[gitarretyp]

I've been working on these for a few months and have finally gotten them to a point at which i'm really happy, so it's time to post. I'll start with some pictures of the design



These were intended, and i feel succeeded,as upgrades from a set of custom dipoles i had Rick at Selah Audio design for me a few years ago employing Accuton, Seas, and BG drivers. I wanted something that had a similar tonality, smooth and neutral, but with better dynamics, high spl ability, higher efficiency, and a smoother power response. On top of those goals, the design needed to be kept slim and decor friendly --the base is 17"x11", overall height is 48", and the baffle tapers from 12" down to 15".

I chose to use the pro-sound Radian 5208 coaxial driver for the mid/tweeter (chosen for efficiency and coax design for better power response) and 4 x GR Research M165X (good parameters for OB, high enough sensitivity with 4 of them, and maintains slim baffle) per channel. As can be seen in the photos, the Radian is on a flat baffle and the 165s are in a shallow, tapered, stuffed u-frame. Crossovers are done actively with a BBE DS48 crossover and are all acoustic LR4: 1.5 kHz between the mid/tweeter, 250 Hz for the mid/woofer, and 75 Hz for the woofer/subwoofer. I have a 12 ohm resistor and .33 mH inductor forming a shelving filter to achieve the initial roll-off of the tweeter, match levels between the mid/tweeter better, and provide protection in the case of component failure. It also helps to keep down some of the noise from the active crossover with a >100 dB efficient driver.

So, on to the objective
First, some gated measurements at ~33" taken with Arta, a Behringer ECM-8000 mic, and a M-Audio Mobile Pre sound card

NOTE: UPDATED MEASUREMENTS ON PAGE THREE

On the intended listening axis (30 degrees off-axis) with minimal 1/12 octave smoothing. If you think it looks jagged, notice the range (35 dB) of the graph. The response is +/- 2 dB from 400-15 kHz if the (diffraction?) nulls at 8.5 and 11kHz are smoothed over


Next, the response from 0-60 degrees off-axis, also gated. This time i used more conventional smoothing (1/3) and y-axis range (50dB). The response falls in the same +/- 3 dB window from 400-15kHz and 0-30 degrees. Even out at 60 degrees, the response is smooth and even up to 9kHz. Aside from the 1.5 and 7.5kHz regions, i'm really happy with the response.


Now, a 1/3 octave smoothed response at the listening position. That's +/-3 dB from 10 Hz - 15 kHz


Finally, some distortion measurements. This was measured on-axis ~ 7" from the baffle. 0 dB on the graph corresponds to ~100 dB at 1m, c-weighted. I don't have a lot of faith in this measurement, but i did the measurement and figured i may as well post it.


Subjectively, i'm very happy with the design. I feel that i accomplished all of the goals i set for the design. Is it perfect? No, of course not. I'd like to see a more well controlled power response, and the radian compression driver is a little on the cold/sterile side and a bit sibilant --both treated as well as possible in the crossover/eq but still noticeable. Having speakers that can produce >100 dB without breaking a sweat and needing very little power is pretty impressive. This aspect is the most noticeable improvement over my previous speakers.

Also, for those that doubt the abilities of pro-sound drivers and horns, let me say that they can sound fantastic if treated well --just the same as any driver. Well designed horn/waveguides do not honk or have the horn coloration i, and i'm sure others, associate with many of the horns around.

[pbrstreetgang]

Looks darn good!

[ttan98]

Very nice wood-work, and thorough measurements.

One query, I feel the speaker freq response drops off(after 1Khz) more than I would have like, but you are the listener not me.

Nice speakers...Cheers

[gitarretyp]

Very nice wood-work, and thorough measurements.

One query, I feel the speaker freq response drops off(after 1Khz) more than I would have like, but you are the listener not me.

Nice speakers...Cheers

Thanks for the compliments.

Are you referring to the listening position measurement or the gated response? If the listening position, that's largely room effects and is fairly typical and often preferred behavior. If you're referring to the gated reponse, keep in mind that's only a 2dB droop.However, a ruler flat response wasn't a goal. I voiced the response in this manner to tame the slight sibilance i noted above and provide a slightly warmer tone.

[ttan98]

BBC dip I assume...

I use a DE250 compression driver, smooth as baby bottom, sometimes too smooth, hence I make freq. flatter not too much dip.

cheers..

[poseidonsvoice]

Hi!

Offline, we've discussed this design before and I am glad that it is working out for you. Do you mind putting up a pic of the rear of the speaker specifically to show off the shallow U-frame that the M-165X's are loaded in?

Great work, I'll definitely drop by the next time I visit Austin.

Anand.

[Nick77]

They look great Jason, and sounded wonderful. You were very instrumental in me switching to a OB design. I love the huge soundstage. Thanks

[nodiak]

That's great, congrats on the successful work! FWIW I have the 5208's, use them in sealed with a single sub for now. Have used them on OB shortly because I enjoy ob's, but haven't had enough time to build a system. Anyway, my experience has been that the tweeter sounded a little cold when I  use SS (gainclone), but not at all with tube amp.
Don

[gitarretyp]

Hi!

Offline, we've discussed this design before and I am glad that it is working out for you. Do you mind putting up a pic of the rear of the speaker specifically to show off the shallow U-frame that the M-165X's are loaded in?

Great work, I'll definitely drop by the next time I visit Austin.

Anand.

I'll try to get some rear pictures up shortly, and i'd be happy to have you over.

BBC dip I assume...

I use a DE250 compression driver, smooth as baby bottom, sometimes too smooth, hence I make freq. flatter not too much dip.

cheers..

Yeah, essentially a bbc dip. I would really like to hear the de250. I wanted to try a coax for this project, though. So, i went with the radian. It doesn't seem to me that the cd is removable without major surgery on the radian, or i might play with some other drivers.

They look great Jason, and sounded wonderful. You were very instrumental in me switching to a OB design. I love the huge soundstage. Thanks

Thanks for the compliments. I've tweaked them a fair bit since you heard them, so they're even better now.

That's great, congrats on the successful work! FWIW I have the 5208's, use them in sealed with a single sub for now. Have used them on OB shortly because I enjoy ob's, but haven't had enough time to build a system. Anyway, my experience has been that the tweeter sounded a little cold when I  use SS (gainclone), but not at all with tube amp.
Don

I've been considering trying the tube amp route for this very reason. What amp did you use on the tweeter?

[nodiak]

phew, glad you already had the curiosity!
I used a Scott 222c el84 push-pull and a Vaughn Audio el84 single ended. The only other tube amp I've had was also el84 se. Am slowly working on a Tubelab SimpleSE that uses el34, kt88, 6550 tubes (one of the varieties in this thread: http://www.audiocircle.com/index.php?topic=48005.0 ). Looking for a little more power and body with it. Still pretty new to tube amp types, but have learned they work for me. Also, my 5208's have a passive xo so the amp goes to their woofer and tweeter.
Also used a couple different tube pres with the gc, helped but not enough for my tastes.
I like your speakers alot, bet the GR drivers mix well sonically with the 5208's.
Don

[Hank]

Jason, looking good!  Good work and congratulations on your full OB baby!  I'd like to hear them - Mark H probably would too - maybe one of these days we could meet at your place for a listen - I could bring my Chinese tube amp for grins.

Should I reveal your secret?  That supposedly ordinary blanket draped over your TV, which is in reality woven from a specific acoustic absorption coeffecient fiber aa

[gitarretyp]

Jason, looking good!  Good work and congratulations on your full OB baby!  I'd like to hear them - Mark H probably would too - maybe one of these days we could meet at your place for a listen - I could bring my Chinese tube amp for grins.

Should I reveal your secret?  That supposedly ordinary blanket draped over your TV, which is in reality woven from a specific acoustic absorption coeffecient fiber aa

I'd be happy to have you guys over. As things are setup, i could only use the tube amp on the mids. But, that could still be interesting.

No one was supposed to know that about the blanket . Now everyone's going to be clamoring to get one.

[Hank]

Now everyone's going to be clamoring to get one.

That was my intent:  you'll make a killing.   Stick with me, I'm your Marketing man.

[Danny Richie]

Wow, what a great looking project. I am sure it sounds great too.

Those smooth off axis responses really make a big difference it creating a nice even in room response. This is an often overlooked key.

They look great too.

Congratulations on pulling off a great design.

[chrismercurio]

Can you contrast the sound quality difference between the Radian Coax and your Selah's that use BG and Accuton? I am familiar with the way the BG and Accuton sound.

I appreciate it as I am considering purchase of a pair of 5208 Radians.

Chris

[laserman]

Jason,

Looks very nice.  Please don't forget to post the pictures of the rear of the speakers.

Thank you,
Lou

[gitarretyp]

As requested. The backs will be covered with cloth, i just haven't made covers yet. Also, i might add a brace to the u-frame.

Can you contrast the sound quality difference between the Radian Coax and your Selah's that use BG and Accuton? I am familiar with the way the BG and Accuton sound.

I appreciate it as I am considering purchase of a pair of 5208 Radians.

Chris

It's been a while since i've had them side by side, but i'll do my best. The top end of the radian has sort of a rougher/edgier sound to it, less smooth and sweet. Also, as i mentioned, the radian can be somewhat sibilant unless managed carefully. I'm not 100% happy with the tweeter on the radians and would really like the try something like the B&C DE250, but they don't seem to be removable. The mids are a little warmer and seem more textured. The way i've voiced them, they're really pretty similar tonally. The radian walks all over the BG/Accuton combo dynamically and under high'ish spl conditions. The mids and dynamics are what made me decide to keep the radians. Also, they'd be darned hard to beat for the price.

[nodiak]

Just thought I'd throw in that I called Radian today with some questions about the 5208C's. The tweeter magnet is bonded to the woofers so they can't be seperated, too bad as I wanted to try the tweets with other coax. He said the tweeter diaphram can be removed and replaced tho. The tweeter isn't one of their stock models either (like 450pb, 465pb, etc.). I'm guessing but I think it may at least use a very similar or same diaphram tho.
The 5208C is a caste frame version of the 508/2B so the same specs apply. I had heard this, was nice to have it confirmed. He said their 322/08B-2 crossover will work for either coax. I don't know anything about the crossover's design or component quality.
Hope this info is useful.
Don

[gitarretyp]

Don, thanks for the info. It's unfortunate the CD's not removable. That would've opened up some nice possibilities.

All of radian's 1" drivers use the same diaphragm. The 322 crossover is speced as 1.8kHz, but slopes are not mentioned and component quality looks to be mediocre at best.

[Saurav]

How top-heavy are they? I have an 8 month old daughter who'll be crawling soon and eventually walking, and I'm concerned that building open baffle speakers may create something that's easier to tip over.

What is the audible effect of the foam? It looks like the gray strips are glued to the side panels, while the white pieces are stuffed in there?