Hi,
My network speakers use a class D (audio) amp to drive the
*attached* speaker elements. Key word is *attached* (i.e., amp is integrated with the speaker, effectively).In one instance, I need to drive some lengths of zip cord to a pair of speakers ~30 (electrical) ft removed from the electronics. What sort of problems am I likely to encounter and suggested remedies?
Am I better off eliding the class D amp in that instance in favor of an alternative approach?
Depends on how Fing cheap it is.
Speaker coils are inductive, so in cheaper, embedded amps they might just s hield it a bit for the FCC and make use of the inductance os the speaker. L ess filtering. Actually probably even more efficiency.
I myself have considered BTL PWM like a class D that would keep the RF down ust by being balanced. It can probably be done and it probably has. Imagin e if you have a 100 kHz class D running a subwoofer that can only produce u p to about 2 kHz at best.
Mom's TV broe down the other year and she borrowed a new elcheapo TV which had no audio outputs. I culd have taken it apart and hooked her audio syste m to the speaker wires but I did not want to do that because there could be too much hash on it. The reason here is that there is nop remote volume on the amp, and to my surprise they no longer put that feature in cbale or sa t boxes.
Less is more.
I would stick a scope on it and see what it is running at. Four coils and t wo capacitors later you got nothing to worry about. If you cannot tell the frequency by the scope (or a freq counter) from the speaker leads themselve s you got nothing to worry about.
This hundred kHz shit is no joke sometimes. I got an amp oscillating at tha t right now I gotta fix. Peixo tweeters would kill that amp, but that amp m ight kill dynamic tweeters. Either way, you do not want that. And you don't want that HF hash in the air.
Actually if you have a turntable that could be REALLY bad.
Gotta see how they are, gotta throw a scope on them.
Speakers aren't all that inductive - about as inductive as a wire-wound power resistor is the usual claim.
Putting the class-D modulation directly onto the speaker leads would probably screw AM radio reception over an inconveniently large area.
If the OP is worried he should probably twist his speaker leads - anything more than one turn per cm would probably be plenty.
-- Bill Sloman, Sydney
** While Da Slowman autistic retard is about as *sharp* as bowling ball.
The idiotic claim made above could hardly be more wrong.
FYI:
Little wonder the technical folk at "Acoustical" laughed him right out of that job interview.
What a stinking fraud & moronic AGW freak.
... Phil
st shield it a bit for the FCC and make use of the inductance of the speake r. Less filtering. Actually probably even more efficiency.
ower resistor is the usual claim.
Resistors are wound as a coiled U shape to avoid inductance, moving coil sp eakers as just a coil. Moving coil speaker impedance rises noticeably with frequency, at least in the top half of frequency range. Zobel networks are used to counter this rise into inductive impedance. Unless I'm mistaken.
NT
But Phil Allison hasn't bothered producing inductance, resistance and (electrical) self-resonance figures for any particular driver unit, which would part of the rational process of demonstrating that the claim was in error.
They didn't. It was all civil enough, but I didn't get the job. Phil may have got every job he ever applied for, but most of us get more job interviews than we get job offers, and not all that many of either.
Phil hasn't yet worked out that you have to demonstrate fraud before you claim someone has committed it, if you expect to be taken seriously. His electronic expertise is respectable, but his self-presentation doesn't really do it justice.
-- Bill Sloman, Sydney
** About one in 100 million are done that way.
moving coil speakers as just a coil.
** Shame about the iron core.Moving coil speaker impedance rises noticeably with frequency, at least in the top half of frequency range. Zobel networks are used to counter this rise into inductive impedance. Unless I'm mistaken.
** Not at all, the Z of ordinary speakers rise from about 1kHz up at the rate of 50% for each octave..... Phil
** Those who make unsupported claims get to prove them. And you have no way of proving the stupid shit you just posted. ** After you left the room, I bet they pissed themselves.
** As matter of fact - I have. ** Da Slowman has not worked out that HE has provided us with far more than ample demonstration already. Be funny, if it were not so pathetic.
Piss off fool.
... Phil
What are you worried about Don? I guess 30' of cable capacitance could short out some of the signal... any idea of the switching frequency?
George H.
Noninductives are bifilar as described, or ayrton-perry winding pattern. Basic coil wound is cheaper of course.
I dont see anything shameful about it
NT
I did this calculation once for a switching amp driving a motor, and found that the contribution of the cable as a transmission line was minimal as long as it was a short fraction of a wavelength at the switching frequency. I suspect the answer is the same for a speaker.
If you're still concerned you can put an LC filter at the amp. If there's already an LC filter at the amp -- stop worrying!
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
It might radiate a lot of EMI, if the amp doesn't have good output filtering. If that happens, and is a problem, use shielded twisted-pair cable or add some filtering at the amp output.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
ower >resistor is the usual claim. "
Very very wrong on that one. May be somewhat true of some tweeters, but not in general. One exception might be like the Bose 901s with the 0.9 ohm alu minum voice coils but in general they are inductive.
In fact when it comes to woofers more inductance is usually desirable becau se it causes more cone excursion per volt at lower frequency. That can be u sed to compenste for the rolloff caused by the cone's smallness in relation to the size of the waves produced.
An eight ohm woofer could have a DC resistance of 4 ohms, but be 100 ohms a t higher operating frequencies. That is a bit on the high end of it, but no t unheard of.
That is inductive.
You can get that from most speaker manufacturers and dealers website. Look up small Theile parameters.
Really. I can understand that the wires are really thin and the inductance is small compared to the DC resistance, but I thought they at least made th e winding buck itself somehow to lower the inductance. Not a U shape but ju st reversing the winding on top of itself somehow.
I remember ordering non-inductive wirewound power resistors in the past. Yo u don't need them all the time. In a power supply dropping or ballast appli cation, that is what capacitors are for. Takes care of it.
But I think in the past they were a little less uncommon. I see how that is simply not all that needed today.
I am at about 95 %, but that includes other fields as well. Like I applied for a job at the railroad and didn't get it.
In fact I could say I got more jobs than I have applied for. I didn't fill out anything for the last three. One time, a long time ago I went to work f or Wellman and Griffith, a super high end Sony dealer (Signature I think th ey call it) and I had been affiliated with them through other means, one o f which was buying their catoffs and selling them in the city after fixing them. We used to kjoke around and call my place "Ghetto TV". They said I sh ould rename the shop that. I did not take that "advice".
But the point is not on,y did I not fill anything out, I worked and then pa yday rolled around and they came and said, we're sorry you don't have a pay check, you don't have a paycheck because WE DON'T KNOW YOUR LAST NAME !
So if you add in the jobs I got without actually officially applying for th em as pluses, they would cancel out the ones I didn't get by quite a bit. I would have to really think about it but I probably have gotten more jobs t han I have applied for. (umm, grammar police, if you have a better way to e nd that sentence please adise)
Yes BUT...
All that capacitance might be detrimental to the health of a class D amplifier.
I think just take a scope to it and find out how bad it is.
Dude, you a re just a pill.
Actually, full range drivers are much less inductive than the run of the mill woofers and midranges. But still a hell of alot more than a wirewound resistor.
At roughly 15 pF per foot, I doubt that the amp would notice the zip cord.
A long zip cord can have enough inductance to, in theory, roll off the HF response of the speaker a tad. In practice, nobody would notice.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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