Need help with speaker placement in 25 X 18 X 12 foot wooden cottage. + Should I add drywall? - AVS Forum
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post #1 of 11 Old 03-30-2013, 06:03 PM - Thread Starter
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Cottage Layout.jpg 172k .jpg file Hey all you audiophiles out there, hope you guys can provide me with some tips to improve my home's listening environment. I'm a young guy who recently built a wooden cottage in Hawaii on a budget. The place sounds pretty good so far considering that It has 450 square feet of tile flooring. This is probably because I had louvered windows installed, they are large and act as natural sound absorbers when opened. Also, there is a massive bookcase (14 x 7 foot) filled with hundred of old books from a family collection. Right now there is no insulation in the house whatsoever...no drywall or fiberglass, just plywood. Considering that a neighbor about 100 feet away from my house complains about the bass a lot, I was thinking about putting in drywall and fiberglass on the wall facing his house. Would it make sense only to insulate one wall, and not the whole house? I don't care about sound leaving from the other sides of the room because its just jungle on the other sides.
Then the other question...regarding speaker placement. I have uploaded a document with my rooms basic dimensions and listening position as they are now. I'm thinking about moving the listening position length wise rather than width wise. Good idea? I'm concerned because of the 3 empty rooms that would be behind the listening position(although there are louver windows). Any tips would be great. And by the way, the ceiling is sloped and about 16 feet at the highest point, it starts sloping at 8 feet.

Thanks,
Kai
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post #2 of 11 Old 04-01-2013, 10:18 AM
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Let's start with some basics.

reflection + transmission + absorption = 1

Your place sounds pretty good because most of the sound is leaking out. Open windows do not absorb sound, they allow it to escape! This is not a bad thing, per se, but one that's out of balance with its siblings, reflection and absorption. The goal in a listening room is fairly uniform decay times as you vary frequency, at a decay time of about 0.3sec for -40dB decay. I'll wager your room decays a lot faster at low frequencies due to all that leakage, yet rings at high frequencies due to lots of tile floor.

You have a lot of options. What's the priority?
- happy neightbors?
- more bass?
- tonal balance

If you want happy neighbors, you will need to soundproof your building to some degree. The same bass frequencies that travel well also travel in all directions; treating one wall won't help. The plus side is that a little bass reverberation makes the bass louder, and a sealed room gets you a strong increase at very low frequencies - room gain. Converesely, if you keep all the energy in the room, you'll need special acoustic treatment for all that bass...

If you want tonal balance, look at some resistive absorption panels for the ceiliing, to counter the reflective tile floor, and on any open, parallel walls. The bookcase has acoustic potential, but not when filled with books. Keep in mind that common residential construction and typical room furnishings result in fairly good room acoustics all by themselves, so the real challenge is figuring out the right tweaks.

Finally, if you want to a) be sure you're addressing the right issues and b) be able to tell you've done something, get a basic measurement system. Parts Express's Omnimic is an integrated product, but you can get the same capability a la carte. I have a Behringer ECM8000 mic, Xenyx 802 mixer and UCA202 external DAC that I use with Room EQ Wizard software.
http://www.hometheatershack.com/roomeq/

Have fun,
Frank
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post #3 of 11 Old 04-01-2013, 11:54 AM
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Quote:
Originally Posted by kaizee808 View Post

I'm thinking about moving the listening position length wise rather than width wise. Good idea?

Yes, you should set up so you face the window on the right side of the drawing. Then move the bookshelves to somewhere else behind where you sit, away from the corners. More here:

How to set up a room

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

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post #4 of 11 Old 04-01-2013, 02:55 PM - Thread Starter
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Thanks for the great response, I would have to say that my priority here is making my rooms low frequency response as efficient as possible...so that I don't need to turn the output up so high. What I have also thought about is placing the subwoofer and couch onto a thick vinyl pad to transfer some energy into the heavy couches...would this even do anything? You are right about how the room sounds in the high frequencies, not ideal...but there are just so many leaks that you don't notice flutter or echo much.

Ive got a firebox interface and this program called tonegen. So just gotta get a decent mic and test out the rooms acoustics, cool. When you say that I can get room gain in the low end by sealing the place off...what kind of seal are we talking about here, because at this point I don't intend on replacing the windows with double glaze, its just too hot out here and I need the breeze. Do the open windows act as absorbers for low frequency also? But yes, if I could get a little low frequency gain out of the room that would be awesome! How much does that acoustic panel run for, i heard that stuff is really pricey? But would some fiberglass and wood thatch on the ceiling help those reflections? I'm also going to add some old persian rugs on top of some vinyl matting over the tile floor.

If I moved the listening position length wise facing the right wall on the diagram (left of center), you think that might help? It would be kind of cool because behind the listening position would be the entry hall which has a massive barn door that opens about 7 x 7 foot. It could act as a big absorber sending the sounds outside into the jungle (theres thick forest facing outside that door). I'm in Hawaii by the way, so we keep everything open generally. It gets really hot inside, so that is why I want to avoid too much insulation..but rather divert the sound away from the neighbors and facing the left and bottom walls seen in the diagram.
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post #5 of 11 Old 04-01-2013, 03:00 PM - Thread Starter
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Thanks Ethan, I was gonna say thats a great idea...considering that the door behind the listening position is massive and could act as a good absorber. I wouldn't mind sound leaving that door because its just dense jungle outside in that direction. Its only the north and east facing walls in the diagram that are facing neighbors. If my listening position was left of center in the room, where would I best place the subwoofer do you think?
Thanks,
Kai
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post #6 of 11 Old 04-02-2013, 09:22 AM
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Let's take a step back. There are 3 frequency regions of interest, starting with the lowest of the low.
1) infra-sonics up to longest wavelength room mode
2) room modes dominate
3) ray tracing reflections dominate

Here's a good resource for this stuff. I'm talking about Part 2, near the bottom, page 6
http://www.harman.com/EN-US/OurCompany/Innovation/Pages/WhitePapers.aspx

Starting now with region 3, high frequencies... these wavelengths are much shorter than any room dimension, behave like light, in that reflections obey Snell's Law - angle of incidence equals angle of reflection - resulting in recommendations to find first reflection points with a mirror. Distances from source to reflection, and reflection to listener matter only in terms of transit time - how long it takes the sound to travel. This is what Toole calls the speaker-dominated region as the loudspeaker's characteristics dominate.

As frequency drops, region 2, wavelengths increase from inches to several feet - comparable to the room dimensions. We now enter the "room dominant" region where standing waves are the primary issue, and line-of-sight no longer matters. We're sloshing water in a tub at the right rate so the waves grow and the water makes a mess around the tub. Room dimensions and distances now matter when they're close to 1/2 integer multiples of a wavelength. In a completely sealed room with no absorbers, you get huge (40db+) peaks and nulls that vary with location and frequency, resulting from wave interference, either constructively (peak) or destructively (dip).

Going even lower, region 1, at some point, the longest room dimension equals half the wavelength of the lowest freqeuncy that can have a resonance in the room. At longer wavelengths, standing waves are not supported, so the peaks and dips disappear and everything gets uniform. The energy has to go somewhere, so it just builds until energy losses equals energy input. Smaller spaces support shorter wavelength modes, so room gain starts at higher frequency. Cars have tremendous room gain; they're tightly sealed, minimizing losses, and they're small, so room gain starts higher up.

Therefore, if your goal is "making my rooms low frequency response as efficient as possible," use a car as your model, seal it all up to maximize room gain, and live with (or treat) room modes.

If you'll again step back a little, maybe the goal could be making "low frequency response as enjoyable as possible?" This approach balances leakage vs reflected energy, and is, I've concluded, how my room works as well as it does. As you decrease bass leakage, you increase bass levels in the room (and make your neighbor happier). How far you go is up to you, but I suspect that temperate dwelling construction will provide some guidance.

I see a room that's nice and tight for bass when all the doors/windowns are closed, but degrades when you open up to those tropical breezes.

Have fun,
Frank
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post #7 of 11 Old 04-02-2013, 01:35 PM - Thread Starter
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Thanks for the link, those are great articles...lots to learn. I'm still having trouble visualizing how these low frequency waves are interacting, this stuff always confuses me..but i'm slowly figuring it out. You say

"Going even lower, region 1, at some point, the longest room dimension equals half the wavelength of the lowest freqeuncy that can have a resonance in the room."

So considering my room is 25 feet long roughly, that would make the lowest resonating frequency about 70 Hertz or so? I don't quite understand that, so does that mean that under 70 Hz I don't have to worry?


But anyways, I think you make a good point...room gain isn't exactly nice sounding, and I would rather be hearing smooth tight bass than reverberating sounds.biggrin.gif Also...how exactly do windows block bass anyways? I thought bass just gos right through the glass and out to the neighbor?

Thanks,
Kai
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post #8 of 11 Old 04-03-2013, 10:12 AM
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You're getting it... but it's 1/2 wave, so in a 25' room, a 50' wavelength of about 25Hz. Below 25Hz, there are no resonances, just pressure. It sounds great, as it's not really "audible" so much as tactile. Here's a link to a room mode calculator.
http://www.harman.com/EN-US/OurCompany/Innovation/Pages/Calculators.aspx

Windows act as filters. When open, all the sound escapes. When closed, only bass escapes, but much less bass escapes than through the open window. The glass forms a resonant system that passes some frequencies better than others. The large glass area in my room is one reason my low bass is flat - letting energy leak out prevents room mode justs as well as absorption.

The goal is a balance of reflected to lost energy. Right now, you have too much energy leakage, and at a frequency with very efficient propagation, as your neighbor attests.

Any change bass shakers would give you the sensation without creating all that acoustic energy?

Have fun,
Frank
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post #9 of 11 Old 04-03-2013, 02:08 PM - Thread Starter
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I ask about the windows because when I close them it doesn't effect the bass much at all...and I figure that louver windows just aren't ever gonna be airtight. Gonna get some acrylic or plexiglass and make a plug for those louver windows...see if that does much.

As for the bass shaker idea, it looks very promising. Just surfing the web for those things..it looks like most of them are made for home theatre amps or car amps. How might I hook those shakers up with XLR cables? I've got 2 XLR in's and 2 outs on the subwoofer, the outs are both running to the three ways. You reckon I could daisy chain it from the 3 way speakers to the shakers for the signal? Then I would also need to power those shakers with something...all my gear is active though.

Actually, I have an old 800 watt peavey mixer amp lying around...its got 2 300 watt quarter inch outputs. Could I just route the sub into the analog mixer amp low-input and then connect the quarter inch output to the bass shakers?

Thanks,
Kai
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post #10 of 11 Old 04-03-2013, 05:04 PM - Thread Starter
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I'm looking at these "Buttkicker Mini-Concert" 2 ohm tactile transducers. The old amp I want to power them with would be this peavey http://medias.audiofanzine.com/images/normal/peavey-xr-600c-399968.jpg[/URL] . You reckon that would work, given it's 300 watt @ 2 ohm....if I bought 2 of these http://www.thebuttkicker.com/mini-concert.php buttkickers? The website says max power handling is 250 watts...but I don't think 300 watts would hurt, what do you reckon?
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post #11 of 11 Old 04-04-2013, 09:22 AM
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kaizee, you have a building that leaks sound. Closing the window is like patching a leak in a seive - there are plenty of other leaks to make up for the patched area.

I have no experience with tactile transducers, but someone here does... perhaps ask about them on a different forum?

Have fun,
Frank
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