Andysu
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It may all seem easy to replace a diaphragm for a compression driver/HF horn. The ones I use JBL 2445 are in fine working condition dated for 1989.
Aligning the diaphragm to the phase-plug is a tricky tedious task that can take maybe minutes to few hours of test checks.
The screws that hold the diaphragm down over the phase-plug must be tested with microphone near to the Horn with a sound generators REW, TrueRTA or WinRTA using
1) Pink Noise
2) Sine Wave
3) Frequency sweep with overlays
Testing with pink noise noise while, tightening down the screws (careful) as too much tightening can decrease/increase a certain part of the frequency range. The frequency should appear as flat as humanly possible within the tolerances of the diaphragm, this is what I have discovered with CD/HF horns.
Sine wave checks to check for any resonate harmonic frequencies as tightening down the screws as well as wiggling the diaphragm around due to how it's voice-coil is settled in the slot of the magnetic may be fraction too close to the edges and there is no visual way I can tell with micro video camera to see if it has good clearance all around the diameter (lol). This is why it can take so long. So I wiggle the diaphragm gently while observing the RTA and listening until I have it just about as best as it can possible be.
Frequency sweep can looking at the graph to how it looks : bad, fine, good, excellent.
Repeating these tests for five JBL 2380A and there will be some tiny fraction differences with all or maybe they can all be made to sound the same but all depends on the frequency graph overlays to see if they all transparently line up together which never often happens as there will be some small dB frequency level differences or maybe more wiggling of the diaphragm and gently tightening down the screws in a certain order maybe the key to getting the frequency overlays to line up over the other. Or there is some actual manufacturing differences or a defective diaphragm?
Those are some of the tests I conduct and can take a day to do all five JBL 2380A - JBL 2445 before I place them behind the acoustically transparent screen.
My cat Bear, sniffs the JBL 2380A, Mmm, JBL Just Bear Lovey.
More Bear JBL sniffing JBL 2445 compression drivers.
JBL 2380A up behind the screen mounted on top of JBL 4647 with JBL 2226 15" bass drivers.
Testing one of the JBL 2380A horns.
I don't have a short video of doing the actual alignment which is in live video of I think 12hours long when I first got these JBL horns I had to clean them test them with multi-meter and sound generator that was 12 hours.
Aligning the diaphragm to the phase-plug is a tricky tedious task that can take maybe minutes to few hours of test checks.
The screws that hold the diaphragm down over the phase-plug must be tested with microphone near to the Horn with a sound generators REW, TrueRTA or WinRTA using
1) Pink Noise
2) Sine Wave
3) Frequency sweep with overlays
Testing with pink noise noise while, tightening down the screws (careful) as too much tightening can decrease/increase a certain part of the frequency range. The frequency should appear as flat as humanly possible within the tolerances of the diaphragm, this is what I have discovered with CD/HF horns.
Sine wave checks to check for any resonate harmonic frequencies as tightening down the screws as well as wiggling the diaphragm around due to how it's voice-coil is settled in the slot of the magnetic may be fraction too close to the edges and there is no visual way I can tell with micro video camera to see if it has good clearance all around the diameter (lol). This is why it can take so long. So I wiggle the diaphragm gently while observing the RTA and listening until I have it just about as best as it can possible be.
Frequency sweep can looking at the graph to how it looks : bad, fine, good, excellent.
Repeating these tests for five JBL 2380A and there will be some tiny fraction differences with all or maybe they can all be made to sound the same but all depends on the frequency graph overlays to see if they all transparently line up together which never often happens as there will be some small dB frequency level differences or maybe more wiggling of the diaphragm and gently tightening down the screws in a certain order maybe the key to getting the frequency overlays to line up over the other. Or there is some actual manufacturing differences or a defective diaphragm?
Those are some of the tests I conduct and can take a day to do all five JBL 2380A - JBL 2445 before I place them behind the acoustically transparent screen.
My cat Bear, sniffs the JBL 2380A, Mmm, JBL Just Bear Lovey.
More Bear JBL sniffing JBL 2445 compression drivers.
JBL 2380A up behind the screen mounted on top of JBL 4647 with JBL 2226 15" bass drivers.
I don't have a short video of doing the actual alignment which is in live video of I think 12hours long when I first got these JBL horns I had to clean them test them with multi-meter and sound generator that was 12 hours.
