Radian 5208c OB project.

[AudioGeek]

I am actually thinking this is the project i want to do. I have noticed that I have had many thoughts about projects but not really started one yet. lol!

Anyways, what i am thinking is using the Radian 5208c in an OB then using a couple of 15" or 12" drivers per side for 300hz and lower.

All passive x-over similar to the MJK projects aka Eminence Alpha15a with Fostex full range driver... which i have built and sounds fantastic.

I am willing to either use 2x Alpha15a per side or even look at other speaker drivers.

I guess i just need help determining which drivers and figuring out the x-over points and final response and sensitivity etc..

Probably want to try to get as close to 95db or so.

Thanks!

Richard Jones

[Bill F.]

Hi Richard,

Sounds fun! I take it that you're happy with your MJK OBs, so what are your performance goals for the new build?

Alpha 15's have an established record as good OB drivers, though any driver with high Qts and displacement will work.

Radian coaxes are nice, though pricey (unless you already have a pair). One consideration, though, might be that they will limit the dipole behavior of your system--you'll have a monopole starting wherever the compression driver takes over. This is not necessarily a problem, just something to note.

Dialing in a good passive crossover will probably be your biggest challenge. If you aren't cloning at least the bass section of an existing successful design, you are diving into deep uncharted waters, and you're going to want tools. I would recommend a measurement package like ARTA, an active crossover--digital or analog--and six amps, one for each driver (or a six-channel amp). The amps can be super-cheap if you're on a budget, you'll only need them for the design phase.

With a few knob twists or button pokes, you can use the active crossover to zero in on the best crossover points, checking the results with ARTA. (Don't just trust your ears. They and your pride can deceive you! Once everything's sorted, then you can build passive crossovers with the same transfer function. Or you may be sold on active and stay that way.

Best o' luck! Keep us updated!

[AudioGeek]

Goals are:

95-97 db sensitivity
all passive
40-50hz -3db response (with room gain etc)
OB.

Yeah i kinda figured about the co-axial not being dipole above 1800Hz or so...

maybe instead go with a wide- range mid driver and a dipole ribbon?

Rich

[Bill F.]

95-97dB sensitivity over the entire passband is practically impossible for a passive OB with any real bass reach, unless you're talking a HUGE baffle with tons of driver Sd. The problem, of course, is that pesky 6dB/octave cancellation that rolls on below the baffle Fpeak. Also, the self-canceling nature of dipoles pretty much eliminates room gain in the bass.

The most practical way to sorta hit that target is to go active on the bass and just let it be its low-sensitivity self. Actively crossed over high enough, the mid and treble can be high sensitivity.

[AudioGeek]

well, maybe then i go with an enclosed design.. either sealed or ported? with the Radian 5208c on top and 2 12" bass drivers.

want to stick with the 96db efficiency though... so i want to do 2 12" drivers instead of worrying about BSC for them and lose efficiency.

any ideas on bass drivers? yeah i don't want to spend a lot on them really... as i probably x them over 200-300 hz or something.

thanks!

[Bill F.]

Sure, you could enclose the bass, put the mid on an OB and hit your sensitivity target. You'll probably have to go ported to hit your bass depth target. Use two bass drivers in a bipole configuration (front and rear of box), and you can skip the BSC. The fact is, you may not need BSC even with a single bass driver, depending on your baffle dimensions and chosen XO frequency.

There's tons of prosound hi-eff. drivers that could work for you. Just pick a price point.

To finish well, I still suggest the development gear I recommended earlier--ARTA, an active XO, and six amps.