On the directivity of dipole tweeters

[cuibono]

I and other have tried using very small back to back tweeters - smaller than the one you've linked to. Unfortunately, the results have been really bad... If you look around the forum some, you'll find a bunch of measurements people have done. The polar response was much poorer than one would have wished for, and was not usable at low enough frequencies - small tweeters just don't have enough displacement. Luckily, the neo3 planar tweeters from B&G are very good. About as good as its going to get without a totally new technology...

[Rudolf]

Originally Posted by cuibono

I and other have tried using very small back to back tweeters - smaller than the one you've linked to. Unfortunately, the results have been really bad... If you look around the forum some, you'll find a bunch of measurements people have done. The polar response was much poorer than one would have wished for, and was not usable at low enough frequencies - small tweeters just don't have enough displacement. Luckily, the neo3 planar tweeters from B&G are very good. About as good as its going to get without a totally new technology...

I wouldn't say it as harsh as cuibono does, but back-to-back-tweeters have an inherent problem:



The lower three drivers are back-to-back tweeters with the Monacor being the largest and the Dayton the smallest package. Note how a "bulging" region moves upward in frequency with diminishing dipole length. The upmost driver is a small cone driver Visaton FRS5X, which does not feature such a bulging region. It is a strong argument for the one-diaphragm-dipole tweeter.
Obviously the Neo 3 is the best dipole tweeter solution available apart from some very expensive AMT tweeters.

[gainphile]

The Klingon battleship polar response!

Seriously though they are not as bad as they look. The balance of front and rear is more important. I'd choose back to back domes over forward-firing only waveguide.

[6.283]

I add one for the gallery.
This is a double-pack of Peerless Platinum NE19VTC-04, for DIYers aka NE 200 VC, a 0,75" (measured at 1m).

P1010939.jpg

The dipole length is more or less the same as Rudolf's Monachor setup. But the polar response is just...not good. The Klingon Bird of Prey seen from the top with a nice first null at 3.5KHz.

Vifa_dipole_FR.PNG
Vifa_dipole_sono.PNG
Vifa_dipole_polar.PNG

Even if one could have a double-dome-dipole (ddd ) with a nice polar response, it would still be difficult to integrate it into the x-over to the mid driver. Not to mention SPL capability.
I think this is a dead end.

Originally Posted by gainphile

The balance of front and rear is more important.

Agreed. Rudolf do you have the data from the backside of the FRS5x ?

Originally Posted by gainphile

I'd choose back to back domes over forward-firing only waveguide.

You made up your mind, hu ?

Originally Posted by gainphile

Seriously though they are not as bad as they look.

Also agreed.
In another recent test I played pink noise while sitting in front of my dipole and slowly turning it. All what really happens while increasing the angle is that the bass fades away (as it should) and then the highs. But it is not that the mids are somehow peaking out all the time. Sure, there still is a spectral imbalance and room for improvement but I think as long as the radiation under angle does not or not significantly (>3dB ?) exceed the 0° SPL you have achieved something. ASW is most likely also impacted by the blooming but that would need a comparison with another speaker being more perfect on paper.
Has anybody ever tested an AMT (2510 without face plate) here ? I would really like to see the response one day. Right now that option is too expensive.

Oh, BTW, the Vifa is mono not bad at all for that money (measured in the same jig).
Vifa_mono_sono_600.PNG

[Rudolf]

Originally Posted by 6.283

Rudolf do you have the data from the backside of the FRS5x ?

If I equalize the front response to somewhat linear, both look like this:



What I still like about the response:



I have tried to keep the colors and the division according to your VIFA diagram. Does the VIFA have some kind of diffusor in front of the dome?

Even if the backside response of the FRS5X rolls off above 4 kHz, the response to the side will stay inside a nice dipole 8 for the front radiation. If I think about it: To me the balance between front and rear is less important than the well reduced radiation to the side.

[6.283]

Originally Posted by Rudolf

Does the VIFA have some kind of diffusor in front of the dome?

To me it rather looks like children and/or transportation intrusion prevention. I don't think it has serious diffusive character.

Originally Posted by Rudolf

If I think about it: To me the balance between front and rear is less important than the well reduced radiation to the side.

You potentially trade depth of the sound stage for potentially harmless ASW effects. You must have some expericence to support this thought. So how's your swinging thingy sounding compared to your other dipole ? You have two to compare. I don't. So what's the difference ? Use some flowery hifi review magazine vocabulary and share the experience

[gainphile]

Originally Posted by 6.283

You made up your mind, hu ?

I think it's the best compromise, and is already a much better topology than any normal speakers out there . The power response needs to be controlled though and SL's DSS does the job fine (and also lowering the tweeter's output).

Of course we strive for the best and much has/need to been learnt. But they usually also introduce other 'issues'.

- using waveguides: what about the rear radiation? What about H O M

- using different diameter/naked drivers. e.g. Nao Note. Nice. But what about baffle width change. Surely it's not inaudible?


I'm now actually using the dipoles I built 3 years ago. Simple, cheap, and great PRaT, a veil had been lifted. Black notes are blacker and I can hear singers spitting on the microphone .. from my neighbour's kitchen .

I've used them in both live (400ms) and dead (250ms) RT60 rooms. Sounded different but equally acceptable.

[PRTG]

I went through this thread within last two weeks, it was great to find so many important (though very often neglected) things discussed together in short time.

Special thanks to Raal regarding things to consider choosing mid-drivers, it was very close to my intuitive thoughts/observations, nice to have someone to confirm it. Also to Gainphile on his works on directivity measurements with different waveguides, and Rudolph for starting this thread

So as far "omni vs dipole" can be summarized as that dipole helps fighting early reflections in cases when room treatment isn't justifiable, still being equally usable within treated room. Some suggest that in well treated room monopoles give somewhat better soundstage. Anyway, for home DIY usage I see dipole as somewhat easier choice.

For me questions that are still unanswered in satisfactory detail are:

a) would close to ideal directivity towards HF improve sound compared to typical "decline";
b) positive effects of baffle width/size in dipole configuration for HF (i.e. drivers with waveguides "hanged" vs waveguides suspended in baffle);
c) omni vs figure-8 in 0.3-1kHz range - should we bother about (human-specific perception factor as having difficulty to locate source point in this range) ?

If a) = true, we could work more on waveguide construction, felt usage, ENABL (wasn't mentioned here - too esoteric?), etc.
If b) = true, we could work more on different baffle size/form for HF/MF;
If c) = not true, we could work on finding driver that covers HF down to 1kHz and don't bother with trying to disperse lower midrange. AND we could go for bipole instead of dipole down here.

So how about building a loudspeaker sensitive enough to work with SET amp (93dB/2.83V or more), using minimum of ways (two?), getting away with respectable bass extension (-3dB at 40Hz), having detailed and dynamic sound due close-to-constant directivity above 1kHz and less impact from room due dipole HF and bipole MF/LF setup and.. getting it all done under 500$ per pair? Am I aiming high enough? Anybody have done this already?

[Rudolf]

Originally Posted by PRTG

a) would close to ideal directivity towards HF improve sound compared to typical "decline";

While "directivity" is another category than "decline": Try to keep as much HF in the reverberant field as possible, compared to the direct field. Think "diffusity" instead of "directivity". But I can't tell you, if this will "improve" your sound. I have no idea, what you understand as "improved".

b) positive effects of baffle width/size in dipole configuration for HF (i.e. drivers with waveguides "hanged" vs waveguides suspended in baffle);

Aren't "waveguide" and "dipole" contradictive?

c) omni vs figure-8 in 0.3-1kHz range - should we bother about (human-specific perception factor as having difficulty to locate source point in this range) ?

I'm not sure where the problem should be. But if it is part of the stereo illusion or the hearing mechanism, I don't see how omni or dipole would make a difference.

[badman]

[QUOTE=Rudolf;2943069]Aren't "waveguide" and "dipole" contradictive?

[QUOTE]

Hornloading the Heil AMT1