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

HenryPercy · « **Reply #240 on:** 22 Oct 2009, 01:51 am »

Wow! Thanks for all the info, Donka!

I'll need to research and absorb a lot of what you posted, but I don't mind doing that in the least.

All I have now is a sabre saw and a circular saw, but I've been planning to buy a table saw or a miter saw. My main use would be building boxes for holiday displays which would go in our living room. The boxes would be sort of like traditional speaker enclosures (but larger and only about 24" deep). Perhaps more like deep bookcases.

My first effort (with plywood) was better than I expected, but still didn't quite meet the Spousal Acceptance Standard. The biggest problem was they were too heavy to move.

So I'm going to try again with Gatorfoam and perhaps a few 1" x 2" braces. Getting perfectly square (and 45 degree) cuts is my biggest challenge at this point.

- Henry

EDIT: I re-read your post (much slower this time) and most of the terminology is familiar to me from previous reading I've done on wood working. Thanks again.

bytheway · « **Reply #241 on:** 22 Oct 2009, 03:10 am »

Its a little small, (3x2 foot), but I wonder if something like this would work:

http://www.wtp.net/DBEST/hcomp/nomex.html

usp1 · « **Reply #242 on:** 22 Oct 2009, 03:48 am »

Does the facing on the nomex panel make a difference? (The panel above has either fibreglass or carbonfibre facing...Podium has a mylar facing.) More broadly, even with the foamboards, are the sonics dictated by the the facing (paper for the foam board and luxcell for gatorfoam)?

I happened to be in Walmart and found a 20"X30"X3/16 foamboard panel (black with black foam) for $2.88. Just for kicks I tried putting 5 exciters on it and it seems to be keeping pace with the gatorfoam! What is more, it does not rattle like the gatorfoam panels at low frequencies.

Donka, I don't have a good enough microphone to do the kind of REW graphs you are doing so I was wondering if you might be able to test a panel made from the material I found at Walmart. (Elmers foamboard - W950069 20"X30"X3/16 Black on Black). The facing material seems to be very similar to the gatorfoam.

usp1 · « **Reply #243 on:** 22 Oct 2009, 04:09 am »

The foamboard is papercoated but seems to be a stiffer paper than on the other foam boards they had at Walmart. Recalling the comment by the Podium guy that the panel should "ring like a bell" I tried tapping the panels and this seemed much more rigid than the other panels. I don't know if it is clay coated (how do I tell?)

I have a gatorfaom panel on the left and the black foamboard panel on the right palying right now and there does not seem to be a whole lot of difference between the two panels. In fact, because it does not seem to rattle as much with low bass the foam board is cleaner sounding.

Also, the imaging is a little more diffused with these panels compared to my regular speakers.

By the way, I have the cheapo $5 exciters and the plastic mounting foot of the exciter tends to come off. I wonder if that is causing the rattling.

usp1 · « **Reply #244 on:** 22 Oct 2009, 11:32 am »

The foot of the exciter panel is very loosely connected to the voice coil and it seems easy for it to come off. But it does not seem to be the cause of the rattle. I tried replacing a loose exciter with a different one and the rattle remains. I dont think it is from loose wires either so it could be that the tape I am using right now is the culprit. I will try fixing with the 3m tape this weekend.

Another thing I noticed with the Walmart panel is that it sounds much cleaner when I lift the whole panel off the ground and suspend it by holding it up in the air with my fingers. I think constraining the bottom edge by placing it on the ground seems to muffle the panel. The gatorfoam panel also sounds clearer when lifted off the ground but the dofference is more apparent with the foamboard.

Additionally having a larger 2'x4' gatorfoam panel does not seem to help with either spl or clarity compared to the 20"x30" panel. Perhaps the larger aspect ratio of the 2'x4' panel makes it less rigid and may require a frame.

sedge · « **Reply #245 on:** 22 Oct 2009, 12:09 pm »

i use a standard lamp and masking tape to suspend panels for testing the sounds i am getting are very good .I use the cheep exiters no problems with high on small panels .must go to work buy for now.

FullRangeMan · « **Reply #246 on:** 22 Oct 2009, 02:19 pm »

Dear USP1,
I wonder if that is causing the rattling. Verify the panel that rattle looking for damages, and structural fails, maybe you can shake it to fell if the panel is firm and strong, like one piece solid.
Just a idea.

zobsky · « **Reply #247 on:** 22 Oct 2009, 02:37 pm »

For what it's worth, A few years ago, when folks started experimenting with NXT exciters, one of the recommended materials was a fedex shipping carton (corrugated plasticized paper). I doubt if they're freely available in large sizes, though. I can't seem to find the thread right now, it may have been at audioroundtable.com or decware forums.

stereogeek · « **Reply #248 on:** 22 Oct 2009, 02:57 pm »

I have been watching this thread with great interest.I have been thinking of corrugated plastic as a panel material.I found a source and it comes in different thicknesses and colors.

http://corrugatedplastics.net/index.html

Any thoughts???

Steve

usp1 · « **Reply #249 on:** 22 Oct 2009, 04:28 pm »

My first panel was coroplast which is a corrugated plastic. The highs are severely rolled off and there is very little bass. They sounded OK when I first made them because I was not expecting much of anything from them. The sound is more like a clock radio.

Donka · « **Reply #250 on:** 22 Oct 2009, 05:13 pm »

On the cheap exciters, the foot detaching form the voice coil is the most common failure I have had so far, but this is after a few prying and re-gluing or taping. I have not had one fail from just playing yet.

I can also say that when running sweeps the panel will physically vibrate violently enough in low frequencies to distort in all methods tested so far, except with the framed panel with TBLR foam wedges. This is what made me originally think the sweeps were causing an abnormal reaction so I went through and tested 40-50 individual frequencies on 2 panels to see if the lone response matched the sweeps, and they were very close.

The setup I have been using to test and listen to the panels is 2 x 3/8" medium density foam strips on the floor near the LR edges, then using a tripod with a strip of foam hanging from the head and a piece of blue masking tape to secure it from peeling off the panel. This method has resulted in a very free to vibrate panel. I also tested hanging panels by jacking up the tripod and letting it hang solely from the foam strip and the measurement were nearly identical, so I continued using the 2 strip floor method.

In conclusion the panel material really seems to depend on density. In the LF range the panel must be able to immediately respond, it became obvious with the wood panel, that due to it's stiffness and slow reaction the exciters were moving on to the next octave before the panel could get moving to produce the previous. This is much less so with the Gatorboard, but is stilll there and is what I believe to be the cause of the sort of rattle as noted by others. Lastly the result of the sheetmetal tests seems to show the exciter is reproducing the HF range, and that it is the GF absorbing.

So, I setup all the test equipment again yesterday evening and glued exciters to various substances I had lying around the garage. I the best sounding besides of course Gatorboard and then cardboard was 1/4" pressed core plywood. I tested 1/8" aluminum sheet and it absorbed the most sound next to 3/32 plastic sheet which was the worst, however. I then tested some 22ga sheetmetal that had no bass but produced the highs very clearly. Overall I am tempted to try my Gatorboard panel with inset metal sheet tweeter.

I also got out a Yamaha NS-10M and did some side by side music listening, it was immediately clear the missing HF of the Gatorfoam panels. So pulled out the old EQ and hooked it inline, gave them roughly a 6-7dB 6.3K and 16K and the panel fell right in line with the reference monitor. I will also say I am not a horn/high-treble fan, I like a laid back sounding speaker, so don't think I am trying to tweek these panels to some overly hot HF level, trust me I am not. I had time to listen to 6 Steely Dan tracks and played a touch with the EQ, it made quite a large difference. I look forward to setting up the DCX2496 this evening, I believe it can save multiple parametric EQ's files and switch on the fly, which will make auditioning various HF levels easy.

Red Gatorfoam vs. Magenta Sheetmetal

Magenta 22ga sheetmetal vs. Black Garolite PCB board vs. Maroon 1/8" Aluminum vs. Orange Plastic sheet

Green Gatorboard vs. Red Carboard vs. Purple 1/4" Ply

Donka · « **Reply #251 on:** 22 Oct 2009, 05:15 pm »

USP1,

I agree the plastic sounded the worst of all I tested yesterday, I think a more rigid plastic like polycarbonate still wouldn't sound good because it's density is too high.

usp1 · « **Reply #252 on:** 22 Oct 2009, 05:27 pm »

Donka,

I don't have a good enough microphone to do the kind of REW graphs you are doing so I was wondering if you might be able to test a panel made from the material I found at Walmart. (Elmers foamboard - W950069 20"X30"X3/16 Black on Black). The facing material seems to be very similar to the gatorfoam. (repeating a request I made earlier)

I found that this board ($2.88) and another panel I made using corrugated cardboard($8) (actually trifold presentation cardboard panels which are used for student science fairs) worked quite well and may be a good option if you do not want to bother with the expense of gatorfoam. I actually thought it was cool how I could use the trifold panel as waveguide to get a more directed sound. I wonder if this might help improve the defused imaging.

scorpion · « **Reply #253 on:** 22 Oct 2009, 10:15 pm »

Oh, yes zygadr, very realistic SPLs.

I suppose that gatorfoam is a find. Here is a link to tech specs: http://files.alcancomposites.com/downloads/5_-_/gatorfoam_en.pdf .

Has anybody tried KAPA boards ? They are not as solid as Gatorfoam but may perhaps do. I have found Re-Board, a swedish product, only paper almost, with a honey-comb inner structure and very rigid. But 10 mm thick the smallest, which perhaps is to much to get a good effect. I shall talk to them. The company is right next to where I live.

/Erling

j gale · « **Reply #254 on:** 22 Oct 2009, 11:40 pm »

Also see http://tri-dee.com/GatorfoamTechnicalBulletin.htm Info on density and differences between white and natural/black.

usp1 · « **Reply #255 on:** 22 Oct 2009, 11:56 pm »

Quote from: j gale on 22 Oct 2009, 11:40 pm

Also see http://tri-dee.com/GatorfoamTechnicalBulletin.htm Info on density and differences between white and natural/black.

Visiting this site may be harmful to your computer. I tried clicking on it and I got a lot of warnings.

Donka · « **Reply #256 on:** 23 Oct 2009, 01:40 am »

Scorpion,

Nice find as can be seen from that data sheet, the WHITE gatorfoam is more ideal to our cause with an elastic modulus 35% greater than the black. Personally I think for availability and price this may be the ace in the hole. $2/sqft is cheap compared to any of the sandwich and honeycomb composites out there.

USP1,

I don't know where the Walmart is near to me and have no time to go purchase foamboard, sorry! Also I limited my testing to materials that are available in full sheets (4x8') for purposes of the final objective which is to go large. I will comment that when testing panel 4, cutting it down between each test that the sound may have only decreased a single decibel, however the sound field became more diminished. Since the white GF is looking to be the superior choice, I am tempted to just throw together some full size variants, as Zygadar has, just so I can hear them in there full glory.

This morning I did take the oblong panel with rounded corners and cut into the side, gluing a 8" x 20" sheetmetal panel with 2 exciters on it. I only had a chance to listen to 2 tracks but the sound was promising.

jonners · « **Reply #257 on:** 23 Oct 2009, 09:29 am »

Quote from: j gale on 22 Oct 2009, 11:40 pm

Also see http://tri-dee.com/GatorfoamTechnicalBulletin.htm Info on density and differences between white and natural/black.

This link didn't work for me, but I got it here: http://tri-dee.com/Gatorfoam%20Technical%20Bulletin.htm
The data on this page show the white Gatorfoam as having a LOWER elastic modulus than the black. I think I would prefer to trust Alcan's own data which gives it the other way round. (Link in Scorpion's post above).
The tri-dee page also states, under "Power Tool Cutting": "Since Gatorfoam is woodlice (sic), it may be cut with standard table saws".

sedge · « **Reply #258 on:** 23 Oct 2009, 11:20 am »

Hello all
I did hear the podiums at a hifi show, the first time that they were shown in England.
At first , I was very impressed .but after a while I started to notice the hf loss and quality of the depth of sound. It gave the impression of a wall of sound.
I had noticed this effect with Wharfdale nxt panels and mission cube nxt[big sound but no life ]

So when I saw Zygadr's forum on DIY audio , I thought "Mmmm, I wonder if he has cracked it ?".
I have 40 exciters and used umpteen panel types [oh my head].
they can give you highs and very very lows, and depth ,but trying to get all of these things at the same time is the problem .
Up to a point i agree with [Mr Podium] about a panel that rings. It is hard to get a bright sound from a dull sounding panel. But if the panel is too bright sounding, you can dampen it down to give a clean sound. I have been doing this for a long time with mid-range cones to get rid of 'self-noise', and cone break-up. My panels seem to respond to this in a good way. Look forward to your comments.

j gale · « **Reply #259 on:** 23 Oct 2009, 02:48 pm »

jonners, I don't know about the accuracy of the specs on the 2 sites but I have found that cutting gatorfoam on a table saw works well. Nice clean cuts, very easy to work with.