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Got this question via email, thought I would post it here so you can check my math:

I am living in an apartment and my next door neighbors Love to play neo-soul music real loud. its great, but it's also not great. Also, I like to watch TV all night. Some of it has screaming like House. How do I sound-insulate my apartment?
When it comes to soundproofing, you need mass (density) and separation (decoupling). This means that any transmissive surface in the room, say a wall, needs to be heavy to reduce the sound waves that are transmitted, and decoupled from other transmissive surfaces, such as the other side of the wall. You also want to keep everything air-tight, no gaps in windows or doors.

To think of it another way, that wall is the head of a drum and the sound waves from you or your neighbors are beating on it.

Short version, there isn't much that can be done to stop your neighbors noise from coming in unless you are willing to do some major construction to your walls. The least expensive option is simply to speak with them about turning it down. Odds are, they may not know how loud their neo-soul is in the adjacent apartment (I've been on the receiving end of that conversation, and really didn't know exactly how loud it was on the other side).

Now, from your end, there are a number of things you can do to make sure your sound doesn't head through the walls towards them. All involve turning it down, in one form or another, but this can be done without sacrificing sound quality.

Most effective, buy some nice headphones and use them. I'm a Sennheiser guy myself. Not ideal for date night.

Next up, invest in a sound system with an AVR that has 2 key features, Dynamic Range Compression and low-frequency EQ-ing. These come by many names. DRC is often called night mode, and many have "brand names" such as Audyssey's Dynamic Volume. Low EQ usually part of a larger EQ function such as Audyssey MultEQ.

DRC make quiet parts louder and loud parts quieter. You don't need to crank up the system to hear the sweet nothings only to be blown out of your seat when the asteroid blows up. These swings are great if you have an environment where you can enjoy the full dynamic range, but not so much if you're trying to let you neighbors sleep.

EQ comes in when you have a bass heavy system in a room with modes (that's every room). A room mode is a particular frequency that, based on the dimensions of the room, is reinforced in such a way that it's much louder than it should be.

http://en.wikipedia.org/wiki/Resonant_room_modes

For instance, I have a room mode in the low 30s. Whenever there is an explosion in that frequency range, it's 6-10db (2-3 times) louder than it should be. For me and the neighbors. In an over simplified explanation, EQing down that particular frequency will keep the volume levels down, and make everything sound better. The Audyssey system, for example, is a one button affair that uses a microphone to identify offending aberrations, and EQ them out (once again, over simplified).

Third up, if you find yourself turning up the TV, not because you can't hear the dialogue, but because you can't understand the dialog, you need room treatments. We sound leaves the TV it travels from the speaker in a straight line towards your ears, which is when you hear the sound. It also travels, like a billiard ball, off to the sidewalls, ceiling, and floor, reflecting off of each of those surfaces and then bouncing towards your ears, arriving a split second after the original signal.

Now, if you were listening in a very large room, there would be enough delay between the signals that you would hear an echo, not smeared intelligibility. Couple this with the fact that the reflected sounds can be almost as loud as the original sound, and you have unintelligible dialogue, which forces you to turn up the main source, and ticks off the neighbors.

By hanging absorptive materials at the exact points that the sound bounces off the other flat surfaces in the room, the sound will be absorbed (the energy turned into movement, friction, heat) and will not bounce back towards your ears.

I know what you're thinking, if I cover my entire room in absorption, won't this absorb all the sound coming in and out and solve all my problems? Only for the high frequencies. Low frequencies are not absorbed easily and will continue to travel through. And your room will sound bad.

Find those points using the mirror trick: http://www.hometheatershack.com/for.../5920-help-first-reflection-mirror-trick.html

Then use heavy curtains, blankets, other furniture to absorb, or a bookshelf filled with books to diffuse (spread around the room away from your ears) the sound. If you get more serious than that, look to purchase or build fiberglass (or similar material) panels for your room.
 

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The dialog issue you refer to is very correct - though it's usually a matter of a lack of bass control (deep bass ringing and masking dialog) rather than reflections.

Also, bookshelves don't diffuse. That's a myth.

Just be sure to also make sure he understands that treatments, EQ, etc. are going to do nothing for sound passing into and out of his space.

Bryan
 

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One point that I want to clarify for myself, absorption panels will reduce the amount of high frequency sound transmission as they are converting sound energy into heat, thus leaving less sound energy to pass through walls, correct?

If I'm incorrect, please help me wrap my head around it from a conservation of energy standpoint.

Also, wouldn't a bookshelf full of staggered books (staggering the books was a point I left out) serve to diffuse sound waves reflecting off the bindings of the books?

And masked dialogue when there is no low frequency sound would be attributed to side-wall reflections, would it not? 2 women talking in a room, for instance?
 

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High frequencies really don't pass between walls anyway, absorption or not. Now, they can potentially pass via holes for outlets, HVAC, etc. but that won't change with panels. HF's dissipate pretty readily in air by itself.

Books are primarily absorbers which are the opposite of diffusion and will kill any meaningful dispersion, random or not.

Reflections can smear an image in space or cause comb filtering in frequency. They won't cause masked dialog. Even with 2 women, you're well down into the 500 and below range. The male human voice can reach in some cases down to 100Hz or even lower.

Bryan
 

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We have a television show here in Canada "Holmes on Homes" He goes into houses where people have had renovation project done completely wrong and against code. Anyhow He did a Condo noise problem that he said is very common The wall separating the two units usually has a door/opening left in it during construction for ease of access and that rarely gets closed up properly as the two walls are usually staggered stud construction with a gap between them for sound proofing. This doorway usually just gets filled with insulation and is not done properly allowing lots of sound through that wall.
 
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