"Diffused" dipole ?

[bzfcocon]

Hi

I am currently planning to move to open baffle - actually, "non-box"- for my midrange units. The drivers are the standar 2 way configuration with a 7" midwoofer and 1" tweeter. They will be crossed at about 160 Hz to my dipole bass units (Y frame).

Now I have to choose a configuration. First, I was thinking about a simple U-frame with narrow baffle and short wings (like 5 cm), resulting in more or less a pure dipole radiation pattern

On a second glance, though, I have constraints wrt the necessary space behind the speakers to allow for proper dipole operation(I do not think I will be able to have more than 3 feet behind). In this case, several solutions occured to me:
1. absorbing the rear radiation to some extent - as far as I understood, not a good solution for dipoles.
2. diffusing the rear radiation - the better solution
3. a different radiation pattern - some sort of cardioid that would radiate less in the back

Then, another idea would be to somehow combine 2 and 3 by using
a difuser element in the back of the baffle, like in the picture. Actually, the back radiation would be allowed to pass only through the lateral openings, hopefully resulting in a better end result

So what do you think ? Will this work ? Or am I worrying too much ? Would there be any way to simulate such an animal ? I think I have seen a similar triangular baffle in a commercial design, but I don't remember where.

[CLS]

Did you read this?

http://www.diyaudio.com/forums/showt...88#post1331188

[bzfcocon]

Hey , thanks, hadn't read that before, looks like the thing I want !

However, at a quick look, I couldn't tell the Karlson slot from the back deflectors - or are only deflectors in the pic ? Are there any considerations wrt to the effect of such things ?

[saturntube]

Why dont you just make the front panel to hold the speakers and play around with all the good ideas you have...sounds like fun.
You can use cardboard even and go crazy with wings and deflectors, etc...
Check out the "Solovox" speaker, it is designed to be used near the back wall...

IME absorbing the back wave is not a good idea.

cheers.

[bzfcocon]

Originally posted by saturntube
Why dont you just make the front panel to hold the speakers and play around with all the good ideas you have...sounds like fun.
You can use cardboard even and go crazy with wings and deflectors, etc...

Yep, that would be fun indeed ! Unfortunately, I don't have very much time to play , therefore I want to set a few starting points.

I do not want to place speakers very near to to wall - to me, tat always sounded bad. I am trying to achieve a compromise between the necessary space and the "boxiness" necessary to control the radiation pattern. In other words, I am trying to sacrifice as little as possible from the no-box concept.

[dlneubec]

Hi,

I think you might have some serious cavity resonances with the shapes you are looking at. FWIW, if it were me, I would try something more like this.

[bzfcocon]

Yep, that's the sort I'm looking for. I also fear that the curved deflectors from the thread pointed above plus the long wings will have resonances.

Do you expect any effect on the frequency response/radiation pattern in the case you depicted ?

[dlneubec]

It's really hard to say. You will be best served to have measurement equipement to pull off this kind of project. That way you can move/modify the diffusers and understand the effect on the resulting frequency response.

[bzfcocon]

I did a very brief test with my speakers in narrow OB with 8cm wings and used a triangularly shaped box to test the effect when put as deflector in the back. As it can be seen, things are very similar to Linkwitz' projects (peak around 500 hz and then 6dB/oct roll-off)

The difference in frequency response(red-without, blueish - with the deflector) is, as expected, an increased resonance peak (measurements taken in the middle of the room from 1m). Not very much otherwise. I guess I'll have to build them first and listen whether there are significant improvements wit a back deflector - which I doubt.

Rather than a big deflector, I am thinking to try some sort of "diffuser" - maybe a set of interlaced columns at the back in order to "spread" the backwave and avoid reflection back in the speaker. But it seems that I need a certain distance even to that diffuser.