B&G RD-75 dipole - baffle and or waveguide?

[StigErik]

Originally Posted by dacen

This type of MRTW fixed at the sides will not be an option for me.

Why not? Even if it measures good and sounds incredible?

Honestly - the big RD-75 is the very best loudspeaker driver I have ever heard. My references also include Apogee and Magnepan planars, as well as various electrostatics and regular dynamic speakers. In my opinion, all dynamic loudspeaker drivers fail to match the RD-75, especially in the low-midrange.

[dacen]

Problem is I have been misinformed myself regarding RD75 and RD50, the taller ribbons. I was on the brink of purchasing a pair of RD75 based on this misinformation. I was told that it was exactly the same principle as the Apogees. That is true, but apparently not the whole truth. This information was probably given to promote sales. As they say in the computer world: Rubbish information in equals rubbish out. I hope this info from ABJensen has enlightened more people in here than just me.

[StigErik]

Well, it should be pretty clear that all BG drivers are planars.... everywhere you find info on them they are called "Bohlender Graebener RD75 Planar Transducer". So they are different from the tweeter ribbon of Apogee, which is not fixed on the sides. The bass section of Apogee's is fixed on the sides by the way.

I did have a pair of Apogee Caliper in my room many years ago. It was fun watching the tweeter ribbon move several cm by the air pressure from the woofer panel. :-)

[koldby]

StigErik
The idea of a waveguide i front of the RD 75 could be a good idea. The RD75 is pretty directive at high frequencies because of the with of the diaphragm and has wider dispersion as the frequency decreases.
At a point it narrows again because of the dipole cancellation.
Perhaps one could construct a waveguide that compensates for this.
A Le Cleac'h is more like a exponentail horn than just a waveguide.
What kind of software x-over did you use?

Dace:
It makes no sense to disqualify a driver just by its working princip!
I have heard extremely good drivers that were horns, palnars, electrostatics, conventional cones and bending waves.
What matters is how they sound.
Apart from that it would be very difficult to make a true ribbon work down to 150 Hz because of the dipole cancellation round the ribbon itself.

[koldby]

StigErik
Where the @¤/(()--:# did you get your RD75 from?
Can't seem to find them in Europe besides BG-Speaker.de who says it will be extremely expensive to have the sent here and the retail without freight is $995,-!!!
PE sells them for $753,50...
Maybe double RD40 will be a solution as they are far more easy to send?
Or Neo - types?

[lolo]

Hello,

have you done any polar plots mesurements, by any chance?

Cheers.

[StigErik]

RD-75's vertical dispersion at high frequencies is not worse that a typical 1" dome tweeter.

I agree that making a waveguide could improve directivity, but that should rather be a dipole horn/waveguide to obtain the same directivity front and rear when its used as dipole.

I got my RD-75's from Parts Express.

[pengesluk]

What's the story on the rather low sensitivity specs. for all these B & G models?? They are listed at 88 dB, not a lot really...

[StigErik]

The main reason is - I think - the use of ceramic magnets instead of Neodymium. An other thing is that the magnet gap is fairly wide to allow a good amount of excursion.

[lolo]

I have own the Orions for over a year now and although I find the sound to be superb and in a total another league compared with commercial products, regardless of price, I have time to time issues on some classical recordings, especially on mass violins and loud horns passages, not completely sold on the high mids transition. I have ordered a new pair of millenium tweeters and a soundcard to check what's going on. Hopefully I will find something and the design itself is not at fault.
This is one of the reasons I have followed your progress very closely StigErik and I definitely see some benefits in your last speaker iteration. But, I have also learned about the utmost importance of smooth polar dipole patern, hence my question the other day. What about the horizontal dispersion? Have you done any mesurements? This is not to be critical, quite the opposite, I am very interested and curious!
Regarding the efficiency, I guess we can safely add 4-6db because of dipole radiation so we should be more into the 92-94db range depending on the walls reflection/absorbtion.