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-   -   B&G RD-75 dipole - baffle and or waveguide? (http://www.diyaudio.com/forums/planars-exotics/193618-b-g-rd-75-dipole-baffle-waveguide.html)

StigErik 29th July 2011 09:43 AM

B&G RD-75 dipole - baffle and or waveguide?
 
I've been using a pair of B&G RD-75 for quite a while. They are used as dipoles with no baffle at all - just the bare driver. This works very well, and there is usable response to 150 Hz.

The frequency response of the driver itself shows a peak around 5 kHz of approx 7 dB. Apart from that, the response is more or less flat. I wanted to find out if this peak could be affected by changing the baffle size or shape.

1. Making a wide flat baffle: did not change anything apart from more level below 1 kHz.

2. "Waveguide" type of baffle: only increased the 5 kHz peak.

3. Smoothing the edges of the driver: this actually reduced the peak by 3-4 dB. In addition, this very small extension of the effective baffle width increased the level below 1 kHz by as much as 3 dB.

The modification I did was quite simple, its just round plumbing foam insulators and duct tape... Se pics below.

Anyone with similar experience or suggestions?

http://www.tangenavdesign.com/projec.../RD75-mod1.jpg

http://www.tangenavdesign.com/projec.../RD75-mod2.jpg

http://www.tangenavdesign.com/projec.../RD75-mod3.jpg

emporiumshed 2nd August 2011 10:14 PM

just got some b&g to play with, i had the wisdom adrenaline some years ago and they were awesome, what sort of crossover are you using, i have some 12db 300hz, will they be ok or will it damage the ribbon

torroid88 3rd August 2011 12:10 AM

Ribbon Peak ?
 
The ribbons do have a peak and some, carver for instance, supplied a passive R-L-C ckt to put in series with the ribbon to tame it. Or it might be eq'ed out. Would probably need some instrumentation to measure the parts and the speaker response after filtering ...

Jim

twest820 3rd August 2011 05:15 PM

I've been meaning to try very similar roundover geometries on my Neo3s and Neo10s--still working on my electronics and haven't got back to the acoustic side of things yet.

Adding a baffle should lower the onset of beaming in frequency so I assume the measurements of post 1 are on axis only. It'd be interesting to see the waveguide shape (I'd default to a Le Cleach profile) and how the polars compare between nude and configurations 1, 2, and 3.

StigErik 4th August 2011 06:59 PM

Quote:

Originally Posted by emporiumshed (Post 2658823)
just got some b&g to play with, i had the wisdom adrenaline some years ago and they were awesome, what sort of crossover are you using, i have some 12db 300hz, will they be ok or will it damage the ribbon

300 Hz / 12 dB should be fine.

I use digital PC-based crossover at 180 Hz with approx 24 dB slope.

You will need EQ as well. First, there is the rather large peak at 5 kHz that you must do something about. Next, the driver will probably need EQ below 1 kHz, depending of baffle size and listening distance. I also think its a good idea to EQ the top end, the driver is more than 10 dB down at 20 kHz.

StigErik 4th August 2011 07:03 PM

Quote:

Originally Posted by twest820 (Post 2659588)
I've been meaning to try very similar roundover geometries on my Neo3s and Neo10s--still working on my electronics and haven't got back to the acoustic side of things yet.

Adding a baffle should lower the onset of beaming in frequency so I assume the measurements of post 1 are on axis only. It'd be interesting to see the waveguide shape (I'd default to a Le Cleach profile) and how the polars compare between nude and configurations 1, 2, and 3.

True - all my measurements were taken on axis.

I didnt keep the baffle or waveguide, they were just experimental anyway. The waveguide was not far from a Le Cleach profile actually.

Will look into doing off-axis measurements of the current solution with the rounded edges (#3 on my list there, and shown on the pics)

lolo 1st September 2011 09:34 AM

Hi StigErik,

I posted two days ago on the older thread, did not notice you started a new one. Your experiments are really interesting, I am myself the proud owner of a pair of Orions. If you have listened to them, how would you compare the B&G+dipole subs?

Cheers

Laurent

PS: I lived in norway for nearly 3 years!

dacen 7th September 2011 12:56 AM

2 Attachment(s)
Attachment 238929

Attachment 238930Here is the recommendation from B&G to take out the peak around 5K (Notch filter)

ntropy 3rd October 2011 11:08 AM

I have seen that B&G used to sell mounting brackets for installing the RD75 inwall (as a monopole). Considering the small space needed if I would install them onwall/inwall, the WAF seems incredible high. Anyone has experience on this?

bear 3rd October 2011 02:17 PM

Don't know if the website still exists, and I do not recall the name of the person who put it up, but he had done extensive baffle tests on the RD75 ribbons when they first appeared on the market.

Iirc, he came up with an asymmetrical tapered and somewhat fat rounded "aircraft wing" profile as providing the best combination of flatness and extension... he tried a LOT of different methods... very good testing location (hung from a gym truss, iirc)

_-_-bear





Perhaps a search will show that it still exists... or someone may remember it.


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