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Hylle 7th October 2012 05:36 PM

Speaker for tubeamp
I would like to make a speaker for tube amps with a relative constant impedance, across the frequency band, and a high senitivity.

But is it best to have an impedance that matches the 8ohm or 16ohm output on the transformer, or is it best to have the speaker impedance as high as possible?

I am thinking a high speaker impedance compared to lowest possible amp output impedance, will make the best dampingfactor?

I am mostly concerned with bas control, how is that best achieved with a tube amplifire?

- I am a bit unsure where to post these questions, in this speaker forum, or at the tube forum, so please bear over with me....

picowallspeaker 7th October 2012 05:48 PM

16 Ω will be nearly impossible to obtain, as is a standard impedance that you will find
very seldom ; otherwise, it might be good to have a load that don't ask much current
to the amp, but it depends...on the amp...and on the drivers !!
For low power tube amp the damping factor may come to...a factor that it characterizes
the bass . Bass transducer should then have a diameter of 20 cm to give enough SPL
under 100Hz ....but I guess I'm generalizing :)

Hylle 7th October 2012 05:54 PM

16 Ohm can be found, but there dc resistance is often around 11 ohm, so it is not possible to reach a constant 16 ohm load, but maybe around the 11 ohm, but is that better or worse than a constant 8 ohm load?

picowallspeaker 7th October 2012 06:00 PM

Re is ( of course ) different from Z . One is static and the other dynamic ;the 4,8,16 Ω
are nominal ratings . plus, a driver has its Z peak at resonance frequency .
The lower the load , it will make more current flow in the amplifier ....

cT equals piD 7th October 2012 11:24 PM

To me bass control means the same as Q of the woofer and enclosure. All you have to do to insure that Q of the woofer doesn't go too high is to factor in the output stage resistance of your amplifier into how that output stage resistance increases Q of the driver and amp as a system.

If you look at my post #7 in the thread "electrical damping freq. range", there is an equation for modified electrical Q. So first you solve for modified Qes or Qes'. Then solve for modified Qts,

Qts' = (Qes' * Qms) / (Qes' + Qms)

Connecting the voice coils of a dual voice coil woofer results in a driver with nominal impedance of 16 Ohm. Getting nominal impedance to be as high as possible would be best to improve sensitivity, I believe.

sreten 8th October 2012 12:04 AM


Its best to aim for 8 ohm nominal impedance, higher you will lose
sensitivity, lower you will lose compatibility with some valve amplifiers.

You can make a speaker with relatively constant impedance, however for
valve amplifiers this usually involves pointlessly drawing more current.

As current, not phase angle matters more for valves, there is no such
thing as a nice "constant impedance" speaker for valve amplifiers, they
prefer high impedance when they can get it, but this also means the
speakers need to to be balanced to match to high output resistance
(nothing to do with load) valve amplifier.

If Ro of the valve amplifier is less than 1R, its not an issue.

rgds, sreten.

Hylle 8th October 2012 11:04 AM

Thanks for all you inputs. I will go for a 8 ohm impedance, but I still belive a relatively constant impedance will be best for a non-feedback tube amplifier, with high impedance output.

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