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
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
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.
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.
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
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
inkasound said:
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.
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
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
inkasound said:
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.
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.
Any manufacturer.AndrewT said:
http://www.radianaudio.com/index.ph...e&category_id=18&Itemid=28&vmcchk=1&Itemid=40
http://www.jblpro.com/components/cmp_drvs.htm#2426HJ
http://www.bcspeakers.com/product.php?c=0000000002
http://www.eighteensound.it/index.aspx?mainMenu=overview
http://www.iakn.com/prosound/titaniumdrivers.html
I wonder about the sonic effect of the "diamond" pattern suspension used on some diaphragms. In a 2445J (2" throat) I was measuring (in my Basement Blasters), there was easily visible (primarily odd order) sinewave distortion (on a 'scope) around 2.5Khz at levels as low as 1Watt, but not at lower or higher frequencies. I can easily imagine how such frequency selective distortion could artificially 'harden up' the sound (Not to say they sound 'bad' at all, but I wouldn't call their midrange 'sweet' by any measure, and they are not the ultimate in sonic transparency - but, hey they're in 'Basement Blasters'). There appears to be no damage to the unit, which sounds identical to the 2445J in the other channel at all SPLs. Both units are crossed over ~3rd order cutoff rate at 700hz and are coupled to a B&C ME75 (their version of a JBL 2380, but in aluminum, which I've extensively damped with mortite on the outside of the flare) horn. I've got both passively eq'd essentially flat out to at least 20khz, btw, and still maintain at least 100db/w/m.
Hi -
I haven't definitively determined that everything is working correctly per se (lack of time & money), but I'm using high quality crossover parts including polypropylene capacitors & all inductors are foil type or potted, and don't hear any distortion or level dependent change of sonic signature on music from the driver that seems to indicate loose or rubbing parts, even at ear splitting levels. I'm working from memory here, but I was estimating the distortion to be absolutely slight (less than 5%) but relatively visible because it appeared to 'flatten' segments of the sine wave with noticeable discontinuities in slope between (maybe micro-oilcanning?). Also, it always seemed a bit curious to me that the diamond pattern suspension design would give "something for nothing" as far as a "free octave" of frequency extension. Just some of my bloviation, I guess.
Btw, as a matter of interest, I have a hardcopy of a couple of plots that somebody did where they swapped both a JBL 2445J and a JBL2446J diaphragm into a 2445 driver (into a B&C ME60), and the difference in the responses were very interesting. The 2445 diaphragm in this setup actually made it a bit past 20khz before falling off a cliff, but the 2446 diaphragm, while having 2-3db more output between 12-16khz than the other, expired completely above 17khz. Same horn, same driver, different diaphragms by JBL.
I haven't definitively determined that everything is working correctly per se (lack of time & money), but I'm using high quality crossover parts including polypropylene capacitors & all inductors are foil type or potted, and don't hear any distortion or level dependent change of sonic signature on music from the driver that seems to indicate loose or rubbing parts, even at ear splitting levels. I'm working from memory here, but I was estimating the distortion to be absolutely slight (less than 5%) but relatively visible because it appeared to 'flatten' segments of the sine wave with noticeable discontinuities in slope between (maybe micro-oilcanning?). Also, it always seemed a bit curious to me that the diamond pattern suspension design would give "something for nothing" as far as a "free octave" of frequency extension. Just some of my bloviation, I guess.
Btw, as a matter of interest, I have a hardcopy of a couple of plots that somebody did where they swapped both a JBL 2445J and a JBL2446J diaphragm into a 2445 driver (into a B&C ME60), and the difference in the responses were very interesting. The 2445 diaphragm in this setup actually made it a bit past 20khz before falling off a cliff, but the 2446 diaphragm, while having 2-3db more output between 12-16khz than the other, expired completely above 17khz. Same horn, same driver, different diaphragms by JBL.
Good to know somebody else thinks that Titaniumm diaphragms are not bad at all.
The RCF Im currently using is the RCF ND3020T3 which is a 3" Titanium with Aluminium phase plug.
Let me clarify that the razorsound just appear on frequencies above 7000hz aprox.
Maybe it could be that Im asking the driver to cover too many octaves?
I was thinking to put a 1" compression driver in a tactrix horn to cover from 8000hz all the way up.
What do you think?
Alan
The RCF Im currently using is the RCF ND3020T3 which is a 3" Titanium with Aluminium phase plug.
Let me clarify that the razorsound just appear on frequencies above 7000hz aprox.
Maybe it could be that Im asking the driver to cover too many octaves?
I was thinking to put a 1" compression driver in a tactrix horn to cover from 8000hz all the way up.
What do you think?
Alan
thoriated said:
I am also a bit suspicious against the diamond pattern, it doesnt feel like a good mechanical solution for something that is supposed to bend.
The RCFs ND3020T3 mentioned in this thread seems to have a sourround that is a lot more intuitive.
inkasound said:
I use my 1incers between 500Hz and 12KHz.
However, my digraphms are homemade with some damping so they will not crack up like commercial diagraphms. instead they sound sweet all the way up to 15K where the response falls off rapidly.
An old saying is that a 2incher shouldnt be used above about 7-8KHz so it seems just right to add something else there.
Use foam on the inside of the horn instead.You dont need to fill the whole horn, it is usually enough to cover the troublesome parts of the horn.
However, with your sharp cutoff at the mouth of the horn, i would also experiment with adding a rounded edge to the opening.
-I guess that the correct term is edgediffraction...
"Use foam on the inside of the horn instead.You dont need to fill the whole horn, it is usually enough to cover the troublesome parts of the horn.
However, with your sharp cutoff at the mouth of the horn, i would also experiment with adding a rounded edge to the opening."
Actually, the horn already has some of both. At the top and bottom, the
'grille cover' includes a 0.875" radius (it is that thick & made of baltic birch with a damped perforated stainless steel cover over the bass drivers but not the horn. It was interesting figuring out how to accurately bend the radius on the perforated steel plate). At the left and right sides of the horn are included within the grill cover 1" of absorptive material to damp diffraction modes. These were part of the Basement Blaster when I built them five years ago. Also, recently, I added some mortite to the inside of the flare at the sides where there are flare diffraction discontinuities to take some of the 'sizzle' out.
However, with your sharp cutoff at the mouth of the horn, i would also experiment with adding a rounded edge to the opening."
Actually, the horn already has some of both. At the top and bottom, the
'grille cover' includes a 0.875" radius (it is that thick & made of baltic birch with a damped perforated stainless steel cover over the bass drivers but not the horn. It was interesting figuring out how to accurately bend the radius on the perforated steel plate). At the left and right sides of the horn are included within the grill cover 1" of absorptive material to damp diffraction modes. These were part of the Basement Blaster when I built them five years ago. Also, recently, I added some mortite to the inside of the flare at the sides where there are flare diffraction discontinuities to take some of the 'sizzle' out.
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