another simple question - 100 Ohm loudspeaker

[graaf]

Hi to all!

let me quote from "Tube CAD Journal":

The big problem tube OTL amplifier face is having to deliver the high current needed to drive the low impedance loudspeaker. One watt into 8 ohms requires a peak current delivery of 500 mA, as (0.5² x 8) / 2 = 1. Which means that a total of four EL509s is needed to meat the 250 mA idle current demand of the push-pull amplifier. If the load impedance were 285 ohms, then the same 500 mA peak current swing would yield 35 Class-A watts. What the world needs is a great 100 ohm loudspeaker!

so the world needs a great 100 ohm loudspeaker!

or even better a 300 ohm loudspeaker

how can it be done?
what about a line array of multiple drivers wired in series?
a line array of 24 8-ohm drivers wired in series is 192 ohm
is it feasible? any obstacles, difficulties?

is anything fundamentally wrong in wiring woofers in series?

dr Griffin (of " www.audiodiycentral.com/resource/pdf/nflawp.pdf " fame) recommends wiring woofers in line arrays in series/parallel connections where for instance four woofers are wired in series giving a 32 ohm total impedance
measurements show that there is nothing wrong in series wiring of woofers: http://www.monstercable.com/mpc/stab...ng_Woofers.pdf

any ideas?

it is not just OTL question because as we all know less current means less distortion
and more ohms means less current

best,
graaf

[myhrrhleine]

Hi,
Wiring woofers in series effects the Qes.
Whether this is a problem I leave to the system designer.
Also, Why not start with 16 ohm speakers?

[graaf]

Originally posted by myhrrhleine
Hi,
Wiring woofers in series effects the Qes

are You sure? are there any formulas for calculating this?
is this the same situation as with adding a series resistance?
a change in Qes results in a change in Qts and in the frequency response or isn't it?
I can't see this in the measurements: http://www.monstercable.com/mpc/stab...ng_Woofers.pdf

and this Richard Clark writes: "the speaker never knows that there is another speaker wired in series with it"

is he wrong? why?

Also, Why not start with 16 ohm speakers?

well, but why not 100 ohm?

I don't know - perhaps John Broskie (the author of Tube CAD Journal: http://www.tubecad.com/ ) knows the answer

he wrote: "What the world needs is a great 100 ohm loudspeaker"

is he wrong? why?

best,
graaf

[myhrrhleine]

Originally posted by graaf


are You sure? are there any formulas for calculating this?
is this the same situation as with adding a series resistance?
a change in Qes results in a change in Qts and in the frequency response or isn't it?
I can't see this in the measurements: http://www.monstercable.com/mpc/stab...ng_Woofers.pdf

and this Richard Clark writes: "the speaker never knows that there is another speaker wired in series with it"

is he wrong? why?



well, but why not 100 ohm?

I don't know - perhaps John Broskie (the author of Tube CAD Journal: http://www.tubecad.com/ ) knows the answer

he wrote: "What the world needs is a great 100 ohm loudspeaker"

is he wrong? why?

best,
graaf

Look at the calculation for Qes.
it includes the series R
That's why some amp damping factor matters.
That's why speaker cable matters, else use 22 Ga. zipcord
--------------
16 ohm speakers are still made.
100?

[pedroskova]

I have a feeling that the inductance of a 100 ohm voice coil would be pretty high...might work for a bass driver?

[Svante]

Once upon a time there were 800 ohm speakers, for this purpose.

The problem with high impedance voice coil is that they require a long thin wire and many turns. This in turn leads to that a lot of insuation material has to occupy space in the precious space of the magnetic gap. This reduces the efficiency, alternatively requires a bigger magnet.

But it is definitely doable.

[Svante]

Originally posted by pedroskova
I have a feeling that the inductance of a 100 ohm voice coil would be pretty high...might work for a bass driver?

Well, the inductance would increase, but only to the same extent as the resistance. This results in the same cutoff frequency in both cases.

[graaf]

Originally posted by myhrrhleine

Look at the calculation for Qes.
it includes the series R
That's why some amp damping factor matters.
That's why speaker cable matters, else use 22 Ga. zipcord

I see
but does it REALLY make no difference if it is just resistance or something more than that
is the situation identical in both situation: when it is a resistor or when it is a coil with moving magnet and back EMF?

[kelticwizard]

When two drivers are connected in either series OR parallel, Qts, Qes, and Qms remain the same.

Here is the chart from Martin J. King on the subject:

http://www.quarter-wave.com/General/Two_Drivers.pdf

[kelticwizard]

Originally posted by Svante
Once upon a time there were 800 ohm speakers, for this purpose.

The problem with high impedance voice coil is that they require a long thin wire and many turns. This in turn leads to that a lot of insuation material has to occupy space in the precious space of the magnetic gap. This reduces the efficiency, alternatively requires a bigger magnet.

But it is definitely doable.

I definitely agree. Moreover, the people most interested in this would likely be tube fans, who could connect a class A tube output stage to an 800 ohm-or even 100 ohm-speaker with an relatively inexpensive film capacitor and save a whole lot of money on an output transformer. Compared to the benefits possible, a few more ounces of magnet is not much of an expense.