cab's ribbon speaker idea

What do you folks think of this idea?

I am thinking about using this slot loaded open baffle bass concept in conjunction with a ribbon ob using a BG RD-50 for mids from 350Hz to 4000Hz, then a Magnepan 60" ribbon tweeter for the highs. I am thinking that 6 pairs of the 8" GRS woofer would give me a slot array roughly the same length as the mid ribbon- the 8" would give a 350Hz upper limit which is perfect for the RD-50. I would mount the wings on the back of the baffle to isolate the mid and tweeter ribbons from the bass backwave.

The idea springs from the XSD Speaker thread here: https://www.diyaudio.com/community/posts/7414759/

Thanks!
 

Attachments

  • baffle idea.jpg
    baffle idea.jpg
    301.8 KB · Views: 141
Disabled Account
Joined 2008
I have a fair deal of experience with the B&G RD-75 and RD-40 drivers. The RD-50 is similar to them, just with a different length. They are interesting drivers in many respects, but they do not sound as good as the Magnepan ribbon tweeter or the Magnepan planar mid/woofer panel. The distortion of the RD's are much higher than the Magnepan stuff. On my RD-75's I measured massive distortion (~10%) around 600 Hz, and general level of distortion 10 times higher than the Magnepan. This is indeed audible.

What I would suggest is to find a pair of pre-owned small Magnepans like LRS, MG-12 or 1.6, and use the panel as high and low midrange. The bass panel should perform very well from 400 to 1,5 kHz, and the mid panel 1,5 to 5 kHz. It will of course result in a much wider speaker......
 
  • Like
Reactions: 1 user
I have a fair deal of experience with the B&G RD-75 and RD-40 drivers. The RD-50 is similar to them, just with a different length. They are interesting drivers in many respects, but they do not sound as good as the Magnepan ribbon tweeter or the Magnepan planar mid/woofer panel. The distortion of the RD's are much higher than the Magnepan stuff. On my RD-75's I measured massive distortion (~10%) around 600 Hz, and general level of distortion 10 times higher than the Magnepan. This is indeed audible.

What I would suggest is to find a pair of pre-owned small Magnepans like LRS, MG-12 or 1.6, and use the panel as high and low midrange. The bass panel should perform very well from 400 to 1,5 kHz, and the mid panel 1,5 to 5 kHz. It will of course result in a much wider speaker......

I have a set of Tympani IVa's currently. The new build is due to dissatisfaction with the bass and size of the Tympani's....I haven't heard many people dissatisfied with the rd-50 and rd-75 but certainly I will investigate....
 
Disabled Account
Joined 2008
I have a set of Tympani IVa's currently. The new build is due to dissatisfaction with the bass and size of the Tympani's....I haven't heard many people dissatisfied with the rd-50 and rd-75 but certainly I will investigate....

Why not use the mid/tweeter panel from the Tympani’s and ditch the bass panels? Cross over to a dipole bass system somewhere around 500 Hz.

I used the RD-75 for 10 years. Was very happy with them… until I heard what a Magnepan could do.
 
  • Like
Reactions: 1 user
I thought about trying just the mid/tweeter panel and using two dipole u or h frame woofers. I will still give that a listen- waiting for my 3 channel amps to arrive then I will be able to give that a go....I wish the Tympani mids had the newer flat aluminum conductors...

I have read of numerous people who replaced the Tympani mid panel with BG drivers and raved about the improvement...I picked up 20 of them and then figured since the baffle isn't really optimal, the tweeter too far from the mid, ect....I might as well start from scratch.
 
Disabled Account
Joined 2008
I’ve have no experience with the Tympani at all, so I can’t comment on that.

The maggies I’ve tested are 1.5, 1.6, 3.6 and 3.7. They measure and sound better than the RD75’s and RD40’s I had. More than 20 dB lower distortion. There was a slight harshness in the sound from the RD75’s, especially in the treble. Used as a pure midrange it might sound better though.
 
Disabled Account
Joined 2008
One good thing with the RD50 is it’s sensitivity, which is quite good at 88 dB. The mid panel of the Magnepan 3.7 is as low as 79 dB. The alu wire midrange on the 3.6 is slightly more sensitive than the alu foil mid. The ribbon tweeter is around 82 dB….
 
@Scott G
You can if you either pay a core charge or return a set of broken cores, at least for the ribbon tweeters.
-well perhaps that and a vertical array of GRS PT5010-8's?

Personally I'd keep the tweeter & mid array on a physically separate baffle - even the base of each array would be different to enhance isolation. IF you really needed to "bridge the gap" between the two panels (to get a bit more low-end from the mid-panel array) then I'd probably look to stiff mineral wool maybe a 1/2" thick to cover the short distance between the two panels (.."flush" with the baffle and encased in an acoustically transparent material).
 
I’ve have no experience with the Tympani at all, so I can’t comment on that.

The maggies I’ve tested are 1.5, 1.6, 3.6 and 3.7. They measure and sound better than the RD75’s and RD40’s I had. More than 20 dB lower distortion. There was a slight harshness in the sound from the RD75’s, especially in the treble. Used as a pure midrange it might sound better though.

That seems at odds with the many accounts of the RD series having low distortion....Odd....

The RD series has a resonance that must be accounted for around 5000HZ and it is true the top end is weak. That's why I plan to use the Magnepan tweeter from around 3000-4000Hz on up.
 
@Scott G

..I am planning to use this bass idea with the rd-50 and the Magnepan tweeter..
While that will work, you’ll have a fair amount (audible) of non-linear distortion as the rd-50 goes lower in freq..

With an array of the GRS drivers (6+) you could easily get to 250 Hz with low distortion and good eff. without a lot of baffle.


In any event, this thread was designed for completed or near completed OB designs with pictures. Probably a good idea to ask a mod. to split off these posts to your own thread.
 
Disabled Account
Joined 2008
I don't have any measurements of RD50, but here's my Magnepan 3.7 bass panels for comparison. They have really low distortion even at high SPL. This is measured at 105 dB at 1 m.

Below 500 Hz it goes sideways. That's why I cross them over at 550 Hz.

MG37-BASS-DIST2.png
 

Attachments

  • MG37-BASS-DIST1.png
    MG37-BASS-DIST1.png
    10.9 KB · Views: 40
  • Like
Reactions: 2 users