Sanity check on my Endeavour project - Page 2 - diyAudio
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Old 21st August 2012, 12:28 PM   #11
6.283 is offline 6.283  Germany
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Always welcome.

Quote:
Originally Posted by wowo101 View Post
For a "real" D'Appolito arrangement, even using a 12W or another 4" driver with the DXT nd cutting back as much of their flanges as possible would result in a required crossover frequency of about 1.2 kHz – not doable with the DXT. And I didn't find any tweeter with comparable dispersion control and a smaller diameter.
I know, but history has proven that even non-text book style MTM configurations result in a reduced but controlled vertical dispersion. That needs simulation, though. Also, many of those "proven" designs use LR4 filters instead of the text book BW3 filters and as far as I know, Joe himself is not really concerned about the design freedom
It is of course your choice but maybe worth another simulation evening.
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Old 21st August 2012, 12:40 PM   #12
wowo101 is offline wowo101  Germany
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Quote:
Originally Posted by 6.283 View Post
It is of course your choice but maybe worth another simulation evening.
That it definitely is.
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Old 21st August 2012, 12:46 PM   #13
6.283 is offline 6.283  Germany
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It would be great if the Seas data were available in Boxsim so that one could see the effect of the diffraction lense in this MTM arrangement. But I think the data is not available, right ?

I also meant to say: In the end the vertical response does not have to be perfect. Horizontal is much more important. So it would just be nice to avoid or minimize the floor bounce. But maybe you have some heavy carpet in front of the speakers. Then it would be a notch less important.
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Last edited by 6.283; 21st August 2012 at 12:50 PM.
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Old 21st August 2012, 12:59 PM   #14
wowo101 is offline wowo101  Germany
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I've used the measurement data from here: http://www.lautsprecherbau.de/user/d...7TBCD__DXT.zip as well as an SplTrace of the data published by SEAS, which seems to be good enough for the on-axis simulation.

As there is no possibility to correctly simulate the lense (or generally, waveguides) in Boxsim, I emulated the general effect by enlarging the sound radiating area, but this obviously doesn't get correct or even near correct results for off-axis FR. A discussion of waveguides and Boxsim off-axis results can be found somewhere in this thread: http://www.visaton.de/vb/showthread.php?t=22618

Last edited by wowo101; 21st August 2012 at 01:10 PM.
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Old 5th March 2013, 12:57 PM   #15
wowo101 is offline wowo101  Germany
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Default A fresh start

Hey all,

after a hiatus of a few months, I've reconsidered the design decisions of my Endeavour project and entered a second design iteration which I'd love to get your feedback on.

First of all, following 6.283's advice, I modeled a pseudo-D'Appolito MTM arrangement using small Discovery 10F drivers as mids in order to get as small a CTC distance as possible while keeping the DXT tweeter. The result was horrendous suckouts in the vertical plane which convinced me not to pursue this avenue further – although the "forward sounding character" of such an arrangement might appeal to some… (6.283, I'm following your recent design efforts at Kierkegaard - Kontrolliertes horizontales & vertikales Bündelungsmaß - DIY-HIFI-Forum with great interest – the combination of even smaller mids, a fullrange driver as tweeter and a very low XO frequency seems a promising path!)

I then reconsidered midrange driver, baffle width and woofer section, starting with the following assumptions:
  • A smaller mid could be used to reduce CTC distance between tweeter and midrange since max. SPL is limited by tweeter and woofer.
  • Front wall reflections should be reduced down to at least 500 Hz, i.e. in the range where our hearing is most acute. Cardioid solutions were ruled out because of implementation complexity and uncertainty about behaviour near walls (cf. Dipole/cardoid midbass - minimum distance from front wall).
  • Boundary effects/room gain simulations showed that a CB configuration would yield the flattest bass response in room (see first attachment); at the same time, impulse response could be optimized by switching to CB.
  • Going 3-way instead of 3.5-way would reduce cost and complexity.

Following this, the design I arrived at differs from the first approach in the following aspects:
  • Scan Speak Discovery 12w midrange driver instead of 15w, which also matches the DXT's directivity at XO frequency better.
  • Baffle width expanded to 26cm, resulting in a baffle step center frequency of 442 Hz; accompanied by larger chamfers to avoid increased edge diffraction effects.
  • Bass is now handled by a single 8" long-throw woofer (TIW 200 XS - 8 Ohm) in a 35 l closed box per side; possible bass extension by adding a Linkwitz transform to a suitable Fc.
  • W-M arranged to achieve a good compromise between floor bounce reduction and driver integration.
  • W-M XO moved to 500 Hz (geometric mean of first woofer and midrange floor bounce nulls).

The preliminary results are these:

Endeavour new.png
(Construction sketch)

Endeavour new FR.png
(Driver and summed FR)

Endeavour new Angles.png
(horizontal and vertical response plots)

Please ignore tweeter behaviour at angles > 0° since the DXT waveguide can't be modeled correctly in BoxSim.

My main concern now is power response at W-M XO which isn't as smooth as I hoped it would be – any hints on that?

And apart from that: Any other feedback?
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File Type: png Endeavour new Room Sim.png (92.3 KB, 65 views)
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Old 5th March 2013, 09:54 PM   #16
wowo101 is offline wowo101  Germany
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Any feedback? Highly appreciated!
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Old 6th March 2013, 06:27 AM   #17
6.283 is offline 6.283  Germany
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Hi Wowo,

I have recently asked myself what has become of this project !

Too bad that it did not work out with the MTM. What cross-overs did you use to simulate the MTM configuration and also this draft?

Anyway, the horizontal response is more important than floor bounce issues down in that freq. range. If you push the mid woofer down to 200Hz then the sub will operate in the modal region of the room and there is simply no floor bounce anymore to speak of, which only leaves the one of the midrange driver.

I would also not worry too much about those room gain calculations. I think they are crude at best if at all applicable to reality.

What drives the F-3 of the woofer is the F of first and second order room modes and the excursion capability of the diver (and of course placement of the box).
So this one has plenty of excursion and could easily be driven down to 25...30 Hz. Use a corrected Qt of 0.5 in CB, stay away from the 1st and 2nd order room modes also by placement (0.25 x room width for 2nd order) and enjoy. It won't get any better than this with two integrated woofers.

Here is the link to my latest project again in English for everybody, who is interested:

Kierkegaard
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Old 6th March 2013, 09:40 AM   #18
wowo101 is offline wowo101  Germany
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Default TMT experiments

Thanks for the feedback, 6.283! I've attached the sim I've done using Visaton's B80 as mid drivers (comparable in size and performance to the 10F). I used 3rd order Butterworth filters; the suckout affects the midrange and, combined with some off-axis flare above that region, leads to a quite uneven power response.

BUT: I've just begun to play around with 4th order LR filters instead of the Butterworth alignment, and things are beginning to look much better in that configuration! Will keep you posted.
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File Type: png Endeavour TMT 3rd order XO FR.png (42.8 KB, 43 views)
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Old 6th March 2013, 12:23 PM   #19
wowo101 is offline wowo101  Germany
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Default TMT experiments, part II

And these are the results of a quick reconfiguration along 6.283's lines (TMT, woofer near floor and crossed low), this time with a 4th LR alignment for mid and tweeter (and 2nd order for woofer and mid).

Now I get a quite large vertical listening window, together with a very even power response an quite smoothly rising directivity. Don't know why I didn't try and change the crossover alignment last time I did these simulations…

Endeavour TMT 4th order XO FR.png
(individual and summed FR)

Endeavour TMT 4th order XO FR angles.png
(horizontal and vertical response plots)

Endeavour TMT 4th order XO directivity.png
(directivity)
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Old 6th March 2013, 01:16 PM   #20
6.283 is offline 6.283  Germany
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Is there any further improvement, if the sub/mid are also crossed with a LR4 ? That would have been my default anyway.
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