Compression ratio and diaphragm size in compression drivers

[454Casull]

Originally posted by AndrewT

which manufacturer do you have in mind?
My question is much more general, what is the norm, if any?

Any manufacturer.

http://www.radianaudio.com/index.php...hk=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.as...nMenu=overview
http://www.iakn.com/prosound/titaniumdrivers.html

[thoriated]

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.

[gedlee]

For distortion to be visible on a scope it usually has to be quite large. Much larger than I would expect at only 1 watt. Are you sure that everything is working correctly. I'd guess that the distortion would need to be > 10% to actually be readily apparent on a scope.

[thoriated]

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.

[inkasound]

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

[inkasound]

Originally posted by electroaudio




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.

You mean that Titanium is your best for midrange and also for frequencies above midrange? or only above midrange?
Alan

[electroaudio]

Originally posted by thoriated
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.

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.

Originally posted by inkasound
You mean that Titanium is your best for midrange and also for frequencies above midrange? or only above midrange?

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.

I was thinking to put a 1" compression driver in a tactrix horn to cover from 8000hz all the way up.

An old saying is that a 2incher shouldnt be used above about 7-8KHz so it seems just right to add something else there.

which I've extensively damped with mortite on the outside of the flare) horn.

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...

[thoriated]

"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.

[tinitus]

I am getting more and more convinced that my planned 2.5way will be a 3.5way
Rationally it may not be, but technologically its beginning to make sense

[inkasound]

Originally posted by electroaudio



An old saying is that a 2incher shouldnt be used above about 7-8KHz so it seems just right to add something else there.

Hi,
For that frequency range 7khz-20khz what would the best 1" compression driver options?
I was thinking on B&C DE25, is it that good?

Alan