Ex Kef Cadenza Kef T27 & B200

[Phitz]

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?

[planet10]

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

[sreten]

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.

[system7]

The KEF spec says 30L closed box or 45L reflex for the B200 SP1022:
http://www.kef.com/uploads/files/en/...200_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.

[2SA991]

Hello
I have a lot off new kef passive radiators
Regards

[Phitz]

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)

[Jonathan Bright]

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

[mcandmar]

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

[Phitz]

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.

[system7]

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.