SpeakerTalk Forum Index SpeakerTalk
This forum has been set up to facilitate discussion of 1970s KEF speakers and drive units. The owner of the Forum has no connection with KEF Audio.
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

KEF CS7 Kit - why not bass reflex?

 
Post new topic   Reply to topic    SpeakerTalk Forum Index -> DIY with KEF drive units
View previous topic :: View next topic  
Author Message
Bazoozoo
Introductory Contributor


Joined: 14 Jan 2005
Posts: 6
Location: Nova Scotia, Canada

PostPosted: Sat Jan 15, 2005 7:15 pm    Post subject: KEF CS7 Kit - why not bass reflex? Reply with quote

Hi,
I'm curious to understand why the CS7 kit was not used in a bass reflex enclosure as it is very similar to the Concerto. Maybe somebody has tried it. Appreciate any comments.
Thanks
Back to top
View user's profile Send private message
ColinR
Über Contributor 1000+


Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Sun Jan 16, 2005 11:13 am    Post subject: Reply with quote

You'll have to make friends with a German to find out about the very successful >105 litre ported Dutch kit - variants come up on German ePay from time to time. Take a CS7 box keep the front and rear baffle widths to maintain the TS parameters and increase the dimensions front to back and height by about 1.15 times, then expand the front profile by adding two >15cm boards at 60 degrees to either side of the front baffle and join up, making a pentagon - have fun Very Happy.
Back to top
View user's profile Send private message
Wouter
Intermediate Contributor 50+


Joined: 18 Jun 2004
Posts: 60
Location: Ramsel (Belgium)

PostPosted: Mon Jan 17, 2005 7:57 am    Post subject: Reply with quote

Hello there,

I once was told that the calcultion of the Concerto was not done correctly.
The approx 60l of the concerto is good for a closed box, but for a bass-reflex, you should need an approx 150l enclosure...
The Concerto would be originally designed as a closed box, but for marketing reasons, they have put a pipe in it (to 'pump up' the bass).
To check if the story is true, I am currently building a 60l closed enclosure. When they are finished (yet one month to go), I will compare the sound to my father's (original) Concerto's.

When you take the data of the B139 and make a butterworth calculation (with Q= 0.707) , the result for a closed enclosure would be about 60l... 3 db. point is situated on 50 Hz.


That's what I was told some time ago.
We will se what the results will be!
But in my opinion, there are certainly reasons (maybe others than mine above), why there's only one model with a 60l bass-reflex (the Concerto)...


Best regards,
Wouter
Back to top
View user's profile Send private message Send e-mail
Bazoozoo
Introductory Contributor


Joined: 14 Jan 2005
Posts: 6
Location: Nova Scotia, Canada

PostPosted: Mon Jan 17, 2005 3:59 pm    Post subject: Reply with quote

Hi Wouter,
Thanks for the reply. I have built both Concerto stlye ( KK3 ) and CS7 configurations. I was a little disappointed with the latter - the top end was much improved but there was a distinct lack of bass ( Reflex versus closed box of approx same volume ). I think your experiment will show the same result.
I've been side tracked for many years by other activities but I now want to refurbish my Concerto's and/or improve the bass response of the CS7's. From what I've read the transmission line provides the cleanest deepest bass ( but the coffin is big ) but I'm open to other suggestions. Do you know of this Dutch 150 L. Bass Reflex CS7 design?
Good luck with your project.
Regards
Dennis Watts
Back to top
View user's profile Send private message
Wouter
Intermediate Contributor 50+


Joined: 18 Jun 2004
Posts: 60
Location: Ramsel (Belgium)

PostPosted: Mon Jan 17, 2005 10:07 pm    Post subject: Reply with quote

Hello Dennis,

No doubt about it! A bass-reflex gives a boost in the lower regions. BUT the curve at the end goes much faster down as compared with a closed enclosure...
A closed one starts falling down ast an higher frequency, but the decrease goes slower. If you understand what I try to explain.
Try some googles; you will surely find some comparisons between both types!

On the other hand, a closed one mostly gives a tighter bass than a bass-reflex. The last one is mostly 'slower' and more 'fuzzy'.

I not sure yet if this is also the case for the concerto and its B139!
I am mad of the sound of my father's Concerto's; but I haven't had the chance yet to compare it with my own speakers (as they are not yet finished)...
Maybe I will add a port to get a better bass.....? Maybe I will advise my father to close the port of his Concerto's....

A TL is excellent for the B139, but it is very difficult to tune. You can calculate a TL, but inreality you will have quite some difference between the spec's of the B139 and the reality....
This won't be only due to the age of the unit!

If you see what a giant enclosure you need for a TL, you can understand that this also counts for a bass-reflex.... In vented condition, the B139 needs a big enclosure....(this to make clear what I have written in the above posts)
My brother has an IMF Reference Mk4 and I can tell you: the bass is amazing; but the speakers are giant ones!

But I have no experience at all in constructing these babies.... Nor a TL, neither a 150l bass-reflex.
I would like to; but the work scares me a little... And I am never sure of the results. I chose the closed one of 60l as compromise...
If you want, I can always send you some pictures of the prototypes.


Good luck in return!!!

Regards,
Wouter
Back to top
View user's profile Send private message Send e-mail
cuwuddle
Introductory Contributor


Joined: 21 Jan 2005
Posts: 3
Location: Newport, South Wales UK

PostPosted: Fri Jan 21, 2005 3:38 pm    Post subject: Old Kef B139's Reply with quote

Hi Sorry to butt in on the conversation, thought you might be able to help me identify a pair of old b139's. These are dated january 1964 and unlike all the other b139's I have with rubber or foam surrounds, these have fabric surrounds. They have no numbers on them at all.

I quite agree with what you have been saying regarding the enclosures particularly the concerto size. I'm building a pair myself. I love the idea of building some TL's but they are far to big and want to achieve the best sound from the smallest enclosure.

This is all quite new to me, would it be crazy to sugest building a test enclosure where the volume can be variable in order to tune it and note the optimum. Something along the lines of a sliding damper that can be forced down from the top reducing the volume.

kind regards
Back to top
View user's profile Send private message Send e-mail MSN Messenger
Wouter
Intermediate Contributor 50+


Joined: 18 Jun 2004
Posts: 60
Location: Ramsel (Belgium)

PostPosted: Fri Jan 21, 2005 7:11 pm    Post subject: Reply with quote

Hello,

Nono, thanks for joining the conversation! That's the exitence reason of these forums!

Well, I think this is a good question for Colin or Terry. Guys? Maybe you have ever seen this kind of B139???
In fact, I have never heard of a B139 with fabric surrounds. Not at all! Are you sure this is a Kef uit and not an imitation or derivative?

Once I have heard that you can get a very tight bass with an enclosure of 40l.... I never did the test. Mine will have 60l internal volume. Heavy MDF of 28mm thick. These cabinets are really big and heavy (40kg!).
But if you want to do test with a variable enclosure, I think you would better make a (strong) big enclosure and fill bit by bit the enclosure with sand (to imitate a smaller enclore).
A slider would vibrate too much, I fear... It's very difficult to control the B139; this speaker is very strong!
But it's not crazy to test these things! Testing is the beginning of wisdom!
And the advantage: when you have finished the tests and have found an ideal volume, you can leave the sand on the bottom. This is good against vibrations!

To get the best sound out of the B139? Maybe someone has another opinion or ideas?

Good luck,
Wouter
Back to top
View user's profile Send private message Send e-mail
cuwuddle
Introductory Contributor


Joined: 21 Jan 2005
Posts: 3
Location: Newport, South Wales UK

PostPosted: Fri Jan 21, 2005 7:26 pm    Post subject: Hi Wouter Reply with quote

Thankyou for the reply!

The B139's are definately Kef and currently sit in a pair of K2 Celeste. Ridiculously small enclosures vertually the size of the B139 itself, they look like the first pair of Kefs ever built!

kind regards
Back to top
View user's profile Send private message Send e-mail MSN Messenger
Wouter
Intermediate Contributor 50+


Joined: 18 Jun 2004
Posts: 60
Location: Ramsel (Belgium)

PostPosted: Fri Jan 21, 2005 7:31 pm    Post subject: Reply with quote

Yes, I think that the K2 Celeste is one of the first Kef's ever build (T15 and B139). But I didn't know that this version of the B139 had a fabric surround.
As far as I know, these Celeste's had a very good sound! This is more or less similar to what I have stated above: a small cabinet makes a tight bass for the B139...
Back to top
View user's profile Send private message Send e-mail
proffski
Über Contributor 1000+


Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK

PostPosted: Sat Apr 30, 2005 8:02 pm    Post subject: Re: KEF CS7 Kit - why not bass reflex? Reply with quote

The transient response is far superior in a sealed version, the group delay is also superior for the same reasons. You only have to run simulation software to see the difference. Ther gain in bass response is minimal.
Will try and send you the graphs if I still have them.
Andy.
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill
Back to top
View user's profile Send private message Send e-mail
Craigb
Intermediate Contributor 25+


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

PostPosted: Sun May 15, 2005 11:43 am    Post subject: Reply with quote

I would like to add another demension to this discussion. I have been toying with the idea of changing my ket kit3's by removing the T27 and B110 to an erzats ls3 5a configuration to sit on top of the main box, and coupling the B139 with a BD139 in the original box. The cabinets are about 80 litres. Any ideas whether this would work?

Craig
Back to top
View user's profile Send private message
ColinR
Über Contributor 1000+


Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Sun May 15, 2005 12:52 pm    Post subject: Reply with quote

Yes it would, I've got a 22k picture of a varient of that particular configuration.

~120 litre if you want to use to two ABR's with a B139B btw.

I've no idea what they would sound like though - any offers of a demo?
Back to top
View user's profile Send private message
Wouter
Intermediate Contributor 50+


Joined: 18 Jun 2004
Posts: 60
Location: Ramsel (Belgium)

PostPosted: Sun May 15, 2005 9:58 pm    Post subject: Reply with quote

Interesting issue.
I don't have an idea of the results, but I remember a question of another memeber of the forum, FrankN: http://www.hifiloudspeakers.info/public_html/viewtopic.php?t=112

Maybe Frank has done some tests in the meantime...?
Frank?


Regards,
Wouter
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic    SpeakerTalk Forum Index -> DIY with KEF drive units All times are GMT + 1 Hour
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group