Omnidirectionals on the cheap...help needed

[Paul Dimaline]

I cobbled together a pair of these the other week. They were made useing the bits that I had to hand, namely a pair of B200's, passive bass radiators and x-overs from a pair of Kef Cadenza's and a pair of Vifa D26TF 05-06 tweeters that I got well cheap from ebay.







I am under orders from SWMBO to make them look presentable so I am going to make another set of cabinets similar to the Shahinian Compass/Starter, I will then put the passive bass radiator on one of the "front" panels rather than the back as I have them now. This will hopefully allow me the option to get them slightly closer to the rear wall and give me the choice of having the radiators pointing inwards or outwards. It will also help break up the large blank panels on show. I will be wanting to make up grills to cover all the drivers.

As I want to get these cabinets looking something special has anyone got any comments or sugestions? I am going to try blocking of the gap between the rear panel and the diagonal brace just above the passive to see what differance that makes otherwise I am reasonably happy with the cabinet design.

The thing I am struggling with most of all is the x-over. At present it is a stock, 30 year old standard Cadenza item . Where do I go from there? I must point out at this stage that I am generally hopeless with computer programes and computers in general. I have no measuring equipment and doubt I could use it if I had so I am going to have to use trial and error....mad I know but its my fault for being a bit dim!
I dont know if there is any time alignment in the standard x-over, if there is then that is obviously not needed (is it?) and then there is the change of tweeter to consider. The B200 crosses over at about 3500 Hz so I am thinking of (sort of) useing the bass section from the Kef with, errrr, the treble section from something that uses the Vifa?? I am going to struggle with this bit...!!

[sreten]

Hi,

going for omnidirectional your only making things much much harder.

http://www.hifiloudspeakers.info/Ana...a/Cadenza.html

If you go for a standardish box with the drivers front mounted the
crossover should be fine, possibly you could experiment with L-pad
resistors on the tweeter to match the mid and treble levels.
(Also try the tweeter in both phases, driver phases may not match)

I'd go for a stand mounting well braced chunky deep
box with the ABR mounted on the rear of cabinet.

IMO an 8" midbass unit is a poor choice for a semi-omni design.

/sreten.

[Paul Dimaline]

Originally posted by sreten

(Also try the tweeter in both phases, driver phases may not match)

Yo! Result This is much better, huge improvement. I was thiking about this today at work, but I was trying to work out if running the tweeters out of phase to the mid bass unit would improve matters.
The way I see it (I think), is seeming as high frequencies are more directional than low, is the fact that both drivers are being reflected from the ceiling, are the HF's having their phase reversed by the ceiling? By reversing the phase on the tweeters have I actually corrected the phase of the system??. Or have I got hold of the wrong end of the stick altogether?

Paul.

[sreten]

Probably that it just works better on the extreme listening axis,

/sreten.

[el`Ol]

I am working on an omnidirectional project with the Ciare HX201 (some kind of B200 for BR). My observation is that for the omni-typical spatial image it is essential to have the driver at 90°. This correlates with my belief that the point about omnidirectionals is coherence (same acoustical center of the direct part of the sound over the whole frequency range). In my listening room the indirect sound is enough to get sufficient treble. I have no measurement equipment, but the subjective test with a function generator sounds OK. If it`s not sufficient in your case I would recommend something narrow (ribbon or slot) in line with the voicecoil of the B200.



regards,

Oliver

[Paul Dimaline]

Hi Oliver,

I want to make my speakers work in small to medium sized room, hence the psudo omni design. The baffle is about 40 degree's from horizontal and I have tried tilting the speaker back and it does improve matters slightly but the sound suffers if I tip them back to far. Pulling them away from the wall would doubtless help but as I say I would prefer them to work in a smaller room. I am building a second pair of cabinets at the moment and will make the baffle 30-35 degree's.

Today I got hold of some polypropylene capacitors to replace the 30 year old electrolytics, hopefully I will get a better idea of how the design works when I rebuild the x-overs.

Have you any pictures of your speakers? I would be very interested to know how you get on with them.

Paul.

[AJ]

Hi Paul

I've been playing with omnis in a small room lately too - with some failures and some successes. The first attempt was a double cone reflector using a Fostex FX200 full range driver and a Fostex FT17H supertweeter crossed at about 9khz.





Success was definitely limited, but mostly because I didn't really like the diffuse imaging and it was tough taming some very annoying brightness that seems to be a part of this type of rig.

I ended up closing off the back 180 degrees and adding a Fountek JP3 ribbon in a front firing configuration, and crossing at 3khz to get under the 4.5khz hump of the FX200. This setup turned out to be pretty darned good. The presentation is huge - like line array huge, but alot more relaxed and with a sweet spot too large to move out of without getting up and moving 3 feet to either side. There's enough directivity to produce very good imaging and with the enormous soundstage presentation, these are really easy to like. (if you can get past the ugly part )



I'm running the same setup with a pair of Audax PR170M0 drivers and Fountek JP2 (5 inch ribbon) on top at the moment, but the FX200/JP3 combo is better I think. The larger ribbon doesn't seem to have the dispersion of the smaller one, an I think that's part of the reason.

Anyway, just another approach to cheap omnis.

[el`Ol]

I still have the Ciares in test enclosures, pictures will follow. I just tested them in 30° setting and I am asolutely not pleased with it. The speakers can be localized and it sound very shouting because of the peak in the upper midrange (treble is more beamy and not affected by the 30° tilt). I have already tested a reflector cone and I don`t like it. It makes the spacial image flat and the instruments and vocalists smaller.



regards, Oliver



P.S. When I say 30° I mean 30° from my 90° setting. i.e. 60° from axis.

[newfinish]

here you will have a better idea
http://www.cd-konzert.com/loudspeaker.htm

[Scottmoose]

Originally posted by AJ
Hi Paul

I've been playing with omnis in a small room lately too - with some failures and some successes. The first attempt was a double cone reflector using a Fostex FX200 full range driver and a Fostex FT17H supertweeter crossed at about 9khz.

Aha! Do I also spot an 18" MLTL subwoofer?

One thought guys -you might want to have a look at the almost forgotten Infinity Holosonic. A friend over on a Quad discussion board (haven't visited that for a few months -I must drop in soon) told me he was rebuilding a pair. Five tweeters in an omni-array, with the cabinets wired together. Interesting idea at any rate.

Cheers
Scott