Advice for a new guy

cminer · « **on:** 24 Jul 2006, 06:20 pm »

I'm kind of new to this and I need some advice.

In about a month I get my own room to set up pretty much however I want. I intend to use it primarily for two-channel listening, but it also doubles as a home theater, so there will be a TV in between the main speakers (Ohm Walsh 4.2s) I've been trying to self-educate on speaker placement and room acoustics, but nothing substitutes for experience, so I'd like to hear from you.

I can't figure out how to insert a picture, so I'll have to walk you through the room instead.

It's a rectangular room 15' 10" by 13' 2" by 8' high. First, there is an unbroken long wall. To the right of that is a short wall with a picture window, maybe 6 feet wide. Turn right again and there's a long wall with French doors on it. Turn right one more time and there's a short wall with French doors. Turn right again and you might start to get dizzy.

As for furniture, it will be two recliners and two loveseats, and my rear speakers are Ohm Walsh 2.1s.

God bless her, my wife already told me she doesn't care if I block one set of doors, and I can install acoustic treatments as long as they're not too ugly. She even found some textured ceiling panels that are supposed to reduce sound by 70% and told me I could line the walls with that. From all I've read that probably wouldn't be the thing to do, but I could if I wanted to.

So, I would appreciate advice on placement, acoustic issues, and anything else to do or to avoid.

Thanks,

cminer (Curt)

klh · « **Reply #1 on:** 25 Jul 2006, 02:55 am »

Curt... welcome!

First things first. It's best if the room is basically symmetric. It's also best if the speakers aren't against any walls, and more or less the same distance from the walls. You also don't want to sit against a wall. If you could have your main listening position 38% in from the rear wall, that would be ideal. Also, you want to put bass traps in the corners (both vertical and horizontal) and have absorptive material on any wall the would reflect the sound from the speakers towards the main seating location. If you sit in your main seated position, and your wife runs a mirror along the walls, floor and ceiling, anywere you can see any of the three front speakers in the reflection requires absorptive material. If you do that, you'll be golden. As for what types of absorptive material are best, compressed fiberglass, rockwool and bonded acoustic cotton are the main staples. Generally speaking, lower densities work best for first reflection points and higher densities work best for bass traps. Oh yeah, don't put a coffee table in front of you, and if you have wood floors, make sure you have an area rug to absorb the reflections from below.

Good luck!

Glenn K · « **Reply #2 on:** 25 Jul 2006, 11:44 am »

For bass trapping you want to make sure the panels are 4" or more thick and you want to straddle corners. For first reflection panels you can go with 2" panels.
Take a look at our FAQ page on our company web site to get a better understanding how room treatment works and set up.

Glenn

cminer · « **Reply #3 on:** 25 Jul 2006, 04:08 pm »

Thanks, but I need some clarification - klh, you say the listening position should be 38% in from the rear wall. The diagram at the GIK website show the ideal listening position 38% of the way back from the FRONT wall, forming an equilateral triangle with the speakers.

Am I mistaken with my terms? To me, the back wall is behind me.

Curt.

Ethan Winer · « **Reply #4 on:** 25 Jul 2006, 04:43 pm »

Curt,

> To me, the back wall is behind me. <

Yes. I don't know when the term "rear wall" began being used for the wall you face while listening / watching, but to me the front wall is the wall you face, behind the speakers. Hopefully, you'll find the drawing below to be clearer. It also shows where to put first reflection treatment, though if you find the full article on my company's site this is explained more fully.

--Ethan

Glenn K · « **Reply #5 on:** 26 Jul 2006, 05:04 pm »

Quote from: cminer on 25 Jul 2006, 04:08 pm

Thanks, but I need some clarification - klh, you say the listening position should be 38% in from the rear wall. The diagram at the GIK website show the ideal listening position 38% of the way back from the FRONT wall, forming an equilateral triangle with the speakers.

Am I mistaken with my terms? To me, the back wall is behind me.

Curt.

Yes the back wall is behind you. Also just to add you can be 38% from either the front wall or the back wall.

Glenn

cminer · « **Reply #6 on:** 27 Jul 2006, 01:17 pm »

Next question - does it make any difference acoustically which way I orient the room? What I mean is, should the front/back be a long wall or short wall or does it even matter?

Thanks again,

Curt

Glenn K · « **Reply #7 on:** 27 Jul 2006, 01:43 pm »

The Front/Back wall should be the short wall. You always want to have the speakers firing down the longest wall.

Glenn

Ethan Winer · « **Reply #8 on:** 27 Jul 2006, 06:05 pm »

Curt,

> does it make any difference acoustically which way I orient the room? <

Yes! The goal is to have the wall behind you as far away as possible. The inevitable peaks and deep nulls are always worse as you get near to a wall. The drawing above is from the article How to set up a room on my company's site, so track that down for the full story. Also, the response curves below were taken in the exact same room with the speakers firing the long versus short way. The difference is very clear!

--Ethan

bpape · « **Reply #9 on:** 28 Jul 2006, 01:52 am »

One other thing. If those have Walsh drivers in them, they're omnipolar in the mids and highs. That means that they're even more picky about things in between them. Plan to have the speakers at the very least, a foot (2 is better) in front of the tv - or you'll get no imaging at all and all kinds of cancellation issues.

Walsh drivers are really nice and can sound great - when set up properly.

Bryan

srlaudio · « **Reply #10 on:** 4 Aug 2006, 12:14 am »

The Walsh driver speakers need to be located out from the front and side walls at least 3 ft. Experiment with final placement. The corners both vertically and horizontally should be "taken out", that is trapped to maximum effect. The current leading edge control room design is using a direct opposite of the old LEDE rooms. Therefore the bass trapping is continued at the rear of the room, a cavity 4 ft deep floor to ceiling should suffice, with appropriate "Hidley" bass trapping (contact us for details). The front and side walls should be all diffusive, to maximize the imaging of the Walsh Drivers. I would use a lot of absorption in the ceiling, except over the monitor position, where we would once again, use diffusion.

chadh · « **Reply #11 on:** 4 Aug 2006, 04:09 am »

Quote from: srlaudio on 4 Aug 2006, 12:14 am

Therefore the bass trapping is continued at the rear of the room, a cavity 4 ft deep floor to ceiling should suffice, with appropriate "Hidley" bass trapping (contact us for details).

A cavity four feet deep? Floor to ceiling? That would suffice? I guess it's not too bad...only a little more that 25% of the entire room. Would it be better to put this in front of the picture window or the French doors?

Chad

srlaudio · « **Reply #12 on:** 4 Aug 2006, 11:23 am »

Unfortunately, If you have a room smaller than a concert hall, there are serious issues with bass. The bass wavelengths are longer than your room, and what happens is the bass waves hit the back wall and fold over (causing cancellation and standing waves). The goal is to force the bass into not folding back by giving that acoustic energy somewhere to go. The wavelengths are large, so you have to have a large area for them to go. We could probably put a few inches back into your room, but count on some voluminous trapping to do the job. (Putting some pillows in the ceiling corners is not going to help.) We have used modeling software to see what it takes, and yes, it does take a serious amount of bass trapping to achieve the goal. Send me an email address and I will send you some drawings and pictures. It would also help if you sent pictures of your room.

bgewaudio · « **Reply #13 on:** 4 Aug 2006, 11:43 am »

Yes, Cminer, just to give you an idea of how long low frequency wavelengths actually are requires simple math. Just take the speed of sound (1150 ft/sec) and divide it by the fundamental frequency say (20hz):

1150/20 = 57.5 ft from start to finish.

15 hertz would be 76.6 ft long

10 hertz would be 115 ft and so on.

bgewaudio · « **Reply #14 on:** 4 Aug 2006, 12:14 pm »

This is actually one of the main reasons (among many) why I don't appreciate car audio, given its trunk dimensions appox. 4ft x 3 ft, with a 20Hz wavelength at 57 ft, think of the interaction there, nevermind a typical listening room!

srlaudio · « **Reply #15 on:** 4 Aug 2006, 12:18 pm »

One of my old pals (God rest his soul) Stephen St Croix came up with a great illuminating test for any audio system/room combination. Cue up track 7 on the Studio Reference Disc (This track is a 30hz sine wave at reference level). No amount of verbiage can prepare you for what happens. Serious budgets for upgrades in all areas are usually created!

bgewaudio · « **Reply #16 on:** 4 Aug 2006, 12:26 pm »

Pretty amazing experience eh?

srlaudio · « **Reply #17 on:** 4 Aug 2006, 11:11 pm »

I have an update from my partner and technical director. We can now use the powerful design tool of modeling to create a low depth requirement Helmholtz resonator trap faced with hardwood slats that both tune the trap and provide a difussive face for the mids and highs. The only drawback is that the attention to detail in building this is extreme. The cavity must be airtight, for starters. We can provide the design...

bgewaudio · « **Reply #18 on:** 5 Aug 2006, 11:11 am »

Sounds pretty cool!

JLM · « **Reply #19 on:** 5 Aug 2006, 01:13 pm »

I listen nearfield in a symetrical room with setup along a short wall, but I'd never live with the setup Ethan shows. There's just no room to get the speakers away from the front wall to avoid bass boom without having them inches from your head. I'd quickly run to using headphones first.

My setup follows the Cardias recommendations and works for me, YMMV. Sorry don't have a link, but it's similar to Ethan's in a somewhat larger room, but allows speakers/me to form a 68 inch equalateral triangle with the speakers 60 inches plus from the front wall.