Jim Bookhard reviews the SAM

here is a reprint of Jim Bookhard's Selective Audionic Membrane review


REVIEW: Michael Green Audio Selective Audionic Membrane (SAM) Review by Jim Bookhard at Audio Asylum



The Selective Audionic Membrane (SAM) by MGD is a high performance acoustical tuning product. The SAM can be custom ordered according to user needs and preferences. The unit I am reviewing (3' x 4' version) consists of a large, stable, welded steel frame bass, which can be mass loaded with lead shot or sand if desired, and is user variably tunable. The SAM itself consists of a rear plywood board, decoupled using brass standoffs (I don't know if this is the new Harmonic Ring Technology MGD has developed for its new high performance PZCs), and a solid hardwood cherry tuning board (contributing significantly to its cost). This whole assembly mounts to the steel frame by 8 bolts that secure the tuning board to two swivel balls and sockets mounting brackets that are part of the steel frame base. Directly in the center of the front tuning board is a tuning bolt attached to a tuning mechanism directly behind the hardwood tuning board and which resides between the tuning board and the plywood rear assembly board. The review represents initial impressions based on minimal placement variations to the rear of the listening position.

Because my listening space is part of a dual purpose room in a condominium, my sitting position requires that I sit about six feet from the rear wall of the listening area. That is not optimum for nearfield listening with most speakers. The optimum listening position with my speakers is to be seated against a rear wall. Up until now, I have been using two Floor Standing Pressure Zone Controllers (FS PZCs) back to back (with the tuning boards facing opposite directions) which will build up the maximum energy two FS PZCs will produce in a given acoustical space in a room. The two FS PZCs were very effective "emulating" a rear wall, but they could not totally emulate what a complete, real rear wall can do. This is where the SAM comes in and performs the task of not just "emulating" a rear wall, but is so effective that it will outperform the entire permanent tunable rear wall of the Michael Green Designs Tunable Room in their Ohio facilities. The construction design of the SAM is also the same construction design of the next generation MGD Tunable Room which will be built in Nashville, TN.

Like all MGD products for home use, the SAMs require good mechanical coupling to the floor and in order to accomplish this, they come with 4 large brass Mechanical Transfer Devices (brass cones called MTDs) for mechanical grounding. Over the past six months, I have had email correspondence or telephone discussions with several PZC users. Some have said the Floor Standing PZCs have had little effect in their rooms. Others have told me that they haphazardly have mounted their PZCs in the corners or even on the walls thinking the brackets that come with them would have little effect on performance. Some have even resorted to literally "stringing" up the PZCs with picture hanging wire. All the PZCs require rigid mechanical coupling and instructions for their use and installation should be followed to the letter in order to reap the benefits of their performance. Just coming near a mechanically grounded FS PZC, you should immediately notice the effect these devices have on acoustical energy in proximity of their location. So, if you have speakers with spikes and thick carpeting with thick padding underneath and you have difficulty getting the spikes to pierce the carpet to the floor underneath, the FS PZCs will probably not work in your room because they require a good mechanical ground in order to operate properly -- otherwise, they will just not perform if they are "floating" around on thick carpeting. This also applies to all the MGD floor standing speakers and their racks. The wall mounted PZCs must be rigidly mechanically coupled to the walls using the supplied wall brackets and [user supplied] drywall screws with plastic anchors also, in order to work properly. I mention this because if anyone has tried the PZCs without getting optimum performance out of them, it may be due to the fact that they were not mechanically coupled properly to room surfaces.

The SAM I am reviewing weighs about 75 pounds, so mechanical coupling of this SAM to the floor should not be a problem in any room and it is stable without using mass loading. So, what does it do? One nice thing about the MGD acoustical products is that you do not have to wait for "break-in" to hear their effects, which are always immediate. The SAM, in my room, increases SPL, increases and enhances bass response, enhances the reproduction of fine texture details of the music like brush strokes on a cymbal, provides accurate harmonic structures of musical notes and correct decay time. I currently have the SAM flanked by 2 FS PZCs angled into the center of the room creating a sonic "wings" effect acoustically. What I first noticed was that the soundstage, which was large before, grew even larger and extended all the way to the SAM behind my listening position. On recordings that have information that allows it to be reproduced in "surround sound" with stereo speakers, the SAM gives you a 3-dimentional soundstage with total clarity and harmonically rich sound. There is no hint of "glare" coming off the SAM in my room, because of its user tunability. The SAM can also be ordered with "acoustical burn materials", which are user detachable, if the rear of your listening room needs it. Mine does not and is probably the area that used to produce the lowest SPL, acoustically, in the room, so I ordered my SAM without the acoustical burn material.

The SAM was originally designed for recording studios, especially those with foam walls that produce "dead' sounding recordings, to provide the artist with a surface with which their instrument could interact to produce the correct harmonics for the instrument. This is how all instruments work -- they interact with surface areas in their vicinity to produce their harmonics correctly. The SAM can also be used to assist in augmenting the enjoyment of the listening experience for those with hearing limitations and Michael Green will work directly with the potential user to determine the needs and configure an appropriate SAM(s) to assist the listener in obtaining the best listening environment possible.

The SAM meets the needs for which I ordered it and exceeded my expectations in its performance beyond what I conceived it would be able to do. It is a well thought out product, though expensive. It is not for everyone. As I stated at the beginning, this is a high performance listening room tuning tool. Each person will have to judge for themselves how far they desire to take the performance of their room and system. There is no need for anyone to do anything more with their system or room, if enjoyment is being reaped from their current setup. The same applies to tuning your room -- if you are happy where you are, then just enjoy what you have. On the other hand, if you have a special requirement/desire for high levels of system/room performance, the SAM technology combined with PZCs are worthy of your consideration.