Just acquired a pair of Kef Cadenzas from a house clearance. The tweeter & mid/bass units seem to be OK but the foam surround on both passive bass radiators has completely deteriorated - in fact it has completely disappeared. The grille cloth is torn, but the incredibly heavy cabinets are not too bad. I haven't been able to find anyone repairing the passive bass radiators.
Is there anything interesting I could do with the tweeter & mid/bass units or should I just stick them on eBay?
Is there anything interesting I could do with the tweeter & mid/bass units or should I just stick them on eBay?
Yours must be the early ones as mentioned here:
Anatomy of KEF Cadenza
There suggestion seems a waste of a B139. You could look for a newer one with rubber surround. Or replace the PR with a vent.
dave
Anatomy of KEF Cadenza
There suggestion seems a waste of a B139. You could look for a newer one with rubber surround. Or replace the PR with a vent.
dave
Hmmm......
New surrounds for the PR's appears problematical,
Though its doable with some serious ingenuity.
(Segmented bicycle innertubing* might work,
but will take a lot of DIY skill and patience.)
FWIW though I'd stick the drivers + x/o's
on Ebay, if you can't get the PR's in shape.
Alternatively, knock up a B139 shaped piece of wood
(ply painted black, double thickness. one the driver
the other the cutout) and put three small vents in it,
centre and the centre of the end radii, so it looks
half reasonable, tune the whole lot to 35Hz.
Thing is to get half decent sized ports your probably
going to need some 90 degree bends, using probably
standard size sink PVC waste tubing.
rgds, sreten.
* Really narrow racing 700C innertube, sliced into sections
and opened up. Petalled around the two curved ends. Its
probably easier to get the edges flat than convince flat
rubber to take up a consistent curved surround profile.
New surrounds for the PR's appears problematical,
Though its doable with some serious ingenuity.
(Segmented bicycle innertubing* might work,
but will take a lot of DIY skill and patience.)
FWIW though I'd stick the drivers + x/o's
on Ebay, if you can't get the PR's in shape.
Alternatively, knock up a B139 shaped piece of wood
(ply painted black, double thickness. one the driver
the other the cutout) and put three small vents in it,
centre and the centre of the end radii, so it looks
half reasonable, tune the whole lot to 35Hz.
Thing is to get half decent sized ports your probably
going to need some 90 degree bends, using probably
standard size sink PVC waste tubing.
rgds, sreten.
* Really narrow racing 700C innertube, sliced into sections
and opened up. Petalled around the two curved ends. Its
probably easier to get the edges flat than convince flat
rubber to take up a consistent curved surround profile.
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The KEF spec says 30L closed box or 45L reflex for the B200 SP1022:
http://www.kef.com/uploads/files/en/kef_units/Datasheet_B200_SP1022.pdf
ABR is just another sort of reflex, so it doesn't look hard to redesign the bass end to suit. The rest should be unaffected.
http://www.kef.com/uploads/files/en/kef_units/Datasheet_B200_SP1022.pdf
ABR is just another sort of reflex, so it doesn't look hard to redesign the bass end to suit. The rest should be unaffected.
Attachments
Many thanks for the advice and links.
Replacing the acoustically coupled bass radiator (ABR) with a vent or three ports sounds like my preferred option and if possible.
I would now quite like to retain the cabinets - they seem to be very solid and with a little work should clean up nicely. According to the QC labels the speakers were manufactured in 1973.
Can you please explain the "three small vents"?
I think I understand the "centre and the centre of the end radii".
How would I "tune the whole lot to 35Hz."? Diameter and length?
Why "90 degree bends"?
The Cadenza internal volume is 45 litres (Anatomy of the Kef Cadenza) and the Kef Datasheet suggests that the internal volume of a suitable Bass Reflex box should be between 40 and 50 litres. How would I come up with the correct dimensions for a suitable port or ports?
I think I should be able to manage all the woodwork, just not sure how to calculate the port dimension(s)
Replacing the acoustically coupled bass radiator (ABR) with a vent or three ports sounds like my preferred option and if possible.
I would now quite like to retain the cabinets - they seem to be very solid and with a little work should clean up nicely. According to the QC labels the speakers were manufactured in 1973.
Can you please explain the "three small vents"?
I think I understand the "centre and the centre of the end radii".
How would I "tune the whole lot to 35Hz."? Diameter and length?
Why "90 degree bends"?
The Cadenza internal volume is 45 litres (Anatomy of the Kef Cadenza) and the Kef Datasheet suggests that the internal volume of a suitable Bass Reflex box should be between 40 and 50 litres. How would I come up with the correct dimensions for a suitable port or ports?
I think I should be able to manage all the woodwork, just not sure how to calculate the port dimension(s)
There are probably graphs/tables with the relevant info' try Google. I also think there are calculators around where you put your numbers in (res' frequency, size of enclosure) and the tube length and diameter comes out as the answer. The suggestion of 90 degree (or other angles) is because sometimes the tube length is too long for the depth of the box so they have to be bent to fit them in........
Welcome to the mysterious world of vented enclosures......!
They are known as Helmholtz resonators if you start at the physics end of things and want to follow up the theory in general.
(With all the initial good acoustical theory (1961) proudly done by an Aussie too!)
Cheers, Jonathan
Welcome to the mysterious world of vented enclosures......!
They are known as Helmholtz resonators if you start at the physics end of things and want to follow up the theory in general.
(With all the initial good acoustical theory (1961) proudly done by an Aussie too!)
Cheers, Jonathan
My vote is to fix them, i have an identical set myself and love them dearly. If you keep an eye on eBay the passive radiators come up for sale fairly frequently, part number is SP1042.
e.g. eBay sold history -> kef sp1042 | eBay
e.g. eBay sold history -> kef sp1042 | eBay
Thanks Jonathan. I have tried Googling but it seems to be incredibly confusing. I ended up at what seemed like a simple page (ehow.co.uk page entitled "How to Tune Bass Reflex Speakers") but it refers to a calculator which I couldn't see and I wouldn't know how to transfer the Kef Datasheet details anyhow - I presume I should be using a tuning frequency of 25 Hz (B200 free air resonance frequency)?
Hi Mcandmar, I really don't think I could ever use cycle inner tubes to repair the ABRs - I will keep an eye out for replacements on eBay though.
Hi Mcandmar, I really don't think I could ever use cycle inner tubes to repair the ABRs - I will keep an eye out for replacements on eBay though.
The reflex tube on 45L is going to be around 60mm diameter and 12 cm long, I'd guess.
Bit like this 8" unit:
W 200 S - 8 Ohm
You could stuff it with straws or socks anyway, and make it more damped reflex.
I used to buy those adjustable tubes. The tuning is somewhere between the closed box resonance and the free air resonance. You are Fs 25Hz and Qts 0.41 IIRC. So about 30-35Hz won't be far wrong.
Bit like this 8" unit:
W 200 S - 8 Ohm
You could stuff it with straws or socks anyway, and make it more damped reflex.
I used to buy those adjustable tubes. The tuning is somewhere between the closed box resonance and the free air resonance. You are Fs 25Hz and Qts 0.41 IIRC. So about 30-35Hz won't be far wrong.
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Hi Phitz very old books (pre 1970) often suggested tuning the enclosure to the bass speaker resonance but that is not the necessarily the case now that the theory is better understood. Things now much more flexible. In your case the tuning frequency is 35c/s. That's from the KEF data sheet.
I'll dig up some of my books and try and come up with port/tube dimensions. may take 24hrs.
Cheers, Jonathan
I'll dig up some of my books and try and come up with port/tube dimensions. may take 24hrs.
Cheers, Jonathan
In the pursuit of my greater understanding, can you please describe how you arrived at the figures of 6 cms diameter x 12 cms length and also how the Fs & Qts lead to 30 to 35 Hz? Presumably straws would have the effect of "reducing" the diameter?
Thanks Jonathan, I would be very grateful; if you could include any "workings" that would be even better - see above for reason.
I would like to use this as a "learning opportunity" so am very grateful for any and all explanations - in layman's terms.
Why don't you just contact 2SA991 and ask him what he wants for a pair. Why go and stuff up two perfectly designed speakers. 2SA991 is in Germany a stone throw away from you!
This looks like a DIY B139 (or DB139) repair with an inner tube.
Possibly from someone called "The Art of Sound":
I wonder how true to the original it would be?
Incidentally, Germany is not exactly "a stone's throw" from the UK and whatever replacement ABRs may cost, I very much doubt they would be cheaper than some plywood and PVC tubing.
Possibly from someone called "The Art of Sound":
I wonder how true to the original it would be?
Incidentally, Germany is not exactly "a stone's throw" from the UK and whatever replacement ABRs may cost, I very much doubt they would be cheaper than some plywood and PVC tubing.
In response to a PM from Phitz, I thought I'd answer within the forum.
You don't absolutely need an ABR here. Speakers of this type, like the similar 1975 Chartwell PM200 came with a reflex tube and about 40L box. Dalesford bass drivers, as it goes. Isophon KK8 plastic tweeter.
Reflex, like closed box, is IMO fairly rough and ready with tuning. You just need to get reasonably close. Bigger boxes just sound bassier really. Undersized ports behave closer to closed box.
Chartwell just used a hole in the baffle and no tube at all. They made the hole effectively smaller by lining it with draft-sealer too. 😀
I'd start by sealing the ABR hole with ply or Chipboard as sreten suggests. Then make a 50mm hole and add about 15cm of plastic water pipe. It's not gonna be far wrong, and you can then make it shorter and bigger or stuff it if that seems to make sense.
You don't absolutely need an ABR here. Speakers of this type, like the similar 1975 Chartwell PM200 came with a reflex tube and about 40L box. Dalesford bass drivers, as it goes. Isophon KK8 plastic tweeter.
Reflex, like closed box, is IMO fairly rough and ready with tuning. You just need to get reasonably close. Bigger boxes just sound bassier really. Undersized ports behave closer to closed box.
Chartwell just used a hole in the baffle and no tube at all. They made the hole effectively smaller by lining it with draft-sealer too. 😀
I'd start by sealing the ABR hole with ply or Chipboard as sreten suggests. Then make a 50mm hole and add about 15cm of plastic water pipe. It's not gonna be far wrong, and you can then make it shorter and bigger or stuff it if that seems to make sense.
Attachments
Thanks for that system7.
I will probably follow your and sreten's advice, it isn't irreversible and I can always "play about" with different port lengths. I just wondered whether there was any recognised science involved in determining port inner diameter and length.
Incidentally, the distance from the back of the baffle to the inside of the cabinet rear wall is 25.5 cms and the foam damping material is 2.5 cms thick giving a clear space behind the baffle of about 23 cms. so there should be no need for bends in any ports? I attach a photo of the interior of the cabinet.
I will probably follow your and sreten's advice, it isn't irreversible and I can always "play about" with different port lengths. I just wondered whether there was any recognised science involved in determining port inner diameter and length.
Incidentally, the distance from the back of the baffle to the inside of the cabinet rear wall is 25.5 cms and the foam damping material is 2.5 cms thick giving a clear space behind the baffle of about 23 cms. so there should be no need for bends in any ports? I attach a photo of the interior of the cabinet.
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There's a simple rule of thumb for home audio. The surface area of the port shouldn't be less than 1/7 of the surface area of the driver. Sd of the KEF woofer is 232 cm^2, hence the port diameter needs to be 65 mm or larger.
The tuning frequency of the Cadenza is not fully clear. The specifications speak of 35 Hz, the impedance curve rather says 30 Hz.
My advise is to use an adjustable port:
66mm Standard Bass Reflex Port Tube
A length of 132 mm gives a tuning frequency of 35 Hz.
A length of 200 mm gives a tuning frequency of 30 Hz.
Tuning to 30 Hz will be difficult, because the inner tube end gets too close to the back wall. That's probably the reason why KEF used a passive radiator. 🙂
<I just wondered whether there was any recognised science involved in determining port inner diameter and length.>
There is, for free: LinearTeam
There is, for free: LinearTeam
Very many thanks for that. I see that they also offer an "80mm Double Flared Bass Reflex Port Tube" where you can vary the length from 170 mm. Would this (wider port) overcome the issues with the cabinet depth?
I have tried playing about in Excel to see if I can determine some "ratio" but without success so far. Are you able to explain how you arrived at the figures above? I ask this simply because I want to gain some insight into how these things work. Still, thanks again.
I take it you are referring to WinISD which I have now downloaded and installed. I can't see how this helps, can you explain please?
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