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Multi-Way Conventional loudspeakers with crossovers

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Old 18th February 2017, 07:11 PM   #11
DonVK is offline DonVK  Canada
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Originally Posted by system7 View Post
Don, a fascinating project, and well documented.

I had a read around, and the prognosis for omnidirectional doesn't look good to me: Sonab OA5 mkII

I seriously wonder whether wall-mounting might not work better than floor mounting. It kind of ends up in the same place with adjacent boundaries. You possibly know about the Allison effect with the first reflection from the nearest boundary which creates a suckout.

I do appreciate the secondary sound of the room as an important part of the sound of a loudspeaker. Especially if you are not tied to a sweet spot for listening.

BTW, to correct the power hole in LR4, you just overlap the bass and tweeter more.
Yes, the -3db fix is easy. I'll add a capacitor to the HF filter and shift the response left. But that has to wait unit after I install the compression drivers and waveguides. Maybe more changes coming.

I will certainly try them in different room positions, but I expect that they need to be away from the wall (currently 1.3m) to get a reflection (7.5ms from incident). If they were positioned too close the reflection is nearly coincident with initial wave. This is like having the musician right against the concert wall to control the reflection. My reference baseline is an actual acoustic guitar played in the spot where the speaker currently stands so I can compare the two.
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Old 18th February 2017, 09:33 PM   #12
Sonce is offline Sonce  Macedonia
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I did. See earlier in the thread. Is a lower reflector needed?
For such a low crossover frequency it is not needed.
Good and inspiring work, by the way!
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Old 18th February 2017, 09:56 PM   #13
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BTW, to correct the power hole in LR4, you just overlap the bass and tweeter more.[/QUOTE]

Hi, hope you don't mine me butting in here. I think I have this problem with my fullrange FAST set up, but I thought this xover was supposed to sum flat
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Old 18th February 2017, 09:57 PM   #14
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sorry messed up the quote function. Haven't got the hang of it
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Old 18th February 2017, 10:06 PM   #15
DonVK is offline DonVK  Canada
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Never a problem. I did simulate my design with spice and happily looked at the -6db amplitudes at Fc , overall flatness and didn't give it another thought. Then I measured the actual acoustic output, rechecked everything, and then it made total sense why my power was down -3db.
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Old 18th February 2017, 10:17 PM   #16
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Thanks. Same here, only found it after EQing LF and then measuring. I shall follow this thread with interest....
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Old 18th February 2017, 10:17 PM   #17
system7 is offline system7  United Kingdom
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LR4 is a flat frequency response solution with a -6dB crossover. The power hole comes from the way you get a null above and below axis. For a 3kHz crossover, you tune the bass to about 2kHz, and the tweeter to about 5kHz.

BW3 is a constant power solution with a -3dB crossover. It also seems to give a flat impedance if you don't correct for bafflestep, which means wall mounting. For a 3kHz crossover, bass and treble filters both tune to 3kHz on component values.

I'm winging it a bit here, but 90 degrees can mean phase alignment or directional alignment. A FAST usually aligns the bass sideways and the tweeter forwards. So you should design for a constant power +3dB crossover peak on a flat baffle and good phase alignment.

Then when you face the bass sideways, on either polarity because BW3 doesn't care, the power stays flat and the +3dB peak goes away. In practise, BW3 works the drivers harder at crossover. It's worth experimenting with polarity IMO. They do different things.

Well, that's my theory. BW3 is quite difficult in practise. Some drivers play nicely, other don't.
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Last edited by system7; 18th February 2017 at 10:28 PM.
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Old 18th February 2017, 10:25 PM   #18
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LR4 is a flat frequency response solution with a -6dB crossover. The power hole comes from the way you get a null above and below axis.

BW3 is a constant power solution with a -3dB crossover. It also seems to give a flat impedance if you don't correct for bafflestep, which means wall mounting.

I'm winging it a bit here, but 90 degrees can mean phase alignment or directional alignment. A FAST usually aligns the bass sideways and the tweeter forwards. So you should design for a constant power +3dB crossover peak on a flat baffle and good phase alignment.

Then when you face the bass sideways, on either polarity because BW3 doesn't care, the power stays flat and the +3dB peak goes away. In practise, BW3 works the drivers harder at crossover.

Well, that's my theory. BW3 is quite difficult in practise. Some drivers play nicely, other don't.
Thanks. That's really interesting. Guess I should have mentioned, it's open baffle too and U frame subs so 90 degree angling is not and option. Lots to mull over though
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Old 19th February 2017, 12:23 AM   #19
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BTW, Don, here's a Visaton SC5 tweeter that I thought could make a good supertweeter above 5kHz. Because most of the 1" and bigger tweeters have dispersion problems at the top end.

SC 5 - 8 Ohm

I really have no idea how it sounds, but the regular mylar sound, you'd guess. And I don't think the ear is very discriminating above 10kHz anyway.

A 0.5" dome ought to have very good and flat power response up to the limit of audibility. Cheap enough to use several, if you wanted too. Audax make one like this too.
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Old 19th February 2017, 12:25 AM   #20
DonVK is offline DonVK  Canada
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Default But is it OmniDirectional?

The shape of my omni sandbox is not ideal. It has a rectangular base, large reflector discs, it's bass ported, and uses posts to support the discs. There's the potential for lots of baffle diffraction and unintentional reflections.

So I fixed the measurement mic w.r.t the room, and rotated the speaker -120, -60, 0, +60, and +120. In hindsight I should have added +180, oh well. The room acoustics are the same w.r.t mic and whats left is the radiation pattern from the speaker at different polar angles. Measurements are 1m out at center disc height. I still have my soft dome tweeters installed so the HF is suffering, and the XO still has the -3db dip from LR4@1800Hz . However the response is very close for all angles.

P.S. I've always had a problem with using the term "omnidirectional" to describe an "omnipolar" response but that seems to be the norm. Once I get the polar stuff working I'll try making this a hemispherical radiator.
Attached Images
File Type: jpg omni left @1m midheight -120 deg.jpg (92.2 KB, 223 views)
File Type: jpg omni left @1m midheight -60 deg.jpg (93.3 KB, 216 views)
File Type: jpg omni left @1m midheight 0 deg.jpg (92.2 KB, 215 views)
File Type: png omni left @1m midheight 60 deg.png (80.2 KB, 213 views)
File Type: jpg omni left @1m midheight 120 deg.jpg (92.4 KB, 213 views)
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