A large two way speaker system paiyng homage to the KEF BBC LS5/1AE

[darkmatter]

My design for a larger two way speaker system paying homage to the KEF BBC LS5/1AE

This is an idea to create a modern speaker very loosely based on the KEF BBC LS5/1AE

I happen to own a pair of these excellent speakers and as a speaker building fanatic have been inspired to build a big two way system.

I have a weak spot for big two way speakers, having owned a pair of Spendor SA3s for a number of years. I still have these.

There is also the BBC LS5/8 whilst I have heard them a few times I have never heard the PM510 made by Rogers which was the passive version.

The LS 5/1AE is larger then the SA3 and the LS5/8 and used a 15" Bass unit crossing over to a pair of Rola Celestion HF1300s at 1.7 Khz

A brief description of the LS 5/1AE here.

1 Goodmans C129/15pr or 1 Plessey (LS5/1), 15-inch paper cone woofer.

2 x Rola-Celestion HF1300 tweeters

Large reflex enclosure net volume 135 Litres tuned to around 40 Hz with a 91mm x 66mm slot 19 mm deep.

History

Raymond Cooke, the founder of KEF in 1961, had close links to the BBC dating back to his time in the BBC Engineering Designs Department in the early 1950s,

where he worked with influential sound engineers such as Dudley Harwood and D.E.L.Shorter.

This connection was re-established in the early 1960s when KEF signed an agreement to manufacture the BBC designed LS5/1A monitor under licence to the corporation

production continued into the mid 1970s.

Also manufactured during this period were the LS5/2, LS3/4 and the 3-way LS5/5 – for which KEF also manufactured the 12” bass and 8” midrange drivers.

KEF's meticulous approach to production engineering was well suited to the manufacture of these tight tolerance monitors.

My pair is from 1968 or so pictures here the internals are not mine, but the rest are my actual speakers.


Internal pictures







My speakers







My idea here is to build a big two way using a 15" Bass unit and a pair of tweeters.

I propose to use a pair of the Audax TW034X0 units crossed over at around 1.5 Khz -6 dbs and to incorporate the 15" bass unit in at -6dbs 1.5 Khz

Similar to the LS5/1AE, my design will use a parallel pair of tweeters, this is used to get the power handling around crossover and a little above.

Searching for a bass driver that

1/ has good sound quality

2/ has a smooth enough response that it can be used up to -6dbs 1.5 Khz

My thoughts are this unit Precision Devices PD.153C01

Though it is a sensitive unit, a bass alignment can be chosen and crossover equalisation (tuning with additional series inductance with parallel resistance)

can bring that down somewhat more inline with the tweeters.

Rogers (Swiistone Electronics) did something similar with the equalisation used in the LS5/8 system and the PM510 passive equivalent.

This set of curves from the BBC LS5/8 design

The bass driver used has a rising response



The top curve is a measure of the response output from the 12" bass driver mounted in the enclosure. The bass driver has a rising response which can be flattened by using series inductance with parallel resistance with it.

The second is the equalisation required to achieve a flatter response.

The third the desired result.

These two drivers have a response that matched the rogers 12" in terms of a rising midband response

http://www.eighteensound.com/Product...id/3366/15w930

This one being closer

http://www.eighteensound.com/Product...d/3365/15nd930

What will make thus fun is that the drivers quoted thus far are a real unknown as far as sound quality is concerned.

This makes selection very difficult unless sound quality is known!!