Brines Acoustics


Design Philosophy


Last Modified 10/10/10

Since high school, I have been a classical music lover. As I matured, music has expanded to include jazz (primarily piano trio with voice), bluegrass and classic country. Basically, these are more intimate forms of music that require speakers with good detail and dynamics, but not great volume or extreme depth. This is reflected in my speaker designs. I look for a speaker that covers 40Hz and up with a normal listening level of 80dB or so.

I am a minimalist when it comes to speaker design. Given no other considerations, I prefer a single driver solution. This does introduce compromises, but the end result can be quite astonishing. If great volume is not demanded, a single driver solution is quite viable. When compromises demand a multi-driver system, I prefer series cross-overs. However, tonal balance is very important to me, so all of my designs have some sort of equalizing filter.

Good midrange and treble response from a single-driver speaker depends almost entirely upon the choice of driver. I prefer the Fostex, Tang Band and Lowther drivers because, at least to me, they provide the best overall sound in their price ranges. There is little that cabinet design can do to help, although failure to attend to the cabinet defraction signature can do harm. Adequate bass from a single-driver system, however, is entirely dependent upon cabinet design.

The definition of "adequate" bass is entirely dependent on the musical tastes of the listener. I define "adequate" as a cut-off frequency no higher than 40Hz. This covers all of the normal instruments in the orchestra, including the double bass, all important to jazz and other acoustic genre. If the driver and cabinet size permits, I like to get down to a cut-off frequency of 30Hz, which covers the entire 16-foot rank of the pipe organ. Anything below 30Hz is the realm of the subwoofer.

In order to get down to the bass cut-off I require, I use variations of the Transmission Line (TL) cabinet, usually the MLTL, or Mass Loaded Transmission Line. With proper choice of geometry, it is possible to get bass output at least a half-octave below the driver's resonant frequency. This allows a single-driver solution covering the range 40Hz-20,000Hz.

You will not that I offer bass reflex cabinets for those drivers that are appropriate. I do so because the bass reflex cabinets look smaller than the corresponding MLTL, although they have the same footprint. This leads to a more acceptable appearance in the living room and provide excellent sonic results when mated to a subwoofer in a home theater setup.

There are many audiophiles who like a "live" cabinet. So be it -- who am I to dictate what sounds good to another. However, a "live" cabinet is adding acoustic information -- distortion -- to the sound produced by the driver. The result is an exaggerated upper mid-range. Some declare this to be "detail", but it is not. It is distortion. I make my cabinets acoustically "dead" as possible.

I believe in acoustically dead cabinets. For years, I used a sandwich of 1/4" cement board glued to 3/4" MDF with Liquid NailsTM. The driver was attached to a 3/4" MDF trim panel, glued on with silicone sealant, which isolates the driver from the cabinet while adding additional stiffness to the front panel. The cabinet was lined with 5/8" rigid fiberglass to absorb standing waves within the cabinet. The result is an acoustically honest cabinet with no added coloration. Unfortunately, MDF has taken a lot of bad press lately and I have been forced to abandon MDF in favor of Baltic birch plywood. I am now using 1" Baltic birch for the floor standing MLTL's (actually two layers of 12mm material laminated into a single 24mm sheet) and 3/4" cabinet grade birch plywood for the smaller bass reflex cabinets. I continue to line each cabinet with 5/8" rigid fiberglass and additional polyester stuffing where appropriate.

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