PIEZO NXT type panel - Page 60 - diyAudio
Go Back   Home > Forums > Loudspeakers > Planars & Exotics

Planars & Exotics ESL's, planars, and alternative technologies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 14th September 2012, 05:35 AM   #591
diyAudio Member
 
Join Date: Jul 2009
I'm not sure if you're directing that at me, but I have concrete floors (no gap underneath) and then floor to ceiling is 2.4mt or 8 ft, and the roof is a large open space. Its a free-standing 2500ft2 home with no adjoining neighbours I have considered in roof OB subwoofers, Theres heaps of space up there and the roof joists are 45cm spaced hard wood(very strong roof)

The NXT panels I plan to build will only be 100hz and up, probably 30cm wide and 90 cm high mounted in a frame of probably 35cm width and 120cm height with tha panel towards the top, basically largish floor standing speaker size i guess

Not many people in Australia have adjoining walls with neighbours, the joys of living in such a big country!
  Reply With Quote
Old 14th September 2012, 06:00 AM   #592
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
I'd suggest trying wider (or overall larger) panel as you can, even at the very beginning experimental stage. Try the board-driver combination first, and then go building the frame (if you really need one).

It's inevitable to meet a lot of trial-and-errors in this game. Be prepared. Although all other audio DIY activities also need trial-and-errors, this one is the king. Being cheap, it's easily overlooked. Very soon you'll have a pile of wasted material.
  Reply With Quote
Old 14th September 2012, 08:09 AM   #593
diyAudio Member
 
Join Date: Jul 2009
I only have limited room where I want these to go, so large panels are just not gonna happen. It' a big area that theyre going into, and I have zero requirement for them to do less than 80hz or big spl. I will probably just have fun with them anyway, but it will only be for experimentation. They wont stay big for long! I can build a longer panel (say 150cm) but they cant go much wider!

Waiting for exciters in the post is annoying, I want to try them out!
  Reply With Quote
Old 23rd September 2012, 05:03 PM   #594
pol_bct is offline pol_bct  Reunion
diyAudio Member
 
Join Date: May 2009
Location: REUNION Island
Send a message via Yahoo to pol_bct
Lunchietey wrote:
"
I know the whole point of most people's NXT experiments have been to build truly full range and usable panels but has anyone tried a 2 way?
I was thinking a smaller panel(say 300mm x 750mm ish
"

Hi,
from my tests, I would say that by trying to use DML the way we were doing with piston loudspeakers, we miss most of the advantages DML can offer.
In fact when considering amplitude response or distorsion, classic loudspeakers are better, no question... but when looking at surface of radiation, angle of radiation, phase variation, DMLs brings us to a better level with fewer efforts.
so my 2cents is, go with the biggest bad panels you can afford,
don't strive for ultralow weight panels, they do zero bass,
instead find some serious drivers (say 20W) and that's it !

POL
  Reply With Quote
Old 4th October 2012, 11:38 PM   #595
diyAudio Member
 
Join Date: Jul 2009
Well I finally got to do preliminary tests. I'm yet to go up and get the EPS that zygadr used, but did find standard 10mm sheets locally for the first test.

The sheets I have are 600 x 1200 with the driver mounted roughly in the no 1 position on the nxt whitepaper. I used very thin double sided tape(no foam) however I also retained NXT's white mounting feet/basket

Well I was surprised that such fullrange sound could come from this, and SPL although limited was ok for the room it was in. Sound had moments of great clarity, followed by shreaking upper mid. Best description I can give is a cheap oem car door speaker. Bass was heavily dependant on distance from the wall like all open back drivers but could still go deep-ish.

I have a feeling I'm going to fall in to the 'usual' trap, be initially encouraged, then experiment soooo much for little improvement. These foam sheets are too flimsy though, so I'll get the other ones first You could really see the edges moving and self noise on bass was easily audible. Still very interesting!
  Reply With Quote
Old 9th October 2012, 06:40 AM   #596
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
That's it

Surface or edge damping can play a big role on this. Many many possibilities ahead, no doubt. Have fun
  Reply With Quote
Old 29th December 2012, 02:24 AM   #597
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
Default Another curved foamcore panel

The last project in post #576 was not good enough (as always), the wooden spine - also the 'bridge' - is too soft and eats up too much vibration energy from the drivers. Also, this spine restricts the vibration along vertical line. All these factors make the efficiency too low. It sounds smooth but too quiet. So I moved on.

The new one is also a curved 3mm thick foamcore board, but this time there's no spine or ribs whatsoever. The board was bent by applying tension between sides - pulling it into a curve. Diluted PVA glue was applied on paper of both surfaces while it's bent. (Wetted paper becomes very soft and it can be bent too hard, if you use thick rubber band for the tension...)

When dried, the curvy shape was pretty much fixed. No more external tension is needed. At this stage, the overall rigidity is much improved (related to an untreated board). I think this is better than adding wooden ribs, spine or the likes.

Now this board can play upto 20kHz pretty flat. The famous flat drop above 10kHz of this material is much improved.

But, this sandwitch structure - with very different densities of layers - is still causing trouble in HF. The vibration is interrupted and reflected between junctions, causing resonance(s). This time I got a peak at 7.2kHz with more than 10dB amplitude.

I think vibration going through the layers of this sandwitch should be avoided. So I tried this - at the position to be driven, in a small area of rear surface, I cut off the coated paper, and carved the core off, left the front paper intact carefully. A piece of plywood is inserted into this recess.

By this, the driving force can reach the front surface (almost) directly because the plywood is much more dense and rigid than foam. It turned out very good, the resonant peak is gone completely.

This is a 5-unit panel, with only one unit driven at full amplitude and other 4 attenuated (to different degrees). 2 of them are wired in normal polarity and other 3 in reversed. It's now the center channel of a 3-ch linear matrix.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.
  Reply With Quote
Old 29th December 2012, 03:02 PM   #598
diyAudio Member
 
Join Date: Dec 2011
Super cool. Is it audibly better too?

The curving reminds me of the way that they stretch sails on the top of parking lots.

Do you still have flooder tweeters on the sides?
  Reply With Quote
Old 30th December 2012, 01:29 AM   #599
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
You bet

Rule no.1 of DML is the panel should be light and rigid. (So we may see the commercial products are bragging for their hi-tech panel material -- synthetic fiber honeycomb board which is not available in retail market...)

By any certain material, a curvy surface is inherently more rigid than a flat one. So this is indeed better than my previous flat panels with the same material. Flat panels reinforced by ribs can be good, too, but there'd be problem in the discontinuous of structure and vibration propagation, especially the ribs are made of different materials.

Panels of DML and sound boards of musical instruments have a lot in common. The major difference is DML needs more damping for shorter decay and avoiding certain resonances. Following this concept, I've been building panels by imitating sound boards of musical instruments.

Piano and guitar have ribs on their sound boards, I've tried to imitate them on the panels previously. Without ideal and identical material of board itself and ribs, I got half-baked results -- improved but also coming with other problems.

Violin (and families) has curvy sound board without ribs. This is what I tried to imitate in this build. It turned out pretty good, more or less as my expectation. A bonus from the curvy surface is better self-damping. I guess both the shape and pretensioned structure contribute.

Oh, there's one thing very important. I'm not saying curved foamcore board is the optimal solution (for DIY DML), it's just one pretty good attempt on what I have on hand. This is the charm (and nightmare at the same time) of this thing -- endless possibilities which are so easily accessible.

And yes, flooder tweeters are still there on side channels, unseen behind the naked array. They are relatively small but still important to the whole system.

Last edited by CLS; 30th December 2012 at 01:36 AM.
  Reply With Quote
Old 30th December 2012, 04:07 AM   #600
nebojsa is offline nebojsa  United States
diyAudio Member
 
Join Date: Feb 2007
Location: seattle wa
Hi Cls a bit off the topic, I was waiting for an update on your baffles speakers. How are they sounding?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 06:22 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2