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Soundproofing basement help please (1 Viewer)

hbk842

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Hello everyone,

This is only my third post and I really have benefited from this website. Thanks to everyone who has had input in my previous questions. I have another one however.

My basement was framed and getting ready to run electrical currently. My main level in my house is all wood floors so you can hear everything on that main level downstairs and vice versa. I am going to mount an in wall surround system and was wondering what I can do to soundproof the room from sound travelling upstairs. What is the best way to go about this? Insulation between the joists? Foam board? Any help would be appreciated. Thanks.

I did search this topic and the results I got weren't quite what I was looking for. Thanks again.
 

Robert_J

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Double drywall, QuietRock, green glue, RISC clips, room in a room, staggered studs, etc are all soundproofing techniques that are used to contain sound in a room. They have all been discussed in depth as well. A quick search will find days worth of reading.

All of this is designed to keep sound IN a room. With in-wall speakers, the back of the speakers is already radiating sound outside of the room so any soundproofing is already compromised. Insulation will stop NOTHING but the highest frequencies.

-Robert
 

hbk842

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Hmmm....so with my in ceiling speakers, I am basically SOL? Is there anything I can do to keep that sound from traveling upstairs?
 

Robert_J

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Build an MDF enclosure around them in the wall. But then that will impact the sound characteristics of the speaker. How much? I don't know. But most in-ceiling and in-wall speakers have woofers with a pretty high Qts since the back will be open to a large wall cavity or the attic. Making a small enclosure around them will raise the Qtc. A high Qtc speaker has an unnatural hump in the frequency response.

Why are you going with in-wall or in-ceiling speakers? The sound from them is compromised from poor placement and you not being on axis with the tweeter.

-Robert
 

hbk842

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Thanks for the input Robert. I am going in wall because I like the cleanliness of them. I am not a fan of having speakers everywhere. I know the other speakers will sound better, but for my purposes these will suffice. I am used to not having any surround watching movies, so this will be a huge improvement. The speakers I bought have the tweeters in them that you can move and adjust, and the placement will be right above where my couch is going to be.

What if I built the enclosure much bigger than normal? Just throwing a number out there, but like 4 feet long in-between the joist it will be in?
 

hbk842

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Thanks again for the input Robert. I will probably build the boxes for the speakers, then use quietrock to do the ceiling instead of normal sheet rock. I will probably also insulate in that room in between the quiet rock for an extra layer.

Does anyone else have any other suggestions?
 

Ted White

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I would personally use a sheet or two of 5/8" drywall. MDF is denser, but drywall is so much easier to work with and cheaper.

You will not get the isolation regardless. You just can't layer in enough mass. But the mass will help.
 

Wayne A. Pflughaupt

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Since the room is already framed, you're probably too late asking this.

As mentioned by others, staggered studs is a good options for soundproofing walls betwee. rooms. As far as I know there is no similar concept for rooms above, so you would need a fully independant ceiling. I'd double-sheetrock the existing rafters, and then constuct a free-standing ceiling below them, that does not contact the existing floor or rafters, and doble-sheetrock that ceiling as well. If that puts the ceiling too low, then you could dispense with sheetrocking the existing rafters (knowing that it will cost you some soundproofing) and try to make the new ceiling so that the rafters are between the existing ones (don't know if that's possible or not). Then triple sheetrock. Again, you don't want the two ceilings contacting each other in any way.

Regards,
Wayne A. Pflughaupt
 

Ted White

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The separate ceiling is a method of decoupling. Like double stud walls or staggered walls. Resilient clips are also a means to decouple.

So for a ceiling you could assemble a floating ceiling with separate joists as Wayne pointed out. Or use clips, though the floating ceiling is a lot better if you can frame it.

The only issue to point out is that you would not want to drywall the existing joists. The goal is to create wall or ceiling assemblies with one large air cavity, rather than two smaller. Even if the system as Wayne described has more mass (more sheets of drywall). As paradoxical as that seems, it is all related to the resonance point of the cavity.

Side note. At resonance, sound passes through a wall or ceiling quite readily. Resonance is therefore bad when soundproofing. Example: massive concrete stops a lot of sound due to sheer mass, but at its resonance point (say 150 Hz) frequencies from 120 to 180Hz will pour through. Again, frequencies at and around a resonance point will travel through quite easily.

OK so a large (single) air cavity will resonante at a much lower frequency than the two small cavities. Think of 1 kettle drum vs. 2 snare drums. Why is this important? Again, because you will not successfully isolate frequencies that are at that resonance point and below.

For example, let's say we have a big ceiling cavity, filled with nice low density (fiberglass) insulation, decoupled somehow and heavy with drywall. Maybe it will resonate at 30Hz. If we measured that ceiling we would see that it stops a great deal of sound above 30Hz., (really well above 45 Hz.) but not below 30 Hz.

Let's build Wayne's (I hope that's OK Wayne) ceiling, which would result in two smaller air cavities. Although heavier, that ceiling will resonate at perhaps 50Hz. So we can stop sound above 50Hz., (really well at 75Hz. and up) but not below 50 Hz.

Technically the math doesn't work exactly that way, but for a quick explanation, it works. The point is to build systems that resonate at as low a frequency as possible, allowing us to isolate as much of the frequency spectrum as possible.

To drive that resonance point down we:

Decouple the framing with double studs, staggered studs or resilient clips

Add absorption, usually using cheap fiberglass batts

Add mass, usually using cheap drywall.
 

Wayne A. Pflughaupt

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Impressive info, Ted! Can't say I've ever considered or heard of the resonance factor. I guess I've always instinctively know that say, increasing the distance between the room where the sound originates and whatever else you're trying to keep it out of would increase the attenuation, but it never occured to me that lowered resonance might be the reason.

Regards,
Wayne A. Pflughaupt
 

Ted White

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There are a lot of good, prudent things that we know work, but no one has ever said why from a physics standpoint.

I just hope that long post made some sense. Thanks for allowing me to post that. So often we get caught up in fancy products (because people are actively selling them) that we lose track of the basics.
 

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