Simple "LS3/5A crossover

[scottjoplin]

I've KEF drive units from some old Concertos. I'd like to use them for small bookshelf speakers similar to the LS3/5A but I don't want to spend a lot of money on them so I'm looking for a simple crossover as opposed to the very complex, expensive crossover used in the originals, perhaps even use an active crossover, can anyone help? Thanks.

 

[Inductor]

It's possible. Make sure to reference your drivers models numbers and impedance (parameters available).

 

[Inductor]

KEF Concerto Crossovers - YouTube
I guess you are going to make a 2-way instead, it's obvious. Best.

 

[scottjoplin]

It's possible. Make sure to reference your drivers models numbers and impedance (parameters available).

Ah yes, good point, they are B110 midrange unit (SP1003), T27 tweeter (SP1032) https://us.kef.com/pub/media/pdf/Datasheet_B110A_SP1003.pdf
http://nedlab.com/wp/wp-content/uploads/2014/06/KEF-T27-SP1032.pdf

 

[planet10]

There are lots of examples of XOs with B110 & T27. The old KEF ones (ie DN12?) are not all that good.

Simple might not be doable, the tweeter really needs a fairly steep LP.

Interestingly i did a triangular shaped box for these drivers (for clients building Friedd H, Freid M kits, the shape later adapoted by the factory), and just found a picture day before yesterday of that plan. I’ll dig it out and post it.

dave

 

[scottjoplin]

Yes DN12, I have the crossovers, how about using the HP section for the tweeters and running the midrange full range?

 

[planet10]

The B11o has some bextrene resonances you probably want to quell, but try it.

For the B139, Scott and i have done a few proper TLs.

dave

 

[scottjoplin]

I've seen the TLs. There seems to be a lot of wood, as in large panels, my understanding is TLs need to be very rigid to work well, isn't that an issue with them?

I've a number of B139's using them in an in wall IB at the moment.

 

[planet10]

Most people do not have walls to take advantage of. A good solution.

dave

 

[xrk971]

You might check out my simple XO for the “Rockville” speaker here (full plans):
RST28F and DC130A Foamcore Homage to LS3/5A

Very low cost drivers and XO but approximates the step response of an LS3/5A quite closely.

Here is Sterling LS3/5A Step Response:

vs. the Step Response in the Rockville:

It sounds very nice - balanced, and musical.

 

[scottjoplin]

Thanks for the suggestion. Do you think that's a steep enough filter for the T27?

 

[xrk971]

I haven’t worked with the T27 so can’t be sure. But if T27 has fs around 700Hz it might work.

 

[planet10]

Factory specifies 1200 Hz +/-200. The pair i measured were about 1.1kHz.

I have a bunch of example XOs but need to dig them out.

dave

 

[scottjoplin]

I could simply remove the high pass section of the midrange filter, that should work ok for my needs?

 

[planet10]

Interestingly i did a triangular shaped box for these drivers (for clients building Fried H, Freid M kits

Had to redraw it.

dave

 

[scottjoplin]

Here's an idea Dave, I butchered the original cabinets so I've still got that part of the baffle for the B110 and T27 complete with the midrange tube, how about using that and make the bass part aperiodic?

 

[planet10]

That could work. IIRC the tube is small for use with B110 as bass driver, i expect bass would be limited.

dave

 

[planet10]

A look for XOs with T27 turned these up.

dave

 

[scottjoplin]

Yes the tube is small and is sealed by the rear of the cabinet in the Concerto. Having removed it though it is open ended, that's why I suggested making it aperiodic with some form of restriction.

 

[planet10]

One could smooth the roll-off at the bototm but you likely won’t get much extention.

6.8 litres, i believe, is about what is needed.

dave