strangeandbouncy
Well-known member
Hi,
I am about to launch into my latest project.
Some background. I have been using a pair of (loaned!) BBC LS3 5a speakers. I absolutely love them to bits, but am very wary of damaging them. The are as rare as rocking-horse-hens-teeth . . . . I always work at about 83dB(Fletcher-Munschen curves n all), so they are never strained. I desperately need to replace them, just for peace of mind! For those who dont know, they were designed by the BBC for use in OB trucks. They are very inefficient(80dB@1W@1m), are incredible for anything vocal, speech or singing, and possess bass far beyond the normal reach of a 6 litre sealed box, thanks to some clever crossover trickery. Effectively, there is a bass boost, or rather a gentle roll off against the rising response of the driver at the expense of efficiency. There is also an eq to cut the lump at @1kHz.
When I worked for Roger Quested in the 80s, it was obvious the advantages of a 3 inch softdome handling the all important vocal range - 350Hz to 3kHz5 or so. True, male vocals extend much lower, but it is the upper reaches that are so important. One of the reasons that I think I love the LS3 5a is that one driver runs all the way up to this crucial point - approx 3kHz, and integrates wonderfully with the tweeter. At Quested, we used to make a nearfield with 4 x 5 inch drivers running into a 1 inch softdome at approx 1kHz6. Cool!
With modern digital crossovers, this kind of design is really childsplay, especially with all the eq built in. I am about to inherit a really good analogue crossover to get the ball rolling. Mnay Many thanks Ruariri! You are a super star.
I have found a number of potential bass-mids, most of which are Old fashioned, 1 inch voice coil, low power, smooth response devices. None of the 3 inch voice coil units look any good on paper! lumpy response curves, early cone break-up, and high distortion. Not worth the power trade off. Nah. I am very keen to explore the possibility of both closed box and maybe transmissionline. I want to avoid ported cabinets, due to the problems of port noise. I figure that if I am going to eq the bass to get more out of the system, eliminating, or suppressing the extreme impedance rise at the resonant frequency of the driver will be highly beneficial. Transmissionline could be the way to go . . .
I am very aware that there is no proper equivalent of Thiele-Small for transmission line theory! Amazing that no-one has yet pinned it down! Truly Heath-Robinson I feel . . .
so my question is this. Why quarter wave . . . could eighth wave make a difference . . . It would be quite easy to build such a box, and not much bigger than the 6 litre cabinet of the LS3 5a.
And given that size is not necessarily important(!), why not half, or even full wave, (other than the sheer real-estate required, not to mention complication of design of such a long cabinet!)
forgive the ramble, any input very gratefully recieved, Gentle People!
Kindest regards,
ANdyP
I am about to launch into my latest project.
Some background. I have been using a pair of (loaned!) BBC LS3 5a speakers. I absolutely love them to bits, but am very wary of damaging them. The are as rare as rocking-horse-hens-teeth . . . . I always work at about 83dB(Fletcher-Munschen curves n all), so they are never strained. I desperately need to replace them, just for peace of mind! For those who dont know, they were designed by the BBC for use in OB trucks. They are very inefficient(80dB@1W@1m), are incredible for anything vocal, speech or singing, and possess bass far beyond the normal reach of a 6 litre sealed box, thanks to some clever crossover trickery. Effectively, there is a bass boost, or rather a gentle roll off against the rising response of the driver at the expense of efficiency. There is also an eq to cut the lump at @1kHz.
When I worked for Roger Quested in the 80s, it was obvious the advantages of a 3 inch softdome handling the all important vocal range - 350Hz to 3kHz5 or so. True, male vocals extend much lower, but it is the upper reaches that are so important. One of the reasons that I think I love the LS3 5a is that one driver runs all the way up to this crucial point - approx 3kHz, and integrates wonderfully with the tweeter. At Quested, we used to make a nearfield with 4 x 5 inch drivers running into a 1 inch softdome at approx 1kHz6. Cool!
With modern digital crossovers, this kind of design is really childsplay, especially with all the eq built in. I am about to inherit a really good analogue crossover to get the ball rolling. Mnay Many thanks Ruariri! You are a super star.
I have found a number of potential bass-mids, most of which are Old fashioned, 1 inch voice coil, low power, smooth response devices. None of the 3 inch voice coil units look any good on paper! lumpy response curves, early cone break-up, and high distortion. Not worth the power trade off. Nah. I am very keen to explore the possibility of both closed box and maybe transmissionline. I want to avoid ported cabinets, due to the problems of port noise. I figure that if I am going to eq the bass to get more out of the system, eliminating, or suppressing the extreme impedance rise at the resonant frequency of the driver will be highly beneficial. Transmissionline could be the way to go . . .
I am very aware that there is no proper equivalent of Thiele-Small for transmission line theory! Amazing that no-one has yet pinned it down! Truly Heath-Robinson I feel . . .
so my question is this. Why quarter wave . . . could eighth wave make a difference . . . It would be quite easy to build such a box, and not much bigger than the 6 litre cabinet of the LS3 5a.
And given that size is not necessarily important(!), why not half, or even full wave, (other than the sheer real-estate required, not to mention complication of design of such a long cabinet!)
forgive the ramble, any input very gratefully recieved, Gentle People!
Kindest regards,
ANdyP