OB 3-way Hybrid

[ctrevith]

I've been following the beyond the Ariel thread with great interest and it has inspired me to try to do a hybrid OB (in the interest of space and bass impact).

Goals/assumptions/criteria:

1. Must cover entire spectrum ~ 20Hz-20KHz
2. Must be somewhat compact
3. Must be OB from ~200Hz to ~2KHz (low and high xover points)
4. Prefer ND midrange
5. System reference eff must be 95db or above
6. Impedance may not dip below 5 ohms
7. Active cross over with Deqx at ~200Hz. Active or Passive xover at ~ 2K.
8. Bass module can be native BR or Closed Box (with eq)
9. Low dyanamic compression
10. Room is moderate size 8'x21'x32' with listening seat at 3meters


Drivers considered at the top of the priority list right now:
- Beyma 18G40 Bass (BR or eq'd closed box)
- Beyma 12MW/ND OB Mid
- Beyma TPL-150 or RAAL 140-15D

Any feedback is welcome

Questions:

1. Any other drivers that I should be considering?
2. Any comments as far as meeting or not meeting the design criteria, or altering the criteria?

[tinitus]

You can get much lower xo point with a compression driver than a ribbon
In this case I am not certain there will be any point in having the 12" in an OB at all
And personally I am not sure I would use a 12" PA driver much above 1khz

[BHTX]

I agree with tinitus.
Ever considered something like a PR170M0, paired with maybe one of the more efficient Fountek ribbons? The Audax should do very well with a 2 KHz lowpass..around 96-97 dB/watt throughout most of its range, with moderate breakup peaking at around 100 dB from 3-8 KHz, and falls off steep after that. A high-end ribbon of sufficient sensitivity should mate very well with it, I would think. I don't see why a combination like this wouldn't have at least a slight chance of suiting your wants/needs. The only negative characteristic I don't like about that particular driver is the need to highpass at 400+ Hz, perhaps more on an OB. If you're like I usually am, and want a mid with a bit more low-end potential, perhaps a modded Visaton B200 as a mid could do well? Mainly your consideration of a 12" Beyma for a midrange provoked that recommendation I guess. And I'd be interested to hear from anyone who's done it too. If you're afraid a B200 wouldn't have enough maximum output or headroom for you, there are quite a few other choices as well, of course. Like several of the PHL mids, etc. But yeah, a 12" pro woofer with a ribbon tweeter is kinda pushing it, imo. I'd try to refrain from using it past 1KHz, if even that. Personally, I'd rather use nothing larger than an 8", perhaps more preferably a 6.5", and have it cover those exact ranges you specified, without anything in between. Oh and...don't expect to obtain 20 Hz from even the largest pro woofers. Even the most expensive biggest and baddest that WILL get that low will usually require a ridiculously MASSIVE vented enclosure.

[tinitus]

Maybe you should take a look at this one ... its a real beauty in simple efficiency

Here's My Usher/Altec Horn Loaded Open Baffles...

[BHTX]

Yeah, I like these too.

[ctrevith]

Thanks for the feedback so far. Here are some thoughts based on the feedback.

The Beyma TPL-150 and RAAL seem to have the balls to get into the 1.8-2KHz region without an issue and have lower distortion compared to compression drivers. One issue I can think of is the polar response disparity as Duke has pointed out many times but I don't know how sensitive I'll be to that.

I haven't been able to find any independant measurements of the Beyma 12mw/nd but the distortion and fr plots at US Speaker seem to be very good up into the area where I would like to cross over with a very smooth roll-off. It's target market may be guitar and PA use but I don't understand why that would knock it out for high fidelity home use.

A single 12" has over 2 times the radiating area of a single 8" driver and 3.4 times the radiating area of a 6.5" driver while also decreasing the issues of using multiple drivers.

The other thing that enters into the goals is to have the least amount of dyamic compression as possible. It's my understanding that the higher the reference efficiency the better this is (although I'm not sure this is true in every case) The reference efficiency of the Beyma 12mw/nd is 2.3%; Audax PR170M0 is 1.8% and the Visaton B200 is 0.8%. I like the Audax but the other limitation with it is the low end cut-off. I don't like the idea of a bass driver having to work up into the 300-400 Hz region.

[tinitus]

Pardon me if I sound harsh, its not intended ... you dont like a woofer to play in the 300-400 region ... but you dont mind pushing a 12 woofer into the 2khz region, or past it with what is left behind the xo point

I bet that the 12" will have a much harder job than the 18" woofer

To be honest, I want the same thing as you do and would also like to use both 18" woofer and 12" mid, but have settled on a compression driver crossed around 1khz

If you push any of the drivers beond their sensible limit you may not reach your goal

NOW THAT YOU SEEM TO INSIST ON "OB" FORE THE MIDBASS DRIVER ... COULD THE 10/12" ALNICO TONE TUBBY BE A CONTENDER ... yeah, I know, no measurements, nada

But why the 12MW/ND when there is a similar 10MW/ND ?

Ribbons may be crossed at 2khz ... but from what I read they dont really like it too much

[ctrevith]

Tinitus, your comments of 12/10 versus 18 etc. seem reasonable. I actually went through part of the same thought process.

What I meant is that I don't like to go into the low midrange region with a driver that I'm also pushing into the sub region. Trying to reproduce lower midrange with a driver that has a fair amount of excursion demand just seems like I'd be asking for problems in the midrange. I was also looking at the number of octaves of duty. (20Hz-200Hz is a little over 3 octaves. 200Hz-2000Hz is is the same number of octaves).

I also looked at the 10mw/nd. It doesn't seem to get any further up and also has less radiating area. The FR and distortion actually looks better for the 12? Maybe there's better controlled de-coupling of the cone with the 12? There are a few examples of 12" drivers being used successfully into the 1.6K-2K region and higher such as Bastanis, PHY, etc.

I read somewhere in this forum that the critical range for OB is (subjectively or objectively, I can't remember) ~ 200Hz - 2KHz. However, the one thing I do like about dipole bass is the decreased complexity of room interaction. That said, it just seems very difficult to get dynamic range and the last octave with dipole bass without getting a divorce.

Any other RAAL or Beyma TPL-150 users out there that can comment on using them down to ~ 1.8K to 2K? Am I asking for trouble?

[tinitus]

Under normal conditions you probably wont see those woofers move at all

But I am no better myself ... I fancy a genuine 100db 12" PA mid driver myself, and use it all the way down 18" woofer will have a subamp with adjustable 6db gain ... well, maybe it will be a 21"

About the RAAL ... I think that Shin found the RAAL to sound better crossed high with 12db slopes

But trouble it is ... all of these drivers mentioned here are indeed very odd creatures in the hifi world

[roland bios]

The Beyma Tpl 150 is an air motion transformer, not a ribbon

Tpl 150 freq
Tpl 150 pic

Regards
Roland