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I believe I've solved the 105.2 bass problem....Vifa!
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adam_audio
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PostPosted: Sun Dec 04, 2005 12:15 pm    Post subject: I believe I've solved the 105.2 bass problem....Vifa! Reply with quote

I personally have always felt that the most glaring weak point of the 105.2 is the woofer. While certainly capable of reproducing low frequencies and sounding 'big', the B300 woofer is slow, muddy, and has a blurpy tonality. Additionally, it is harmonically challenged and does not integrate well into the system....leaves a hole in the lower mid-bass as well. It has a signature sound/coloration that wreaks havoc upon an otherwise world class loudspeaker.

My first experiments were to try some other 12" woofers. I tried a doped paper Bozak woofer that was designed for a similar size box and at first it seemed to work very well. Then I came to notice that it was not only to lean, but it was clouding up the midrange....not working with the B110 at all. After trying a handful of other vintage paper drivers, I installed the B300 again and was shocked as to actually how good it really was. It sounded like it belonged there, yet still had some major issues.

I then decided to try some 10"s. A friend of mine suggested I try a Vifa woofer, so I found a pair of M26WR-09-08's on ebay for about $75. My friend assisted me in mounting them and for experimental purposes, we've simply cut MDF adapter plates and mounted them using the three screws/holes for the B300. The first incarnation included some gasket between the MDF and 105.2 bass box to protect the cabinet from scratches.

Part of the fundamental problem with the bass in this speaker is the mounting system and cabinetry. It's obvious that KEF was really trying to cut costs here. 105.2 owners....just knock on front of the cabinet an inch or two below the woofer and you'll immediately see what I mean. I also feel that the woofer mounting system is responsible for absorbing some of the harmonic energy of the bass and robbing it of speed and extension. This theory was substantiated by the sonic results of removing the gasket ring on the back of the MDF adapter plate which held the Vifa 10". When the MDF was flat against the 105.2 cabinet, the bass was more extended, faster, and tighter. Clearly the woofer works better when firmly coupled with the box.

With the Vifa M26WR-09-08 in place, the bass is amazing....LIGHT YEARS ahead of the B300. The most amazing thing is that the Vifa woofer integrates ABSOLUTELY seamlessly into the system. The overall effect is that the speaker is more transparent, fuller, and more coherent. Tonally, the Vifa sounds like it was made to belong there...is wonderfully balanced and works absolutely flawlessly with the B110. It is fast, harmonic, tuneful, tight,...and the blurpy colourations and impressions of the speaker being top-heavy or disjointed are gone. With the Vifa, the 105.2 is now a top shelf, possibly unbeatable, reference loudspeaker.

Now my only complaint is lack of ultra-deep bass extension. I would guess that this woofer is doing about 45Hz right now, but I think I understand why and plan to fix it. I believe when I'm finished, bass extension will not be a problem. Here are my thoughts:

1) The M26WR-09-08 is designed to be in a ported system. Ultimately, I may have to rebuild the bass box for the 105.2. This would not be a bad thing as then I would have a decent cabinet to work with, as opposed to the inadequate, cheap box that comes stock with the system. However, I'm hoping not to have to go to the trouble and just use the Vifa in a sealed box.

2) The M26WR-09-08 pair were brand new....not broken in...when I purchased them. Apparently these woofers require 100 hours to be at their best, so at this point it is premature and inappropriate to make any real judgments or decisions about cabinet design.

3) My next step is to take this to the next level as simply as possibly. I will ditch the absurd mounting rings that I am currently using and cut a large piece of MDF that will cover the entire front of the speaker. I will knock out the plastic plugs used for mounting the grilles and use those holes and the ones for the original B300 mounting hardware to fasten the new baffle to the cabinet (thus keeping the original cabinet free of screw holes so that all of this is reversible at any time should I choose to abandon the project). This will serve as proper mounting, sans rubber, of the Vifa woofer and also help in damping/strengthening the cabinet...an area where KEF dropped the ball. If this incarnation works well, I will round the edges of the new front baffle and paint them flat black so it will look just like an extension of the headpiece and appear just fine cosmetically.

4) Other tweaks:
A) I plan to get rid of the casters and put the cabinets on floor spikes, which I'm sure will help.
B) I will not alter the original crossover design, but may improve the components...only as far as the bass is concerned. There is no reason to alter the mids or highs in any way.
C) I have removed the screens on the midrange drivers. Just did that tonight...not sure if I like it or not yet.
D) If you wiggle the headpiece, you can see how it is just dancing around there, quite flimsy. During bass-heavy program material, I have no doubt that the vibrations are causing some blurring or other problems on some level that I believe can be dealt with. I would like to clamp the underside of the pole that holds the head piece in place so that it pulls the head down firmly against the cabinet preventing it from moving.

Comments/discussion welcome and encouraged.

Sincerely,

adam
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adam_audio
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PostPosted: Sun Dec 04, 2005 12:27 pm    Post subject: Reply with quote

I might also state that I am running my 105.2s in on 6BQ5 tube mono blocks, which drive the speakers beautifully and don't even hint at running out of steam AND we're talking about rock music here, folks. My room is smallish...11' x 13'...so perhaps this is why this seemingly impossible scenario actually works.

Those of you who are running high powered solid state amps are welcome to claim that my reasons for disliking the B300B woofer are related to the fact that I am using low powered valve amplification. Please note that I have tried the 105.2s with a variety of amplifiers and am quite confident that this is not the case.

Sincerely,

adam
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proffski
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PostPosted: Sun Dec 04, 2005 7:13 pm    Post subject: Reply with quote

Hmm, if I had the time I'd be tempted to run the present setup on my simulation software. There are only a few ported systems which are "fast" in my opinion. Looking at the Group Delay of a speaker in a Hermoltz Resonator does it no favours for speed...
Transients are not in the forte of bass reflex.
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proffski
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PostPosted: Sun Dec 04, 2005 7:28 pm    Post subject: Reply with quote

Here is a mildly interesting thread regarding sealed Vs reflex and the Vifa unit: http://www.diyaudio.com/forums/showthread/t-24464.html

Observe with some caution however, not all has much to do with Hi-Fi! Wink
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proffski
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PostPosted: Mon Dec 05, 2005 2:11 am    Post subject: Reply with quote

Another though several hours later.
If you go ahead with the modifications then of course you fall foul of the remit of these pages as the speaker will cease to be a KEF!

Have you looked if you must at Volt drivers as well as behemoths by "Precision Devices"? All UK made!

The KEF driver may well be a bit lethargic, but it has the KEF sound that I would steal for, well, almost! Try different mountings as you have already done so with the Vifa.
Newton is right!

Now I must get back to Donizetti & Lucia de Lammermoor. Sublime excellence!
Back Monday evening… Andy.
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adam_audio
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PostPosted: Mon Dec 05, 2005 3:25 am    Post subject: Reply with quote

proffski wrote:
Another though several hours later.
If you go ahead with the modifications then of course you fall foul of the remit of these pages as the speaker will cease to be a KEF!

Have you looked if you must at Volt drivers as well as behemoths by "Precision Devices"? All UK made!

The KEF driver may well be a bit lethargic, but it has the KEF sound that I would steal for, well, almost! Try different mountings as you have already done so with the Vifa.
Newton is right!

Now I must get back to Donizetti & Lucia de Lammermoor. Sublime excellence!
Back Monday evening… Andy.


The point I want to stress is that what is special about the Vifa is that it most certainly DOES have the "KEF sound". It integrates so seamlessly with the B110 that it most certainly sounds more at home in the system than the B300B. This is unique to this particular Vifa. It's not a matter of trying any old 10" woofer....and I have no desire to do so. My friend tried this with a pair of Cantatas and went through a dozen or so different 10"s and NONE of them sounded right and all of them clouded up the midrange to some degree. I suspect this woofer I am using is the 1 in 1000 drivers that will actually work in this scenario. I just happened to get lucky and find it. It maintains all the 'house sound' of the B300B, but without the B300B's fundamental flaws. Believe me, I am the last person on earth to monkey with a speaker system. Were it not for the fact that the midrange and high frequencies are so spot on and smooth in the 105.2, I would never have attempted this. The 105.2 is a superb loudspeaker...absolutely superb. It's so close to perfection, yet so far away due to some whacky ideas on the part of the manufacturer. 'Fixing' the woofer is the first step in creating the ULTIMATE reference monitor.

BTW...if anyone needs a pair of B300Bs, I'll most likely be selling mine soon.

-adam
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Gary
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PostPosted: Tue Dec 06, 2005 1:41 am    Post subject: Reply with quote

I hope you post pictures............... Smile
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adam_audio
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PostPosted: Tue Dec 06, 2005 8:26 am    Post subject: Reply with quote

Gary wrote:
I hope you post pictures............... Smile



I definitely will.
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adam_audio
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PostPosted: Tue Dec 06, 2005 8:27 am    Post subject: Reply with quote

Just picked this up from a guy's ad selling a pair of 105.2:

"KEF REFERENCE SERIES 105.2 WITH WOOFERS REBUILT 10/05 THEY WERE BUZZING AT LOW VOLUME WAS TOLD THE SPIDER WHICH SUPPORTS THE CONE WAS SHOT,SINCE THEY WERE REDONE BASS IS TIGHT AND NICE NOT BLOATED LIKE BEFORE"

So does this mean that my B300B woofers are tired and that there really isn't a problem with the woofer after all sonically? My woofers have NEVER buzzed, so I'm not sure about that....but I'm curious to see what Colin and others have to say about this.

-adam
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clem_o
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PostPosted: Tue Dec 20, 2005 5:48 am    Post subject: Reply with quote

adam_audio wrote:
Just picked this up from a guy's ad selling a pair of 105.2:

"KEF REFERENCE SERIES 105.2 WITH WOOFERS REBUILT 10/05 THEY WERE BUZZING AT LOW VOLUME WAS TOLD THE SPIDER WHICH SUPPORTS THE CONE WAS SHOT,SINCE THEY WERE REDONE BASS IS TIGHT AND NICE NOT BLOATED LIKE BEFORE"

So does this mean that my B300B woofers are tired and that there really isn't a problem with the woofer after all sonically? My woofers have NEVER buzzed, so I'm not sure about that....but I'm curious to see what Colin and others have to say about this.

-adam


My brother has a pair of 105/2, and your assessment of the bass is pretty much correct, in my opinion - it goes deep but doesn't exactly have the punch/speed. We've tried swapping them out with an 'brand new' pair of Constructor Series B300Bs, the resulting sound was pretty much the same, so I'd think that generally this is 'really' what it is...

Interesting point to note: the recommended enclosure size for the 300B is pretty much what the 105/2's LF chamber is; this is the same volume seen in the CS9 box. If you care to have a look at the specs of the B300B, you'll find (sorry, this is really from memory) that this puts the system Q pretty close to 1.0...


Cheers!
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qguy
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PostPosted: Wed Dec 21, 2005 2:49 am    Post subject: Reply with quote

Has anyone tried a PP KT88 with the 105.2..it might change your opinion on its bass performance with the original woofer
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proffski
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PostPosted: Wed Dec 21, 2005 3:39 am    Post subject: Reply with quote

KT88s? I am not worthy...
Tell us more, I'd have thought that the KEF driver would have demanded a good damping factor, but am wiling to learn and be converted!
GOSH! Embarassed
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qguy
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PostPosted: Wed Dec 21, 2005 4:02 am    Post subject: Reply with quote

A friend loaned an el cheapo china made Solid State Rectified , PP KT88 amp ..well what can I say ...Bring out the Drum Test Track Disc !!!...

qguy saving up for a Vintage Audio Research PP KT88/6550 Power amp
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proffski
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PostPosted: Wed Dec 21, 2005 4:08 am    Post subject: Reply with quote

Replace the Solid State Rectumfriers with a decent bottle!
Then listen to the system realy take off!

Rectumfrier Diodes in a valve amp? Aargh.... Shocked NASTY!!!
Horrid noisy non lnear etc...
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speakerguru
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PostPosted: Wed Dec 21, 2005 3:04 pm    Post subject: Reply with quote

Of course rectifiers are non-linear- else they wouldn't rectify. Durh!

Re the bass: you'll find it makes more difference changing the position in the room (off the floor, away from walls, etc.) than tweaking the box f or Q by +/- 20%.

Also have a look at the Linkwitz stuff on dipole woofers at http://www.linkwitzlab.com/woofer.htm , if you like experimenting and you're searching for the Holy Grail of Bass Sound.
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