Brines Acoustics



Last Modified 6/30/12


T7-A7 T7-A7

Mark Audio Alpair 7 Transmission Line

The T7-A7 speaker is a tapered transmission line with a nominal length of 36" and a taper ratio of 6:1. The Alpair 7 driver has built in baffle step correction and with a Xmax of 4mm, this driver can be run low and hard like no other I have encountered. As with all of my speakers, this speaker is designed to reproduce the more intimate genre, Baroque and early classic, jazz trio and female voice, although they handle the larger forms quite credibly. The T7-A7 is best in a smallish room or as computer speakers. However, if high passed at ~120Hz, the T7-A7 does a very nice job as HT main speakers. This how I intend to use them. When I want to listen to a CD, I simply bypass all of the processing in the HT receiverand listen to pure stereo.

Frequency Response Graph

Frequency Response

Note: The colors are White=0o,Red=10o, Blue=15o,Green=30o,  Yellow=45o, Violet=60. SPL is relative. The notches at 55Hz and 95Hz are room modes. Measurements were made at 1/2m

Impedance Graph

T7-A7 Impedance



Total Harmponic Distortion



For my entire career of building speakers, I have avoided drivers smaller than 6" class because the small drivers wouldn't produce usable bass below 60-70Hz. My goal has aways been to have the F10 point at least as low a 40Hz. Then I came across the Alpair 7. This is a 4" class with stellar mids and top, and surprise, it actually does decent bass.I played around with a number of possible alignments for the Alpair 7, having in mind that I wanted to do a metronome style cabinet. Unfortunately, the line length turned out to be ~36", and the optimum driver position was so low that the speaker would need to be stand mounted. So, I looked into a folded transmission line with the intent of producing a stand mounted speaker that looks like it actually belongs on a stand. The folding involves three separate passages, and getting the anges right became something of a problem. I then modeled the pipe with three constant area sections. The results were almost the same as a constant taper pipe. This is how the line is folded:

T7-A7 Interior

The resulting speaker is very open and detailed. No thought of a tweeter on this one. The bass is good, but not overpowering. Let's face it. This is a 4" driver, not a 15" sub. Tiako drums and the Telarc "1812 Overture" are not appropriate.

A note about the Alpair 7 driver: This is an aluminum tri-mixed alloy cone driver designed by Mark Fenlon, who was also involved with the development of the Jordon JX6 6HD driver. The Alpair series is Mark's design and is assembled in Hong Kong. Mark's line of drivers runs from 3" class to 6" class. Needless to say, I have my eye on a couple of these other drivers

I offer limited custom production here at Hot Springs Village, AR. I will provide plans, flats and completed speakers. Of course, prices may vary at my whim or due to the cost of materials. Since I am doing one-off production, I get no discounts from suppliers. I simply pass on the actual cost of drivers and filter parts. The current price list is:

Plans1 $25
Flats2 $195
Complete Speakers3 $845 Contact me4


Prices are for two speakers, delivered to your door. All shipping and handling is included. The cabinets are made of 1/2" Baltic Birch plywood, the baffle and top doubled.  Non-standard materials or finish are negotiable. If you feel that you will need grills, see Grills.

  1. Plans will be delivered as PDF documents attached to e-mail. Snail mail delivery can be arranged.
  2. Flats include all panels ready for glue-up. Drivers and hardware will be provided by the customer. Shipping weight is 20lb.
  3. Complete speakers are ready to hook up to your amplifier. The standard finishes are oak,  African mahogany, cherry or walnut, stained to your specification and finished with polyurethane varnish. For more information about available finishes, see Fit and Finish. Shipping weight is 20lb.
  4. Why Contact me? We need to discuss the finish and any other options before we can execute a contract.

The T7-A7 uses proprietary design procedures licensed to me by Martin J. King. Any commercial use of this design, including third-party construction for hire, requires a license agreement from me.

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