NHT speakers ???

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Prometheus:

For even more info, go to: http://www.nxt.co.uk/

Click on "Surface Sound" in the column on the left. Then click on "Technology". Then click on "FAQ's". They sure don't like to make it easy, do they?

Here is an ABC news article on them: http://abcnews.go.com/sections/tech/CuttingEdge/flatpanel990402.html . Apparently they are non-directional even in the high ranges.

I just thought that I would throw in that there are similar flat panel speakers on the market. Also, for at least 15 years people have been hooking voice coils up to various flat materials. Sumo made a large dipole with a flexible plasic sheet excited by a conventional type motor. There were others.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
To my knowlege the NXT style speakers are meant to be hooked up to an amplifier just like any other speaker. I have seen some indications that flat panel speakers are 25 ohms. If they are hooked up to their own channel, that is no problem at all-in fact, your amplifier will love you for doing it. Piezoelectric tweeters are in use in professional equipment largely because they have a high impedance-it is a plus.

One thing though-some articles I have read said that this style of speaker is not particularly localized-that is, it sounds the same wherever you are in the room. Before you dismiss that, I might point out that line-source speakers-very tall and skinny-have a similar effect. They drop only 3 dB every time you double the distance, where a normal round speaker drops 6 dB. The Beveridge electrostatic loudspeaker-a couple of inches wide, six feet high-had a sensitivity of something like [email protected] 1 meter/1Watt-hilariously low. but because it was a line source, by the time you get 15 feet away, if was about as loud as a speaker rated at a normal 88 [email protected] 1Meter/1Watt.

Since these NXT type speakers operate on a principle of many many points of radiation, and it has been proven that they have non-directional characteristics, I would not discount the possiblility that you might not be able to tell where the sound is coming from.

True, these are only rear speakers in a home theatre system. But I assume the soundtrack of a movie has some effects designed to be heard from the left rear, and some from the right rear-these speakers might not be able to pinpoint very well.

On the other hand, if you picked them up for cheap, it might not be a bad idea to experiment. Some flat panel speakers admit that the frequency response isn't great-but rear speakers in a home theatre setup really don't need great frequency response. They don't even get a signal below 200 Hz, anyway.

Good luck on your experiment. Sound panels in the wall are guaranteed to look really good anyway-and they might be just what you need for rear channel speakers.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Just re-read your post:

"Has anybody an idea how I can hook up these drivers to a panel of my choice ?"

I don't think these things were supposed to be glued to another panel on their face, if that is what you mean.

If you mean how to attach these to a ceiling tile, how to do a neat cutout, etc., I would have to see the unit first. I am thinking along the lines of taking the speaker down to your local home improvement store and looking at some of the things they have there for air conditioning and heating ducts to make a nice neat match for your wall or ceiling.

Good luck!
 
Line source speakers are funny about that. The radiation pattern isn't symmetrical. It's a vertical cylinder with the driver as the axis. They're quite precise in the horizontal plane; I can move about (from side to side) in front of the speakers and still get a very, very precise image. The cute part is that they're the same vertically; no matter whether you're sitting on the floor, sitting in a chair, or standing, the image (and frequency balance, etc.) remains the same; all the ears on a totem pole would hear the same thing.
Now if you mount them horizontally, you'll end up with the vague, unfocussed kind of sound you describe. A lot of people thought they'd be really nifty for the front center channel in HT systems, because the drivers are narrow, and generally inherently shielded. Unfortunately, they were disappointed, as the sound refused to localize on the screen as the action (and sound panning) went back and forth.
Moral of the story: For hifi/HT use, they need to be vertical. Leave horizontal mounting for airports and such, where they need equal intelligibility for all the folks wandering around, and don't care about imaging.

Grey
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Thanks, Grey. Yes, I have heard many good things about line source style speakers.

However, I did not mean to imply that flat panel speakers would have the same characteristics as line source speakers. I only wanted to use line source speakers as an example to show that the sound patterns can change dramatically depending on what kind of speaker is used. The rules that apply to cones don't necessarily apply to other speakers.

Since the flat panel speaker works on the principle of many different pinpoints working together in a chaotic manner, I think that the imaging characteristics are very likely different from a cone of the same size. Indeed, several reviewers have said that it didn't seem to matter where in the room the listener was located, it sounds the same. I do not know how much of this has to do with the fact that these speakers were dipole, and how much to do with the nature of the way the sound is generated. My purpose was to question whether this was desirable in a home theater setup where you want the listener to be able to identify the source of the sound.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Prometheus:

Armstrong tile makes ceiling panels with these speakers in them. They have the Armstrong ceiling tile designs on them!! I don't know if they use Armstrong tiles in Germany, but it looks like this might simplify installation for you. This link contains another link which gives you a pdf file from Armstrong on the matter.
http://www.classroomdesignforum.org/pages/Update on flat-panel speakers.htm

Here is another article that mentions the dispersion characteristics of the flat panel speakers.
http://popularmechanics.com/technology/audio/1998/9/_Flat_Panel_Stereo_Speakers/index2.phtml

The author seems to think that the ability to hear them all over the room makes them work well for home theater-go figure. I would also mention that Dr. Floyd Toole, who works for the American distributor of NXT technology, is a well respected audio engineer who has written several articles published in the Journal of the Audio Engineering Society.
 
Hands down, the most spooky speakers I can remember hearing were the Walsh (later Ohm used the same concept) speakers. They were omni-directional at all frequencies, yet imaged decently. You could wander around the room...even <i>behind</i> the speakers and still get a decent image. They had other limitations, unfortunately.
I've seen pictures of these chaotic panels that were quite large (perhaps 2'x2'), and some smaller. I confess that I haven't studied the concept in detail, but on the face of it, it seems counter-intuitive. Probably need to get some papers and read up. However, be that as it may, my guess is that their ability to act as a point source is going to be frequency-dependent unless they pull some tricks such as Quad do with their electrostats where they stagger the signal to various parts of the panel in order to simulate a point source.
Wizard, can you enlighten me here? What are these critters up to?
Bose(o),
The Bose folks are extremely good at marketing, but little else. Clearly, it worked for you.
Mass market bafflegab is nice for profit margins--it looks nice in the advertisements, you see--but is of little use when it comes to building speakers that sound like live music.

Grey
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Grey:

From what I can gather, and I am no expert, this is what NXT is up to.

Some time ago, large dipole speakers appeared that were flexible plastic sheeting, similar to the type you can buy for clear plastic dropcloths, loosely stretched across a square wooden frame. They were several feet high and a foot or more wide. In the middle of the back side was a magnet and voice coil which was glued to the plastic sheeting-naturally, the weight of the magnet/voice coil assembly was supported by a bracket anchored to the wooden frame.

The purpose of this setup was NOT to give a piston-like motion as an electrostatic or magnetic equivalent, (Magneplanar, etc.) but to have the sound wave emanate from the center of the speaker out toward the edges, giving wide dispersion like characteristics. The effect was supposed to be similar to dropping a pebble in a still pond-that was the effect they went for. One manufacturer was Sumo-there were others. I have no idea if that company has any relationship to the amp manufacturer of today named Sumo either.

I never heard the speaker, but it seemed to me that it looked like a cheap way to get something that visually resembled an electrostatic or planar speaker without having to go to the bother of actually building one. I remember thinking, "Anybody with a Skilsaw and a couple of hours can make a frame, stretch a plastic dropcloth across it, take a cheap four inch speaker mounted on a bracket and can do as well".

Be that as it may, this new thing is different in an important way. Here, the design philosophy seems to be, "It's so crummy, it's actually good". Instead of a pliable plastic sheet to gracefuly carry the soundwaves to the edges, the NXT uses a solid plastic piece, similar to the translucent ceiling tile that covers recessed fluorescent lighting in offices, or the type that is used in bathroom tub sliding doors. And they don't even try to suppress resonances-they want as many resonances as possible. The theory is that if you have a situation of virtually infinite resonances, they all cancel each other out and you have no resonance at all. Every part of the surface is doing just what we try so hard to get a speaker's cone NOT to do-have adjacent pieces of the surface vibrating out of time and phase with each other in a chaotic manner. They all cancel out. So you have the original signal left.

Since the surface of the speaker is composed of almost infinite points vibrating out of time with each other, I frankly do not know what the dispersal patterns are. Since the freestanding units seem to come in dipole form, I do not know if the lack of directionality of the speaker is due to it's nature, or due to the the fact that it is a dipole, which tends to give that effect even with cone speakers.

For what it's worth, NXT does do something with "bending waves", that is, there is some engineering involved. Apparently they do more than take random pieces of plastic and hook up a magnet/voice coil to the center. There is some bending of the diaphragm involved. But the NXT people almost fall over themselves telling you that they could use almost anything solid-even cardboard-and get it right. I am under the impression that a home builder could probably conduct some simple experiments on bending the piece and get it close to what NXT does.

I am no expert, but this is what I have been able to deduce from reading several articles.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Well, Grey and Prometheus, here is white paper on the subject:
http://www.nxtsound.com/www/technology/soundvu/technical_1.htm

References 1 and 2 refer to articles published in the Journal of the Audio Engineering Society. I think it costs 5 bucks each to download them.

Before I spent any money on "exciters", Prometheus, I would try the following experiment. I think that "exciter" is just a fancy name for a magnet/voice coil combo. Buy a piece of stiff plastic, and hook up an old spare speaker to it. An old car speaker would be ideal. Use an old piece of stiff tubing to make a solid contact betwen the speaker's voice coil and the plastic. See how it sounds with no pressure applied to the edges.

Then, press down and flex slightly. Now see if the sound changes, and if you like the sound.

Just a suggestion for an experiment before you start buying parts. You might find something that convinces you to proceed with the project, or just buy a ready made one.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Prometheus:

Here is some flat panel computer speakers that cost between $5 and $10 a pair that might give you an idea. With a little cutting and splicing, you should be able to run them off your main amp instead of off the computer.

http://www.cpusolutions.com/pw.htm
Click "Compnents" on left. Then click "speakers". This should bring you to the correct page.

Good luck!!
 
I suddenly remembered the name of the company that held the patent on the Sumo design, Highwood Audio Inc

<a href="http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1='4924504'.WKU.&OS=PN/4924504&RS=PN/4924504">US Patent 4,924,504 Burton May 8, 1990</a>

<i>"Audio speaker</i>
<center><i>Abstract</i></center>
<i>An audio full range speaker which achieves the propogation of a peaked wavefront from the diaphragm instead of generating a substantially planar wavefront as in the case of the common speaker construction utilizing a diaphragm driven as a piston. The speaker has a substantially planar, thin, flexible film forming the diaphragm mounted within a frame. The diaphragm is driven by a driver which imparts motion to the diaphragm at a small source area, the motion being imparted in a direction normal to the plane of the diaphragm so that ripples radiate from the drive area and travel at the same time across the flexible diaphragm, one behind the other, towards the frame. The rest of the diaphragm is driven by the central moving portion, endowing it with a built-in time delay. Because of the time delay involved in spreading the energy across the diaphragm, the wavefront radiated by the speaker ges a head start at the center and lags towards the edges. The result is that of a spreading spherical wave front for a point source and a cylindrical wave front from a line source, and allowing a large diaphragm to behave as a small virtual audio source. The full range transducer requires no crossover, equalization or time delay circuits."</i>

I remember an article on them some years ago, the main problem they had to solve was terminating the wavefront; when it his the frame it reflected back causing all sorts of problems.

They also claimed when they dispensed with the spider and just let the diaphragm centre the voice coil the distortion dropped dramatically.
<hr width="95%" align=center>

<center><a href="http://www.tdk.com/speakers/s60specs.html"><img src="http://www.tdk.com/speakers/img/s60whitebglargenew.jpg"></a>
"TDK Tremor Tremor Multimedia Speakers
Revolutionary NXT technology activates omni- directional sound for an immersive listening experience."</center>

Saw these in a store today, cheapish too, the link says $60.00/pr


Regards
James