KEF technical info sought on B160 bass driver

[Simon Barr]

Hi - won a pair of KEF 103.4's at auction and the tweeter and mid are fine however I knew the surrounds of the bass drivers were likely to be shot. I also knew if the last owner had driven them with perished surrounds the bass drivers could be shot. The bass drivers are B160 (SP1275), 6.5” inch paper cone drivers.

All four of the drivers had rubbing and two were OC. All had been subjected to overdriving & heat to the point that the plastic guide in the centre for 2 of them had melted.

I managed to knock the price down as half the speaker is working fine. As I got them so cheap - Im happy to tolerate a "close enough" approach for bass repair. It doesnt seem like I can get a recone kit for these drivers. Sending them to and from KEF (from NZ) isnt an option due to weight.

Anyone know of a potential replacement driver for these. I know that the xover etc will be tight spec however as I say above, “close enough” will be fine. I have found online specs for this B160 driver (there is more than one B160, however this is described as a “bass” driver, which is what these are):

KEF B 160 / 8 Ohm, 8 Ohm, 50 W, woofer

thiele-small data:

Re 7.4 Ohms
Le 0.61 mH
fs 40 Hz
Qms 5.45
Qts 0.30
Qts (8Ohm) 0.33
Sd 131 cm3
Vas 42 Liter
Cms 1.75 mm/N
Mms 9 g
B*l 7.3 N/A
SPL 91
I have found a probable replacement driver which has a lot of specs looking favourable (The Vas is close, the resonant freq is close, the only issue is the spl is 86db, compared to the former 91. This is disappointing but its been very difficultly trying to find a driver with close vas).

parts-express.c0m/visat...eated-paper-cone-8-ohm--292-568#lblProductQ&A

I have also emailed KEF in the UK and US however don’t expect too much help from that channel.

 

[KenM10759]

If I'm not mistaken, you need the B160 SP1275 bass drivers or for the magnetically shielded version, the SP1311. Those have a hole through the dustcap, through the pole piece and out for a tension rod. Very specialized.

They do show up on the US eBay site now & then. Right now there's a pair of working 104/3's for $300 US and they're only about a hundred miles from me. Pay me to buy them and dispose of the carcasses, I'll strip the drivers out and post them to you. Just a thought.

 

[TLS Guy]

Hi - won a pair of KEF 103.4's at auction and the tweeter and mid are fine however I knew the surrounds of the bass drivers were likely to be shot. I also knew if the last owner had driven them with perished surrounds the bass drivers could be shot. The bass drivers are B160 (SP1275), 6.5” inch paper cone drivers.

All four of the drivers had rubbing and two were OC. All had been subjected to overdriving & heat to the point that the plastic guide in the centre for 2 of them had melted.

I managed to knock the price down as half the speaker is working fine. As I got them so cheap - Im happy to tolerate a "close enough" approach for bass repair. It doesnt seem like I can get a recone kit for these drivers. Sending them to and from KEF (from NZ) isnt an option due to weight.

Anyone know of a potential replacement driver for these. I know that the xover etc will be tight spec however as I say above, “close enough” will be fine. I have found online specs for this B160 driver (there is more than one B160, however this is described as a “bass” driver, which is what these are):

KEF B 160 / 8 Ohm, 8 Ohm, 50 W, woofer

thiele-small data:

Re 7.4 Ohms
Le 0.61 mH
fs 40 Hz
Qms 5.45
Qts 0.30
Qts (8Ohm) 0.33
Sd 131 cm3
Vas 42 Liter
Cms 1.75 mm/N
Mms 9 g
B*l 7.3 N/A
SPL 91
I have found a probable replacement driver which has a lot of specs looking favourable (The Vas is close, the resonant freq is close, the only issue is the spl is 86db, compared to the former 91. This is disappointing but its been very difficultly trying to find a driver with close vas).

parts-express.c0m/visat...eated-paper-cone-8-ohm--292-568#lblProductQ&A

I have also emailed KEF in the UK and US however don’t expect too much help from that channel.

The driver you picked is not close to working. You picked a high Q driver and the KEF driver is low Q. So it won't tune, and it is low sensitivity.

Your speaker is a second order coupled cavity design and tuning is absolutely critical. In addition you have the rods to deal with.

It is almost always virtually impossible to match a driver.

The specs of that driver are low Fs plus high sensitivity. Right away that makes it an expensive driver.
I have looked at the data bases and the only driver remotely close is this one, but even then Vas is off by about 30% as the suspension compliance is lower.

This is the driver.

I don't think I would spring for 4 of those drivers. You really need exact replacements or junk the speakers. With the driver I picked you would have to pad the mid and tweeter down 2 db.

Really you paid too much for those speakers. In fact at present they are worthless.

Did the speaker come with the Kube by the way. If not that is another issue as they don't have any deep bass without it.

Realistically if you can't find original replacements your best bet is to remove the coax drivers and crossovers. Get rid of the lower section of the band pass filter, so you just have the top end of the band pass filter and the high pass to the tweeter. Then build a new enclosure round another bass driver. Get an electronic crossover and biamp the speaker with two amps. You will need to cross from the woofer at 180 Hz.

That is your best bet for salvage short of exact replacement woofers.

 

[Simon Barr]

Thanks TLS. This situation sucks indeed.

Yes that cost is high. Thanks for looking up that driver. Madisound have offered to run some calculations once I supply the internal cabinet volume. So I will get them those and see what they come up with. It may well be this driver.

Im also looking into a recone kit that would fit. The measurements of the cone, spider, VC all seem fairly standard (ie: not unusual) however of course the specs of the driver will be different after a recone, however it may be the best option that I have in this case.

I certainly dont have the appetite to do a total cabinet rebuild however your suggestion doesnt sound bad. I was going to end up biamping whatever option I end up with for these, plus using an EQ in line with the bass section as a substitute KUBE as well.

 

[TLS Guy]

Thanks TLS. This situation sucks indeed.

Yes that cost is high. Thanks for looking up that driver. Madisound have offered to run some calculations once I supply the internal cabinet volume. So I will get them those and see what they come up with. It may well be this driver.

Im also looking into a recone kit that would fit. The measurements of the cone, spider, VC all seem fairly standard (ie: not unusual) however of course the specs of the driver will be different after a recone, however it may be the best option that I have in this case.

I certainly dont have the appetite to do a total cabinet rebuild however your suggestion doesnt sound bad. I was going to end up biamping whatever option I end up with for these, plus using an EQ in line with the bass section as a substitute KUBE as well.

I should have stressed more that this is not like a usual enclosure. I have designed and built coupled cavity enclosures.

The alignment is very critical. You must remember there is no cone radiation directly to the room. There is a little of course via the port, but that is unwanted and steps are taken to keep that to the minimum.

So what this means is that the entire output is from the port with the enclosure resonating correctly. If the alignment is not spot on then the enclosure will not output from the port, so you get virtually no sound at all.

With other types of enclosure you at least get output from the cone whether perfect or not. In this type of enclosure you risk no useful output at all.

Personally I'm pessimistic about the success of this project, unless I could get a good model indicating a reasonable chance of success.

I will be happy to review any data Madisound produce and also run a model.

The coupled cavity has largely been a passing vogue except for Bose. Not that you can't get some good results, but the concept has draw backs. The attraction is that you get a ported enclosure you can Eq to a point, because one side of the driver faces a sealed cavity. So a driver can never completely uncouple from the box. However Eq below the Fs of the driver and for those original drivers 40 Hz distortion becomes very high. I did not Eq my designs below Fs like KEF.

Other draw backs are that efficiency is not that good which is why you need high sensitivity drivers. (That is the reason the drivers have severe thermal damage) It does give you control over Q to a point. However to get a nice low Q system you have to have narrow bandwidth. If you widen bandwidth then Q rises and reproduction becomes increasingly colored.

The bandwidth of those KEFs was high, like Bose, which leads to an over resonant bass for my taste.

The three enclosures I designed all have lower Q and a much narrower bandwidth. That of course mandates biamping.

If you recone those drivers, you will have totally different drivers, and you won't know what you have until you measure them. The chance of that plan working is probably less then winning the lottery!

 

[TLS Guy]

I have been thinking about this problem, and have been slow to realize the obvious solution.

We need to make the speaker better and not settle for a downgraded speaker.

We should forget miserable 6.5" drivers and the coupled cavity system. The solution is to mount a 10" driver on one of the side walls of the cabinet and reconfigure the vent. The construction should result in mirror image pairs.

I suspect this driver will work with the volume we will have.

If you let me know what the volume is we have to work with I will model that driver and if not suitable I will find one that is.

The speaker should be biamped at 180 Hz with electronic crossover.

You will end up with a speaker far better then the original.

 

[Simon Barr]

Thats funny you should say that - I was thinking of trying out some solution like this with maybe sticking an 8 or 10 inch driver on the side.

Would this solution require closing off the other two adjacent chambers, or leaving them open?

Im chasing up another couple of potential leads but will post the volume measurements and vent details soon. Thanks!

 

[TLS Guy]

Thats funny you should say that - I was thinking of trying out some solution like this with maybe sticking an 8 or 10 inch driver on the side.

Would this solution require closing off the other two adjacent chambers, or leaving them open?

Im chasing up another couple of potential leads but will post the volume measurements and vent details soon. Thanks!

I am aiming to leave them open. I made an estimate from the outside dimensions of the speakers of the inside volume of the three cavities minus the Mid range enclosure. I hope that driver will fit the bill. It will need a different port though.
The driver I picked has an excellent reputation.

I have to stress that this will be a lot better speaker than the original.

As soon as I have accurate dimensions from you, I will pick the optima; driver and do the design.

 

[Simon Barr]

Cheers TLS. Please see full measurement data on the speaker attached.

Appreciate your help with this.

I also dont want to be a downer, but in terms of cost considerations - with any part from the US, I need to factor in US-NZ dollar exchange rate as well as shipping (and potentially customs costs).

FYI, I also have a pair of fully working 104.2's which use the same bass system - which I love. So with that in mind, I would need to consider keeping a reasonable cost-cap on repairs to these 103.4's.

Cheers!

 

[TLS Guy]

Cheers TLS. Please see full measurement data on the speaker attached.

Appreciate your help with this.

I also dont want to be a downer, but in terms of cost considerations - with any part from the US, I need to factor in US-NZ dollar exchange rate as well as shipping (and potentially customs costs).

FYI, I also have a pair of fully working 104.2's which use the same bass system - which I love. So with that in mind, I would need to consider keeping a reasonable cost-cap on repairs to these 103.4's.

Cheers!

I estimated that volume exactly. The driver I specked would be perfect. Do you have any raw drivers available in New Zealand that I could model? Any suppliers?

 

[Simon Barr]

Things in NZ tend tend to be overpriced, and there isnt much in the way of raw driver range here. I like getting stuff from Partsexpress or madisound usually. Of course that usually means cost compromises once you factor in dollar value and freight.

If theres something along the lines of a good Eminence driver, or anything else from partsexpress or madisound that could work, that should be good.

I can have a look at their selection. Generally in terms of specs, what should I be looking for?

Cheers

 

[TLS Guy]

Things in NZ tend tend to be overpriced, and there isnt much in the way of raw driver range here. I like getting stuff from Partsexpress or madisound usually. Of course that usually means cost compromises once you factor in dollar value and freight.

If theres something along the lines of a good Eminence driver, or anything else from partsexpress or madisound that could work, that should be good.

I can have a look at their selection. Generally in terms of specs, what should I be looking for?

Cheers

It is very unlikely anything from Eminence will work. I will look tomorrow and do some modelling. Today was my wife's 70th birthday and we are going to the opera tomorrow.

For a quality driver that Sartori is good value for money. I am not in the habit of working with junk. For this to work a driver of decent quality is required.
It has to be capable of decent bass extension in the space available. Unless it can extend into the low 30 Hz range it is useless for this project.
Regards, Mark

 

[TLS Guy]

As usual with all speaker mods it turns out more difficult than imagined.

There is no cheap driver that is feasible.

The Sartori 9½” Satori WO24P-8 is the only one that really works and is not ideal.

Your space available is less than ideal. I have played with it and you can get a smooth response with an f6 of 30 Hz. Tuning is precise with nice symmetrical peaks of impedance.

The only slight glitch is that the vent velocity is a little too high at max power. However I doubt you will be playing at 106 db.

This is better than original where F3 was 50 Hz.

In an ideal enclosure in other words the optimal box F3 is 29 Hz. So you have only lost 3 db of output at 30 Hz by the less than optimal box volume.

In the end though this design makes a good speaker, that will sound excellent.

I really think that driver is very good value for money. It is half the cost of quality drivers from Scanspeak and SEAS.

Can you remove the crossover and make a schematic of the crossover so I can tell which components to remove? That is assuming you don't already know which ones to remove.

An amp of 100 watts per channel will drive this bass section. You will need an electronic crossover and I think 180 Hz is the best place to start. Probably second or fourth order will work the best.