Hello from North Carolina and France

Hi,
I am overjoyed to have found this interesting board full of useful information.

I now live in North Carolina but will shortly move back to France.

I am a software engineer/manager and was working in the Telecom business until recently.

I just built two Tripath digital amplifiers based on Tripath eval boards and details from Chris Brodersen. In the past I mostly built ported speaker enclosures or turn-table boxes. I am planning to assemble a speaker that will be bi-amped with the Tripaths and a Marchand XM9 xover kit.

Using what I have on hand I can assemble a speaker with Triangle mid-woofers, a 40" true ribbon from Magnepans 2.6 and a REL Storm subwoofer. Other options are to match the Magnepan ribbon with a 50" BG ribbon or with a Magnepan 1.6. Both will fit in the space of the MG2.6 bass panel. Another option yet is to assemble a speaker based on Newform Research ribbons and mid-woofers either Scan-speaks or Triangle.

I already found a wealth of information on the board and am open to any comments on my plans.

Guy
 
I used the Bohlender-Graebener RD-75s with the Maggie ribbon. Lovely match, I highly recommend it, as both are true line sources and the sonics are close enough that you won't have vast tonal differences between the two.
Having lived in various places in the Carolinas, I prefer North Carolina by a long shot. However, fate has cast me ashore here in South Carolina. So it goes. Never been to France, so I have no opinion about life there. Hope all goes well for you.

Grey
 
Open Baffle for Bohlender-Graebener ribbons

Thanks for your replies and encouragements. I love North Carolina. Le Penis has been defeated in France so that's good and I can safely go back there at the end of June.

Grey, I am interested to know more about how you baffled the RD-75. I am thinking to place them in a 14"x72" baffle made by cutting a vertical piece off my MG2.6. I saw curves on John Whittaker's web site that showed very different response depending on the baffle size or shape. If you used the Tympani as a baffle where exactly is the BG located. It would be nice to see and hear yours.

I assume the 50" BG will be somewhat less dynamic and be more restricted in vertical dispersion than your 75" but hopes for the best. I am trying to exchange my 40" Magnepan ribbon for a 60" for better vertical dispersion above 5Khz.

Thanks,
Guy
 
Guy, yes, I got your e-mail, but have been so immersed in the X-line stage and a certain (<i>ahem</i>) amplifier project, that I haven't been responding to any but the highest priority mail over the last week or so. Apologies to all who have mailed and not received replies.
Well, now you've gone and raised an interesting point. For a few months I did run them in an open baffle that I put together out of scrap. I've been dipole for years, excepting subs, and decided to try absorbing the rear wave, just for a change. The ribbons from the old T-IVs are the 60" variety, so I put together a very narrow, very deep cabinet, and stuffed the dickens out of it to absorb the rear wave of both (BG RD-75s & Mag. ribbons) drivers.
The resulting mid/tweeter cabinet is something like 7 or 8" wide and 7' tall--a good match for my subs. Front corners were rounded with a 3/4" router bit to cut down on diffraction. Yes, the T-IV woofer panels are still open. This is inconvenient, to say the least, but I haven't come up with a good mid-bass (70-250 Hz) alternative.
So, how does it sound?
In a word...different. The image width is far more defined than it ever was with the stock T-IVs. Whether you wish to chalk that up to the cabinetry or the new midrange driver is open to debate. I lean towards the idea that each contribute. Centerfill, in particular, is so solid that some recordings almost sound as though I'm running a center channel. Spooky. Image depth is about comparable. Tonally, I think the RD-75s manage to side-step a resonance that the original T-IV mids had--your first impression is that there's something missing, but I've come to the conclusion that between the two the RD-75s are better. Detail retreival is, I think, better with the RD-75s, but not so much as I might have hoped before I bought them. In terms of efficiency, the ribbon and the RD-75 (not a ribbon, though some people call them such--they're technically planar drivers) are comparable, meaning upper 80 dB range.
It would be nice if they were more efficient. It would also be nice to find a good way to handle the mid-bass. The Genesis 1s used the RD-75s all the way down to the subs, but I'm reluctant to push them that hard. I've heard the 1.1s and though that the mid-bass was less than it could be. B-G specify a lower crossover point of 150 Hz for the RD-75--and that only with a higher order crossover. They're happier if you cross them over about 250-300 Hz with a lower order slope.
As always, my system is in transition as I drag it, kicking and screaming, out of the mid-'80s up into the early days of the 21st century. May the stereo gods forgive me for any mis-steps along the way.

Grey
 
BG quasi-ribbons matched with Magnepan ribbons, BG RD50 vs BG Neo8

Grey, thanks for this very useful information.

I wonder if the better image width comes from the closed enclosure or from the better line definition of having both line sources very close. The Magnepan MG1.6 is perfect in this regard since the quasi ribbon shares the same mylar membrane with the bass. And reports are that it has very good spatial imaging.

Initially I will match the ribbon with a pair of MG1.6 giving good mids and bass complemented by the splendor of the true ribbons and the subwoofer. I will have to make sure to position the ribbons very close to the mylar panel. I heard it should not be further than 1/4th wavelength at crossover point, so for 3.5Khz this is less than an inch and at 5Khz it is about 1/2", not doable since the ribbon enclosure is 1" thick on both sides.

I am intrigued by the Bohlender-Graebener Neo8 which seems to offer better performance than the RD series (93db sensitivity vs 88db for the RD series). It is a push-pull design, uses Neodymium magnets and usable range is about 500-18000 but based on dispersion characteristics I would use it as a mid driver 500Hz-5Khz just like you did with the RD. Since it is 8" you need to place a number of them in a line source configuration. They are $58.30 each at partexpress so 6 drivers forming one 50" source would cost about $360 vs $515 for the RD50. Too bad it stops at 500Hz. VMPS has a similar ribbon that goes down an additional octave to 250Hz but they don't sell it separately. It would be interesting to compare a Neo8 solution to an RD75 with a powerful amp.

There is also a 3.5" Neo3 PDR tweeter at $40 which covers 2Khz-28Khz. But my take is that it cannot touch the Magnepan ribbon especially in horizontal dispersion.

Guy
 
Magnapan ribbons

Is it possible to buy just a ribbon from Magnapan? Or, does one purchase a used speaker and canabalize it for the tweeter?

I've been contemplating building a three-way dipole line array using the RD75. I considered using Fountek JP2s for a tweeter array, but the Magnapan ribbon might be just the ticket if it can be purchased.

Any idea how much it costs?

Thanks.

Paul Ebert
 
Magnepan does not sell their ribbons separately, you have to send them a damaged ribbon to get a fixed one. The best as you said is to "cannibalize" a second hand speaker. Ideally you would find a 3.3 whose large panel has been damaged. It is best if the ribbon has been replaced in the last 5-6 years because the recent ribbons have a better system to hold them and thus less of a risk to be blown up by air (don't let anyone vacuum them!! or lay them briskly on the floor, there is a magnetic ribbon cover for handling/moving them). Also don't get the 2/3 rd length ribbons of the MG2.6 because the sound is not whole.

The best deal is to go with the older ribbons from the MG 3.x series before the 3.3 but the ribbons do not have quite the same range and are a bit more fragile I believe. Also be careful, I think the inital MG 3 did not have a ribbon yet.