SpeakerTalk

[Lee in Montreal]

I will be running two sets of 105/2. The first set in their original cabinets with redone crossovers. The second set with custom made cabinets. I am very tempted to experiment with tri-amping and active crossover.

Basically, from the Technic Flat SU-9070 pre-amp to the active crossover (most likely a Behringer CX3400) then to two Quad 405 (mid and high) and a 606 (bass). My fear is that even if I send a signal for high frequencies only to the power amp feeding the tweeters, some parasite low frequencies might still sneak in and kill the tweeters. Is may fear founded?

Behringer CX3400


I already have a Behringer DEQ1024 digital equalizer (24bits-94Khz)

_________________
Kef Calinda - since 1979
Kef Cantata - since 2009
Kef 105/2 - since 2009
Evo 105/2 - in the build

[audiolabtower]

I don't see why it should but you could always protect the tweeter with a series cap rolling off an order of magnitude or more below the design crossover frequency which should not interfere with the target crossover response. I would use say 30 or 40uF.

[proffski]

Oh!
So, if you go down the active crossover path will you be taking the same steps as KEF did with the passive system or just ignoring the essentials and purely going for the theoretical crossover points and hoping for the best?
_________________
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

[Lee in Montreal]

[Lee in Montreal]

[proffski]

[audiolabtower]

I've actually built this active crossover, both boards are done, but I haven't finished the power supply or tested anything yet (the power supply uses dual regulators in a "pre-regulator" arrangement, much better then regulators in series and hopefully better than the kube supply since things have moved on since the 80s), I've used OPA134s for bandwidth and super low noise in the circuit heavily decoupled.

We discussed changing the values to a 400Hz crossover like the passive, but after a lot of thought I believe the active 150Hz will actually be superior.

It makes the head more like a "super" LS3/5a but without having to output any cone vibrating bass and the low mid room interaction should be better through the midrange higher off the floor. The only reason 150Hz was not used in the passive was the problems inherant in the inductance of the B300 coil messing up voltage output and impedance, higher up in freq this effect reduces. At ~150Hz I don't think overall the power handling capacity will be much different since the B300 is still handling all the excursion program.

Later on Kef actually used 150Hz passive crossovers in their coupled cavity designs by having a LOT more components to compensate the drive unit impedance, so as a design objective it is quite logical and actually better because the phase difference between B300 and B110 is less, but at that time I presume they did not see the point in making the design even more expensive with an appreciable increase in the cost of the passive crossover? By the 90s top end Hi-Fi was on the way to super-money territory so they had the leeway to get more and more expensive whilst seeming "normal" to the rest of the market

Anyway you can try both, but try to get near the curves in the active circuit for a flat acoustic response

[Lee in Montreal]

Soooo... It seems I am not alone to be insane, wanting to try active filtering on a 105/2. Cutting at 150Hz vs 400Hz might indeed seem more logical with an active crossover. Anyway, the Behringer is only $149cdn, therefore, I have absolutely nothing to loose. Especially that making changes in frequency cut-off, or levels, or phase will cost nothing. While rebuilding the passive crossovers will cost arout $250cdn and it is a fixed unit...

For the Canadians on this forum, I recommend www.axemusic.com for your Behringer needs.
_________________
Kef Calinda - since 1979
Kef Cantata - since 2009
Kef 105/2 - since 2009
Evo 105/2 - in the build

[ColinR]

The CX-3400 has a useful ident at 160Hz, so I don't bother with specifics when running an active bass horn/folded damped pipe with an existing B110A/B + KEF/Celestion/Isophon/Peerless/Audax/SEAS/Decca/Motorola tweeter design .
_________________
This post or any other information supplied to this website or any other by myself is not available for any form of commercial purpose i.e. to hi-fi magazines or as sales and marketing material for sleezeBay or Audiodogging pimps and the like.

[Lee in Montreal]

BTW Looking at the frequency graph above, I can see there's a bump centered around 250Hz on the B110. Is it natural, or was it pushed up with the active filter?
_________________
Kef Calinda - since 1979
Kef Cantata - since 2009
Kef 105/2 - since 2009
Evo 105/2 - in the build

[ColinR]

There's a minima in the B110B's impedance at 280Hz, so a bit more juice in an active system will be required in that region.
_________________
This post or any other information supplied to this website or any other by myself is not available for any form of commercial purpose i.e. to hi-fi magazines or as sales and marketing material for sleezeBay or Audiodogging pimps and the like.

[Lee in Montreal]

[audiolabtower]

the shape of the active has been carefully designed to provide a flat acoustic response for those drivers in that particular cabinet configuration, the same as the target design for the passive crossover.

Anything else will certainly sound different but that is down to personal preference. Myself I'm inclined to go along with all the research that Kef originally did.

[SaSi]

I'm on the same path with Lee.

Since two heads from 107/2 landed on my lap but the bass units were shot, I decided to build something different.

I have finished one cabinet of 180lt housing two compound B300 that I will be trying in sealed and vented mode tuned to 19~20Hz.

Will be using a Behringer DCX2496 active crossover bi-amping the bass cabinets and the heads.

I also have a pair of CS1 equivalents that I can bi-amp so that goes to a tri-amping scenario.

Right now I am focused on gated frequency response measurements of my existing and newly restored 105.1, so that I can try things out and have means of measuring when things are going for the better or the worse.

[BobL]