Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

Carbon fiber + nomex honeycomb sandwich DML panel construction project
Carbon fiber + nomex honeycomb sandwich DML panel construction project
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 7th January 2017, 03:05 AM   #91
altie is online now altie
diyAudio Member
 
Join Date: May 2010
Location: Portland, OR
I didn't think I had a cable that would work for loopback but finally found one. The signal chain minus the speakers, mic and amp is +/- something like 0.5dB across the band, 0.1-0.2% THD, microseconds of group delay, so it doesn't seem to be a major contributor.
  Reply With Quote
Old 7th January 2017, 03:41 AM   #92
bentoronto is offline bentoronto  Canada
diyAudio Member
 
Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
Carbon fiber + nomex honeycomb sandwich DML panel construction project
Yes, proper procedure to ensure test gear is working well.

I think what I'd do next is to examine speaker performance from loud to soft, step by step. You might find a knee-point below which the speaker is working notably better. that will be a hint for what to explore next.

I'd also try a 50-Ohm resistor in series with the exciter to see if impairing the amp damping influence on the exciter matters. Nice to run an impedance curve on the exciter - all you have to do is read the voltage across the exciter when the 50-Ohm resistor is in series (doesn't have to be calibrated, you just want to see where the resonance(s) show up in the electrical back EMF... make sure you know which is the ground side).

Then two exciters, push-pull to explore that 2nd harmonic issue.



Ben
__________________
HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio (and just posted data for a folded 17-foot pipe sub)

Last edited by bentoronto; 7th January 2017 at 03:45 AM.
  Reply With Quote
Old 28th October 2017, 08:07 PM   #93
JunoComposites is offline JunoComposites
diyAudio Member
 
Join Date: Oct 2017
Post Carbon fiber store www.carbonfibreshop.com

Quote:
Originally Posted by altie View Post
Sourcing materials

Carbon fiber and nomex are both individually regarded as unobtanium for most of us DIYers. Personally my threshold for a DIY project is that if I'm already investing my time, even if it's probably going to sound really good, I'd like to keep it under $100 in case the whole project is a wash.

You can buy prefab carbon + nomex honeycomb sandwich in form very close to what's in the Tectonic video I posted earlier (probably thicker, but probably not substantially heavier or less stiff): here it is at Dragon Plate for $40/6x6" square: Carbon Fiber Nomex Honeycomb Core 0.5" x 6" x 6"

In larger sheets for a little under $100/sq. ft.: Carbon Fiber Sheet with Honeycomb Core, 1/8 inch thick - Pegasus Auto Racing Supplies

Even if you buy separate, nomex honeycomb itself is pretty expensive, like $120 for a 40x48" sheet: Nomex Honeycomb Sandwich Core Material in stock | Fibre Glast. Bigger than I thought I'd need, at least for an initial build, but also over total budget.

Likewise carbon fiber: $27/sq. ft. panel: Carbon Fiber Sheets & Fabric - Carbon Fiber Gear.

So I had to get a little more creative...
No longer 'unobtanium'.
Small quantities available to large consumers and DIY'ers
https://carbonfibreshop.com
Attached Files
File Type: pdf Juno Catalogue OCT17.pdf (879.7 KB, 36 views)
  Reply With Quote
Old 3rd November 2017, 10:58 AM   #94
Adam Bernau is offline Adam Bernau  Czech Republic
diyAudio Member
 
Adam Bernau's Avatar
 
Join Date: Sep 2010
Location: Prague
Hi guys,
I must say that i highly admire your dedication and will to experiment, the DML technology has certainly huge advantages in many aspects.
Just a thought about the possible issues with your sandwich- is it possible, that it is just too thick and too stiff to start bending properly, and isnt this the exact reason for surprisingly low sensitivity and bad frequency response? Perhaps the thick, stiff sandwich that you have used is just not willing to participate on the bending and is absorbing a lot of the energy?
I am attaching a picture of a back of small BMR speaker, which works on similar principle and the membrane is of size about 4 inch. You can clearly see, that there are two layers of relatively thin paper with a not so thick honeycomb in the middle.
The overall thickness of the sandwich is around 3-3,5 mm max, so perhaps you could try to focus on something less stiff, less thick and more cardboard like
Attached Images
File Type: jpg WP_20171103_11_43_47_Pro.jpg (972.8 KB, 397 views)

Last edited by Adam Bernau; 3rd November 2017 at 11:07 AM.
  Reply With Quote
Old 2nd April 2018, 09:23 PM   #95
ldc is offline ldc
diyAudio Member
 
Join Date: Mar 2018
Hello everyone... Another person getting caught with the DML bug..

So far i have just been reading up on the technology and trying to understand it all, and there is *alot* of new things to grasp..

I did come by something when browsing one of the links posted in this thread and that is:
* Soller Composites * Epoxy & Related products
"Carbon Nanotube Enhanced Epoxy Resin"

Was thinking is might be possible to coat XPS sheets with this at home, but don't have a clue about the performance.. But for $50 for a pint or quart for $80 it may be something worth trying out.


My target is to replace my current home-theater setup with DML speakers and, preferably increase the size of the sweet-spot.

My wants:
- Thin, preferably enclosed, wall mounter speakers with as little vibrations passing to the wall. (suspending the panels with either fish-line or foam?)
- "good enough" sound that at least matches clarity of my QLN 604 MKII but do not have to match in power.
- The front-speakers can be up to 1m x 2m in size. Center up to 1.5m square. Rear should preferably be no larger than 1m square. For imperial people - 1m is about 40 inches
- Not a strict requirement to go below 100hz, but nice if it had a bit at least for casual viewing. (some seems to have had some promising results in this thread)


What thoughts might you have on this? Achievable? Just a dream? Willing to put in some work on it, but would be nice to get some feedback first.

Thanks in advance for any suggestions or "continue dreaming" replies.

My first build, when my first exciters arrive, will probably be a pair of smallish (similar in size to WrineX's DML's) stero-speakers to start trying things out.. But could not wait with posting here to thank you all for publishing your results so far..
  Reply With Quote
Old 8th April 2018, 07:54 PM   #96
esl 63 is offline esl 63
diyAudio Member
 
Join Date: Aug 2010
An externally hosted image should be here but it is no longer accessible. Please upload images instead of linking to them to prevent this.


Its importent with low mass!!
  Reply With Quote
Old 25th April 2018, 02:24 PM   #97
ldc is offline ldc
diyAudio Member
 
Join Date: Mar 2018
Perhaps not always, but being able to control mass/stiffness is extremely important when designing a panel. This seems to be one reason why so much is built around honeycomb-structures since they can be easily adjusted to the wanted weight/stiffness-ratio.

https://pdfs.semanticscholar.org/469...21918e6172.pdf

Page 27 is quite interesting when designing a panel.
What i get from this is that the higher the mass the less stiff, and the lower the mass the stiffer it should be.

Quote:
As a consequence, one usually wants the B/m ratio lower, which means either the
mass per unit area should be higher, or the bending stiffness should be lower. The
choice is often to find a material with lower bending stiffness since high density
implies low radiated sound power and that is usually one does not want to see.
Another important reason to keep f0 low is that the asymptotic modal density is
inversely proportional to the ratio of bending stiffness B and the mass per unit area
m, and one wants it as high as possible. The same reason applies for the critical
frequency, because below the critical frequency the directivities of DML behave more
omni-directional. However, to achieve a proper radiation efficiency and radiated
sound power, the Youngs modulus cannot be too low. Thus one needs to carefully
trade between E and the density ρ to accomplish ones goal of designing
Not making any claims since i have still not done any types of tests myself, but it's a good read, for novices, to try and understand the physics behind DML's.


If only my exciter-delivery would arrive.. Been stuck in transit for a week now.
  Reply With Quote
Old 26th April 2018, 04:13 AM   #98
DMLBES is offline DMLBES
diyAudio Member
 
Join Date: Mar 2017
After reading and wasting my time on that long *** article the only conclusion and suggestion for future improvement in sound quality was to use a EQ. SMDH
  Reply With Quote
Old 12th June 2018, 01:05 AM   #99
zanter is offline zanter  Singapore
diyAudio Member
 
Join Date: Jun 2018
I have been reading this thread and in all the DML sounds I have heard online, the best sounding board came from this guy who used an guitar as a sounding board. YouTube


Natural sound..Well comes from a guitar so guitars sound amazing! He put the exciter behind, which is not ideal as it should be placed at the sound board spruce top near the bridge. As a result the vocals sounded "hollow" as the sound is reflected from inside the guitar before exiting from the front hole.


So if we use exciters in respective instruments like violin, piano, drums etc, I believe we would get sounds which are smooth and natural to that instrument.
  Reply With Quote
Old 12th June 2018, 10:11 AM   #100
WrineX is offline WrineX  Netherlands
diyAudio Member
 
WrineX's Avatar
 
Join Date: Mar 2004
Location: Den Haag
Quote:
Originally Posted by zanter View Post
I have been reading this thread and in all the DML sounds I have heard online, the best sounding board came from this guy who used an guitar as a sounding board. YouTube


Natural sound..Well comes from a guitar so guitars sound amazing! He put the exciter behind, which is not ideal as it should be placed at the sound board spruce top near the bridge. As a result the vocals sounded "hollow" as the sound is reflected from inside the guitar before exiting from the front hole.


So if we use exciters in respective instruments like violin, piano, drums etc, I believe we would get sounds which are smooth and natural to that instrument.
well i dont want to stick a feather in my own ars but i think mine sounded better. but then again he used very cheap of the shelf exciter so in terms of simplicity he got the better of me for sure

YouTube


another problem with a guitar body is.... well it is a guitar body thats is tuned to a specific task. making guitar noises primarily

Last edited by WrineX; 12th June 2018 at 10:14 AM.
  Reply With Quote

Reply


Carbon fiber + nomex honeycomb sandwich DML panel construction projectHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Honeycomb composite panel enclosure, dual opposed configuration rhapsodee Subwoofers 6 1st September 2010 03:26 PM
A Carbon Fiber store!! DaveThreshold Analogue Source 9 11th May 2009 04:52 AM
carbon fiber earing Instruments and Amps 8 13th March 2007 05:04 AM
How do I use carbon fiber + MDF wood + glass fiber to make speaker? sonyacer Multi-Way 16 10th May 2004 03:57 PM
CArbon fiber enclosure jouch Multi-Way 1 14th March 2002 10:49 AM


New To Site? Need Help?

All times are GMT. The time now is 08:47 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki