As the title states, I'm trying to understand more about the possibilities of swapping out compression driver diaphragms with different diaphragms. On another thread I was told that it can be done, and possibly some CDs have multiple diaphragms that can be used? But I'm finding zero information online. And I thought I should make a separate thread for this question.
The reason this question comes up is because I'm using coaxial drivers (B&C 12FHX76). This coaxial design shares the magnet, so I can't swap out the entire compression driver. But what if I can find other diaphragms that would work? Could I improve the unfiltered response of the CD?
I am a noob as far as compression drivers, so I don't know how much impact the diaphragm has on the CD's performance vs how much of an effect the internal structure has. I suppose it is entirely passible that changing the diaphragm will not have much of an effect, but I want to ask. If I had parts laying around I'd swap them and see. But unfortunately I don't have any parts to play around with.
If we find that the diaphragm makes a difference, what is the chance that a diaphragm from one manufacturer will fit and function well in a different manufacturer's CD? I don't know if the curvature of the diaphragms is going to be the same, and it seems to me that the internal clearances are important. But at the same time, I suspect that physics involved forces the internals to be pretty similar?
I've seen some designs using polymer diaphragms that seem to perform quite well. And then there is the Eminence carbon fiber diaphragm. It'd be sweet if I could mix and match to fine tune my driver's performance. But will it work?
The reason this question comes up is because I'm using coaxial drivers (B&C 12FHX76). This coaxial design shares the magnet, so I can't swap out the entire compression driver. But what if I can find other diaphragms that would work? Could I improve the unfiltered response of the CD?
I am a noob as far as compression drivers, so I don't know how much impact the diaphragm has on the CD's performance vs how much of an effect the internal structure has. I suppose it is entirely passible that changing the diaphragm will not have much of an effect, but I want to ask. If I had parts laying around I'd swap them and see. But unfortunately I don't have any parts to play around with.
If we find that the diaphragm makes a difference, what is the chance that a diaphragm from one manufacturer will fit and function well in a different manufacturer's CD? I don't know if the curvature of the diaphragms is going to be the same, and it seems to me that the internal clearances are important. But at the same time, I suspect that physics involved forces the internals to be pretty similar?
I've seen some designs using polymer diaphragms that seem to perform quite well. And then there is the Eminence carbon fiber diaphragm. It'd be sweet if I could mix and match to fine tune my driver's performance. But will it work?
Are you planning/trying to use there without processing? Unlike most other driver types processing really isn't optional with CDs.
The diaphram will effect tone and HF extension while the internal structure(waveguide) accoustically loads the driver to increase sensitivity and collects the output from different areas of the diaphram to produce a coherent output at the throat. As such the waveguide to diaphram clearance is critical.. they have to be the same shape so while it is possible it's not likely some random diaphram with the same VC diameter will work correctly.
In my experience diaphram materials do sound different, non metalic versions often produce smoother mids while metallic diphrams have better HF extension, but there are exceptions to both. And as mentioned above processing can often have a hugh effect on everything, it can transform a driver that is unlistenable raw into something that is stunning.
I am and I will be using DSP. I'm wondering how much is needed per channel, and if that can be changed.
On my B&C drivers, it is taking 9 out of 10 PEQs to "tame" the response. Art (Weltersys) says I measured it wrong (too close), but I don't think changing the measurements will change the result in terms of filtering required. (I'm using a MiniDSP HTx as my processor.)
I'm planning to expand my current system into multichannel. I'm interested in the MiniDSP plate amps for both amplification and processing, but they have just 6 PEQs on the outputs. I was concerned this wouldn't be enough.
But while writing this I looked up the manual again, and I found that they have 12 input PEQs. So I guess that is solved.
I had to ask! I don't have a problem with the sound of my current drivers. But whatever I choose for my center channel will probably be the horn I stick with for the rest of the surrounds, so I don't want to overlook possibilities.
Here's a new question. If I am trying to match compression drivers, should I play it safe and pick a B&C CD that uses the same diaphragm, same efficiency, and same power handling? Or would any titanium CD be a close match? Maybe it is a silly question, but I don't know. I looked at spec sheets for the different B&C CDs that use the same diaphragm, and the published response was not identical. I'm not sure why.
And if the horn pattern is similar, does the throat diameter make a big difference? The horns I'm most interested in are the FaitalPro LTH102 (1", 60x50 pattern) and the Ciare PR614 (1.4", 60x40 pattern). My B&Cs are 1.4", 60x40 pattern. (The Faital LTH142 is 1.4" and 60X50 pattern, but the width across the narrow side is roughly 1" more than I'd like for my design.)
don't know about modern stuff but recall a few diaphragm/driver swaps that worked on some JBL compression drivers like using a 2470 with a 2420 diaphragm installed on a 2345 horn made a nice tweeter for my PA back in the day...
i've had a play with coating aluminum diaphragms using P10's EnAble idea with good results.
i've had a play with coating aluminum diaphragms using P10's EnAble idea with good results.
I did not say you "measured it wrong", I wrote "your unfiltered measurement curve deviates at points by more than 8dB from the published response curve, perhaps because it was made too "close up" to the horn.
Your 9 PEQ choices made for that measurement location will not result in the same response at other measurement locations."
The HF section of the B&C 12FHX76 could be brought to reasonably flat on axis response with the crossover LP filter, two peak cuts, and a HF shelf boost.
That said, it's horn's nominal 60 x40 directivity response is poor (typical for a co-ax), going past basic EQ on axis will tend to make response worse off axis, note how the frequency peaks and dips correspond to directivity changes:
Compare both frequency and polar response to the B&C DE900TN (same diaphragm as the 12FHX76) and the DE900 (mylar surround) on the nominal 80x60 degree ME90 horn:
A single filter could render those drivers reasonably flat on and off axis, other than the HF breakup peak.
I don't know why you chose to discuss home theater choices in the PA forum, but the coverage pattern required/desired for L/R center and surround speakers are seldom the same.
As you can see above, the horn has far more influence on response than the driver.
I can't think of many listening situations where less than 90 degree horizontal would be desired for a center speaker.
Your drivers have a 1.3" (33mm) throat exit.
Generally, any "big difference" will be in the upper high frequency, where wavelengths are similar or multiples of the exit diameter. The horn's design makes more difference in dispersion (and frequency response) than the driver exit diameter.
Art
The phenolic 2470 diaphragm could handle 500Hz, but it's response dropped steeply at ~8kHz.
The aluminum 2420 would shatter to pieces if used as low and loud, but had usable response an octave higher than the 2470.
The titanium 2425 diaphragm in the same driver could go as low and higher, not shatter, but was not quite as smooth as either the 2420 or 2470.
Other than the addition of co-ax high frequency drivers, plastic diaphragms, and higher power handling (with more distortion..) nothing has changed too much in the last 50 (or 100..) years of compression driver design.
There are a lot more (good and bad) horn design options now.
Art
Yes. Exactly what I said. There was no reason to tell the whole story.
Ok. There is a compromise with the coaxial? That is fine. There is always a compromise, right? When I get around to doing outdoor measurements (as you suggest are necessary), I can compare on and off axis measurements to decide what I'm happiest with.
It was meant to be a specific question about modern PA compression drivers and diaphragms. The question is still about pro audio gear regardless of my specific use.
It depends on the driver and horn.. some work very well others don't but in general the lower you want to go the larger the diaphram needs to be. The reason for going lower is about utilizing a crossover frequency where the polar response of the CD and the driver operating below it are the same, this is more of a challenge when that driver is a 12" or 15" cone.
Yes, there are always compromises in audio.
A horn's compromised directivity response can't be fixed by replacing a diaphragm or with EQ.
I did not suggest that outdoor measurements were necessary, only that your "close up" measurements were not representative of your modern (or any vintage..) PA compression driver's horn response other than at the specific position you measured, which was quite different (almost an order of magnitude) from B&C's measurement.
B&C's measurements are usually representative of typical factory units.
Outdoor measurements may not help much with making you happiest in your room, where off axis response makes a large contribution to the sound you hear.
Cheers,
Art