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 

Simulating the Kef Kube filters
Goto page Previous  1, 2
 
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF speakers
View previous topic :: View next topic  
Author Message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Mon Feb 10, 2014 10:40 am    Post subject: Reply with quote

Sorry but I'm going away for a few days and have no time to look at your simulation or give a full answer atm. However, the plot needs to be in dB, i.e. log not linear, in the vertical axis to make any sense of it.
Back to top
View user's profile Send private message
theozaurus
Junior Contributor 20+


Joined: 05 Sep 2013
Posts: 21

PostPosted: Fri Feb 14, 2014 11:55 pm    Post subject: Reply with quote

I've been visually matching the simulation data with a Linkwitz calculator. So far the values look like:

f0 = 57
Q0 = 1.1
fp = 26
Qp = 0.42

These values look seem possible to me. This is looking at the BEC stage in isolation. The input stage seems to have a 3db boost up to around 200Hz, and the contour section does more alterations.

The values for the Z domain look like:

a0 = 1
a1 = 1.991917852130950
a2 = -0.991929388490413
b0 = 0.999353476592651
b1 = -1.991895897210170
b2 = 0.992597866818542
Fs = 48000

There are also some analogue coefficients available (which make no sense to me):

d0i = 128265.378796557
d1i = 325.58323864476
d2i = 1
c0i = 26687.4103005456
c1i = 388.959090444451
c2i = 1
gn = 95999.7639175758
cci = 9253321340.49686

I'd love to see if these seem broadly right.
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Sat Feb 15, 2014 10:08 am    Post subject: Reply with quote

see EQUATION 32-2 on page 595 of http://www.dspguide.com/CH32.PDF for the biquad transfer function with variable s.


For the steady state response you substitute jw for s. This means that your coefficient d01 is equal to (jw)squared, where w=2(pi)f.
Up to 4 or so figures your d0i is equal to [2x(pi)x 70] all squared. So 70Hz rather than 57Hz is probably correct. I doubt that KEF would have equalised such a small speaker down to 26Hz so that probably is not correct either. However, If you can trace out the schematic and get me some BEC (Friend circuit) component values I can calculate the transfer function for you.

My Biquad "app" will calculate s coefficients from f and q values and vice versa. PM me if you want a copy (Windows exe file only).
Back to top
View user's profile Send private message
theozaurus
Junior Contributor 20+


Joined: 05 Sep 2013
Posts: 21

PostPosted: Tue Feb 18, 2014 2:21 pm    Post subject: Reply with quote

speakerguru: Are you referring to the 104ab? I'm planning on using this with my 104/2's.

The values for the friend circuit are the same as the ones from the KEF Kube 200 schematic. Perhaps my simulations are slightly out as I'm using an ideal op-amp for the model.

The graphs can be seen here: http://www.partsim.com/simulator/#15762

Clicking: Spice -> Run -> Run
Then going to the "AC analysis" tab
Back to top
View user's profile Send private message
theozaurus
Junior Contributor 20+


Joined: 05 Sep 2013
Posts: 21

PostPosted: Tue Feb 18, 2014 2:22 pm    Post subject: Reply with quote

Having trouble sending a PM, keep getting the error:

Failed sending email :: PHP ::

DEBUG MODE

Line : 234
File : emailer.php

Is your app available to download anywhere?
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Tue Feb 18, 2014 7:11 pm    Post subject: Reply with quote

Biquad sent.

For general info
the KUBE 200 BEC equalises a f=56 Hz Q=1.1 system down to f=26 Hz with a Q=0.45
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF speakers All times are GMT + 1 Hour
Goto page Previous  1, 2
Page 2 of 2

 
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