Finished Attic + Omni-directional Tweeters

seraph321 · « **on:** 25 Apr 2006, 08:04 pm »

I've recently moved my two-channel system into a new room and I'm interested in treating it. I haven't determined a budget yet, but I'm not constrained by WAF.

The room is a finished attic, so it's long and has slanted walls on both of the long sides that start at about 5' from the floor and slat in at about a 40 degree angle. The only thing in the room will be the speakers, my recliner, and a dresser. It's carpeted, and there's no table between the listening position and the speakers.

My speakers are Gallo Reference 3s. http://www.roundsound.com/reference-3-speakers.htm
Two things make these speakers somewhat unique: 1. They have side-firing 10" woofers, so you can choose to have those firing away or towards each other. 2. The ribbon tweeter is meant to be omnidirectional. I'm interested in opinions on how these aspects might factor into room treatment.

I'm new to this, but from what I understand I need to address the first reflection points first. I have 4 acoustic foam pads that are about 5'x'3 (given to me by a friend with a studio) and have irregular surfaces. I am willing to buy/build more if required. I'm thinking I'll put two of them on the flat part of the side walls, one on the cieling, and perhaps one on the front wall? There are windows on the front wall, but there is room to put the pad in between them.

I'm thinking the slanted walls don't need treament, is that correct? They certainly shouldn't produce standing waves, but I don't know about reflections. And the back wall should be far enough away to prevent <20ms reflections.

The pads I have obviously won't do much for bass, and these speakers definitely get down into the 20hz range, so bass treatment is probably necessary. I am planning to download the ETF program and run sweeps, but I'm hoping to get suggestions for the obvious stuff first.

Ethan Winer · « **Reply #1 on:** 26 Apr 2006, 01:19 pm »

seraph321,

> I'm not constrained by WAF. <

Yeah, that helps a lot!

> I understand I need to address the first reflection points first. <

That, and bass trapping. They both deserve "first" status.

> I have 4 acoustic foam pads that are about 5'x'3 <

If they are made of legitimate acoustic foam they'll work fine as first reflection absorbers. But they must be acoustic foam, not mattress or packing foam, and even if they're sold as "acoustic" foam they still may not be. The best test is to put one right in front of your face and "talk into" it. If it sounds like you're talking into a total void, it's probably okay.

> I'm thinking I'll put two of them on the flat part of the side walls, one on the cieling, and perhaps one on the front wall? <

Yes, though the rear wall behind you is more important than the front wall. Unless your loudspeakers send mid/high frequencies toward their rear (ie: dipoles).

> I'm thinking the slanted walls don't need treament, is that correct? <

You can tell using the "mirror trick." Do you know that one?

> They certainly shouldn't produce standing waves <

That's what you think!

> I am planning to download the ETF program and run sweeps, but I'm hoping to get suggestions for the obvious stuff first. <

ETF is great - much better than the typical third octave analyzer. And once you run a high-res sweep you'll see why angled walls don't avoid standing waves, and why you need plenty of bass trapping!

--Ethan

seraph321 · « **Reply #2 on:** 26 Apr 2006, 01:40 pm »

Hi Ethan. Thanks for the reply.

I'll test out that foam when I get home this weekend (I travel for work most weeks). And I've read about the mirror trick. It sounds simple enough.

As far as standing waves, I was under the impression that they were mostly dependent on parallel surfaces. Part of the walls are parallel though, so I knew I would need bass traps regardless. I will be reading more of your articles on this in the next couple days, but when you say I need bass traps are you thinking the type that can hang on the wall or the cylinder type?

Ethan Winer · « **Reply #3 on:** 27 Apr 2006, 02:35 pm »

> As far as standing waves, I was under the impression that they were mostly dependent on parallel surfaces. <

Well now you know.

Seriously, you can even have standing waves outdoors caused by a reflection off a single boundary.

> when you say I need bass traps are you thinking the type that can hang on the wall or the cylinder type? <

I'm not a big fan of tube shaped traps unless they are very large. That's really the issue - total surface size. But regardless of shape, all bass traps work best when mounted straddling corners, or at least near corners. And the more you can manage, the flatter and tighter the low end will become.

--Ethan

bpape · « **Reply #4 on:** 27 Apr 2006, 04:03 pm »

Just for a little clarification, when you refer to standing waves, I'm assuming you're really referring to room modes.

You will not get any AXIAL modes from non-parallel surfaces. However, you can still get tangential and oblique modes which are formed by bouncing off of 4 or 6 surfaces instead of just 2.

While lower in intensity than axial modes, they still need to be considered as there are TONS more of them and when you get several that overlap with each other and at points, with the other axials, they can certainly cause some issues.

Bryan

seraph321 · « **Reply #5 on:** 2 May 2006, 03:07 pm »

I haven't done the measurements yet, since I've been busy moving the rest of my stuff in, but I've taken a picture of the space and how the system fits into right now. I'm adding a big recliner today that I expect will change the room response some, so I'm going to take a baseline after that.

You can see I already put up the acoustic pads I have, but they aren't attached yet. I think they help even without having really thought too hard about where I put them.

*edit - Fixed broken image link

seraph321 · « **Reply #6 on:** 22 May 2006, 01:56 am »

I have been way too busy to do the measurements in this room, but I'm still planning to do them. Hopefully soon.

I have a question though - How should I handle putting bass traps in the upper corners of the room when they are irregularily shapped like this? Would I need some kind of custom fit, or will putting traps in the lower two front corners be sufficient?

Ethan Winer · « **Reply #7 on:** 22 May 2006, 03:50 pm »

> How should I handle putting bass traps in the upper corners of the room when they are irregularily shapped like this? <

I see plenty of potential corner surface. Below is a photo of my living room showing how I put 2 by 4 foot traps in the wall-ceiling corners. The traps I'm talking about are on the far left and right of the photo, "riding up" along the angled ceiling.

You could do the same where your front wall goes up at an angle. Or is that span less than 4 feet? If so, you could still fit 2 by 2 foot traps there. The best way to approach this is to first figure how many traps you're willing to get, then find the best places for that many traps. The general goal is to put them all in corners, spread around the room as evenly as you can.

--Ethan