Speaker impedance patterns - how to read them?
I know this has probably been discussed ad nauseam, but here's my question. I'm grateful for any sensible opinion.
Premise.
A speaker system may have a complex impedance pattern that can vary from 3-ohms to 30-ohms depending on frequency. Some speaker systems with similar impedance patterns may be stated as being 8-ohm loads because the speaker is 8 ohm in an important part of its frequency response, but only there.
A tube amp, as a voltage amplifier, likes a regular impedance pattern. Almost no speaker system has a constant, regular impedance pattern. I am aware that solid state, powerful amps are built to compensate for modern speakers' complex impedance patterns, but there are tube amps around and people who love them. It's difficult to understand what average load a given speaker system will present to the amp.
Question.
When looking for suitable speakers for a tube amp - mine is a PrimaLuna EVO 100, 40w x 2 from EL34s - what must be looked at? How to best interpret the impedance pattern, whenever available? Assuming that one listens at normal levels in a medium-sized room, what are the criteria for matching speaker and amp?
Thanks for your views. M.
Premise.
A speaker system may have a complex impedance pattern that can vary from 3-ohms to 30-ohms depending on frequency. Some speaker systems with similar impedance patterns may be stated as being 8-ohm loads because the speaker is 8 ohm in an important part of its frequency response, but only there.
A tube amp, as a voltage amplifier, likes a regular impedance pattern. Almost no speaker system has a constant, regular impedance pattern. I am aware that solid state, powerful amps are built to compensate for modern speakers' complex impedance patterns, but there are tube amps around and people who love them. It's difficult to understand what average load a given speaker system will present to the amp.
Question.
When looking for suitable speakers for a tube amp - mine is a PrimaLuna EVO 100, 40w x 2 from EL34s - what must be looked at? How to best interpret the impedance pattern, whenever available? Assuming that one listens at normal levels in a medium-sized room, what are the criteria for matching speaker and amp?
Thanks for your views. M.
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- 46 posts total
A tube amp, as a voltage amplifier, likes a regular impedance pattern. All power amplifiers are actually voltage amplifier, but tube amps typically have higher output impedance, which makes the output vs. frequency load dependent. Please see the first graph’s black trace for a very typical example: https://www.stereophile.com/content/doshi-audio-evolution-monoblock-power-amplifier-measurements I am aware that solid state, powerful amps are built to compensate for modern speakers’ complex impedance patterns, I would not use this phrasing. Solid state amps tend to be more ideal voltage amplifiers, with a lower output impedance. There is no particular compensation, unless you mean a feedback loop, which tube amps can have too. They aren't compensating, they are lacking things like output transformers, which reduces the output impedance of the amp. When looking for suitable speakers for a tube amp This is actually a little complicated as a lot goes into this. The sound of your room, and your personal preferences may complement each other quite well. There are some general guidelines, which is to avoid speakers who dip below 4 Ohms, and those with sensitivities lower than 92 dB or so. Generally also avoid ESLs or you’ll lose all the treble. Of course, you may have an overly bright room, or amps which are less sensitive to this. |
Keep in mind that a higher impedance speakers, say one that peaks at 10 or 12 Ohms but is rated at "8 Ohms", will require more voltage to drive it than one that peaks at 8 Ohms. It won't need as much current at 10 or 12 Ohms obviously, but it will require more voltage. The only way you can get more output voltage is to use a higher wattage amplifier if you going solid state or use a higher impedance tap if you are using a transformer coupled output stage, such as most tube units. Remember the Dahlquist DQ-10's? They had a relatively low impedance dip but also had a high impedance midrange, so they required both higher current and higher voltage to drive them properly. Not too many amplifiers back in the day could do both. |
- 46 posts total