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-   -   Cardoid M+T ribbon (http://www.diyaudio.com/forums/planars-exotics/85877-cardoid-m-t-ribbon.html)

LineSource 3rd September 2006 11:41 PM

Cardoid M+T ribbon
 
Recent discussions about the "new Apogee" company introducing a full range speaker with a M+T ribbon similar to the original Apogee Scintilla caught my interest to start some technical discussion. The Scintilla used one magnet assembly to drive both a 54" long 1.9" midrange dipole aluminum ribbon centered in the gap, plus four 0.5" tweeter aluminum ribbons arranged in a bipole radiation pattern next to the pole magnets in front-of and in back-of the midrange ribbon. 6db crossovers at 500Hz bass to mid, 3kHz mid to tweeter.

T.....T
MMMM
T.....T

This M+Ts arrangement would seem able to generate a cardiod radiation pattern, but should also have the problem of having the M-ribbon modulate the T-ribbons, plus high frequency combing from having two T-ribbons centered 1.5" apart. Any deep science explanation why this MT ribbon received such good reviews to where the "new Apogee" company has decided to adapt it? Does coherence trump modulation and combing distortion? Will 2006 measurement techniques show faults that 1985 could not?


From reviews "The Apogee Scintilla true ribbon section is a composite mid/treble driver employing an array of five ribbons, four 0.5in. wide and one 1.9in. The central ribbon rolls off above 3.5kHz, while the flanking 0.5in. ribbons - two at the front and two at the back- operate in the main above this range. An interesting twist occurs here since the central mid element naturally operates as a dipole, with 'in theory 'the rear radiation out of phase with the front. However, while the front flanking treble ribbons are run in-phase with the main ribbon, as one might expect, the rear-facing treble ribbons are wired in reverse. In effect, the HF range is unipolar, representing a pulsating cylinder mounted in the 2.25in. wide vertical slot in the baffle. In the overlap region between the mid and upper treble ribbons, the sound is reinforced to the front but decayed to the rear, forcing a cardioid-type response in this range. The unusual ribbon configuration means that all five elements can share a single, costly magnet system. The location of the treble ribbons is a function of optimum placement, both in terms of the non-linear field distribution over such a wide gap, and also with respect to the acoustics of the main aperture."

bear 4th September 2006 11:22 PM

Do we have a picture of the real thing??

Seems like a really bad idea IF what you are saying is that the tweeter ribbon is in front of the midrange ribbon?? In the same gap??

But what do I know? ;)

I always had problems with the way the Apogee sounded... regardless of the model. Something odd in the sound.

I found that the bass "ribbons" on the pair that I have here have overlap between the foil and the gap/poles, which means to me that some of the ribbon is either not driven or is flying out of phase on the surface... which might account for part of the sound.

The ones I have are true ribbons... I forget the model now, short older ones, and the ribbons sounded audibly higher in artifacts than a really low distortion SA ribbon that I had around... so...

_-_-bear :Pawprint:

Edit: I think they be Calipers...

LineSource 5th September 2006 12:32 AM

2 Attachment(s)
Hi bear, thanks for jumping in.

The Scintilla ribbon is 54" tall. I attached a picture plus a top down diagram of the ribbons. There is nothing between the midrange ribbon and the tweeter ribbons to block reflections. The tweeter Al foil wraps over the top of the pole piece to create the reverse current direction between the front and rear tweeter ribbons. All the tweeter foil is connected in series to sum to a 1 ohm resistance. The midrange ribbon is 0.2 ohms and uses a 0.8 ohm series resistance to pad it up to 1 ohm.

I traded my Scintillas for the Full Range because I thought I heard modulation distortion on the tweeters, so I'm curious how the "new Apogee" company's M+T ribbon will be designed. Hoped the diyAudio minds might have some ideas.

The Apogee Scintilla reviews from 1985-1988 are very good. I'm curious to see what today's measurement techniques produce.

bear 5th September 2006 01:29 AM

Yeah, I'll give odds they did that at the time in order to get the impedance up from 1/2 ohm!! :rolleyes:

I'd agree with your assesment of the likelyhood of IM from that arrangement no matter what anyone does between the two bits of foil!

An audio friend of mine got some replacement ribbons from the people who are supposedly restarting Apogee... for his blown Apogees and he put them in himself and says they are an improvement over the old, and was very happy with them. So... I guess we shall see what we shall see...

All I can add is that if I was asked to update the design there are a number of things I think I'd do quite differently today. Would that be an Apogee then? In principle yeah. In practice, a bit different.

That means the magnetics, the magnetic circuit, the ribbon patterns, and design, etc...

Hey all it takes is time and money, mostly money.

:D

_-_-bear :Pawprint:

Paul W 5th September 2006 12:30 PM

If it really works, a clever approach to cardiod and, with a 1st order xo, the front tweeters may not "fight" with the mid as much as we might think...but I don't understand what they are doing about combing.

Perhaps one piece of the puzzle: A truly uniform 2" gap is probably not commercially viable so the outside edges of the 1/2" ribbons are likely moving more than the edges nearest the center of the gap...in other words the 1/2" ribbons may be twisting. The twisting action may throw a different radiation pattern than we normally think of...the launch may not be perpendicular to the baffle.

Do you have any links for further reading?

LineSource 6th September 2006 02:23 AM

Quote:

Originally posted by Paul W
Do you have any links for further reading?
From the new owner http://www.apogeeacoustics.com
"The new speaker is called SYNERGY 1.5, and was designed using the legendary 1 ohm Scintilla as the only benchmark. Scintillas strengths and weaknesses were considered, and discussions had with several long term owners with good working examples to see why they were so attached to the speaker (in their words) and what they would love it to do if it's sound could be improved in their opinion. Thanks to those people, your input was invaluable. Industry "heavyweights" were consulted about xovers - more on that later.

To clarify - SYNERGY is not a Scintilla remake - far from it! It is "similar" in size and original-Apogee in flavour, but the engineering of the ribbons, frames, and how it is kept upright is different in many ways.

The result is in line with my targets, and is a medium-high efficiency 3-way planar, with a reasonable resistive load. Whilst low watts tubes are not ideal - they will get a sweet sound from them, albeit low. Ideal power is a very high quality 50-100w amp, able to drive loads in line with the old Apogee Caliper Signature."

DAMIC 13th September 2006 08:56 AM

Hi,

I see some ribbon people there. Here is the link with a lot of interesting ribbon and Apogees information.

http://audioworld.com/cgi-bin/sw/Ultimate.cgi

Regards

LineSource 27th September 2006 02:40 AM

2 Attachment(s)
Attached photo of the new Apogee Syngery 1.5.

The basic design is essentially an updated Scintilla, as the MT ribbons are configured exactly the same as the original Scintilla. The midrange ribbon is flanked by tweeter ribbons, front and back (4 total). while the mid is a dipole the tweeters are a bipole in operation. The build quality is reported as very high, as is the 95db/watt sensitivity. I'm watching for a review with modern measurement techniques and equipment.

DAMIC 28th September 2006 07:56 AM

Some basic information about Synergy 1,5 direct from the man who made them (Graz post of 27.09.)

http://audioworld.com/sw/Forum1/HTML/005636.html


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