[JohnR]

My recent experiments have me wondering if I really do want 20 Hz to 20 kHz dipole radiation. In particular at the top end.  I notice that the Linkwitz Orion has the rear tweeter attenuated by 3 dB (if I'm reading the page right), but I haven't been able to find very much on other speakers.

I've also run into the issue of having the mid starting to attenuate the rear wave before the crossover point, then above the crossover it's full bore out the back again. So I was thinking that if I stick with the Neo3 I'll try attenuating the rear wave with some kind of acoustic baffling. Then I wonder if - since I'd like to increase the sensitivity of the system anyway - I should perhaps try something like a B&C DE35 and a rear "ambience tweeter" instead.

Has anyone experimented with varying the amount of rear radiation in the treble? What about using different types of tweeter for the front and rear - does it matter?

Any other thoughts or links appreciated

[nullspace]

Hi John,

I myself have done no experimentation. My setup transitions from dipole (direct radiator on OB) to cardiod (narrow directivity CD horn). I like what I have so haven't messed with it.

Paul W who hangs at diyAudio and HTGuide - Mission Impossible has messed around with attenuating the backwave. Here's a link to an experiment he did: Large midrange for OB??? Scott G ?. If you scan through his posts he might have gone into more detail or posted measurements.

Regards,
John

[Rudolf]

John,

the dipole radiation pattern is not a value in itself. It is a means to achieve a more uniform energy distribution in the room. In his book "Sound reproduction" Toole states time and again, that the energy distribution (over frequency) of the reflections should be as similar to the original sound source as possible. 

The first consequence is, that we can`t discuss this item without discussing the room were the loudspeakers are in. If you are not familiar with SLs living room , have a look at it: http://www.linkwitzlab.com/stereo%20reproduction.htm
There should not be many people having such a "live" room end behind the dipoles as SL has. It is mainly glass and rock, where the reflections from the rear are coming from. Not much absorption of high frequencies.

So in fact SLs attentuation of 3 dB in his room would be equivalent to a boost of some dB for anybody with large drapes or wall-to-wall bookshelves on the front wall.

Have you seen these polar measurements of an Orion "clone"? http://www.2pi-online.de/html/measurements.htm

The rearward energy loss at 1-2 kHz is almost inescapable for a three-way dipole system. But it happens for one octave only and you can easily return to a well balanced pattern afterwards. We are talking about a loss of max. 6 dB in the middle between 1-2 kHz. Do you really want to elongate this imbalance for 3 more octaves - up to 16 kHz?

Rudolf

[JohnR]

I'm thoroughly confused  If absorbing more high frequencies behind the speakers is better, then how is that different to reducing the amount of the rear wave at high frequencies?

[Rudolf]

I'm thoroughly confused 

Now, I am totally confused . Where did I say that absorbing more high frequencies behind the speakers is better? I tried to say the opposite .

In common rooms (with some furniture, decoration and a piece (at least) of textile on the floor) high frequencies are the first to get attenuated when bouncing around in the room. So they should be the last to be attenuated by additional means.

The problem with Linkwitz' Orion and all other tweeters in wide baffles is the off-axis "blooming" of the frequency response. In combination with very reflective side walls this can lead to the impression of too much high frequency energy in the room. But as said - this depends very much on the individual properties of every room.

May be you find it necessary to reduce the level of the rearward tweeter in your room, but I would not make a recommendation to start with an attenuated rear tweeter in general.

Rudolf

[JohnR]

Hi Rudolf, sorry for the delayed response. OK, I understand what you're saying now. And that's a very interesting point about the baffle and the resulting response, as it happens I am using a fairly wide baffle (30cm) - I will try the Neo3 in "free air" in the next prototype and see how that goes.

[matevana]

Hi Rudolf, sorry for the delayed response. OK, I understand what you're saying now. And that's a very interesting point about the baffle and the resulting response, as it happens I am using a fairly wide baffle (30cm) - I will try the Neo3 in "free air" in the next prototype and see how that goes.

John,

My OB project is true dipole up to about 6k. My mids/highs are a single point source, made up of an emi 8" coaxial driver and a Morel MDT-20 which fires through the mesh dust cap of the emi. I preferred this configuration to my previous experiment which used a peerless 3" driver up top and was dipole past 18k. I gave up on trying to deal with an irregular radiation pattern from the front wall of an unusually shaped room. Just recently I began experimenting with a rear firing Dayton neo tweeter, that is mounted on a pivot which allows me to (somewhat) control the vertical dispersion. The Dayton Neo has the same overall sensativity as the Morel .  I have  also found that mounting the rear tweeter at the base, and firing up at about a 45 degree angle toward the front wall seems to show some proimise in MY listening room in trying to tame some otherwise pesky reflections.