Using a diffuser cone for up-firing speakers

[tspringer99]

I would like try building a speaker cabinet for use with amplified musical instruments that is less directional than the units that I have seen. The approach that I would like to try first is to orient the speaker upward in a sealed cabinet so that it faces into a diffuser cone that deflects the sound 360 degrees.

I would appreciate input on several questions:
First, could anybody point me toward information regarding the design of a similar speaker-diffuser system? In particular I'm interested in how the coupling of the speaker to the room air is effected by the cone (similar in concept to the coupling you get in horn-loaded speaker enclosures). For example, would an exponential flare to the speaker cone be better than other shapes? How close to the speaker should the diffuser be?

Or maybe I'll be lucky - Is there a commercial product on the market that would serve as a proper diffuser cone for a twelve inch speaker?

[Ed LaFontaine]

Does something like the Beo Lab 5 fit the description?

http://www.bang-olufsen.com/web2/sys...=ls&prodid=544

[Nanook]

Duevel

also I recall seeing an old plan for a fostex, lowther or similar called the "solo", can't recall where (it was a full range up-firing fullrange loudspeaker ... I looked. Not sure but closly matching the contour of the driver may be a way to go. I had , (and still have ) ideas regarding these. It's just that the JE Labs open baffles I built (while looking absolutely ugly) seem to be "it" for me:-)

[Rudolf]

Full Range Speaker Photo Gallery

Omnidirectionals on the cheap...help needed^

And don´t forget to look into the links given in these threads.

[Nanook]

a lowther plan, that could be adopted...
the ace

[angsuman]

Maybe something like mirage omnipolar waveguide? But less complex offcourse.

[el`Ol]

I tried simple 90° cones and the result was that the image became flat, maybe bacause of the low vertical dispersion. Somebody in a German forum suggested to use rocket tops, could be better in this respect. I am using the Ciare HX201 without diffusor now, the rising frequency response allows this.


Greets, Oliver

[dnsey]

Check out any number of designs of the 1970s - omnis were very popular them!

[tspringer99]

Thanks for getting me pointed in the right direction. Ive looked at a number of commercially designed up-firing omnidirectional speaker systems now. There seem to be two basic design philosophies regarding the shape of the diffuser cone. One design is a concave cone (V-shaped but flaring at the top). The other is a convex cone (V-shaped but bulging in the middle, like a missile nose cone). The diffuser cone for some of the concave cones is as large in diameter as the speaker, whereas many of the concave cone designs are considerable smaller than the diameter of the speaker. There must be some basic engineering principles that could be applied here, but the diversity of designs makes me wonder. For example, the presence of the diffuser cone close to the speaker cone must change the free-air resonance of the speaker system and thus affect the low frequency response of the speaker. Will the diffuser cone rduce the efficiency of the speaker, or is there a chance it could increase efficiency if designed like a horn-loaded enclosure?

[KBK]

The cone shape that is used in the best - full range speakers, is the cone shape you want to use as a diffusor for your omni-directional design. Some might say otherwise, as not all full range cones are created equal. (some of a cone's shaping is not simply acoustical loading issues, but is also designed to a specific shape--for stiffness reasons.