Atlantic Technology AT-1 loudspeaker Associated Equipment

Sidebar 2: Associated Equipment

Digital Sources: Theta Miles (via S/PDIF output), Bel Canto CD2 CD players; Benchmark DAC1 & DAC1 HDR, Bel Canto DAC3.5VB with VB-1 power supply, Weiss DAC202 DACs; Sony Vaio laptop computer.
Power Amplifiers: Rogue Audio M180 monoblocks, Plinius SA-103.
Loudspeakers: Revel Performa F30, Thiel SCS4T.
Cables: Digital: Stereovox HDVX coaxial, Silver Sonic D-110 AES/EBU. Interconnect: Sain Line Systems Pure (balanced). Speaker: Kimber Kable BiFocal X. AC: Sain Line Systems Reference.—Erick Lichte

Atlantic Technology
343 Vanderbilt Avenue
Norwood, MA 02062
(781) 762-6300

mrplankton2u's picture

The above speaker is a decent performer - for a bass reflex. However,  there is nothing unique, patent worthy, or even new about the design. PMC has been using resonance traps in its speakers for years.The "patent" shows a tapered transmission line shape with an anti resonance trap whose opening is located at a pinch point within the line. The distortion measurements shown in the patent are as misleading as the marketing hype for this speaker - distortion figures are presented only for select frequencies  to make it look better on paper than it really is. In fact, the impedance plot shows the telltale sign of an anti resonance trap - a impedance peak around 100hz. This is actually not a good thing. If you were to measure THD at that frequency, you'd find a noticeable increase. "Anti resonance traps" or acoustic filters have been around since the beginning of transmission lines. Their use actually demonstrates a lack of knowledge/skill in design - not an advancement. 

Moreover, the claims of mixing bass reflex with transmission line are totally bogus. True transmission lines possess a gradual 12db per octave rolloff in the bass region below the transducer's Fs or fundamental resonant frequency. This speaker clearly does not. It's rolloff is representative of a reflex design (steeper 24 db/octave roll off below transducer resonance). Compare the low frequency response of this to that of the Vivid Giya "quasi" transmission lines:


What this AT speaker is is a bass reflex with a small horn attached to the port opening and an acoustical filter incorporated to help dampen the upper resonances of a primitive design. Phil is just warming over a 25 year old transmission line patent with the application of an internal restrictor.  

Despite the false claims of this speaker's "designers", there is no continuum between a true transmission line and a pseudo "mass loaded transmission line". Mass loading means bass reflex - PERIOD. The velocity of low pressure pulses escaping a transmission line should be in the neighborhood of 340 m/s. The velocity of air transfer in most reflex designs is about 18- 20 meters per second (notice I said "air transfer" - not low pressure acoustical pulses - big, big difference). The mechanical tuning of a reflex design is centered about a Helmholtz resonance - a slug of air being forced through a restrictive pipe. The time it takes to ram the air slug through the restrictor determines the tuning frequency. With a transmission line, there is not supposed to be any "restriction" beyond the slight tapering of the cavity behind the speaker diaphragm that follows the natural reduction in acoustic pressure that occurs when sound radiates a given distance from its source (the 1/distance attenuation rule). The timing (frequency tuning) of a transmission line is established by distance from the source and the frequency whose peak presssure occurs at that distance. Contrary to now unfortunately common assertions, the two approaches can't be mixed. You either have restrictive timing and the inherent 24 db/octave rolloff or you don't.The design concepts are worlds apart and so are the results - particularly when you attempt to feed both designs with sub bass programme material at high volume. The reflex design unloads (over excursion) below tuning frequency and the transmission line just keeps humming along. The frequency response and impedance plots always give them away.

10basetom's picture

@mrplankton2u thanks for the info -- I was just about to bite on a pair of used AT-1s until I read your mini review. Which speakers would you recommend (towers, monitors, it doesn't matter) that would be able to reproduce good quality bass you can feel down to 30 Hz without a subwoofer?