Need basic advice to make a pair of magnet to cone configuration Isobarik sealed chamber bass woofers.
I am confident with making the cabinets just not the technical side.
I have 4 x B139 SP1044
2 Kef Concerto Falcon Crossover Dn12 Upgrade. Can I connect 2 bass units to one bass output/crossover?
(I guess will be better than the regular KEF concerto crossover DN12? I have a pair of these as well) OR should I be using all 4 crossovers, 1 for each bass unit?)
Not sure how big the spacing should be in the 2 chambers and if I need some material in between the driver units? Best glue/sealant to make air tight?
Thinking of using thick MDF for the interior and 12mm Birch ply for exterior.
I am confident with making the cabinets just not the technical side.
I have 4 x B139 SP1044
2 Kef Concerto Falcon Crossover Dn12 Upgrade. Can I connect 2 bass units to one bass output/crossover?
(I guess will be better than the regular KEF concerto crossover DN12? I have a pair of these as well) OR should I be using all 4 crossovers, 1 for each bass unit?)
Not sure how big the spacing should be in the 2 chambers and if I need some material in between the driver units? Best glue/sealant to make air tight?
Thinking of using thick MDF for the interior and 12mm Birch ply for exterior.
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For four drivers, you'll need to either adjust the crossover values for series or parallel wiring, or just use 4x low-pass sections, one for each driver.
When it comes to isobaric chambers, you need to minimise chamber volume, unless you're going for a particular effect. The smaller the volume, the closer the drivers are to working as one.
If your cuts are good, PVA has worked fine for me for many years, up to and including a 1800w RMS 21" subwoofer (which has seen full power a few times!). Plenty of glue and clamps.
MDF isn't a great speaker building material - birch ply is much stronger, so you can use thinner (lighter) panels which come out as strong as thick MDF. Ideally, you want to push the panel resonances out to frequencies where they won't be excited easily. Tweeters aren't likely to excite panel resonances much, so people generally aim to push the resonances up as high as possible. Cross bracing etc also helps with that.
From this, we can see that birch ply (strong and light) is a very good speaker building material.
Chris
Thank you Chris,
I will use all 4 Crossovers using just the LF out from each.
I will try and copy size scale of the lower part of a Linn Isobarik.
I think there might be slightly more volume/size space behind the inside/back bass unit?
Yes will deffo use all birch ply.
Inspiration:
MY BRIKS | GALLERY
I will use all 4 Crossovers using just the LF out from each.
I will try and copy size scale of the lower part of a Linn Isobarik.
I think there might be slightly more volume/size space behind the inside/back bass unit?
Yes will deffo use all birch ply.
Inspiration:
MY BRIKS | GALLERY
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The space behind the inside driver is considered the "working" enclosure volume for the system. The space between the two woofers is the chamber Chris referred to and needs to be as small as possible for tight coupling.
Do you have schematics for the crossovers? There are a couple of issues to address regarding unused sections and how to pair them.
Do you have schematics for the crossovers? There are a couple of issues to address regarding unused sections and how to pair them.
I don’t know any technical stuff like ‘schematics’ The crossovers are from KEF concerto speakers that have B139 SP1044.
Some say not using the mid and high is not a big problem.
If the crossovers are 1st order filters that's true, but I'd be surprised to find that in a KEF.
It's not a big deal, you should be able to disconnect a couple of components to render the unused sections out of circuit. Otherwise, it's most likely those sections will present unfriendly impedance variations that could cause trouble for your amp.
Perhaps someone with firsthand knowledge of the Concerto will step in.
As far as pairing them, like which crossover to use with which speaker, it's a little questionable. You want the isobaric pairs to be as identical as possible, in order to emulate a single driver. That would suggest pairing your identical filters for right and left.
Which brings up other questions, like what is the crossover frequency and is it appropriate for the rest of the system that you'll be using. Without looking, I can tell you that they won't really be operating as subwoofers using those crossovers.
It's not a big deal, you should be able to disconnect a couple of components to render the unused sections out of circuit. Otherwise, it's most likely those sections will present unfriendly impedance variations that could cause trouble for your amp.
Perhaps someone with firsthand knowledge of the Concerto will step in.
As far as pairing them, like which crossover to use with which speaker, it's a little questionable. You want the isobaric pairs to be as identical as possible, in order to emulate a single driver. That would suggest pairing your identical filters for right and left.
Which brings up other questions, like what is the crossover frequency and is it appropriate for the rest of the system that you'll be using. Without looking, I can tell you that they won't really be operating as subwoofers using those crossovers.
Thanks tssmith,
Yes they are not going to be actual 'subwoofers' was going to try to set them up bi-amped.
It's for some extra bass in my workshop (sometimes garden) space, im not looking for total perfection, just want it to work reasonably ok.
Yes someone familiar with concerto may be able to help.
Yes they are not going to be actual 'subwoofers' was going to try to set them up bi-amped.
It's for some extra bass in my workshop (sometimes garden) space, im not looking for total perfection, just want it to work reasonably ok.
Yes someone familiar with concerto may be able to help.
I am 1/2 way making these now and wanted to know about the significance of the material sheet that is found in between the bass units in original Isobariks.
In early Briks the material was quite woolly/fiberuss and I think in later models a thinner cotton.
If the idea of the chamber being 2 bass units in perfect harmony why the material?
Is it essential and what should I use?
In early Briks the material was quite woolly/fiberuss and I think in later models a thinner cotton.
If the idea of the chamber being 2 bass units in perfect harmony why the material?
Is it essential and what should I use?
I have two pairs of these drivers in storage and have considered a clamshell isobaric build but I know that the t/s parameters vary quite a bit from the original values through storage.
These drivers offer the possibility of bonding the two driver faces together giving zero volume between them which is perfect for isobaric. How would you treat the t/s parameters though for vas and box volume calculation. Take the actual driver measurements and run those through an isobaric setting on say winisd Or measure the two bonded drivers t/s parameters considering them as one driver? Difficult to do added mass method for vas
As it is winisd has given me a nice flat, low response in a 43 litre box to a -3db of sun 30hz as a clamshell isobaric. (No extra internal volume for second driver)
If two of these drivers having differing t/s parameters are bonded together face to face their individual parameters will be averaged between them, no/yes?
These drivers offer the possibility of bonding the two driver faces together giving zero volume between them which is perfect for isobaric. How would you treat the t/s parameters though for vas and box volume calculation. Take the actual driver measurements and run those through an isobaric setting on say winisd Or measure the two bonded drivers t/s parameters considering them as one driver? Difficult to do added mass method for vas
As it is winisd has given me a nice flat, low response in a 43 litre box to a -3db of sun 30hz as a clamshell isobaric. (No extra internal volume for second driver)
If two of these drivers having differing t/s parameters are bonded together face to face their individual parameters will be averaged between them, no/yes?
The best choice is to use a push-pull manifold, with the drivers spaced as closely as you can (while respecting that they need at least 2cm of clearance between cone/magnet for safety). From there, you can take the driver specs and plug them into a box designer with 2 drivers. Fc and will likely be a touch lower due to the airload, but it may not be measurable in impact (on a downfiring manifold, you get effectively a much more bandpass-like behavior, beneficial for a sub).
But in any case, push-pull is like a better isobaric for distortion and output reasons (but with 2x the box size).
But in any case, push-pull is like a better isobaric for distortion and output reasons (but with 2x the box size).
I was under the impression that a clamshell isobaric set up was probably best. The B139 drivers are perfect for this because of their flat faced cones allowing, as mentioned, the possibility of bonding the two cone faces together therefore giving zero enclosed air mass, which also helps with overall box size. I’ll probably give it a go and then measure the resultant combined double driver and see what the t/s specs turn out to be.
jerryo, read again and you'll see that badman is not suggesting an isobarik system, but a manifold.
It's two drivers loaded into a slot with an open end, with one driver mounted backwards, thus wired out of phase. "Push-pull" is relative to the baskets, not relative to the manifold/listener. The output of both cones radiates through the slot. Isobarik pairs only have one radiating surface.
Clamshell mounting gives the same, if not better, properties of cancelling basket resonance/distortion because the baskets are usually mounted on opposite sides of the same baffle, thus more closely coupled. Sensitivity is 6dB better in the manifold, at a cost of 4x the required internal box volume.
It's two drivers loaded into a slot with an open end, with one driver mounted backwards, thus wired out of phase. "Push-pull" is relative to the baskets, not relative to the manifold/listener. The output of both cones radiates through the slot. Isobarik pairs only have one radiating surface.
Clamshell mounting gives the same, if not better, properties of cancelling basket resonance/distortion because the baskets are usually mounted on opposite sides of the same baffle, thus more closely coupled. Sensitivity is 6dB better in the manifold, at a cost of 4x the required internal box volume.
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