My omnidirectional project.

[Acoustic Absorb]

Greetings.
In am contemplating building an omnidirectional speaker using conical dispersers below downward facing drivers. My design will probably be two way with widerange HF and woofer with crossover about 500Hz. Has anyone experience with conical dispersers? What are the difficulties?
Your comments appreciated.

[CeramicMan]

How do you plan on making the speaker stands? Presumably they'll be in the path of the sound, so maybe they could be profiled in a way that gives the system a bit of horn loading?

[Acoustic Absorb]

Hi CeramicMan.
I have seen designs using a 360 degree horn like you seem to be suggesting. I reckon that I should try to avoid horn effects since horn reinforcement would be in a restricted frequency range with amplitude ripples outside that range. I am not a horn expert and so I intend to keep it simple. I am aiming at diffusion rather than reinforcement, and wonder if there are difficulties in achieving that.
What do you think?

[CeramicMan]

I'd probably go for two sections. E.g.: midwoofer with a dispersion cone underneath it, and a similar system for the tweeter placed on top of the midwoofer box.

The stands could be a tripod-like design, or maybe they could converge onto the cone?

You'd have to make some drawings to see what angles the reflections would go in. And you might find that some other shape is better suited rather than a cone, e.g.: a bullet tip?

[dlneubec]

First, I'm not expert but have built one omni design and I'm working ont he second and third ones.

First, you are essentially listening 90º off axis to the driver. This means you will have a very quick natural rool off with most drivers. The diffuser can help flatten this out and extend it a bit. A diffuser, combined with a waveguide, can do an even better job of flattening and extending the response.

You want to think about the wavelengths at your contemplated crossover points. Diffusers/dfelectors do little to nothing down low because the wavelengths are too long. For example the woofer you crossover to at 500 hz will not be helped by a diffuser, except perhaps to smooth out its roll off up high, well above the crossover point.

The spacing between the diffuser and the driver will be critical and have a major effect on it's response. IMHO, do not even try this kind of project unless you have full measurement capabilities and can test lots of different scenarios until you find the FR you are looking for.

My experimentation seems to indicate that concave cone diffusers work best. I have them to have better FR than dome shapes or straight cone shapes.

Below are a couple pics of the projects I have done or are in the prototype stage. The first one features a downfiring 12" sub, an up and downfiring midwoofer, and a front firing tweeter. It is only omnidirectional up the the crossover to the tweeter, however I believe the front firing tweeter improves the imaging.

The second one is fully omnidirectional, at least horizontally9the one one the right in the pic). It features up and downfiring woofers, an upfiring dome midrange, which is in a modified waveguide and fires up into a concave cone diffuser, and an upfiring tweeter, which is in a modified waveguide and recessed in the diffuser for the mid. the tweeter fires into another concave cone diffuser.

Also, there are two threads on the process I went through to get these done over at HTGuide that you might find helpful in terms of understanding what diffusers, etc. will do to driver response. There are lots of measuements, graphs, etc. detailing my journey.

There is little to no information out there in the DIY community on these kinds of speakers and they are very challenging to get right. Good Luck!

http://htguide.com/forum/showthread....mnidirectional
http://htguide.com/forum/showthread....mnidirectional

[CeramicMan]

Re: pics... So essentially it looks like a form of horn-loading anyway, right? The profile is essentially rotated around a circle.

[dlneubec]

The second pic or the prototype is essentially 360º horn loading, yes.

It's the same concept that Duevel uses in their commercial omni's.

[dlneubec]

Here is a pic that shows what is happening up closer.

[Acoustic Absorb]

Post #5
First, I'm not expert but have built one omni design and I'm working ont he second and third ones...

Hi dlneubec
Congratulations for going and doing it. There is a feast of information in your thread which I will digest later.
Thanks.
AA

[JinMTVT]

Could you guys explain to me the hole point about omnidirectional ( well i know they aren;t doing it seriously, but you guys are actually trying to get to it)

Is it because you like to have a lot of reflections?
ambiance?
i've owned a few Mirage OM loudspeakers, and though the quality of the drivers and the system was very high,
they were introducing a lot of problems in small rooms with too much reflections soo close to the original signal

is it for dispersion / off axis listening ?


and how does your "deflectors" work with different frequency ranges ? i would tend to think that a certain mecanical deflector could only work with a limited frequency range ( lower would be not affected and higher wouldn'thave time to take a serious radius/angle change ?? )