Pics of my 3rd front to back 55-2421 Isobaric box. A friend gave me a sheet of ½” MDF and I had one more pair of 55-2421, so couldn’t leave that combination sitting around.
½” is too light, so decided to build the box complete and then go back and “wrap” it with a second layer, lapping the joints and thickening the walls up to 1”.
The second ½” layer will be added today also I did use ¾” scrap for the tunnel.
As far as isobaric design, I’ve tried side by side speaker boxes - two speakers in one huge sealed cabinet - two speakers in ported box, on and on. I’ve gone back and isobaric mounted them, it does work better as far as low bass, rumble, and that sensation of power.
For another example, I took an old pair of 10” NTH woofers, (pretty old but in good shape,) again with a small tunnel and a box one half the size, the best bass ever. I wish I built them years ago
½” is too light, so decided to build the box complete and then go back and “wrap” it with a second layer, lapping the joints and thickening the walls up to 1”.
The second ½” layer will be added today also I did use ¾” scrap for the tunnel.
As far as isobaric design, I’ve tried side by side speaker boxes - two speakers in one huge sealed cabinet - two speakers in ported box, on and on. I’ve gone back and isobaric mounted them, it does work better as far as low bass, rumble, and that sensation of power.
For another example, I took an old pair of 10” NTH woofers, (pretty old but in good shape,) again with a small tunnel and a box one half the size, the best bass ever. I wish I built them years ago
Attachments
To follow up on this thread, attaching pic of finished box/design. The ½ over ½ MDF worked out well, a little more time/energy than I had planned, but glad I did it.
I have two of these in the back of the HT room, the bass is fantastic and loving it. The bass response is low, powerful and defined; I did find some 2" black foam “floor stands” to get them up off the floor a bit.
I connected them to two channels on a 5X200watt amp. and moved the rear speakers (shown left) to an older 100watt stereo amp. The 4ohm, MCM woofers are wired in series.
During the signal generator testing, there is noticeable bass enhancement down at 25hz, it rolls off pretty quickly after that (down to 20hz).
I like this project, somewhat easy to build, it works well and the costs are low. I also like that they sound great at low volumes; no need for "loud", bass enhancement, etc.
The 2 MCM woofers are $60 (sale price); I don’t think there is a single woofer out there for that amount that can do what this combination can achieve, if so, I would be curious what is out there that compares.
I have two of these in the back of the HT room, the bass is fantastic and loving it. The bass response is low, powerful and defined; I did find some 2" black foam “floor stands” to get them up off the floor a bit.
I connected them to two channels on a 5X200watt amp. and moved the rear speakers (shown left) to an older 100watt stereo amp. The 4ohm, MCM woofers are wired in series.
During the signal generator testing, there is noticeable bass enhancement down at 25hz, it rolls off pretty quickly after that (down to 20hz).
I like this project, somewhat easy to build, it works well and the costs are low. I also like that they sound great at low volumes; no need for "loud", bass enhancement, etc.
The 2 MCM woofers are $60 (sale price); I don’t think there is a single woofer out there for that amount that can do what this combination can achieve, if so, I would be curious what is out there that compares.
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I’ve been watching your thread; and yes I may come over to the dark side. Any speaker project sounds good to me and I have 1 driver left on the bench. I was going to ask if you can take some shots during fabrication. I think I understand it, but pics would be great.
Truth be known, that was a three coats before lunch project. That’s a flat, water based paint by Valspar, but when sprayed it has a bit of sheen. Since it was MDF there’s another easy trick to fill the flat surfaces (most will shout no-way). I skim coated it with regular green lid drywall compound; probably the fastest way to fill everything at once. The “mud” was applied very, very “tight”; on a gray primer (1st) coat and then sanded lightly.
nice finish ,
to bad they don't sell in europe.
Sure I wil. I have few Things to finalize before building start, if every thing goes well I will start next week.
well some relatives asked me to bild a ht subje(dus ik dacht lekker goedkoop)
but on the other hand i have plenty of other commitments right now,so ill put it in the fridge for now.
Jbells SS15 from 18mm "vezelplaat" with a DAP AB-15 driver (36 Euro's at 'marktplaats') can be built for lesswell some relatives asked me to bild a ht subje(dus ik dacht lekker goedkoop) but on the other hand i have plenty of other commitments right now,so ill put it in the fridge for now.
Hi,
I'm quite familiar with that woofer, and with its extremely low Qts it
would be one of my last choices to use in an isobaric configuration.
Two of them are far better used in a normal configuration for a lot
more output. They could be wired to provide the only distortion
cancellation advantage clamshell isobaric provides.
Suitable boxes for the drivers are tiny anyway, isobaric just makes
them silly small, there is no sensible point AFAICT for isobaric.
Two drivers isobaric :
Sealed : box volume is around 3L max.
Vented : box volume is about 6L max. Porting is impossible. PR's required.
Two drivers normal :
Sealed : box volume 7.5L to 15L.
Vented : box volume is about 24L max. Porting is problematic. PR's useful.
rgds, sreten.
See : http://www.diyaudio.com/forums/subwoofers/80138-sillys-1st-sub-8-mcm-55-2421-a.html
Pity MCM no longer sell the 10" PR that went well with this driver.
I'm quite familiar with that woofer, and with its extremely low Qts it
would be one of my last choices to use in an isobaric configuration.
Two of them are far better used in a normal configuration for a lot
more output. They could be wired to provide the only distortion
cancellation advantage clamshell isobaric provides.
Suitable boxes for the drivers are tiny anyway, isobaric just makes
them silly small, there is no sensible point AFAICT for isobaric.
Two drivers isobaric :
Sealed : box volume is around 3L max.
Vented : box volume is about 6L max. Porting is impossible. PR's required.
Two drivers normal :
Sealed : box volume 7.5L to 15L.
Vented : box volume is about 24L max. Porting is problematic. PR's useful.
rgds, sreten.
See : http://www.diyaudio.com/forums/subwoofers/80138-sillys-1st-sub-8-mcm-55-2421-a.html
Pity MCM no longer sell the 10" PR that went well with this driver.
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Sreten,
I have put a lot of time and energy into this woofer. I purchased 10 drivers originally and have tried many boxes, from single driver Bass Reflex boxes to 6 -7 isobaric.
At one time, I had 4 2cf cabinets set up, just for kicks, the bass was incredible, but 4 just didn’t fit the motif.
You can believe me, they work great, I personally enjoy tons of bass and these fit the bill.
I have compared them to store bought woofers and other sub woofer projects, for the $100 bucks (total), this blows them out of the water.
I have put a lot of time and energy into this woofer. I purchased 10 drivers originally and have tried many boxes, from single driver Bass Reflex boxes to 6 -7 isobaric.
At one time, I had 4 2cf cabinets set up, just for kicks, the bass was incredible, but 4 just didn’t fit the motif.
You can believe me, they work great, I personally enjoy tons of bass and these fit the bill.
I have compared them to store bought woofers and other sub woofer projects, for the $100 bucks (total), this blows them out of the water.
Hi,
Be that as it may, all indications are the boxes shown in this thread
would work better with a single driver fitted, rather than isobaric.
So what is the point of spending twice as much on drivers ?
It will go no louder, its half the impedance for no real purpose.
You appear to have very overdamped vented boxes.
With single drivers it will still be overdamped but less so.
What is your box volume and vent tuning frequency ? I'll model it.
Going overboard on overdamping does not give you tons of bass,
neither does going isobaric when it does not suit the situation,
it gives you less bass, for no real purpose.
rgds, sreten.
The design Silly built also blows stores stuff out of the water,
but it is done properly, optimised for the driver and situation.
Be that as it may, all indications are the boxes shown in this thread
would work better with a single driver fitted, rather than isobaric.
So what is the point of spending twice as much on drivers ?
It will go no louder, its half the impedance for no real purpose.
You appear to have very overdamped vented boxes.
With single drivers it will still be overdamped but less so.
What is your box volume and vent tuning frequency ? I'll model it.
Going overboard on overdamping does not give you tons of bass,
neither does going isobaric when it does not suit the situation,
it gives you less bass, for no real purpose.
rgds, sreten.
The design Silly built also blows stores stuff out of the water,
but it is done properly, optimised for the driver and situation.
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Hi,
Thought I'd do some estimates any way :
Assume internally box is 10" wide, 16" deep and 14" high. = 37 litres.
Port is 10" wide, 3/4" high and 13" long = 30Hz tuning.
The situation is worse than I thought. Your boxes are far too big.
The isobaric (green) has no advantages whatsover. Its worse than
using a single driver (blue). Red is what I'd suggest for a single driver.
Isobaric is pointless for these drivers needed PR's and a tiny box ~ 7L.
Given those boxes the drivers should be moved to the side walls
for force cancelling and +6dB in output. Result is (yellow).
rgds, sreten.
Thought I'd do some estimates any way :
Assume internally box is 10" wide, 16" deep and 14" high. = 37 litres.
Port is 10" wide, 3/4" high and 13" long = 30Hz tuning.
The situation is worse than I thought. Your boxes are far too big.
The isobaric (green) has no advantages whatsover. Its worse than
using a single driver (blue). Red is what I'd suggest for a single driver.
Isobaric is pointless for these drivers needed PR's and a tiny box ~ 7L.
Given those boxes the drivers should be moved to the side walls
for force cancelling and +6dB in output. Result is (yellow).
rgds, sreten.
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Hi,
No. You can't get rid of the bump, loading the box with both drivers is the best bet,
as the box is far too big, it will effectively quarter the box size for each driver, and
of course you'll get +6dB in efficiency and maximum output, with no real loss in bass
depth with a far superior transient response, a much tighter low bass effect.
rgds, sreten.
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Hi,
I'll also point out due to the drivers low Qts venting is almost mandatory.
Due to that, and the low Vbox's required PR'S are also mandatory IMO.
That is if you want to get the best out of this particular driver.
In europe this is decent value :
W69-1042J - TB spealers 6-9 inch paper subwoofer - Europe Audio
Would need a double flared port I imagine for the low tunings.
rgds, sreten.
I'll also point out due to the drivers low Qts venting is almost mandatory.
Due to that, and the low Vbox's required PR'S are also mandatory IMO.
That is if you want to get the best out of this particular driver.
In europe this is decent value :
W69-1042J - TB spealers 6-9 inch paper subwoofer - Europe Audio
Would need a double flared port I imagine for the low tunings.
rgds, sreten.
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it's a weird woofer
Thanks for the modeling, I am not surprised it doesn't look good on paper. I knew about that before I bought them. I called the MCM folks (way back when), they said "it's a weird woofer, use a 2cf BR box, tune to 30Hz."
These are all in the 1cf - 1.25 range (less the port) tuned to 30hz. The port is 10" wide 13 1/2" long 3/4" (1/32" less actually).
There are two in the HT, they bass never stops, it just keeps going, chug along like a church pipe organ sometimes. Shake the floor; chairs whatever you are looking for.
I did have three at one time, it was too much. I'm selling one off to a buddy, he found a 200W SA240-B for $99 on Amazon.
I did use one of the die cast woofers in the front of one of them (shown), I do think that does have a little more definition, and hope they start making them again. I might retrofit some of the others (the driver is a little bigger).
I don't know guys...this is a pretty easy, low cost project, some of these boxes were from slabs of MDF recycled from the bigger 2cf boxes that were made.
I don't think anyone would be disappointed if they built one. They do go on sale on for $30.
Thanks for the modeling, I am not surprised it doesn't look good on paper. I knew about that before I bought them. I called the MCM folks (way back when), they said "it's a weird woofer, use a 2cf BR box, tune to 30Hz."
These are all in the 1cf - 1.25 range (less the port) tuned to 30hz. The port is 10" wide 13 1/2" long 3/4" (1/32" less actually).
There are two in the HT, they bass never stops, it just keeps going, chug along like a church pipe organ sometimes. Shake the floor; chairs whatever you are looking for.
I did have three at one time, it was too much. I'm selling one off to a buddy, he found a 200W SA240-B for $99 on Amazon.
I did use one of the die cast woofers in the front of one of them (shown), I do think that does have a little more definition, and hope they start making them again. I might retrofit some of the others (the driver is a little bigger).
I don't know guys...this is a pretty easy, low cost project, some of these boxes were from slabs of MDF recycled from the bigger 2cf boxes that were made.
I don't think anyone would be disappointed if they built one. They do go on sale on for $30.
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Hi,
Useless advice from the clueless. The siimple fact is they are like some
of the Tangband 8" drivers and have been developed for very small
commercial subwoofer boxes, but DIYers don't like being limited
to small boxes, hence the nonsense advice given above.
Its not a weird woofer if you understand what its designed for.
Silly's sub link gives all the relevant design details, pity
the 10" PR that suited it very well is no longer sold.
One driver is your box (blue line) is only a little better than two (green).
Using two drivers side mounted for force cancelling will give just
as deep bass with far more definition and +6dB volume capability.
rgds, sreten.
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