Scanspeak D2904 980000 crossover / breakup

[charliemouse]

Hi,
I'm trying a scanspeak d2904/980000 for a project and wondered if any users with experience could advise on taming breakup etc. I've found various mentions of the speaker but can't seem to find answer anywhere.

1. Does the large (above 20KHz) breakup need taming? I guess Jon's use in Avro has two filters, but both aimed at 500Hz resonance. Also - noting the two filters: is strong inhibition of resonance paramount compared to other speakers?

2. Has this speaker changed in its life? Jon's picture shows no wavguide like here, and that appears to be aluminium coloured not black like the version here.

3. What is the waveguide for? Off axis measurements? What would happen if I remove it?

4. I find the response (aside from 'actual' dB) is 5 dB less than Seas H1322 at all distances, though it should be the same within a few dB and is hugely less than fountek neoCD3. I'm not all that experienced: this could be normal, but I wonder if anyone knows whether this is normal? It might be to do with unusual waveguide/directionality of the other two tweeter I have.

Thanks hugely!

[augerpro]

1) Only if you think you can hear it. As far as taming the resonance at Fs, I found it impossible to get the tweeter to adhere to LR4 slope without a trap.
2)I believe Jon removed the phase shield. Don't know about the non-black version. Maybe and early version? Or a short lived version that didn't sell well?
3)They are used on metal dome tweeters to shape the upper FR I believe. I think they smooth the response and push the resonance up, but they can cause some energy storage in the top octave. I don't know how it would effect the sound if you removed it, check teh Arvo Part thread where Jon compare's the difference.
4) It's not a very efficient tweeter, although 5dB sounds like a bigger difference then it should be.

[TacoD]

You don't need to suppress the dome breakup of the 9800. The notch @ 500 Hz is to attenuate the resonance (Fres), the x-over filter also works better. The latest 9800 tweeters have a black anodized dome and all have a waveguide (but Jon removes it). Early versions are not treated (this tweeter is an old design). IIRC removing the waveguide improves the off-axis response. The sensitivity of this tweeter is not great, modern tweeters (like the Seas) have more efficient motors. Comparing with a ribbon tweeter is not fair , due to the increased radiating surface and huge magnets you get higher SPL.