The Cardas Room Setup Guide: FAQ: Room Design

A collection of questions we've received over the years about room design


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New Home Theater Room

Q.) Hi George, I'm a frequent visitor to your site and often go through the FAQs to read your suggestions to other people. I am currently in the process of building a basement and will be dedicating a room to Home Theater. The HT room will be used primarily for watching movies. The dimensions of the room are: 21' L x 13' W x 8' H.

I have all the electronics, which are setup in a temporary room. I use Athena AS-F2 floor standing speakers in front, AS-C1 in the Center and four AS-R1s at the sides and back. I use an SVS sub. It's the big 110 lb PB-2 sub.


I use a projector for my video. Since I haven't really finalized the size of the screen as it is in my control depending on the screening distance. I am planning to sound proof the walls a bit . I have built 4 of bass tube traps using fiber glass insulation tubes. Their dimensions are 18" Diameter and 3' high. Would you suggest any other room preparation to improve the sound.


Looking at all the dimensions what would you suggest the size of the video screen and speaker/sub placements for a complete satisfactory HT experience.


I would really appreciate your suggestions and expertise. Regards, Raj


A.) Hi Raj, Nice room! I like to use a light, uniform absorption material in Home Theater rooms. A layer of carpet felt or cotton batting on the walls, covered with a material of you choice, works well. If practical, I like venting the room into the attic or another space, to relive the bass pressure.


I like a single small sub in the middle, near the rear wall. Go easy on the sub, you don't want to "hear it".


I like video screens as big as practical. Place your projector on a box or something and move it around to find what your situation will tolerate. Cheers, George




Speaker Placement in a Golden Trapagon Room

Q.) George, I read the article on room setup in your insights section and I have some questions. In a room design like the golden trapagon (Diagram I), how would the speaker placement be?  Do I have to follow Diagram D or does it allow me total freedom of speaker placement?  Is there any diagram for this case? I am making my room drawings now and this info is crucial since I have to allocate room for my screen and the required clearances. Thanks! Carlos


A.) Speaker Placement in a Golden Trapagon is approximately the same as in a rectangular room of the same length. There is more tolerance in a Golden Trapagon because the room nodes are much softer since you are not setting up to a parallel wall. The calculator on our website will work fine. If you want o be exact, use a width of .275 x Room Length for the distance to the rear wall. Cheers, George




No Easy Solution

Q.) Hello there I recently moved my stereo to an asymmetrical room where the left speaker has a rear wall and a side wall next to it, but the right speaker only has the rear wall behind it. The side is open. Both speakers are positioned 18" from the rear wall, and the left speaker is 36" from the side wall. The speakers are 72" apart from each other. All of this resulted in a very noticeable shift in the stereo image towards the left speaker. Is there anything I can do to correct this, aside from adjusting the channel balance on the amplifier? Regards, Adam


  A.) Hi Adam, The symmetry of the system is a critical element in any set-up. The frequency/phase response and amplitude of the speaker is directly determined by the proximity of the surrounding walls. You can make a simple high pass filter for the left speaker to compensate or lower the volume. The problem with turning down the volume control is that it does not compensate for the spectra change and you will always have noticeable smear at some point. George  


Q.) Hi George, Thanks for the reply! I am a mechanical engineer by trade, so I am relatively clueless when it comes to electrical design. How would I design the high pass filter so as to only filter out the unwanted frequencies, and not lose any of the true signal? Regards, Adam


A.) Yeah, sorry. I guess you have to be a bit of a experimenter to do something like this and I don't suggest that you dive into it if you are not. I was just trying to relay my understanding of the asymmetrical layout problem of your room. Again, I am not advising you to do this, but the easiest way is to decrease value of the output capacitor in the pre amp, or series-in a capacitor on the input of one amp channel. In any case, it would be a trial and error thing. I would probably buy a mixed bag of caps at radio shack and experiment until I found the right value, then replace that cap with the best cap money can buy.


If you have access to an electrical surplus store (or eBay) you can buy something called a "Capacitance Decade Box" which can be used to sort values more quickly. A bag of capacitors will be close enough though, if you understand the way they work. What you are trying to do, is roll off the low frequency at the point the wall begins to boost it and match the speakers. I have done this and it is effective, but more that a bit tedious, Cheers, George


Q.) Thanks George! I think I might have an easier time moving the wall... Regards, Adam


A.) LOL, Thanks Adam. I guess I have to learn when to stick with the short answers. Best Regards, George




Book Cases

Q.) I read a quick blurb in Stereophile regarding your recommendation to put bookcases against the wall parallel to speakers placed in the room. I would be interested in reading more information about this - what it does, why it works, how it works, what size bookcases, etc. -Helen


A.) A standard book case works as a "wave trap". Parallel shelves about 13" apart not only make good record and book shelves, they are also at a quarter wave length of roughly 250 cycles. This is approximately the standing wave length between the speaker and the side wall, thus they provide excellent low frequency damping. If the shelves have books or records they are also an excellent diffuser. Buy "keying" the shelves into the wall structurally, you can stiffen the walls immensely. I like to make them extra deep and inset acoustic foam in the back of the shelf. I make a very special hi-density "acoustic wall paper". It is only 3/8" of an inch thick. It starts absorbing at about 300 cycles and eliminates all slap and reflection between the walls it is applied to. This combination of shelves and absorption make the best room damping combination and does it with out being obvious. The shelves in my room run across the wall behind the speakers and along the side walls to behind the listening area. They start at 10" wide on the side walls, behind the listener, and increase to 18" wide at the corner behind the speakers. They are mechanically keyed in to the walls themselves. - George