Tweeters and crossover for ScanSpeak 18W/8544

Looks like one of the easier flatter Scan 18W woofers, and very low inductance which is a help. Seems to be 89dB loudness.

Quite flat, just needing a breakup notch at 5kHz, I reckon. Kevlar is a bit notorious for nasty breakups.

Around 1.5mH bass coil, and a series LCR notch in the shunt after that. Maybe 5uF, 2R and 0.2mH.

You should try some ideas out in Software | Visaton using the similar W 170 S - 8 Ohm | Visaton and typical G 20 SC - 8 Ohm | Visaton.

Try out this circuit too: CA18RLY/22TAF-G

The 18R + 0.47uF/1.5mH tank notch will just need dropping from 7kHz to 5kHz in my guess. So maybe 0.68uF, but it does little harm to be a bit higher.

Just how it works, but once you have one drivers curve defined, the other one follows, so you can mix and match similar designs, IMO:

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Level adjustments on tweeters is easy.
 
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Rallen

Member
2010-06-09 4:48 pm
Thank you for your thorough answer - it is highly appreciated.
Being all new in this world, theres a lot of terms in your answer that I need to research before understanding it fully, and that itself is a great inspiration for further reading.

Can you think of any specific tweeters, that you think will be a good match for the woofer? Would that just be G 20 SC - 8 Ohm?
 
I think Yoda the Jedi said "Do, or not Do. Not try!"

Which means it is best to just get on with it! Technique will follow.

Here are two types of notch filter, this from Goran aka gornir of Audio Excite:

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I used one in this slightly complicated experiment. You could probably lose the second half of the bass section:

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All seemed to line up:

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Tweeters are a matter of taste, IMO. But you probably want a 1" 90dB type since the woofer is loud:

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deonaudio's R3004/662000 look splendid. :cool:
 
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I'd be very wary of a simple bass coil on a 6" Kevlar driver.

Lynn Olson said:
At present, though, even the best Kevlar, carbon-fiber, or aluminum cones show at least one high-Q peak at the top of the working range, requiring a sharp crossover, a notch filter, or both to control the peak. Unfortunately, this peak usually falls in a region between 3 and 5 kHz, right where the ear is most sensitive to resonant coloration.

Most audiophiles and magazine reviewers are unaware of the sonic signature of Kevlar or carbon-fiber resonance, misidentifying it as "amplifier sensitivity," "room sensitivity," or other problems that point away from the real culprit. Since few reviewers have auditioned the raw, unmodified sound of commonly-used drivers, they can’t evaluate how much "Kevlar sound," or "aluminum sound," remains as a residue in the finished design. It is the task of the designer to skillfully manage the crossover and cabinet profile to minimize the driver coloration. Despite advertising claims or the opinions of nationally famous reviewers, the characteristic signature of a driver can never be removed completely.

When working with rigid-cone drivers, there are some hard choices to make: if you lower the crossover frequency to minimize driver coloration, tweeter IM distortion skyrockets, resulting in raspy, distorted high frequencies at mid-to-high listening levels; if you raise the crossover frequency to improve the sound of the tweeter, the rigid-driver breakup creeps in, resulting in a forward, aggressive sound at moderate listening levels, and complete breakup at high levels. (Unlike paper cones, Kevlar, metal, and carbon fibers do not go into gradual breakup.) With the drivers we have today, the best all-around compromise is a 2nd, 3rd, or 4th-order (12-24dB/Oct.) crossover with an additional notch filter tuned to remove the most significant HF resonance of the midbass driver.

I should add, by the way, that I like Kevlar and aluminum drivers very much ... but no question about it, they are very difficult drivers to work with, with strong resonant signatures that must be controlled acoustically and electrically.
The Art of Speaker Design, Part II

B&W did this on their Kevlar 6" 685, which is 1.35mH bass and 4.7uF tweeter, positive polarity. B&W Group North America Service & Support - Home

The smaller 686 gets a scathing review: B&W 686 S2 Review

Life is easier with the old Vifa P17WJ-00-08 polycones: Vifa P17WJ-00-08 Woofer

I've heard some B&W Kevlar, and I don't like them. Breakup is very audible. But most of it is fixable with a 5kHz notch, I reckon.
 
Some Kevlar is rather well behaved. The HiVi F6 for example, requires a notch at 1kHz for a resonance, but the rolloff can be hit with a standard second order and sound supreme.

I know a lot will have a dip and peak higher that is nasty, but not all do.

The other bit of info, is that the 8544 had a treated foam surround, and the breakup was minimized slightly due to this. I think the cone may have been coated by a clear-coat as well for some damping.

Not all Kevlar drivers are created equal.

Later,
Wolf
 

Rallen

Member
2010-06-09 4:48 pm
Thank you for all the inputs. I definitely have some reading in front of me ;-)

To elaborate a little more, I stumbled upon a pair of Carlsson OA51 speakers some months ago. After realizing the fitted woofers werent the original ones and that the tweeter sounded a little of, I ended up buying new units (Scanspeak 8545 and Vifa D25AG) along with new resistors for the crossover.

This inspired my interest for experimenting with speakers and has led me to buy a finished pair of diy speakers, fitted with the mentioned 8544 woofers, Dali Hybrid tweeters (the ones from Dali 700/710/810) and a crossover inspired by Troels Gravesens CSM. I am planning to use these as basis for experimenting with different DIY setups. I haven't received (and therefore not heard..) the speakers yet, but I dont have biggest faith in the Dali Hybrid tweeters, so replacing the tweeters seemed like a reasonable place to start.

I might end up selling the woofers as well, and start looking for another woofer/tweeter setup where I can reuse parts of the crossover. The cabinet leaves space for additional units, so theres a lot of possibilities :)

Once again - thanks for your great inspiration.
 
I'm a bit confused here, Rallen. :confused:

You have a lot of drivers:

18W/8544
18W/8545 maybe a K00 version
Whatever woofer and tweeter was in the modified Carlsson OA51
Vifa D25AG aluminium tweeter
The Dali hybrid cone and ribbon tweeter

Two crossovers:

One based loosely on the Troels Gravesen CSM: Compact-Studio-Monitor

Which is an 18W/8545-XXX, R2604-832000 design.

And whatever was in the modified Carlsson

I also waded through Troels' Dali renovation: Dali 800 renovation

I thought Troels could have done a very different job on the Dali, which admittedly had problems. But I don't know why he swapped out the hybrid tweeter for an R2604-832000 at all.

I don't know where to start, and I doubt you can, till you listen to the new CSM 8544 clone with the Dali hybrid tweeter!

But I do notice the 8544 and whatever 8545 you have are very similar parameters for reflex. And you could probably modify the CSM crossover easily enough to be more suitable for an 8544. 15R and 1uF tank across the 1mH coil might do the job for a 5kHz notch, but I'd model it. The R2604-832000 tweeter is almost identical to the Vifa XT25TG30-04, and might get you into some good projects.

But I wouldn't sell anything yet, for sure. These are top woofers!
 

Rallen

Member
2010-06-09 4:48 pm
Sorry for confusing you. Reading my previous replies, I kinda get what you mean :D

The Carlsson OA51 were just what inspired me to play around with different woofer/tweeter setups. Those ones are now finished as "original" OA51.2.

--

New project are the DIY speakers I have just bought, which are based on the CSM project but using a 8544 woofer, Dali Hybrid tweeters and a slightly modified crossover. I will definitely try them for some time as they are before figuring out what to do with them..

Since I don't have the biggest expectations for the sound of the Dali Hybrid speaker I figured it would be good starting point to replace them. Especially since I could probably get a good price for them - there doesn't seem to be too many on the market. Same thing with the 8544 really - if I could sell them and get 8545 for about the same price, that might be 2 free "upgrades".. Hmm :confused: