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Multi-Way Conventional loudspeakers with crossovers

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Old 19th February 2017, 01:46 AM   #21
DonVK is online now DonVK  Canada
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Quote:
Originally Posted by system7 View Post
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.
Thanks for the suggestions.

My experience so far, with firing a dome into a reflector, has been that it resulted in too much loss and possible interference patterns. I also need to go down to 1.8Khz. My sandbox is intentionally restricted to a 2 way to make it easy for me to try ideas. Once I "get it working" the omni shape will be refined and it will emerge as a 3/4 way in a more eye pleasing package.

I'll be using a Dayton Audio H10RW 10″ Round Waveguide (good down to 1.6Khz) coupled to a Fane CD-130 compression driver. If it works as advertised, I'll get 106db/W and a properly formed wavefront into the reflector. Once I remove my approx 10db path loss I'm left with 96db to the air. Enough margin for tweaking.
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Old 19th February 2017, 03:25 AM   #22
DonVK is online now DonVK  Canada
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Originally Posted by scottjoplin View Post
Thanks. Same here, only found it after EQing LF and then measuring. I shall follow this thread with interest....
I was thinking of an compact explanation for this.

At Fc, spice shows -6db which is a voltage measurement. So 20*log(Vo/Vi)=-6db or 10^(-0.6)=0.5, meaning the voltage applied to a driver is down to 0.5 w.r.t input. If you prefer vectors the voltage is [0.486+0.12j] which is the same as -6db.

If you add those vectors, or the db voltages you will be back to 0.5+0.5=1.0 and spice shows a flat voltage response or 20*log(1/1)=0db. This is where I missed it the first time.

Power is essentially proportional to v^2, so if we had 0.5 voltage we get 0.25 power at each driver. Adding 0.25+0.25=0.5 power total, or 10*log(P1/P2)=-3db . Presto.

A side note : the polynomial that created LR4 (double cascaded 2nd order Butterworth) ensures uniform (linear) phase response and group delay and maximum flattness (of voltage). Its what makes it special. You can tweak it alittle but at some point you will degrade those qualities. You cannot arbitrarily select different cutoff frequencies as they are matched in a 2way. I need to fix mine and I can share a solution, as I want to minimize the parts count change.
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Old 19th February 2017, 08:54 PM   #23
graaf is offline graaf  Poland
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Quote:
Originally Posted by DonVK View Post
I did. See earlier in the thread. Is a lower reflector needed?
You did a measurement, I mean extensive listening.

no, You don't need any reflectors, rather a reflecting ceiling
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Old 19th February 2017, 10:49 PM   #24
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by DonVK View Post

Power is essentially proportional to v^2, so if we had 0.5 voltage we get 0.25 power at each driver. Adding 0.25+0.25=0.5 power total, or 10*log(P1/P2)=-3db . Presto.

Ha, yes of course, sometimes it's hard to see the wood for the trees.

A side note : the polynomial that created LR4 (double cascaded 2nd order Butterworth) ensures uniform (linear) phase response and group delay and maximum flattness (of voltage). Its what makes it special. You can tweak it alittle but at some point you will degrade those qualities. You cannot arbitrarily select different cutoff frequencies as they are matched in a 2way. I need to fix mine and I can share a solution, as I want to minimize the parts count change.
I should like to see your solution. For completeness, my xover is at 125Hz, which is too low for Jordan Eikona in open baffle, although it is effectively quite large.
I have tried to divide this quote, hope it's worked No not quite as I intended, I am guilty of inserting something into yours above. Can someone tell me how to do this please
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Last edited by scottjoplin; 19th February 2017 at 10:51 PM.
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Old 19th February 2017, 11:36 PM   #25
DonVK is online now DonVK  Canada
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Originally Posted by graaf View Post
You did a measurement, I mean extensive listening.

no, You don't need any reflectors, rather a reflecting ceiling
I understand what you mean. I have temporarily tried this when I was testing the XO, speakers on the floor pointed up to the ceiling. The sound does reflect.

I have a cathedral ceiling but it's been stippled so it acts like a diffuser, and I have floor with carpets which act as an absorber. So the sound does reflect from the ceiling but I wouldn't be able to tell left from right and its does not reinforce the incident wave properly, at least not to my ears. I do plan on using the ceiling in the future when this project becomes a hemispherical radiator, in an attempt to add more "spaciousness".
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Old 20th February 2017, 12:02 AM   #26
Xaborus is offline Xaborus  United States
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Don, no idea if it would improve anything, but just a quick thought

You documented problems with firing a tweeter into a cone due to the radiation directivity of such a small acoustic radiator.

Possibly a larger fullrange radiator would give better results by using the natural beaming of high frequencies? The 3.5" TC9FD is exceptionally flat for a full-range and cheap around $11. Should start beaming around 3khz due to it's size.

It would also be interesting to see if there are any differences firing into a cone, a "reverse horn" shape (no idea what to call this), a half hemisphere, and a full sphere.

Another idea is using a compression driver mounted to a 360 degree horn.

Click the image to open in full size.

Last edited by Xaborus; 20th February 2017 at 12:11 AM.
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Old 20th February 2017, 01:03 AM   #27
DonVK is online now DonVK  Canada
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Good suggestions. Beaming does help as I see an improvement at the higher freq. However its not the only problem. The drivers suffers from high attenuation as the pressure is spread from 120deg (or less) out to 360deg (reflector).

Next up is a waveguide and a compression driver. I should have the parts and results by end of this week. I believe that's what the Duevel (in your image) is doing. I'll be using a Dayton Audio H10RW 10″ Round Waveguide (good down to 1.6Khz) coupled to a Fane CD-130 compression driver.

Last edited by DonVK; 20th February 2017 at 01:08 AM.
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Old 20th February 2017, 01:46 AM   #28
Xaborus is offline Xaborus  United States
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Ahh yes, that makes sense that the radiation pattern effects SPL at distance.

If this is the problem and the above full-range driver configuration worked wonderfully, you could increase efficiency by an omni line array; using a tower of half-sphere enclosures firing into back of the next enclosure.

There are many ways to skin a cat, for sure!

Good luck with the experiment! I'll be watching this for sure

Last edited by Xaborus; 20th February 2017 at 01:48 AM.
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Old 20th February 2017, 01:01 PM   #29
anji12305 is offline anji12305  United States
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I wonder if you could achieve this HF dispersion pattern with two identical waveguides "nested"?

Tweeter mounted to plywood panel, facing up.

First waveguide mounted to this base panel, exit points up also.

Second waveguide suspended above "fixed" assembly, with mounting flange capped.

This would allow tuning if the nested guides can be adjusted to control the gap created.

http://www.daytonaudio.com/index.php...-threaded.html

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Old 20th February 2017, 01:35 PM   #30
DonVK is online now DonVK  Canada
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Thanks. I'll try it and post results, its an easy experiment. Those are the waveguides I have on order already. If that works it would be a convenient solution, the waveguide and reflector being the same shape. My initial concern was I'd have constant gap width from transducer to exit from nesting identical structures and no control of flare at the exit. We'll know within a week.
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