Replacing vintage stereo speakers

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The attached graph tries to show that 80Hz is the probable limit of the speakers.

I estimate the open baffle will roll-off at 6dB per octave below 200Hz.
This is the white line on the graph. (ignoring ripples above 200Hz).
Note a normal driver (Q<0.7) would always be under the white line.
A driver of Q ~ 1 would ~ follow the line then rolloff below Fs.

The main response shows a unit with Q=2 Fs=80Hz - yellow line.
not unlikely parameters see here :
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=290-262

The green lines show an approximation of response, flat
down to 80Hz and then a 18dB per octave roll-off below Fs.

The blue lines show an approximation of Q=2 Fs=50Hz.

For a flat response created by a high Q driver 80Hz is around the limit.

:) sreten.
 

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Ah, I see what you mean now about the difference between the open baffle and the sealed box. The 20/20s are studio monitors, sealed and with foam, thus even if the old speakers are rated at 50hz bottom, I'm losing the lower frequencies due to cab design. Like a kick drum with no blanket thrown in it, eh?

Okay, so my choices are:

1) Buy speakers with the right impedance (8ohm) and place them in the cabinets. Easy, and I know this will sound ridiculous, but I kind of feel like it's a cheat, like putting a '55 T-bird shell over a Hyundai and calling it a '55 T-bird. Going this route will always bother me and I'll wind up restoring them again in the future.

2) Create sealed boxes out of the baffles. Not an incredibly difficult project it seems, and the one I am considering. But what do you think about stuffing the cab with foam first just to see how much bass I reclaim? Living in a mid-century apartment I always have to make concessions and losing some bass may be one of them.

3) Place a power amp between the VM amp and my speakers. But which won't do anything for the bass at low levels anyway. Correct?


BTW, this unit is now 55 years old and still works. As of yesterday, the display on the brand new Tivoli CD player that I bought in December of 2003 is dead. So much for 21st century workmanship!

Cheers,

Giacomo
 
giacomo said:
Okay, so my choices are:

2) Create sealed boxes out of the baffles. Not an incredibly difficult project it seems, and the one I am considering. But what do you think about stuffing the cab with foam first just to see how much bass I reclaim? Living in a mid-century apartment I always have to make concessions and losing some bass may be one of them.

3) Place a power amp between the VM amp and my speakers. But which won't do anything for the bass at low levels anyway. Correct?


BTW, this unit is now 55 years old and still works.
Cheers,Giacomo

1) you don't need this forum for this.

2) foam stuffing and lossy baffle extensions won't cut it with
60's Ska IMO, annoying bass is usually not genuine low bass.
Reworking the cabinets is the way to go, it will not be difficult
if you approach it correctly, but it will take some time.

3) Sacrilege to any valve afficienado, higher power would allow
more bass boost, 12W per channel will be fine for the reworked
loudspeakers IMO.

Of interest is does your picture of the complete system show
its intended positioning in room ? this is how it will be used ?
This does affect final loudspeaker design.

born in 59 I make it 45, unless I really did lose some drug addled years.

:) sreten.
 
Okay, so thinking about this, if I go the reconstruction route then what I'm doing is, in a sense, making a box within a box again, just like putting the new speakers inside the baffles. So what do you think about a new speaker design based on the sealed box approach and I buy empty enclosures to put these new speakers in and then shove the whole thing in the baffle? I really don't care what the enclosures look like as they'll be covered anyway, so I won't be paying a manufacturer for their laminated pulp wood. Plus I can then install speakers that will be exactly right for this amp rather than finding something that may or may not work. :)


Stereo layout:

I've tried this stereo in several configurations around my apartment, and the only thing that works right now, is how it is in the picture. Though in the future I do plan on separating the speakers from the console by a few feet. That is, when I finally get wise enough to get out of NYC and get some wall space.

As always, kind regards,

Giacomo
 
Just my personal opinion but a box within a box is not ideal.

Buying boxes that fit will be a problem, as are
lots of other minor acoustic issues i can think of.

Rebuilding the boxes is the way to go IMO, but there are
lots of details to consider, if considered it not too difficult,
if you go this way then I can post further details of how
to go about it.

as Frank says, we are talking a closed box reflex design here.

:) sreten.
 
Sreten,

I've been listening to material through the Event 20/20s and I have to say after a few days of it, they are definitely not the right sort of speakers/cabs for this unit. Everything is muffled and I think the bass is a lot more washed out than with the original speakers. So based on the factors of:

1) I don't know what I'm doing

-and-

2) That based on the above factor #1 there is a high probablility of my mucking up perfectly good speakers and a vintage cabinet set.

-and-

3) Even if I managed to muddle through this, somehow, I'm unsure if the end result will be what I'm looking for.

I think we need to go back to Plan B with the open baffle,
and from what I understand, you believe the best set up would be:

Tweeter : Fostex fe107e

Woofer: Goldwood GW-212/8 12"

Capacitor: DAYTON 4.0uF-250V POLYPROPYLENE CAPACITOR

And this would be all I need. I only have to solder the one capacitor between the woofer and tweeter which will limit everything under ? hz from going to the tweeter. And that all this combined will present 8ohm impedance to the amp as needed. I hope I understand this correctly, and again, please correct me if I'm still missing something.

Thanks for bearing with me through all this, and all your suggestions. You should think that I could find a shop in NY that could have got me through all this, but really, all I've got so far has been blank stares and scratched heads.

Very best,

Giacomo
 
Hi Giacomo,

I have to say that I'd have far more confidence in the rebuilt
cabinets, with drivers fitted to suit the period of the piece,
than sticking with the open baffles.

As I said before I'm no expert on open baffles, and my further
investigations related to the post indicate some problems I
hadn't originally envisaged, mainly the large ripples in frequency
response you get above the baffle roll-off.

Also that the 12" inch unit might have very unusual parameters
suited to the open baffle design, and these parameters are very
hard to find in modern drivers.

I'm not surprised you get quizzical looks from retailers,
it was built in 1959 after all, and open baffle designs are
not common.

If you don't rebuild the cabinets then I'd advise some caution.

I remember in my youth fitting modern drivers to a old Decca
1/4 wave corner speaker with disastrous results, boom city.

Take your time and think about, make a decision and
I'll post details of the way I think you should proceed.

Is adding a subwoofer into the equation an option ?

:) sreten.
 
OK - the simplest option.

(Addition of a modest subwoofer will hopefully sort out any bass issues)

Drivers :

bass : 2 x http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=290-335

main range : 2 x http://madisound.com/fe107e.pdf

treble filler : 2 x http://www.speakercity.com/clearance/clearance_drivers.shtml
second driver down.

Mount the fostex and the filler tweeter on the front of the baffle.
For the bass unit it doesnt really matter, front or back.

Mount the filler driver below the right corner of the fostex on
the left speaker and below the left corner on the right speaker.
Mount it in as far as it will sensibly fit, you will need a hole for it.

Obtain some heavy duty nylon carpet, it should allow sound
through it but at an attenuated level. Cut sections to fit tightly
into the side sections behind the baffle and the section in the
base. I estimate two layers will be about right.

Stuff the back of the cabinet behind the baffle. This will keep
the carpet in place and damp the open hardboard back.
Use BAF, dacron, Polyfill, Fibreglass, Rockwool or similar.

The crossover for the bass/main unit is first order series at 280Hz.

This requires :

An inductor of 4mH in parallel with the fostex.

A capacitor of 82 uF in parallel with the bass unit.

The two units are then wired in series maintaining phase.

The 82uF capacitor is made up of a number of capacitors
in parallel, 68 + 6.8 + 6.8.

http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=027-336
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=027-424
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=027-356
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=226-562

The filler tweeter with a capacitor in series is wired across
the input. Suggest buying a series of cheap bipolar caps
for tuning of this unit and then replace with a polyproylene
type.

Suggest capacitors of 1uF, 1.5uF and 2.2uF. In combination
you can try 1, 1.5, 2.2, 2.5, 3.2, 3.7 and 4.7 uF.

http://www.partsexpress.com/webpage.cfm?webpage_id=3&SO=2&DID=7&CATID=31&ObjectGroup_ID=161


Maintain phase with the Fostex unit.

:) sreten.
 
Sreten,

Okay, I understand everything now except the wiring. I' m not able to visualize what components are to be soldered together. Do you have a small layman's diagram that you can post or e-mail?

From the way I read it, you suggest the speaker design should be like this crude drawing. Correct?

Giacomo
 

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Vintage Sound

G,

I'm not sure how badly you want to recreate the sound of that particular cabinet, I wouldn't, but most of the great old U.S. console units had Jensen, Magnavox, even RCA drivers. They are so far superior to those made today, when paired with the tube amp you have, or one of its ilk, that you will miss a good deal of the allure that got many of us in this hobby to begin with. Good used 12" replacements may exceed your budget, however. If patient, they may turn up cheap as most folks scrap out this stuff.

I would forget the open baffle, at least on the 12". I would try to find a 12" Jensen or Magnavox of the same vintage, and the field coils are truly wondrous sounding. You need a separate supply for those to power the coil, but worth it.

Barring that, use a vintage Altec 414 12" woofer. The box size looks good for it, once enclosed. This is ~ 97dB efficient woofer, which you will need for the low output of the amp. It was built for these kinds of applications. The mid/hi unit should be in the 92 -93dB range unless you are willing to add additional crossover components.

To replace the existing high freq unit with a Fostex is a good plan, but will probably need a separate enclosure to isolate it from the woofer, a box within the new box.

Alternatively, a small horn crossed in at 1000-1200 Hz will also work, but attenuation (L-pad) will be needed on the crossover.

Vintage woofers and the salvaged amp are a great match. They just require larger enclosures than are fashionable these days.

Adding to your confusion...

Tim Moorman
 
Open Baffle

sreten,

If G's intention is to re- use the open baffle, he may as well just replace the caps with equal value, scotch tape the tear in the HF unit, and load all back into the box. At least he may still be able to use the amp he's got. Odds are the existing 12" will sound better than any replacement unit, anyway, in that compromised design. It never could sound full and rich, just all midrange.

If, on the other hand, he wishes to actually improve on the original design, then he will need to enclose the open chamber as you discussed early on, and install good high efficiency woofers.

The PE 12" woofers will be a poor match for the amp with their low efficiency, provide no bass in an open baffle without a Linkwitz transform circuit or serious EQ, but they will make sound.
Not sure just what kind.

Additionally, it is my experience that a first order 6dB filter will probably not work with the new drivers suggested. Generally, as the freq drops the excursion continues to increase, even below the crossover, due to the shallow slope. The Fostex will not abide this very well with anything but a few milliwats of power as it has no excursion to speak of, and the 12" will soar undeterred into the 1000's Hz, though down some in amplitude. The combination will no doubt combine negatively. Plus, loads of capacitance and inductance really sound bad, even in a series filter.

Not my wish to cause further problems, but G needs to either stick with what he's got, or reconsider the situation from the viewpoint of bettering the original with a thorough make-over. The open baffle is a big design limitation.

Tim Moorman
 
Sreten,

Okay, that clears up thing a bit more. However, I'm still unsure of how those three capacitors are wired. Are the ends just to be soldered together, or do I need some sort of circuit board? Plus, is there any sort of special guage wire that I need to do this? AND, (ugh) where is that all this connects to the speaker wire? I'm presuming the plus and minus on the left of the diagram (though msot of my presumptions have been wrong haven't they?)

As to Tim's suggestion: Now that I've learned from Planet that the speakers were made by carbonneau, I've done some research on them (or at least tried to) and from the paucity of information I've found, that usually indicates that there isn't much acclaim for them. The absence of anyone pining for the sound pretty much means 'no one cares.'

Right now I've got a set of Carbonneaus set up on the left channel and the 20/20's on the right. I've got to say the bass is livable through the carbonneaus but I think the real problem with it is that the unit was designed in an era of flux. My 50's rockabilly records with double bass play fine at loud volume -because of the lack of tightness from that instrument. Putting on some Stax/Motown material, or anything with electric bass, the volume has to be low else at a loud level the speakers start to vibrate and rattle. Very annoying. Perhaps I'm wrong but I don't think re-coning will solve this problem. There's a guy who'll recone the woofers for $40 each and the tweeters at $25 each. So a big investment for speakers that I still won't to be play loudly.

Do you think I'll still have this problem with the rattling with the new speakers? Or should it be rectified?

Kind regards,

Giacomo
 
Re: Open Baffle

Tim Moorman said:
sreten,

If G's intention is to re- use the open baffle, he may as well just replace the caps with equal value, scotch tape the tear in the HF unit, and load all back into the box. At least he may still be able to use the amp he's got. Odds are the existing 12" will sound better than any replacement unit, anyway, in that compromised design. It never could sound full and rich, just all midrange.

If, on the other hand, he wishes to actually improve on the original design, then he will need to enclose the open chamber as you discussed early on, and install good high efficiency woofers.

The PE 12" woofers will be a poor match for the amp with their low efficiency, provide no bass in an open baffle without a Linkwitz transform circuit or serious EQ, but they will make sound.
Not sure just what kind.

Additionally, it is my experience that a first order 6dB filter will probably not work with the new drivers suggested. Generally, as the freq drops the excursion continues to increase, even below the crossover, due to the shallow slope. The Fostex will not abide this very well with anything but a few milliwats of power as it has no excursion to speak of, and the 12" will soar undeterred into the 1000's Hz, though down some in amplitude. The combination will no doubt combine negatively. Plus, loads of capacitance and inductance really sound bad, even in a series filter.

Not my wish to cause further problems, but G needs to either stick with what he's got, or reconsider the situation from the viewpoint of bettering the original with a thorough make-over. The open baffle is a big design limitation.

Tim Moorman

1) I agree the open baffle is a big problem.

2) I think you'll find 1st order series crossovers are quite different
to the parallel variety, which is why I've recommended it.
The fostex Fs resonance will reduce fed power, in the same way
the bass units inductance will add to its roll-off, not fight it.

The result will be a c/o of higher order than simply apparent.

so I think :

Additionally, it is my experience that a first order 6dB filter will probably not work with the new drivers suggested. Generally, as the freq drops the excursion continues to increase, even below the crossover, due to the shallow slope. The Fostex will not abide this very well with anything but a few milliwats of power as it has no excursion to speak of, and the 12" will soar undeterred into the 1000's Hz, though down some in amplitude. The combination will no doubt combine negatively. Plus, loads of capacitance and inductance really sound bad, even in a series filter.

Is only true for parallel crossovers.

3) the bass unit - you find something better. I can't.
Its quite possible the original units would be better but
one is dodgy, so two new units it is.
If I knew a sub was going to be added I'd reccommend
the higher efficiency higher Q but much higher Fs 10" unit.
Without Bass EQ I know the PE woofers will not cut the
mustard, but I also know they will do well with bass EQ.

4) I reckon the Fostex and filler driver can be
reused if G eventually goes for a closed box.

I've used a Rogers Cadet III in the past with 87dB/W
speakers, real 8 ohm rating mind you, 12W per channel
and its fine until you hear what 100w will do.

:) sreten.
 
giacomo said:
Sreten,

Okay, that clears up thing a bit more. However, I'm still unsure of how those three capacitors are wired. Are the ends just to be soldered together, or do I need some sort of circuit board? Plus, is there any sort of special guage wire that I need to do this? AND, (ugh) where is that all this connects to the speaker wire? I'm presuming the plus and minus on the left of the diagram (though msot of my presumptions have been wrong haven't they?)

As to Tim's suggestion: Now that I've learned from Planet that the speakers were made by carbonneau, I've done some research on them (or at least tried to) and from the paucity of information I've found, that usually indicates that there isn't much acclaim for them. The absence of anyone pining for the sound pretty much means 'no one cares.'

Right now I've got a set of Carbonneaus set up on the left channel and the 20/20's on the right. I've got to say the bass is livable through the carbonneaus but I think the real problem with it is that the unit was designed in an era of flux. My 50's rockabilly records with double bass play fine at loud volume -because of the lack of tightness from that instrument. Putting on some Stax/Motown material, or anything with electric bass, the volume has to be low else at a loud level the speakers start to vibrate and rattle. Very annoying. Perhaps I'm wrong but I don't think re-coning will solve this problem. There's a guy who'll recone the woofers for $40 each and the tweeters at $25 each. So a big investment for speakers that I still won't to be play loudly.

Do you think I'll still have this problem with the rattling with the new speakers? Or should it be rectified?

Kind regards,

Giacomo

You can hardwire the crossover as shown.

As to the rattles what rattles ?
generally not difficult to fix once you know the cause.

:) sreten.
 
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