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Educational Resources
Articles written either for MIX
Magazine or Recording Engineer/
Producer Magazine or Modern
Home Theater.
– by Bob Hodas

Gain insights into studio listening environments and rooms.

Sound Advice 7: Choosing a House with a Good Audio Room
Modern Home Theater, May 2004 – by Bob Hodas

A number of years ago a good friend of mine built a big beautiful new house in Napa, CA. He had made a bundle working for a professional audio company that had taken the industry by storm with a forward thinking new product. I want you to note in the previous sentence “forward thinking” and “audio”. I went up to visit him and boy was I impressed with the house. It was spectacular in almost every way. What wasn’t spectacular was the acoustics of the room in which he set up his speakers. He set the system up in his living room or great room or whatever you want to call it, and it had an Rt60 (reverb time) that rivaled my high school gymnasium. All I could think of when he put on some tunes was “what were you thinking?”

So, this month we will address some of the issues you should think about when you start looking for a new house. What always seems like common sense to me not always occurs to a new house buyer who has to worry about mortgages and bathrooms and where to put the in-laws.

By now you should know that I advocate a rectangular room. No L shapes, no squares. The room should have doors. No 3 walled rooms or large unsealed openings to a walkway or another room. Look for symmetry, no bay windows on one side unless that is the wall the speaker’s back will go on. The same goes for a fireplace. Something like bay windows or an opening on one side can ruin the imaging since the first order sidewall reflections will not match.

A cathedral ceiling can be a bad thing as it can focus reflections back down into the listening area and bass can build up in the peak. A slanted ceiling, like at my house Sound Advice 4, can be a good thing as long as the speakers are at the low side of the ceiling. The angled ceiling will throw some of the first order reflections to the back of the room and away from the listening area.

You should also refer back to Sound Advice 2 regarding room size. You don’t want a room with a bunch of ugly modes piled on top of each other. Would I venture a minimum size? That’s a difficult question since I’ve heard some very small rooms sound spectacular, but I think you want at least a 13.5’ x 12’ floor plan, assuming an 8’ ceiling. For me, the higher the ceiling, the better. Considerations are more complex if you plan to put in A/V and have two rows of seats. Even though the best placement for the speakers may be the long wall, this may not work out for the projector throw or seating.

There is not much you can do about wall construction unless you decide to tear off the existing sheet rock. Look for an minimum 16” stud spacing, not 24”. Most houses are going to be built with sheetrock. You can always add to the isolation and wall stiffness by adding a layer of QuietRock (see below). For that matter, putting the audio room in the basement will solve some issues with wall stiffness as well as isolation. If you are lucky, you will find a room that has wood on the walls. I’m not talking about that fakey plastic wood panel crap. I mean real wood. Wood has a rich sound all it’s own. It tames the high frequencies just a bit and to me, creates a very smooth, natural sound. Do I have to tell you that walls made of windows are very bad? Hard plaster walls can be tough too (see below).

I like the look and feel of floors covered in rich Corinthian leather. No, sorry, wood, I meant wood. Same reasons as above. I don’t like cement, Mexican tile, stone or linoleum because they can add too much reverb time to the room. Of course you can always carpet any of the above floors and at a minimum I would recommend large area rugs.

Personally I think windows should be kept at a minimum. This will be especially true if you are going to put in a projector and need the room dark. Of course there are also the isolation issues with the neighbors to consider. Then there is the overall reverb time. If you do have a big window like I have at my house Sound Advice 4 hopefully that can be the front or back wall and not on the side. Sidewall windows can be problematic for imaging. A window in the front has a possibility of allowing some of the speaker’s rear firing low frequency energy to pass out of the house, thus eliminating loading, and out of phase reflective energy at the listening position. Speakers designed to be flat in free space work well in this situation.

As I mentioned above in several instances, reverb time is very important in your listening room. Small room Rt60 measurements are not easily quantified but common sense and simple listening tests tell us that shorter is better. My friend’s room described above had tile floors, high angled ceilings, plaster walls, and it was a large floor plan that incorporated a dinning room and sitting room. It was just a big reverb chamber. Rooms with long reverb times have very poor measurable coherence. Common sense says that the more hard surfaces you have in a room, the less coherent the sound will be. If you can afford it, there is a product from PRG Inc. that my friend could have used on his acres of hard plaster walls. It is a sound absorbent plaster, believe it not. As stated above, solutions will include area rugs and draperies.

While electricity is not my domain, it is something you need to think about. How old is the house you are buying? Does it have grounded outlets? Mine didn’t, circa 1956. If not, you will want to run a star ground to all of the outlets in the room. Additionally, can you run a separate circuit for the listening room? There must be enough power at the main breaker box for this so ask an electrician or the inspector. You will want to consider if there is room to put in a balanced power box as well.

The issue of sound isolation is going to affect you in a big way. Unless you live alone, you generally can’t make as much noise as you want at all hours of the day or night. Addressing isolation in an existing house structure is a difficult issue. Most homes are not built with much sound isolation in mind and the hollow walls and stud spacing is not ideal. Unless you are prepared to build a room within a room, you will never get yourself totally isolated from the rest of the house or your neighbors. Some of my clients know their neighbors and made arrangements to listen in the neighbor’s house while they had the music cranked up. This will give you a good idea of how much work you have ahead of you.

On the cheap, you can do several things. Replace your interior door with a solid core exterior door. Make sure you address the air spaces around the doors with some type of insulation as well. Remember that any little air space with leak sound like a sieve. Understand that this applies to your HVAC ducts as well, but that is something most home music room budgets can’t deal with. If you have some more money, you can find some medium priced, mid quality doors being used in home theaters like those at QuietRock.

Some basic isolation can be added to the walls and ceiling simply by adding another layer of mass. If your going to go to this amount of trouble, instead of using 5/8” sheetrock, go for some MDF or Wonderboard. These materials have much more mass than sheetrock. Be sure when you install an extra layer that it is glued and screwed and that the new seams do not overlay the existing seams. If you can afford it, there is a new material on the market that has a significantly increased amount of isolation. It is called QuietRock and QuietWood and you can get more information about it at QuietRock industry solutions. I recommend it and you may find that you simplify the construction process with this material. Any of these wallboards can be made more effective by floating them on resilient channel. This creates an insulating air space and isolates the new wall movement from the existing wall, very effective and of course more labor and money. There are various forms of this channel so shop around. Here are some links to get you started: Silent Source or Kinetic Noise or Aural Exelite.

I hope I don’t have to tell you that two or three layers of glass are better than one. Glass is expensive but if you get complaints from the neighbors, you’re history. Find a good window dealer that can help you find some insulated windows.

Unless you plan on floating a floor (expensive) you’ll have structure born transmission that you will have to live with. It is tough to control. An alternative is to treat the ceiling in the room below you with some QuietRock but that will still only give you minimal low frequency isolation since the bass will travel throughout the house in the supports. RPG now has some total floor solutions.

I hope this months article has been informative and will help you to enjoy hours of listening your new home.