Double Back Horn MTM project

[baggystevo82]

Hello everyone,
I've been throwing some ideas around again today after being inspired by some Cain & Cains last night. This is what I've come up with so far anyway, using Fostex FE208EZ drivers run fullrange and a T90A supertweeter. I've developed the horns in hornresp and they seem to be fine, assuming I haven't overlooked anything. Any comments/suggestions/problems you can see would be really appreciated.
Thanks all,
Steve

[Nappylady]

That just makes me want to build a pair...

What kind of SPL and bass entension could one expect from such a beast?

[baggystevo82]

Hi,
Well this is what hornresp tells me, for a single horn. So I guess add 3dB to everything for the double horns in parallel. I'm fairly sure that that graph represents what would happen if the speaker was right in the corner of a room, so I'll probably end up taking in room measurements when they're built to position them well. As far as direct radiation from the drivers goes, the FE208EZ's are rated at 97dB each, so I'm aiming at an overall sensitivity of around 100dB. Hopefully any baffle step problems (if it is a problem with horns?) can be solved by careful room placement. As to outright max nice sounding SPL, enough I hope!
Thanks,
Steve

[baggystevo82]

forgot the pic, that was pretty stupid of me...

[dhenryp]

Beautiful!

The only concern I would have is lobing caused by having all three drivers running to very high frequencies (10k +) and with relatively large center to cnter spacing. The general rule of thumb is that MTMs should be crossed over at a frequency whose wavelength ~= the mid to tweeter spacing.

[baggystevo82]

Cheers Henry, I did wonder about that, but I read some reviews on the Seventh Veils and they just said it lacked treble if you're stood up, but are fine when you're sat down with your head at the correct level. in my design the tweeter is bang on head height (1m) and the mids point inwards so they converge 2m away from the speaker, though im not sure if that helps. If it does turn out to be a big problem the top box is identical to the bottom one, so I could just take the tops off and use them for rears for SACD in the future...
I've attatched a response curve for all drivers with a 1uF cap on the tweeter and 2 fostex's run full range. (this doesn't include the horn response so ignore the low frequencies) though I don't know if this will help sort out the lobing issue. Tweeter to mid distance is 163mm btw, which would mean approximately 2000kHz? (344 divided by 0.163). But then if lobing isn't a problem if your heads on the 'centerline' im not too worried.
Thanks again,
Steve

[baggystevo82]

Just remembered this too, on the T90A datasheet here fostex themselves seem to advocate the use of MTM with these identical drivers (This datasheet combined with Cain & Cains stuff was my inspiration for this, hehe) or at least using two fullrange drivers together anyway.

[wigginjs]

What did you use to do the 3D model?

[Hesky]

Awesome!! or should I say intimidating

I've been lookin into these full range drivers, there not exactly the last word in high frequency extension when compared to lowthers or the SV's little bandors. Somethin like 14K role off, so if that’s the case HF lobing may not be much of an issue if at all.

SolidWorks Student Edition? that blue background is such a give away

Hesky

[DeonC]

Hi Steve

Hopefully any baffle step problems (if it is a problem with horns?) can be solved by careful room placement.

How about solving two problems with one go. How about dipping the upper driver with 3dB - 6dB obove the baffle-step. That will solve any problems with lobing and such due to the large spacing relative to XO frequency. The overall efficiency will still be very high.

Enjoy,
Deon