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Re: Redirector - Any one have any experience with this type of acoustic treatment

Posted by Jon Risch (B) on June 21, 2005 at 21:25:10

In Reply to: Redirector - Any one have any experience with this type of acoustic treatment posted by AmirB on June 21, 2005 at 09:46:20:

Folks have talked about reflectors before.

In most cases, the size of the panel is too small to do much good, because the ability to reflect LF depends on sheer size.

The basic panel as shown is approx. 18" wide, about 5 feet tall, and only 7 1/2" deep. The height is good, getting you down to a decently low frequency, but the other two dimensions fall far short, and the panel will only reflect frequencies above about 800 Hz UNLESS you use several side by side, then they may get down to around 400-500 Hz.

Below those frequencies, the sound will not be reflected, but will diffract "around" or past the panels. This assumes that the panels are totally rigid, and do not flex or absorb any energy through flexing motions. Obviously, 3/4" MDF is not absolutely rigid, so there will be some frequency dependant absorption in the bass, perhaps at a series of panel resonance points.

Likewise, the depth of the absorbing material on the back side is only about 2" deep, and is positioned against a hard surface, thus loosing any help from an air space behind the absorbing material. Using the most effective density so that none of the useful operating range is lost, the LF limit of good absorption will be approx. 1700 Hz. You might be able to stretch it down a bit lower, bu then the HF's would start to be relfected at the very high end.

So these panels suffer from many of the same issues that typical reflector panels have in the past. While they do go down a little lower in operation, they are still primarily midrange and HF devices, and as such, will not equate to an RFZ room.

In fact, to equate these to an RFZ room is rather misleading, kind of like saying that a small handfull of sound absorbing panels placed in a room can create an LEDE room.

In terms of absorbing bass modes or preventing standing waves, they are just not deep enough to do this down to any low bass frequency, so this is a claim that can not be true.

Given the relatively large investment in materials (nice looking wood, probably foam absorbing material, and what looks like grill cloth in the finished photo section, these are not that cheap either, and will require a lot of labor and work to make them solid, look good and function to the limits of what they are capable of doing.

If one were to spend that money and time on some of the other DIY acoustic treatments, it would probably be better spent.

For instance, properly constructed sound absorbing wall panels can absorb down to around 200 Hz or so, even lower with a little extra materials and/or thickness than normal. The end result would not be that much deeper than these are, and as long as the panels were about 30-36" wide (minimum of 4 feet tall), they would readily outperform the Redirector concept.

A set of DIY bass traps in the corners would tame the room modes, diffuse the HF's, and the total combination of DIY panels and traps would be no more expensive, probably no more labor, and work better overall.

DIY room lens have a similar range of action, and some of the DIY versions are easier to build, if one wishes to experiment with diffusion.

If we look at the total number of device needed to implement them in a room, his very simplified diagram (titled "Early Reflection Free Zone) shows 8 being used, but this is not really enough, and in other diagrams and photo's it looks like you really need about 16 to 20 of these in order to get something happening.

Constrast this with my minimum recommended room treatment using traps and panels: 4 traps, one in each corner, and about 6 or 8 panels.

Given that they will take a similar amount of time to build, and cost about the same (which may be very generous to the Redirectors!), it is apparent that the Redirectors are going to cost more and take more time, due to the greater total number of devices needed.

The biggest problem I see with the Redirectors, aside from the limited LF action, is that they would have an unpredictable bass absorption somewhere, possibly even a series of peaks/dips in the bass range,
due to the flexing of the long skinny MDF panels, which would tend to make the bass sound in a room worse than raw, not better.

I am sure that they would sound better than nothing at all, but for the money and time invested, they are not the best bang for the buck.

Jon Risch

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