Replacing vintage stereo speakers

[planet10]

Supravox 215 RTF Bicone

A whole lot of overkill for the application thou... I'd try the FE207e by itself 1st (still perhaps overkill but within budget), i think you will find it has more extended highs than the 4" himble tweeter you pulled out. As well with the amp, as designed, you will want to not push the range of the speaker too much, because it will start showing up the ragged ends of the amps frequency spectrum.

If you need it you can always add a helper tweeter later.

dave

 

[sreten]

Hi Giacomo, P10,

Right then, seems we have a way forward !

The VM speakers are rebuilt as a reflexed single FE207Es.

We should concentrate on this first.

(After doing this then you can consider the add-on.
This would contain the tweeter, its crossover, the filter,
and some switching and adjustment facilities, but there
is no need to worry about this until after the speakers
are finished.

What's with the cigar box?

The idea is that its an add-on that sits on top of the VM speakers proper.
So the VMs are rebuilt in a very pure way in keeping with the main console.
The add-on is exactly that - an optional "hifi" extra ).

I'll post details of the port next post.

sreten.

 

[sreten]

Messing around with various Q's etc because the damping
factor of the amplifer is not known indicate that the port
should be 3" external diameter piping 3.5" long is as good
a guess as any, tuning frequency ~ 44 Hz.

sreten.

 

[sreten]

Hi giacomo,

some construction notes :

The art of box design is a sadly neglected area, but you can't go
too far wrong with a varied plywood box. The idea is to have some
"wooden box" warmth rather than an uber stiff enclosure.

Given your photographs the short side section is probably not
needed, if its wide enough to cover the holes in the opposite
side then its probably all that is needed for that side.

Sealing the bottom baffle mounting is a problem. Suggest you
use car filler or similar to do this. Secret with this stuff
is to work it as its setting before it gets too hard. You
should be able to extend the bottom mounting to seal it off.
A nice sharp chisel will help greatly here.

The Speaker should be mounted on the baffle top left for left
and top right for right, layout for the left speaker shown.

Port should be mounted on the baffle if you ever want to change.

I reccommend bracing the baffle with a 2" section glued
edge on, shown is the diagram is approximate placement.
Its not critical, niether is driver / port placement.

For sealing the baffle you need some foam strip around 20mm wide,
3mm thick, should do the job, something less wide for the rear.

Reccommend brass countersunk screws of the correct
length with matching brass washers for the rear panel.
Also suggest fitting brass terminals to the rear panel.
It may need a few more screws adding.

Damping should be as detailed in the Njord design, 3" of
fibreglass / rockwool, or 2" of acoustic foam. I'd suggest
rockwool sections for cavity walls are the easiest to get
hold of and more in keeping with the period.

If placed correctly the rockwool sections will be self supporting.

Ask if you need further clarifications.

sreten.

 

[sreten]

P.S. when you glue the back onto the original hardboard piece :

Using a brush or similar really soak the hardboard edge
that is left with with glue, this will help stiffen it up.

sreten.

 

[giacomo]

Sreten,

I've been busy with work, but I'm ready to get on this now. There are a few points though that I need to go over:

1)

The idea is that its an add-on that sits on top of the VM speakers proper

I'd like to keep the unit self contained. I already have a tuner and cd player on the speakers and placing the tweeters on top of them, with wiring and all, I think is going to be a bit of an eyesore. What issues do we have with mounting the tweeter on the baffle and then sealing it off from the Fostex by using the same felted cigar box construction? (so the tweeter will be mounted on the baffle, and the box will cover the rear)


2)

Suggest you use car filler or similar to do this. Secret with this stuff is to work it as its setting before it gets too hard. You should be able to extend the bottom mounting to seal it off.

Sorry, but I don't follow here at all. I have the plywood board covering the bottom now. Perhaps I'm not sure by what you mean, bottom baffle mounting. Do you mean the bracket that holds the baffle in place (By 'baffle' I'm presuming now that you're talking about the board to which the speakers are actually mounted)

3)

Port should be mounted on the baffle if you ever want to change

What is meant by 'port'?

4)

I reccommend bracing the baffle with a 2" section glued

I'm unsure of this too. I may need further clarification.

Sorry for all the questions this time; I'm just a bit confused by the new layout. If you believe the fostexes are what we should use then I'm going to order them today. If you believe I need tweeters, filters, etc. Let me know, because I'd like to get them all shipped at the same time, if I can get them all from parts express.

Thanks and kind regards,

Giacomo

 

[sreten]

1)
Personally I don't think putting the
tweeter on the baffle is a good idea.
TBH there is not a good place to put it, and IMO the VM's
would be better rebuilt as a pure single driver speaker.

Your CD player and tuner placement would become a problem.

2)
The bracket that holds the baffle now appears to have holes
either end as you've lifted it up. These holes need sealing.

3)
A port is a tube fitted to many speakers. The air in the port
is tuned to the cabinet volume. It gives greater bass extension
and greater power handling, and is absolutely need for the 207.
The attached file shows the response with the port and
without the port, as you can see you can't omit it.

4)
Just a 2" section (5/8" thick) turned on its side and glued as shown.

PE do not sell Fostex as far as I'm aware.

I'll send you a list of parts to order from PE.

sreten.

 

[sreten]

For the speakers you need 2 of these ports :

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-404

A set of these for connection :

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=091-1250

A set of these for mounting the drivers :

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-778

sreten.

 

[sreten]

VM add-on box

VM add-on box
************

Two boxes are needed, decorative wooden boxes seem ideal.

The Fostex FE207E due to its limited off axis response
will not have too many problems with the VM speakers
angled baffle mounting. A separate mounting of the
"helper" tweeter has many advantages, not least the
adjustability to tune the "sweetspot" of the speaker.


Parts per box :
************

Pack of feet to suit.

Audax tweeter.
The tweeter is mounted on the end of the box.

http://www.partsexpress.com/pe/show...tnumber=276-156

Pack of 4 terminals.
The terminals are mounted the other end of the box.

http://www.partsexpress.com/pe/show...number=091-1250

(You don't need mounting hardware for the tweeter)

3 locking push or rocker switches :

Filter on / bypass.
Tweeter on / off.
Tweeter 5KHz / 10KHz.

Choose these for ease of mounting in the box.

Mount these above the terminals on the rear of the box.

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=060-424

(Best part from PE, you may be able to find something better)


Filter circuit
--------------

This is wired in series, i.e. between the red input and output
terminals. It consists of a 5.1R resistor in parallel with a
2.7 mH air cored inductor in parallel with the on/bypass switch.

Due to the tweeter a Zobel is not really needed.

(The black input terminals are joined together)

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=004-5.1
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=255-272


Tweeter circuit
------------------

This is wired in parallel with the output, i.e. between the
red and black output terminals. The on/off switch is wired
in series with two 2.7uF capacitors connected in parallel
in series with the tweeter. The 5kHz/10Khz switch is wired
in series with one of the capacitors to remove it.

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=027-416


Options
---------

An L-pad could be used

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-250

additionally for tweeter level (and as a Zobel turned
down, with the frequency switch set to 10Khz).

sreten.

Another lousy diagram :

 

[giacomo]

Sreten,

I've ordered the Fostex, ports, and, plugs. I want to hook all this up before I move on to the tweeters, just to see how it sounds. I understand completely about the construction now. Thanks! I can't seem to find where to buy rockwool. I think they call it stonewool here in the States. (We can't seem to agree on anything here) If you know where I can get that and how much I need, I'll send for it.

Regards,

Giacomo

 

[sreten]

In the UK "rockwool" is sold by (house) builders merchants.

It comes in blocks suited for cavity wall insulation.

The port will need shortening, remove one or two of the rings.
I'd say removing 1 ring is the safer option, slightly too
low tuning is much better than slightly too high.

Yes, get the speakers working first !

sreten.

 

[sreten]

Hi Giacomo,

as a complete aside :

Given the age of the unit have you serviced the turntable ?
(Its not difficult at all)
Suggest start a new thread for details on how to do this,
if your interested.

I'm also curious as to what cartridge is fitted, an
option a little kinder to your records may be available.

sreten.

 

[giacomo]

Sreten,

The only thing that doesn't work on the turntable is the changer. I've already replaced the idle wheel and oiled everything else. The needles designed for these units are nothing complicated as they are separate from the cartridge which I also just replaced.
- New old stock from VM.

I did get the Fostexes today and it could be me but while they are warm and clear, they are very much in the mid-range. Of course I haven't mounted them yet but I did want to get your opinion on this before I did because madisound won't take them back once they've been mounted. I suppose my problem all along was that today's speakers are not designed for open baffle and that has become glaringly apparent. I hooked up the original carbonneaus again and the difference in sound is really night and day. The Carbs are full-sounding and loud even with their problems. Of course, they were designed for an open baffle so they're going to sound bigger but I'm wondering how much of a difference the enclosure is going to make with the fostexes. Should these sound good, or at least passable, without having to be mounted, sealed, etc?

Regards,

Giacomo

 

[planet10]

I did get the Fostexes today and it could be me but while they are warm and clear, they are very much in the mid-range. Of course I haven't mounted them yet

Without being in a box they will have no bass. They also take a couple hundred hours to break in... go ahead. mount them up and let them play...

dave

 

[giacomo]

P10,

Yeah, that's what we're doing now. They are growing on me. They do have their own characteristics. My girlfriend seems to be of the same opinion though, a lot of midrange but very clear. I'm measuring the holes for the drivers and ports now and will see if I can get them cut tomorrow. I'm going to try to do as much as possible without actually screwing them down. Thanks for the opinion and info. It is GREATLY appreciated.

Kind regards,

Giacomo

 

[sreten]

Sreten,

Should these sound good, or at least passable, without having to be mounted, sealed, etc?

Giacomo

Simple answer is no, they'll sound awful, as P10 says no bass.

(A larger unit with a high Q for open baffle
will make passable noises unmounted )

The difference mounted in box with the port will be huge.

You can only really get an idea of response above 1KHz
unmounted, i.e. judge treble extension and its balance
with the upper midrange.

You should also be able to get an idea of the smoothness
of response in the upper registers, hopefully this is a major
step forward from what you had before.

I don't really agree 200 hours run in required, though it may
take that long for the suspension to fully run in to final value.

When mounted in the box I expect the midrange to be forward
but hopefully not dominate (as it does unmounted ), if you think
it sounds warm and clear unmounted then things are looking
good. The warmness may be a lack of treble extension but
TBH that is somewhat to be expected, when choosing the 207.

I do wonder if a cartridge upgrade is possible.

sreten.

 

[sreten]

I'd try the FE207e by itself 1st (still perhaps overkill but within
budget), i think you will find it has more extended highs than
the 4" himble tweeter you pulled out.
If you need it you can always add a helper tweeter later.

dave

Hi P10,

According to the specs the 207 dies above 10KHz, going from
100dB at 10KHz to near 90dB at 15KHz. 30 degrees of axis
looks smoother but treble output is in the high 80's dB region.

The audax tweeter meanwhile is 90dB on axis and 30 degrees
off axis, with a mild plateau on axis to 94dB in the top octave.

Looks good to me as a "helper" tweeter, also have heard
the tweeter used as a replacement with a very simple
crossover, and it sounds remarkably good for the money.

sreten.

 

[Tim Moorman]

Tweeter

Here's one that is cheap but looks right for the task.

http://www.apexjr.com/speakerstuff.html

With only a few watts, durability shouldn't be a problem.

Buy two pair if concerned.

Tim

 

[Tim Moorman]

Tweeter

I'd roll this above 10K Hz with a single cap. The waterfall plot above 10K (see graphs) looks good.

Tim

 

[sreten]

TM,

Price wise it has an advantage over the Audax, half.

Size wise its far more inconvenient for the add-on box than the Audax.

Response wise the two are very similar towards the top end.

Sensisitivity wise one graph shows them to be similar,
(the graph showing the off axis responses),
the other I'm not exactly sure what it is showing.

The sensisitivity of the Audax is enough to do the job.

The add-on box has first order 5KHz and 10KHz options.

Personally I've heard the Audax and like it, and IMO the $15 saving
would not be worth the inconvenience of a bigger box for a larger driver.

sreten.