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Old 8th September 2012, 03:06 AM   #1
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Default Reverse engineering to drivers

Hi. I just picked up a pair of the famous (infamous) 1980 "Fourier 1" speakers for $25. These speakers feature solid mahogany boxes. They were well reviewed in their day and sold for $1100 each.

Unfortunately, the drivers (10" woofers, mids, and probably the tweeters) are shot and need to be replaced. I'm can't find information about the design. So what I'm left with are some nice boxes with stuffing and crossovers that certainly look nice, with no data on which to base my driver replacement choices, and I'm really not a speaker design guy.

So my challenge is -- without really knowing what I'm doing -- to learn (from you I hope!) whether it's possible to reverse engineer the design enough to make reasonable choices for new drivers?

Any advice? I'm a technically capable person but I'm not knowledgable about speaker design, per se.

Kind regards,
Kevin Sullivan

Last edited by kevinsullivan; 8th September 2012 at 05:04 PM.
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Old 8th September 2012, 04:02 AM   #2
DUG is offline DUG  Canada
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I would suggest to get a program like BOXPLOT that will allow you to select a driver, enter in the parameters, and see if the results would work with the box dimensions that you have.

If it does not match, select another driver and try again.

Sort of reverse engineering.

Or post the inner dims of the boxes and some of the more knowledgeable members here could recommend a few choices that you could start to look at.

Have fun and don't rush.
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Old 8th September 2012, 04:24 AM   #3
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Just Googled photo of the speakers and I am willing to bet that the tweeter is a 1" Audax soft dome. These were "the bee's roller skates" in the mid to late '70's in the UK and seemed to be in every second top end speaker sold there.
Something very similar could still be bought. They had 91dB/w/mtr sensitivity. Resonance around 900c/s I recall and crossed over anywhere from about 2.5kHz up. Often a 3rd order network.

Couldn't guess the others.
Are there notations on the back of the drivers?
Thought of getting the originals repaired?
Cheers Jonathan
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Old 8th September 2012, 04:36 AM   #4
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Hi Kevin,
Let's be positive about this. You are not limited by the existing port size. That can be changed to suit the new driver/box combination. So that's one fixed item that is now a controllable variable. (For that matter it could end up a sealed enclosure too).
You're obviously no fool. It wouldn't take too long to read up on speakers. Stacks on the web.
Cross overs can be "cannibalised" and probably should be. By that I mean the capacitors will probably be electrolytics and may be dried out by now. Plenty on new and better quality ones around these days. New drives will require new values for the cross over (usually) and that, again, can be worked out. Coils (inductors) are pretty much indestructible so they can be recycled....Need to determine existing values but that's not impossible.
You do have a challenge, but a good one. Nice shiny, solid cabinets are a good place to start assuming you like the aesthetics which presumably you do as you bought them in the first place...
Which you DO I see (just re-read your first post, doh!).
Good luck. I am sure a number of people here will gladly co-operate in this venture.
Cheers, Jonathan
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Last edited by Jonathan Bright; 8th September 2012 at 04:41 AM.
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Old 8th September 2012, 04:48 AM   #5
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You're actually spoiled for choice. Many in your position would not favour a bass reflex anyway. Depends what you are after. Sealed boxes are simpler. Do you wish to create "a very similitude" of the original CONCEPT or trying to achieve a really nice pair of domestic speakers irrespective of the acoustic theory behind them......?
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Old 8th September 2012, 05:24 AM   #6
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Found a picture on the web at Fourier 1 Speakers Very Beautiful and Very Rare Photo - Canuck Audio Mart

It looks like the drivers were:

Audax 1" dome tweeter, as previous poster noted about 90dB sensitivity, fs about 900 Hz, 8 ohm nominal, could probably replace it with
Dayton Audio DC28F-8 1-1/8" Silk Dome Tweeter 275-070

A better option may be:
http://www.parts-express.com/pe/show...umber=264-1040
but you'll have to add a 2ohm or 2.5ohm resistor in series with it for it to approximate the efficiency and impedance of the original tweeter.


Midrange
Looks like old Peerless 4" midrange (probably in a sealed mounting cup) w. flat surround, about 90dB sensitivity, 8 ohms, this one's going to be hard to find an exact match, but one TangBand unit may be a good, albeit pricey choice, similar extension, efficiency and impedance, and in fact it is a much, much better quality midrange driver, really impressive transparency, this would be a huge upgrade over the original. You may have to use a long 4" diameter tube behind it, and fill it with stuffing. It may be better if you can get the tube to go all the way through the back of the box.
Tang Band W4-1805S 4" Neodymium Midrange Driver 264-890

Woofer
Peerless (old Peerless germany) woofer. It's the 10", and probably has fs of about 25Hz, Qtc about 0.4, sensitivity 88 or 89dB or so. This unit could be a suitable replacement, may not need to adjust the port:
Dayton Audio DS270-8 10" Designer Series Woofer 295-432

or maybe this one (but may need port adjustment)
Peerless 830668 10" Paper Cone SLS Subwoofer 264-1110

Definitely plan on replacing the capacitors, I recommend the Dayton Polypropylenes.

Personally, I would redo the entire crossover to optimize for the new drivers, but that's a whole different level of work. The driver options I've suggested would probably work fairly well as drop-ins without needing to change the original crossover values much if at all.

Good luck with the project.
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Last edited by Jack Caldwell; 8th September 2012 at 05:41 AM.
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Old 8th September 2012, 06:02 AM   #7
Shaun is offline Shaun  South Africa
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Quote:
Originally Posted by kevinsullivan View Post
Unfortunately, the drivers (10" woofers, mids, and probably the tweeters) are shot and need to be replaced.
Looks like a nice project.

What, particularly, is wrong with the drivers? Have you considered getting them repaired?
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Old 8th September 2012, 01:23 PM   #8
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Quote:
Originally Posted by Jack Caldwell View Post
Found a picture on the web at Fourier 1 Speakers Very Beautiful and Very Rare Photo - Canuck Audio Mart

It looks like the drivers were: ...
Doug, Jack, et al.,

Thanks very much for your responses. They're very helpful. To further the discussion I'm attaching some detailed pictures: of the boxes, the condition of the drivers (the surrounds on the woofers look like something from Andromeda Strain -- mostly gone and what's left is crispy), crossover, and identifying marks on and pictures of the drivers.

The boxes are 38 1/2" H X 16" W X 11 3/8" D exterior, and the wood (at least on the front) is 7/8". Assuming it's the same thickness all around (I have not unstuffed the boxes), that'd make the interior dimensions

36 3/4 X 14 1/4 X 9 5/8 = 5040 in^3 = 2.9 ft^3, i.e., about 3 ft^3.

The port is 4" diameter and 6.5" from the back to the face of the speaker.

As for what I'm looking for ... I'd like to get the best sound possible from the speakers (not necessarily optimizing to replicate their original sound) without doing a whole lot of work and without spending a fortune.

I understand that old caps probably ought to be replaced, but if I could get upgrade these and get some mileage while saving the crossover upgrade for some future time, that'd be great -- thus my desire to have some sense of (rough) compatibility of the original and "near drop-in" replacement drivers.

I really appreciate the help all you folks have already provided. If there is anything else I can tell you or show you, let me know.

Kind regards,
Kevin
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Old 8th September 2012, 01:57 PM   #9
sreten is online now sreten  United Kingdom
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Hi,

Classic mid unit and treble unit from the period.
Bass unit has a humungous magnet for the period.

Refoaming the Peerless bass drivers should't be a problem.
Equivalent new drivers would be expensive.

The Peerless mid units have poked in dust caps which can
be sucked back out, are you sure that they don't work ?
(Its the coated version, apparently two coats.)

The tweeters are the ubiquitous Audax.

The crossovers do not need changing, they look fine.

Have you individually checked all the drivers to see if they work ?
(use a multi meter to measure the voice coil resistance).

It shouldn't be a problem finding near equivalent mids and treble.
You really need to repair the bass units though.

rgds, sreten.
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Last edited by sreten; 8th September 2012 at 02:14 PM.
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Old 8th September 2012, 02:18 PM   #10
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Quote:
Originally Posted by sreten View Post
Hi,

Classic mid unit and treble unit from the period.
Bass unit has a humungous magnet for the period.

Refoaming the Peerless bass drivers should't be a problem.
Equivalent new drivers would be expensive.

The Peerless mid units have poked in dust caps which can
be sucked back out, are you sure that they don't work ?
(Its the coated version, apparently two coats.)

The tweeters are the ubiquitous Audax.

The crossovers do not need changing, they look fine.

Have you individually checked all the drivers to see if they work ?
(use a multi meter to measure the voice coil resistance).

It shouldn't be a problem finding near equivalent mids and treble.
You really need to repair the bass units though.

rgds, sreten.
Sreten, Thanks a ton. As I said, I'm not knowledgeable about speaker repair. But now, thank to you, I know I can refoam the darn woofers. I didn't know that before! So, I plan to fire up the things, test the drivers, and if lucky, all I'll have to do is glue on some new surrounds. I watched a video on PartsExp and there's nothing to it. *Thanks*

Kevin
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