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3" driver for CBT array?

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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 29 February 2020 at 2:47pm
The next step is to measure the impedance curve to determine if there is a sudden rise in resistance. A rise in resistance at 5 kHz would have the Beyma offer a dip within the 5 kHz range.

Based on my earliest measurements the Faital Pro looks about right using a typical swift sine wave sweep.



After being whacked with a good amount of power, the response curve is more like this...


Best Regards,


Edited by Elliot Thompson - 29 February 2020 at 2:59pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 29 February 2020 at 2:57pm
Originally posted by snowflake snowflake wrote:

low frequency response. this nearfiled measurement is very different to the previous measurement below 400Hz - room response was dominating before. the faital has a lower fs (110Hz vs 160Hz) and a higher Qts (0,7 vs 0.49). on an open baffle, I think this will make up for a some of its lower xmax and power handling - is that right? haven't really decided where to high pass these yet.


That's right!

The Qts, fs and VAS work together for the final result. Try matching both drivers at the same dB level at, I would say, 100 Hz and, make a measurement. The driver that remains the flattest from 100 Hz downwards will require less xmax within the flattest frequency range.

The drivers will go out of phase at it's fs. So High Passing either driver above the fs should yield an in phase response up to 20 kHz.

Best Regards,


Edited by Elliot Thompson - 29 February 2020 at 3:26pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2020 at 10:56pm
made some progress


used 11.5mm ply as it's what I had lying about. it's not quite bendy enough so going to leave it bending for a couple of days then screw it to a base and some curved side piece to stiffen it up. the more you curve it the lower the pattern control is maintained.


got some more crimp spade connectors on their way to keep all the wiring neat
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 04 April 2020 at 3:17pm
Nice!
The traditional way to get wood to bend is to use steam or hot water - maybe you could use some wet towels to apply the heat and steam, and then screw it to a former whilst still warm? 
Or, use a kerf cut between each driver - as long as your front laminate runs top to bottom grain wise? 9mm deep with a 2mm blade should give you more movement without compromising strength too much. You would still want plenty of reinforcement and glue in the kerfs. But this way should help to keep each driver's "land" flat.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 05 April 2020 at 3:42pm
Originally posted by studio45 studio45 wrote:

Nice!
The traditional way to get wood to bend is to use steam or hot water - maybe you could use some wet towels to apply the heat and steam, and then screw it to a former whilst still warm? 
Or, use a kerf cut between each driver - as long as your front laminate runs top to bottom grain wise? 9mm deep with a 2mm blade should give you more movement without compromising strength too much. You would still want plenty of reinforcement and glue in the kerfs. But this way should help to keep each driver's "land" flat.



think I can get it to 40deg arc of a 2m circle - should give pattern control down to 120Hz. I'd be afraid to steam this cheap ply in case it delaminated. Fine line between bendy and falling apart. might try some kerfs - might try doing them freehand with a narrow router bit. there's a reasonably thick gasket and there seems to be some flex in the mounting ears so think the drivers will fit okay.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 06 April 2020 at 8:22am
That is a perfect project to do during these chaotic times. Have you tried implementing the outcome with EASE Focus?


Best Regards,
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2020 at 2:25pm
got it wired up a couple of weeks ago and have been testing it side by side with my regular hi-fi speakers. still open baffle and haven't even put sides on it at yet as still palying around with the curvature.

needs a bit of eq but has useful response down to 100Hz. sound  is great with no midrange mudiness. plenty loud enough for home use but runs out of excursion on bass-heavy material.

might experiment with another driver with lower Fs and more xmax

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2020 at 2:29pm
You might expect the bass response to improve a bit and excursion to reduce when you turn it into a sealed box.  Might get you low enough to cross over comfortably to a sub.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2020 at 5:20pm
Originally posted by ceharden ceharden wrote:

You might expect the bass response to improve a bit and excursion to reduce when you turn it into a sealed box.  Might get you low enough to cross over comfortably to a sub.


I am tempted to try making it sealed back. but I'm quite liking the midrange sound of the open baffle. U-frame might give it a bit more authority down low.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote imageoven Quote  Post ReplyReply Direct Link To This Post Posted: 10 April 2021 at 12:22am
Did you ever complete this project?

I'm still sitting on 12 x 4" drivers, with an option on 4 more , and I'm interested in the options
Keep pushing on, things are gonna get better.
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