Class D audio amp driving long leads

** And are just as rare as I claimed.

All the rest are made with a simple spiral and it does not matter in practice.

** The shamefulness is in how carless you are with facts.

.... Phil

May be somewhat true of some tweeters,

** Only ribbon types.

One exception might be like the Bose 901s with the 0.9 ohm aluminum voice coils

** Aluminium wire makes a nice inductor, just like copper.

Only by adding a copper cap to the pole piece can the inductance of a voice coil be tamed.

** Nonsense. ** Usually is it 6 or 7 ohms of DC resistanc.

Nominal impedance is measured at 250 or 400Hz and is the lowest value in the operating range.

but be 100 ohms at higher operating frequencies. That is a bit on the high end of it, but not unheard of.

** The famous JBL2226 15 inch woofer is speced at 100ohms at 20kHz.

.... Phil

** Yep.

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 the winding buck itself somehow to lower the inductance.

** Nope.

** Never seen that and it would not buck inductance anyhow.

.... Phil

What are you on about. Its a coil, like so many coils, with a metal core. That's a coil.

NT

** You are making it worse.

The "coil" of a loudspeaker moves and so generates back emfs.

The "metal" is soft iron hence highly magnetic so inductance is large.

A WW resistor is merely a coil, a speaker is a motor.

.... Phil

Possibly EMI. Since the voice coil is close to the amp, it might also be part of the output filter. Adding wire puts an antenna in the middle. You can fix this with a couple of inductors on the output side of the amplifier (value dependant on switching frequency).

It should work with the above modification. Three is nothing magic about class-D amplifiers.

ound power resistor is the usual claim.

ll.

Wrong. It's those who argue with the unsupported claim who have chosen to t ake on that responsibility. I posted what was common knowledge in the UK ab out thirty years ago. I've not done any measurements myself, but the guys I was quoting had. It struck me as relevant information, and you've yet to p ersuade me (or probably anybody else) that it was misleading.

I don't have to.

t of that job interview.

Seems unlikely.

The suggestions are that you aren't an employee and haven't been one for a long time, so the number of applications may be limited.

u claim someone has committed it,

n ample demonstration already.

So you aren't interest in the kind of electronics where I've got patents an d published articles in peer-reviewed journals. I even got a couple of tech nical letters published in the old HiFi News and Record Review. No surprise there.

Piss off cantankerous Johny One-Note.

--
Bill Sloman, Sydney

so?

so?

so?

Its wound as a coil. Simple fact. As I said. The speaker winding is a coil. Excepting things like ribbon tweeters, electrostatics, piezos etc.

NT

:

just shield it a bit for the FCC and make use of the inductance of the spea ker. Less filtering. Actually probably even more efficiency.

power resistor is the usual claim.

speakers as just a coil. Moving coil speaker impedance rises noticeably wit h frequency, at least in the top half of frequency range. Zobel networks ar e used to counter this rise into inductive impedance. Unless I'm mistaken.

A Zobel network presents a resistive load to an amplifier at high frequenci es. It's designed to decouple the amplifier from the capacitative part of t he impedance of the loud-speaker and it's leads. Paired loudspeaker leads c an contribute about 50pF of capacitor loading per metre of cable.

Some wire-wound resistors are wound to be "non-inductive" - which is to say , less inductive - and they cost more than regular wirewound resistors, bec ause they are more trouble to make.

I wasn't saying that speaker coils were non-inductive, just that their indu ctance isn't high, and not high enough to make them all that useful in bloc king the high-frequency content of class-D PWM waveform.

--
Bill Sloman, Sydney

e. That's a coil.

But not all that much.

But the core doesn't fill the coil's magnetic path, and the iron-free gap is quite large. The inductance of a loudspeaker coil may be higher when it is located within the speaker's magnetic structure than it is in free air, but it's unlikely to be all that much bigger - I wouldn't expect more than a factor of two

A speaker is a very inefficient motor. I've occasionally wondered why nobod y has built a speaker based on a linear synchronous motor - which can provi de reasonable efficiency and essentially constant driving force over most o f it's travel - but the answer seems to be that nobody needs all that much power from a loudspeaker, and it's cheaper to build a higher-powered driver than a more efficient transducer.

--
Bill Sloman, Sydney

** No you are 100% WRONG and stupid. The "burden of proof" IS with the claimant.

** Another blatant lie.

The folk at Quad would have laughed out loud if you came out with such crap at the interview.

** Go ahead - look like an utter ass.

You do all the time anyway.

.... Phil

** Your f****it post was misleading.

Wrong on each point. As bloody usual.

.... Phil

nd power resistor is the usual claim.

** Idiotic.

l speakers as just a coil. Moving coil speaker impedance rises noticeably w ith 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 .

cies. It's designed to decouple the amplifier from the capacitative part of the i mpedance of the loud-speaker and it's leads.

** Amplifier "Zobels" do that - but have small inductors in them along with R and C elements.

Simple RC Zobels are often used across woofer, mids and tweeters to counter inductance and make x-over networks behave as intended.

Which is what the OP alluded to.

... Phil

its a simple fact that moving coil speakers are wound as a coil. Your response is as ever abusive and antisocial. Get over your problems Phil, honestly, its not helping you enjoy your life or achieve your goals any.

NT

** At resonance, the effect is enough to raise the impedance by factor of 5 to 10 times. That's plenty.

.... Phil

It might be in a court of law. This is an informal discussion group, and unsubstantiated opinions get thrown in pretty regularly.

How would you know? I can only speak about the places in the UK where I worked, but it was true of them.

Of course. At job interviews you aren't in the business of being helpful, but in the business of looking ultra-competent.

Your example isn't one I'm tempted to follow.

You may think so. That's your right. There's no guarantee that your opinion will be widely shared - krw does seem to, which doesn't exactly worry me.

--
Bill Sloman, Sydney

Bill Slowman:

** Also true of debates and discsusions.

** You cannot show it was common knowledge cos it never was. ** Then you have nothing at all. ** Wot a lying moron.

.... Phil

ound power resistor is the usual claim.

oil speakers as just a coil. Moving coil speaker impedance rises noticeably with frequency, at least in the top half of frequency range. Zobel network s are used to counter this rise into inductive impedance. Unless I'm mistak en.

encies.

impedance of the loud-speaker and it's leads.

th R and C elements.

er inductance and make x-over networks behave as intended.

The classic hifi Zobel was a big 10R resistor with some thickish wire wound around it to make about 1uH of inductance. It doesn't "counter" inductance because it's own inductance is too small, but it does decouple a capacitat ive load.

Audio frequency designers used them because they worked. Few of them knew w hy.

--
Bill Sloman, Sydney

If your enclosure isn't damped - some cheap boom boxes aren't but they sound pretty horrible.

It's not going to be relevant to radiation from an unfiltered class-D drive, which is modulated at much higher frequencies than a speaker's air-resonance.

--
Bill Sloman, Sydney