In need of some Econowave-ish help and advice

[MunkeyQ]

Hello all, I'm in need of a bit of help regarding my latest build. It's a sort of Econowave, using the Celestion CDX1-1745 (used in QSC HPR152i) on the conical HPR122i waveguide. Note to anyone else trying this combo - it's not a straight bolt-together build as unlike most waveguides, the holes are tapped since the 1425 bolts through from the other side. I drilled the threaded brass inserts out and had to use studs +nuts to attach the driver, after cutting away some bracing plastic fillets to get pliers in there to tighten the nuts.

It's biamped with a DBX Driverack, which makes playing around with crossover and EQ goodness a lot easier.

Since apparently this combination hasn't been used before (and I lack any measuring gear!), I'm having trouble dialing in the CD EQ. I'm basing it on the 1425/HPR122i here. However, it sounds very nasal with a harsh hump at about 4khz, making vocals sound unnatural and electric guitar harsh. Wonderful on bluegrass though! I've been fiddling for a couple of days with no luck, so I'm wondering if anyone here can offer anything. Oh yep, here's the datasheets for the CDX1-1425 and CDX1-1745.

I'm using it with a Beyma 8BR40 woofer, which plays nice up until about 2khz and gets seriously nasty after that. It's tameable with a high Q notch filter, but I'd like to keep it playing <2khz if possible. Otherwise, it's a very nice woofer in a medium sized sealed cabinet - lots of smooth bass, low Fs and oodles of linear excursion. Seems to be the same cast basket as many Beyma midranges...smaller motor though.

However, I've got a niggling feeling that the nasal-ness is due to the woofer's HF limitations. Would be nice to get rid of the harshness though.

Currently, it sounds outstanding with bluegrass, acoustic guitar and simple vocals, but feed it some Metallica or Guns n Roses and it's a harsh, nasal mess. By ear, I'd guess it's peaky around 5-6khz and lacking near the crossover point...2khz or so.

If anyone's wondering why I didn't go for the conventional E'wave build, it's because Selenium parts are unobtainable in the UK, and JBL charge a fortune for the waveguide. £7 for the part, £45 each for shipping! Over $160 just for the base-level waveguides...that's 18sound money. QSC are much more reasonable, although shipping was very slow. Screw-on drivers are also uncommon over here, but Celestion parts are plentiful. I understand the 1745 uses the same diaphragm as the 1731, albeit on a ceramic motor.

Thanks in advance for any replies. I've tried over in Audiokarma, where I normally post...but alas, no luck.

[MunkeyQ]

Forgot something - link to the woofer's datasheet.

Hopefully someone can help! Thanks again.

[AllenB]

You would be best measuring this yourself. Even if you found someone who has done similarly, your implementation will be different. Designing filters blind is difficult at the best of times, and component interaction is sometimes so intense as to remove all logic from the process. You wont regret plugging a good mic into your computer.

[MunkeyQ]

Duly noted. I actually ordered an ECM8000 and Art Dual Pre (only thing I have with phantom is a honking great desk!).

I'll put some FR plots up when my stuff comes, and have a play with LSPcad.

Thanks for the reply!

[MunkeyQ]

Just had a fiddle and replaced the woofer with a cheapo Skytronic 8" pro driver. Instantly a million times better, so the harshness was probably down to a midrange hole caused by the woofer going into a breakup mode at ~1khz. Beyma obviously intend for this to be used as a lower midbass or subwoofer driver...

The box is about the right size for the Skytronic, although the accuracy of the Thiele-Small parameters Skytronic give are debatable... So, now I'm on the hunt for a suitable 8" driver with reasonable pattern control up to 1.7khz. Fane Sovereign 8-125 models nicely...anyone had any experience with it? I'm suspicious of the low price at only £50 a pair.

In terms of bass in a simulation, it outperforms the Beta 8A in terms of group delay and F3. I can't find any polar response plots though, so no idea on the HF side of things.