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Old 27th Mar 2018, 3:40 pm   #1
ITAM805
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Default Polystyrene speakers?

Throw out your Tannoys! Who knew that polystyrene and balsa would make decent speaker sounders? Some interesting results - here
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Old 27th Mar 2018, 3:55 pm   #2
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Default Re: Polystyrene speakers?

Have NXT given up chasing up their patents on Distributed Mode Loudspeakers (DMLs) - does the company still even exist? There were all sorts of dubious claims put about for these 10, 15 years ago - many of which centred on most people being unable to get their heads around the time- and frequency- response of a finite panel with something like simply-supported boundaries.

At a conference I heard a well-known global figure in the audio scene describe (privately) the whole thing as a 'stock scam'...
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Old 27th Mar 2018, 5:51 pm   #3
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Default Re: Polystyrene speakers?

Loudspeaker manufacturers also minimise cone resonances so this is just a flat loudspeaker with very little cone movement and open to the back so no bass response. Doesn't address the stereo (or reflection) phasing issue at all.

Is there an argument for adding a 3rd central speaker to a stereo setup with R+L input? Perhaps not if the recording was made with 2 mics and it would reduce the 'sound stage'.
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Old 27th Mar 2018, 6:55 pm   #4
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Default Re: Polystyrene speakers?

Although the NXT versions of these made a lot of the Modal bit of dMl, in general they used fairly heavily damped materials so as not to accidentally produce a plate reverb! I spent some time modelling these back in the day (analytically, rather than using FEA, which meant a few assumptions about boundary conditions but hey). The surface velocity is fairly low although there is a kind of 'direct field' of circularly-propagating wave fronts near the exciter(s), in a 2D analogy of sound radiating in a reverberant enclosure. But since source strength is velocity *radiating area, and sound pressure is proportional to source strength, they can be loud enough if they're big enough. Yes, the dipole thing means there's not much LF - also the modal density is a bit low at LF which affects the source strength.

I think they were a product looking for an application, really. The best use I saw was as an active ceiling tile for shopping-centre type PA. The small displacement amplitude of the exciter suggested they'd work for a long time maintenance-free, and since they are a lot more omnidirectional at mid-high freq than a piston in a baffle, they work well as the shopper walks by underneath them.
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Old 27th Mar 2018, 7:03 pm   #5
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Default Re: Polystyrene speakers?

IMHO adding a third R+L speaker would destroy the channel separation which the whole record / reproduce chain had been striving to maintain.

There may be some merit in having a proper three channel system of course.

It has been my experience in listening over a 60 yr period to many recordings; mostly classical in earlier times, that simple microphone methods produce the most realistic results. Early EMI group crossed figure 8 response microphone recordings for example.

There are also the two basic philosophies for making recordings.

1) Bring the musicians here and

2) Take the listener there.

Very small scale works which could possibly fit in the listening room can sound very good
using type 1.

However, trying to cram the Vienna Philharmonic Orchestra into one's lounge is not going to sound "right".

Apologies to moderator, I may have strayed off topic a bit here.
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Old 27th Mar 2018, 7:55 pm   #6
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Default Re: Polystyrene speakers?

I used to have a pair of Goodmans Planax 3 speakers - moving coil driving a large polystyrene diaphragm. Reasonably good midrange, but poor HF and LF response, but they looked quite good at the time!
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Old 27th Mar 2018, 11:54 pm   #7
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Default Re: Polystyrene speakers?

KEF B139 are foam!!
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Old 28th Mar 2018, 7:50 am   #8
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Default Re: Polystyrene speakers?

30 odd years ago there was a product called the poly planer a flat polystyrene unit quite cheap worked well flat about 1 inch thick all the rage for a while
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Old 28th Mar 2018, 8:02 am   #9
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Default Re: Polystyrene speakers?

The polyplanar used an expaded polystyrene basket and an expanded polystyrene piston. The piston to basket flexure was a bead of silicone rubber.

Back in the early 70s they had a few in the comms engineering lab and I had some fun with them and the B&K mikes, BFO and plotter. They worked surprisingly well.

Polystyrene has its part to play in the legendary KEF B139 of course.

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Old 28th Mar 2018, 9:34 am   #10
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Default Re: Polystyrene speakers?

A very good friend of mine is virtuoso pianist and musical innovator. He had a company - Podium - which manufactured distributed mode speakers that were patented over and above the NXT ones.

He later invented the Symphonova. The best person to describe this is Shelly. This is the first ever demonstration in 2012, and you can see two distributed mode speakers, and what role they play here https://www.youtube.com/watch?v=c3p3WmEL6xE

And this is what it looks like five years later. The distributed mode speakers have become skeleton musical instruments, similarly excited. The principle is that in order to sound like a simulated cello - a speaker ought to have the acoustic characteristics of a real celllo.

https://www.youtube.com/watch?v=Fmyq34Kxeww

Slightly earlier, pre-musical instrument speakers, this is what 10 instruments sound like.

https://www.youtube.com/watch?v=DuyJ28afjHg

And the current, absolutely glorious status - with full digital augmentation from distributed mode driven musical instruments. The gestural baton has gone, and the system (and small orchestra) now responds to hand conducting gestures. Amazing!

https://www.youtube.com/watch?v=BGVUE8zgFEc

So I'm afraid the guy in the original link is the odd decade or two behind the times.

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Old 28th Mar 2018, 12:38 pm   #11
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Default Re: Polystyrene speakers?

I have two Leak Sandwich woofers that have polystyrene cones, there must be some old brochures on the ethos behind it, but a quick search reveals nada.

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Old 28th Mar 2018, 1:41 pm   #12
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Default Re: Polystyrene speakers?

Two things are being conflated here. The Leak sandwich and KEF B139 used expanded polystyrene as a method of making a piston-like woofer with no break up modes over the low frequency range.

A distributed mode loudspeaker, as the link from the OP, needs a large flexible plate with a local drive. The aim being that it *always* operates in break up mode. But because of the geometry the modes are so densely packed in frequency that the response is flat. And because of the way that such a panel interacts with room modes the imaging is staggeringly insensitive to listener position. Indeed you can approach the panels, and the image remains solid even when you walk between them and into being behind them. Very very unlike either box loudspeakers or "conventional" dipoles like electrostatics, which have a distinct sweet spot listening position.
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Old 28th Mar 2018, 1:47 pm   #13
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Default Re: Polystyrene speakers?

Quote:
Originally Posted by Radio Wrangler View Post
Polystyrene has its part to play in the legendary KEF B139 of course.
Certainly true - I used B139's back in the day. But they were only that shape to get around Purchase Tax. The regulations anticipated a loudspeaker driver that was either circular or elliptical. So KEF decided to take a 9" circular driver, conceptually cut it in half and put two straight sections in. So it was neither circular nor elliptical. And with a bound they were free.
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Old 28th Mar 2018, 7:06 pm   #14
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Default Re: Polystyrene speakers?

Yamaha also used to make some huge ear-shaped speakers!

This was back in the '60's, and these were of a polystyrene material.
They sounded impressive at the time, but didn't catch on.
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Old 29th Mar 2018, 10:37 am   #15
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Default Re: Polystyrene speakers?

Sinclair Q14.
I so nearly bought a pair during my student times but knocked-up a pair of Goodmans boxes instead.
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Old 29th Mar 2018, 2:39 pm   #16
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Default Re: Polystyrene speakers?

Sinclair was not a polystyrene speaker but made of pressed fibre board I used to for my sins sell them
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Old 2nd Apr 2018, 1:01 pm   #17
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Default Re: Polystyrene speakers?

For your sins or one of them?

Probably only venial, though.....
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Old 12th Apr 2018, 11:40 am   #18
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Default Re: Polystyrene speakers?

I bought one of the smaller 3W ones (to fit inside the case of a BBC micro but connected to a more modern sound card) and I was impressed by the results.... until my daughter decided she would wrench at it and pull the voice coil out that is!

I'll not be chucking out my GEC metal coned speakers yet but I _have_ ordered some larger ones to experiment with. I have a pair of monitor speakers in my long/cramped office and the imaging is poor when I move from one desk to another, I'll have to give these a go...
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Old 10th May 2018, 11:10 am   #19
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Default Re: Polystyrene speakers?

Quote:
Originally Posted by Vintage Engr View Post
Yamaha also used to make some huge ear-shaped speakers!

This was back in the 60's, and these were of a polystyrene material.
They sounded impressive at the time, but didn't catch on.
I remember them in some of the early Yamaha organs. Excellent smooth bass response. I never got round to trying one on a full range (orchestral) source, but I would be suprised if they didn't give a good account of themselves in that role.
A Yamaha engineer said that the aim of the ear shape was to reduce cone resonance.
Beautifully made, with an aluminium alloy (I think) die-cast chassis.
I suspect the bean-counters stopped them, as they must have been quite expensive to produce. Tony
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Old 10th May 2018, 12:51 pm   #20
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Smile Re: Polystyrene speakers?

Quote:
Originally Posted by mark_in_manc View Post
Have NXT given up chasing up their patents on Distributed Mode Loudspeakers (DMLs) - does the company still even exist?
It seems not (Wikipedia comes up trumps, as usual).

Though, after the company called in the administrators, it seems that someone thought that they could get a few bargains (some more info here and here).

Quote:
Originally Posted by mark_in_manc View Post
I think they were a product looking for an application, really.
I got one of these as my first digital radio. It does OK as a bedroom radio (it has a clock and can be used as an alarm) but at louder volumes, it doesn't cope with bass frequencies very well. I usually listen to it (via its headphone output) through a small TEAC receiver system. Looks quite novel, though…
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