Hi - I thought I should probably start a new thread instead of having it tacked on to a thread with a misleading subject.

I have built Big Betsy style open baffles using the Lii Audio F15 full-range driver mounted on 40mm bamboo baffles.

I have ordered the Aurum Cantus AST2560 Aero Striction Tweeters which can be seen here: www.parts-express.com/Aurum-Cantus-AST2560-Aero-Striction-Tweeter-276-440?quantity=1&custcol1=Aurum%20Cantus%20AST2560%20Aero%20Striction%20Tweeter&custcol_ava_item=276-440&custcol_ava_incomeaccount=General&custcol_ava_upccode=844632089312&custcol_ava_pickup=F&custcol_disableshopping=F

and I would appreciate any advice regarding how to mount them on the baffle. The baffle is 40mm thick - should the tweeters be front or rear mounted, flush or inset, radius of rounding router bit, etc. Or is it just a matter of experimentation to see what sounds best?

Also I would like to order the capacitors I will need for a range of crossover frequencies - say 6khz, 7khz, 8khz and 9 khz

Can anyone recommend a good quality capacitor, and the values needed for the frequencies I would like to try?

What considerations do I need to make for the fact that the full-range (Lii F15) drivers I am pairing the tweeters with, are 8ohm and the tweeters are 4 ohm?

Any and all suggestions appreciated


Cheers,
Steve

Just a quick response. Although the Lii F15 driver that you are using is rated as 8 ohms (7 ohms DC resistance) it like many speakers has a rising impedance with frequency and is about 15ohms at the frequencies that you intend to crossover from. Its frequency response is flat to 7 khz and drops a few db until it falls off a cliff at about 12k. So I suggest that you run it full range and use your super-tweeter for above that frequency. The kind of amplifier that you are using is important. With a valve amp the Lii by itself might sound a bit 'toppy' and a 4ohm tweeter whilst probably not ideal might work okay. With a ss amp the Lii won't have this rising response but the 4ohm tweeter will draw more current and therefore be subjectively louder. Because it is a ribbon tweeter the impedance is a flat 4 ohms throughout the operating range. Appropriate crossover values can be obtained from an online calculator (DIYaudioandvideo) and for 6khz this is about 6uf for a first order crossover and a 4ohm tweeter. A 9khz first order crossover needs a 4.4uf capacitor. I suggest that you stick to a first order crossover for the tweeter (only) and consider raising the crossover point to 12khz which all other things being equal would require a 3.3 uf capacitor. However all things aren't equal (valve or ss) and there are some unknowns. For example whilst the Aurum Cantus has an efficiency of 95db there is no information on the Lii. However I suspect that it is also in the high 90s so the main problem is the low tweeter impedance. I suggest that you start with a 1uf capacitor on a valve amp and work up from there until you get the balance of treble that you like. If you start with a 3uf capacitor and this sounds too bright, you could consider adding a 2 or 3 ohm capacitor in series. So I suggest a bit of trial and error using 1,2 or 3 uf capacitors. Ideally the tweeter should be inset and as close to the Lii as possible. However from your photo it doesn't look like the Lii is inset and if so I wouldn't bother with the tweeter. You might like to consider putting a layer of felt around both if they are flush. Mounting the from behind is a sin.

Great info thanks Peter! The amp is a Willsenton R8 valve amp, and the Lii Audio F15 is supposedly rated at 97db efficiency ( www.lii-audio.com/product/recommended-15-full-range-speaker-driver-for-music-loudspeaker-with-tube-amplifier-f-15-in-pair/ ). Thanks for the online calculator link, and your numerous suggestions. Would you recommend a particular brand of capacitor, or is your garden variety Jaycar unit good enough? Is the felt to absorb reflections? Your last sentence is a teaser - are you saying 'Mounting THEM from behind' or 'Mounting the tweeter from behind'?
Cheers
Steve

No mounting of the tweeter from behind! Strange that all drivers were mounted from behind until the 1970s. I'll pm you with some capacitor suggestions but I wouldn't splash out on expensive stuff until you have established an optimum value. I'll pm you with a remedy that doesn't include Jaycar.

Thanks so much Peter!

Peter, I have a Deqx DSP/DAC which I use mainly for crossover and time delay correction for the Lii full-range driver and the subs. I could also use it for a crossover to the tweeter at from 48 to 300 db/octave, either linear phase, LinkwitzRiley or Butterworth, if that's any help?