[bernard991]

as I am still in the design stage of my OB project I want to work out the details best as possible via the group ... before I fire up the tools

as stated earlier I am thinking of a large-ish baffle maybe 18" x 48 or 50 " with a pair of 15" bass drivers and starting out with an 8" FR up top ...
I have read that these mostly roll off after 10-13K ,   would it be possible to incorporate a tweeter above to extract the highest octave without a sonic penalty ....transparency ?

would a guy need active like a Behr 2496 ...or could passive suffice ?
anyone done this ?
thoughts ...?
thanks
Bernard

[nullspace]

Hi Bernard --

I use a Fostex FT96H supertweeter rolled off with just a .68uf cap to fill in the top octave above my 8" fullrangers. I like it very much and find that it is definitely a sonic '+' for my system. I'll even go so far as to say that it helps smooth over some of the whizzer-related nasties, which in the last year I've become somewhat more sensitive to.

Regards,
John

[Michael V]

Bernard -

I use a Aurum Cantus G2Si ribbon tweeter above my B200's (run fullrange), with just a 1.5uf cap to the ribbons.  I can't recall exactly but I think it comes in around 12K.

The B200's are pretty extended though, especially with phase plugs.  It's a pretty good match on all accounts, even though these tweeters are a little too 'polite' for my tastes.

Regards
Michael

[bernard991]

thanks John & Mike

so the question is how well do the tweeters and FR drivers integrate ...?
would you say they are seamless or less so ?
I have been listening to Martin Logan stats this last little while , they have a wonderful mid / hi frequency clarity that seems 'right'...I hope I am not being 'hopelessly ' spoiled by this ...
because I want OB's but they have to be right too
regards B

[DanTheMan]

Correct me if I'm wrong here, but aren't the MLs already OB just with electrostatics?  Maybe they could be considered no B   I doubt you'll equal the MLs from the MR up through the treble.

[Luigi]

I also use the FT96H with a single cap, to add the top end to the OB B200s. Cant recall the cap value but crossover is around 9K.

They attach to the back side of the open baffle, so fire towards the front wall, ie, opposite direction to the B200s.

I have tried with and without the tweeters. I cant do without them. They add significantly to the staging and imaging as well as merely filling in the top end, in my view.

Luigi

[nodiak]

A while ago I tried a Scanspeak 9300 in a small waveguide (same as Zaph uses in his TMM design) with the 8" Hemp (whizzers removed, phase plugs added). Iirc used a .5 mH on Hemps and experimented with 2-4 uF caps on 9300. Worked well. I think the rise in Hemps upper range allowed the 90db tweeter to blend in ok.
Just ordered Neo3pdr's from GR Research to try this again.
Don

[Dmason]

I have used the Aurum Cantus 2i, and the Fostex 96T very well. The latter went well with the Fostex FE208E-Sigma as well, the AC ribbon, which I find abit bland.

Tone Tubby makes a wideband 8" now without the whizzer, and claims a tweeter can be brought in as high as something like 8.5kHz. Some may find even that is plenty of highs. I would absolutely try that driver, as it would guarantee success, as would the B200. B200 doesnt really need a tweeter at all. Spend the money on phase plugs for a much better driver, in both cases.

[Duke]

I have worked with the Tone Tubby 8" sans wizzer that Dmason mentions, and if you're going to add a tweeter anyway then I think this driver makes more sense than the version with the wizzer.

In my opinon this driver's response calls for some equalization, which may violate the spirit of "fullrange driver plus tweeter" but I think it's worth it.

Duke

[Dmason]

Duke,

 can you elaborate on the Hemp 8 response? On its tonal properties, now that your ears have been wined 'n dined on the good stuff, how do you like those? Rising response to 8.5kHz? Anyone with a hard disk front end can do the contouring without any trinkets in the way of the driver.

 I would like to purchase two of those, but I simply will not, until they publish some technical data for the sake of customer prospects. No data, no sale. that thing looks to me like a VERY good choice in non ALnico, non-spendy drivers, and likely has a mid Qts of .45, same as the FR8, we could I suppose consider the overall parameters are likely identical to it, sans whizzzz.

"if ever a whiz there was.." -Judy Garland put it succinctly.

Don't like those things, at all, but the presence band of the FR8, and indeed the bigger 10 & 12 with their nice magnets, is very, VERY colorful, and almost addictive.

I do not see how you could go wrong with the Tone Tubby 8.

[Duke]

Hi Dmason,

I can't find offhand the T/S parameters that I measured, but my recollection is that the wizzerless version has a slightly higher resonant frequency and therefore slightly higher efficiency.   

The response curve is similar to the wizzer'd version up to about 5 kHz, above which the response rolls off.   If you equalized with a notch filter, you could probably cross over at about 8.5 kHz.   

The copper shorting ring is a rare feature to find in a $120 driver, and I think this and the wizzer'd version are the least expensive wideband drivers with such a feature.  Flux modulation is most likely to rear its blurry head in a fullrange application.  I like the sound of this driver and don't know how much of that is due to the hemp cone and how much is due to the shorting ring, but it seems to do much better than average job maintaining articulation when pushed a bit.  I have some concerns about the small x-max; if used OB, I'd recommend a high-pass filter to keep the voice coil from going outside its linear region.

Duke

[Dmason]

Duke

I would suspect used OB, high passed @ ~200Hz, to relieve it of any lower register signal, would be very sweet indeed. Crossing @ 8.5kHz would then be easy, First Order... something similarly inexpensive, high quality, and known to work well would be the B&C D10 little Mylar diaphragm compression driver.

I want that driver, but not until Jason publishes some information. Jason?

[Duke]

Dmason,

I tried to reply to your PM but your inbox is full.

Anyway, I found the parameters that I measured on an UN-BROKEN-IN 8" Hemptone extended range driver (no wizzer):

Fs = 53 Hz
Qms = 2.70
Qes = .53
Qts = .45
Vas = 68.9 liters
Mms = 7.2 grams
Re = 6.3 ohms
Le = .11 mH
calculated 1-watt efficiency = 94.7 dB

With break-in, Qms will go up and Vas will go up while Fs will go down.  Efficiency will stay the same.

If these parameters conflict with the ones Hemptone later publishes, trust their numbers instead of mine.  I'm sure they're better at this than I am.

Duke

[nodiak]

Duke, that does look like a good hemp driver for this purpose. I like the notch filter idea. The fr hemp I have definitely still reaches high in the treble even with whizzers removed. I think the cd's and waveguide approach (like you use) could be a good idea for it too. I've only had 2 cd's, a low end titanium and the Radian used on 5208c coax's. The Radian was smooth, and I'd love to hear it or similar in the DDS Eng 1-90 (which I haven't experienced yet).
Don

[panomaniac]

I did much as Nodiak did.  Hemp FR8c in series with 0.6mH. Big ScanSpeak D3806 mid/tweeter with 5uF.  Worked just great, almost perfect blend. The D3806 blends well with paper woofers, BTW.

I'll be trying some paper cone tweeters in the weeks ahead to hear how well they work.   It's a good concept.