[Hank]

Parts Express has the Bohlender Graebener RD75's on sale for $459 through November 4, and I am MIGHTILY tempted to order a pair.  For years, I've read/heard that the BG's are the ne plus ultra midrange drivers, and after all, that's where most music resides.
I'm thinking my ultimate speaker, as I've noted here before, is an open baffle line array, so the BG75's would be the anchor.  Then, what goes with them to cover the ~80 Hz - 400 - 600 Hz band?:
A stack of really good 6 - 8" mid-woofs of good design (anybody around here know of any?)?
A couple of electrostatic panels?
Then, do I add the complication of a super tweet ribbon or BG 3's?  With a boost at the top, some say the BG75's are good enough if you're in the sweet spot for serious listening.  Then again, I probably can't hear above 16kHz anyway.
Just thinking about midrange nirvanna here...

[pbrstreetgang]

I thought there were some acoustical properties with longer planars like that. Isnt that why Danny chose the 8" for the line arrays instead of the easier task of just one long planar?

[sbrtoy]

The BG's a nice speakers, like most though they come with their own unique issues.  BG's white papers explain some of them a little, but there are some things that need to be done to make them shine.  Have you listened to their own Radia line to see if you like their sound?

[poseidonsvoice]

The BG radias are sweet speakers. You can build them either as monopole or as dipoles. I know of several who did back in the mid 90's and even Wisdom Audio took it to the ultimate. A fella named Rudi ?Blondia did design active crossovers for them, but he seems to fallen off the audiophile radar for a while.

As far as:

A stack of really good 6 - 8" mid-woofs of good design (anybody around here know of any?)?

Might not have to look to far. Danny's XBL 6 inch drivers and/or Kevin Haskins midwoofer on his Kepler both come to mind for starters.

I wouldn't add a super tweeter first. See if you like it without them, you might be plenty happy without the added complication. Then all you've got is a simple two way.

Another person to ask is Mike Dzurko. He had a speaker based on the BG RD75 back in the mid 90's. Since its been so long, he might spill some secrets of the design.

Best,
Anand.

[ebag4]

A stack of really good 6 - 8" mid-woofs of good design (anybody around here know of any?)?

Might not have to look to far. Danny's XBL 6 inch drivers and/or Kevin Haskins midwoofer on his Kepler both come to mind for starters.

A little self promotion if I may. I have 4 of the M-165X driver for sale at a good price, the ad is under the speakers for sale section here on AC.

Now back to our regularly scheduled thread, thank you for your indulgence!

Best,
Ed

[Hank]

Thanks for your input, guys.  "Acoustic properties":  besides dead-accurate midrange, a good acoustic property is their inherent limited vertical response, which just about avoids ceiling and floor bounce issues.  Negatives:  although they go down to 150 Hz, they should be crossed over higher for protection from high SPL's - cross at maybe 500 - 600 Hz.  The design is supposedly a bit "beamy" above 5kHz, but these 75's are long enough so that shouldn't be an issue.  HF response tapers off above 15kHZ, so a bit of EQ would fix that.

I was, of course thinking about Danny's M130X or M165X for the 80 - 600 Hz band.  I think the M130X would be the choice.  A line of them operating well within their lowest distortion pistonic range should be quite accurate and clean.

I think the reason you don't see many designs with them and therefore the lack of "secret" design tips, is that very few DIY-ers have used them because of cost.  Over the years they have been $700 - $900 EACH, so this $459 PE special is one real bargain.

Downside:  I have not listened to them in person, although lots of audiophiles say they're the best midrange reproducers.  So, laying out that expense sight unseen (unheard?), makes me nervous.  Anyone know of any RD75's operating in the Austin, TX area?

[Danny Richie]

They have their limitations Hank.

For one, the sensitivity is really low. Realistically they are at about 85 to 86db at a 1 watt/1 meter scale. This makes mating a line of woofers almost impossible. A line of my M-130's would hit about 96db in output with that same input.

Secondly, just about the time you have enough power on them to really hit some real SPL's you run out of power handling.

Then they are just not as fast, as detailed, or have the resolution of the smaller BG planar magnetics.

They do have an advantage of playing down low, but the lower you play them the less the power handling and the quicker they move into distortion. My test have lead me to favor a more pistonic driver (one that can move some air) up to the 800Hz range. The big ribbons or even lots of the smaller BG planar magnetic drivers just don't have enough ability to move enough air to hit any real SPL levels below that point. Plus crossing over in the heart of the vocal range has its issues as well. Since the heart of the vocal is in the 300 to 500Hz range getting one octave above that helps a lot.

Another misnomer is that the length will result in a minimal amount of floor and ceiling reflections. This is true but is frequency dependent. As frequency decreases it will become more omni and as frequency increases it will become more directional and limited to the length of the line. This is the same with any line of drivers and any line of drivers the same length is going to have about the same vertical dispersion whether it is a line of woofers or one long tweeter.

I have been going at this line source deal for a while, and the best that I can come up with, especially considering the price point, is the LS-6 and LS-9. 

[Hank]

Thanks for your input Danny.  My basic concerns are effeciency and crossover point that's high enough to keep them safe, but not get into the vocal range.  Might be a deal killer.

[BobM]

The RD40's are on sale for that price. The RD75's are in to $700 range.

Bob

[cujobob]

The RD40's are on sale for that price. The RD75's are in to $700 range.

Bob

The RD75s are on sale in the PE catalog...for whatever reason, the website price was higher last time I checked.  Just under $500 IIRC

[WerTicus]

im yet to hear a better mid range than the accuton ceramic 4inchers.

[Jed]

im yet to hear a better mid range than the accuton ceramic 4inchers.

Hey that's my kitchen counter behind that midrange 

[Hank]

im yet to hear a better mid range than the accuton ceramic 4inchers.

They may be equal, but what would a 6-foot line of them cost?

[richidoo]

im yet to hear a better mid range than the accuton ceramic 4inchers.

Accuton are excellent, but if it's really "bar none" we're talking then I vote for these:

Usher's 4" beryllium midrange.

[Danny Richie]

Actually after designing an upgraded crossover for the Usher BE-20 (beryllium mid) and the Usher BE-718 (paper cone mid) I think the paper cone mid in the BE-718 clearly sounds better.

[pbrstreetgang]

Paper please.

[Hank]

Same question as with the Accuton's:  what would a line of the Usher's cost? 

[BrassEar]

I owned the B&G 50-inch speakers. That driver is good but it can sound thin and has specific frequency problems that require intelligent EQ-ing. I could never get over the thinness of their sound so I sold them. They do have great clarity but must be listened to at a long distance for best effect.

[richidoo]

Hank, the only way to get the Usher beryllium drivers at this point is to buy the speakers. Not available DIY. So I guess the Usher mids cost 8400 each pulled from Be-10s... hehe

I auditioned the Be718 and Be-20 for a couple months each before buying the Be-20. To my ears there is no comparison if the electronics are up to the challenge. I prefer lower distortion of beryllium than the prettier distortion of paper. For classical music the beryllium has a clear advantage due to less color and more detail. True stereo recordings of acoustic instruments played on all tube gear is just unbelievable. I still can't believe the sounds that it makes. Danny what ever happened to your Be-20 crossover design?

The Accuton in the Kharmas at RMAF were awesome too. But I think the MBL SS electronics held them back. They deserve low-mass pp tube amp.

I like paper too, I own Feastrex full range D5nf made of washi paper. It is exquisite and wonderfully  colored, making any music come to life. But the beryllium mid has no color except what the electronics bring, allowing the recording to be the only source of 'life.' I assume ceramic is similar, as well as the magnesium Esoteric.
Rich

[Danny Richie]

Hey Rich,

The funny part is that with the stock BE-20 crossover most of the mid range is being handled by the 11" Eton woofers. The heart of the mid-range is the 300Hz to 500Hz range and the crossover point to the Beryllum mid is 500Hz.

Danny what ever happened to your Be-20 crossover design?

My upgrade made a considerable improvement across the board, but they decided not to go with it.