Reverse engineering the SL Pluto

[tomchr]

Hi,

I'm rather intrigued by Linkwitz' Pluto omni speakers. I'm trying to reverse engineer them as I would like to replace the Peerless drivers he's using with some Tangband W5-1611SA (because I have the Tangbands handy).

At first glance, the Pluto looks like a sealed enclosure speaker. So armed with an enclosure calculator and the datasheet for the Peerless 830873, I arrive at a box volume of 3.53 liter.

SL states that the pipe is 4" (10.16 mm) ID, 28.5" (724 mm) long. That's a volume of 5.87 liter.

So playing with the enclosure calculator some more, I arrive at a Qtc = 0.60 for the Pluto as built.

So if I am to build a Pluto-like speaker that fits the Tangband W5-1611SA, would it be reasonable to plug the values above into the calculator and use that as a starting point? Or am I barking up the wrong tree here? I'm not quite sure that my initial assumption of the Pluto being a box speaker is completely valid and would appreciate some input from the more experienced speaker builders here.

~Tom

[rob g]

You need to do some reading on SL's website!
The speaker has to be active to work properly, or be prepared to build an inefficient power sapping passive crossover to marry the drivers if you plan to go passive. Then with passive you need a LOT of power so forget tubes/valves.

The speaker is a closed box design. It is actively equalized to produce more bass in the low end than would be expected from a small bass mid.
For this purpose you need a very long throw low distortion drive unit.

Pluto uses a low crossover point unsuitable for normal tweeters. The treble drive units needs to not have a faceplate, that will ruin the broad dispersion.

The peerless driver went years ago, it was only used for Pluto 1, Linkwitz is now on Pluto 2.1 with far superior bass performance.
Pluto uses a custom version of a Seas drive unit made specifically for the design. This bass drive unit could be successfully replaced with an inevitably more expensive unit. The treble drive unit should really be the same Aura whisper drive unit. You may get away with a peerless 2 inch fullrange like in the Platon pluto copy but this has more narrow dispersion.

Interesting DIY Pluto and Orion:
Platon

If you do attempt to copy Pluto keep the speaker as slim as the drive unit basket, it is meant to be a point source.

[rob g]

Maybe you could try something with a reflector style waveguide like Demokrit?
Demokrit

You would probably want to add a tweeter at the high end.

[6.283]

Originally Posted by rob g

You would probably want to add a tweeter at the high end.

Rob, you don't because that defeats the entire purpose of the design and from first listening tests it is absolutly not required although not visible in any diagram or datasheet. If you want more highs then another FR is required. But as things stand now you need to roll off the highs anyway otherwise it will sound too bright.

Cheers
Oliver

[rob g]

Hi Oliver,
Maybe my memory is faulty, didn't you discuss adding a tweeter with this Speaker?
Anyway that is good to hear, if you can get away with equalization alone.

Perhaps you should link this discussion with the omni popularity thread!

[6.283]

Originally Posted by rob g

Hi Oliver,
Maybe my memory is faulty, didn't you discuss adding a tweeter with this Speaker?

Nope

Originally Posted by rob g

Anyway that is good to hear, if you can get away with equalization alone.

That's the goal. It might even be possible to get away without reflector but first things first.

Originally Posted by rob g

Perhaps you should link this discussion with the omni popularity thread!

Well, I can't really add anything to the original question. Omnis are pretty popular here And if I would do anything into this direction
then I would try to make them more popular since they're worth it.

[6.283]

...but since I am here anyway, I have a few comments on topic:

Tom, the TB W5-1611SA has an underhung motor and I am not sure it can produce enough punch below 100Hz. If you believe data in datasheets then it might. However, it would easily find its limits in excursion capability, which are required down there. So you would have to add a sub, which is primarily not required with Pluto. Also, the PP cone is too floppy for usage without sub. Then you need either a rigid metal or otherwise stiff cone. Dried paper, Nomex and Kevlar come to mind.
The "special" Seas unit is really the best out there for the money since years.

Originally Posted by rob g

You may get away with a peerless 2 inch fullrange like in the Platon pluto copy but this has more narrow dispersion.

It does but the magnitude is such that it will most likely not make a huge difference in listening tests since it counters with a smoother roll off.

In short:
If you want to listen to music and be done then you should buy plans from SL. The speaker is absolutely worth the money. If you want to fiddle and learn, well, then nobody can stop you anyway. But then be prepared to do measurements otherwise you will not hit the mark.

Cheers and have fun !
Oliver

[rob g]

I see Demokrit has become a two way now, just not in the direction I imagined!

This might make a nice surround speaker for multi channel omni with Pluto.

[tomchr]

Originally Posted by rob g

You need to do some reading on SL's website!
The speaker has to be active to work properly, or be prepared to build an inefficient power sapping passive crossover to marry the drivers if you plan to go passive. Then with passive you need a LOT of power so forget tubes/valves.

I think you're jumping to conclusions here. I'm very well aware that the Pluto uses an active XO to
1) compensate for driver resonances/squiggles in the frequency response
2) extend the low end

Nothing says I can't do that as well. I'm well versed in analog filter design and own the test equipment needed to engineer them, so no issue here.
What I don't know much about is speaker design. That why I posted this thread to start with. I have the W5-1611SA's and was wondering if they could be used in a Pluto clone. I'd probably use the AURA tweeters for the same reasons as you point out.

I'm not looking to start a tube vs sand yelling match. How much power is needed depends entirely on the desired SPL in the room where the speakers are located. Along with speaker efficiency, of course. I'm not looking to rock my house off its foundation. If an LM3886 can power the Pluto, I'm sure a 6L6 Push-Pull stage would be able to do so as well.

The guys at the Parts Express Forum actually made a passive Pluto. No word on efficiency - at least not according to my quick glance-over, but the frequency response is pretty nice...

Originally Posted by rob g

The speaker is a closed box design. It is actively equalized to produce more bass in the low end than would be expected from a small bass mid.
For this purpose you need a very long throw low distortion drive unit.

That's more along the lines of what I was looking for in an answer. Thanks!

Originally Posted by 6.283

Tom, the TB W5-1611SA has an underhung motor and I am not sure it can produce enough punch below 100Hz.

Ah... That's the sticking point. Yeah, the Tangband has an Xmax of 3 mm. I think that's 3 mm peak = 6 mm p-p, but that's probably the physical limitations of the motor and not the limit for low distortion.

Originally Posted by 6.283

If you want to listen to music and be done then you should buy plans from SL. The speaker is absolutely worth the money. If you want to fiddle and learn, well, then nobody can stop you anyway. But then be prepared to do measurements otherwise you will not hit the mark.

Well, yeah.... I was hoping to learn a thing or two in the process. Who knows. Maybe I'll use a DSP for the XO. Who knows. At this point the project is in the idea stage.

~Tom

[markus76]

Oliver,

Did you do any polars for your deflector/speaker combination? I just measured a quick and dirty deflector on a B200 today and it didn't look too promising.