fairly obvious from the graph that you did indeed have your sub connected. I agree that the cushions had the desired effect. Now you need to increase the loudness of the sub amplifier to bring the level back up to match the mains.

brucek

[abhi]

I am in the same boat. I've been weighing DIY against readymade panels to treat the back wall.

[bpape]

The level has nothing to do with sub level in this case. The major reduction overall is way above the sub xover - plus there are still 15-20db swings in the sub range and a general overall dip in the 2-400 range. Consider a large solid absorber on the floor behind the couch, a minimum 4" thick absorber on the rear wall behind the seating position, and playing with the sub/mains position in the room.

Bryan

[mikie]

Been out of touch for a while - my laptop died & it's been a challenge getting back in action . On a positive note, I found a local source for UltraTouch . I hope to get started with the corner traps next week. Stay tuned -- Mikie