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Offline Pete_w  
#1 Posted : 15 March 2020 14:29:53(UTC)
Pete_w


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Hi All

I've just swapped my Martin Logans - Bye-bye Ascents, hello Prodigy. Prodigy was ML's top-of-the-range speaker 15-20 years ago, and these have allegedly recently been re-panelled. Haven't got the placement/bass sorted out yet, but the panel does a lot of the work and they're sounding nice already - I've just dropped them in more or less where the Ascents came out.

However, I may not able to sort the bass out in their current form, and this is where I'll need help. Each prodigy has 2 x 10" bass drivers - one at the front and one at the back. They came out of the factory with an alloy cone at the front and a paper cone at the back. The front cone does the bass "proper", the rear cone appears to be used to cancel some of the rear radiation from the front one. (Martin reviewed it all for HFN 20 years ago and seemed to like it...). Each is in its own sealed compartment.

The rear cones on mine are original but the front ones are clearly polypropylene, so they've been "done" at some point. Googling suggests that alloy-coned woofers weren't one of Scanspeak's brighter ideas in terms of reliability, at least with the glues available circa-2000.

The internet hive-mind suggests that ML have a suggested replacement driver (Scanspeak Classic 25W/8565-00) so I've mailed them to confirm, so I get the correct answer from the horse's mouth. In the meantime, if I get a set of US-sized Allen keys tomorrow (rolls eyes) I can drop out one of the existing polypropylene units and see if it has a name or number on it.

Would I then be right in assuming that if we can find some Thiele-Small parameters for the polypropylene units, you guys will be able to advise as to whether they're "near enough" or whether I just have to stump up the £400 for a pair of new drivers...?

Or is the answer always going to be "buy the scanspeak drivers"? :-)

Thanks!
Pete


Offline Pete_w  
#2 Posted : 16 March 2020 14:47:12(UTC)
Pete_w


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So, I think, as promised in the title, that I'm a completely numpty. I just dropped one of the drivers out, and they're scanspeak 25W/8567-01. Which appears to be the original factory-fit alloy woofer. So is it really the case that I can't tell alloy and plastic cones apart? Doh.

They are both chuffing and hissing when gently pushed, which suggests that at least some new lengths of sealing gasket may well be required....

Offline Simon Briggs  
#3 Posted : 17 March 2020 17:08:38(UTC)
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Originally Posted by: Pete_w Go to Quoted Post
So, I think, as promised in the title, that I'm a completely numpty. I just dropped one of the drivers out, and they're scanspeak 25W/8567-01. Which appears to be the original factory-fit alloy woofer. So is it really the case that I can't tell alloy and plastic cones apart? Doh.

They are both chuffing and hissing when gently pushed, which suggests that at least some new lengths of sealing gasket may well be required....



Just a thought?

If they are chuffing a possibility it could be the voice coil rubbing? try rotating the drivers through 180 degrees and refit them, may take a day or so to settle down
Offline Pete_w  
#4 Posted : 18 March 2020 16:27:42(UTC)
Pete_w


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Thanks, Simon. No, what I meant by chuffing was that when I (gently!) push the woofers in and out, then (a) they go in and out without much obvious air-spring and (b) I can hear air escaping and re-entering through the gaps.

You design speakers, I don't, so I don't know how damaging air leaks are in a bass system (the crossover up and away from it is centred at about 250Hz) which is intended to be sealed? I like fast bass :-)

I presume a few meters of gasket would be a sensible buy and work my way round all 4 woofers? What's in there (from new, I presume) is looking very flat and tired. The bass bin is leaking as well through its binding posts, I need to drop the back panel off and tighten those up - if they're the same ones that were used on my Ascents then they should have nuts on the inside.

At least these drivers are nicely attached - allen bolts with captive nuts. One way that they clearly made the Ascent cheaper was to just use self-tappers straight into the chipboard...

Full marks to Martin Logan for tech support by the way - I dropped thgem a mail in the middle of a pandemic asking how to get the back panel off a 20 year old speaker, I got a mail back with a service manual and helpful advice just a day later, and an apology for the delay in replying! There's more than a few UK companies could learn a bit from that!
Offline Martin Colloms  
#5 Posted : 26 March 2020 17:33:14(UTC)
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at risk of boring us all :

The ML electrostatic upper panel is a dipole, directional where the rear sound radiation is out of phase with the front and thus has a characteristic sound in the room.

A box type woofer is omnidirectional ,ie spherical.

Superimposing these two in one loudspeaker is awkward and their sound fields fight.

ML designed a double box woofer where the rear radiation is partly out of phase with the front, more closely aligning with the dipole panel above, and with a more natural sound, but adding power bass.

Martin
Offline Pete_w  
#6 Posted : 26 March 2020 19:54:05(UTC)
Pete_w


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Originally Posted by: Martin Colloms Go to Quoted Post

ML designed a double box woofer where the rear radiation is partly out of phase with the front, more closely aligning with the dipole panel above, and with a more natural sound, but adding power bass.

Martin


Which is the one you tested 20 years ago, and the one I've just bought. Well, probably not the *same* ones, unless you happen to keep a record of serial numbers? :-). I can't see that ML can have sold that many Prodigies in this country, it's not a particularly friendly design for UK rooms and I've never seen another pair offered secondhand (whereas the Ascents, that I had for years, tend to turn up on ebay every month). We're building a room for music and cinema so we don't much care what they look like...

Lockdown means I'm getting almost no chance to listen - 24/7 care for disabled child takes priority - but what I have briefly heard suggests grace, pace and bass, to paraphrase the old Jaguar car slogan. And it does do dialogue of children's movies very clearly!

Got an interesting speaker cable with 'em - I'd never heard of Acoustic Zen. Californian, I believe. Well worth a listen, I think. Clearly not just cheap mains cable with a fancy jacket on it. Having just reterminated it (aaargh, me fingers!) it's far from off-the-shelf. I can't vouch for the individual conductors being 6n monocrystalline copper, or whatever, but my battered hands will vouch for the bass & treble halves (it's a bi-wire cable) each being of different construction, with each being made up of several (a dozen or so) individually insulated conductors of varying diameters. The bass had mostly thick ones with a few very thin ones in the mix, all seperately insulated, while the treble side probably has less copper overall and has individually insulated conductors laid round a fine twisted copper core. All very interesting, makes for great fun when stripping it (NOT!) and certainly not off-the-shelf...

Pete




Offline Pete_w  
#7 Posted : 30 March 2020 19:51:51(UTC)
Pete_w


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Well, I got an hour or two to play with the new toys. I'm clearly going to have to dance my way around the sitting room with them to get some optimal performance, but there's very clear signs of promise.

The bass is by some margin the best I've had in my room; that's not necessarily saying a whole lot, I know, but... With past speakers, walking around the room has yielded plenty of ill-defined bass, but actually getting it to arrive solidly at the sofa has always been problematic. ML's somewhat complex dual-woofer arrangement, that Martin mentioned above, does indeed seem to be doing something useful. The actual forward-facing woofers are still 10" units, the same as in my previous MLs, but what they're delivering is significantly improved - there's real depth, there's clear note differentiation and - based on playing some "Zumba for Kids" (!) from Youtube this afternoon - there's real Slam when the source material has been (over-)engineered for it. Bass is playing tunes, without a whole lot of effort at room placement. It should only get better from here.

The panels are glorious. With a crossover down at a nominal 250Hz, the tonality is gorgeous. Slightly warm and honeyed, at least based on what I've played so far, but that doesn't seem to be a trick pulled at the expense of the treble. Definitely on the warm side of neutral; whether this is an artefact of the speaker in general or of the Acoustic Zen cable, I can't currently say, having stripped the terminations off of my VDH cables in order to terminate the AZ! So it ain't a monitor, but it is lovely. And the layers of detail - singers have lips and teeth and they breathe, and all those sorts of cliches. I'm at a bit of a loss as to why it's much better in this respect than the Ascent was - after all, the panel is the panel, albeit the Prodigy panel is 25% larger (4' high, but 16" wide rather than 12"). I can only assume that it's being held more rigidly, and that more money was spent on a better and more transparent cross-over. But "difficult" voices - Cowboy Junkies' Margo Timmons, or Springsteen, for example - are portrayed very nicely indeed.

Pace and timing, as Martin reported 20 years ago, are good. Dynamics are excellent, they go extremely loud with no sense of strain. Going old-school, Oxygene IV is just a hilarious romp!

So that was the good bits.

I haven't got the positioning right yet; firing straight down the room, I get pace and timing and excitement and a hole in the middle. Toed in a bit, I get lovely spread and great delicacy but a sense of wanting to keep turning it up to wake 'em up some more.

Anyway, promising :-). Have to wait til lockdown is over now until I can find a "dance partner" to help me move them....





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