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Compact PA - in a car handled by a single man.
Compact PA - in a car handled by a single man.
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Old 9th October 2019, 06:06 PM   #21
pelanj is offline pelanj  Czech Republic
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Glad that you mentioned the RCFs. If everything goes well, I will be able to get a barely used pair second hand for 2/3 price of a new single unit.
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Old 9th October 2019, 08:03 PM   #22
kipman725 is offline kipman725  United Kingdom
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Another thought, if your looking for the ultimate in compact coaxial drivers are very attractive. Expensive for the good ones though. Also I would recommend going 3 way with them to avoid the waveguide come moving too much. I had an idea for a speaker in the form of a cube with the low frequency driver on the side of the box, sealed and with a lot of power. About 5x the cost of the 4*6" idea though!
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Old 9th October 2019, 09:29 PM   #23
pelanj is offline pelanj  Czech Republic
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CX12N251 looks good. And is not that expensive.
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Old 9th October 2019, 10:11 PM   #24
kipman725 is offline kipman725  United Kingdom
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The killer is the directivity plots, very few coaxs have nice polar responses. I don't know about the rcf one but b&c sell similar coaxs which have polar plots that you can look at. From memory the good looking ones where the 15" drivers that used the cone as the waveguide but these are very expensive.
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Old 9th October 2019, 11:11 PM   #25
kipman725 is offline kipman725  United Kingdom
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I found some picture of typical transitions in coaxial driver:
Detriments of a coaxial woofer?
pretty ugly those sharp discontinuities cause diffraction which mess up the polar response you also get diffraction around the horn in the type like the RCF with a fixed horn.

The Denovo from DIY sound group managed to fix this to get good polars:
Vortex Speaker Kits | HiFiCircuit
its unclear if there is something special about their drivers or if its the same driver as the KL3015CX-8. I would suspect considering the cost of custom machining and the pointlessness of making a driver that performs worse their driver probably has the same transition as the normal version...
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Old 10th October 2019, 03:24 AM   #26
Think is offline Think  Netherlands
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Compact PA - in a car handled by a single man.
If you put the 4x 6.5" drivers in a square, you get approximately the off axis response of a single 15" driver; narrowing at ~ 1kHz.

Edit: The comb filtering from drivers in the horizontal plane is much more noticeable then the same combfiltering in the vertical plane because our ears are in the horizontal plane.

I would put them in a vertical line with the tweeter in the middle: MMTMM then you get the horizontal off axis response of a single 6.5" (narrowing at ~2.5kHz and the vertical of axis response from a (4x 6.5"+tweeter) ~ 30" or 2x15" driver; narrowing at ~500Hz. Which will match a CD horn or ribbon/planar/AMT tweeter quite nice.


If you use a tweeter with more height then the 6.5" mids, then you start to get nasty vertical comb filtering and you are probably better off with the tweeter on top; TMMMM. That also depends on the crossover frequency but the closer the mids, the better.



You can also use a line of tweeters, i.e. a line of planers in front of the mids. But then the high end of the tweeters is as loud as a single tweeter due to comb filtering and you will have to EQ that back in. Which is not a big problem as there is not much energy in the highest frequencies. Video about line point source and line array/source speakers.

I would not use a line of coaxials as that will be a combfiltering disaster; a big suck out of the top end.

Last edited by Think; 10th October 2019 at 03:34 AM.
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Old 10th October 2019, 07:41 AM   #27
pelanj is offline pelanj  Czech Republic
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Think, what is the formula for the directivity of a piston driver? I know there is one that says how many degrees at which frequency, but could not find it. I only remember the rule (hope correctly) that beaming starts at half the wavelength.

Was there also any software that would calculate the polar responses with different driver arrangements and crossover?

Below is a sketch of the front baffle options with a small 70*70 waveguide mentioned before, it is usable down to 2 kHz (if I interpret the linked measurements correctly) and better be crossed over at 2.5 kHz. Visually, I like the middle one the most.
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File Type: jpg 4x6FE200BaffleOptions.jpg (44.7 KB, 85 views)
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Old 10th October 2019, 10:46 AM   #28
kipman725 is offline kipman725  United Kingdom
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I think Software virtuixCAD can do it or if your looking for something quick to get an idea Tolvan Data .
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Old 10th October 2019, 01:35 PM   #29
Think is offline Think  Netherlands
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Compact PA - in a car handled by a single man.
Narrowing starts where the wavelength is less then the (effective) width of a driver. Wavelength calculator

Faital Pro produces often good very good 45 degree off axis responses next to their on axis response. I suspect this has something to do with the shape of their cones, but it can also be that they lose some output in between 0 and 45 degrees off axis compared to others.

To bad most manufactures like Eminence don't publish any off axis data. But here is the Alphalite6a
Click the image to open in full size.

and the 6FE200 (watch the vertical divisions in the graph)

Click the image to open in full size.
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Old 10th October 2019, 02:34 PM   #30
pelanj is offline pelanj  Czech Republic
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I found out I need to use the 4 ohm version anyway. It has a Qts of 0.41 while the 8 ohm has 0.67. I should get away with a 20 - 30 l closed box crossed over at 150 Hz to the RCF sub(s).

Edit: The waveguide is round, so if rotated, it can be squeezed a little bit more.
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File Type: jpg 4x6FE200BaffleMin.jpg (11.9 KB, 66 views)

Last edited by pelanj; 10th October 2019 at 02:40 PM.
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