So I’ll start with an apology and inform you that the title of this thread is not so much a declamation as an invitation to participate in a discussion on the subject, although I will be talking about our plans for rebuilding a pair of Divas to a considerably higher spec than the originals. “Our” refers to myself and the UK Apogee restorer, Jon, who will actually be doing the rebuild. Calling it a rebuild is in fact a bit misleading because the only parts that are likely to be reused are the magnets and their perf steel supports. Everything else will be completely new, including all the ribbons / panels. Significantly the MR ribbon will be a true pure foil ribbon.
The first thing to address is the structure of the internal frame. The goal is for this to be extremely rigid and non-resonant. There is likely to be a combination of materials used including some or all of the following; valchromat, panzerholz, GPO3, aluminium and carbon fibre.
More to come in due course.
The first thing to address is the structure of the internal frame. The goal is for this to be extremely rigid and non-resonant. There is likely to be a combination of materials used including some or all of the following; valchromat, panzerholz, GPO3, aluminium and carbon fibre.
More to come in due course.
So here’s something I’d welcome views on. In the opening post I mentioned the MR will be a pure ribbon. There is another option though; because the frames / cover will be made from scratch it would not be a problem to tweak the layout to allow the use of the unique MR ribbon from the Grand. Setting aside the impedance differences, which of those two MR would you choose for best sound quality?
When you bolt the midrange/ tweeter combo to the MDF frame you do 2 things, straighten it lengthwise and automatically damp
the chassis.
When you glue the bass magnet assembly to the chassis you again add mass and damping. Gorilla glue works wonders here as it has an expansion rate to fill some of the holes along the screw down perimeter edge.
Its a must to have a perfectly flat table when gluing the bass magnet structure. - I used a 1/2” thick glass table
Some pics of a simple jig and plugs I used . More surface area than the steel stock plugs
What I didn’t like about the Divas MDF chassis was its thickness (3/4”) and could have been 1” or more easily. The stuff they sell today has a better dense
fiber structure than what they used in the early 80,s when these came out. The stock diva used a relatively soft fine density in comparison and by default the MDF you buy today will be more rigid if you go this way
The scintilla,s chassis material was a disaster a had to be remade..,.
One can keep going in rigidity and weight and price ! but the last thing you want is to introduce a high Q peak from a rigid frame that may become audible and extremely hard to damp out in the end, that is possibility in a quest to stiffen everything even more .Think Martin Logan CLS,s solid wood frame and it’s bonk signature.
Also a pic of my scintilla build where I put bracing and additional support by extending behind magnet rows for additional torsional strength
just some food for thought
the chassis.
When you glue the bass magnet assembly to the chassis you again add mass and damping. Gorilla glue works wonders here as it has an expansion rate to fill some of the holes along the screw down perimeter edge.
Its a must to have a perfectly flat table when gluing the bass magnet structure. - I used a 1/2” thick glass table
Some pics of a simple jig and plugs I used . More surface area than the steel stock plugs
What I didn’t like about the Divas MDF chassis was its thickness (3/4”) and could have been 1” or more easily. The stuff they sell today has a better dense
fiber structure than what they used in the early 80,s when these came out. The stock diva used a relatively soft fine density in comparison and by default the MDF you buy today will be more rigid if you go this way
The scintilla,s chassis material was a disaster a had to be remade..,.
One can keep going in rigidity and weight and price ! but the last thing you want is to introduce a high Q peak from a rigid frame that may become audible and extremely hard to damp out in the end, that is possibility in a quest to stiffen everything even more .Think Martin Logan CLS,s solid wood frame and it’s bonk signature.
Also a pic of my scintilla build where I put bracing and additional support by extending behind magnet rows for additional torsional strength
just some food for thought
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Thanks Avwerk, I‘ll take that on board. The largest areas of the internal frame will be Valchromat, which is a very stable and flat form of High Density Fibreboard and we intend to use 30mm thickness. There will be additional rigidity and anti-resonance added using spars of some or all of the other materials I mention in the first post. I take your point though about Q and we will take that into consideration.
When you're physically moving the speakers I can understand a need for strength and rigidity. But, in normal usage, a non-resonant scheme is much higher priority.
Your plan for the internal frames sounds like a highly expensive and complicated endeavor.......for little acoustic benefit relative to much cheaper and more available materials.
Dave.
Your plan for the internal frames sounds like a highly expensive and complicated endeavor.......for little acoustic benefit relative to much cheaper and more available materials.
Dave.
At least 50% of the construction ideas are aimed at making them as non-resonant as possible. As regards rigidity I’ll just relate the following; a friend of mine has had Quad 989s for years. A couple of years ago he had some metal frames made to replace the surprisingly flimsy frames of the standard 989. The resulting improvement in sound quality was not subtle and certainly enough to convince me that it was a totally worthwhile upgrade.
As Dave mentions , the other even more important issue was the stock alumium base support. They used a cheesy, what, 10/32 bolt not far up the frame to hold the speaker ? I could hardly believe it when taking these off for rebuilding
with entirely too much Longitudinal twisting of the bass diaphragm every time you rocked the speaker into place
Moving the attachment points higher up (37 1/2”) with more leverage overall works wonders and is single most important upgrade to
these that you can do without spending big money.
One can get real creative in this area to great effect
with entirely too much Longitudinal twisting of the bass diaphragm every time you rocked the speaker into place
Moving the attachment points higher up (37 1/2”) with more leverage overall works wonders and is single most important upgrade to
these that you can do without spending big money.
One can get real creative in this area to great effect
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Interesting project! (I have Stages and Duettas, neither working.) A few thoughts: (a) a stiffer frame is probably a good idea, but as others have said, it'll be important to get a complete construction that is well damped, as well as rigid. (The standard mdf/steel sandwich does actually seem to work pretty well, especially given how flimsy the mdf frames are on their own.) (b) I do like the idea of a tall support frame, like AVWERK has done. (c) Jon will be sorting out your magnet alignment, I'm sure - it astonishes me how poor a job the factory did on this, in most cases.
(d) In an ideal world, I'd consider changing the magnets to stronger ones. But that would not be cheap, and it might not be simple.
A pure alu ribbon is a bold idea!
(d) In an ideal world, I'd consider changing the magnets to stronger ones. But that would not be cheap, and it might not be simple.
A pure alu ribbon is a bold idea!
Thanks for dropping by ianbo. Re (c) yes Jon has said to me on a couple of occasions that the magnet positioning on the originals was often pretty sloppy and he makes a priority of putting that right. Re(d) I have discussed with him the possibility of replacing the magnets with stronger ones, neos being the ultimate. However it seems that in practice they are almost impossible to work with because they are so strong. They are also VERY expensive, so we will be sticking with the originals.
Re the MR ribbon, I am currently oscillating ( c’mon keep up
) between the choices of the pure ribbon or the wide kapton backed ribbon from the Grand.
Re the MR ribbon, I am currently oscillating ( c’mon keep up
) between the choices of the pure ribbon or the wide kapton backed ribbon from the Grand.
Well done Rob . The nice thing about steel is reasonable costs all around , heavy and very little warping from welding.
I had to spend a considerable amount of time pounding everything straight again ( aluminum) and learned on the Scintilla stands as shown , to plug the vertical pieces ends and Tig them in , then tap/drill thru the support pieces rather than welding everything solid
Another issue if you don’t spike the feet and want to move things around easily, consider the weight imbalance of the heavier ribbon side…,
It will tilt on that side and sink into your carpet more
I had to spend a considerable amount of time pounding everything straight again ( aluminum) and learned on the Scintilla stands as shown , to plug the vertical pieces ends and Tig them in , then tap/drill thru the support pieces rather than welding everything solid
Another issue if you don’t spike the feet and want to move things around easily, consider the weight imbalance of the heavier ribbon side…,
It will tilt on that side and sink into your carpet more
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I use aluminium ribbons only.
It's a full range clone but the mid and tweeter are with neodymium magnets.
And I didn't corrugated the bass membrane
Rob
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Hi Rob, Hope it‘s oK to overload you with questions 🤓
how do you enable movement of the Bass foil? Is the foil framed by rubber bands?
Do you use transformers for mid- and high ribbons?
I suppose the Bass is tunable, Right?
best regards
Olaf
Hi Olaf,
The aluminium is on foil and it can stretch enough.
I did use transformers and resistors, but now I build an amplifier that can drive the ribbons direct.
The Bass panel is 1,5 Ohm the mid ribbon 0,1 Ohm and the tweeter 0,4 Ohm.
Yes the bass is tunable.
Rob
10 years ago Linesource posted this in another Apogee thread:
“I suspect Apogee had 4 reasons behind the Scintilla M-T ribbon design:
1) KEY.. Reduce cost by having only one magnet gap for both the M and 4xTs.
2) Reduce comb filtering by having Ts on top of the M. In the Full Range Apogee the 0.5" wide T was crossed at 10Khz with a 6db/octave slope to the 2" wide midrange, and even physically adjacent this M-T just met a 1-Lambda spacing and not 1/4 Lambda ideal goal.
3) M and 4xTs put 4xT aluminum foil in series to increase the resistance + SPL_area and hence give an easier amplifier load.
4) I suspect the Apogee engineers like the sound of the M-4T cardiod radiation and decided that they could both reduce cost and also provide greats sound even with a simple low order Xover. There were several positive reviews for the Scintillas which describe how coherent the M-T sounds.
If money is no object, I think a separate M and T ribbon is superior with the proper crossover frequencies and slopes.”
I’m interested in what others think about the Scintilla MR/TW arrangement vs the side by side configuration found on the FR and Diva models.
“I suspect Apogee had 4 reasons behind the Scintilla M-T ribbon design:
1) KEY.. Reduce cost by having only one magnet gap for both the M and 4xTs.
2) Reduce comb filtering by having Ts on top of the M. In the Full Range Apogee the 0.5" wide T was crossed at 10Khz with a 6db/octave slope to the 2" wide midrange, and even physically adjacent this M-T just met a 1-Lambda spacing and not 1/4 Lambda ideal goal.
3) M and 4xTs put 4xT aluminum foil in series to increase the resistance + SPL_area and hence give an easier amplifier load.
4) I suspect the Apogee engineers like the sound of the M-4T cardiod radiation and decided that they could both reduce cost and also provide greats sound even with a simple low order Xover. There were several positive reviews for the Scintillas which describe how coherent the M-T sounds.
If money is no object, I think a separate M and T ribbon is superior with the proper crossover frequencies and slopes.”
I’m interested in what others think about the Scintilla MR/TW arrangement vs the side by side configuration found on the FR and Diva models.