SpeakerTalk

brucegseidner · Junior Contributor 10+ Joined: 05 Jul 2009 Posts: 12

KEF B300 bass unit SP1071 vs. SP1196
I would appreciate learning the differences between these iterations of the B300.

The SP1071 was loaded in the KEF 105.2's during its 8 year run. I'm unsure how the SP 1196's were employed. I want to know the consequences of replacing the SP1071's in some 105.2's knowing how serious KEF was about creating crossovers way beyond my ken.

Thank you in advance.

Bruce

audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

oops.. it's the one in the KM1?

audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

There can't be many of those around.

audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

here?

http://www.ebay.ca/itm/1-KEF-B300-SP1196-Removed-From-Working-KM1-Studio-Monitors-/232009561964?hash=item3604d8f76c:g:XJwAAOSw2GlXINx7

what a shame to cut up a working pair.

brucegseidner · Junior Contributor 10+ Joined: 05 Jul 2009 Posts: 12

This is odd. When I clicked the email link earlier there was the most complete and expert information I could have asked for, essentially describing differences in the way the drivers mounted. Now it is gone. Not sure how that happened.

This is part of a project that began in 1984 with the purchase of a kit from Falcon Acoustics of B139/B110/T52 and separate low and high pass crossovers. Last year I started seeing 105.2's being parted out and I got empty head units and crossovers. I had some ideas about making the B139's active but now I'm thinking of just getting some B300's and be done with it.

The volume was 70 liters for the original KEF B300 bass unit SP1071.

I will assume it will be unchanged for the sealed enclosure I will now build for the SP1196.

speakerguru

brucegseidner · Junior Contributor 10+ Joined: 05 Jul 2009 Posts: 12

That is fascinating. Thank you.

I have 4 crossovers, SP1119 Serial#2830,2831 and #3767,3768.

Sounds like they are expecting a different load. Is this consequential?

What is a potential remedy?

I very much appreciate your support.

speakerguru · Posted: Tue Jul 19, 2016 4:57 pm Post subject:

brucegseidner · Junior Contributor 10+ Joined: 05 Jul 2009 Posts: 12

Well, I'll be (blank). But as the Chinese observed crisis=danger+opportunity. And it is so much easier these days to go active. JRiver Media Center slices and dices the spectrum and you have a choice of filter models. Many AV preamplifiers allow you to bi-amp by assigning the rear speakers to front LF.

I read the Fraken KEF posts and enjoyed his journey. So, it makes sense for me to make the best of this and go active. With my B300's shipped and paid for, I'm all in.

These being close relations to you, how would they be happiest? I can build any size home, with or without a window, sealed, reflex, Onken, etc. My guess is 80liters plus/minus 10 sealed. I would also appreciate your direction for how to specify the filter.

Thank you for your insights and help.

Bruce

speakerguru · Posted: Tue Jul 19, 2016 10:16 pm Post subject:

Standard KM1 alignment was to load each B300 in 70 ltr sealed box and eq electrically to produce an acoustic bandpass response about 6dB down at 20Hz at the low end (off the top of my head).

In very difficult circumstances like BBC Maida Vale studios 4 and 5, which had a bass black hole where the sound mixer sat, we had to resort to porting the boxes. They were tuned for minimum driver excursion at 70Hz, where all the kick drum and bass guitar content was concentrated, and then eq down to 30 Hz (?) by means of two Friend biquad circuits, as used in the Kubes.

Usual caveat - it is necessary to eq for non flatness due to voice coil inductance and pass band non flatness as well as box cut off. Close mic measurements would probably yield good enough data for subsequent design to produce acceptable results for the hobbyist.

brucegseidner · Junior Contributor 10+ Joined: 05 Jul 2009 Posts: 12

Maybe you could direct me to a discussion of the XO. I will start looking as well. I have seen discussions of the LS3/5A and the complexity of those boards is impressive. This SP1119 is beyond anything I have worked with.

In general, how are the frequencies negotiated between the drivers on the SP1119? How do the MF and LF drivers cross at the published spec of 400Hz? How should I set up the top end for this SP1196 in the active XO? I now understand the low end and if that answered my new questions I don't see it because of my lack of background.

If the XO doesn't see a LF driver will this affect the speaker protection? If so what is the remedy?

I hope this does not demand too much of you. I really appreciate actual data and not arm chair opinion.

speakerguru · Posted: Wed Jul 20, 2016 8:36 am Post subject:

look at all the KEFTOPICS publications from KEF on this page: http://www.hifiloudspeakers.info/Anatomy/KEFDocuments/DocumentsIndex.html
That should at least help you ask the right questions.

If you have any very specific questions, I will attempt to answer them. But the following from your last post

brucegseidner · Junior Contributor 10+ Joined: 05 Jul 2009 Posts: 12

I appreciate your forbearance but I'm not asking for more than a description of what I need to model in an active DSP crossover. I understand the published crossover frequency of 400Hz. But I didn't find the order of the filter, the type of filter, and if there is any shelf or delay. If it were a 1st Order Butterworth for instance that would be information I could use to model an active filter. If it were a 2nd Order LR, that would give me a lead. I can't find a description of this crossover at this level of specificity. And the additional wrinkle is my substituted and non standard B300. The reason that makes my current crossover inappropriate. Thank you for thinking this through with me.

Bruce

speakerguru · Posted: Wed Jul 20, 2016 9:56 pm Post subject:

Most of the KEF crossovers of that era were 4th order Linkwitz-Riley (AKA LR4, same as 2nd order Butterworth squared) because they are in phase at the crossover frequency...

BUT,

this was the ACOUSTIC response which is made up of the raw drivers in their boxes' acoustic response multiplied by the crossover electrical response. If you just dial up LR4 transfer functions on some DSP, you are just setting up the electrical response. The final total response will not be that. There is no getting round measuring what the unequalised drivers are doing in their enclosures first.

brucegseidner · Junior Contributor 10+ Joined: 05 Jul 2009 Posts: 12

So, what I'm hearing is that this will be empirical. I need to start from scratch and work this out by measuring actual room response and tweek or dial as I go?

Do I understand correctly that it is not possible to anticipate how this iteration of B300 will do in my specific room in a 70liter sealed enclosure? That we can not anticipate nor recommend standard parameters of Q, filter model, shelf or delay?

Cheers,

Bruce