Sreten, Tim:
I will agree that the open baffles are a big problem but what do you believe is the problem with the 20/20s? These are flat studio monitors/ sealed boxes. (1" dome - 8" woofer) To me they sound muffled and, as Tim wrote: all mid-range. Having the carbonneaus left and a 20/20 right let me hear a lot of difference. In fact, to match the level of the left to that of the right, I had to turn up the volume of the right channel to equal the same output from the left. I'll have to presume that this means I'm needing more power for the 20/20s to drive them to be as loud as the carbonneaus. Is it possible that a sealed box approach to this won't work at all because of the limitations of the amp?
Re-working vintage gear/appliances and even my car has always been difficult because, of course, I always want the best of both worlds: Great design with modern efficiency. Thanks to all for helping me make a good decision to effect that end.
Cheers,
Giacomo
I will agree that the open baffles are a big problem but what do you believe is the problem with the 20/20s? These are flat studio monitors/ sealed boxes. (1" dome - 8" woofer) To me they sound muffled and, as Tim wrote: all mid-range. Having the carbonneaus left and a 20/20 right let me hear a lot of difference. In fact, to match the level of the left to that of the right, I had to turn up the volume of the right channel to equal the same output from the left. I'll have to presume that this means I'm needing more power for the 20/20s to drive them to be as loud as the carbonneaus. Is it possible that a sealed box approach to this won't work at all because of the limitations of the amp?
Re-working vintage gear/appliances and even my car has always been difficult because, of course, I always want the best of both worlds: Great design with modern efficiency. Thanks to all for helping me make a good decision to effect that end.
Cheers,
Giacomo
giacomo said:
I'm beginning to despair.
All engineering is a compromise, you can't have it all.
Tim is correct to be concerned, there are severe compromises
related to the use of open baffles. With the Goldwood woofers
the absolute limit is ~ 40hz, they will die below this frequency.
They will need the bass knob turned up.
And I have to agree with Tim its not a good idea.
But keeping the open baffles what other options are there ?
I'd say :
1) swap to 10" high Q high Fs and add a subwoofer.
2) just add a subwoofer.
so there is a way forward ?
sreten.sreten,
First order electrical is first order, no matter the configuration - series or parallel - and 6 dB/octave is the slope. You may be confusing this with the acoustic slope. I have built series xovers, even owned Fried speakers.
Acoustic roll-off may combine with the electrical filter to yield a higher order roll off, but it may not be enough, even with inductance factored in. Depends entirely on the behavior of the driver at the upper end of it's bandwidth.
On the down side, as excursion increases, so, too, does distortion. It's possible to generate a 2nd harmonic that is equally loud as the fundamental, but an octave higher. Almost always the case with subs driven beyond their linear region.
The free air resonance of a driver doesn't reduce power being fed it. The power goes to the voice coil, like it or not, unless the amp can't effectively produce output into that impedance.
Oh. Looks like G's driver is shot.
Tim Moorman
First order electrical is first order, no matter the configuration - series or parallel - and 6 dB/octave is the slope. You may be confusing this with the acoustic slope. I have built series xovers, even owned Fried speakers.
Acoustic roll-off may combine with the electrical filter to yield a higher order roll off, but it may not be enough, even with inductance factored in. Depends entirely on the behavior of the driver at the upper end of it's bandwidth.
On the down side, as excursion increases, so, too, does distortion. It's possible to generate a 2nd harmonic that is equally loud as the fundamental, but an octave higher. Almost always the case with subs driven beyond their linear region.
The free air resonance of a driver doesn't reduce power being fed it. The power goes to the voice coil, like it or not, unless the amp can't effectively produce output into that impedance.
Oh. Looks like G's driver is shot.
Tim Moorman
Tim Moorman said:
I'm sorry, but I don't confuse theory with reality.
In this application first order series is vastly superior to first
order parallel, and if you consider the impedance variation
of the drivers this will rapidly become self evident.
Your not really helping by quoting simplistic principles.
sreten.G,
Nasty woofer. Death rattle is more like it. Probably not worth rebuilding.
Well, let's look at alternatives. No direct replacement, no easy fix because the original cabinet has no WALLS in it. There are good quality woofers available like the Adire DPL 12 and the Dayton IB 12" from Parts Express, however these are not cheap and not really compatible with your amp. If these were added with a separate amp - even a plate amp - then we would just add a wide range driver to cover from, say 150 Hz up.
So, can you get some one to cut plywood for you? If you can, then it is a matter of picking a woofer of suitable efficiency/bandwidth for the enclosure area you have. Then pairing up something like the Fostex with it.
What do you think?
Tim
Nasty woofer. Death rattle is more like it. Probably not worth rebuilding.
Well, let's look at alternatives. No direct replacement, no easy fix because the original cabinet has no WALLS in it. There are good quality woofers available like the Adire DPL 12 and the Dayton IB 12" from Parts Express, however these are not cheap and not really compatible with your amp. If these were added with a separate amp - even a plate amp - then we would just add a wide range driver to cover from, say 150 Hz up.
So, can you get some one to cut plywood for you? If you can, then it is a matter of picking a woofer of suitable efficiency/bandwidth for the enclosure area you have. Then pairing up something like the Fostex with it.
What do you think?
Tim
Re: Replacing plywood, etc.,
It was a project I really didn't want to undertake right now but if I must, I must. In a nutshell, I was just wondering that if it was going to be expensive to have the speakers rebuilt then shouldn't I just replace the speakers altogether? Especially if the speakers weren't that good to begin with. But if I'm correct in reiterating what I've learned from all this, modern speakers are not designed for open baffle systems. And they're certainly not designed for low watt amplifiers.
Harumph! Funny, I went through all this last summer with a 50s kitchen set I wanted to have re-chromed (too expensive, no one would do it, scratched heads, etc.) Well I wound up restoring that myself too and so I really believe there's got to be a way around this too. Let's put it this way: What will sound just as good as the originals or better?
Sreten, I may be mistaken, but I really do believe you're enjoying the academic challenge of this one!
Regards,
Giacomo
It was a project I really didn't want to undertake right now but if I must, I must. In a nutshell, I was just wondering that if it was going to be expensive to have the speakers rebuilt then shouldn't I just replace the speakers altogether? Especially if the speakers weren't that good to begin with. But if I'm correct in reiterating what I've learned from all this, modern speakers are not designed for open baffle systems. And they're certainly not designed for low watt amplifiers.
Harumph! Funny, I went through all this last summer with a 50s kitchen set I wanted to have re-chromed (too expensive, no one would do it, scratched heads, etc.) Well I wound up restoring that myself too and so I really believe there's got to be a way around this too. Let's put it this way: What will sound just as good as the originals or better?
Sreten, I may be mistaken, but I really do believe you're enjoying the academic challenge of this one!
Regards,
Giacomo
Giacomo,
Well, with the woofers rattlin', you are into some dough for a repair/recone, and this for a woofer which is not exceptional.
So, here's the deal. If you are serious about keeping this relic you may repair as needed, wait for replacements to turn up on ebay or at a vintage repair facility, or just rebuild it with new/other vintage stuff. But, without a box to house the woofer you are wasting your time. No drop in replacement, to my knowledge, without high cost.
As I said before, the Altec 414 woofer will sound good in this cabinet if you wish to use the same amp, and are willing to just enclose the box in wood. The wood frame is already there. Just screw 3/4" plywood panels onto the framing, creating a box, then seal the joints. You'll need a new 3/4" front baffle with a speaker opening in it for the chosen woofer. it doesn't have to be pretty. The fabric will hide the enclosure for that vintage look. The back panel needs to be removeable.
Measure the insides of the thing, and I can tell you what driver might work (W X H X Depth) given that box size and your amp.
Tim Moorman
Well, with the woofers rattlin', you are into some dough for a repair/recone, and this for a woofer which is not exceptional.
So, here's the deal. If you are serious about keeping this relic you may repair as needed, wait for replacements to turn up on ebay or at a vintage repair facility, or just rebuild it with new/other vintage stuff. But, without a box to house the woofer you are wasting your time. No drop in replacement, to my knowledge, without high cost.
As I said before, the Altec 414 woofer will sound good in this cabinet if you wish to use the same amp, and are willing to just enclose the box in wood. The wood frame is already there. Just screw 3/4" plywood panels onto the framing, creating a box, then seal the joints. You'll need a new 3/4" front baffle with a speaker opening in it for the chosen woofer. it doesn't have to be pretty. The fabric will hide the enclosure for that vintage look. The back panel needs to be removeable.
Measure the insides of the thing, and I can tell you what driver might work (W X H X Depth) given that box size and your amp.
Tim Moorman
Sealed Box Suitability
Well, first of all, I don't know ANYTHING about designing speakers . . . but I do have several Voice of Music tube amps (as well as many other vintage tube amps) that have similar power and I can tell you that sealed box speakers absolutely WILL work with these type amps. I use vintage Advents and KLH sealed boxes and they sound great with these. Of course they are not nearly as efficient as some other designs so they might not be suitable for really loud partying. But at the levels I usually listen 12 w/ch is more than enough. I'm currently using a DIY SET amp called the Bugle that uses type 45 tubes. The designer (Gordon Rankin of Wavelength Audio) claims it puts out all of 2.5 w/ch and it even works fine with these vintage speakers although not as loud as with the VM amps. So, given a suitable speaker, I would think that enclosing the box and sealing it would work fine. If the Altec speaker mentioned is that efficient you should be able to party too. . . . Charlie
Well, first of all, I don't know ANYTHING about designing speakers . . . but I do have several Voice of Music tube amps (as well as many other vintage tube amps) that have similar power and I can tell you that sealed box speakers absolutely WILL work with these type amps. I use vintage Advents and KLH sealed boxes and they sound great with these. Of course they are not nearly as efficient as some other designs so they might not be suitable for really loud partying. But at the levels I usually listen 12 w/ch is more than enough. I'm currently using a DIY SET amp called the Bugle that uses type 45 tubes. The designer (Gordon Rankin of Wavelength Audio) claims it puts out all of 2.5 w/ch and it even works fine with these vintage speakers although not as loud as with the VM amps. So, given a suitable speaker, I would think that enclosing the box and sealing it would work fine. If the Altec speaker mentioned is that efficient you should be able to party too. . . . Charlie
giacomo said:Sreten, I may be mistaken, but I really do believe you're enjoying the academic challenge of this one!
Hi Giacomo,
your not wrong,
but i wish some people would read all of the thread,
instead of repeating some stuff thats been said before.
If the boxes after stuffing and lossy baffle extensions
do rolloff from ~ 200Hz then by 40 - 50Hz bass will be
shy by ~ 12dB. The Goldwood 12" with give you 4dB
back, if we assume low amplifier damping + the series
resistance of the inductor perhaps 5dB.
(Note the Goldwood, though rated a 88dB/W
should be around 92dB/W at 40 to 50Hz.)
So now we are around 7/8 dB shy at 40 to 50Hz.
IMO the corner placement with the baffles near
walls will add around another 3dB to bass levels.
So now we are 4/5 dB shy.
IMO to balance the Fostex and Goldwood the bass control
will need to advanced approximately to mid boost and this
will boost bass by around 4 to 6dB.
So 40 to 50Hz is about flat.
Bass cut off will be 40Hz, Fs of the Goldwood.
IMO it has a good chance of working, but by definition
maximum bass levels will be lower by around 6dB than
a closed box overdamped reflex design.
sreten.
giacomo said:
These are not worth rebuilding -- 1st it is probably not possible to get parts, but the cost of the labour alone would far exceed the price of a better replacement. Similar drivers should be findable fairly easily... on the WE i picked up an RSC (Radio Speakers of Canada) OEM driver built for Jensen that came out of an open baffle console -- haven't tested them yet, but they should be a close match to your dying ones.
dave
Re: Open Baffle
Just to put some numbers to this :
For the series at 80Hz -
Z inductor = 2 ohms || Z Fostex ~ 35 ohms
Z capacitor = 24 ohm || Goldwood guesstimate ~ 16 ohm
As C and L are the same values for series and parallel c/o's
inspection should make it obvious the series is far better
for reducing bass power fed to the Fostex.
It is also far betting at "shorting" the Fostex at low
frequencies allowing a low Q to reject excursion.
It should also be obvious that a parrallel crossover is a poor
choice , 24 ohm in series with ~ 35 ohms at 80Hz is not good,
and as the the Fostex is becoming open circuit via C, it will
be tending towards its Qms, at 2.56 this is not a good idea.
At 1kHz
Z inductor = 25 ohms || Z Fostex = 8 ohms
Z capacitor = 2 ohm || Goldwood guesstimate ~ 12 ohm
Not fantasic attenuation but we are only 3 x c/o frequency,
Still the Goldwood should be 12dB down at this point.
Note that for the series the Goldwoods inductance helps
the c/o, whilst for the parrallel it works against the series
inductor.
For the 1st order series c/o, impedance compensation
of the bass unit is a very pointless exercise.
So all first order crossovers sound awful by definition ?
I don't know why people are bashing the Goldwood so much.
At 40 to 50Hz it takes all of the Fostex units to the cleaners
for efficiency, and nearly everything else available too.
92dB/W at 40 to 50Hz for genuine 8 ohms is pretty good going.
sreten.
Tim Moorman said:
Just to put some numbers to this :
For the series at 80Hz -
Z inductor = 2 ohms || Z Fostex ~ 35 ohms
Z capacitor = 24 ohm || Goldwood guesstimate ~ 16 ohm
As C and L are the same values for series and parallel c/o's
inspection should make it obvious the series is far better
for reducing bass power fed to the Fostex.
It is also far betting at "shorting" the Fostex at low
frequencies allowing a low Q to reject excursion.
It should also be obvious that a parrallel crossover is a poor
choice , 24 ohm in series with ~ 35 ohms at 80Hz is not good,
and as the the Fostex is becoming open circuit via C, it will
be tending towards its Qms, at 2.56 this is not a good idea.
At 1kHz
Z inductor = 25 ohms || Z Fostex = 8 ohms
Z capacitor = 2 ohm || Goldwood guesstimate ~ 12 ohm
Not fantasic attenuation but we are only 3 x c/o frequency,
Still the Goldwood should be 12dB down at this point.
Note that for the series the Goldwoods inductance helps
the c/o, whilst for the parrallel it works against the series
inductor.
For the 1st order series c/o, impedance compensation
of the bass unit is a very pointless exercise.
So all first order crossovers sound awful by definition ?
I don't know why people are bashing the Goldwood so much.
At 40 to 50Hz it takes all of the Fostex units to the cleaners
for efficiency, and nearly everything else available too.
92dB/W at 40 to 50Hz for genuine 8 ohms is pretty good going.
sreten.Re: Altec 414
Well, after a search around the net and e-bay I see these are going for about $250.00 a pair, and I don't see too many of them out there. That's a lot of scratch to still have to rebuild the cabinets around them. If they'd work with the open baffle, then I might consider getting a pair just to get this over with.
Anyway, onward. I'm posting the pictures of the cab - top, bottom, sides - to illustrate what I have to work with. If I have to seal the joints, then it looks like I've got a bit of construction to do. Note how the inside right corners do not exactly meet. There's a bit of a jog in the design as the front brace for the cloth meets the right edge. (see closeup) On the left, there is that single wall from midway to the back. Why they only put a wall on the short side is anyone's guess. I'll presume a wall on the right would have caused sound to bounce around and put it all out of phase. (this is, of course, reversed in the other speaker)
The top of the cabinet is going to be particularly tricky because the wood that forms the top is actually the outside surface. If I split that by accident, I'm going to be cursing myself. Perhaps some glue will do instead. The bottom doesn't look too bad. I can pull out the angled bracket and lay in a piece of plywood.
I like the idea of the speakers being angled inside the cabinet so that way I don't have to have each unit awkwardly angled in a corner. As noted in an earlier post, I'm unsure if the degree of the angle is exactly optimum. But I'll have to also presume that the designers at VM tested this unit out in their labs and thought this was the best design.
So my question is, now, if I'm going to create a sealed box out of this, what's the easiest way to get around all these braces. And if it is not exact, then how much will my sound suffer.
Kind regards,
Giacomo
Well, after a search around the net and e-bay I see these are going for about $250.00 a pair, and I don't see too many of them out there. That's a lot of scratch to still have to rebuild the cabinets around them. If they'd work with the open baffle, then I might consider getting a pair just to get this over with.
Anyway, onward. I'm posting the pictures of the cab - top, bottom, sides - to illustrate what I have to work with. If I have to seal the joints, then it looks like I've got a bit of construction to do. Note how the inside right corners do not exactly meet. There's a bit of a jog in the design as the front brace for the cloth meets the right edge. (see closeup) On the left, there is that single wall from midway to the back. Why they only put a wall on the short side is anyone's guess. I'll presume a wall on the right would have caused sound to bounce around and put it all out of phase. (this is, of course, reversed in the other speaker)
The top of the cabinet is going to be particularly tricky because the wood that forms the top is actually the outside surface. If I split that by accident, I'm going to be cursing myself. Perhaps some glue will do instead. The bottom doesn't look too bad. I can pull out the angled bracket and lay in a piece of plywood.
I like the idea of the speakers being angled inside the cabinet so that way I don't have to have each unit awkwardly angled in a corner. As noted in an earlier post, I'm unsure if the degree of the angle is exactly optimum. But I'll have to also presume that the designers at VM tested this unit out in their labs and thought this was the best design.
So my question is, now, if I'm going to create a sealed box out of this, what's the easiest way to get around all these braces. And if it is not exact, then how much will my sound suffer.
Kind regards,
Giacomo
Attachments
Manufacturer/ Dia. Power Z SPL Vas
Model RMS ohms 1W/1m Fs cu ft Qts xmax
-------------------------------------------------------------------------
Altec Lansing:
414-8B 12" 50W 8 96dB 29Hz 13.4 0.254 ?
414-8C 12"? ? 8 97dB 30Hz 8.13 0.21 0.15"
Open baffle ? Q's of 0.25 and 0.21 not a chance.
Vas of 13.4 cuFt and 8 CuFt -needs big boxes.
Though the C version :
I estimate your boxes will be around 1.5cuft if converted to closed.
With the C a sealed box would give a Q of 0.53 and Fb of 75Hz,
they will be ~ 6dB down at 75Hz.
Q of 0.53 means you can reflex them at 40Hz which would help.
TBH we are really back into using the Eminence Beta with a
compression tweeter territory if you are considering the Altec.
Shown : sort of box you need, and high frequency driver to match.
If you do convert to a closed box there are far more sensible options available.
sreten.Attachments
Hi Giacomo,
looking at your new pictures I'm becoming more and more
convinced you should leave them as open baffles and hang
the consequences.
IMO its a question of having something different because you can.
As said before I think the open baffle plan has a good chance of
working, and a very modest added subwoofer would sort out any
bass issues if you have them.
I think rebuilding the boxes to a good standard is possible,
(but time consuming and a lot of work to do properly)
but on consideration dull, I think you should keep the boxes
pretty much the way they are.
IMO you should close off the section in the base behind the
baffle with a piece of plywood, add two layers of carpet to
the side with holes in it and stuff the cabinet and refit the back.
sreten.
looking at your new pictures I'm becoming more and more
convinced you should leave them as open baffles and hang
the consequences.
IMO its a question of having something different because you can.
As said before I think the open baffle plan has a good chance of
working, and a very modest added subwoofer would sort out any
bass issues if you have them.
I think rebuilding the boxes to a good standard is possible,
(but time consuming and a lot of work to do properly)
but on consideration dull, I think you should keep the boxes
pretty much the way they are.
IMO you should close off the section in the base behind the
baffle with a piece of plywood, add two layers of carpet to
the side with holes in it and stuff the cabinet and refit the back.
sreten.Just qualify my last post somewhat as I've been pondering it.
If I'm not mistaken the cabinet has a number of relatively thin
sections that would need to be beefed up for a closed type box,
due to the higher air pressures in a sealed or reflex design.
In an open baffle they are much less of an issue.
Due to the way the front is built, adding a new baffle is not simple.
If the base opening was closed off we'd have a fairly large
folded baffle. The holes in the longest side hopefully reducing
airspace type resonances somewhat, as will stuffing.
According to here :
http://melhuish.org/audio/baffle.html
And a reasonable estimate of baffle size being around 20",
bass will roll-off 6dB/octave from 140Hz.
Which means at the low frequency target of 40 to 50 Hz bass will
be shy by around 7 to 9dB, unless I've misunderstood something.
The Goldwood 12" Q of around 1.5 will give 4 to 5 dB back
only leaving us short of 3 to 4 dB , which isn't too bad.
Which leaves the differences in sensitivity of the two drivers, 3dB.
I'd suggest mild bass lift would sort this out easily, and the speakers
would be very usable at levels designed not to annoy the neighbours.
But no good for parties, hire some PA type speakers for this !
sreten.
If I'm not mistaken the cabinet has a number of relatively thin
sections that would need to be beefed up for a closed type box,
due to the higher air pressures in a sealed or reflex design.
In an open baffle they are much less of an issue.
Due to the way the front is built, adding a new baffle is not simple.
If the base opening was closed off we'd have a fairly large
folded baffle. The holes in the longest side hopefully reducing
airspace type resonances somewhat, as will stuffing.
According to here :
http://melhuish.org/audio/baffle.html
And a reasonable estimate of baffle size being around 20",
bass will roll-off 6dB/octave from 140Hz.
Which means at the low frequency target of 40 to 50 Hz bass will
be shy by around 7 to 9dB, unless I've misunderstood something.
The Goldwood 12" Q of around 1.5 will give 4 to 5 dB back
only leaving us short of 3 to 4 dB , which isn't too bad.
Which leaves the differences in sensitivity of the two drivers, 3dB.
I'd suggest mild bass lift would sort this out easily, and the speakers
would be very usable at levels designed not to annoy the neighbours.
But no good for parties, hire some PA type speakers for this !
sreten.- Status
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