When matching an amplifier to a speaker, damping is a term one should become familiar with. Especially as it relates to the amplifier, where it may be more appropriate to refer to damping as output regulation, as this will have an impact on how the signal generated by the amplifier will control the speaker cone. It has been my experience that when you get the amplifier and speaker interface correct, it makes it easier to have everything upstream fall into place. It does not matter which one you start with, but if you do not get that interface correct, you will be wasting time and/or money getting the rest of the system to synergize and sound optimal. Sure, you can work from upstream to downstream, but unless you get lucky, I do not think that is going to end well for you.
I would also like to note that this discussion pertains to box speakers. While damping also applies to electrostatic and planar magnetic speakers, the method used to damp them is different and the rules are applied a bit differently. It is common knowledge, or should be, that for a while now most box speakers are manufactured to be highly damped mechanically. Speaker designers use all sorts of materials to strengthen and tune the boxes so the resonances are benign, and this is measurable. Again, what is really the issue is electrical damping and how the signal from the amplifier affects the speaker cone and the resonant frequency of the moving system. Unlike years ago, when 8, 16, and even 32-ohm speakers ruled because tube amplifiers were the norm, today’s box speakers primarily have a 4-ohm nominal impedance. Also worth noting is that it is no coincidence that the increased popularity of solid-state amplifiers drove the shift to 4-ohm speaker designs.
A 4-ohm speaker requires the amplifier to have lower output impedance (higher damping), and due to speaker impedance dips the amplifier may need more current capability as well. Typical solid-state amplifiers have constant voltage and variable power (a McIntosh amplifier with autofomers is a notable exception). You can easily see it in the specifications such as 100 watts @ 8 ohms, 200 watts @ 4 ohms (but 50 watts @ 16 ohms, which typically is not shown). Now you can use a tube amplifier with a 4-ohm speaker, but it will most likely be a push-pull design and better have enough feedback to lower the output impedance to 1 and in some cases lower. Higher power may need to be a consideration as well. Also, that speaker better be a smooth 4-ohm load as typical tube amps have variable voltage and constant power, (Roger’s Music Reference RM-200 amplifier is a notable exception) so not enough current may be available to address significant impedance dips, especially in the bass frequencies.
I believe a good speaker designer has a particular amplifier topology in mind when making their speaker. However, the amplifier they used is rarely disclosed. Generally, the specification will note a rated power range for their speaker, for example, 50 to 100 watts. So, if you are interested in a speaker, ask the designer what amplifier they used in their testing. I am highly skeptical, and you should be too, of any speaker designer who says their speaker is amplifier agnostic or was designed for and sounds best on a particular genre of music. I doubt any of the greats such as Allison, Klipsch, Lansing, and Snell ever said such a thing about their speakers. Then again back then there was more reality in audio than today. Audiophiles now get too easily sucked in by superlatives and other marketing gimmicks from today’s “designers”. The laws of physics and engineering do not lie, and it is very simple to test this. You will most certainly hear the difference and so the point becomes: Do you care?
Where Does Damping Comes From?
Roger A. Modjeski
Now I suppose I should tell you the answer to the question of where damping comes from. It is most easily obtained by use of feedback, lots of feedback as in amplifiers that have damping in the hundreds. The current they can supply is an independent factor and the damping will be unchanged until the current limit is reached. Then they fold up the tent and go home.
Triodes have long been recognized for their high inherent damping factor which is available without any feedback at all. I chose the 13EM7 tube because its plate resistance is a very low 750 ohms. That is about the same as a 300B and 3 times lower than the 6DN7 that Bottlehead uses. It also happens that the gain and transconductance of the EM7 are very close to the 300B. So, in essence, within its rating it behaves like a 300B. One could well consider this a low-cost alternative which is attractive from the initial cost and cost of replacement tubes that are 1/5 to 1/10 the price of a 300B.
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