Hivi B3S + Foster Ribbon Tweeter in a TL

[Westy37]

Firstly I should justify posting this here seeing as my title clearly indicates the use of some sort of crossover! I figure that the people who frequent this sub-forum may be better informed as to using supertweeters / very high crossover points to augment wideband/extended range speakers that don't quite cut it in the treble deparment.

Basically I'm looking at building a small TL for nearfield listenign at a computer. I will be using the hivi BS3 and a Foster Ribbon as I have these on hand. I'll use Zaph's filter to deal with the 8khz peak and address baffle step compensation (baffle width of Zaph's and the alternate design are practically identical).

Enclosure Plans - u-B3N (in Italian, use google translate or similar application)

Hivi B3S - http://www.parts-express.com/pdf/297-427.pdf

Foster Ribbon - http://www.allenorgan.com/forsale/fosterWithFacePlate.pdf

The B3S performance above about 10khz gets pretty shakey so I'm planning on passively crossing over to the ribbon somehwere around here. Any advice on component values to achieve this would be greatly appreciated. I'm a bit of a beginner regarding speaker design so diagrams of how to implement this would help A LOT!

Depending on how these end up sounding I'll consider crossing them actively to a 8" or 10" sub. I understand that Zaph condemns the use of these drivers without a sub but at the low level, nearfield listening, in the small room they'll be used I might be able to get away with it.

Cheers, Westy

 

[croat47]

The B3S rated at 81dB and the Foster at 92 dB? That's a lot of padding, isn't it? Why not a 3 or 4" Fostex like one of planet10's designs and you can add the Foster or some other ribbon if the HF is disappointing? I think there is a member here who does that on an small OB and is happy.

 

[Westy37]

For this build it's all about utilizing what I've already got lying around. That happens to be, a pair of hivi BS3 a pair of foster ribbons (although they're apparently not true ribbons) and some larger 8, 10 and 12 inch drivers to play with if I feel it needs support in the bass department.

Would it be detrimental to the sound quality to attenuate the tweeter so much? Is this just achieved using series resistors?

 

[poldus]

I have been using those tweeters for years and they hard to beat for the price, but you do need the faceplate though. I find their sparkle and clarity in the highest octaves quite addictive.
I would say experiment with a single capacitor in the 4.7 to 2u range and see what you like best. With 6.8u you are pushing things too low but, depending on the application, may even work for you.

 

[Westy37]

Thanks for the suggestion there poldus, and I'm glad to hear that you enjoy the tweeter. I don't have the faceplate but figure if I rear mount the tweeter then I can experiment with different shaped lenses/mini horns by using a router roundover bit and essentially making my own faceplate in the speaker baffle.

Should I also be rolling the B3S off using a small inductor? Otherwise both drivers will be playing at the same frequencies and it will result in a peak as I understand it. I could be wrong here.

 

[poldus]

Indeed, you may want to low pass the HiVi. I know I would, and pretty low too, but you have to experiment with what sounds best to you in your room. Trying different values and listening for differences is big fun, as long as it does not become obsessive, and it often does!

 

[Westy37]

I have a related, but different question. In making these speakers I aim to get them on axis vertically (namely at my ear height when sitting at my desk). To do so I need to raise the height of the speakers, spikes will get me an extra 25mm but is it feasible to move the driver further towards the TOP of the baffle or will this ruin the transmission line design? Really I need to get the driver another 75-100mm further up. Would anyone be able to model this difference for me?

I would appreciate any responses, Cheers.