[sedge]

just found an old pic of my metal panel from a year or two ago!

[CLS]

Wow, the metal panel looked so smooth. Was the sound quality as good as it looked on the RTA?

[sedge]

Cls
Smooth is the optimum word for the sound of the metal panel .
This panel needs a more powerful exciter to perform well,I could try a cluster of 4 exciters in the middle (one day maybe).
I felt the panel was a little slow and heavy sounding ,a little like my transmission line speaker ,good for jazz and classical music.
The poly panel sounds more realistic and alive and is so efficient.
That was the 60cmx70cm panel with the exciter stuck on with tape .
I do have a larger panel 80cm x100cm with the exciter glued on,this gives a better HF ,stays within the 5 db band to 20k.
LF is also improved a little but not a lot.
The off axis was very interesting but I would have to do more tests before I said anything more about that.
I cut the LF to stop the panel wobbling about all over the place and to help stop the exciter from over heating.
The quick measurements of the poly panel are not that great but I think they give you the idea about the HF drop at 10k and the suck out problem.
It also shows the side off axis response tends to follows the on axis frequency response below 10k very well.
An ordinary speaker would have a huge loss off axis below 10k.
Normally the poly panel would have a fairly good level  response from 250HZ or so to 20K,but the panel was firing into a corner with double glass doors giving it a lift in the 1k to 2k region and making it a little wobbly.
I have  a paper somewhere on another computer that states that for this type of speaker you should have multiple mic readings (the more the better)to ascertain the total output (frequency response)of the panel.
sedge 

[CLS]

Hi Sedge,

Thanks a lot for sharing.

Funny that I feel my glass panel trial (in office) has a more extended HF then my PS foam panels at home. (but as mentioned, there're too many variables... ) And, like your comments on the sound, I also feel my PS foam panels have a more natural sound overall. (after proper EQ)

Talk about the EQ on PS foam panel, I did two things recently.

1. Rounding the corners (previously they were chamfered)
2. Adding some damping material (nonewoven fabric) to the rear surface 





By a rough & quick check by RTA, I discovered I could get rid of the 2 notch filters at 2.5kHz (-6dB) and 6.3kHz (-12dB) for previous annoying peaks. But TBH I can't make sure which one contributes more to this improvement. 

Sonically, the change is subtle. It seems very slightly more detail and clearer in the higher mid ~ lower treble.... But it can be mental, from my expectation.

Another factor I can't measure, I think the fabric might change the rear radiation slightly. Listen very close to the panel, it's quieter at the fabric areas. So the rear refections are changed, too.

I'll need more listening tests to this stuff. And/or adding other damping/treatment... 

 

[zygadr]

Good work guys!

I recall with all the literature and reviews on the Podium panels that their positioning in a room makes all the difference to their sound and can vary from bad to brilliant

Also, the reviewers mentioned how difficult it was to measure the frequency response (especially in the H.F. due to the nature of how the sound is produced with this technology.

I think that it would be a good idea to go back to these reviews sedge and CLS, and filter through some of the hidden information they contain.
Shelley Katz, the maker of the Podiums has quite a bit to say regarding ''tuning'' the panels, the glues and tapes used, and many other factors.

To me I find that the VH EPS has heaps of H.F. response............maybe a bit too much?
However, in the BASS department, the Gatorfoam was superior if memory serves me correctly.
This could be that the GATOR was stiffer and had more mass than the ultralight and very flexible 10mm thick EPS

[zygadr]

Will try to pick up some 25mm thick sheets of VH EPS this week.

The panel size won't be as large as originally intended as the rigidity in an 8X4 sheet would suffer, so it may be a 6x3 foot to be sensible and smart

I will order them with the corners cut off at 45 degrees (similar to CLS's panels).
Hopefully(and I will check in the shop first), the panels will stand upright on their own and the H.F. transmission at 25mm thick won't cause any problems.

[bobloblob]

CLS-

Nicew work.  That fabric on the back of your panels looks similar to the felt triangles that Mamboni used in the Walsh clone thread at diyaudio.  Were you thinking along those lines when you did this?  Seems like it could be a good idea, at least worth experimenting with.

[CLS]

....  Were you thinking along those lines when you did this?  ....   

Yes 

Well, sort of, at least. Talking about 'bending wave', Manger might be one of the biggest name. It also has such damping around the outer edge. 

I'm thinking of adding more, or even trying EnABL...

I made the conclusion too early in the previous post. After more listening, I feel the notch at 6.3kHz is still needed, with less depth, at least for most records at this stage. That means the resonances are not thoroughly cleaned. More damping is needed.

Nevertheless, the overall effect of the fabric is still positive. The sound is even more natural, with more smooth details in the critical band - higher mid to lower treble. Or, the slightly less rear firing energy (or in different behaviors) helps on reduce the reflection, and this may also improve the clarity.

I've never done these on ordinary drivers. (diluted PVA glue is the only treatment I've tried on my cone drivers... ) Now with such panels, I think these 'edge damping' techniques make more sense.

[CLS]

Adding some more:



 

[zygadr]

Well CLS?......................verdict??

I hope you realise that by adding the fabric, those areas that are covered will have the sound that normally eminates from that point ''muted'' somewhat.
That's where you will hear a difference in the sound and thus a measured response change.

When I used the much more different and heavier and more damped GATORFOAM, the sound was totally different to the VH EPS : much less sensitivity, rolled off highs, better bass.........I think?

Also, why have you positioned the exciters in the way that you have?
A large panel like yours needs to be energized evenly buy an equally ''even'' spacing of exciters over the entire surface area of your panel material.

If this basic rule isn't followed, you will need to apply true NXT formulas for exciter placement. Have you already done this?

If not, you will be in no man's land between an NXT panel and a Podium and may be the reason for your odd frequency response?

Don't get me wrong, I'm not trying to criticise your design, I'm just concerned that odd placement of exciters in my experience, never has sounded right to me

As soon as I followed the straight line up the panel placement, it was an immediate clear winner

[CLS]

Hi zygadr,

The arrangement of the excitors on my panel followed the 1/3 suggestion by Pol. (and only the single one is singing fullrange; the 4-unit group works under, uh... several hundred Hz, I don't remember the number... )

I'll try other styles of distributions, once I figure out the securing means.... Appearently it'll happen on another set of panels since this pair can not take the abuses of repeated trials. Meantime, I guess I'll add the ribs/frames into the whole thing...

About the newly added fabric, I think they do good things to me. By them I really eliminated all high Q notch filters in my DEQ. Now there're only minor EQ's (-3dB ~ +1.5dB) at some areas for the FR shaping. It's always good to remove those deep notches in DEQ, by which it means I loose the revolution (less bit depth). Generally it'd be better if the problems were taken care of physically (or acoustically).

After the 2nd round of fabric damping, the sound is now even smoother and singing with more natural details. I love it. (so I'm enjoying the result very much, and somewhat lazy for the next trial...    )

Other than edge damping, I think the change (attenuation) on the rear radiation contributes to the overall sound, too. Slightly less rear wall reflections make the sound clearer and the space information is more real to me.

[zygadr]

Sounds good CLS 

Let us know if anything improves as you experiment

[irishpatrick33]

Here's the pics I promised months ago.










I didn't include a picture of the other speaker. That one has the warping on the 2 corners that really angered me. You really have to look to see it, but I am still pissed regardless. It's about half an inch out of whack on the two diagonal corners.

[pol_bct]

Here's the pics I promised months ago.

nice design ! which transducer is that?
how is done the "suspension"

POL

[zygadr]

Looks like the more expensive, flange mounted ''high shove'' version...........used on the Podiums.

[irishpatrick33]

Correct. There is a single driver on each panel that is the Dayton Audio DAEXSFH Steered Flux High Shove Exciter 25mm. It's mounted on the top third, even though the pictures deceive a bit.

The suspension and design is ziggie's suggestion: gaffer tape with about a 1/2" gap between the panel and frame.

The connector is some partsexpress cheapy.

The rest of the frame is wood and hardware you can find anywhere.

However, the feet cost a bit of money. They are Magnepan replacement feet. I think I paid $100 for them.

[zygadr]

And how do they sound?

[irishpatrick33]

They sound good. They sound much better than my last incarnation, which is probably about 30 pages back. Much more efficient, way more bass, pretty accurate throughout the entire range, not bright. In truth I have never put them through the musical paces. I have just listened to TV and movies through them. Just haven't had the time to move my music collection to the source connected to the speakers.

That being said, I kind of hoped for more (though my source/amp is suspect). I wonder whether my project ran in contradiction to the entire purpose. It wasn't dirt cheap to make. Even a piece of crappy wood costs money these days. I might have gotten up around $300 or so. Which is starting to get close to the price of some quality professional builds. Did I mention it was a ton of work?

[zygadr]

Yes, there is money to be spent on these to get a working speaker, but look at the sound benefits compared to a $300 speaker as you have mentioned.

There is no way a 300 buck commercial job is going to sound as open, coherent and lifelike to any of our panels. That will always be their advantage and domain where they spin their ''magic''

[CLS]

To framed, or not to framed, that is a question.

That's a beautiful build for sure   However, I thought of a tambourine when looking at the pictures.

There'd be some tension on the 'surrounding', am I right? If so, it'd become a resonant system -- there'd be an obvious low end fs (with an impedance peak), like normal speakers. I'm not saying it's bad (or good). This might probably contribute to the bass response, I guess.

On the contrary, a freestanding (frameless) panel has a fs too low to affect the audio band.

What's their major differences in performance? I've only built the frameless ones. So the inputs from you guys with more experiences will be much appreciated