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Room Acoustics 201 - Part 2

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Customer email newsletter dated: March 15, 2007.

Room Acoustics 201 - Part 2


This is the second of a three part series on the various approaches to room acoustic treatment. In the first part we wrote about our preferred mid-room speaker placement approach, and also about the basic treatment of the room, which we feel is best accomplished using the new Cathedral Sound Acoustic Panels. The final diagram from Part One appears here for easy reference, and you can read this first installment in our Archives.

Two notes before proceeding to Part Two:

1. Although we wrote last time about our mid-room speaker placement preference, these acoustic treatment suggestions, and those that follow here in Part Two, also address other speaker placement scenarios.

2. We omitted discussion of an alternate placement for the Cathedral Sound Acoustic Panels, and wish to correct this omission here. If the upper corners of the room are not available for some reason, the best alternate placement for these panels is in the corners near the floor, either hung on the wall, or even laying face up on the floor. The corner near the ceiling is functionally preferable because the energy flows are completely unimpeded by furnishings, etc., near the ceiling, and so are typically greatest there,  but the next best location is in the corner near the floor, which is the other point in the room where three large, flat surfaces - two walls and the floor in this case - are "dumping" all the acoustic energy that they are collecting.

Reminder: To celebrate the (eventual) completion of this room acoustic writing project, we will have a special 12% discount on ALL acoustic products for the months of March and April.
Now on to Part Two - decision time:

At this point our acoustic series will cease to have direct application to home theater systems, but will continue to be relevant to two channel stereos even if using an alternate placement to our mid-wall suggestion.  If your interest is primarily home threater, get your Cathedral Sound Panels in the corners, and be happy, or wait until next month for our discussion in Part Three of some absorbing/diffusing acoustic products.

For our two channel readers we are at a fork in the road acoustically. One option at this point is to begin treatment with absorbing/diffusing acoustic panels such as the products from ASC, Echobusters, Eighth Nerve, Furutech, or our old friend Michael Green. Our experience, however, strongly suggests as our second step the introduction of the unusual Shakti Hallograph product to our room.

The Hallographs have been around for 3 or 4 years. The first reaction most people have is to their appearance. It is what it is. If you can't live with it in your room, consider another of the designs below, or wait for Part Three next month if you want to consider traditional acoustic panels, or be happy with the easy-on-the-decor Cathedral Sound Panels on their own.

Hallographs should be used in pairs - either one pair in the two corners behind the speakers - or better still, add a second pair in the other two corners behind the listening position.

The top of....
...the Hallograph swivels on its base. As you orient the head more towards the central listening position you will "focus" the sound and firm up the center image. Orient away from the listening position to open up the sound stage. Some experimentation will be needed to find the proper balance between expansiveness and focus.

If using the preferred two pair approach, get close by adjusting the Hallographs behind the speakers first, and then fine tune with the Hallographs at the listening end of the room. In a "dialed in" room, the impact of minute adjustments to the Hallographs at the listening end of the room is jaw-dropping. $998 per pair ($879/pr on special during this survey).

Does this sound like voodoo? The Hallographs fall into the category of things that I don't fully understand the "how" of, but I am nonetheless 100% convinced that they are effective. Clearly they are resonating in "sympathy" with the music frequencies. But why do they look like this? How does the focusing concept actually work? Can't answer, but we really like this effective and predictable product.

More voodoo:-)

If I recall correctly the first company that commercialized acoustic products that "play along with the music," let's call it "sympathetic resonance," was Shun Mook.  Their website is pretty limited, and the basic "Spatial Control Kit" they mention on the linked web page hasn't been available for many years, but the "Spatial Control Quartet" and "Sextet" still are, and though I would say they may be less powerful than the Shakti Hallograph, they do also work very well, and to my eye are quite elegant. Costs are $2400 for the Quartet, or $3360 for the Sextet, but because of limited production, be prepared to wait!

A third option....
in the sympathetic resonance camp, and most likely the easiest to coexist with in most listening rooms, are the Acoustic System Resonators.   As this manufacturer characterizes this concept of sympathetic resonance:

The resonators are activated by sound waves in the room and produce overtones – subtle overtones, which also define the sound colour. This colouring is often lost during the recording process, and when replaced always improves, and never worsens, the sound experience. Every listening room affects the music with its own specific audio characterics, and from this point of view it can be said that the resonators by Acoustic System simply modify the acoustic properties of the listening room."

The product line is a series of small cups made from various metals. A cup will sit on a wooden base that attaches to the wall. The website has an easy to follow six step process for application of a total of nine appropriate cups in a music room. The cups are half the size of a thimble and the bases are the size of a box of matches!

This raises a point of consumer interest: sometimes when we talk to people about room acoustic treatments the first thing they say is that they don't want to fill the room up with big panels and other acoustic stuff. Because the Acoustic System Resonators are so small, they would seem to fit the bill of a nearly invisible acoustic product, but then we get into "perceived value," which given their small size and relatively high cost ($200-$950 each + one even more expensive model at $2200 per piece) can make these products tough to swallow. Invisible is expensive!

Or as Srajan Ebaen writes in his January report on these products in 6moons audio:

Because these resonators are small; because they use precious metals; because they aren't cheap; because they apparently defy conventional acoustic theories - the howls of ridicule in the peanut galleries become a predictable response.

Note: Acoustic treatment products which use the sympathetic resonance approach can be difficult to integrate into rooms with a lot of conventional absorbing/diffusing products. An overdamped room will rob this type of device of much of it's effectiveness. Be forewarned, and if you want to use resonating products like these, go light on the absorbing/diffusing products.

In Part Three next month we will get into the selective use of absorbing/diffusing products, either in combination with, or instead of taking this resonating products approach to room acoustic treatment

As we move forward in this series of acoustics articles we are increasingly dealing with products requiring placement "trial and error." Because more users will get better results from products that require less experimentation, it is both appropriate for us to continually recommend the "no-brainer" Cathedral Sound Panels, which work every time in the corners, and also in this installment to lead with the Shakti Hallographs, which also make use of consistent corner placement, albeit with some fine tuinng required.

For best results the Shun Mook and Acoustic System products need a little more experimentation than the Hallographs. But the experimentation quotient for ALL of the resonating-type products covered today is considerably less than what will be required in our next installment when we are dealing with the more traditional absorbing/diffusing acoustic products.


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