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

OB_Newbie · « **Reply #2360 on:** 14 May 2015, 02:22 am »

Hello fellas,
This is a good video discussing how HF are generated by the panel and exciter. When the wave length is the same or small than the diameter of the exciter voice coil the panel create an oil can resonance with increased output... the smaller the coil the higher in frequency the resonance is pushed and generally the better the HF response is. Can't remember the posters name but someone on this board had the DML Design Studio software and you could clearly see this effect as he changed the exciters VC diameter.

https://www.youtube.com/watch?v=GJiyndZaX_4

Best,
Rich

sedge · « **Reply #2361 on:** 14 May 2015, 11:59 am »

Ob_newbie
Thanks for the YouTube link ,nice to hear professional's talking about high quality dml panals ,watched them all with great interest ,interesting about the hight width ratios,will have to try this and compare the response to my panels.
In one of the vidios Tim mentions that he is normally dealing will 10 watt home audio and is learning a lot from the pro audio side,wonder if there are vidios of the home audio side and how they would differ from the pro design.
Interesting that they call the exciter area the primary source area,I've always called it the direct radiating area,which acts like an ordinary piston type speaker,the combination of the two is the area I am most interested in and getting the balance right to me is most important.
Calling the centre of the exciter the tin can effect is a little harsh as any drive unit with a coil would have the same problem ,but as he state's this can be mainly sorted with damping.

This is obviously a good pro PA speaker and if I'm not mistaken they use a tweeter to handle fr above about 4k ,the goals of this speaker design are certainly different from mine ,but I do understand why.
Once again thanks for the thread,very interesting .
Steve

sedge · « **Reply #2362 on:** 19 May 2015, 12:17 am »

frank40

this is an old photo of one of my 5mm panels being coated with thin pva ,after sanding and thinning in the coil area.
the panel size was out of the box 85x60cm ,the exciter position I think was the parts express position.

sedge · « **Reply #2363 on:** 19 May 2015, 12:51 am »

this is a smaller and larger panel from my gallery,

a few of my other test panels

Frank40 · « **Reply #2364 on:** 19 May 2015, 05:48 pm »

Thanks for the pictures Steve, It look like you have done a lot of experimenting... nice collection

.

I see what you mean by making a cone like dip in the membrane.... I am still not decided on the type of membrane I will use..... But right now I am leaning to a sandwich construction, maybe 3mm Depron with my cone material.

I did a neat experiment to combine a normal cone speaker with DML.... It works nicely. At higher frequency it work like a normal cone, but as the frequency lowers
it transforms to a DML unit.... extending the lower frequency range.

I took apart a 3” full range unit (not my own design) and mounted it on a 100 X 60 cm sandwich construction. The extension at low frequency was amassing. Any way I just wanted to share the info of this experiment.

Odal3 · « **Reply #2365 on:** 19 May 2015, 06:30 pm »

Nice! You should check out the old webpage for the company that sold Podium. If I remember it correctly, they have something of similar concept (but think differen design)

What freq do the panels take over? Do you use natural rolloffs or crossover?

Odal3 · « **Reply #2366 on:** 19 May 2015, 07:49 pm »

Found it: http://layeredsound.com/layeredsound.php

Frank40 · « **Reply #2367 on:** 19 May 2015, 08:26 pm »

Thanks for the link Odal3, guess I am to late for a patent

...

The crossover frequency is a function between the weight of the cone and the compliance of the surroundings (spring and mass effect) No crossover.....

Odal3 · « **Reply #2368 on:** 19 May 2015, 11:47 pm »

I'm sure you can come up with something better

sedge · « **Reply #2369 on:** 20 May 2015, 01:51 pm »

Oral3
And I thought I had a great idea,if I had spotted this in 2007 I could have saved myself a lot of hard work

this is the problem ,the information is out there ,it's just trying to find it

I was wondering if on the thicker say 25mm panels ,the thinning could be mad into a shallow horn type Controlled dispersion shaped ?
Or would the vibrating surface screw it all up? Someones probably already done this as well, and could save me even more hard work, I hope

Steve

Odal3 · « **Reply #2370 on:** 20 May 2015, 02:22 pm »

A wiki would be nice.I'd be happy to help contribute if set up as a team effort.

Sedge I believe you mentioned this before, but remind me again the theory why thinning the panel and not complete through hole the size of the ID of the mounting ring.

Btw: oDal is a reference to a street

sedge · « **Reply #2371 on:** 21 May 2015, 01:58 am »

Thought Odal was a reference to a character from game of thrones .

The area inside the ring outputs a lot of energy,if you run your fingers across this area while outputting pink noise you will hear a loud swishing noise ,the same would happen if you ran you fingers over a dome tweeter .
Cutting the whole centre of the ring out would be like cutting the whole centre ring of the dome,although the ring does output some hf it sounded phased and odd sounding.
I used to use thin strips of bluetak to tame the peeks and dips in the ring area ,this gave a smoother response but ultimately sounded restrained.
If you wave a microphone across the panel you will also see a large increase in output as you cross the exciter area,near field response in this area will be approx 20HZ to 20KH(primary output).
Steve

Odal3 · « **Reply #2372 on:** 21 May 2015, 03:26 am »

Thanks for the explanation!

Well - didn't really think through the username that much since I didn't think I would post so much - if I would do it again, I'd probably use something with my real name instead.

sedge · « **Reply #2373 on:** 21 May 2015, 12:41 pm »

Odal 3
It surprises me that nobody that I can remember on this thread has talked about the problems within the exciter ring area,except the nxt and bmr which use damping pads ,not my preferred choice.
You can have large peeks and dips in the 10 to 20k region caused by the cancellation and summing effect ,basically the central area can be quite a messy area especially in the hf region.
I play my music at realistic listening levels and sometimes very loudly as my wife will testify,these problems make themselves known all too well at these levels.
So the thinning gives you a more clear intimate direct sound (primary radiation) and the damping flattens out the hf response

Steve

Frank40 · « **Reply #2374 on:** 23 May 2015, 06:42 pm »

I did this small video to show you what I mean when combinig a cone with DML. The sound of my camera is not good... sorry about that.

https://www.youtube.com/watch?v=QTqsX7d9A6A&feature=youtu.be

Odal3 · « **Reply #2375 on:** 23 May 2015, 06:46 pm »

Unfortunately can't see the video since it us private. Check to see if you can change the security settings.

Frank40 · « **Reply #2376 on:** 23 May 2015, 07:05 pm »

Sorry about that, should bee OK now.

Frank40 · « **Reply #2377 on:** 25 May 2015, 12:34 pm »

I finished the two spider exciter here is how it turned out......

Odal3 · « **Reply #2378 on:** 25 May 2015, 12:38 pm »

Quote from: Frank40 on 23 May 2015, 07:05 pm

Sorry about that, should bee OK now.

Nice - thanks for sharing. The color match nicely too.

Frank40 · « **Reply #2379 on:** 29 May 2015, 06:55 pm »

This is my new exciter, it works great..... The two spider system makes it very stable, see the video and you see the membrane is hanging on the exciter only without any other supports. The membrane is a sandwich construction of glass fibre and a sheet of 3 mm Depron.

I was a bit suppressed... first I thought the sub was turned on but it wasn't. Thesis membranes can go low in frequency but still lacking a bit at high frequency, will do more experiments on the membranes.

link to the video: https://www.youtube.com/watch?v=UZTozqs1oHY&feature=youtu.be