On the directivity of dipole tweeters - Page 25 - diyAudio
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Old 28th October 2012, 10:43 PM   #241
Rudolf is offline Rudolf  Germany
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soundaatma,
thanks for your kind words.
Quote:
Originally Posted by soundaatma View Post
Did you also experiment with the two tweeters wired in phase thus making a bipole tweeter.
I didn't look into bipoles because I want narrow dispersion, not a wider one.
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Compared to dipole phasing, believe a bipolar phasing would have the benefit of :
1)no dipole cancellation and hence lower cutoff
A 1" dome dipole would better a 1" bipole above 3 kHz. That is with a 3x3 cm "baffle" between the back-to-back tweeters. Don't try a much wider baffle (6x6 cm for instance) because that would ruin the radiation homogenity of the bipole.
Quote:
2)wider dispersion due to wrap around from the opposite tweeter, providing near omnipolar radiation before beaming starts.
Near omnipolar radiation only as long as the baffle is small enough. With a 6x6 cm baffle (which equals a 3 cm distance between front and rear dome) the directivity will fluctuate somewhat above 5 kHz.
In general tweeters with 4" faceplates or with (big) ferrite magnets won't work properly as bipoles.

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Old 30th October 2012, 03:01 AM   #242
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Thanks for your suggestions Rudolf.
I was actually planning a bipole using the Pluto driver Aurasound NSW2-326-8AT . Mounted back to back as close as possible, to be used from 500Hz and up, with bipole phasing to resemble an omnipole to the extent possible.
Any ideas
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Old 30th October 2012, 09:57 AM   #243
Rudolf is offline Rudolf  Germany
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Quote:
Originally Posted by soundaatma View Post
I was actually planning a bipole using the Pluto driver Aurasound NSW2-326-8AT . Mounted back to back as close as possible, to be used from 500Hz and up, with bipole phasing to resemble an omnipole to the extent possible.
No good idea at all
I simulated the situation with two Visaton BF45, which appear to have somewhat similar dimensions, in Boxsim:

Bipole45_1.gif

I mounted both drivers at just 6 cm distance, which wouldn't even let room for the rear exits of the Auras to breath. You can see how the on-axis response almost immediately becomes a mess. The off-axis response isn't any better:

Bipole45_3.gif

The directivity index finally proves that this configuration isn't worth any further thought :

Bipole45_2.gif
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Old 31st October 2012, 12:14 AM   #244
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Thanks for the sims on Boxsim Rudolf.
The bipole dip is clearly evident in the sims. However for a 6cm distance between the drivers I was expecting the half wavelength bipole dip when the 2 waves meet out of phase at about 2800Hz. Anyway the polar response disarray is nasty. Was not expecting this for a bipole. Guess I have to follow the advice of making the cabinet wider than deeper, to allow the baffle step fill in the bipole dip
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Old 31st October 2012, 09:33 AM   #245
Rudolf is offline Rudolf  Germany
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Quote:
Originally Posted by soundaatma View Post
However for a 6cm distance between the drivers I was expecting the half wavelength bipole dip when the 2 waves meet out of phase at about 2800Hz.
The distance between the drivers has to be calculated from the ears (where it counts).To the nominal 6 cm distance between the drivers you have to add the distance from the rear driver rim to its center, which is another 2+ cm.
If interested, you might try to mount the drivers one below the other. This could reduce the effective driver distance, but would certainly lead to other problems.
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Old 31st October 2012, 10:23 AM   #246
Telstar is offline Telstar  Italy
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Quote:
Originally Posted by Rudolf View Post
No good idea at all
I simulated the situation with two Visaton BF45, which appear to have somewhat similar dimensions, in Boxsim:
Hi Rudolf,
could you sim two slim tweeters (like scan-speak 710003 with the 6 magnets) in a round baffle about 20cm diameter and 10cm thick (to enclose the motors and some stuffing)? ah, connected in series.
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Old 31st October 2012, 11:05 AM   #247
Rudolf is offline Rudolf  Germany
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Originally Posted by Telstar View Post
Hi Rudolf,
could you sim two slim tweeters (like scan-speak 710003 with the 6 magnets) in a round baffle about 20cm diameter and 10cm thick (to enclose the motors and some stuffing)? ah, connected in series.
I'm not sure if this worth my time, but since you are curious :

Bipol SC10_1.gif

I simulated the Visaton SC10 which should be equal enough in its geometry. Boxsim doesn't do circular baffles, so I made it 18x18 cm square. Depth is 10 cm, drivers in series.
I add the boxsim file for this simulation as .zip. Note that it is not zipped. Just download it and change ".zip" to ".bpj" and you can open it in boxsim.

Bipole SC10.zip
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Old 31st October 2012, 11:17 AM   #248
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Rudolf- a slightly off topic question, but im interested in simming 2 tweeters in side panels. Im quite competant using Boxsim, but im unsure if it is possible to simulate this. Would you be able to confirm if it is possible?
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Old 31st October 2012, 01:30 PM   #249
Rudolf is offline Rudolf  Germany
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Originally Posted by mondogenerator View Post
Rudolf- a slightly off topic question, but im interested in simming 2 tweeters in side panels. Im quite competant using Boxsim, but im unsure if it is possible to simulate this.
Yes, you can point any driver to any of the speaker geometry axis - x,y,z.
Select driver x from the "Drivers & Enclosures" menue (where you select/change drivers).
At the top of the "Edit driver" window select the tab "Baffle and position".
The lower third of the window starts with the selection "Direction of beam". Select as you wish.
The position of the driver in space has to be given in xyz coordinates below. You can't do that in the "Common outer housing" window. Working with those xyz coordinates can be tricky. You could tell me, where you want your drivers on the side panels and I could position them in a "test" .bpj-file. Or you could start by yourself and let me look into it afterwards (if you feel so).

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Old 31st October 2012, 02:03 PM   #250
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Thanks Rudolf. The method you describe is what i expected, and that is why i hoped it was possible. I thought there may be other 'hidden tricks'. Thank you again, i shall spend some time experimenting!
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