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KEF B300 bass unit SP1071 vs. SP1196
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speakerguru
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Joined: 18 Nov 2005
Posts: 958
Location: Green Hut, Tovil

PostPosted: Sun Jul 24, 2016 11:34 am    Post subject: Reply with quote

Going back to basics, I don't believe you have actually stated what you are trying to do; just that you have the wrong replacement B300s.

re your last post
brucegseidner wrote:
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?
No. I did not mean to imply either.

brucegseidner wrote:
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?
The nearfield low frequency high pass filter shape can be approximated by using the lumped constant model of a boxed speaker (fs, Q, etc.) but it can only be calculated accurately by modelling the system from the measured impedance of the system. This includes the effect of the bass unit voice coil semi-inductive characteristics, box and lining losses, not just the lumped constant resonance parameters.
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brucegseidner
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Joined: 05 Jul 2009
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PostPosted: Sun Jul 24, 2016 2:43 pm    Post subject: Reply with quote

I have taken to heart your encouragement to go active in my substitution of B300's in this 105.2 Franken KEF project. I will build 70liter enclosures and mount the B300's and use the original 105.2 heads on top. I will be using the original XO's for the HF/MF drives. I need to specify the parameters for the active XO.

So, after I get the enclosure built, I will measure all of the parameters you have asked for. I see that the way I have been doing this takes a lot for granted using tables with some trial and error. I can already measure my actual drivers and find they are always significantly different from published specs and from each other. Now I just need to step it up and measure actual sound in my projects going forward. The cost of this equipment is reasonable these days. I have to chuckle and shake my head at the systems I built 35 years ago. But it's been fun.

Thank you for your support. I estimate a few months to get this all together.
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speakerguru
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Joined: 18 Nov 2005
Posts: 958
Location: Green Hut, Tovil

PostPosted: Mon Jul 25, 2016 1:44 pm    Post subject: Reply with quote

If the original B300s work well enough to act as xo loads, then, using the original bass section xos and the units in boxes, all you have to do is measure the terminal volts across the the B300s wrt to frequency and then design the active part to regenerate the same terminal voltage curve. It's a relatively simple copying process as long as you know what is and what is not possible using biquads.

Good luck with your work.
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