What Do You Think . . . and How Does It Work?


While watching vids on YouTube, I came across this pipe speaker design from a Dr. Linkwitz (see below).   The sound of this speaker is said to be impressive.  I was wondering if you know about this, how it works and what you think of this speaker design.  Also, what do you think would be the best room placement for such a speaker, and would you be tempted to build them?

https://www.linkwitzlab.com/Pluto/intro.htm
bob540
Plenty of people have built the Pluto and most reports suggest it can compete with designs costing multiple times more.

The Pluto might not quite get you to the levels of the LX521 or the Orion, but then, as things stand, not much else will either.

Given time I’d fancy having a go myself as going active seems to be the coming future of high end loudspeaker designs.
Linkwitz was one of the contemporary gurus of speaker design (think LINKWITZ-Riley crossover, etc). His site is full of invaluable info
The Pluto is an impressive speaker for its size, it needs room around it to breathe (IMO) and will reproduce details and dynamics. What it won’t give is the full scale of a large orchestra -- no small speaker will do that -- but it acquits itself better than most (the small ATCs, well driven, being another contender -- to my limited knowledge).
Are you considering it?
A bit unrelated but look at his recommendations for speaker placement and how he uses a different speaker placement for a speaker with a different radiation pattern. I think this shows nicely how speaker placement "calculators" are at best approximations and why you need to adjust the speaker (and acoustics if possible) to match the room and speaker.
Must be half a dozen times now I've suggested people build a sub from ABS, lay it on the floor or stand it in a corner. Hsu made a sub for cars that was little more than a pipe with a driver at one end. Its physics- the pipe is a good shape, cheap, easy, and favors the physics of acoustics. On the inside its shape is strong and resists vibration. On the outside its curves diffract and disperse. What's not to like?
i heard these speakers at AXPONA a few years ago.  it was in the madisound room that sells these kits online.  
very incredible deal for the $230 for the kit less the PVC piping.  in this case they used minidsp for the active crossovers.  
sound was deep, rich and had very good bass impact. not the last word in midrange transparency though.  
I’m sorry, and I’m not trying to be a jerk, but they’re pretty dang ugly in my humble opinion.  You asked... I answered!
Didn't HSU make home subs from cylindrical cardboard concrete forms back in the day?
@b_limo 

+1.  My feelings exactly.  How is the leg coming along?
@stereo5 , lil better everyday!  Thanks for asking.  
@bob540, I’ve been somewhat obsessing over speaker kits lately. I’ll send over my favorites here in a sec...

twoleftears
2,407 posts05-20-2020 9:53am

Didn’t HSU make home subs from cylindrical cardboard concrete forms back in the day?


Sonotube, and a lot of us, poured the concrete, too. Concrete Tubes are dead silent. No problem, with vibration, just placement.. 18" vary from 60-100 lb a foot. Depends on wire size, the mix and thickness. Taller the tube deeper the tone. I used an underground vault on time.. Two PA drivers. It has had, 12,15,18" drivers. Settled on 15, last time I looked 1 block of BASS... 2-400 watts

"T" base bens too. The uprights were passives the crossbar was active.
Talk about boom boom, very easy to room tune also.. length or PR, true glass breakers..Very space hungry laying down..

OP is on to an oldie for sure, they been around for a while. I’ve seen a few, different designs, We called them 3x2. Three way, Two driver

Pipe organ design, Length x diameter.... for the blend....... ahhhh the blend
Can also stuff the tube and move the stuffing up and down for tuning.

Bull horn style is fun to.. Honk Honk.. Think Ampa...


Regards

Looks like there should be a submarine in the basement. 
@gregm:  I’m don’t really have the room for them, especially since they need space to sound their best.  But for the price, they are interesting.  If my patio were covered or enclosed, that might be an application worth considering.

I wondered what the two drivers at the top, one facing up and then one facing forward right above it, do for the sound?  
Usually when I think ... I doesn't work well.
Linkwitz was one of the contemporary gurus of speaker design (think LINKWITZ-Riley crossover, etc). His site is full of invaluable info
i dont know any speakers made by him. The crossovers bear his name but they were WRONG. 
PVC pipe for a speaker box is a hoax. After all the effort wilson and magico go to with their cabinets, PVC cannot be the answer. 


I love it..Rollin' on the ground...

Regards
I use a SVS Sound Cylinder (round tall sub) for my home theater room. It hits pretty hard and tight, but then again I’ve not heard the best in class, etc.

It beats a poke in the eye with a sharp stick, as we say in these parts!
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I have an opportunity to by a linkwitz Orion speaker Right now. The problem is it needs 3 amps to run it. The sound is amazing. The bass astonishing. It’s the 3 amps I’m not nuts about. Supposedly, the amps don’t even need to be that great. My energy bill is already high. 
I've made copies of the Bose Cannon for movie theaters.  Used Sono tubes in 8, 10 and 12 inch diameter.  At about 14 foot long, rather hard to hide.  Thought about using the attic space above the living room ceiling, just never did that.  still have a 10 inch model in the attic.  Open at both ends, no build up of air pressure.  Back then, when testing it, was watching a movie and a fog horn went off, very loud and realistic sound.  Nelson tried a pair of 15 inch diameter Sono tubes in Grass Valley.   Quite eleaborate with a thick marble base and the 15 firing up into what appeared to be a 10 foot tall tube.  There are many roads to subwoofer nirvana.  Currently using a swarm of 10s and a 12 for bass.
@mickeyb You don’t need 3 amps. What amp were you listening to with the Orion’s you heard? What you do need is at least 3 channels per side for a total of 6 minimum. You could use the amp that Linkwitz recommends on his website which is the ATI AT6012 which has 12 60 watt channels. Use a couple of extra channels in bridge mode for the woofers if you wish. I bought Orion’s, built the Lxmini, Lx subs, and the Lx 521.4. I love them all. I use a mix of analog and minidsp boxes for eq/xover. Buy or build any one if you like fussing around with gear. They are not plug and play but for my ears the time invested to get them set up right has been well-rewarded.
@mickeyb, I was going to suggest those inexpensive Crown amps — you could buy 3 of those and not have too much money in it.  The 12 amps alymere mentioned would be interesting too.  Maybe one of you guys with plenty of room and some loose change could put this together and video the result.  That would be a hoot.  Too bad Dr. Linkwitz isn’t still around to serve as technical consultant. 

@soix, too funny!  It does look like a periscope, doesn’t it?   Add a lens and play the theme song through it for “Twenty Thousand Leagues Under the Sea”.  ☺️
It’s a little late for an April Fool’s Day joke. 
alymere

Thanks for the clarification.

Many of us are only familiar with using the 2 channel amplifiers that the advertising branch of high end audio (the press) prefers to talk about.

Habits and all that...

https://homemedialimited.co.uk/product/ati-at6012-12-channel-power-amplifier/
Kenjit, I’d say millercarbon is correct and the effects of pressure on the inner walls of a tube (incidentally, specifically engineered to uniformly hold pressure) is a great idea. Cabinet resonance would be low using this material and geometry, especially if you used schedule 80. Talk about inexpensive DIY!

If designing a tube shaped cabinet, it would be logical to use at least an inch or two larger radius (inner dimension of the tube) than the ports on the driver basket to allow the driver to breathe correctly, with a beveled edge on the baffle to allow unrestricted airflow from the back pressure of the driver.

The bazooka style used in car audio worked well.

Kenjit, explain to me why it wouldn’t work??
(Oh and I don’t specifically think it’s not the material so much as the geometry of a tube that makes it such a good idea).



Kenjit, explain to me why it wouldn’t work??
of course it would work. It just wouldnt be state of the art. Look at all the other high end speaker companies and the great lengths they go to with their cabinets. There are no PVC speakers out there among them. Only PVC speakers out there are the cheap ones on amazon. 
Kenjit, um... concrete pipe?
And yeah, certainly competitive with other devices claimed as state of the art. A cabinet's audible colouration (coloration) has a significant signature to the overall sound, a tube will do well in such a situation as the tube itself lends to withstand pressure from the driver.

Let's face facts though, best engineered for sound quality, isn't necessarily aesthetically the most pleasant.


kenjit,

from an engineering standpoint a tubular shape is inherently the most rigid and deflects the least under pressure than a box shape.  
that's why pressure vessels are cylindrical- e.g. pressurized gas, liquid nitrogen storage dewars, compressed air cylinders and HVAC boilers.  
as a speaker enclosure this translates into ultra low resonance and coloration.  Magico in fact sees the value in ultra rigid enclosures by making theirs from aluminum.  
The downside of using PVC tubes for conventional speakers include the difficulty of the manufacturing process and cost of adding adaptations for stands, speaker mounting interfaces, speaker terminal interfaces and finishes.  
The higher end B&W diamond towers mimic this to some extent- they remind me of trash receptacles. 
The downside of using PVC tubes for conventional speakers include the difficulty of the manufacturing process and cost of adding adaptations for stands, speaker mounting interfaces, speaker terminal interfaces and finishes.
Its not really difficult. All you need to do is attach the tube to the driver. Takes about 2 minutes. You are wrong. 

from an engineering standpoint a tubular shape is inherently the most rigid and deflects the least under pressure than a box shape.  
It depends. A pvc tube can be bent easily by hand if you squeeze it across the width. But its harder to bend lengthways. The material matters more than shape. An mdf box is still more rigid than the pvc pipe used for the linkwitz speakers. 
PVC tubes are great for building Helmholtz resonators. There’s a simple formula for figuring out the resonant frequency Fr based on volume, nozzle length and nozzle diameter. I built a 60 Hz resonator out of 6” PVC pipe sections and PVC elbow joints. The trick is using the purple prep stuff just before applying PVC cement. My resonator was 15 foot long folded S shape.
At the same thickness PVC is similar in strength to MDF. With the "bend" forces exerted on a speaker enclosure, a tube is a significant advantage over a box making the comparative thickness higher but that would be compared to an unbraced box.
Aluminum, is a good material for low resonance, and great strength.

The problem is cost. Oh my. 

MDF
13-15 ply plywood, void free 3/4"
Hardwood
Aluminum

As far a cost, lowest to highest. 
Some hardwoods can exceed Aluminum for sure, but normally they are veneers.

There were a few companies that used PVC enclosures. Advent, 
Same era, Infinity was using cast Aluminum/magnesium at 10 times the cost, and 5 time the Retail. 

I'd like to say my speakers were CNC from marine aluminum, but paying for them, is a whole different story..

Here the thing though, cylinders, have an inherent characteristic to ECHO
and GAIN... not disappear, or blend like you want.. They're usually have pretty high mechanical distortion. Even with a lot of baffles..
Concrete pipe... ECHO, even long square tubes echo, and GAIN..

Big BASS Yes especially loading a tube inside a tube, and porting both enclosures. That's a 6th order, band pass. Home use.. OH my, you couldn't do it. Pictures would be falling off walls.

Columns... They work. Less real estate, less distortion, more bass, BASS, B A S S..
Aluminum, is a good material for low resonance, and great strength.
not really. it rings like a bell. 
Aluminum is actually one of your softer metals. Way down ⬇️ on the Mohs scale of hardness. 2.75 to be specific. It’s still an interesting material when thick, like 2-3”.
Here the thing though, cylinders, have an inherent characteristic to ECHO
and GAIN... not disappear, or blend like you want.. They're usually have pretty high mechanical distortion. Even with a lot of baffles..
Concrete pipe... ECHO, even long square tubes echo, and GAIN..
which is why im saying its not good. 

At the same thickness PVC is similar in strength to MDF

We are talking about the linkwitz pluto speakers. They are not concrete pipes. They are not 2 inch thick PVC. They are PVC pipes that are about 2mm thick. I dont want to hear any more excuses. Do you know how bendy 2mm thick PVC is? Theres nothing rigid about it 

Actually...

The PVC pipes used would have a minimum wall thickness that well exceeds 6mm.

DeKay
These PVC pipe speakers are all hearsay. NOBODY has done any comparisons to check if a $2 PVC pipe beats a $50k high end Wilson. 6mm is a joke. Even cheap box speakers use at least 15mm mdf. Do not be duped by this cheap PVC hogwash. 
" NOBODY has done any comparisons to check if a $2 PVC pipe beats a $50k high end Wilson."

Nobody is claiming that either.

But somebody is committing a straw man argument fallacy.

Duke
I think it’s generally agreed in the industry that a box is the worst possible shape for a loudspeaker cabinet.

The main reasons why most are built this way seems to be consumer expectations of domestic acceptability and manufacturing convenience.

The following extract is taken from diyaudioandvideo.com


What is the best shape for the box?

Internal reflections in the box combined with the vibration of the box itself can cause spikes in the frequency response of the system.

Different box shapes have different effects, with perfect cubes being the worst and spherical or egg shaped boxes being the best.

Although spheres have advantages, it is very difficult to create a spherical speaker box that is as strong as a typical rectangular box.

One good example of a spherical speaker is the Gallo Nucleus Solo above on the left which is made of rolled steel or brass.

An even better design is the sphere/tube concept by B&W shown on the right.

This design gets the benefits of a spherical design, but also adds a tapered tube at the back to eliminate all internal resonances.

Shape Variation
Cube +-5.0 db
Rectangle +-3.0 db
Cylinder +-2.0 db
Beveled Cube +-1.5 db
Beveled Rectangle +-1.5 db
Sphere +-0.5 db

https://www.diyaudioandvideo.com/Guide/BuildSpeaker/
To those who think it's ugly, put your creative hat on and build a nice wood veneered cabinet over it. The guts doesn't have to change and your can be tailored to your visual preference.
not really. it rings like a bell.

Yes it can, when used for TT platers, and is forged, but there is a reason for that too. Galvanization issues.

With Metal housed planars. Forged, won't GROW Barnacles (as fast) as cast will. Cast alu without a treatment, can get flakey in less than 5 years..
Double in thickness in 15 years. Aviation shot peen, stress relieves and removes, pocket resonance, issues, also..

Most speakers that use Aluminum, use it for it's milling ability.
EX: GR Research LS9 (Beta) and a few other.
Infinity Infinitesimal  v.5 and 1.0 (cast)

CAST.. is actually the best , Highly porous, (to a point) dead silent.
Light, strong, easy to cast, easy to mill. A lot like a cast aluminum
engine block (neutralizing agent required)
Cast, Alu/Mag (no barnacil alloy) rims, dead silent. There is a reason they cast rims.. A lot quieter than a steel or spoke.

Columns.....

Regards..
Schedule 40/6" is 7mm thick. Schedule 80 is 11mm thick. I am rusty on my structural eng.

Cylinders echo and gain? ... no, they behave pretty much like any other "tube" whether it is square or rectangular, but more consistent and easier to deal with.

All materials "ring". If you have a material that does not ring (at all), then it is probably not stiff (or only stiff in one dimension). You can always add dampening. Open the hood of your car and knock on the likely aluminum block. Tell me if it "rings".

This design gets the benefits of a spherical design, but also adds a tapered tube at the back to eliminate all internal resonances.

Shape Variation
Cube +-5.0 db
Rectangle +-3.0 db
Cylinder +-2.0 db
Beveled Cube +-1.5 db
Beveled Rectangle +-1.5 db
Sphere +-0.5 db

Interesting, for a complete speaker system, round. smooth, tapered interiors, are a way to reduce pocket resonance. It can also be used to incorporate a resonance into an enclosure also.. That was my point, the GAIN factor, for BASS is a real issue for distortion in the bass region 250hz<

You have to use it or lose it, but you can't keep it.. 

When speaking of spectral decay effects on enclosure vs mechanical distortion (GAIN based) there is no comparison in how much one increases over the other. (The 20% bass distortion crowd, and don't even know it)
Interiors that are rough inside, not smooth are a much quieter enclosure.. The SQ is always better..

Remove the Highlands Scottish wool from behind the mids, let that blister your ears a bit..
or Remove the VERY coarse fiberglass from the bass enclosure...
BOOM....forever........

INSIDE, Smooth is bad.
OUTSIDE, Smooth is good, but just for the dust factor.
if it wasn't for that rough would be better.

Regards