Using a diffuser cone for up-firing speakers

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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?
 
look here...

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:)
 
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
 
diffuser cone design

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?
 
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.
 
Not sure how to articulate this next thought... Lets try it this way. In a normal horn-loaded speaker cabinet, the speaker essential fires through a slot that leads into a horn. Could you topologically transform the horn so that the speaker fires upward and the sound is deflected laterally through a wrap-around slot into a radial horn? I've attached a cross-sectional sketch of what I have in mind.
 

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Oh yeah! Didn't look closely enough at the Duevel. It is claimed to be horn loaded. Thanks Nanook. I think that the the sides of the diffusion cone in systems like this form a paraolic surface where the radius of the cone (r) is a function of the distance from the tip (z) of the cone. That is,

r=z^2.

The supporting the speaker needs to slope away from the speaker some, but maybe that angle is not critical. I can guestimate the distance of the speaker from the diffuser cone from the pictures of the Duevel speakers. I suspect that this iIS a critical factor in determining the efficiency gain from the horn loading, and the optimum is probably speaker dependent. Right? Any ideas about this?
 
Nanook - you are right again. The cross section is closer to exponential than to quadratic. I can't measure accurately enough on the photo to see if it is exactly exponential but it's close. For anyone who might be interested, estimating the parameters of the equation for the cross section of the cone I get

d=0.8775 *exp(0.7776*z)

where d = distance from tip of diffuser cone
and d = diameter of the cone at distance d from the tip of the cone

This diffuser cone was matched with an 8 inch speaker, and the equation gives the diameter of the cone up to z=3 inches which is the distance to the tip to the upper lip of the diffuser cone that was used.

At 3 inches from the tip of the diffuser the diameter is about 9 inches. I assume that you can just scale-up the diffuser for a 12 inch speaker using the same equation. For example a diffuser cone whith z of 3.5 inches gives a diffuser cone diameter of 13.3 inches.

Now if I can just figure out how close to the speaker the tip of the diffuser cone should be...
 
Try:
Nolte Audio - Home
Very nice sounding and they really do disappear in the room.

I wish everyone out there would give these type of devices a try. The Beolab lens is my favorite, but there are many ways to do it. The sensation that the sound is 'floating' above the speaker is way cool. I've never heard the Linkwitz Plutos but I'll bet the effect is similar.
 
Google for images of a Tannoy Orbitus (Omnidirectional) speaker from early '70's.
Fascinating, upward firing into an exact copy curve of the speaker cone contraption.
Like all Tannoys an outstanding performer.
Except they were a bust in the market place.
Who wants a speaker in the middle of a non dedicated for Music room?
Damned few apparently.
 
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