Axiom Home Page Forums General Discussion Home Theater Sound isolation for basement theater

Assuming I'm able to build a house like I want to in another 5, 6, 7, or 8 years, and I plan on making the home theater in the basement, how quiet can I realistically hope to make the room if I'm planning the design around it from the start? What's a really respectable native SPL?

I'm thinking the quieter my room is by default, the lower my system's volume has to be to hear all of the detail. The reason I'm planning on a basement home theater is so I don't have to do so much sound isolation for the walls (as well as the fact that it would take up less space on the lot). It would just be the ceiling, really. I figure it may as well all be in the initial plans.

I'm planning on the home theater taking up the entire basement, except for the walk-in closet for the electronics, so going by standard code I would only need one emergency exit, right? I'll still look into local codes, but I wanted an idea for the usual. You don't need a certain amount of window in addition to the emergency exit, right?

If you are planning a basement location, the noise you will have to contend with is what's coming from above, through the windows and heating/ventilating/air-conditioning (HVAC). If you insulate the joists and glue and screw 5/8" drywall for the ceiling, the only noise you will have to worry about coming in or going out through the ceiling is frequencies below 100Hz. With the construction I just mentioned, you'll get about 10dB of attenuation at these lower frequencies and 20dB or more at higher frequencies. With this crude but effective construction, you typically shouldn't have to worry about noise coming in from the floor unless you have someone jumping or operating power tools.

Now HVAC is much trickier. Every vent is a conduit for noise. I had three heat vents and one intake in my main room. When I renovated, I got rid of the three heat vents and installed a corner fireplace. The cold air intake is still there and although it makes noise, it's significantly attenuated due to a larger opening. My advice regarding HVAC is to eliminate the problem at the source by doing away with machine and air-borne noise. Use radiant floor heating for example.

Windows you can't do much about except eliminating them or getting shutters which would help a little. I don't recommend a basement without windows.

The other thing you should do is get STC-rated doors for your rooms in the basement and seal these with a suitable "weather-stripping" so that they don't rattle and also to isolate noise.

For the walls, use 5/8" dry-wall there too with off-set studs for the walls between rooms. And insulate the interior walls too.

If you do all of this, your basement theatre should have an ambient noise of 20 or 30dB when your lights are off. The TV itself may add another 10dB.

Ambient noise. That's the term I was trying so hard to remember. Thanks for the response, Mojo. I definitely want to look into radiant floor heating. It sounds like a good idea all around.

Out of curiosity, what is considered an average ambient noise level without all of this sound isolation being done?

Also, why don't you recommend a basement without windows?

Interesting discussion of sound and noise levels here , Charles. Note that a 40dB ambient noise level is termed a "quiet room" in fig.2. Mojo's old basement with the furnace going at 83dB presumably would have been characterized as "unbearably loud".

Thanks for the link. It seems like I'll be doing really good if I can actually get it between 20 and 30. Something to strive for.