Sreten,
Right speaker:
Left side - closest angled point of mounting board to back (Measuring to the where the new back will sit when sealed) = 5.5"
Right side - farthest angled point of mounting board to back (measured as above) = 13."
Left speaker is obviously reversed.
Outside dimension of front is 15.5" but of course we don't care about that, do we?
Mounting board width is approx 15"
The horizontal angled brackets were there to begin with. I removed them from the slat that ran across the open bottom. Then I slipped in the base board. Then I replaced the angled bracktet on top of this. Thus I lost some height on the mounting board - 5/8" which is the width of the base plywood. We lost 1 1/4" width total on the inside due to the width of the plywood. Due the original constuction of the cab, all boards pretty much slip into 'frames' formed by the crosspieces.
There are no vertical angled brackets to speak of. The board just gets mounted to the horizontal brackets.
If you need more close-ups, let me know.
Hanx!
Giacomo
Right speaker:
Left side - closest angled point of mounting board to back (Measuring to the where the new back will sit when sealed) = 5.5"
Right side - farthest angled point of mounting board to back (measured as above) = 13."
Left speaker is obviously reversed.
Outside dimension of front is 15.5" but of course we don't care about that, do we?
Mounting board width is approx 15"
The horizontal angled brackets were there to begin with. I removed them from the slat that ran across the open bottom. Then I slipped in the base board. Then I replaced the angled bracktet on top of this. Thus I lost some height on the mounting board - 5/8" which is the width of the base plywood. We lost 1 1/4" width total on the inside due to the width of the plywood. Due the original constuction of the cab, all boards pretty much slip into 'frames' formed by the crosspieces.
There are no vertical angled brackets to speak of. The board just gets mounted to the horizontal brackets.
If you need more close-ups, let me know.
Hanx!
Giacomo
Speaker repair
Speaker repair can be done for $40 or one can buy the parts and do it yourself. One can replace the existing speakers and buy a better crossover network or make their own. Here is a good place to check for 2 way crossovers. http://www.partsexpress.com/webpage.cfm?webpage_id=3&SO=2&&DID=7&CATID=48&ObjectGroup_ID=193
One can check the voice coil resistance to see if the voice coil is damaged. The resistance usually matches the impedance rating on most speakers. A lower reading means the coil is burnt and some coils are shorting out which will damage solid state amplifiers. Higher resistance readings are usually either from bad solder joints or the flexible wires are going bad between the diaphram and the lug connector.
I would use the woofer if it is still good, add a hole for a mid range driver, replace the tweeter and install a 3 way crossover network. Here is a good place to check for 3 way crossovers. http://www.partsexpress.com/webpage.cfm?webpage_id=3&SO=2&&DID=7&CATID=48&ObjectGroup_ID=194 Crossover Examples
http://www.partsexpress.com/resources/crossover/xoverhelp.html I would recomend this 3 way crossover. http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-210 Get this tweeter. http://www.partsexpress.com/pe/pshowdetl.cfm?&PartNumber=275-070&DID=7 I would get 4 of these, install 2 in each cabinet, wire them in series, then connect them to the 3 way crossover. http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=265-285
Speaker repair can be done for $40 or one can buy the parts and do it yourself. One can replace the existing speakers and buy a better crossover network or make their own. Here is a good place to check for 2 way crossovers. http://www.partsexpress.com/webpage.cfm?webpage_id=3&SO=2&&DID=7&CATID=48&ObjectGroup_ID=193
One can check the voice coil resistance to see if the voice coil is damaged. The resistance usually matches the impedance rating on most speakers. A lower reading means the coil is burnt and some coils are shorting out which will damage solid state amplifiers. Higher resistance readings are usually either from bad solder joints or the flexible wires are going bad between the diaphram and the lug connector.
I would use the woofer if it is still good, add a hole for a mid range driver, replace the tweeter and install a 3 way crossover network. Here is a good place to check for 3 way crossovers. http://www.partsexpress.com/webpage.cfm?webpage_id=3&SO=2&&DID=7&CATID=48&ObjectGroup_ID=194 Crossover Examples
http://www.partsexpress.com/resources/crossover/xoverhelp.html I would recomend this 3 way crossover. http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-210 Get this tweeter. http://www.partsexpress.com/pe/pshowdetl.cfm?&PartNumber=275-070&DID=7 I would get 4 of these, install 2 in each cabinet, wire them in series, then connect them to the 3 way crossover. http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=265-285
Hi Giacomo,
Note :
do not glue the bottom section in place, it may be good
place for a port, a lot easier to cut outside the cabinet.
Well I've just about run the gamut of my "full range" driver
knowledge and learned a few things in the process.
The new box volume doesn't change things a great deal,
because we are already dealing with non-optimum volumes.
TM is right, if you go full range the filter can be added later.
My earlier concerns regarding amplifier pre-eq may be relevant,
and if the console has seperate bass and treble controls its
quite possible good results can be achieved by setting these.
But with both 8" units you are running in to bass excursion
issues, they are not ideal from a reggae bass perspective.
I'm going to look at some other options
sreten.
Note :
do not glue the bottom section in place, it may be good
place for a port, a lot easier to cut outside the cabinet.
Well I've just about run the gamut of my "full range" driver
knowledge and learned a few things in the process.
The new box volume doesn't change things a great deal,
because we are already dealing with non-optimum volumes.
TM is right, if you go full range the filter can be added later.
My earlier concerns regarding amplifier pre-eq may be relevant,
and if the console has seperate bass and treble controls its
quite possible good results can be achieved by setting these.
But with both 8" units you are running in to bass excursion
issues, they are not ideal from a reggae bass perspective.
I'm going to look at some other options
sreten.Attachments
A budget alternative (around $100)
Chucking out any full range driver, vintage sound and simple
crossover concerns, and noting your speakers did have a 4ohm
tweeter, so I'm not that sure under 8 ohms is out of the question :
For the cost you could do a lot, lot worse than this :
http://www.adireaudio.com/miscellaneous/free_designs/the_bang!.htm
Cheap drivers do need complex crossovers.
Your box size is near enough to be viable, an educated
resizing of the port would be required, tuned to 37Hz.
sreten.
Chucking out any full range driver, vintage sound and simple
crossover concerns, and noting your speakers did have a 4ohm
tweeter, so I'm not that sure under 8 ohms is out of the question :
For the cost you could do a lot, lot worse than this :
http://www.adireaudio.com/miscellaneous/free_designs/the_bang!.htm
Cheap drivers do need complex crossovers.
Your box size is near enough to be viable, an educated
resizing of the port would be required, tuned to 37Hz.
sreten.
Sreten, Planet,
Is there any section in the schematics that will tell us what ohms should be presented to the amp? i've been in contact with the owner of VM Enthusiasts. He bought out VM's wearhouse when they went bankrupt in '79. He does not have speakers but he was fairly certain that we should be going 8 ohms with this. My only concern about going with 4 ohm is that if the amp gets fried, then I've got a heck of a time getting it out and getting it serviced.
Point two: How much more volume are we going to lose with the dampening material? If it's carpeting or something as thick, I should think we will lose up to another 1.5". Perhaps this doesn't matter?
Point three: If we go with one of the fostex full range, the 207E, let's say (i'm gathering from the posts that the treble on this is better thatn the 206) could we then add a subwoofer to take care of the bass. Or going the other way, the 206 with a tweeter? Perhaps I don't know what I'm talking about here. So let me know if that's true.
Kind regards,
Giacomo
Is there any section in the schematics that will tell us what ohms should be presented to the amp? i've been in contact with the owner of VM Enthusiasts. He bought out VM's wearhouse when they went bankrupt in '79. He does not have speakers but he was fairly certain that we should be going 8 ohms with this. My only concern about going with 4 ohm is that if the amp gets fried, then I've got a heck of a time getting it out and getting it serviced.
Point two: How much more volume are we going to lose with the dampening material? If it's carpeting or something as thick, I should think we will lose up to another 1.5". Perhaps this doesn't matter?
Point three: If we go with one of the fostex full range, the 207E, let's say (i'm gathering from the posts that the treble on this is better thatn the 206) could we then add a subwoofer to take care of the bass. Or going the other way, the 206 with a tweeter? Perhaps I don't know what I'm talking about here. So let me know if that's true.
Kind regards,
Giacomo
Hi G,
p1 - I don't know, hopefully someone can tell you if 4
ohms is out of the question, or a reasonable thing to do.
p2 - don't worry about it.
p3 - the 206 has more treble than the 207. The 207 has a better
bass balance, but both drivers maximum bass levels are identical,
and can be reached with your amplifier.
sreten.
p1 - I don't know, hopefully someone can tell you if 4
ohms is out of the question, or a reasonable thing to do.
p2 - don't worry about it.
p3 - the 206 has more treble than the 207. The 207 has a better
bass balance, but both drivers maximum bass levels are identical,
and can be reached with your amplifier.
sreten.
p1/ the only easy way to tell is by putting an ohmmeter across one of the 12s. You have no fear of blowing the amp, only that if the impedance strays to far from optimum you start to loss power -- if it gets to low you will typically get a bit more distortion, if to high a little less.
p2/ the nature of damping material, fiberglass, ployfluff, is to increase the apparent volume of the box.
dave
p2/ the nature of damping material, fiberglass, ployfluff, is to increase the apparent volume of the box.
dave
Sreten,
I'm unsure about it. I can only go by what the guy from VM wrote to me - that it should be 8 ohms total. I can tell you that from attaching the 20/20s, which are 4 ohms, that they would not produce nearly the same volume as the original speakers.
So going by what Planet has taught me about impedence:
I'd say that this jibes with my results.
Keep smiling!
Giacomo
I'm unsure about it. I can only go by what the guy from VM wrote to me - that it should be 8 ohms total. I can tell you that from attaching the 20/20s, which are 4 ohms, that they would not produce nearly the same volume as the original speakers.
So going by what Planet has taught me about impedence:
I'd say that this jibes with my results.
Keep smiling!
Giacomo
Here are the specs on the 20/20s. They were manufactured by Event. i bought them about 5 years ago, new. When I tested the old speaker against the 20/20 i had to turn up the volume on the 20/20 by about double. So if the old one was at 4 I had to go to 8 on the 20/20 to get equal volume. Does this make sense?
Attachments
If your wondering where I'm going with this 4 ohm lark :
http://www.fortunecity.com/rivendell/xentar/1179/theory/dddllqd/dddllqd.html
Using the FE206E with this with the tweeter cone removed.
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-045
sreten.
http://www.fortunecity.com/rivendell/xentar/1179/theory/dddllqd/dddllqd.html
Using the FE206E with this with the tweeter cone removed.
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-045
sreten.To show that I may not be losing my marbles is the sanity
check from the above article. Shown are the two units
individually loaded with 20L and reflex tuning of 40Hz,
(as though each cabinet was physically split in two)
Amplifier damping in this case is not considered.
Shown are my amateurish attempts to join the dots.
To allow for phase differences (though they are remarkably
close) I've used +5dB instead of +6dB for the equal level
points shown in orange, the white dots are estimations.
The result is rather excellent efficiency down to 100Hz,
and a rolloff suited to adding a really serious subwoofer,
if matching levels of the pair above 100Hz is required.
(I'll start a seperate thread regarding the configuration)
sreten.
check from the above article. Shown are the two units
individually loaded with 20L and reflex tuning of 40Hz,
(as though each cabinet was physically split in two)
Amplifier damping in this case is not considered.
Shown are my amateurish attempts to join the dots.
To allow for phase differences (though they are remarkably
close) I've used +5dB instead of +6dB for the equal level
points shown in orange, the white dots are estimations.
The result is rather excellent efficiency down to 100Hz,
and a rolloff suited to adding a really serious subwoofer,
if matching levels of the pair above 100Hz is required.
(I'll start a seperate thread regarding the configuration)
sreten.Attachments
Other choices
No doubt the amp would like to see higher impedance...just wondering if there are 4 ohm taps on the output transformer(realize chances are slim with the VM guy insisting on 8 ohm).
Although rare, some vintage tube amps are so equipped, you just can't always see them.
As things are bound to get crowded on the baffle, one could still set it up as a two-way with a larger woofer(to better match efficiency), if the Thorsten Loesch thing doesn't look promising, by removing the bottom diagonal brace and firing the bass unit straight down. This assumes that the woofer suspension will not deflect to the point of distortion from the "hanging mount".
http://www.adireaudio.com/tech_papers/driver_orientation.htm
If crossed low enough, the bass unit will be omnidirectional.
Tim
No doubt the amp would like to see higher impedance...just wondering if there are 4 ohm taps on the output transformer(realize chances are slim with the VM guy insisting on 8 ohm).
Although rare, some vintage tube amps are so equipped, you just can't always see them.
As things are bound to get crowded on the baffle, one could still set it up as a two-way with a larger woofer(to better match efficiency), if the Thorsten Loesch thing doesn't look promising, by removing the bottom diagonal brace and firing the bass unit straight down. This assumes that the woofer suspension will not deflect to the point of distortion from the "hanging mount".
http://www.adireaudio.com/tech_papers/driver_orientation.htm
If crossed low enough, the bass unit will be omnidirectional.
Tim
some efficiency numbers re volume
Hi giacomo,
Thought I'd point out some basic principles.
The 20/20 are 20L volume, bass to 50Hz, 88dB, reflex.
Those with a seasoned eye will immediately find the 88dB/W
rating rather dubious. It far more likely to be 88dB/2.83V.
(2.83V is one watt into 8 ohms), i.e 2.83V into 4 ohms.
Which yields a real efficiency of 85dB/W.
This is not certain however. They are described as near field
monitors. Near field monitors can be 3dB to 6dB louder in the
midrange than normal far field speakers, used far field as you
are doing they can have weak bass, depending on how much
the design is really "nearfield".
(The chosen bass reflex alignment is a poor choice for farfield
listening and typical room placement. IMO bass will be "tubby".)
Your speakers are 40L. I can tell you that a reflex of about
88/89dB/W (8ohms) will go down to ~ 40Hz, more in-room.
Box volume, efficiency and bass cutoff are all interelated.
For a given box size, 40L, you trade off efficiency and bass extension.
Efficiency divided by f3 cubed is constant.
So for every doubling of efficiency (+3dB) bass extension
decreases, i.e. f goes up by the cube root of 2, i.e. x 1.26.
So :
91/92 db/W will cutoff ~ 50Hz.
94/95 dB/W will cutoff ~ 64Hz.
97/98 dB/W will cutoff ~ 80hz.
sreten.
Hi giacomo,
Thought I'd point out some basic principles.
The 20/20 are 20L volume, bass to 50Hz, 88dB, reflex.
Those with a seasoned eye will immediately find the 88dB/W
rating rather dubious. It far more likely to be 88dB/2.83V.
(2.83V is one watt into 8 ohms), i.e 2.83V into 4 ohms.
Which yields a real efficiency of 85dB/W.
This is not certain however. They are described as near field
monitors. Near field monitors can be 3dB to 6dB louder in the
midrange than normal far field speakers, used far field as you
are doing they can have weak bass, depending on how much
the design is really "nearfield".
(The chosen bass reflex alignment is a poor choice for farfield
listening and typical room placement. IMO bass will be "tubby".)
Your speakers are 40L. I can tell you that a reflex of about
88/89dB/W (8ohms) will go down to ~ 40Hz, more in-room.
Box volume, efficiency and bass cutoff are all interelated.
For a given box size, 40L, you trade off efficiency and bass extension.
Efficiency divided by f3 cubed is constant.
So for every doubling of efficiency (+3dB) bass extension
decreases, i.e. f goes up by the cube root of 2, i.e. x 1.26.
So :
91/92 db/W will cutoff ~ 50Hz.
94/95 dB/W will cutoff ~ 64Hz.
97/98 dB/W will cutoff ~ 80hz.
sreten.Neighborhood
Giacomo,
You never said you had to please the guy in the apartment under you, too! May I suggest a)headphones; b)bribes.
Actually, the direction the woofer is mounted doesn't matter, as far as bass penetrating the floor. It will be audible, given sufficient volume and extension, in any position, with any size speaker. You may have to ease up on the rap and hip-hop.
In this case, generating bass is more about setting up the balance of the overall sound correctly.
One big benefit of the vintage woofers was the ability to remain articulate at low volume (with milivolts of power), and still develop some bass. The presentation was balanced, even at a murmur. As you may have noticed, the low efficiency 20/20s, or any of the vast majority of current offerings, do not share that trait.
Tim
Giacomo,
You never said you had to please the guy in the apartment under you, too! May I suggest a)headphones; b)bribes.
Actually, the direction the woofer is mounted doesn't matter, as far as bass penetrating the floor. It will be audible, given sufficient volume and extension, in any position, with any size speaker. You may have to ease up on the rap and hip-hop.
In this case, generating bass is more about setting up the balance of the overall sound correctly.
One big benefit of the vintage woofers was the ability to remain articulate at low volume (with milivolts of power), and still develop some bass. The presentation was balanced, even at a murmur. As you may have noticed, the low efficiency 20/20s, or any of the vast majority of current offerings, do not share that trait.
Tim
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