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]

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]

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]

Re: Re: 3-Way Pluto?

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]

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/Produkte/Ebellaluna.htm

 

[ScottG]

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/Produkte/Ebellaluna.htm

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

 

[el`Ol]

There is a reason why Mr. Linkwitz doesn`t use a "real" tweeter. With small midrangers (and better dispersion) it can work. I would use narrow ribbons like Swans and maybe an arrangement like this:
Variations are possible, but the ribbon has to be on the axis of the midrangers.

 

[bzfcocon]

How about using a small fullrange like:

http://www.visaton.de/en/chassis_zubehoer/breitband/frs8_8.html

as the "midtweeter" ? Or is it already too big ?

I have a couple at home, I always liked the sound and i would like to give it a try. . It appears to go to 20 kHz, sensitivity is lower than Aura but there is a new version at 88dBm.

 

[sreten]

Hi,

The obvious thing to do would be to step up to a 3" main driver.
Crossed over time aligned 1st order series passive to a mini-neo.

Then drop the crossover point bass to mid by about an octave.

Pretty much follow the rest of the design principles.

Whilst most of the Pluto design I agree with - the bass alignment
IMO does not consider other optional extremely valid compromises.

Arranging vented low tuning is good IMO for active EQ + power handling.

/sreten.

 

[sdclc126]

Wow - interesting that this thread has been resurrected - 2 years old! Someone must have been searching.

I have not built the Pluto; my first build is a conventional TM with Dayton RS-150s & SEAS 27TBFC/G, XO designed by Jay_WJ, which sound incredible. OBs & omnis will have to wait until I have the appropriate listening space.

Currently planning a vented, floorstanding version of Mark K's Dayton Reference RS225/RS28A, adapted for the TBFC, which can better handle the low crossover point. Mark will be working on the XO. Jay_WJ modeled the vented idea and came up with a "1.5 cu ft (about 42.5 liter) cabinet with 27.5 Hz port tuning freq (by 5 1/8" long 2" diameter port) - gives the speaker 3dB down at 33 Hz and 0 dB tuning peak."

With limited listening space & budget I want to try really pushing the 2-way envelope to squeeze every last drop of performance out of each driver, for full range musical listening with decent bass. Originally was going to add the 225s to my 150 TMs, but have re-thought.

Incidentally, Mark says he's planning an OB with two RS225s & the TBFC - which sounds very exciting; don't know if it's active or passive. John Krutke has threatened a passive OB design too so I'm salivating for that one also - it will be passive.

 

[sreten]

Hmmm......... 2 year old ........ I didn't realise ......... /sreten.

 

[sdclc126]

Hmmm......... 2 year old ........ I didn't realise ......... /sreten.

It wasn't a criticism of anyone, by the way, just an observance. I was thinking that the only way a thread that old could be found was through a search.

Anyway, your input is always welcome Sreten!

 

[bzfcocon]

I was thinking that the only way a thread that old could be found was through a search.

Ok, it was me
I was indeed searching for Plutos and I would give it a try and build them, but first I would make a "proof of concept" using the drivers that I already have.

The small Visaton FSR 8 is used for example in Cyburg Needle horns.

 

[Andersonix]

And just for completeness I'd like to remind everyone that with the Pluto+ subwoofer, the Pluto is now a 3-way.

I'm playing around in CAD with orienting the 10in woofer facing sideways at the bottom of a modified 'one-box' enclosure. Since the 10in woofer is less than 6 inches deep and only needs 14 liters, I can keep a 6 in dia pipe extending downward from the mid and expand the additional woofer volume rearward...

 

[classdpwr]