Need some suggestions for OB design using IB,TD, & Dipole 15

Posted In: Lambda Drivers

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    tinnitusintx on #1354

    Over the course of the last few years I’ve grabbed up the following drivers as they became available on the used market…

    (2) Dipole 15-8
    (2) TD15M
    (4) IB15

    What I’d like to do is utilize them in an OB design along with a Radian 475PB compression driver (in a QSC wave guide) to cover upper mid range/HF. I have an open back cover for the compression driver so it can propagate a rear wave, effectively making it dipolar as well. My room is 20x16x8 and I’m fairly unrestricted wrt speaker placement as it’s more or less a dedicated listening space (which also has rather extensive acoustic treatments).

    My initial idea was to use the Dipole 15 on the bottom of the baffle and perhaps house it in a U-frame. Above that would be the TD15M and above that the Radian in the QSC wave guide. I was thinking crossover points would be around 20-300 and 1.5k-2.5k as my inclination is to have the mid band driver cover as much of the mid range region as possible. My understanding is that off-axis response for the TD15 starts to fall off around 2k, but I’ve also been told it’s best to try to match the dispersion angle of the mid driver to the dispersion angle of the wave guide…which I believe is 90 degrees for the QSC….so I’m not sure what effect this would have on the crossover point except I assume it would push it well beyond 2k.

    Not really sure exactly what to do with the IB15’s but I’ve been pondering the idea of slot-loaded open baffle or w-frame type subwoofers. If they could be integrated into the main panel, maybe one on top and one on bottom, to relieve the Dipole 15 drivers of the really low stuff perhaps that would be a course to consider. I have another active crossover (Rane AC23) I could dedicate to them.

    I intend to go active with all this using an Ashly 3-way if that unit would be sufficient (since it a fixed 24db/octave slope) but the use of something like a MiniDSP is certainly not out of the question. I have several amplifiers to choose from, both tube and SS, to power all these drivers.

    But then again I might be going about this all wrong and that’s why I’m asking for a little guidance here. Do any of you see a more fitting implementation of these drivers in an OB design or could you offer any tweaks to what I’m proposing?


    Face on #11364

    You’ll want to cross the 15M lower, around 900hz will be a closer directivity match to your waveguide.

    I would not want to put the IB15s in slot loaded or w style bass enclosure, you’ll bottom them out very easily. A regular flat, H, or U will give you a good amount of bass.

    tinnitusintx on #11365

    Thanks for the reply, Face. I thought the 15M didn’t start to narrow until upwards of 2k? ❓

    These drivers are capable of reproducing frequencies of up to 2Khz off axis, and much higher with a more narrow dispersion pattern.

    You’re saying it’s actually down to 90 degrees at 900 Hz? And if I’m only concerned with response at my seated listening position, is it really that critical to make sure the dispersion angle of the Lambda driver isn’t less than the dispersion angle of the wave guide?

    Face on #11366

    Yes, much of what we hear is a result of what the speaker plays off axis as well.

    The 15M will play clean up to 2K, cleaner than any other 15 I’ve worked with, but the problem is that it’s already beaming like a laser at that frequency…but so would any 15″ woofer. The advantage to being so clean up high is that there are no out of pass band nasties creeping into the audible range when crossed at 900-1K.

    In another month or so the SEOS15 will be readily available for purchase. It’s similar to the QSC waveguide, but with no sharp edges in the mouth, meaning less internal reflections in the horn and a smoother sound.

    tinnitusintx on #11367

    Got it. Well, that’s a bit of a bummer. I’ve read in a few places the Radian seems to be getting out of its “happy place” when asked to play below 1.4-1.5k. Does the Dipole 15 have similar directivity characteristics as the 15M?

    Face on #11368

    @tinnitusintx wrote:

    Got it. Well, that’s a bit of a bummer. I’ve read in a few places the Radian seems to be getting out of its “happy place” when asked to play below 1.4-1.5k. Does the Dipole 15 have similar directivity characteristics as the 15M?

    Any 15″ woofer will, with the 15M and LO15 being the cleanest above 500hz.

    Listen to a 1K or higher test tone on a 15″ woofer and you’ll see exactly what I mean.

    As for a CD, check out the DIY Parts Group DNA-360, B&C DE-250, or BMS’s 1″ CDs for something that can be used that low.

    tinnitusintx on #11369

    A different CD is worth considering, but I built a two-way once using a JBL 2225 and Altec 511 horn and tried a few different CD’s (Radian, Renkus, 802) and it seemed like the mid range always lost a lot of the “meat” when the CD was playing down around 1K. Also, I’d rather not be crossing between two drivers in the 1k region and would really prefer to have the mid driver covering 2k or beyond. I’d definitely consider a better suited driver for mid range duty if what I have on hand simply isn’t designed to do what I’d like to do. How high can the LO12 play before directivity becomes an issue (assuming the LO is better than TD since this is an OB design)? Or, is there another AE driver that best satisfies what I’m trying to accomplish…which is cover 250 or so up to or beyond 2k in an OB?

    stryke on #11371

    If you plan to go up to 2KHz you really need a 3way system. The TD8M or TD6M could cover that range nicely.

    You will typically need some EQ at the lower end of a horn in a system like that. Actually not so much to boost there but to cut the main rise you get from the horn itself.

    tinnitusintx on #11372

    Thanks for the reply, stryke.

    What I’m considering will be at least a three way, perhaps even a four way, as I’d like the IB15’s to handle up to around 80 (so the Dipole 15’s don’t have to work so hard), the Dipole 15’s from 80-ish to 250-ish, the mid band driver from 250-ish to 2k-ish, and the cd horn beyond that (with the appropriate cd compensation applied to tame the rising response you spoke of). So you think the TD8M or 6M would be best in this region for an OB application?

    stryke on #11370

    If the range is from 250hz to 2KHz either option would work well. I think the best option would really be for the Dipole6 to cover that range if you are going fully open baffle.

    You will have plenty of overlap between drivers. You could take the Dipole15’s down a little lower to 50-60hz range and up higher as well. The same with the Dipole6 that could go down to 200hz or up to over 3KHz. This makes things much easier when you are using drivers well within their intended bandwidth.

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