?
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?
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.
You're welcome.
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.
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.
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
/Erling
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
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
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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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.
LOL - yes ! that makes it plain easy !
Michael
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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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.
LOL - yes ! that makes it plain easy !
Michael
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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.
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.
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.
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.
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.
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.
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!
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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!
Likely to set off your rubber allergy, though.
Would make things easier, yes, but not any likely to happen
Michael
That's the 21" - enough punch down into the 30 Hz range....
Its been a while (almost a year) since we created the XO for this combo, and we did hear that it needed some adjustments. Currently we XO at 350 Hz and 1550 Hz. I think that the upper XO point will be shifted upwards a little bit, but 350 Hz will remain I guess.
Its been a while (almost a year) since we created the XO for this combo, and we did hear that it needed some adjustments. Currently we XO at 350 Hz and 1550 Hz. I think that the upper XO point will be shifted upwards a little bit, but 350 Hz will remain I guess.
We're interested in optimizing driver selection for 50 or 60dB SPL listening rather than the more typical design pattern of choosing drivers to hit 100+dB. Michael has a hypothesis going---which I subscribe to, based on the static friction data he posted a few pages back on this thread---that high Qms/low Rms/high Vas/low Mms drivers tend to play better at low SPLs since the cone moves more freely. Unless Michael's done a lot of measurements I haven't heard about, neither of us has enough data to assess the strength of the correlation. But we've both had good luck using the hypothesis to guide driver selection and, anecdotally, the tendency of low Qms/high Rms/low efficiency hi fi drivers to need to be turned up to play well suggests there's something going on in this direction.
I'm curious of your thoughts here as Seas drivers in your dipole are in the low Qms/high Rms category and the 21SW1600Nd is low Qms/high Rms by large driver standards.
Thanks. Why the 18G50 over the 18LX60? Just what you've used? I was favoring the 18LX60 since 1) the distortion figures are slightly lower, 2) low bass efficiency is slightly higher, 3) it's higher Qms/lower Rms, and 4) at least in the US the 18LX60 is about 15% cheaper. The 18G50 is 15% lower moving mass, 5% lower inductance, and the coil and gap on the 18G50 are larger though Beyma rates the two drivers to the same xmax. But it feels like net advantage to the 18LX60.
Yeah, I remember that theory of his now. I've usually looked for high Qms woofers, but ignored that parameter for midranges.
Low cone mass can result in breakup modes, which I think is important to aviod in the working range of the drivers. Thats why I have a fashion for rather heavy metal-cone midranges.
18LX60 might be even better, I haven't tested it so I dont know.
Low cone mass can result in breakup modes, which I think is important to aviod in the working range of the drivers. Thats why I have a fashion for rather heavy metal-cone midranges.
18LX60 might be even better, I haven't tested it so I dont know.
Yeah, more recently I also outlinde it here:
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-137.html#post2253222
and also illustrated with some simus here:
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-137.html#post2253401
and added some correction to my previous statments here:
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-137.html#post2254585
Though theory I think is watertight (LOL - if that ever can be said of any theory) bad thing is we stab in the dark taking Qms as a yard stick any further than I've outlined.
Possibly one more assumption can be made:
*If* we seek a low Qms speaker to perform well with respect to volocity indepenent friction – we have better chances to find them with spider and voice coil NOT fully vernted.
This is, because the low Qms indicates high friction – which does *not* violate quatlity per se – but once we have a lot of friction already, this friction *must be* velocity dependent to *not* violate quality.
So what is left as highly velocity dependent friction is all that pumps air through small cavities – meaning - all the mainstream veeery open driver constructions are most likely not our candidates from that point of view when they are of low Qms as well.
Thats not very intuitively, I know – and we have no *real* prove other than the "anecdotal" as well
Just take it as my 2 coins - for what ever its worth
Michael
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-137.html#post2253222
and also illustrated with some simus here:
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-137.html#post2253401
and added some correction to my previous statments here:
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-137.html#post2254585
Though theory I think is watertight (LOL - if that ever can be said of any theory) bad thing is we stab in the dark taking Qms as a yard stick any further than I've outlined.
Possibly one more assumption can be made:
*If* we seek a low Qms speaker to perform well with respect to volocity indepenent friction – we have better chances to find them with spider and voice coil NOT fully vernted.
This is, because the low Qms indicates high friction – which does *not* violate quatlity per se – but once we have a lot of friction already, this friction *must be* velocity dependent to *not* violate quality.
So what is left as highly velocity dependent friction is all that pumps air through small cavities – meaning - all the mainstream veeery open driver constructions are most likely not our candidates from that point of view when they are of low Qms as well.
Thats not very intuitively, I know – and we have no *real* prove other than the "anecdotal" as well
Just take it as my 2 coins - for what ever its worth
Michael
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I actually do not see this friction issue restricted to any special kind of speaker (not even to speakers alone).
Lets take the ribbons for example versus the usual dome tweeters. What is the main difference and what people think could made up for that – and then think along the lines of friction – ups ...
Michael
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There's another aspect of the low Rms thing to consider. Musical transients are basically delta functions within the driver's bandwidth, and the cone's ability to play them accurately depends on the power amp being able to flick it back and forth. In this situation all friction and inertia is bad since it reduces the motor's ability to obtain the desired cone movement (though presumably one wants a Cms of roughly 1/Mms so that the cone remains in the vicinity of critical damping). As Michael's observed, low Rms/high Qms drivers tend to be high efficiency and efficiency, in turn, correlated with both strong motors and low Mms. It seems to me this is an argument for construction styles typical of pro drivers and taking advantage of EQ in a digital crossover to flatten out the resulting SPL and phase wiggles.
It occurs to me Rms is a measure of velocity dependent friction whereas other forces on the driver tend to be proportional to both Mms and velocity. Hence the relation which matters for assessing a driver's performance in this area is probably that of Rms to Mms. That implies something like an SB17NRXC35 with an Mms of 11g and Rms of 0.44kg/s has twice the frictional effects as an 18G50E with 170g and 3.54kg/s. Hmm.
It occurs to me Rms is a measure of velocity dependent friction whereas other forces on the driver tend to be proportional to both Mms and velocity. Hence the relation which matters for assessing a driver's performance in this area is probably that of Rms to Mms. That implies something like an SB17NRXC35 with an Mms of 11g and Rms of 0.44kg/s has twice the frictional effects as an 18G50E with 170g and 3.54kg/s. Hmm.
Agree; I've measured 15dB rises in distortion as cones go into breakup. Some modern coated cones are pretty good in this regard, though.
Zaph's argument is it's distortion; see the summary section here.
Have you seen something like this before?
An externally hosted image should be here but it was not working when we last tested it.
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!
Hi Stig.
Those are some marvelous looking speakers your friend now has - I am jealous.
Although the Fireface 800 is significantly above my budget - it's currently pretty close to the value of my entire audio system - I am still curious. What kind of computing power do you need for your XO and EQ filters? Would it be viable (pun not intended) to run them on something like a VIA C7 (single-core, 1Ghz) computer? Or a similarly weak older computer system one might have lying around the house?