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In Reply to: Re: What about Transcendent Sound? posted by Bulla on November 1, 2002 at 08:57:52:
The 33 dB figure is from the Transcendent web site (the white paper concerning amplifier output impedance):"OTL
Let’s look at the Transcendent T8 as an example. It uses 8, EL509 tubes in push-pull. Each 509 has a plate impedance of about 150 ohms. 150 ÷8 = 18.75 ohms. This is unacceptable. Negative feedback is employed to achieve proper performance. The amplifier uses 33 dB of negative feedback which reduces the output impedance to 0.4 ohm thereby achieving outstanding woofer control and the ability to drive 4 ohm speakers. This specification was verified by Stereophile when they reviewed the amplifier."I don't own Quads or have any personal experience with them. My Atma-Sphere amps drive Maggie MG-20s in a bi-amp setup. This thread started with a request for advice on medium-powered tube amps for (I believe) Quads, and someone asked about Transcendent. My understanding is that others have found Atma-Sphere amps better suited to electrostatic speakers with high impedance in the bass range than typical transistor amps because of the limitations of a voltage source confronted with a capacitive load. The Transcendent uses massive feedback to achieve low output impedance, so it will perform similar to a typical transistor amp in the bass with the Quad. If you are happy with the bass performance of the Transcendent/Quad pairing, then I'm glad to learn that someone has direct experience instead of my chain of inference.
Amplifier damping factor is easy to measure, but has implications that are complicated. It is by no means "simple physics." I would expect any panel speaker to be overdamped already by the free-air cancellation effect, so adding the additional damping of an amplifier with low output impedance might diminish the bass. The real question is what amplifier damping factor was used by the designer to "voice" the speaker.
Cone woofers are a different topic. Most cone speakers made these days require amplifiers with high damping factors to achieve critical damping for optimum bass response with mimimum distortion. However, speakers made in the golden age of audio, in the 1950s and 1960s, sometimes had very powerful magnets and required fairly high amplifier output impedance to achieve critical damping. See the article by Dan Tomcik on the URL provided for a full explanation.
Recognize that cone woofer efficiency is pinned to a fairly low level by the present convention of low amplifier ouput impedance. While this has kept planar speakers viable, it has stalled high-end audio on the path of better amplifier design because we are stuck with the need for monster amplifiers that sound bad.
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Follow Ups
- Re: What about Transcendent Sound? - Leisure7 11:22:20 11/01/02 (0)
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