Quick question

Resistors convert current to voltage, these figures suggest to me that the difference between current drive and voltage drive is about 1/400 (or about -32dB)

it does, only after you compensate for coil resistance, eg: build an amp with negative resistance to compensate (probably not a good idea, a small offset voltage would detonate your speakers or amp)

A carefully chosen ferrite bead in the base of the upper device is usually all you need, along with good bypassing, shield cans, and avoiding long traces (even bypassed ones) with no series impedance.

Cheers

Phil Hobbs

If the speaker had a hi-z resonance it wouldn't make the slightest difference to a current drive, which would force exactly the same current through the coil as at any other frequency (if it could apply enough volts across the coil).

Quite where this high-z resonance would come from is an interesting question. Loudspeakers are notoriously inefficient so it won't be anything acoustic, and the voice coil's inductance is generally swamped by its resistance.

it is acoustic

and in a bass reflex box you can clearly see the two resonances, the driver and the port

-Lasse

I've heard Audio Experts say, "There is no need to mention Scientific proof of quality, when the end result must satisfy my ears."

Interesting articles and references in your other posting. Thanks for posting the URLs.

My ear is pretty good. Being trained from prenatal age, your brain tends to make those neural connections that then haunt you the rest of your life. Especially listening to highly accoladed singers, that to me sound like fingernails down a blackboard. Or, hear a concert piano pulled out of tuning during the initial performance as van Cliburn 'destroyed' the strings. Yes, they restrung the treble end of the piano when he left. [Even using that bashed grand, he was incredible.]

You have much more access to articles than I, did you find any 'blind' listening tests comparing speaker sets driven with current vs voltage drives?

I've read a lot of descriptions of tests done comparing orchestral performances to speaker sets, perhaps those same people expanded to include the drive comparison. [I read the articles and their test procedures, which were impressively controlling to make certain the results were comparing apples to apples, perhaps done by speaker manufacturers? Audio Society? don't recall]

For what it's worth, I changed the stepper motor design from a voltage drive at high speed, and current drive at stop, to more of a constant power into the motor, with a 'tail down' of power when you know the motor has been asked to stop and now is likely to be stopped. Worked well enough, so project done.

Has anybody compared speaker perfomance when using voltage drive, current drive, and POWER drive? It would seem that POWER drive would accomplish the best attributes of all drives. To restate, the idea is that one has power in the audio drivers that they want to transfer into power in the air, therefore 'constant' power drive would do that and ignore all those pesky problems, hmmm except for the spiking resistive losses in the coil, which should be easy to remove. Didn't the Hall brothers of Velodyne of Sunnyvale, CA [now of Morgan Hill, CA] make the world's best woofers by winding an extra coil on the speaker and monitoring that, plus doing excessively complicated non-linear corrections? I didn't really follow speakers, sound systems, etc. because they all sound so bad to me.

I have no way to effectively search for articles/references of 'listening' tests, so hope you find some. Perhaps, Erland Unruh, who is a strong supporter of tube amplifiers for producing high quality sound, may know of some tests, or performed them himself. [he wrote the article on the improvement of CD sound quality by reclocking the sound to remove clock jitter]

Very interesting discussion here, hope it continues a bit more.

Yes. A low-Z drive damps acoustic and mechanical resonances, and a constant-current drive emphasizes them.

A loud speaker Spice model is horribly complex. See...

LoudSpeakerSpiceModel.pdf

on the S.E.D/Schematics page of my website. ...Jim Thompson

That's because he was a Doctor, not an engineer, Jim.

Kevin Aylward B.Sc.

"Jim" ?? 'Tweren't me, it was "John" who said that. ...Jim Thompson

On Wednesday, 2 July 2014 00:18:22 UTC+10, Lasse Langwadt Christensen wrot e:

ll force more power into the speaker, making a boom peak at that frequency .

erence to a current drive, which would force exactly the same current thro ugh the coil as at any other frequency (if it could apply enough volts acro ss the coil).

stion.

ic, and the voice coil's inductance is generally swamped by its resistance.

er and the port.

The example shown is scarcely high-z - the peak impedance isn't quite three time the 10R resistive impedance, and IIRR that sort of boost isn't so muc h a "boom peak" as stretching the speaker's low frequency response below th e natural limit imposed by the speaker diameter.

In any event, a speaker designed for current drive would have a differently shaped frequency response.

That's the subjectivist heresy aka the golden-eared boys.

Peter Baxandall was on the objectivist side, and had rather better evidence.

ill force more power into the speaker, making a boom peak at that frequenc y.

ference to a current drive, which would force exactly the same current thr ough the coil as at any other frequency (if it could apply enough volts acr oss the coil).

estion.

tic, and the voice coil's inductance is generally swamped by its resistance .

ver and the port

nt-current drive emphasizes them.

A low-Z voltage drive puts less drive current into the coil at resonance, w hich isn't exactly damping the resonance, while a current drive ignores it

- which isn't emphasising it.

The sort of speaker housings that produce perceptible resonances are in fac t shaping the frequency response of the transducer to extends it's - more o r less - frequency independent range. If you are playing that kind of trick , you play a slightly different trick if you are designing for a current dr ive rather than a voltage drive.

Talking about "damping ratio's" is the sort of rubbish one reads in down-ma rket audio periodicals, shortly before putting them back on the rack.

I caught it as an old Star Trek reference. deforest kelly was constantly saying that. or at least attributed to him.

I was never into Star Trek, so it went right over my head. ...Jim Thompson

I understand the concept of, "Who died and left them boss?"

but a good scientist always remembers that science DESCRIBES what we observe, not DEFINE it.

when science starts defining/shaping what we're supposed to see it becomes a bit useless.

but you knew that already.

I'm still locked in the 'water witching' controversy. and a more modern example, there is treasure hunter instrumentation selling for $10k to $15k that I can only describe as a different form of 'water witching'. Scientifically, not much justification, but may tap into something inside the human that indeed makes it work. So...I'm open.

Another, but old example, back when CA first started their lottery, I wrote a very complex BASIC program to predict lottery numbers. It was too difficult to write all the code, so required a great deal of interaction as you ran it. Using it, I statistically 'broke even' not winning much, not losing much, with the obvious potential of one big win. Was this scientifically supported, NO WAY! But, the program did work. I broke even for about a year, until they increased the numbers by four, then I was only getting about 1% return, Seems nobody liked that, so they took away two numbers, and left it there. Sadly, then I was getting only 10% return, not enough to keep me in it. I attributed the breaking even to a form of 'water witching' with my program, you somehow got a human involved and things act a bit differently.

Back to audio. I sometimes 'liked' what I was supposed to like and sometimes didn't like what I was not supposed to like, but the correlation was pretty loose. Hearing is one of the MOST complex psychologically linked senses with more nerves FROM the brain to the ear than nerves from the ear TO the brain. Who would design a system like that?! So, to 'satisfy' a system like that it seems unlikely to me that a simple, straight forward scientific proof that THIS sound production is better than THAT sound production will hold up under close 'subjective' scrutiny. anyway my two cents.

I got in a _big_ argument with my first boss' wife, when I declared that art was good only if _I_ liked it. ...Jim Thompson

Take a look at a typical driver's impedance curve:

This is an "8-ohm nominal" woofer. The impedance is around 8 ohms through much of the useful bandpass (e.g. 100 to 2000 Hz), and rises to above 32 ohms at 50 Hz (which is approximately the F3 frequency of the driver when used in one of the suggested vented-cabinet alignments).

If you fed this driver using a current-drive system, I would expect that you'd see a big bump in the SPL graph at around 50 Hz, as the power delivered into the driver would roughly quadruple at resonance.

You'll see a similar resonant impedance peak in the graps for midranges and tweeters as well.

LOL! Wrong! Art is what THEY like, wait, am I the only one to see a correlary here?

I'm back to "Who died and left them boss?"

I remember back when Reagan wanted to pull all the 'art' funding, was I against that! I bought into that adage the poor artist needs to be supported by the government, and it was ok for expert panels to decide where the funding goes to ensure quality etc with the idea that govt funding of art would bring art more into the community since there was no real fair market way otherwise, yep I bought that crap!

After he pulled the funding, I never saw so many 'artists' show up with their hands out for funding! Didn't even know 90% of them existed! Plus, these artists started becoming 'responsive' to the community's tastes and there were no longer art showings consisting of stacking glass blocks on top of each other, pouring sand around on them, and declaring THAT art.

So in response to the govt stopping spending of the arts, artists made the communities aware of themselves AND the quality of art improved, both of the stated goals of the govt funding! In other words, funding actually prevented the two stated goals from ever happening! In reality, two worthwhile goals were achieved by NOT funding!

So now I completely back the concept of getting the govt out of EVERYTHING! They only muck it up.