Compression ratio and diaphragm size in compression drivers - diyAudio
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Old 31st December 2008, 05:46 AM   #1
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Default Compression ratio and diaphragm size in compression drivers

Hi,

Could somebody clarify how the size of the diaphragm and the compression ratio affect the sound of a compression driver?
I read in this forum this comment from Lyn Olson:

"Apparently, the real differences sonically are the compression ratio and diaphragm material - higher compression ratios are more "focussed" and intense in the midrange, and lower compression ratios are more relaxed sounding. With a 3" diaphragm and a 2" exit, the 850-PB has a lower compression ratio than the 835-PB, with its 1.4" exit. This alters the sonic presentation"

Also, some people said, for example, that a 3" or 4" diaphragm is better to reach low frequencies than a 2"

Could somebody explain further into these areas?
Thanks
Alan
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Old 31st December 2008, 09:39 PM   #2
gedlee is offline gedlee  United States
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An exit aperature area difference does not necessarily mean that there is a different compression ratio. I would also say that compression ratio has little to nothing to do with sound quality. This ratio is defined as the ratio of diaphragm area to gap area in the phase plug. After the initial gap the phase plug expands and this expansion can be taken to a 2" throat area or a 1.4" throat area with a different length on the phase plug extension, but the same compression ratio.

A larger diaphragm will handle LF better, but it will also have more seveer HF limitations. I prefer the 1" throat varieties because these will go all the way up to 15 kHz, which the larger throats won't. A larger throat driver will necesitate another HF unit above about 8 kHz.

The larger diaphragms are more intended for power handling than LF capability, although there is some LF improvement in a larger diaphragm. But for home use power handling in a compression driver is never an issue, and waveguides that can go down to 500 Hz - as opposed to 1 kHz - are eight times larger - that makes them prohibitive in size for a home.

So if this is for use in a home setting, stick with a good 1" driver. There are lots of them. Some will even go down to 700 Hz.
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Old 1st January 2009, 08:06 PM   #3
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Thanks for the answer Earl.

So, there is no truth in that lower compression ratios are more relaxed. I was basically trying to compare the Radian 950pb and the Community M200 for the frequency range between 400hz-4000khz. Some people believe that the M200 has a really good midrange due to the material of the diaphragm and the lower compression ratio.

Currently Im using RCF ND3020T3 from 400hz to 7000hz which is a 3" titanium diaphragm and I notice some harhsness in the upper mid part of the spectrum.

Let me ask you another question, regarding diaphragm materials. Is there any particular influence in sound from diaphragms made from titanium, aluminun, mylar etc?

Alan
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Old 1st January 2009, 08:20 PM   #4
AndrewT is offline AndrewT  Scotland
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can you confirm if a 1" throat compression driver generally uses a diaphragm and Voice Coil of around 2" diameter?
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Old 1st January 2009, 08:54 PM   #5
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Quote:
Originally posted by AndrewT
can you confirm if a 1" throat compression driver generally uses a diaphragm and Voice Coil of around 2" diameter?
Such information is readily available from the manufacturer.
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Old 1st January 2009, 09:17 PM   #6
gedlee is offline gedlee  United States
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Quote:
Originally posted by inkasound
Thanks for the answer Earl.

So, there is no truth in that lower compression ratios are more relaxed.

Let me ask you another question, regarding diaphragm materials. Is there any particular influence in sound from diaphragms made from titanium, aluminun, mylar etc?

Alan

I would say that there are no valid studies relating compression ratio of sound quality. Diaphram materials yes. The diaphragm material differences will cause frequency response differences that have been shown to be audible - but audible does not mean that any one is any better than another. I know that there is a general feeling that Mylar and plastic diaphragms sound better because the metal ones have very low damping of some of the higher Freq resonances. The plastic diapragms have resonances lower in freq, but are far better damped. I don't think that there is solid data to support this subjectively however, just a bunch of personal opinions.
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Old 2nd January 2009, 08:09 AM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by 454Casull

Such information is readily available from the manufacturer.
which manufacturer do you have in mind?
My question is much more general, what is the norm, if any?
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Old 2nd January 2009, 09:41 AM   #8
tomtom is offline tomtom  Slovakia
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1,75 inch are most common

I don't see driver yet that hasn't specified voice coil diameter. This is number you are looking for...
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Old 2nd January 2009, 10:46 AM   #9
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Basically, what seems to be is a popular belief that titanium diaphragms are hard metallic sounding and are not supossed to be used in home audio. In my experience using the RCF ND3020T3(titanium) in a 320hz exponential horn, the sound of the driver all the way from 400hz to 5000hz-6000hz is really good. But in the upper part of the spectrum you can sense that the driver doesnt sound relax(like in the mids) even you can really feel the metal material. I think if people would use these titanium diaphragms only until 5-6K, they could be in for a surprise.
Another fact, is that the titanium being a heavy metal requires a very thin diaphragm, that probably can be translated into very dynamic and very transparent sound. Could be that the mylar, and the phenolic ones give some soft round edge to the sound while the titanium is more razor edge?

Alan
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Old 2nd January 2009, 05:40 PM   #10
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Quote:
Originally posted by inkasound
Basically, what seems to be is a popular belief that titanium diaphragms are hard metallic sounding and are not supossed to be used in home audio. In my experience using the RCF ND3020T3(titanium) in a 320hz exponential horn, the sound of the driver all the way from 400hz to 5000hz-6000hz is really good. But in the upper part of the spectrum you can sense that the driver doesnt sound relax(like in the mids) even you can really feel the metal material. I think if people would use these titanium diaphragms only until 5-6K, they could be in for a surprise.
Another fact, is that the titanium being a heavy metal requires a very thin diaphragm, that probably can be translated into very dynamic and very transparent sound. Could be that the mylar, and the phenolic ones give some soft round edge to the sound while the titanium is more razor edge?

Alan

Titanium is very light, light as aluminium and strong as steel.
That is why it is used, the result is very low weight for the necessary domestrength.
Titanium also has a very high soundspeed which means that it is easy to dampen it, even if it never is done in commercial units.
But with dampening it will sound very good all the way up to atleast 12-15KHz for a "normal" 1inch horn.
That razorsound you describe is either reflections within the diagraphm or reflections within the hornpath.
Without those reflections then titanium is in my experience the best choice above midrange too.
-However, i am not a fan of titanium domes with mylar surrounds that is used in some drivers from RCF for instance.


Quote:
I would say that there are no valid studies relating compression ratio of sound quality
Air cant be compressed in infinity, so when the air gets too compressed then the air itself will distort.
However, you cant get close to those levels in a domestic enviroment without destroying your ears.
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