Do Exotic Cone Materials Affect the Sound of Loudspeakers?

[gene]

Tonight at 10pm EST, we release a live premier YT interview with Shane Rich from RBH Sound answering the question: Do Exotic Materials Affect the Sound of Loudspeakers? We will be available via live chat to answer questions/feedback. Don't miss it!

 

[ichigo]

Interesting video although the discussion seems to be mainly about whether the drivers ring or not.

 

[Swerd]

Interesting video although the discussion seems to be mainly about whether the drivers ring or not.

ALL drivers ring at higher frequencies. Other terms for ringing are resonation or breaking up. Most or all those stiffer and lighter cone materials make speakers that sound very good, until they are driven at high enough frequencies to start ringing. The solution is to identify the frequency range where the ringing begins, and create a crossover that avoids or suppresses it.

 

[ichigo]

ALL drivers ring at higher frequencies. Other terms for ringing are resonation or breaking up. Most or all those stiffer and lighter cone materials make speakers that sound very good, until they are driven at high enough frequencies to start ringing. The solution is to identify the frequency range where the ringing begins, and create a crossover that avoids or suppresses it.

Was hoping they'd go over people's stereotypes of how certain materials sound and either validate or debunk it

 

[Swerd]

Was hoping they'd go over people's stereotypes of how certain materials sound and either validate or debunk it

Most of those stereotypes are wrong, or at the best, exaggerated. For example, the stereotype that metal speaker cones sound brighter than paper cones. I've heard a demo of two DIY 2-way speakers where cabinet and drivers were identical, except that one had a coated paper cone woofer and the other had an aluminum cone woofer. The builder designed different crossovers such that both speakers sounded identical. The idea is that as long as a crossover keeps a driver within a passband that prevents audible ringing or break-up sounds, speakers of different cone materials can sound very much alike.

The same goes for metal vs. fabric dome tweeters. Just because a tweeter looks shiny doesn't mean it must sound bright.

There are speakers notorious for doing the opposite. Some B&W models have a crossover at such a high frequency that it allowed too much resonance created by those yellow Kevlar mid-woofer cones to come through. Doing that did create a characteristic 'B&W sound', but it also created ugly sounding resonance or ringing. Fortunately, in recent models B&W seems to have abandoned that approach.

 

[shadyJ]

Most of those stereotypes are wrong, or at the best, exaggerated. For example, the stereotype that metal speaker cones sound brighter than paper cones. I've heard a demo of two DIY 2-way speakers where cabinet and drivers were identical, except that one had a coated paper cone woofer and the other had an aluminum cone woofer. The builder designed different crossovers such that both speakers sounded identical. The idea is that as long as a crossover keeps a driver within a passband that prevents audible ringing or break-up sounds, speakers of different cone materials can sound very much alike.

The same goes for metal vs. fabric dome tweeters. Just because a tweeter looks shiny doesn't mean it must sound bright.

There are speakers notorious for doing the opposite. Some B&W models have a crossover at such a high frequency that it allowed too much resonance created by those yellow Kevlar mid-woofer cones to come through. Doing that did create a characteristic 'B&W sound', but it also created ugly sounding resonance or ringing. Fortunately, in recent models B&W seems to have abandoned that approach.

+1 This. Many audiophiles are just about the dumbest MFers on the planet (our readership excepted, of course). They think that since a cone or dome is made out of metal, it must sound metallic. This really is their logic. Or that a paper cone or silk dome must sound 'warm.' I suppose we should expect as much from the crowd that thinks that the more expensive a metal must be, the better of a conductor of audio signal it is. Audiophiles are just the worst.

 

[killdozzer]

+1 This. Many audiophiles are just about the dumbest MFers on the planet

To even think I'll live to see the day!!

The solution is to identify the frequency range where the ringing begins, and create a crossover that avoids or suppresses it.

Not that long ago I linked the JA / Oclee interview where Oclee explains one other, creative approach. The idea wasn't his, he just explained that (I apologize for the inaccurate layman’s language) certain side channels help air dispersion on the inside right behind the cone and this further lowers the brake up problems.

I just thought it might be interesting.

 

[baronvonellis]

It was interesting, but a pretty long and rambling video to be honest. I wish you would have mentioned kevlar or plastic drivers. Not sure if you discussed ribbon drivers either. What about bamboo or papyrus ? It would have been helpful to just show each type of driver, and discuss the pros and cons of each type and how it might or might not affect the sound.

What happened to Hugo? The videos with him were funny, entertaining, concise, and I learned alot at the same time.

 

[AcuDefTechGuy]

First of all -- thank you Shane for designing the RBH speakers!

I've owned speakers with different types of driver - Diamond (B&W 802D2),Beryllium (Revel Salon2),Titanium (KEF 201/2),Carbon Fiber, Magnesium, Aluminum, Silk, RAAL, AMT.

Take home message: Exotic drivers can make a difference, but it depends on the design and implementation.

Just because it is a Beryllium or Diamond or Ribbon or any other driver type/material doesn't guarantee great sound or better sound than anything else that's well designed and implemented.

Even if it's a good difference, you have to rely on the actual speaker measurements and your ears to determine if these exotic drivers are worth your money, and ONLY you can determine it's worth.

 

[Swerd]

It was interesting, but a pretty long and rambling video to be honest.

I tried watching more than once, about 1½ times. The first time I fell asleep, and the second time, I stopped before I fell asleep again.

Shane Rich clearly seems to know what he's talking about, but I also found it hard to listen for that long. I'd like to think I know all about that subject, but I can't be sure because I couldn't listen long enough.

I wish you would have mentioned kevlar or plastic drivers. Not sure if you discussed ribbon drivers either. What about bamboo or papyrus ? It would have been helpful to just show each type of driver, and discuss the pros and cons of each type and how it might or might not affect the sound.

I think the conversation was limited to those driver cone materials that RBH uses in its speakers. Maybe that's why kevlar, other plastics, bamboo or papyrus cone materials were not mentioned.

Ribbons drivers, or other planar types, seem to be a different beast than the standard cone type drivers. I'm not aware of break-up or other high frequency problems in their frequency responses. Is that because of something inherently different in those type of drivers? Or is it mainly because most of those are tweeters, where frequencies higher than roughly 18 kHz simply don't matter? Unless you're a dog or cat.

 

[gene]

Interesting video although the discussion seems to be mainly about whether the drivers ring or not.

That is a really important concern in driver design. Resonance control is everything.

 

[gene]

I tried watching more than once, about 1½ times. The first time I fell asleep, and the second time, I stopped before I fell asleep again.

I'd like to think I know all about that subject, but I can't be sure because I couldn't listen long enough. Shane Rich clearly seems to know what he's talking about, but I also found it hard to listen for that long.
I think the conversation was limited to those driver cone materials that RBH uses in its speakers. Maybe that's why kevlar, other plastics, bamboo or papyrus cone materials were not mentioned.

Ribbons drivers, or other planar types, seem to be a different beast than the standard cone type drivers. I'm not aware of break-up or other high frequency problems in their frequency responses. Is that because of something inherently different in those type of drivers? Or is it mainly because most of those are tweeters, where frequencies higher than roughly 18 kHz simply don't matter? Unless you're a dog or cat.

I know this was a loooooooooooong interview, and hard to listen to. I told Shane next time we do these, we set a timer for 10 min. Shane has looked at Kevlar drivers as well. I probably should have brought it up. Kevlar is an overrated material for driver materials IMO. Never really the best material to use, hence why B&W stopped using it in their latest driver tech.

 

[gene]

It was interesting, but a pretty long and rambling video to be honest. I wish you would have mentioned kevlar or plastic drivers. Not sure if you discussed ribbon drivers either. What about bamboo or papyrus ? It would have been helpful to just show each type of driver, and discuss the pros and cons of each type and how it might or might not affect the sound.

What happened to Hugo? The videos with him were funny, entertaining, concise, and I learned alot at the same time.

Hugo is making a killing selling real estate. Audio just isn't profitable enough, sadly.

 

[Swerd]

Shane has looked at Kevlar drivers as well. I probably should have brought it up. Kevlar is an overrated material for driver materials IMO. Never really the best material to use, hence why B&W stopped using it in their latest driver tech.

I agree. I always wondered if Kevlar was so overrated because B&W over-marketed it.

 

[Swerd]

Was hoping they'd go over people's stereotypes of how certain materials sound and either validate or debunk it

This is actually a very interesting subject. So instead of whining about a video that went on too long about this, I thought I'd try and tackle it with the written word…

In a perfect world, an ideal speaker cone would be infinitely light weight and infinitely stiff. The cone would always move to and fro, as if it were a piston. In the real world, speakers can’t always move as a single piston. As sound frequencies increase, the piston-like motion begins to fail, often called “break up”, also known as resonance or ringing. The sound of break-up can be benign, as in some softer cone materials like paper where the response drops significantly at break-up frequencies. Or can sound genuinely ugly as with most metal cone speakers. It always should be avoided.

See the cartoon gifs demonstrating piston-like motion and a speaker cone breaking up here http://www.pafec.eu/audio/fsacbens.htm. As sound frequency gets higher, a cone speaker begins to fail at moving like a piston. As you might expect, larger diameter cone speakers fail at lower frequencies, and smaller diameter speakers fail at higher frequencies.

The physical reasons behind this so-called break-up are complex, and I don't understand it well enough to explain it simply. Resonance is caused by interaction of sound waves as they travel between cone material and the whole mechanical system formed by the cone, surround and suspension. At high enough frequencies, resonance occurs instead of simple piston-like motion. Speaker designers have long ago learned that different cone materials or cone coatings can affect the frequency at which a cone goes into break-up. They look for materials or coatings that raise that break-up frequency, or that minimize the loudness of the ringing.

One of the most important jobs of a speaker crossover designer is to avoid sending music signals that could cause a driver to go into break up.

Infinity has published a white paper describing their speaker cones made with Ceramic Metal Matrix Diaphragms (CMMD) – written by Floyd E. Toole and Allan Devantier. It describes Infinity's proprietary method of producing a cone material stiffer and less prone to resonance modes than standard aluminum. CMMD is their name for aluminum speaker cones coated with aluminum oxide, also known as anodized aluminum. http://www.cieri.net/Documenti/Infinity/Documenti tecnici/Infinity - CMMD (Ceramic Metal Matrix Diaphragms).pdf. This paper discusses the stiffness of various speaker cone materials and how that stiffness can (under the right circumstances) be turned into better sounding speakers. It's a worthwhile read, and I borrowed some info from it that appears below.

I should note that Infinity uses the term CMMD for it's 'coated' aluminum cones, but other speaker manufacturers have similar cone materials with different trade names. But they didn't publish such a nice document as Infinity did.

This is a good place to stop and wait until those interested read the CMMD paper. Then I'll have more to say.

 

[Swerd]

Those who read Infinity’s CMMD paper should now realize there’s a stiffness hierarchy among various speaker cone materials. The paper talks about measurements of stiffness of these materials (expressed as Young’s Modulus). Speaker cones with a high Young’s Modulus will go into break-up at higher frequencies than more flexible cones. This wider pass band makes it easier for a crossover to prevent a listener from hearing a speaker cone in break-up mode.

This stiffness hierarchy translates into a hierarchy of frequencies at which speaker cones go into break-up mode. The CMMD paper talks about “First Cone-Bending Mode”. Table 2 (summarized below) shows “the frequency of the first natural cone-bending mode for the entire moving assembly of a 5¼" driver for each of six different cone materials attached to a typical voice coil and surround.”

Cone Material – Frequency (Hz) of First Cone-Bending Mode
Polypropylene (1500 Hz)
Kevlar (1920 Hz)
Paper (2160 Hz)
Aluminum (6700 Hz)
Titanium (7440 Hz)
Ceramic (10800 Hz)
CMMD (10190 Hz)

From that table, I believe “first cone-bending mode” translates into the frequency at which a speaker’s begins to go into break-up mode. However, it’s clear that the frequency of first cone-bending mode of a cone material is different from the frequency at which a driver goes into break-up. The size of the drivers plays a role. So does the composition of a speaker’s frame, surround, and spider. So, let’s keep the driver sizes the same and compare driver’s made by one company, SEAS, to minimize the effects of frame, surround, and spider composition to try to extend this comparison. My goal is to directly show that cone material has a direct effect of widening a speaker’s pass band by moving the break-up peaks to higher frequencies.

A few years ago, I put together this graph comparing the frequency responses of 2 Dayton 6” drivers, one with a paper cone (DC 160-4, blue trace) and the other with an anodized aluminum cone (RS 180-4, red trace). The driver sizes weren’t identical, and the frame, surround, and spider materials may not have been the same, but putting both frequency responses together showed exactly what I’m after. Both drivers had similar looking curves as long as they were not breaking up. The paper driver goes into break-up possibly as low as 1500 Hz, certainly by 2500-3000 Hz. The metal driver doesn’t break-up until 4000 Hz. Note how the paper break-up peaks are smaller and they coincide with the driver’s natural roll-off. The metal break-up peaks are bigger and the driver’s roll-off doesn’t begin until higher frequencies.

To further illustrate this, let’s look at a number of frequency response curves of a series of SEAS drivers of similar 6½” size but made with different cone materials. As you'll see below, these frequency response curves are all made with the same horizontal & vertical dimensions, allowing easy comparison among them. Pay close attention to the right side of these graphs, at 3000 Hz and higher, where roll-off and break-up modes appear.

Coated Paper – CA18 RNX

Woven polypropylene – U18 RNX/P

Reed-paper – ER18 RNX

Aluminum – L18 RCY/P

Magnesium Alloy coated with magnesium oxide – W18 E001

Graphene treated magnesium – W18 EX003

As the driver cones get stiffer, the break-up modes are shifted to the right, at progressively higher frequencies. This results in wider regions where the sound is flat, well behaved, and not affected by resonance or break-up.

Seas does not offer drivers with cones made of uncoated paper, fiberglass, Kevlar, coated or anodized aluminum, or ceramic.

From all this, I hope it's clear that different cone materials can offer the possibility of more detailed and less distorted sound, free of ugly sounding resonances. But they don't automatically guarantee better sound unless careful tweeter selection and crossover design is also done.

 

[Ricardojoa]

Danny Ritchie at GR research made a video about speakers measurement. I think is relative to this post so check it out.

 

[Swerd]

Not that long ago I linked the JA / Oclee interview where Oclee explains one other, creative approach. The idea wasn't his, he just explained that (I apologize for the inaccurate layman’s language) certain side channels help air dispersion on the inside right behind the cone and this further lowers the brake up problems.

Is this the interview?

Or is this it?
https://www.stereophile.com/content/kefs-jack-oclee-brown-talks-loudspeakers

Would you please identify which minutes of the interview you are referring to? I'd like to know what he has to say, but I get much too impatient to listen to all the polite chit chat in these videos.

 

[killdozzer]

I get much too impatient to listen to all the polite chit chat in these videos.

I don't recognize you anymore!

It's this one:

And you go to 23:10 for UniQ brake-up tackling and to 19:50 for the woofer brake-up tackling.