Choosing Compression Drivers

[Pbassred]

For the 3.5K and up in a tiny PA rig (600W ), I would like to use Bullet style rather than Horn because space is limited. The mid range will be a single 8" .

What specs should I look for?

[djdan]

You can choose 1" Selenium D210Ti + HL 14-25 horn or 2" Selenium D3305Ti-DPD + HL 14-50 .

I will choose the 2" becouse it is much stronger and will survive at any kind of abuse .

[Brett]

As you're in the UK, I'd suggest a Beyma CP380M and a small flare of your choice depending on dispersion requirements etc. This driver is beautiful sounding and very sweet, with none of the hardness that metal dome drivers have. Best HF compression driver I've ever used. Most bullet style drivers aren't going to be really comfortable down to 3k5, and I'm guessing, not sound really good either.

Stupidly I lent my 380's to someone who now refuses to return them (because he likes them so much), so when you buy yours, get another for me and post it on down to Oz so I can use it in my bass rig.

[Pbassred]

................and if I wanted to use a BULLET style?

[Swedish Chef]

I pretty much agree with Brett here, "bullet" style tweeters aren't exactly happy when crossed too low.

But if you want to give it a try, then give it a try but chances are you're gonna pop a membrane or two at high power levels.

I have no experience with the Selenium drivers but they might be a good choice. Others include JBL2402 (very spendy, but can be found second-hand pretty cheap) or the Beyma CP22 (quite cheap brand new). Both are excellent IMO. Both have a "long-throw" narrow dispersion pattern that is as beamy as a pencil in the top octave but I reckon that's what you want.

You are going to need a very steep crossover slope to not blow the tweeter, 2nd order could do at low power levels but preferably 3rd or 4th order. And you will need an L-pad or similar to attenuate the tweeter to match the sensitivity of the 8''. I assume you are crossing the 8'':s active or?

Designing such a crossover pretty much requires a spectrum analyzer with tracking generator for reaching adequate results IMO.

Cheers
/Magnus

[Brett]

Originally posted by Pbassred
................and if I wanted to use a BULLET style?

Then with every bullet I've ever seen, you'll need to filter the hell out of it at the bottom (ie active xover) as the distortion increases greatly and this region coincides with the area of greatest sensitivity in hearing, so you need to be careful what you do. Otherwise, all you'll succeed in doing is give the punters earwire, and they won't want to stay. You might also do damage to the driver if any LF gets into it and the FMD will make it sound bad too and lessen intelligibility.

I looked at some of the manufacturer sites and my choice if I had to, would be the Beyma CP22, 24dB/oct at 3k5. I've not used it, but it looks OK.

I was at a gig tonight, as a punter, and I "fixed" the sound by taking a low Q scoop out of it centred around 2-3k (hard to tell exactly with an uncalibrated dial) with several dB of attenuation as the POS system was screaming at both ends from the 12" driving too high into breakup and the tweet working too low. People were actually moving away from the system because it sounded awful; most only put up with it as the artists were so good.

But I have to ask, are you actually designing the system to sound good, or just looking to chuck drivers in a box and make a loud noise?

PS. Just saw Magnus response as I was finishing typing. My concern with suggesting the CP22 was it's pattern control, and Magnus' experiemce confirms my concerns. One of the tips to putting together a GOOD sounding system is to try to match the dispersions for the drivers around the xover frequency. And as I mentioned before the 3k region is very sensitive.

[Swedish Chef]

Brett, I have only listened to the Beyma CP380/M once but it sure sounded sweet. Have you any experience with the CP385/Nd? I am considering it as an upgrade for my home system, and since maximum driver diameter is an issue I can not go for the 380.

And yes, there is nothing better than a quality pro sound system with clean, clear and crisp output and high SPL. But there is nothing worse (oh well, actually there is but anyway... ) than an ear-piercing POS system cranked up all the way into 110% distortion.

/M

[Brett]

Originally posted by Swedish Chef
Brett, I have only listened to the Beyma CP380/M once but it sure sounded sweet. Have you any experience with the CP385/Nd? I am considering it as an upgrade for my home system, and since maximum driver diameter is an issue I can not go for the 380.

Sorry, no experience. Beyma drivers are quite rare down here, so I've never seen them. My gut hunch is they will be similarly excellent.

I'm going to import some Beyma's over the next few months for a big(ish) bass guitar rig as nothing I can find locally seems to perform the way I want.

And yes, there is nothing better than a quality pro sound system with clean, clear and crisp output and high SPL. But there is nothing worse (oh well, actually there is but anyway... ) than an ear-piercing POS system cranked up all the way into 110% distortion.

/M

I hate getting earwire from sound systems. It ruins the performance and makes me want to leave. I would have tonight, except a friend was performing and I wanted to hear the set.

If you get the 385's please let us know how they perform.

[Sjef]

The Fostex FT66H is one of the only small horns (it's a ring radiator, not a bullet) wich can go as low as 3.5 a 4 kHz with proper filtering (24db/oct) Don't expect much from the power rating in that area but for a very small PA system it might be just right. I see you are planning to use an 8"driver as midrange wich will also be limited in max SPL so I think the Fostex will hold up.

Stay away from the typical bullet tweeters because they simply all sound very awfull at 3.5 kHz, these are designed as supertweeters NOT as tweeters. In fact every horn will sound awfull when used below the cutt-off frequency of the horn itself, distortion figures of several tens % are very common there.

[GM]

Originally posted by Pbassred
For the 3.5K and up in a tiny PA rig (600W ), I would like to use Bullet style rather than Horn because space is limited. The mid range will be a single 8" .

What specs should I look for?

This is the only bullet I'm familiar with that meets your needs, though there may be similar units by others: http://www.partsexpress.com/pdf/294-400.pdf

All the cheaper ones I browsed at Parts Express require at least two to get the power handling down low, so considering the JBL's cost I'd go this route and inductor one off at whatever point it flattens the response. This should allow for a simple 2nd order XO if the horn's Fc is <2.5kHz. The only other consideration then is measuring the 8"er's polar response at 3.5kHz and finding a bullet that comes closest to matching it.

GM