FoL1 has been running a mostly free-to-him bitza system culminating in a rather nice pair of Wharfedale Super Lintons that seem to date from 1968 and was very happy until his 2 year-old got very interested in one of the woofers and damaged it beyond recovery. The damaged unit is marked as a PDC 1 and is 8" dia.
He’s just been given a pair of 8" Wharfedale drivers with whizzer cones labeled Super 8 / RS / DD and would like to use them in place of the originals - he’s looking for a steer on where to find advice / direction on crossover design / values.
Does anyone here have knowledge of these drivers, or can you recommend a good resource for modelling a suitable crossover circuit? I should say he’s done some research and is looking to keep the original tweeters in use rather than relying fully on the whizzers for HF.
Just reading Troels Gravesen - he suggests that removing the whizzers and using a 4th order crossover at 3k might get the best out of them, otherwise there’s a lot of crazy above 3k with the whizzers operative… Does that sound credible?
Troels Gravesen has been around a long time and has enough of a technical approach that it’s worth paying attention to what he says.
It’d be worth checking out the surrounds of these drivers. If they’re rubberised fabric then the rubber can be prone to perishing and falling away as dust, making the surrounds porous. I once re-sealed some (not on these 8" drivers) with a thin layer of diluted water-based latex glue which seemed to work OK.
Thanks Graeme, I’ll get him to have a careful look at the surrounds and see if they look dusty or porous. He’s a composites technician with Airbus so he should be able to have a decent go at re-sealing if that’s needed.
I’ve found any number of crossover calculators online and a range of different network designs - are any better / worse or are the ones Google offers pretty much all the same?
They aren’t, sadly. The old one is a 4 ohm, the replacement is marked as “10 - 15 Ohms”. If they were the same, I suppose the original crossovers would have been a good starting point.
That could be a bit of a challenge, although anything is possible if you’re prepared to sacrifice some sensitivity. A better approach might be to use a matching transformer. It doesn’t need to be an isolator - an autotransformer would do. A 2:1 ratio would transform 16ohms to 4ohms. So if you could find a couple of reclaimed output transformers (one for each speaker) which have 4ohm and 15ohm/16ohm secondary tappings then you could try putting the replacement speaker across 0-16ohm and drive it from the crossover across 0-4ohm. The electrical impedance shouldn’t then be too far adrift. Keep the 2-year old away from the primary terminals on the transformer though. There might be rather a lot of volts on them.
I’m no expert but another complication (and this would be true even if the electrical impedances matched) could be that the new driver and old driver might not interact the same way with the speaker cabinet. More sophisticated crossovers can be designed to counteract awkward driver/cabinet interactions. If the original crossover did this then it might not work so well with the replacement driver. The devil will be in the detail though and I’m already out of my depth …
Me too! Looking on diyaudioandvideo,com gave me some hope that starting from scratch would work though - here’s an example of what their calculator gives (and many other calculators are also available):
Does that assume that the two drivers are equally sensitive (not sure if that should be dB/V or dB/W) at the crossover frequency ? Does it have anything to say about the limits on the inductors’ internal resistances ?
I suspect it does, but we don’t have any data yet on driver sensitivity. Will search on the driver identifiers and see if that pops up somewhere. I’ve assumed that getting the crossover behaviour about right would be stage 1, followed by stage 2 of adjusting levels with a resistor or bridge… but I’m getting way outside any form of comfort zone or actual knowledge here.
The other search I know FoL has started is whether anyone else has already done this conversion on a pair of original Super Lintons. That may yet yield fruit.
