Kef 105/3 Reference Speakers - Bass Distortion

[Boyse6748]

Dear all,

Can anybody out there assist or advise with the problem detailed below.

I have a pair of Kef 105/3 Speakers and one of the speakers has developed a Bass problem. I can only describe this problem as, very low bass (in comparison with the other speaker) and is distorted.

All the bass units have been re-foamed in the last few years and on limited inspection the units appear to be in perfect condition. I have also visually examined the crossover units and again I can see no damage, burning or bulging. However, I have not electrically tested the crossovers due to lack of expertise in this area.

I really didn't want to pull these speakers apart due to the complex build configuration, but that may have to be an option to find the fault. I would of course, prefer a professional repair but at present cannot find anybody that can do a repair investigation. "Unless anybody on the forum can advise differently"

At present, I am unsure as to whether there is a problem is with the Bass Unit/Units or something has gone wrong with a component on the crossover and really didn't want to pull the speaker units if this Is not the cause.

So, if anybody can respond with either pearls of wisdom / advice or indeed a possible repairer that could help, it really would be much appreciated. You have my thanks in advance.

[struth]

Sure there are a few guys here who have worked on these so hope you get an answer. Kinda sounds like the driver to me

[Boyse6748]

Many thanks Grant, I do hope someone can help. Just got this feeling of tripedation and terror about removing these bass units.
Regards Peter

[Reffc]

I've worked on many of these, had to pull them apart and also recapped crossovers. The issue could be a few things. The bass double coupled cavity arrangement contains a reinforcing rod which reduces acoustic distortion and transfers energy to cabinet walls which are a particle board designed to damp unwanted resonance. If the woofers were removed for refoaming and this rod wasn't properly torqued (it either isn't tight enough or has worked loose) or the drivers properly aligned, then it can lead to audible distortion on bass.

The other obvious issue relates to the refoaming. I always supply a printout of a rub and buzz test which confirms that there is no voice coil rubbing in operation when I refoam drive units. Most other specialists don't because they satisfy themselves by pushing down on the centre of the drive unit but this is not always a reliable method. If the bass voice coils(s) are rubbing it will cause distortion.

Finally, if the crossovers were not recapped, these are getting on in age, and every single pair that I have tested has had the specifications of the electrolytics used drift so they were miles out of spec. In these complex multi-pole crossover designs, it is pretty critical to match like for like to very tight tolerances, as specified by KEF on their data sheets (available with a little searching) otherwise system efficiency will drop and crossover points will drift increasing out of band phase distortion.

Of the above, my money initially would be on the reinforcing bar not being to correct torque given the woofers were presumably properly refoamed.

If you can get the bass unit in question out and send it to me, I can test if for you FOC if you cover the postage costs. That way, at least it narrows things down. That is after checking that the rod itself is adequately torqued down!

[struth]

Was going to say they use a bar. Lol. sealed bass box is it Paul?

Paul is your man for these

[Arkless Electronics]

It's extremely unlikely to be the crossovers first of all. Have you tried swapping the channels from the amp to rule that out? (again this is unlikely.
Is the tie rod between the bass units loose? What about the plastic ring in the port? is it loose and rattling?
More info on the nature of the distortion would be useful!

[plastic penguin]

Can't give any advice as the obvious reasons have already been explained.

I know someone who used to own these speakers, and all Kef Ref speakers demand high quality amplification. Therefore would be good to know what amp the OP is using with them -- and what volumes he plays at. Clipping is a killer for speakers.

Might be worth calling Kef and seeking their advice.

[Reffc]

Was going to say they use a bar. Lol. sealed bass box is it Paul?

Paul is your man for these

It's a coupled cavity bass design Grant, with the bottom cavity port loaded.

As Jezz suggests, it's unlikely to be the X-overs (but those will still benefit from being re-capped as almost certainly are adrift by now) and more likely the coupling rod assembly.

The other issue, on bass is that the driving amp may be clipping as despite the claims, these demand a fair amount of current, especially in the bass region.

[struth]

It's a coupled cavity bass design Grant, with the bottom cavity port loaded.

As Jezz suggests, it's unlikely to be the X-overs (but those will still benefit from being re-capped as almost certainly are adrift by now) and more likely the coupling rod assembly.

The other issue, on bass is that the driving amp may be clipping as despite the claims, these demand a fair amount of current, especially in the bass region.

Knew they were coupled. Thanks for clarification.

[Boyse6748]

Dear Paul, many thanks for all that information. (I am reasonably near and live in Melksham Wiltshire). Unfortunately, I feel very nervous about taking these speakers apart without some hard and fast instructions but don't feel confident at all.

I had looked at the reinforcing bar for tightness and it does appear to be very tight but as you say perhaps not correctly aligned (although all sounded fine initially).

Limited information from the previous owner confirmed that the re-foam was carried our by Wembley Audio (about three years ago) together with some re-caps to the crossovers but I don't have any real detail other than all the speakers look like new.

I really do appreciate your offer to look ant the units, all I have to do now is to get the things out for you to check.

At the moment I can't even figure how to get the front unit off as it seems theres' more than just the visible hex bolts that hold this on..... nervous, to say the least.

I don't sUppose you would take up the mantle ? Obviously not for free and you do sound like a bit of an expert in these matters. (No pressure... but I had to ask)

At least I'm a step nearer knowing what it might be and would love to take up your offer to look.

Best Regards Peter

[Boyse6748]

Forgot to mention, no problems with clipping or power. I Drive these Speakers with a McIntosh MA 2275., more available power than a formula one GP Motor ��

[Boyse6748]

Hi Jez,

Torsion bars are very tight and so are the plastic port inserts. I can only describe the bass a being extremely low or virtually non existented, which omits a sort of fart occasionally (sorry didn't mean to rude) but it's the only way to explain.

Regards

Peter

[walpurgis]

If, as you say the cone surrounds have been replaced, could it be that a cone is slightly misaligned and allowing the voice coil and former to bind within the magnet gap?

Actually, I don't remember these speakers having foam cone surrounds, but perhaps I'm wrong.

[Reffc]

By all means drop them over Peter and I'll take a look for you. I can run a full impedance V's frequency test for each unit for you. Could be something as simple as a dodgy solder joint.

[Arkless Electronics]

It could indeed be something as simple as a dry joint...

The front baffles are indeed held on only by the hex bolts but the gasket may be "gluing" it down and a bit of leverage may be required...
There are two crossover boards per speaker but you probably already know that.

As an aside, the bass system is two infinite baffle enclosures (one at the top and one at the bottom) driving a central cavity. This has a very wide (5" or so) port and the idea is that a "plug" of compressed air forms in the port and this acts as the actual "driver".. IIRC from a long while ago when I read up on KEF's coupled cavity bass loading technique. I once spoke on the phone to a KEF design engineer who told me that they stopped using the system partially due to expense but mainly, bizarrely, because they had complaints from customers that "my mates aren't impressed enough at the bass drivers 'cos they can't see them as they're inside"! :eek:

The two 8" bass units per side (equivalent in cone area to a single 12" driver) have foam surrounds whilst the mid drivers don't...

They have KEF's conjugate load matching technique (the last model to have it AFAIK and due to cost, again according to the KEF engineer I spoke to) which theoretically makes them a perfect resistive load, 4 Ohm in the case of the 105.3.

I have often seen remarks along the lines of "they take a lot of current and need a meaty amp to drive them"... in my experience this is total rot!
They are 93dB/W efficient IIRC and I can personally attest to the fact that even my Leak Stereo 20 drives them really well and to amazing volumes for a 10WPC amp... The lack of any "awkwardness" to the load, due to the conjugate load matching technique, no doubt helps here.

[karma67]

I am reasonably near and live in Melksham Wiltshire

small world! i was there a few weeks ago fitting a new turnstile building at the local football club :)

[Boyse6748]

Hi Jez,

Many thanks for that information. I did removed the Hex Bolts but didn't use any exsisve force to detach the Pod if fear of damage, that I might live to regret.��

Reffc ( Paul) has offered to sort this issue out and the speaker will be with him on Monday Week. Nedless to say, I am delighted .

Many thanks to you good self and all the members for there valued comments.

Regards

Peter

[Wilbur]

Mine need re-foaming....If only I was brave enough!!

[Light Dependant Resistor]

Mine need re-foaming....If only I was brave enough!!

Why not use rubber surrounds ? which last a lot longer. :)

[Reffc]

Why not use rubber surrounds ? which last a lot longer. :)

Not usually recommended because it will change compliance, mechanical Qms and therefore free air resonance and hence tuning. Whilst this may not be much of an issue in some designs, it will be in others, especially at crossover where natural slopes from smooth roll-off transition are often used for woofers (ie it will shift crossover point and create phase inaccuracy problems).

[Light Dependant Resistor]

Not usually recommended because it will change compliance, mechanical Qms and therefore free air resonance and hence tuning. Whilst this may not be much of an issue in some designs, it will be in others, especially at crossover where natural slopes from smooth roll-off transition are often used for woofers (ie it will shift crossover point and create phase inaccuracy problems).

Using rubber surrounds in both AR7 and Gale 401a has been a step forward for me. both which are acoustic suspension designs.
I heard quite an improvement in each model, particularly the AR7

The original material AR used was cloth, not foam. Likewise Bose originally used cloth as well. https://www.youtube.com/watch?v=O5Ta2gWMeMI

Swapping to foam was an economics choice by these firms and from what I see not much else, other than unhappy customers seeing their speakers rotting away.
The compliance of cloth is much closer to rubber I would think.

Cheers / Chris

[walpurgis]

Are you sure the Gales had original drivers Chris? My recollection is that the 401/401a used AR6 bass units and those had foam surrounds.

I've never seen AR7 speakers with cloth surrounds. They've been foam on mine. The AR4xa usually had cloth though.

Maybe different specs for different markets though.

[Light Dependant Resistor]

Hi Geoff
The bass drivers Gale used were made by Chicago Telephone Company. http://0339436.netsolhost.com/WordPress/gs401-speaker/
I have 2 pairs of 401's The first set bought new in 1978 have cloth surround drivers
the second pair are also the same physical bass drivers, but have rubber surrounds.

I also have AR6's also with cloth surrounds and are working perfectly some 40 plus years later.

From what I can see all original AR speakers that had the nice off white front covers had cloth surrounds.
My recollection from seeing a wide range of models in shops in 1976 was, they all had cloth surrounds.
It is only when AR went to the brown front covers the foam started appearing . Of course subsequently some
off white grill models have been afflicted with foam.

With the AR7 fitted with rubber surrounds, bass response was both cleaner and even lower, in fact staggering from such a tiny cabinet.

Cheers / Chris

.

[walpurgis]

Hmm. Looks like the specs were chopped and changed a bit.

[Reffc]

Using rubber surrounds in both AR7 and Gale 401a has been a step forward for me. both which are acoustic suspension designs.
I heard quite an improvement in each model, particularly the AR7

The original material AR used was cloth, not foam. Likewise Bose originally used cloth as well. https://www.youtube.com/watch?v=O5Ta2gWMeMI

Swapping to foam was an economics choice by these firms and from what I see not much else, other than unhappy customers seeing their speakers rotting away.
The compliance of cloth is much closer to rubber I would think.

Cheers / Chris


That may be true for a small minority of manufacturers Chris, but the main reason for using foam is to increase mechanical compliance which helps with both lower Fs and improve overall drive unit damping.

[Light Dependant Resistor]

Some manufacturers are returning to cloth including Bose for the 901's, and cloth is available as a kit as well

"CLOTH EDGE roll surrounds. Unlike foam, these edges will last a lifetime! "
http://www.simplyspeakers.com/speaker-cloth-edge-repair-kit-clsk-8.html

[Reffc]

Well, the mystery has partly been solved.

Peter dropped off the offending loudspeaker today (as near a mint example as you'll ever find...it could have just come out of the showroom). A quick test and inspection revealed that the lower coupled cavity woofer's voicecoil was not only rubbing but partially seized. Measurement revealed an impedance across the coil of min 400 Ohms, max 500 Ohms, so definitely a woofer issue!

The mid range drivers also have a very high impedance of 300 odd ohms across them, so in their case, there's a crossover or wiring problem but the main woofers have either been poorly refoamed or wrongly assembled resulting in the cones binding due to mis-alignment. It's a full speaker strip down job, possible woofer repair (or re-cone) possible crossover repair and reassembly. These are well worth doing though as they are superb examples (cabinet wise).

Peter is a complete gent too and it was a real pleasure meeting with him. I will not be charging Peter for my time in fault diagnosis or stripping these down (just glad to help) and it will be up to Peter what happens after the full extent of the problem is revealed.

[struth]

Nice gesture Paul. Thought it might be a driver problem... some pics when done young man :)

[Boyse6748]

Well, what can I say.... I've never encountered such dedication or assistance. Paul has diagnosed, stripped down the offending units within a few hours of delivery, and will send the bass units of for repair. Apparently, they have been poorly re-foamed, and are not central or aligned and the voice coils are rubbing. (Perhaps from the start or someone else has messed with these speakers...... we will never know.

I can only say that Paul is a star turn and hope he posts some photo's (explanation) to warn others !!!

God bless the members of "The Art of Sound Forum" for the help received.

My special thanks to Paul for being so just damed helpful + the honor of listening to some very fine Tannoy's.


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[Reffc]

Well, what can I say.... I've never encountered such dedication or assistance. Paul has diagnosed, stripped down the offending units within a few hours of delivery, and will send the bass units of for repair. Apparently, they have been poorly re-foamed, and are not central or aligned and the voice coils are rubbing. (Perhaps from the start or someone else has messed with these speakers...... we will never know.

I can only say that Paul is a star turn and hope he posts some photo's (explanation) to warn others !!!

God bless the members of "The Art of Sound Forum" for the help received.

My special thanks to Paul for being so just damed helpful + the honor of listening to some very fine Tannoy's.


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You're very welcome Peter. Just glad that I could help.

Here's the bits that make the noise!:


http://i1140.photobucket.com/albums/n577/24pacman/RFC%20Cables/IMG_1034_zpsvjvgdypj.jpg

The problem is, that well meaning folk often re-foam these without first de-soldering and removing the cones and cleaning out the voice coil gaps. The issue with SP1256 drive units (the bass drivers with the hole in the middle) is that the original "doughnut" surrounds perish and leave a sticky residue which gets into the voice coil gap, which doesn't allow the cones and voicecoils to move freely when re-foamed, and I think that might be what has happened here. The good news is that disconnected from the crossovers which all look to be ok, the minimum impedance on both is close to 7.2 Ohms which is spot on for these (ie voice coils ought to be ok), BUT the free air resonance measures closer to 300Hz, and not the 25 Hz or so that they ought to be. You can clearly feel that they are rubbing. The only cure is to remove the nice new surrounds, desolder the cones and remove them. The voice coil gaps in the motors then need cleaning out, and the voice coils themselves need carefully cleaning off but not using IPA or solvents which might break down the insulation on the wires. Patience and detergents on Q buds!

The best bet then is to either obtain new surrounds from Wembley Speakers and do a DIY re-foaming, this time with nice clean voice coil gaps, or package them up and sent to Wembley to re-do them for you. When you receive them back, I'll give you a hand and we'll re-assemble everything for, hopefully, a nice healthy loudspeaker.

[Lawrence001]

Were these recently purchased and is a refund/ebay claim a possibility. I have seen a pair for sale in south london for.over a year when I called the first time the lady I spoke to had no idea about the internal speaker issues, then a few months later they reappeared having been spparently sorted. They were also on eBay I think.

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[Boyse6748]

Lawrence, yes these were from a lady in South London (Croydon in Fact). Originally advertised on eBay but foolishly purchased by myself direct. She insisted that these had been fully refurbished.
We live and learn...... a fool and his money are easily parted.
However, not disappointed, as I got these at a reasonable price, even with the impending headache to come. Perhaps too trustworthy. With Paul's help, I will get these fixed.


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[Lawrence001]

Hmm I always had my suspicions about this seller. I was finally proved right when I saw a valve amp for sale and when she called me (she always calls as soon as she gets a text) she said she knew nothing about hifi and it belonged to her late father and she was selling off his belongings. As I had seen her selling gear for several years I was disgusted she would use such a story to try and flog it.

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[Boyse6748]

Well, what goes around comes around.

A warning to all you impending DIY Re-Foamers. Cleanliness is next to Godliness!!!

It transpires that the bass distortion was caused by extremely poor re-foaming / donuts. Initially, found by Paul (Reffec) who has been just sooooooo helpful and removed the bass units for me.

The Voice coil gap was completely seized with foam / adhesive and never cleaned out by the total twerp who carried out this work.

To say say this work had been carried out by a five year old, is complementary. The cones were completely distorted, both at the outer foam and the donut connection. How they worked initially is beyond me.

So, until I get more information...... take care in what you do !!!!

Clean / Re-Clean and then Clean again to make sure the voice coil cap is totally symmetrical and no pressure is imposed to the cone by the re-foaming exercise.

Hear Endth the sermon for now, or at last until I get the speaker back from the professionals.

I will try to get some photos in the next weeks.


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[Lawrence001]

I have a feeling the lady in question purchased my kefs last night. She phoned off the back of my gumtree advert and said she was helping her son buy some speakers but he didn't have much money. When she arrived with her husband the gave them a good inspection and wanted to buy my other gear. After she left I found I had also received an ebay message the same time as she had called from a lady who, lo and behold, had a pair of Kef 105s in her listing history.

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[Lawrence001]

We'll soon find out as within a week she will list them for substantially more than the £275 she paid.

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[Boyse6748]

Lawrence, very interesting.... hopefully we will see.!!!

I think 'this particular lady is a bit of a advertising aficionados,,,,, or word that our leader wouldn't let me use.

Let me hoe it goes !!! [emoji851][emoji851]


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[Boyse6748]

Now sorted. Thanks to all for your valued advice and recommendations.

These truly are stunning speakers [emoji41]


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