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KEF B300 bass unit SP1071 vs. SP1196
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brucegseidner
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PostPosted: Mon Jul 18, 2016 3:30 am    Post subject: KEF B300 bass unit SP1071 vs. SP1196 Reply with quote

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
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audiolabtower
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PostPosted: Mon Jul 18, 2016 12:17 pm    Post subject: Reply with quote

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

Last edited by audiolabtower on Mon Jul 18, 2016 2:56 pm; edited 1 time in total
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audiolabtower
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PostPosted: Mon Jul 18, 2016 12:36 pm    Post subject: Reply with quote

There can't be many of those around.
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audiolabtower
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PostPosted: Mon Jul 18, 2016 3:02 pm    Post subject: Reply with quote

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.
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brucegseidner
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PostPosted: Mon Jul 18, 2016 4:54 pm    Post subject: Reply with quote

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.
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speakerguru
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PostPosted: Tue Jul 19, 2016 9:58 am    Post subject: Re: KEF B300 bass unit SP1071 vs. SP1196 Reply with quote

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


When we designed the KM1, which used 8 modified Quad 405 mk2 amplifiers, I performed a series of tests to determine the optimum driver impedance to extract the maximum power from the 405s. The B300 SP1196, 5 Ohm unit was the result.

Using 8 Ohms, the amplifier would always voltage limit first, using 4 Ohm, the amplifier would always current limit first. By using 5 Ohms we could get 150W from each 405 with voltage and current limiting happening at substantially the same point. The heatsinks in the KM1 were bigger than the Quad 405's
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brucegseidner
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PostPosted: Tue Jul 19, 2016 12:51 pm    Post subject: Reply with quote

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.
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speakerguru
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PostPosted: Tue Jul 19, 2016 4:57 pm    Post subject: Reply with quote

brucegseidner wrote:
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?


If the SP1119s are from a 105|2 system then they are designed for use with 8 Ohm B300 SP1070 in a 70 ltr enclosure. The XOs and SP1196 drivers are incompatible.

If you want to use the XOs then you must get some SP1060 or SP1071 drivers.

If you want to use the SP1196 drivers, you need to scale all the reactive components in the XOs (all capacitors and all inductors, by the ratio of the driver impedances - not recommended without accurate measurements and access to an electrical ladder network optimiser).

In short - don't do it / I wouldn't start from here if I were you.

Build an active bass section instead?
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brucegseidner
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PostPosted: Tue Jul 19, 2016 5:59 pm    Post subject: Reply with quote

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
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speakerguru
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PostPosted: Tue Jul 19, 2016 10:16 pm    Post subject: Reply with quote

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.
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brucegseidner
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PostPosted: Wed Jul 20, 2016 2:11 am    Post subject: Reply with quote

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.
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speakerguru
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PostPosted: Wed Jul 20, 2016 8:36 am    Post subject: Reply with quote

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
Quote:
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?

are too vague and do imply a lack of background knowledge. It would require a course on practical speaker design to cover all the possible ramifications. Sorry.
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brucegseidner
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PostPosted: Wed Jul 20, 2016 9:07 pm    Post subject: Reply with quote

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
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speakerguru
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PostPosted: Wed Jul 20, 2016 9:56 pm    Post subject: Reply with quote

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.
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brucegseidner
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PostPosted: Thu Jul 21, 2016 2:06 am    Post subject: Reply with quote

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
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