NXT.......rubbish??....THINK AGAIN!

Kludden · « **Reply #1280 on:** 29 Mar 2011, 06:32 am »

Hi PLC!

It was very nice to see some pictures of this panels

Gave me some ideas how I will mount my panels.

Regards
Kludden

pol_bct · « **Reply #1281 on:** 29 Mar 2011, 06:40 am »

Quote from: CLS on 28 Mar 2011, 02:13 am

Hello there,

This is my first post here, and I'm glad it's in this wonderful thread.

First of all I'd like to thank all your contributions. I've learned a lot. Here are my recent experiments about these little excitors and big panels:

My 2nd trial with CC (in front of my previous system):
....................................... ....................................
....................................... ....................................
Already long, more later....

Hello CLS, not bad for a first post

I am so to say, speechless !

maybe you jumped a little fast out of C.C.
to me, it sounds more natural than all the foam I've tried
but needs a hardened side, with coating or any else method.

Bass are a little tricky to get, the lighter the panel the thinner the bass
I'm a little suspicious about the multiway DML, I would keep it simple...

best regards

POL

CLS · « **Reply #1282 on:** 29 Mar 2011, 07:34 am »

Hi,

Thanks for the responses and kind words.

My initial impressions of CC were very good. It's just I can't get the 'proper' size for the time being, and I look for high efficiency (uh... you may see some parts of my previous horn system in the picture), so I took PS foam board first.

I believe this is just the beginning. I'm prepared for all kinds of problems and experiments. Applying damping to the panel will be a part of them. (that nasty peak at 6.3kHz is now taken care by EQ - DEQ2496, which can easily dail in deep and narrow notch, pretty handy for this)

About the 2way setup, I also felt something wrong by listening test. I've tried two methods up to now, both actively xover'ed: (a) ordinary 2-way [HP/LP]; (b) 1-unit in fullrange + 4-unit for bass augmentation.

To my ears, (b) is better in overall coherence. And the phase change in (a) is audible (even with 1st order filter, together with other requirements in response shaping...), thus a sound with smeared mid to midbass.

I also got a feeling that the passive series filter for 4-unit group has better coherence than the active version. But it needs some more shelfing filter in upstream digital EQ, thus some loss in digital resolution in the attenuated zone. Doing it actively resolves this problem and is easier to dial in the bass augmentation. Tradeoffs, tradeoffs....

As to the bass reproduction, it's to my surprise that light panel is getting thinner bass. (My earlier CC versions are smaller in area, so I got no apple to apple comparison.) I thought lighter load (higher mass ratio of excitor/panel) could give higher excursion, no?

Or, the sound propagation on the panel needs some 'inertia' to keep the wave moving along? Like shaking a metal chain vs cotton rope - the latter is light and soft (higher self-damping), so the wave stop earlier... ?

If we need heavier material for the bass, then I guess there's another set of compromises...

I've read about concepts of multi-panel, but has anyone really tried it? Or did I miss it?

mkstat · « **Reply #1283 on:** 30 Mar 2011, 07:37 am »

Hi CLS!

I find your your 2-way approach a very interesting thing.

To augment the bass output you could try a series/paralell connection of the bass section together with a 1st order series crossover - this will give best phase response, at least 6db gain for the LF-section and a more constant impedance.

you could use this as a starting point:

although mounting the exciters with screws is handy, it will add losses and compression at high excursions, if steel screws are used you may disturb the magnetic field - cooling will also be affected negatively -> higher distortion at lower levels.

regards
m

bobloblob · « **Reply #1284 on:** 30 Mar 2011, 04:15 pm »

POL-
I may have misread or assumed wrongly the lay-out of your 4-exciter alignment in the center of your single panel. When you wrote that you mounted all four as close to each other as possible, I had assumed that the four were mounted nearly touching, but in a vertical array, not grouped together in a circle/square. Common sense (which isn't always common, and not always sensible) told me that that would give better bass. Was I wrong?

pol_bct · « **Reply #1285 on:** 30 Mar 2011, 04:55 pm »

hi bobloblob
I have done both with little or no noticeable differences
I did the supposition that a line array of transducers would act as a single exciter in the prefered direction (longest side), IE perpendicular to that pseudo linearray UNDER a certain frequency.
but there are many others parameters which may "damp" the best config.

what surprised me more was the use of this config in a two panels "classic stereo" config, because I have definitely switched for a single stereo panel.
but any new cut&try is a usefull source of informations.

POL

sedge · « **Reply #1286 on:** 30 Mar 2011, 11:59 pm »

cls
in your pics you seem to have mounted all of your exciters in the bottom third of your panel .
For the four exciters to drive into LF should they not be mounted in the center or in a line down the middle of the panel.
the panel also looks like foamboard

that is a very good looking horn setup you have ,people are going to think you are as mad as the rest of us on this circle.
sedge

CLS · « **Reply #1287 on:** 31 Mar 2011, 03:22 am »

Sigh~ one hour of typing is all gone! Gotta do it again

--------------

Hi sedge,

My exciters are not in the center. Both groups are at the 1/3 postions (horizontally). They are placed in the lower third because it's easier for implement my idea of 'up-side-down pendulum' supporting method, and it looks more stable in my minimal frame.

Luckily (and to my surprise), the height of image is irrelevant to the postion of exciters. I even heard some treble appearing very high, approaching the top of the panel, just amazing.

Yes, the panel is some kind of PS foam. I'm looking for high efficiency so I tried it. 2 major annoying resonant peaks in the current setup: the nasty one is @ 6.3kHz with > 15dB higher than average (probably the same sharp squeak when it's rubbed), the other is broad and mild around 2.5kH, 2~3dB hump with a sharper 6~7dB peak at the center. Both are taken care of by DEQ2496, for now.

I'm thinking of panel damping in the next step, both "EnABL" and "Manboni" are in mind, will surely try them in the next step. (uh~ there're so many things to do in the 'next' step...)

As to "you are as mad as the rest of us on this circle", I take that as a compliment, thank you

(I'm surely crazy, I know that. When spotting the first complete panel on its frame, my wife said to me, what's that? are you going to build a sailboat in the living room?

)

to mkstat,

Thanks a lot for your idea of series xover (and your time and effort in the sim and chart).

But I guess you would have missed one point in my previous post - my chip amp is very unusual with a 20 Ohm output impedance. It's setup by a mixed voltage and current feedback method brought up by Mr. Rod Elliott here: http://sound.westhost.com/project56.htm

And in the last page (reply # 1279) I posted the impedance plot of the trial system, with all 5 excitors wired in series with 4 of them bypassed by a cap (that can be seen as one half of a 'normal' series xover). Because of the bypass cap, the group of 4 is unseen (shorted) in the higher range, thus a clear trend of high impedance in the bass and low impedance in the mid and high frequencies. (plateau under 200Hz, broad valley center around 2.5kHz)

The high impedance drive interacts closely with load impedance, thus an output curve almost tracking the impedance curve:

With 20 Ohm output impedance and the series connection of the exciters, effectively I got a 7.5dB of shelfing filter built-in between amp and speaker. Unforturnately this is still not enough. I need another 15~18dB of shelfing in upstream DEQ to make it flat down to 40Hz. That's why later I turned to active setup for more boost and freer adjustment.

Interestingly it's the first time I feel passive version is better to my ear - smoother and more coherent. So I'll probably explore it more...

And thanks a lot for the reminder of screw / magnet circuit thing, which I overlooked indeed. I'll try to compare the difference of securing means.

Ah~ more experiments are needed for sure. I'll try anything I can, including augmented by cone woofers for the bottom octave, or separate panels by bass shakers....

Will keep you guys updated once I find something new and interesting. But I'm a slow builder, so don't hold your breath for this.

See you...

irishpatrick33 · « **Reply #1288 on:** 6 Apr 2011, 01:57 am »

So here's my opinion. Though I would like to thank all contributors prior to said opinion.

Anyway, I am disappointed. It is WAY too much time and effort. With the exception of buying Magnepan 1.6 feet ($90) for my zigmaplanars... the rest of the items are standard issue and nothing extravagant. Even wood costs a lot these days. I spent upwards of $300. That's not a lot of money for speakers--but much more than I was expecting/hoping.

There are too many hoops to jump through. Finding a large panel is a miracle. I had to settle for 3'x3' cardboard. Unfortunately you can't buy individual sheets of this size. I had to buy a stack of 50 which costs around $60. Though the stack of 50 might have saved me--as only a handful were straight. Not sure how much that mattered, because the cardboard turned into a roly poly the second shellac hit it. I never got the entire warp removed from one panel, even with weights. It would keep popping right back to form days later.

Anyway, this is the second set I have created. The first set was a cheapy foamcore unit. The sound was decent, cost very little, and was assembled in no time at all. I posted pictures previously if anybody wants to search. The price and labor were in line with the performance. I can not say the same thing about my new set. The performance is an upgrade: more efficient, better bass, improved soundstage, and such. But the upgrade isn't night and day. I might consider them marginal improvements. Probably still a good speaker for the money. But not worth the time... I''m guessing over 100 hours spent. That's an inflated number for a myriad of reasons--most importantly I wanted my speakers to be beautiful (and they are--warp and all). No matter how you slice it, they were a LOT of work. And the performance hasn't justified it.

I'll post pictures soon when I have time. Maybe I am still a bit miffed at how much time and effort these took. I'll give them some time to break-in and post pictures with an update.

CLS · « **Reply #1289 on:** 6 Apr 2011, 05:30 am »

Effort vs money vs performace.... hmmm

So far so good here. I spent US$100 for excitors (10 pairs, that's their min. order), and $40 or so for panels (2 pairs). I've used one half of them up to now.

For the performance they give, it's the greatest c/p project I've ever had. No regret for dismantling my old horn system. Crazy? maybe

Along the experiements, I thought I'd better release the LF load on the flimsy panels and poor little drivers. So I added cone woofers for bass augmentation - my old 18" pro woofer on OB.

I kept the panel running fullrange, but not anymore in the stress of additional LF boost. The OB (dipole) cone woofers are arranged so that they cancel a portion of LF produced by the panel at the rear side (negative lobe of the dipole bass meets bipole NXT panel).

At first it seemed not so clearly cancelled. Then I tried reversing the polarity of OB sub -- by contrast, the constructive interference is very obvious -- a big boomy bass lobe is formed at the center. Switched them back, then the bass sounds go back to both sides, as I walk around them. The destructive/constructive interferences between them are not clean-cut, but clearly audible. I guess this also reveals the 'fact' that NXT panel is radiating mostly bipole (same polarity at both sides), and indeed very ramdom (can't be cancelled out very cleanly).

Two major goals for this: less LF trapped between panels and wall, and keeping the bass sounds appear at far left and far right. After some tunings, they perform very good now. Excellent overall coherence (you all know), plus very strong and tuneful bass.

As you might get a hint by my posts, I have zero "loyalty" to any specific technology. I like anything that works and take their best part(s). (and hopefully I can blend them well...)

The journey goes on...

pol_bct · « **Reply #1290 on:** 6 Apr 2011, 11:13 am »

Irishpatrick33

I, too, spent more than expected, but I learned A LOT about those little transducers
and this has a huge value to me. It is not everyday that we get to a new principle of radiation,
and this one has his own advantages, no other loudspeaker can come close.

POL

zygadr · « **Reply #1291 on:** 7 Apr 2011, 02:32 am »

Some nice work there CLS!

I am a bit concerned about what the panel material is after your description of it's properties.
It may well be a thin EPS .....who knows?............however if it feels very soft to the touch, it's most likely a different form of foam that may be detrimental to the sound.......bass and most likely the highs.

Having not heard your speakers, I probably shouldn't be commenting any further other than to say that splitting the sound to subs etc. is not what this speaker is all about........not to me at least.

Corrugated cardboard is back in my home at the moment.
It's uncoated as all attempts to stop it from warping have failed..............sorry if I have given you false hope here as the initial experiments were with small peices, not large panels.

C.C. as we may recall way back in this thread, sounds very, very ''natural''.
I will be the first to admit that EPS is easier to get up and running to achieve good highs where C.C has a weakness.

Going back on some history, you may recall that I tried a small peizo on the back of the panel, just wired in paralell to the NXT exciters to increase the high frequency output?
The cone was removed entirely from it's plastic housing, the wires desoldered, and extension wires used to position the peizo at the middle and to the inside edge of each panel, making a ''left and right speaker pair''

I have repeated this technique recently and believe that this method and combination produces the most natural and listenable sound...............emulating a quality, but giant full range twin cone driver.

I still use 4 exciters per panel, equally spaced, but the size of each panel is 6 ft by 3 ft.
Currently they are unmounted as CLS has also given me some ideas thanks to his great photos.

CLS · « **Reply #1292 on:** 7 Apr 2011, 05:48 am »

Hi,

Thanks for the kind words

I'd love to try CC again with bigger size I had, but that won't happen very soon. I've not finished experiments I want to do on the current foam panel. I've not applied any damping to the panel, yet.

(Although I got the materials ready on hand. Too much to do with too little time, as always... )

Before I tried this NXT stuff (and posted), I've read through this whole thread several times. So yes I remember the piezo tweeters. On my current foam panels, the HF needs about 3~4dB EQ boost to be reasonably flat to the top. And then I feel there's no lacking. (Personally, I like slightly warmer balance)

But anyway, later I tried adding a supertweeter, too, but wired as mono, placed at the center.

(it's not in the picture) Why mono? Refer to this: http://www.diyaudio.com/forums/multi-way/10962-stereolith-loudspeakers-question.html

This additional tweeter is up-firing. With its contribution to overall HF response, that previous EQ boost is no longer needed. (I got so many helps from EQ during setting up, but I also keep trying to eliminate them...

)

I'd also love to try all three LCR channels in a single big panel as POL suggested. (I'm also striving for solid center image.) However it's not practical in my place, for now. I can't get rid of the TV just yet.

The fixture of my panel is built as minimal as can be. The original thought is to make its vibrations as free as possible. Now I realize some control (damping) is needed...

pol_bct · « **Reply #1293 on:** 7 Apr 2011, 09:51 am »

CLS

> I'd also love to try all three LCR channels in a single big panel as POL suggested. (I'm also striving for solid center image.) However it's not practical in my place, for now. I can't get rid of the TV just yet

maybe you could put the TV in front of a huge panel

POL

CLS · « **Reply #1294 on:** 7 Apr 2011, 10:24 am »

But! There'd be not enough space between rear wall and the panel

And the center image is right at the position of TV and blocked by it.

bobloblob · « **Reply #1295 on:** 7 Apr 2011, 04:42 pm »

What has intrigued me for several years is the idea of a panel speaker that could also be used as the screen for a projection tv. This single stereo panel concept with the exciters seems perfect. One of the uses touted for the exciters is mounting them behind pictures and posters to provide sound for advertising. Why not tv? The projectors now seem to have come down in price and size considerably, though of course they are not as convenient as thin panel lcd/led tv's.

pol_bct · « **Reply #1296 on:** 7 Apr 2011, 04:54 pm »

> But! There'd be not enough space between rear wall and the panel

good point

>

And the center image is right at the position of TV and blocked by it.

bad one,
this is the magic of DML, on a big panel you can walk in front or put anything you want in the way , no serious obstruction

POL

CLS · « **Reply #1297 on:** 8 Apr 2011, 02:43 am »

Quote from: pol_bct on 7 Apr 2011, 04:54 pm

...

this is the magic of DML, on a big panel you can walk in front or put anything you want in the way , no serious obstruction

POL

Hmmm... I'm not quite sure about that. Maybe my panels are not big enough (!!). When my wife is standing in front of one panel, some sounds are indeed blocked. It's audible, clearly enough.

Two things I should add:

1) She's not fat at all

2) The blocking effect is indeed much less than other type of speakers, especially those smaller ones. More sounds are travelling through, no matter how.

...

BTW, I got another special feeling, about its natural presentation. My kitchen is open to living room, in a single space as a whole. When I'm doing the dishes (yes, that's my job

), with the water running, I still can hear pretty good details of the sound.

It's odd. The sound of the tap water is quite a loud broad band noise and can usually cover a lot of other sounds. But not on DML panels ! (?)

Also, the sounds from these DML panels seem more immune to other type of environmental noises. The music is just flowing through. It's not the higher loudness fighting against and suppressing the noises, it just becomes one of the sounds, naturally. Of course there'd be inevitable some loss in the most delicate small details, but generally the playing music stays listenable to a much greater extent compared to other type of speakers.

This didn't happen in my previous speakers.

Is it because of the big radiating area?

zygadr · « **Reply #1298 on:** 8 Apr 2011, 03:00 am »

Quote from: CLS on 8 Apr 2011, 02:43 am

Hmmm... I'm not quite sure about that. Maybe my panels are not big enough (!!). When my wife is standing in front of one panel, some sounds are indeed blocked. It's audible, clearly enough.

Two things I should add:

1) She's not fat at all
2) The blocking effect is indeed much less than other type of speakers, especially those smaller ones. More sounds are travelling through, no matter how.

...

BTW, I got another special feeling, about its natural presentation. My kitchen is open to living room, in a single space as a whole. When I'm doing the dishes (yes, that's my job ), with the water running, I still can hear pretty good details of the sound.

It's odd. The sound of the tap water is quite a loud broad band noise and can usually cover a lot of other sounds. But not on DML panels ! (?)

Also, the sounds from these DML panels seem more immune to other type of environmental noises. The music is just flowing through. It's not the higher loudness fighting against and suppressing the noises, it just becomes one of the sounds, naturally. Of course there'd be inevitable some loss in the most delicate small details, but generally the playing music stays listenable to a much greater extent compared to other type of speakers.

This didn't happen in my previous speakers.

Is it because of the big radiating area?

CLS, .............Yes, ...............this is the magic of what ONLY this technology is capable of.

You only have to switch back to normal forward firing speakers (or even your horns, as I have) to experience this strange phenomenon at work.

The sound seems to carry even the small details right accross very large areas as if a real band, orchestra, trio or whatever is actually playing in that room.

This ''projection'' is weird..............very weird...............but GOOD!
They play music in a more ''controlled'' way..............treating dynamics as they are on the recording, not fudging or synthesising them.

Take dynamic speakers for a start........................listen to some music- the same each morning..........jazz trio is a good example.
Now connect the panels and match the volume level so that they sound as loud as the dynamic speakers.
You will VERY SOON notice that something has dramatically changed...........for the better!

The same track is now ''flowing'' in a much more ''musical'' fashion. Dynamics are not being compressed, they are being released as needed...........nothing is artificial.............just natural.

The NXT principle is the only panel technology that I have heard that does this. It's approach to musical reproduction is not perfect, but it is more real to the sound of live instruments and the way they project and energize the listening area around them.

pol_bct · « **Reply #1299 on:** 8 Apr 2011, 12:19 pm »

Quote from: CLS on 8 Apr 2011, 02:43 am

BTW, I got another special feeling, about its natural presentation. My kitchen is open to living room, in a single space as a whole. When I'm doing the dishes (yes, that's my job ), with the water running, I still can hear pretty good details of the sound.

It's odd. The sound of the tap water is quite a loud broad band noise and can usually cover a lot of other sounds. But not on DML panels ! (?)

Also, the sounds from these DML panels seem more immune to other type of environmental noises. The music is just flowing through. It's not the higher loudness fighting against and suppressing the noises, it just becomes one of the sounds, naturally. Of course there'd be inevitable some loss in the most delicate small details, but generally the playing music stays listenable to a much greater extent compared to other type of speakers.

This didn't happen in my previous speakers.

Is it because of the big radiating area?

I think this is related to the big radiating area.
I get the same feeling, this fine "next room" natural listening effect

think of a point source in a room, there will be lots of wall, floor and ceiling reflexions, who have a strong phase coherence because they originate from the same single point, only delayed, the room signature overcomes the loudspeaker.
with a big panel, the room acts more like a wave guide, with less or little reflexions.

POL