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Kef 104aB Rebuild

 
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Stuart Booth
Junior Contributor 20+


Joined: 14 Jan 2006
Posts: 24
Location: Manchester UK

PostPosted: Sun Jan 15, 2006 8:18 pm    Post subject: Kef 104aB Rebuild Reply with quote

Hello,

this is my first posting. I recently inherited a pair of 1st rate Kef 104aB a model that I had owned thirty-odd years ago when they first came out. Funny how we oldies (57) like to go back to our youth isn't it?

Please don't be too angry, but I have decided to dispense with the B139D and use the T27 and B200 as the basis for a large 3-way enclosure with the addition of a B110 sound-alike from Wilmslow Audio, who have also helped with my cabinet design and are holding my crossover design on file. So far, so good!

My problem is that I used to own Rogers LS3/5a's which were stolen and I made the mistake of conversing with their website, which has resulted in my becoming totally muddled. The original design was to be made of Mdf and ported, but I have received conflicting advice from LS3 site and am now struggling with the concept of sealed -vs- ported boxes. I was always brought up to favour sealed boxes for the tightest sound, even though the 104 / ABR could be regarded as semi-ported, but there are those who say that you can get more from a ported box. I suppose its a question of attack - vs - Hz. I still believe in fidelity as much as possible.

It has also been suggested that the B200 was not designed to be used in a ported application....?

I have built the boxes (900H x 265W x 330D) from multi-ply birchwood - too large to use the ABR, all internal angles are glued, screwed and battened and there are three cross-braces. I am now ready to cut the holes for my three speakers - can anybody give me concrete reasons why I should / should not cut that extra hole.

Yours hopefully,

Stu. Confused
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ColinR
Über Contributor 1000+


Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Sun Jan 15, 2006 9:12 pm    Post subject: Reply with quote

As your box is more than twice the size of a Ref 103 and a third bigger than the SP1039 endowed 157mm * 48 mm dia reflex ported Monitor Audio MA4.

I cannot see any point of having a port.

I assume the rational is, a bigger box requires a smaller ABR until such a point the ABR can become an equivalent sized port.
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Stuart Booth
Junior Contributor 20+


Joined: 14 Jan 2006
Posts: 24
Location: Manchester UK

PostPosted: Thu Feb 09, 2006 9:52 pm    Post subject: Re: Kef 104aB Rebuild Reply with quote

Since making this posting I have had a few chats with Colin and Wilmslow and was proceeding well untill today I got a message from M.Jones, he of Kef and Falcon saying that the SP1039 B200 was not designed to be a stand alone driver and my speaker would rip it apart due to its small excursion design.

I am now completely bewildered and demoralised as my 12 month old dream of converting to a Kef style 3-way is totally shattered.

My only hope is in the fact that I had indicated my prefference for a sealed box and I am hoping he will come back to me and say I can still go ahead if I go for a ported box, but from the way he expressed himself, I have my doubts.

I have my mid-range speaker to hand and wonder if there is any way I can mount that and the T27 in a small box and perhaps tighten up the sound of the 104 whilst leaving the B200 / ABR in situ and running the two sets of speakers in tandem. Alternatively could a mid range be inserted into the 104's in some way.
Stu.

===========================================
Stuart Booth wrote:
Hello,

this is my first posting. I recently inherited a pair of 1st rate Kef 104aB a model that I had owned thirty-odd years ago when they first came out. Funny how we oldies (57) like to go back to our youth isn't it?

Please don't be too angry, but I have decided to dispense with the B139D and use the T27 and B200 as the basis for a large 3-way enclosure with the addition of a B110 sound-alike from Wilmslow Audio, who have also helped with my cabinet design and are holding my crossover design on file. So far, so good!

My problem is that I used to own Rogers LS3/5a's which were stolen and I made the mistake of conversing with their website, which has resulted in my becoming totally muddled. The original design was to be made of Mdf and ported, but I have received conflicting advice from LS3 site and am now struggling with the concept of sealed -vs- ported boxes. I was always brought up to favour sealed boxes for the tightest sound, even though the 104 / ABR could be regarded as semi-ported, but there are those who say that you can get more from a ported box. I suppose its a question of attack - vs - Hz. I still believe in fidelity as much as possible.

It has also been suggested that the B200 was not designed to be used in a ported application....?

I have built the boxes (900H x 265W x 330D) from multi-ply birchwood - too large to use the ABR, all internal angles are glued, screwed and battened and there are three cross-braces. I am now ready to cut the holes for my three speakers - can anybody give me concrete reasons why I should / should not cut that extra hole.

Yours hopefully,

Stu. Confused
Crying or Very sad Confused
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ColinR
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Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Fri Feb 10, 2006 12:42 am    Post subject: Reply with quote

You have a 762 X 343 X 381 Proac 3 / Celef PE1 sized box, so you need a resistive port constructed out of drinking straws.

Cut so that the port operates just above F(b) / or whatever you get with these box design programs.

OR

Port tubes with long straws with have very deep bass but at a reduced level. It can be tuned as low as ~25 Hz, but the low end output will be greatly reduced and extremely overdamped.

Port tubes with short straws (or no straws) will have a lot of output but higher in frequency. The speaker will produce a whole lot of boom at that one frequency.

A tuning of between 35 and 39 Hz can be achieved using ~5" straws in a 3.5" dia port.

Note it is not carved in stone what tuning will be best for the room and equipment.
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Craigb
Intermediate Contributor 25+


Joined: 12 May 2005
Posts: 33
Location: New Zealand

PostPosted: Fri Feb 10, 2006 10:03 am    Post subject: Reply with quote

Sp1039s are very expensive to replace via Ebay and judging by my experience deveishly hard to get repaired, so please tread carefully.

900X365X330 assuming 18 mill thickness should give internal volume of 75l.
Sp1039 spec sheets say 20-25 litre for a enclosed box and 30-40 litre for a reflex. If you enclose the B110 and T27 that should still leave 68l.

So unless you put a baffle inside you cabnetsto reduce the volume......

I am out way out of my depth here but and I am hoping some experts can add sage advice, but have you thought about turning your cabinets into transmission lines? Maybe with the BD139 as the port the back? If stuffed with all that wool the B200 may not extend too far?
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proffski
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Joined: 22 Aug 2003
Posts: 1296
Location: Tewkesbury UK

PostPosted: Fri Feb 10, 2006 10:31 am    Post subject: Reply with quote

Hmm, what made you build an enclosure of that size to start with?
You could I suppose fill the excess with dry sand...

Puzzled of Gloucestershire.
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Stuart Booth
Junior Contributor 20+


Joined: 14 Jan 2006
Posts: 24
Location: Manchester UK

PostPosted: Fri Feb 10, 2006 5:59 pm    Post subject: Kef 104aB Rebuild Reply with quote

The original 60ltr ported design was by Wilmslow, I merely increased the depth and width to what I considered a more aesthetic shape as theirs looked a bit dumpy and placed the T27 at ear splitting level. Ironically, Colin has since suggested that I put the tweeter in the middle, which brings it back to exactly the same position. - Ho Hum!

However, thanks to last night's posting, I have already been offered a pair of B139's and am actively pursuing TL's. The 104aB's will probably end up an the unspeakable web site, one day.

Cheers
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Stuart Booth
Junior Contributor 20+


Joined: 14 Jan 2006
Posts: 24
Location: Manchester UK

PostPosted: Sun Feb 19, 2006 8:14 pm    Post subject: Kef 104 Rebuild - Project cancelled Reply with quote

In my search to obtain a speaker with a greater detail across all frequencies, I have recently(yesterday) taken delivery of a superbly crafted pair of Chris Rogers Pro9TL transmission line (labyrinth) loudspeakers.

The bass is not just low in terms of Hz , but the pitch is so accurate as to be sonically comparable with my overstrung upright grand piano. The stereo imaging does not appear to be exciting and contrived, but rather the placing of performers, of whatever genre, is sensible and superbly balanced. No instrument, soloist, or group of instruments suddenly jumps loudly from the left or right speaker, but rather pops up somewhere over there, does its little bit, then hands over to somebody else.

It has only been a little over 21 hrs., but I suspect I have a lot more pleasant surprises ahead of me.

For the techniclly minded, the units comprise Kef B139 SP1044, Peerless K040 Mid and Isophon KK8 in a 140 ltr cabinet - Big! The crossover is a 16 element 18dB/octave at 480Hz ans 3.4kHz
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proffski
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Joined: 22 Aug 2003
Posts: 1296
Location: Tewkesbury UK

PostPosted: Sun Feb 19, 2006 8:36 pm    Post subject: Re: Kef 104 Rebuild - Project cancelled Reply with quote

Fascinating insight and well adjudicated!

I'd agree with your sentiments in total. Why do TLs sound wrong in Oz?
Is it because they are uside down? Wink
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harry h
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Joined: 15 Oct 2004
Posts: 24
Location: Kapiti coast. New Zealand

PostPosted: Mon Feb 20, 2006 10:18 am    Post subject: Re: Kef 104 Rebuild - Project cancelled Reply with quote

proffski wrote:
Fascinating insight and well adjudicated!

I'd agree with your sentiments in total. Why do TLs sound wrong in Oz?
Is it because they are uside down? Wink





Can,t be cos there upside down cos they sound pretty good in NZ and were rite next door Smile
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proffski
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Joined: 22 Aug 2003
Posts: 1296
Location: Tewkesbury UK

PostPosted: Mon Feb 20, 2006 12:08 pm    Post subject: Re: Kef 104 Rebuild - Project cancelled Reply with quote

Must be just one disgruntled member then. Sad
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speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 954
Location: Green Hut, Tovil

PostPosted: Tue Feb 21, 2006 2:20 pm    Post subject: Reply with quote

Malcolm Jones is correct. The SP1039 is a short coil in a long gap woofer with consequentially lower distortion (until overdrive moves the coil out of the gap).

With this type of woofer, a well designed reflex/port/ABR (they can all be equivalent) box alignment keeps the excursion down, as the port does most of the work over its bandpass region (the woofer excursion is a minimum at the box/port resonance. The depth of the null is governed by the box and port losses. This is why if you want the port to do anything useful at all, you should never introduce any losses like drinking straws!*?! ).

If you play vinyl, you will need a rumble filter or all the available excursion will go into producing inaudible record warp.

The 104aB was/is a finely balanced design with a woofer optimised for that application. My advice is, don't mess with it. If you want a bigger box with a different bass sound, sell the 104s and start from scratch.
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Almtb
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Joined: 28 Jun 2006
Posts: 6
Location: Bristol

PostPosted: Wed Jun 28, 2006 11:32 am    Post subject: Reply with quote

My first DIY speaker was used a B200 SP1039 in a 50L sealed enclosure and I found it worked superbly. Bass went low (not infrasonic) and cone excursion only became a problem when I was waking the neighbours (and this is with Dance music). The bass was quite well damped and the thought of using a B200 in a smaller enclosure with a reflex port or ABR makes me shudder! Laughing

If you really want a form of reflex I'd be tempted to use a large port tuned to a very low frequency to provide a little more output (and reduced cone excursion) at low frequencies without compromising the transient performance too much.

Cheers,

Al
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