My open baffle dipole with Beyma TPL-150

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Originally Posted by mige0

The "long throw" type are the 18" Selenium 18WS600 for example with a "linear excursion range" gap-coil of 20mm versus roughly half of that for the 15" Selenium 15PW5.

....

?

According to the datasheet of 18WS600:

Xmax (max. excursion (peak) with 10% distortion) . . . 3.8 (0.15) mm (in)

3.8 mm shouldn't be considered long throw. Or did I miss something?

[twest820]

Originally Posted by mige0

The "long throw" type are the 18" Selenium 18WS600 for example with a "linear excursion range" gap-coil of 20mm versus roughly half of that for the 15" Selenium 15PW5.

That sounds like more xlim (displacement to damage) rather than xmax (Selenium gives displacement to 10% THD, though many manufacturers use some sort of geometric xmax as their definition of the driver's linear range). The Selenium datasheets I have list xmaxes of 2.3, 2.0, 5.7, and 3.8mm for the 6W4P, 8W4P, 15PW5, and 18WS600 respectively. I've looked at most 18s made and nearly all of them with xmax approaching 10mm or more are high Rms. Selenium's WPU1805-X is an unusual 18; 6.25mm xmax and a Rms of "only" 1.45kg/s. The suspension's pretty stiff though.

Originally Posted by mige0

Thanks for the paper

You're welcome.

Originally Posted by mige0

I did not experience problems on higher SPL though, did you ?

I have 8W4Ps and am dissatisfied with the distortion below 450Hz at typical listening levels. Tinkering with the equalization's helped, but I'm inclined to try a couple other woofers and see if I can find something that's a better fit for a three or four way system. Current leader's a nude SB17NRXC35-8 with the flange milled down to raise the dipole peak.

Originally Posted by mige0

Did you check Doppler intermodulation to keep low with appropriate XO ?

I'm not set up to measure phase distortion, but with a nude two way I'd say it is what it is and one just lives with that. Three ways and four ways mitigate phase modulation just like they mitigate other excursion related problems. I'm curious to see what's required to get good bass distortion if one has modest SPL requirements; it'd be handy if a nude 18WS600 sufficed.

[skorpion]

Regarding OB and Baffles, Rudolf has translated his very up to date German summary 'Open Baffle Dipoles - How they work, and how to use them well' into English. This is recommended reading with Simulations and interesting Examples! You find the paper on his web: Offene Schallwand (OB) , in the Download area.

/Erling

[J.R.Freeman]

Good morning all,

Thank you Cport, Erik, and Keyser for your responses. Fascinating stuff - I'll be watching this thread. Those Excel drivers are just gorgeous by the way, and though I know this is just aesthetics, I like that these free-air designs show off the back of the drivers as well.

Jim

[mige0]

18WS600 :
Guys, thanks for correcting me - what a pity - I took the wrong numbers to calculate overhung in some hurry.

Selenium's WPU1805-X sadly seems to be discontinued (but I first go with the bunch of 15" I have anyway).

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Originally Posted by twest820

I have 8W4Ps and am dissatisfied with the distortion below 450Hz at typical listening levels.

Ahh, haven't listened that way - I like to augment the 8" a in that department already.
Interested what you come up with. Stig Erik's solution of multiple speakers is a good way as well.
I love the Selenium 8" for its "responsiveness" - but as Lynn has obviously observed with the Dynaudio's he is happy with (center speaker) - good "dynamics" is not restricted to high Qms speakers, though IMO, its more likely that you find 'em there - or maybe better put - its more unlikely that you do *not* find them there.

Originally Posted by twest820

I'm not set up to measure phase distortion, but with a nude two way I'd say it is what it is and one just lives with that.

LOL - yes ! that makes it plain easy !

Michael

[twest820]

Originally Posted by mige0

Selenium's WPU1805-X sadly seems to be discontinued.

The WPU1805 is discontinued. So far as I know the WPU1805-X remains in production; I talked to Parts Express about special ordering WPU1805-Xs a few months back and they quoted USD 200 plus shipping per driver.

Originally Posted by mige0

I love the Selenium 8" for its "responsiveness"

Same here. Though I wonder how much high Qms/low Rms matters as the amount of dipole compensation is increased. For example, a reasonable starting point for a three way nude dipole is Neo3 from 2-20kHz, five incher or compact six incher from 200Hz-2kHz, and an 18 from 20-200Hz. If equalized flat 18 will be operating with around 8.5dB of boost at the top of its passband, so it sees an average signal level somewhere close 20dB "louder" than the actual listening level. This leads me to suspect accepting a higher Rms but longer excursion driver might generally be wise, though obviously the distortion characteristics of the driver itself are rather important. Selenium's 18SWS1100 is one of the more interesting drivers if you start thinking along these lines. Rms is still pretty low for an 18 at 2.7 kg/s, the 9.3mm xmax is higher than usual, and the price is still on the lower end of the range for 18s.

Originally Posted by mige0

Interested what you come up with. Stig Erik's solution of multiple speakers is a good way as well.

Me too. I'm hoping I can get satisfactory results with something close to that three way starting point I just described. I'm considering a few options with push/pull driver pairs but not really coming up with anything I like; main thing I need to do is to actually get a better midrange candidate and figure out how low it'll go.

Originally Posted by mige0

LOL - yes ! that makes it plain easy !

Or at least it gives me a lot of time to think about what sort of boards I want to do for tri and quadamping.

[mige0]

Good catch on the 18WS1100 but price already comes close to Beyma's when I have to add shipping to Europe.
Beyma besides Selenium being the second brand that consistently aims after high Rms - as I can tell.

Michael

[twest820]

Most Beymas I've looked at are unexceptional with respect to low Rms, though they do offer a few decent 18s around the 18SWS1100 price point. The 18G40 and 18LX60 are among the better alternatives to the 18WS600 and 18SWS1100 which I've come across.

Both SB Acoustics and Scan Speak have strong lineups of low Rms drivers in hi fi sizes useful for dipole mids. Likely to set off your rubber allergy, though.

[StigErik]

Why do you want low Rms?

I can recommend Beyma 18G50 by the way, very nice and not too expensive, worked great in open baffle.

[StigErik]

Have you seen something like this before?





Oh yes, this is the best version if my dipoles when they still had baffles. My good friend Lars is the owner of these. In fact - he was the one that got me into building dipoles in the first place.

They have integrated Class-D amps mounted inside the woofer U-baffle. All that's needed in addition to these active speakers is a multichannel audio interface (like my RME Fireface, you see it lying on the floor there), and a computer to run the XO and EQ filters. Very neat setup indeed, and whow... it sounds great!