Can't Reproduce a Square Wave.

roddyama

diyAudio Moderator Emeritus
2002-01-19 9:25 am
Michigan
I didn't mean to hijack a thread, so I started a new one.

How do you make a speaker output a square wave?


Quote from Bill Fitzpatrick
Now, tell me why YOU think I need to go digital and time delays to get a square wave.
Square wave. The fundamental frequency plus all odd order harmonics. Now this you can reproduce. What I can't see is how to reproduce the harmonics with their original phase relationship to the fundamental frequency with a multi-way system.

If you go active xovers to eliminate the the passive xovers, you still have the frequency dependent phase shift.

If you run bandpass boxes with no xovers, you still have frequency dependent phase shifts associated with the inductive and capacitive components of a speaker in a box.

It doesn't make sense to make a multiway system with full range drivers. That might get you close in the speakers bandpass, but the system wouldn't sound very good.

There is no reasonable way to eliminate the frequency dependent phase shifts of analog circuits.
The only way that I can think of is digital FIR filters and digital time delays to contend with variations in the acoustic centers of the drivers. Even then, I fear that the best you'll get is a rough approximation of the original square wave, but if this could result in a phase coherent reproduction of the leading edge of the square wave, I would be very happy with that.:D

ok? Did I miss anything?
Rodd Yamas***a
 

roddyama

diyAudio Moderator Emeritus
2002-01-19 9:25 am
Michigan
Hi F4ier,

Interesting read. John K indeed has ample knowledge on loudspeaker and how they work. He frequents the Madisound speaker forum. He's a very solid participant there. Unfortunately, he has not reproduced a square wave with his system. He has done a number of simulations. He has also reproduced an impulse of 0.1ms (20kHz). This is only the tweeter responding to a high transient input.

What he has not shown is a phase coherent response from the real speaker that includes a low frequency (<500Hz) fundamental + all odd order harmonics up to 20kHz.

Thanks for the reply.
Rodd Yamas***a
 
Hi Rodd,

Yup, that guy knows a lot about loudspeakers. Have you seen his prototype 2-way measurements? His square wave measurements can be found at http://www.geocities.com/kreskovs/CrossoverdocN2.html Though his prototypes may not be able to reproduce recognizable square waves accross a wide frequency spectrum, it is an achievement nonetheless; especially considering he uses analog components :)

He's bound to produce a digitally-filtered/EQd speaker set one of these days now that his favorite CAD program has digital design and simulation capability. Perhaps he'll produce a prototype out of curiosity :) We all know these things can easily be done in the digital domain, but where's the fun in that :D

Isaac
 
Hi Rodd

I don't believe that a perfect sqarewave will ever be reproduced by a loudspeaker either (apart from the non-existence of perfect sqare-waves in the real world). But it is possible to get closer to it than >95% of the speakers can.

From the versatility point-of-view an all digital active solution would be the best one (time response, possibility to equalize driver's responses etc).
By the use of automated test procedures it would even be possible tweak batch production speakers so they are almost like clones, performance-wise. But this would require a HUGE development effort and expensive production facilities.
Me personnally, I prefer analog filters.

To come to the point: Also an all digital solution wouldn't allow the reproduction of a real square-wave. To achieve this, a reproduction system must have a flat frequency response from 0 Hz to infinity, which doesn't exist in real life.

The closest thing one can build is a system of very high bandwidth (< 20 Hz up to > 40 kHz, 12dB/octave slopes !!) that has a reasonably flat amplitude AND phase response in between. I.e. whose crossover doesn't introduce any additional phase shift.
It's square wave response would still not look perfect, i.e. the rising and falling edges will not be infinitely steep and the top and the bottom will be tilted. But it's response to falling or rising edges does at least not look like a series of responses, starting with the tweeter's response and ending with the woofer's one.

Regards

Charles
 
Hi ALW

I agree with you that electrostatics are amongst the best ones in this respect* but I would still say that ABSOLUTELY NO speaker is capable to produce a real square-wave. I.e. a signal with infinitely fast rising and falling edges and horizontal top and bottom (I think you can imagine what I mean by this, I don't know the correct English terms for it) because this would ask for an FR fom DC to infinity which not even the best ESL will ever achieve.
But some speakers are indeed getting closer to it (ESLs, FRs, some active concepts...) and some less (mainly the classic multiway with crossovers of order 2 or higher).


Regards

Charles


*I am listening to the MSW FR transducer whose manufacturer also claims that it should be able to reproduce a square-wave.
 
yes - few if any speaker can reproduce a square wave. the problem lies with the physics of the issue. to reproduce a squeare wave one must have a very high acceleration factor (using dynamic drivers) that means a high BL and low Mms or Mmd. The speaker must also have very good braking. Now that is damn diffcult. lets look at Acceleration fctor only....

A high Bl/Mms ratio can be achieved within a narrow frequency band but over a band that for practical pruposes covers 30Hz to 24kHz it gets crazy esp. for lower frequenies.

make a driver with low Mms and the low frequencies suffer. Make a driver with high Mms and the highs suffer. XOs only make matters worse.

Braking factor means the magnet / motor are in absolute control all the time. It means the cone has negligile (if any) inertia. See the problem?

BTW why would one want to reproduce a square wave?

Regards
Navin
 

roddyama

diyAudio Moderator Emeritus
2002-01-19 9:25 am
Michigan
Hi Guys,

It's clear that there are no speakers of this earth that are going to reproduce a "perfect" square wave. It is, however reasonable to ask that we strive to make speakers that are phase coherent. Reproduction of the odd harmonics up to physically attainable frequencies is also a reachable goal.

My goal is to do this with a multi-way system. ESL's have their advantages, but they also have their shortcomings. Here's a (tongue-in-cheek) quote on a particular ESL from Tom Brennan over at the AA forum. "...Rube Goldberg contraptions in which wire is glued to a large sheet of kazoo diaphragm material. These wires are lined-up opposite arrays of refrigerator magnets and somehow the kazoo material moves.";)

Ok, it's a joke, but I couldn't resist.:joker: I just thought it was soo funny (Sorry Thatch:D).

Anyway, I would go with ribbons before I went with ESL's. The point being, I don't want to sit there listening to square waves any more then any of us do. I would like to hear the faithful reproduction of the hammer hitting a piano string at the low end of the scale, or a finger pluck of the string on a bass fiddle, or the strike of the hammer on the head of the kick drum. The common characteristic in all of these examples is the initial onset of the sound which is the sum of the fundamental + all the harmonics all starting at the same time; in a word, IMPACT. This is not impulse or transient. The first is a high frequency characteristic and the latter is a vague relative term. If we can faithfully reproduce the impact of a low frequency note with a multi-way system, then that system will be able to reproduce anything we want it to. We will have captured, as Bill puts it, speaker Holy Grail.

Now go chop down all the trees in the forest... with a... herring.:D
Rodd Yamas***a
 
roddyama said:
Here's a (tongue-in-cheek) quote on a particular ESL from Tom Brennan over at the AA forum. "...Rube Goldberg contraptions in which wire is glued to a large sheet of kazoo diaphragm material. These wires are lined-up opposite arrays of refrigerator magnets and somehow the kazoo material moves.";).... Anyway, I would go with ribbons before I went with ESL's.

That isn't a description on an ESL, it is a description of a magnetostat (specifically a magnepan) - ie most of the things people call ribbons (which are actually pusedo-ribbons) - real ribbons are few and far between, and i've yet to see a FR one.

dave
 

roddyama

diyAudio Moderator Emeritus
2002-01-19 9:25 am
Michigan
Hi Dave,

That isn't a description on an ESL, it is a description of a magnetostat (specifically a magnepan)
Yes, you are right, of course. I stand corrected. I let my comedic impulse get the best of me. Sorry.

...ie most of the things people call ribbons (which are actually pusedo-ribbons) - real ribbons are few and far between, and i've yet to see a FR one.
Now this has me wondering.:confused: Isn't a ribbon speaker a "ribbon" conductor/diaphragm in a magnetic field that is moved by this magnetic field acting on the signal current passing through the conductor/diaphragm??

If this is not true, what is a "real ribbon", and what is a "psuedo-ribbon"??:confused:
Rodd Yamas***a
 

lieven

Member
2002-08-11 4:42 pm
Belgium
square????

its fairly simple (at least that's what I think)

Apply DC, don't, apply dc, don't,......

That's the essential square wave, he?

others will say,

apply negative dc, apply positive dc, apply neg, apply pos,.....

ok, same result:

only thing you can hear is speaker going forward and back to rest position, or speaker going forward, backward, etc....

This is NOT sound, this is DC.... it's like an on-off-on-off, the 'sound' you hear is due to transient distortion. It isn't supposed to be there, but due to the slowlyness of the cones (less but also with electro-stats) this is generating a 'noise'.

Only thing a speaker does while receiving dc is that the coil is heating up, same thing that destroys speakers when amplifiers are clipping wich is in it's ultimate form: also a square wave....

Don't try to analyze it into odd harmonics and other blahblah, keep it simple, this is making a heating-resistor out of your loudspeakers, NOTHING ELSE.
While applying dc you have...... energy without motion..... this is ....heat.
Take this picture, what happens if you block any rotating motor???? it burns , yes??
awel this is the same but with a linear motor.

zij bracht rozen op gerrit's graf bij vies grijs weer....
 

lieven

Member
2002-08-11 4:42 pm
Belgium
sorry rod, was still editing previous message a bit.

but replying to your latest message, if you high-cut frequency, you don't have a perfect square wave anymore.

square wave is dc with interuptions, this means NO MOTION at the top, this means NO MOTION....... this means NO harmonics whatsoever (or a cancelation of harmonic waves etc.... but end result zero motion, nada motion, nothing, NO motion)!!!!

10-4-6=0
20-6-14=0

many ways, only one result ZERO motion.

...overall result ..... HEAT.