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

j gale · « **Reply #2340 on:** 4 May 2015, 03:09 pm »

Hi, Just my 2 cents

I get the impression that some of you are trying to run before you can walk. Before effort is put into finding exotic materials or the best exciter you need to have a base line of info. to work from. Get one of the medium to higher power exciters available (they're cheap) and mount it on a piece of cardboard at the MONACOR position. Try a piece about 3'x4' with 6" or so wings bent back so it will stand. Be prepared to be astounded by what it can do. I have tried 8 or 9 different exciters but the panel material makes the biggest difference by far. I think that until you have done this you are trying to work the dark without any real appreciation of the possibilities. Forget what you know about speakers most doesn't apply here. Also some are playing with tiny panels. Don't bother until you have heard what 3'x4' or bigger can do. Again my 2 cents after playing with this since 2009. Jim

sedge · « **Reply #2341 on:** 5 May 2015, 02:44 am »

J Gale
I agree with most of what you say ,it is easier to get a larger panel to sound good than a smaller panel ,but a good sounding small panel is possible if you don't have the room for an 8ft x4ft panel.

Frank40
I am at the moment using a panel called vitrex it is used as underlay for flooring ,it looks similar to your depron ,the panel size is 85cm x60cm by 5mm,this is the largest size they seem to do?
the el cheapo exciters I use (10 watts or so)drives these and the larger poly panels to very very loud levels ,so not sure how the panels wood take more power?
But the flexibility to EQ the response without over heating the exciter can only be good,
I would think?
I had a 6x2ft x3mm ply panel that I couldn't use because of the low output ,a high power exciter like yours would have sorted that problem I think.
A 2mm panel might be a little too lossy (flexible) but give it a go and let us know ,some depron panels seem to have paper surfaces ,this can over damp the panel.
Steve

j gale · « **Reply #2342 on:** 5 May 2015, 04:51 am »

Sedge, I agree that a small panel is possible. The point I was trying to make is that a 3'x4' cardboard with 6" wings leaving a 2'x4' face will give a taste of almost full range sound. I see guys playing with small panels complaining about no bass. I see others trying to fashion an exciter never having heard a cheap commercial one. My suggestion was to have something to compare these efforts to first, otherwise how can you make an assessment. Just trying to suggest a cheap and easy test.

Odal3 · « **Reply #2343 on:** 5 May 2015, 05:22 am »

...and at page 117 the discussion on the never-ending thread starts up again.

Fun to see both new and old members adding their thoughts. Please keep it going!!!!!

Very large panel sizes get tricky to make it rigid enough and still being able to drive them. The largest I tried was a 4 x 8 ft panel of XPS but the sound was a bit floppy - probably would have needed to use a thicker board.

The 40W exciters drives the large plywood boards pretty loud - at least for my listening taste. A 2.5 x 5 wood panel (1/4" thickness) gets you a frequency response from about 30 to 10kHz with a drop after that (a thinner board is too flexible and sounds bad unless framed for stiffness at the expense of bass). With some more care to treat the edges and "skin" treatment it should push it a bit higher. But for someone who is a bit sensitive to high pitch sounds, the lower HF fits me perfectly.

BTW: The new exciter I'm trying is quickly becoming a favorite. Similar clarity as the Ultras (flatter response 6-10kHz) on the top-end, and great bass with no "knocking" sound. Hoping the reliability is a bit better!

As OB_Newbie stated earlier - if you plan to play them with a sub, a smaller panel might actually be a benefit.

Odal3 · « **Reply #2344 on:** 5 May 2015, 05:39 am »

Quote from: soldermizer on 4 May 2015, 01:39 pm

Your comment bolsters my feeling that DML is very much an art form. Surely it is one of the cheapest DIY projects available for the stereo nut And believe me, I know cheap!

It's the easy and cheap experimentation that makes it fun. It's freaking addicting and it's hard to stop. Consider this a warning

As with anything audio, there are many different DML solutions leading to good result so it's nice to see new experiments going on.

soldermizer · « **Reply #2345 on:** 6 May 2015, 12:31 pm »

Although I am a novice, my panels so far are coroplast plastic stolen advertising signs (ok) but for larger panels, from Lowe's [I am in USA] I get 4x8' of
http://www.rmax.com/products/wall-products/rmatte-plus-3/

Which is not the cheapest stuff but the cheapest 4x8 is even lighter, too damped, and little crumbs fall off of the panel as you are carrying it to the check-out, which does not inspire confidence in me

The R-MAX is a "polyisocyanurate", a material I had not heard of before. I think for DML applications this is good, it has aluminum facing on both sides. All I've read of DML suggests that a skin is a good thing for highs; the sand-it-and-white-glue-it man to the contrary of course

In any event, using my autosound drivers, this material has made a very good first attempt for "big" panels (I started about 4x4' each.) Just like with materials, appears there is little consensus on shape or alleged "golden ratio". I tried the 0.95:1 (square more or less) but rapidly tried an irregular trapezoid. No audible difference, but I haven't run any detailed tests.

Since right now one of my goals is unreasonably loud, and to use materials on hand (cheap autosound drivers), I am going to try the "dual opposed" mount on my panel(s) for now. Of the many beliefs and assertions that blossom like a child's wishes when drafting his list for Santa (that's Saint Nicholas for you foreigners

) that have appeared in this "thread" (it is more a tapestry now) that seem to have some plausibility is this: to use a single exciter for maximum DML Magic. I make the Bold Assertion that I am doing the same or nearly the same thing if I have a push-pull pair on my panel, since they is massaging a single point on the panel

Odal3 · « **Reply #2346 on:** 7 May 2015, 04:25 am »

I tried one of the crumbling panels once - I tore off the silver facing and that was a mess with small white fluff all-over. :oNot sure if that is the same as you have.

If loud is your goal, you should also try placing a few more exciters on the same side and compare it to the push-pull. I still have four low power exciters on two panels and they sound OK and louder. They are mounted monacor position 1-4. You get a bit more of dips and peaks in the frequency spectrum but not too bad.

Odal3 · « **Reply #2347 on:** 7 May 2015, 04:32 am »

Here's a thing you probably should not do: I have my heavy wood panel suspended using metal wire. Somehow the length of the wire combined with the tension in the wire from the weight of the board creates a good guitarr string! So when the speaker vibrates the metal wire vibrates a lot and creates a sound. You can especially hear it when quickly muting the sound and the wire continues to vibrate for a second or two.

Frank40 · « **Reply #2348 on:** 7 May 2015, 06:00 pm »

Hello,

Serge, it sound like the board I got is much the same as the one you have, the ones I got is 60 by 120 cm.... I was thinking of cutting or milling the suspension directly in the foam, also making some geometric cuts to minimize the twist of the voice coil when the membrane moves back and forth.

It is also possible to make the membranes with different thickness in relationship to center and edges, that way to can have some control over the movement of the membrane.

I have made a schematic of what I mean, see pic.

sedge · « **Reply #2349 on:** 8 May 2015, 05:57 pm »

Frank40
The best advice I can give is to just glue the exciter to one of your panels and listen to the changing sound as you try to restrict or damp the panel edges ,only then will you be able to understand why it only takes small changes to the panel to completely ruin the sound.
Personally I prefer a lossy type panel ,not to rigid not to floppy .
Using paper or foil on the panel surface is not a good idea as this will probably over damp the panel (poor HF and soft sound).
These things you will only find out with hands on experience .
It can drive you mad sometimes ,so be prepared.
Steve

Frank40 · « **Reply #2350 on:** 9 May 2015, 07:09 pm »

I just found this material, looks like a nice material for making a sandwich membrane.

http://shop1.r-g.de/item/5001832-050-PA

TXATC · « **Reply #2351 on:** 9 May 2015, 11:27 pm »

Hello again guys! No updates yet. Storms her in North Texas haven't allowed me in the workshop for a bit as the Mrs. Has her van in there in case of hail. The things I do

Just wanted to tell ya'll a little story. This morning we had a babysitter so the little lady and I could have some kiddo free time so we decided to go see a movie. Found one we wanted, went and got all our goodies, finally movie time. Room goes dark, screen comes on............
.....aaaaaannnnddddd total disappointment. She and I looked at each other and with faces scrunched up and said almost in unison " This sounds like crap"

We have been spoiled by our panels. The sound in the theater was muffled, veiled, and not distinct. Not to mention a lack of bass. No kick in the chest, no sense of directionality, no wow factor. The theater was a THX rated room and I was bored. If I ever doubted having my own panels and movie room, it was dispelled today. We will NOT ever be going back to the expensive tickets and concessions again. Henceforth we will watch from the comfort of our own home with our own reasonably priced snacks, and dare I say it, yes, even in my underwear if I damn well please!

To anybody lurking here or on the fence about these panels, DO IT! It is fairly cheap and you will love the sound from them!

Just my $0.02

Updates soon!

Semper Fi

Frank40 · « **Reply #2352 on:** 10 May 2015, 02:27 pm »

Just a small update,

I am in the proses of making some full size membranes 1200 X 600 X10 mm. It is made of Sodolite XPS300 foam that I cut with a hot wire and I made it as a sandwich, with the same material as I use for my full range units. It will take some days to cure, so I will get back to you on how it turns out.

TXATC, thanks for your story, rely enjoyed it.

sedge · « **Reply #2353 on:** 10 May 2015, 08:01 pm »

TXATC
Many years ago when I was experimenting with my 25mm xps panels ,I played a track off a test disc ,the track was a machine gun being fired ,you could feel the pressure of the shock waves hitting you it was as if there was a real machine gun being fired in the room,ordinary speakers don't even come close.
While I was doing this some friends popped in to see my wife ,next thing I know this head pops round the door and he says wow I can feel my teeth rattling .
He was very keen on audio and showed a lot of interest in the panels ,but his wife wasn't to pleased at the thought of 6x2ft panels in her living room! So that was the end of that!
This was the main reason I tried to see if I could make a small panel sound as good as a large panel.
I get very disappointed at live gigs these days ,everything is played through the PA even at very small venues ,I want to hear the trumpet or acoustic guitar not the PA speakers.

I too prefer to stay at home and listen to the real thing!

Steve

Odal3 · « **Reply #2354 on:** 11 May 2015, 05:16 am »

TXATC - good story.

I did the reverse. Have you ever watched one of those home improvement shows when they trick the owner away and they have a crew fixing up the house while he or she is away. Friday night was movie time at home. When my wife was upstairs I rushed getting some panels from the audio-lab-cave to set-up in the living room. And yes, I really enjoyed using the panels for the movie - the realism is spectactular. Wife liked the sound too. But then reality hit the following morning when it only took the kids 20 min to run into the panels....
So next time they come up they will need to be permanently mounted on the wall.

Played with a new test-mule panel today. I also like to have a smaller panel with the goal to have a width approaching 1 foot but still produce good bass and volume. I put two panels together with a 120 degree angle (like the Wedgie OB in the GR thread) - 1ft width front-facing and 2 x4 side phasing. Worked OK considering my attempt was at the duct tape level with un-treated panels. Result was promising enough to make a real attempt. I played it with exciters on just the thinner front facing panel as well as with exciters on both front and side phasing. Using both was a bit tricky to get to match and would probably need some cross-over/eq/dsp to work out well. End vision is one piece of bent plywood but we'll see how that goes with my limited wood working skills

The DAEX30HESF-4 still sounds good on my birch boards. Happy! They come in just a bit hot 4-10khz so I need to tweak the boards slightly.

Odal3 · « **Reply #2355 on:** 11 May 2015, 05:20 am »

+1 to Steve's comment. Went to a local jazz concert recently and I kept thinking that wouldn't it be nice if they at least could use panels as speakers!
Frank - thanks for sharing the pictures! Looking fwd to see the end-result.

Frank40 · « **Reply #2356 on:** 11 May 2015, 05:56 pm »

I have seen many who mount the exciter on the back of the membrane, but to me it would be logical to make the connection to the front as well. The reason is...... Most material will compress and expand when excited, especially foam, this will lead to loss of energy especially at high frequencies.

Also I have been thinking of combining DML and a “normal” speaker, to improve the high frequency. My thought is to use the wizzer from my full rang unit, as an exciter....With the compliance of the surrounding of wizzer I can control at what frequency the DML will take over. It's basic a speaker without a basket but mounted on the DML membrane.

I got the new magnets today... they are Hugh

, it will be one massive exciter. Here is some pic. And data.

sedge · « **Reply #2357 on:** 12 May 2015, 12:23 pm »

FRANK40
No overheating coil problems with that driver then!
I thin the panel in front of the exciter in a concave cone ish shape ,this gives a more detailed and intimate sound .
Last week I was given two tannoy auxiliary bass radiator units, one of which I dismantled and replaced the cone with a 3mm by 7inch round poly panel,I must state that the sound of a round poly panel is very bad (offsetting the exciter on the panel helps the sound)but hoped the roll surround would sort out the problems by damping the reflections.
This worked to some extent ,all the sounds were there ,but all the life ,realism and excitement of the live performance had gone! I New this would sound like this but had to try it ,just for my own curiosity.
The sound was Ok but it just sounds like any other cone or BMR driver.
The floating panel sound is very special but does not like any form of restrictions .
The best way I have found to hang the light poly panels is with a light foam strip,this does not buzz or unduly effect the performance .
Steve

Frank40 · « **Reply #2358 on:** 12 May 2015, 08:20 pm »

This is what I learned today

I did some experiments today... I cut the membrane I made to 600 by 200mm just to get started and clued the “small” exciter on the back of the membrane. And it works!!! but I did miss the top end of the frequency range. It is not to sensitive to how you suspend it but I did notes some difference, I guess it is because it is very stiff but the best result was when suspend at the long ends.

By accident I noted that it sounded better at the back of the speaker all the high frequencies was there!!!, that lead me to believe that the exciter should have contact on both sides of the membrane as I mentioned in a other post.

Sedge, thanks for sharing your your experience. What is the thickness of your panel? Can you please post some pictures.

sedge · « **Reply #2359 on:** 13 May 2015, 12:01 pm »

FRANK40
This is the problem with these long threads ,the information is in there somewhere but even I wouldn't know where to find it,reading the whole thread would be the only way to fully understand the problems ,but there is also to much miss information and miss understanding of how the panels produce the best sound ,that it's probably best not to go there.
I am happy to help In any way I can ,but if you are going to use a honeycomb or sandwich type panel ,there is probably not a lot I could say that would help as these panels are already over damped.

Years ago when the podium 1s were first shown at a main audio show in the UK(can't remember which)practically the first thing I noticed while walking around them was that they sounded brighter from behind .
When I measured my panels from the exciter side the hf above 3or4k dropped off heavily but the DB below 3k was louder ,the sound also was phased ,odd sounding probably caused by the exciter.
A lot of the hf above 10k is directly radiated from the centre of the exciter area so if an exciter is placed on each side of the panel you will block out everything above 4k or so,plus you will have the phasing problem .
I have tried extending the coil tube to reach the front of the panel but lost the hf ,this was a very messy bodge up,I decided it was easier to thin the panel in front of the exciter ,this also worked very well.
I also agree with j Gale that the best thing to do to start with is to use the largest size xps panel possible ,then you will understand just how good these panels can sound,the revelation of hearing a real trumpet being played in your room,it takes your breath away.
Steve