Why are the diaphragms of pro woofers always made of paper?

[Ant_222]

The diaphragms must be firm and light. Hence the conical form (firmness) and use of paper mass (lightness). It's extremely difficult to move something heavier at high acceleration.

Acceleration is proportional to square of frequency, so

ACCmax=Xmax*(Freq*2Pi)^2 — very high, where Xmax is a function of Frequency, of course.

[noah katz]

Not that it matters, but I meant to say "sat next to a speaker designer on a plane flight".

[mrshow4u]

Of the best subwoofer systems I've ever heard, most had paper cones. I don't know if the cause was the driver, or the implementation. Most of the systems where the bass was very good, I didn't even know they were paper cones. I only found out after the good listening experience. Lot's of variables with subs. Placement, room, driver, box, etc. I don't know what Velodyne uses in their Servo'd subs (paper/plastic) , but they work pretty well (for a small box, not screaming SPL). Has anybody done THD sweeps on paper vs. plastic? Maybe transient response?

[sardonx]

just ran into this thread and thought i'd bump it...


When it comes to woofers I've always thought that paper sounds the most natural and balanced. And i wouldn't agree that it's the cheapest either, as i understand there is always consistency problems, hence, a lot of throwaways.

Of course, everyone will agree that every material has a signature sound, some 'high tech'(rigid, piston like) materials sound more alike than different from eachother (IMO). To me, metals reproduce the initial transients more accurately (bells, cymbals esp) and on some recordings is top notch but on a lot of other stuff is lifeless. But I listen to a wide variety of music and find the signature of paper to be the least offense and most 'musical', dare i say, of all!

Could this be because wood is a natural material which has been used to make instruments since the dawn of mankind and its acoustic properties are genetically rooted in us as pleasurable?

just some thoughts!

[Original Burnedfingers]

Having used Pro drivers in commercial systems I can tell you they are tough and deliver the efficiency that you won't find with the bargin subwoofers. The electrical parameters have a lot to do with it. Oh, forget about trying to repair in the field as it isn't done in commercial applications. Maybe this has been tried in the DJ set. Just for S's & G's look up the specifications on a Altec,EV,or JBL driver and you will see the efficiency is there but so is the price.
You get what you pay for....

Heavy cones generally sound differently than paper. Yes, I am still a believer that larger drivers just don't sound as punchy as the 15's or 12's do.

[phase_accurate]

Could this be because wood is a natural material which has been used to make instruments since the dawn of mankind and its acoustic properties are genetically rooted in us as pleasurable?

Or maybe because wood is a natural material that is intended to be used as construction material right from the start. It is not just used by humans as such it IS a very sophisticated construction material !

Regards

Charles

[Baseballbat]

Regarding the material sound:

in the german HiFi-Forum (DIY area) we developed a theory about this issue.

This picture http://img339.imageshack.us/my.php?image=csdk1k3km2.png shows an overlay of two waterfall plots, the red one the fundamental wave, the green one the 3rd harmonic distortion raised 40dB. The speaker is an ALR Jordan Entry2M, a 2-way with aluminium woofer and fabric dome. The measurement was quasi-anechoic, SPL approximately 90dB.

The woofer has a cone resonance at 5kHz, leading to a high K3 (less than 40dB below K1 => >1%) at 1.6kHz, even with a crossover which contains a notch filter at 5kHz. This can be seen in every HD-measurements, and every cone material which causes a resonance has this issue.

The difference between metal and other (soft) materials is that the metal cone resonance decays very slow, and so does the K3 - but at 1/3 of the real resonance.

After two periods (look at the y axis, it is in periods, not in milliseconds), K1 has decayed down to -25dB, where K3 is still at -10dB. This means, after a short time K3 is not -40dB but -25dB below K1.

Out theory is that this is audible. We suspect the same slow decay for IMD products, but until now I have not measured it (getting an impulse response of IMD products is quite tricky).

You do not need to measure the decay of K3, you can also predict its behaviour with a standard CSD an HD measurement. If you see a CSD with a slow decaying resonance and a HD peak, you can be sure that this driver will sound like a bicycle bell.

Greets
Baseballbatboy

[Pit Hinder]

Originally posted by phase_accurate


Or maybe because wood is a natural material that is intended to be used as construction material right from the start. It is not just used by humans as such it IS a very sophisticated construction material !

Regards

Charles

Charles,
we might be getting somewhere, if from different angles. Our senses are, after all, highly sophisticated survival instruments evolution has refined over millions of years and hardwired into our brains - only, spoiled as we are, when our senses try to signal us "this sounds/tastes/looks/feels unfamiliar and might be dangerous" we dont recognise it as a warning, we just don't like it.
Now compare the bandwidths HiFi vs. PA drivers have to cover. In HiFi a 12" is bass only, while in PA it's a midrange - little wonder the resonance spectrum of a "boutique" cone makes you want to

OK, just my two cents. As usual, it's rather a gut feeling than a scientifically solid theory.

Pit

[phase_accurate]

The difference between metal and other (soft) materials is that the metal cone resonance decays very slow, and so does the K3 - but at 1/3 of the real resonance.

I was aware of the "exagerating" of the harmonics due to resonant peaks. I didn't think about the temporal behaviour of the distortion products so far. This is indeed an intersting view.

Another way of looking at the problem is that the motor of drivers with very hard cones has to be more linear than the motor of a paper-cone driver in order to have any advantage at all.

Now compare the bandwidths HiFi vs. PA drivers have to cover. In HiFi a 12" is bass only, while in PA it's a midrange - little wonder the resonance spectrum of a "boutique" cone makes you want to

One just has to watch out not to use PA drivers too high. Most P.A. drivers only excel over Hi-Fi ones in home applications (in terms of dynamics and distortion) when they aren't used the same way as in a PA.

Regards

Charles

[Baseballbat]

Originally posted by phase_accurate
Another way of looking at the problem is that the motor of drivers with very hard cones has to be more linear than the motor of a paper-cone driver in order to have any advantage at all.

Yes, of course. These HD peaks are highly related to the linearity of the motor. If the driver's motor in that box wouldn't produce significant distortion at 1.6kHz there would be no problem. A positive example of this is the Visaton AL130 ( http://www.visaton.de/en/chassis_zub...n/al130_8.html ). Look at the CSD plot on that page. There is a resonance with a very high Q, but the HD is below 0.3%@90dB at the expected frequencies (measurement taken by the german magazine Klang&Ton). There is a peak, but very low.

Greets
Baseballbatboy

BTW, in Germany we say K1, K2, K3, ... for the 1st (fundamental), 2nd, 3rd,... harmonic. Is this the right term in English? Or must I say something like HD1, HD2, ... I can remember that I have seen such notation.