3-Way Pluto?

[sdclc126]

I have been thinking of a design idea for a 3-way speaker based on SL's Pluto.

The goal would be an omni-directional speaker appropriate for a relatively larger listening environment than that for the Pluto, but perhaps smaller than for the Orion, at a cost point in between the two.

The addition of a midrange for this configuration would allow for a more "full range" design, with a larger, lower-reaching woofer and a "true" tweeter, extending beyond 15khz.

I'm thinking perhaps an 8 inch woofer, mounted exactly as in the Pluto, but perhaps at the top of a more "traditional" tunable box-type enclosure.

The tweeter would also mount facing forward, as in the Pluto, which leaves the question as to what to do with the mid. For an omnidirectional effect, it would either have to be mounted in an open baffle or at something like a 45 degree angle toward the listener & ceiling, or both?

This is a very vague initial description of an idea that has no real speaker design science behind it, so I'm totally open to any thoughts anybody has as to the feasibility/practicality of something like this. There could be all sorts of problems or drawback that I can't envision yet.

If anybody is interested in commenting on this, please fire away!

[joe carrow]

While I think this is interesting, I think you need to ask a few focusing questions before you proceed.

You said:

"The goal would be an omni-directional speaker appropriate for a relatively larger listening environment than that for the Pluto, but perhaps smaller than for the Orion, at a cost point in between the two. "

The main problem you run into with this proposition is excursion. The tweeter is crossed relatively low, and the woofer is small and sealed. Since the tweeter is fairly large and crossed around 1khz, I don't think it will be the weak link. I think you'll find that an active crossover to stereo subwoofers will buy you the most added performance.

Lets look at the benefits of the Pluto:

1) The pipe. This is an extremely rigid bass enclosure, doing a lot toward preventing cabinet coloration due to cabinet flexing and vibration. Secondarily, it contains the backwave in such a way that the stuffing kills most of the sound before it can reflect and re-radiate through the cone.

2) The woofer mounted vertically. This is great, since the horizontal radiation pattern is extremely uniform, and any high frequencies from cone breakup or distortion are more directional and tend to go up toward the ceiling instead of at the listener.

3) The crossover frequency. I'm less sure of this one, but it seems that both drivers are fairly close to omnidirectional at the crossover frequency. This causes the change of directionality to be in the upper frequency, and entirely due to the pistonic area of the tweeter. Yes, the two inch tweeter is beaming a bit by the top of its range (15 khz), but the response pattern narrowed slowly and evenly with no sharp jumps.

The weaknesses, as I said, are all about excursion. The tweeter is playing somewhat on the low side, and the woofer doesn't get any help in the bass from a port.

[bogicp]

Originally posted by sdclc126
I have been thinking of a design idea for a 3-way speaker based on SL's Pluto.

The goal would be an omni-directional speaker appropriate for a relatively larger listening environment than that for the Pluto, but perhaps smaller than for the Orion, at a cost point in between the two.

Your idea is great but...
if you read carefully what Siegfried Linkwitz said about listening experiences with Pluto, you will find that Pluto IS designed for small space and some good alternative for dipole speakers which needs slightly bigger rooms (at end, you must have some space for placing dipoles in your room)
You must be near to Pluto speakers, in large or small room...

The addition of a midrange for this configuration would allow for a more "full range" design, with a larger, lower-reaching woofer and a "true" tweeter, extending beyond 15khz.

If you need more than 15kHz, you can add some small "real tweeter" crossed with Aura small drivers (IMHO). I think that S. Linkwitz work at Pluto project for a long time, and I'm sure that he has real tweeters to try this. But possibly, very low crossover point is "secret" of Pluto sound, and only Aura drivers can do this.
Second, "lower-reaching" woofer cannot be easily equalised to work good at 1kHz in Pluto (up firing) setup.

I'm thinking perhaps an 8 inch woofer, mounted exactly as in the Pluto, but perhaps at the top of a more "traditional" tunable box-type enclosure.

They cannot reach 1kHz off axis (see above), or I'm missed something.

The tweeter would also mount facing forward, as in the Pluto, which leaves the question as to what to do with the mid. For an omnidirectional effect, it would either have to be mounted in an open baffle or at something like a 45 degree angle toward the listener & ceiling, or both?

True mid range (up to 1kHz) omnidirectional effect is possible only with up firing equalised mid woofer. And woofer dimensions must be same (or smaller) as in Pluto, if wee don't need even lower crossover point.

This is a very vague initial description of an idea that has no real speaker design science behind it, so I'm totally open to any thoughts anybody has as to the feasibility/practicality of something like this. There could be all sorts of problems or drawback that I can't envision yet.

If anybody is interested in commenting on this, please fire away!

I'm interested too, and when Pluto is promoted, I'm think about same as you. But when you analyse carefully Pluto's concept, you will find that Pluto must be designed with woofer-mid with same dimensions, and with "tweeter" with very large excursion like Aura's.
Aura drivers is only one that have characteristics needed for Pluto, and I'm prety sure that Auras can be replaced with better designed drivers... but they don't exist for now.

At low end you may use any subwoofer design, crossed with Pluto woofer, and below 150Hz any subwoofer is omnidirectional... but at this point dipole woofer is better because room modes.
Also you can use bigger pipe and different driver... you can obtain couple of Hz lower than original Pluto (his volume is about 9l, if I remember)




Best regards

boggy

[sdclc126]

Thanks Joe and Boggy - these are very informative responses. This idea was just that - an idea, and I had a feeling there might be some "issues" with it.

Boggy, thanks for those very fine details about SL's design - I did want to clarify one thing you said - I understand about an 8" woof not reaching up to 1k - that's why I was suggesting a mid - so the woofer can be crossed lower and the tweeter higher. But given your very thorough explanation it appears the idea is moot.

I am actually very intrigued by the Pluto and would love to build a set some time. I'm thinking the only way to "improve" it is to supplement with a sub and possibly some kind of supertweeter.

[bogicp]

Originally posted by sdclc126
Thanks Joe and Boggy - these are very informative responses. This idea was just that - an idea, and I had a feeling there might be some "issues" with it.

Boggy, thanks for those very fine details about SL's design - I did want to clarify one thing you said - I understand about an 8" woof not reaching up to 1k - that's why I was suggesting a mid - so the woofer can be crossed lower and the tweeter higher. But given your very thorough explanation it appears the idea is moot.

No problem
I think that Peerless mid-woofer and Aura "mid-tweeter" are crucial for Pluto performances, not because manufacturers, but because geometry (cone diameter and Xmax) of this drivers. I think also that this is a "core" of Pluto, all other things can be added or modified, but geometry of Pluto in 1kHz area must be the same... (IMHO)
Think also about the fact, that this "core" cover all sensitive region of our hearing abilites... mounting "super tweeter"
and adding subwoofer can be personall preferences... only


There are a some number of designs with up firing mid woofer lying around at Internet, but all this designs has no tweeter or poor polar response with regular tweeter (crossed too high) mounted at wrong place (front baffle of mid woofer cabinet)

I am actually very intrigued by the Pluto and would love to build a set some time. I'm thinking the only way to "improve" it is to supplement with a sub and possibly some kind of supertweeter.

Yes, me too. I try Vifa P17WJ with simple 1m tube with some stuffing, and without any tweeter, equalised to be flat off axis as much as possible... using it in stereo nearfield listening is a great experience... try this if you can... even forget Aura "tweeter" for some time


Best regards,

boggy

[wingwing]

Originally posted by bogicp

I'm interested too, and when Pluto is promoted, I'm think about same as you. But when you analyse carefully Pluto's concept, you will find that Pluto must be designed with woofer-mid with same dimensions, and with "tweeter" with very large excursion like Aura's.
Aura drivers is only one that have characteristics needed for Pluto, and I'm prety sure that Auras can be replaced with better designed drivers... but they don't exist for now.

I'm interested too....Do you think that Jordan's new JXR6 HD can be an upgrade to the Aura?

[Landroval]

A bigger Pluto can be used in a bigger space, but in order to keep the idea of the original, the listening distance must be small. A good approximation would be that the listening distance should be smaller than the speaker's distance from any wall.

[ScottG]

Originally posted by Landroval
A bigger Pluto can be used in a bigger space, but in order to keep the idea of the original, the listening distance must be small. A good approximation would be that the listening distance should be smaller than the speaker's distance from any wall.

..actually that was SL's initial assumption (he's big into trying to minimize room effects). (i.e. closer to the listener, the futher from room boundries.. at least if you sit near the center of the room.)

note what he said here:

"..Actually more so when listening from a greater distance than I had suggested below and with the PLUTOs at least as far apart as the comparison speakers."

In otherwords while it is important.. its not nearly as important as it appears to be.

I think that wingwing has a rather good idea there with the JXR6. I'd then top it off with a good super tweeter with much better off-axis high freq. dispersion. If possible, keep as small a diameter for the woofer as possible, both for its off-axis behaviour and its field pressurization nature with regard to acoustic center (i.e. a smaller driver usually sounds more "focused" than a larger driver). I would also be concerned with reflections from mid-tweet "box" and do NOT use a waveguide (a'la duvell speakers).

[LineSource]

This type of omnidirectional speaker continues to hold my interest. The horns could be cut from styrofoam and painted to seal if a lathe is not available for a wood turning.

Omnidirectional 2-way-full range horn:

http://www.duevelloudspeaker.com/Pro...Ebellaluna.htm

[ScottG]

Originally posted by LineSource
This type of omnidirectional speaker continues to hold my interest. The horns could be cut from styrofoam and painted to seal if a lathe is not available for a wood turning.

Omnidirectional 2-way-full range horn:

http://www.duevelloudspeaker.com/Pro...Ebellaluna.htm

Beyond altering phase.. a waveguide like that seems to be detrimental to sound quality (in comparison to a design like the pluto).