Here's Mr. Watkins explanation of his invention:
"Trevor, I believe it's time I explained what happened
here. My dual-drive woofer works so:
A second voice coil (vc-2) is wound over the main voice
coil (vc-1) in the woofer, this second coil having a
single layer and very low impedance. Now vc-2 would
normally have an impedance too low for safe operation.
However around fundamental resonance the impedance of
_any_ coil will ~triple. Now we activate vc-2 _ONLY_
in the region of fundamental resonance (around 45 Hz)
and it rises to ~8 ohms or so (being ~2.5 in the
first place) which is safe. This is accomplished with
an LC circuit tuned to 45 HZ and with the Q of the LC
circuit adjusted to provide the response shape and
impedance desired. Please note that the exact value
of vc-2 and the characteristics of the LC circuit give
_COMPLETE_ control of the impedance. The benefit of
the dual-drive may then be taken in extended bass or
higher efficiency in a given size box, or a smaller
box for a given efficiency or bass extension.
Now I set the parameters of the original QLS-1 in a
prototype and shipped it to Infinity. It had a minimum
impedance of 3.2 ohms, acceptable for a 4 ohm speaker.
At that time we were operating a retail store selling
Infinity. Our first shipment of the QLS-1's arrived,
we tested a pair and found the impedance to be
~1 3/4 ohms from ~50 - 80 HZ. Now, the fun begins...
Mr. Nudell wanted a spec down to 20 HZ, he got to
18, as I recall, by adding ~35 grams of mass under
the dust cap, _BUT_ he did not re-tune LC to the
lower resonant frequency, leaving vc-2 operating
somewhat above the new fundamental resonance, and
creating a low impedance in that area. My name
was already on the royalty agreement, which had no
stipulation to cover such... I did voice my
disapproval to no avail.
If you check, you will find our WE-1, built and
marketed by _my_ company had no impedance problems,
and neither did thousands of other speakers we
built have any impedance problems. Perhaps this
makes things clear for the technical people here.
Bill Watkins "
"Trevor, I believe it's time I explained what happened
here. My dual-drive woofer works so:
A second voice coil (vc-2) is wound over the main voice
coil (vc-1) in the woofer, this second coil having a
single layer and very low impedance. Now vc-2 would
normally have an impedance too low for safe operation.
However around fundamental resonance the impedance of
_any_ coil will ~triple. Now we activate vc-2 _ONLY_
in the region of fundamental resonance (around 45 Hz)
and it rises to ~8 ohms or so (being ~2.5 in the
first place) which is safe. This is accomplished with
an LC circuit tuned to 45 HZ and with the Q of the LC
circuit adjusted to provide the response shape and
impedance desired. Please note that the exact value
of vc-2 and the characteristics of the LC circuit give
_COMPLETE_ control of the impedance. The benefit of
the dual-drive may then be taken in extended bass or
higher efficiency in a given size box, or a smaller
box for a given efficiency or bass extension.
Now I set the parameters of the original QLS-1 in a
prototype and shipped it to Infinity. It had a minimum
impedance of 3.2 ohms, acceptable for a 4 ohm speaker.
At that time we were operating a retail store selling
Infinity. Our first shipment of the QLS-1's arrived,
we tested a pair and found the impedance to be
~1 3/4 ohms from ~50 - 80 HZ. Now, the fun begins...
Mr. Nudell wanted a spec down to 20 HZ, he got to
18, as I recall, by adding ~35 grams of mass under
the dust cap, _BUT_ he did not re-tune LC to the
lower resonant frequency, leaving vc-2 operating
somewhat above the new fundamental resonance, and
creating a low impedance in that area. My name
was already on the royalty agreement, which had no
stipulation to cover such... I did voice my
disapproval to no avail.
If you check, you will find our WE-1, built and
marketed by _my_ company had no impedance problems,
and neither did thousands of other speakers we
built have any impedance problems. Perhaps this
makes things clear for the technical people here.
Bill Watkins "
I didn't mean it like that. What I meant was that I can't see any other way of doing it passively. In other words, I'm not that smart or experienced.
If you're NOT using a separate subamp, then there really isn't much way to highpass the satellites without staying passive speaker level.
One could of course build a TL to smooth the impedance spike, allowing a more normal highpass to do the job.
That's interesting, thanks.
In the old days, there was a rumble filter switch on the amp. I suppose this was at line level, as you describe.
Hi,
Fair enough, but that wan't in the link posted.
I accept a very low impedance secondary winding (rather than
typical dual equal impedance coils) will give almost complete
control of the drivers impedance peak and its effective Q,
but not remotely in the way implied above, allowing any
current in the secondary coil will reduce Qts and sharpen,
not reduce, the impedance peak of the driver.
High Q drivers have low impedance peaks, low Q high.
The arrangement, though it sounds like it should, cannot
cancel the drivers impedance peak, only make it sharper.
I don't accept the usual marketing guff that the laws of physics
have been rewritten, they haven't, as they never can be.
These things tend to end up as you could simply make a driver
with equivalent parameters, here I'm not sure what is going on.
rgds, sreten.
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What happens here is that one voice coil has a lower xover point than the other VC. The same could be accomplished electrically; it is exactly the thing Linkwitz does to extend the bass response. It is not the same as putting a notch on the Fs of the driver (which just makes no sense in mho).
vac
Hi, there is a huge difference between actual facts and BS pseudo-technical marketing claims, rgds, sreten.
Gentlemen, choose your weapons...
dirkwright:
In your first post, you talk about a "series RLC filter".
Is your RLC filter connected across the driver (in parallel with the driver), or in series with the driver (between the driver and the amplifier)?
sreten and others appear to be assuming that the network is in parallel with the driver. If it is really in series with it, then we need to clear our assumptions and start again.
dirkwright:
In your first post, you talk about a "series RLC filter".
Is your RLC filter connected across the driver (in parallel with the driver), or in series with the driver (between the driver and the amplifier)?
sreten and others appear to be assuming that the network is in parallel with the driver. If it is really in series with it, then we need to clear our assumptions and start again.
Hi,
Its a series RLC connected across the driver in parallel.
For other purposes you can connect a parallel RLC in series with the driver.
Series is :
in - R - L - C - out
Parallel is :
.... | - R - |
in - | - L - | - out
.... | - C - |
rgds, sreten.
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OK, then:
Connect a driver (woofer) to a normal (low impedance output) amplifier. It will exhibit an impedance peak at its resonant frequency. Connecting a correctly calculated RLC network across the driver will compensate for that peak. This is true, but it is irrelevant in most cases. The output of the driver will be unchanged, because the RLC network is shorted out by the amplifier's (effectively) zero output impedance. The amplifier will notice that the impedance curve has been "flattened", but the only practical result of this is that the amplifier will work a bit harder, heating up the RLC network.
Even if the driver (woofer) is being driven via a crossover, the crossover's impedance is normally very low at the frequency of the resonant peak. Again, the RLC network is effectively "short circuited".
It might make sense to use such an RLC network for a midrange or tweeter. Their resonant frequencies often fall close to the crossover point, where the impedance of the crossover is increasing. You might do this in order to make a driver work correctly with a crossover which was designed for an ideal, constant impedance driver.
In practice, it doesn't make sense to build a crossover for ideal drivers and then add components to make the real-world, imperfect drivers work with it. What normally happens is that the crossover component values are adjusted to compensate for the less-than-ideal drivers. In other words, instead of adding RLC networks to compensate for the peaks, just alter the RLC values in the crossover to compensate for the peaks.
Regarding the Infinity woofer driver, they use LC networks to modify the response of the driver. The impedance of the networks is placed in series with each voice coil, not in parallel.
Does anyone have any disagreement with any of the above?
Connect a driver (woofer) to a normal (low impedance output) amplifier. It will exhibit an impedance peak at its resonant frequency. Connecting a correctly calculated RLC network across the driver will compensate for that peak. This is true, but it is irrelevant in most cases. The output of the driver will be unchanged, because the RLC network is shorted out by the amplifier's (effectively) zero output impedance. The amplifier will notice that the impedance curve has been "flattened", but the only practical result of this is that the amplifier will work a bit harder, heating up the RLC network.
Even if the driver (woofer) is being driven via a crossover, the crossover's impedance is normally very low at the frequency of the resonant peak. Again, the RLC network is effectively "short circuited".
It might make sense to use such an RLC network for a midrange or tweeter. Their resonant frequencies often fall close to the crossover point, where the impedance of the crossover is increasing. You might do this in order to make a driver work correctly with a crossover which was designed for an ideal, constant impedance driver.
In practice, it doesn't make sense to build a crossover for ideal drivers and then add components to make the real-world, imperfect drivers work with it. What normally happens is that the crossover component values are adjusted to compensate for the less-than-ideal drivers. In other words, instead of adding RLC networks to compensate for the peaks, just alter the RLC values in the crossover to compensate for the peaks.
Regarding the Infinity woofer driver, they use LC networks to modify the response of the driver. The impedance of the networks is placed in series with each voice coil, not in parallel.
Does anyone have any disagreement with any of the above?
Yes, that's basically it. As I mentioned in the first post, I wanted to know if it was useful and why. I didn't want to be lectured, berated, or talked down to about this idea. I had a simple misunderstanding about correcting the impedance phase shift at woofer resonance and the acoustical response of the driver.
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