Positioning of speakers in echo-ey room

[ivan]

Anyone got good advice for siting speakers in a room with terrible accoustics? I want to mount 2 x Peavey 15" speakers in a large room (approx. 16m long and 9m wide), with two walls of glass and two walls of concrete blocks. There isn't a ceiling - just the inner surface of the roof (plastic -faced). So very echoey, but it's what I've got to work with. Going to mount the speakers on the wall using top-hat mounts. So the speakers will be relatively close to the wall. I'm planning to mount the speakers on the long wall (concrete block). Question is how far from the corners should I mount them. I've read some texts that say get them right in the corners, and others that say they should be 2' away from the corners. And others that say get them much closer to the middle. Unfortunately, as the brackets take 6 or 8 heavy screws, I don't want to be experimenting with the speaker position - just screw them to the walls and forget about them.

[dan_b]

My decades worth of listening to hifi suggests to my ears that the closer you put speakers to the corners, the more boxy and boomy the sound will appear. But then if you go too far the other way, the stereo sound field will get narrower and narrower.

Are you able to experiment with temporarily placing them on the floor or on a couple of tables or something just to give some clue as to the impact of moving them closer to the corners?

Will you be able to put any soft treatment into the room at some point to reduce the echo? You can buy wall-mounted acoustic panels these days which you can have printed up as posters/art so they don't look too terrible!

[Stinsy]

I've always mounted them as high as possible right into the corners. If you mount them too close to the middle then you get the sound straight from the speaker followed by the sound bouncing off the side walls and they interfere with each other making is tound rubbish.

Additionally you need to sort some coverings for the concrete walls. Old school is carpet. Nowadays, you can buy acoustic panels that look pretty nice, they mostly seem to be slatted wood...

[Stig]

Mounting them in the exact centre is probably the worst thing to do as you'll get the same reflection from each side. Mounting them right in the corners will give some reinforcement to the bass end -I'll leave it to you to decide if that's a good idea or not -but you'll also get the same reflections from each end of the room. To spread the reflections a bit I'd suggest mounting them in, say, 20-30% from the corners and preferably asymmetrically if that doesn't look too crap. With bare concrete/glass walls it's never going to sound very good though.
Can you try them out sitting on the floor in different positions before committing to wall mounting them?

[ivan]

Yes, all good suggestions, thankyou - I'll get a couple of tables or chairs in there and have a play. Any particular type of sound best for experimenting speaker position with? Bassy? Clear, undistorted (like classical), or speech?

[Stig]

Given the size of the room I suspect that echoes rather than resonances will be the main issue so (fast) speech is probably a good test but try a variety of stuff -choral or organ music is probably going to sound ok as it's designed for big echoey spaces, faster music probably not so good.

[jonc_uk]

You can't fight the acoustics of a very active room with volume - the absolute worst room I have ever put a PA system in was a round room with a domed ceiling which used to be a chapel. The best way to deal with that type of room is to use as many speakers as possible at lower volumes (with suitable delays).

Your room doesn't actually appear that bad!

You don't say whether you are dealing with sitting or standing audiences, but assuming standing you should aim to get the speakers just above people's heads and ideally angled down slightly so you are not aiming directly at the opposite walls. Furniture and people will help reduce the echoes in the room, I would not worry about the low frequency room resonances. If you put the speakers right into the corners, you will get a coupling effect from the wall which will enhance the bass which you may or may not want. The same would happen if you put the speakers on the floor for testing purposes so I would avoid this. The glass walls will reflect the higher frequencies so the angling down of the speakers will help with this.

The room will sound very different between empty and full of people, particularly in the higher frequencies. Curtains or drapes would help normalise this but you can always alter the EQ.

I am assuming playback rather than a PA system with an open mic since you don't appear to have a stage.

[Stinsy]

I was in B&Q this morning. They had acoustic panels that were approx 8ftx2ft for sale for £80 a piece. I think putting them on one wall would make more difference than any amount of messing about with speaker location...

[MikeNovack]

I agree, dealing with those highly reflective surfaces would be more effective that speaker placement/power,'

The glass wall the worst. Curtains? I assume that being able to remove/open would be important.

Block wall -- hooks along top edge allowing cloth to hang an inch or so from the wall.

"Ceiling" -- suspended cloth.

NOTE: cloth used this way should be fireproofed. Cotton could be a DIY project (borax solution)

IF the glass wall needs to transmit light but bot "vision" could use bubble wrap.

[sharpener]

Yes, all good suggestions, thankyou - I'll get a couple of tables or chairs in there and have a play. Any particular type of sound best for experimenting speaker position with? Bassy? Clear, undistorted (like classical), or speech?

You do not say what the overall goal is or what the audience will be, it is for background music at a party or a recital or live performance, or where in the 16 x 9 m they will be located.

Male speech is probably the most unforgiving programme material for this kind of test.