Hi to all!
let me quote from "Tube CAD Journal":
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
theory and measurements also show that there is nothing wrong in series wiring of woofers because "the speaker never knows that there is another speaker wired in series with it": www.monstercable.com/mpc/stable/tec...ing_Woofers.pdf
so why not?
any ideas?
best,
graaf
let me quote from "Tube CAD Journal":
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
theory and measurements also show that there is nothing wrong in series wiring of woofers because "the speaker never knows that there is another speaker wired in series with it": www.monstercable.com/mpc/stable/tec...ing_Woofers.pdf
so why not?
any ideas?
best,
graaf
100 ohm spk.
In older design, there was an amp. using 8X 6080 in parallel, and requires a 16 ohm speaker, the circuit employed OTL design. This told us if more tubes in parallel, the output impedance could be lower, that's why we use output transformer for impedance matching. Usually the primary impedance for tube is from 2K to !0K ohms, depends on which tube to be used. The sound quality depends on the output tranny quality. A pair of high quality output tranny is very expensive, but we still have to use it.
If the in / out impedance doesn't match ideal, lost of power or low efficiency or distortion would occur. Careful design the matching and select good quality tranny is a must for best audio reproduction.
In older design, there was an amp. using 8X 6080 in parallel, and requires a 16 ohm speaker, the circuit employed OTL design. This told us if more tubes in parallel, the output impedance could be lower, that's why we use output transformer for impedance matching. Usually the primary impedance for tube is from 2K to !0K ohms, depends on which tube to be used. The sound quality depends on the output tranny quality. A pair of high quality output tranny is very expensive, but we still have to use it.
If the in / out impedance doesn't match ideal, lost of power or low efficiency or distortion would occur. Careful design the matching and select good quality tranny is a must for best audio reproduction.
So it sounds like an amp for an infinite baffle subwoofer would be the ideal application of OTL. Two manifolds with four 16ohm speakers in each. 
But seriously I suppose a high impedance speaker with normal coil system would have trouble with high Frequencies due to coil inductance but some sort of electrostatic or piezo setup should work.
mike
But seriously I suppose a high impedance speaker with normal coil system would have trouble with high Frequencies due to coil inductance but some sort of electrostatic or piezo setup should work.
mike
Re: 100 ohm spk.
I think the point that Broskie was making is that there's more to it than output impedance; you need the capability to deliver current as well.
One section of 6080 used as a cathode follower has an output impedance of about 150 ohms, so 16 of them in parallel would be roughly 10 ohms. You might get 50mA of drive current from each one swinging 40 Vrms, so 800mA total.
We can use Ohm's Law to figure out how much current we would need to swing 40 Vrms across 16 ohms:
i = v/R = 40/16 = 2.5 amps!
That's three times what all those parallel 6080 cathode followers can deliver despite the fact that the output impedance would seem to be low enough.
We can work the problem from the other direction. Suppose we expect our 8x6080 amp to deliver 20W into a 16 ohm load.
Power P=i^2 x R, or i = sqrt(P/R) = sqrt(20/16) = 1.1 amp. Not gonna do it. The best we might do (based on my assumptions) is
P = i^2 x R = 0.8^2 x 16 = 10 watts.
If that seems disappointing it's all because each 6080 just can't deliver as much current as the low output impedance seems to suggest.
-- Dave
18thell said:
I think the point that Broskie was making is that there's more to it than output impedance; you need the capability to deliver current as well.
One section of 6080 used as a cathode follower has an output impedance of about 150 ohms, so 16 of them in parallel would be roughly 10 ohms. You might get 50mA of drive current from each one swinging 40 Vrms, so 800mA total.
We can use Ohm's Law to figure out how much current we would need to swing 40 Vrms across 16 ohms:
i = v/R = 40/16 = 2.5 amps!
That's three times what all those parallel 6080 cathode followers can deliver despite the fact that the output impedance would seem to be low enough.
We can work the problem from the other direction. Suppose we expect our 8x6080 amp to deliver 20W into a 16 ohm load.
Power P=i^2 x R, or i = sqrt(P/R) = sqrt(20/16) = 1.1 amp. Not gonna do it. The best we might do (based on my assumptions) is
P = i^2 x R = 0.8^2 x 16 = 10 watts.
If that seems disappointing it's all because each 6080 just can't deliver as much current as the low output impedance seems to suggest.
-- Dave
graaf said:
Just like voice coils are made: Plenty of carefully wound thin copper wire.
I would choose that approach, because if you connect many woofers in series, you get many separate acoustic radiators. It is not a problem in very low frequencies, but if you want a full range speaker or even bass/midrange, you will get a comb filter effect.
Sch3mat1c said:
Hi Tim
Actually Philips at the time used 800 Ohms and 400 Ohms.
The Philips speakers with 800 Ohm voice coil can be recognized by an A in the type number, e.g., 9710A, and 400 Ohm speakers have a B .
http://people.cs.uu.nl/gerard/RadioCorner/Articles/SerBalOut.htm
Regards
An OTL with two output bottles delivering 56W into an 8 ohm load....
Is it possible...?--Yes....
The usual valve of choice is the 6C33C-B--That rather heater-power-hungry Russian Voltage-Regulator....
Its Max Static Anode-Current is listed as 600mA, and has a 60W Pa....
This is for Continuous Service as a Voltage-Regulator, which is its design purpose--Lifetime is quoted as 1000 hours at this current and at Max Dissipation.....
For quite short periods of time, say-a minute or s and at a lower dissipation it could quite happily pass double that, without sustaining damage, all things being equal.....
It has a Max 'Peak' capability of 3.75A-allegedly!....
What we are looking at is Average Power/Current.....
A 6C33C-B built like a brick outhouse with its huge cathodes and high perveyance couldnt survive very long past a minute or two at say, 1A Continuous Current flow at full dissipation or higher....
But with only the peaks of signal wave-form exceeding the double 600mA 'max' --the valve survives....
My OTL, uses just two bottles each containing two triodes wired in // They are biassed at 75mA and at 200V. The dissipation is therefore pretty low.....
To get the output impedance down for damping etc,, each 'side' of the output stage is used as a buffer stage, driven from a pair of Differential Amplifiers where NFB keeps things under control
A member here, Hans who is a great enthusiast of the OTL has designed a set-up which uses 2 tubes in each channel, and although not as high power as mine, has done extended (24 hour) tests at 25W, full-power in his equipment. He says that apart from everything getting very hot, there were no failures or other issues....
He has used the same set of tubes in his equipment for 6 years, so several hundred hours at the least with great reliability.....
My own OTL while a different design and using a higher +B for the Circlotron rails, (200V) as opposed to 140V for Hans'es amp has also proved quite reliable. I havent had any out-put valves go faulty, apart from one which I hadn't burned in--I just shoved it in and regretted it later!
These large triodes really do need burning in well before proper use--Worth remembering if you use these...
I do like the idea of wiring up several speakers in series, and have been thinking of doing just that--It would give me a greater Efficiency from my current amp and a greater choice of out-put bottle choice for future projects...
Only down-side is it could work out expensive
Is it possible...?--Yes....
The usual valve of choice is the 6C33C-B--That rather heater-power-hungry Russian Voltage-Regulator....
Its Max Static Anode-Current is listed as 600mA, and has a 60W Pa....
This is for Continuous Service as a Voltage-Regulator, which is its design purpose--Lifetime is quoted as 1000 hours at this current and at Max Dissipation.....
For quite short periods of time, say-a minute or s and at a lower dissipation it could quite happily pass double that, without sustaining damage, all things being equal.....
It has a Max 'Peak' capability of 3.75A-allegedly!....
What we are looking at is Average Power/Current.....
A 6C33C-B built like a brick outhouse with its huge cathodes and high perveyance couldnt survive very long past a minute or two at say, 1A Continuous Current flow at full dissipation or higher....
But with only the peaks of signal wave-form exceeding the double 600mA 'max' --the valve survives....
My OTL, uses just two bottles each containing two triodes wired in // They are biassed at 75mA and at 200V. The dissipation is therefore pretty low.....
To get the output impedance down for damping etc,, each 'side' of the output stage is used as a buffer stage, driven from a pair of Differential Amplifiers where NFB keeps things under control
A member here, Hans who is a great enthusiast of the OTL has designed a set-up which uses 2 tubes in each channel, and although not as high power as mine, has done extended (24 hour) tests at 25W, full-power in his equipment. He says that apart from everything getting very hot, there were no failures or other issues....
He has used the same set of tubes in his equipment for 6 years, so several hundred hours at the least with great reliability.....
My own OTL while a different design and using a higher +B for the Circlotron rails, (200V) as opposed to 140V for Hans'es amp has also proved quite reliable. I havent had any out-put valves go faulty, apart from one which I hadn't burned in--I just shoved it in and regretted it later!
These large triodes really do need burning in well before proper use--Worth remembering if you use these...
I do like the idea of wiring up several speakers in series, and have been thinking of doing just that--It would give me a greater Efficiency from my current amp and a greater choice of out-put bottle choice for future projects...
Only down-side is it could work out expensive
poynton said:
Hi Andy
Don't know!
But , maybe you can find same old Philips speakers , in Ebay...
http://images.google.ca/imgres?imgu...0A&start=20&gbv=2&ndsp=20&svnum=10&hl=en&sa=N
Good hunt...
SY said:
here is a candidate midwoofer (with a fullrange potential, available here in Europe) - for high Z array loudspeaker without robbing a bank
http://www.tvm-valmez.cz/index.php?id=80&catit=73&l=1&catg=1
very wide response (declared 50-16 000 Hz), fs of 55 Hz, DVC 2*8 ohm i.e. giving 16 ohm when wired in series
Tesla from Czech Republic, price per unit around 10 Euro in retail
but 144 units would be perhaps considered as a wholesale
this "144" is a total driver number per pair in a matrix of 6*6 drivers on the front and on the back of an enclosure giving a high Z bipole with drivers arranged in a kind of pseudoplanar rather then line array:
OOOOOO
OOOOOO
OOOOOO
OOOOOO
OOOOOO
OOOOOO
72*2*8 - a 1152 Ohm nominal impedance loudspeaker
an active response linearization of such a matrix would be necessary
the frequency response of the woofer somewhat degrades above around 5 kHz with resonance peaks
but perhaps this peaks can be somehow fixed (I mean to a adequate degree) with appropriate cone treatment
best,
graaf
well
as to this one:
http://www.tvm-valmez.cz/index.php?id=80&catit=73&l=1&catg=1
it's Qts is 1.13
so it is possible to make it a simple dipole, an 8*8 matrix giving a nominal impedance of 1024 Ohm
best,
graaf
as to this one:
http://www.tvm-valmez.cz/index.php?id=80&catit=73&l=1&catg=1
it's Qts is 1.13
so it is possible to make it a simple dipole, an 8*8 matrix giving a nominal impedance of 1024 Ohm
best,
graaf
AndrewT said:
Hi, Andrew:
I don't think spk term. could cause any fatal action!!! Don't you know on Public Address Systems, those Amp. have equipped 50V 70V and 100V line output. those are for far distance transfer without losing power. Especially designed by Maclintosh 225, 240 and 275 models.
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