[captainjack115]

With all due respect, I really think putting a hole in the panel convolutes the basic NXT technology.

"Any" plate connected to the exciter will function as a low pass filter to some degree. Now that we're seeing exciters that handle more power, I see nothing wrong with adding a little high frequency EQ. Sooner or later materials used by professionals will trickle down to DIY.

I haven't been on here for a while, but I thought I'd share a photo of something I put together a few years ago. It uses low power exciters, mainly because there was nothing higher wattage available at the time.

I used corrugated plastic panels floating in four separate frames and EQ'd the high end. Bass was very substantial to 50 hz, and sounded pretty nice on a wide variety of music.

[Odal3]

Thanks for sharing the picture. Looks nice.  So do you have one exciter on each of the four floating panels? Are all full range?

[captainjack115]

Thanks for sharing the picture. Looks nice.  So do you have one exciter on each of the four floating panels? Are all full range?

Yes, I forgot to mention that there is one exciter per panel. I discovered early on that using one exciter produced the best high frequency response, and yes, they all run full range.
The frame is made from 1x2's, the panels are held in place with white duct tape. There is a 1/2 inch boarder around the frame and the edge of the panels.

My listening room at that time was about 16 feet long, listening distance was around 14 feet.
Running pink noise my spectrum analyser showed bass was very good to 50 hz., with a fairly sharp drop from there.

Again while running pink noise and the spectrum analyser, I was able to move the microphone in many directions, left, right, up down. As expected, frequency response looked pretty much the same, proving that NXT technology actually works.

[Odal3]

Neat. Thanks for claifying.

There has been some discussion on multiple smaller panels like this but I haven't heard of anyone tried it before (Or I forgot from the long thread). Often the recommendation is large panels are good for bass, but your set up proves small ones works as well. Did you ever compare the souND from your smaller panels with one larger? I'm curious to hear what your impression is. Not as wide and large would be easier to place in the living room plus it looks better imo when the panels are not too large (like the big ones I have currently)

[captainjack115]

Neat. Thanks for claifying.

There has been some discussion on multiple smaller panels like this but I haven't heard of anyone tried it before (Or I forgot from the long thread). Often the recommendation is large panels are good for bass, but your set up proves small ones works as well. Did you ever compare the souND from your smaller panels with one larger? I'm curious to hear what your impression is. Not as wide and large would be easier to place in the living room plus it looks better imo when the panels are not too large (like the big ones I have currently)

A curious thing, I did in fact make a larger panel version. or should I say the same number of square inches of all 4 panels. Bass was noticeably weaker, vastly lacking in tonal balance.
Maybe not such a mystery, as one exciter was connected to 4 times as much mass.

I think there's merit in using multiple smaller panels. it's not like stacking conventional drivers into a line array because a DML radiates up to 180 degrees. In other words, I don't think there is a comb
filtering issue here.

Big panels would be out of the question for me now. I moved from the East to the Mid-West after retirement and my listening environment is very cramped.
With this design I don't know how much would be gained by going taller than 4 panels. I have no proof of concept, but I see no reason not to make multiple panels double wide.
Arguing that vertical stacking presents no real world comb filtering problem, I can't see why doubling the width would produce beaming.
From what I can see the advantage here would be greater power handling and the ability to play louder with less distortion, especially since exciters with larger power handling capacity are readily available.

What's your take on this?

[OB_Newbie]

With all due respect, I really think putting a hole in the panel convolutes the basic NXT technology.

"Any" plate connected to the exciter will function as a low pass filter to some degree. Now that we're seeing exciters that handle more power, I see nothing wrong with adding a little high frequency EQ. Sooner or later materials used by professionals will trickle down to DIY.

I haven't been on here for a while, but I thought I'd share a photo of something I put together a few years ago. It uses low power exciters, mainly because there was nothing higher wattage available at the time.

I used corrugated plastic panels floating in four separate frames and EQ'd the high end. Bass was very substantial to 50 hz, and sounded pretty nice on a wide variety of music.

Now that's what I'm talking about!   Good looking panels... what are the dimensions??

[captainjack115]

Now that's what I'm talking about!   Good looking panels... what are the dimensions??

This is where I plead "guilty"!

The panels are 12x12 inches, the frames are made to allow a 13 inch opening per panel. I know.......I know, no golden ratio! Guilty on the first count. Also the exciters are mounted dead center, guilty on the second count.

There was nothing all that technical or arbitrary about panel shape or exciter placement. I simply ran pink noise into test panels of various shapes and sizes and tried moving the exciter around until the spectrum analyser showed the flattest response. The center was also the spot that sounded best to my ear.

How many loudspeaker "designers" have achieved their goals through empirical means? Plenty, I'm sure!
The exciters are freely mounted, no individual or common spines were used.

[Frank40]

Captainjack115,
Thanks for sharing you pictures... they looks awesome. I agree with you, you should not put a hole in the panel, it will create a low pass filter.

Just want to share a bit of info that I learned.

I have done some experiments regarding the membrane material and properties of the membrane, in respect to the lower frequency respond. It looks like the same rule are at work as a normal cone speaker..... The low end is a result of the weight of the membrane and the compliance of the suspension. You can make a speaker that goes very low but at the expense of the reproduction of high frequency (at least with the membrane type that I used) and efficiency.

I did a 40 X 90 cm membrane with a weight of 215 grams this was suspended to the frame with broad tape. The reproduction of bass was amazing, did not make any measurements, but I would estimate the output was good for as low as 25-30Hz.

[Odal3]

If you check some of the recently linked technical papers you will find the theory that confirms some of your findings regarding weight and suspension. Perhaps can give you further clues to help optimize your design. Will take a peak this weekend if I can find the particular paper I'm thinking of.

I think you can get both low and high frequency with the right design. Efficiency is another matter...

[OB_Newbie]

This is where I plead "guilty"!

The panels are 12x12 inches, the frames are made to allow a 13 inch opening per panel. I know.......I know, no golden ratio! Guilty on the first count. Also the exciters are mounted dead center, guilty on the second count.

There was nothing all that technical or arbitrary about panel shape or exciter placement. I simply ran pink noise into test panels of various shapes and sizes and tried moving the exciter around until the spectrum analyser showed the flattest response. The center was also the spot that sounded best to my ear.

How many loudspeaker "designers" have achieved their goals through empirical means? Plenty, I'm sure!
The exciters are freely mounted, no individual or common spines were used.

I really like the tall and thin and surprised by the bass response!  Imagine they are efficient as well.

One of the first panelsi built were square and they sounded very nice.  According to one of the papers very close to square is optimal for the most efficient generation of nodes so given that and what I heard with my ears a square panel is not terribly off the mark it appears.
In regards to exciter placement Monacor placement is probably best however with my array I do plan on moving excites to different positions on the panel to randomize the freq. response somewhat for what I hope is an overall smoother summed response.

Again, thanks for the pics and explanation!

[OB_Newbie]

If you check some of the recently linked technical papers you will find the theory that confirms some of your findings regarding weight and suspension. Perhaps can give you further clues to help optimize your design. Will take a peak this weekend if I can find the particular paper I'm thinking of.

I think you can get both low and high frequency with the right design. Efficiency is another matter...

Hey Odal... good to hear from you man!  Just curious what papers point to suspension impacting high frequency response?   I may be wrong (my wife points this out every chance she gets) I believe its the weight of the panel and its stiffness and dampening qualities that impact HF response!?!

btw - Happy Friday everyone!!

[Odal3]

I might have confused it (happens all the time to me   ) but I read suspension as edge condition, which affects the low end. Let me see what I can dig up.

[captainjack115]

I really like the tall and thin and surprised by the bass response!  Imagine they are efficient as well.

One of the first panelsi built were square and they sounded very nice.  According to one of the papers very close to square is optimal for the most efficient generation of nodes so given that and what I heard with my ears a square panel is not terribly off the mark it appears.
In regards to exciter placement Monacor placement is probably best however with my array I do plan on moving excites to different positions on the panel to randomize the freq. response somewhat for what I hope is an overall smoother summed response.

Again, thanks for the pics and explanation!

Yep efficiency was pretty good. I was able to power them with a little Lepai LP-2020A, no problem.

I too prefer the tall thin look, ironically my wife absolutely hates the look of them.

I experimented with Monacor's placement scheme and used 4 exciters on one panel. Excellent loudness, but things just didn't seem as good as one exciter per panel.
That's why I wound up with one exciter and multiple panels. The duct tape seemed to do pretty good at taming  corner vibration. The whole speaker is very light and easy to move around. Cheap and easy construction.

[OB_Newbie]

Hey Capin'
Yeah, I'm not a proponent of multi exciter panels.  1 exciter per panel is why I want to create a thin tall panel for high output and ability to EQ with the extra available power handling.   I mention Monacor as I am planning to distribute the exciters in different positions on each panel to randomize the FR so given the 4 panels the overall FR (I hope) is smoother.

That is the thought anyway, we shall see if the theory proves out. 

Funny your wife doesn't like the thin and tall look... I think that's a really nice look and should provide a focused array at most listening distances I would think.  Will probably have mine pulled a bit off the ground so the center of the panel is about at the listening height to maximize the distance that you can listen to them in the focused (line) array... really like listening to them as a line array... always imagined that was one of the contributing factors of why the guys like the bigger panels(!?!).

[captainjack115]

Hey Capin'
Yeah, I'm not a proponent of multi exciter panels.  1 exciter per panel is why I want to create a thin tall panel for high output and ability to EQ with the extra available power handling.   I mention Monacor as I am planning to distribute the exciters in different positions on each panel to randomize the FR so given the 4 panels the overall FR (I hope) is smoother.

That is the thought anyway, we shall see if the theory proves out. 

Funny your wife doesn't like the thin and tall look... I think that's a really nice look and should provide a focused array at most listening distances I would think.  Will probably have mine pulled a bit off the ground so the center of the panel is about at the listening height to maximize the distance that you can listen to them in the focused (line) array... really like listening to them as a line array... always imagined that was one of the contributing factors of why the guys like the bigger panels(!?!).

My priorities have changed since I am cramped for listening space.

These days I really can't have large panels in my listen room, that would be like having an elephant in a phone booth. I can see where you're headed and I think your project will work out quite nicely for you. As for me the 4 stacked panels are still a good fit. If I can find a way to make them look "just" like my Magnepan MMG's, my wife will be ok with them. I hope!

BTW, I used a passive EQ between my preamp and power amp. A 100k resistor and .0001mfd capacitor in parallel both put in series with the line. It worked for my setup, since it's passive it may not work well in all cases.

[OB_Newbie]

Yeah, I'm in the same position as you really.  The size of my room isn't bad but just no good spot to set up a nice audio system so at the beginning I was interested in these as they are light and could be picked up and moved to a closet or some other spot.  Funny, I'm shooting for a MMG or Eagle look as well.  We should be able to do this without to many problems I would think!?  I'm going to use black ink in the PVA:water treatment, paint the frames black and use grill cloth to cover everything except the sides.  Still deciding on whether to use natural wood sides or also stain them black.  I like wood but the all black look pretty killa.







The Eagle's are also very nice looking..



Now to find the time and motivation...   

[captainjack115]

Yeah, I'm in the same position as you really.  The size of my room isn't bad but just no good spot to set up a nice audio system so at the beginning I was interested in these as they are light and could be picked up and moved to a closet or some other spot.  Funny, I'm shooting for a MMG or Eagle look as well.  We should be able to do this without to many problems I would think!?  I'm going to use black ink in the PVA:water treatment, paint the frames black and use grill cloth to cover everything except the sides.  Still deciding on whether to use natural wood sides or also stain them black.  I like wood but the all black look pretty killa.


The Eagle's are also very nice looking.

I think where I made my mistake was choosing white for a color, it stands out like a sore thumb. Black would have been the way to go, more dramatic yet understated.
I get so wrapped up in the R&D of speaker building that all of my prototypes wind up looking like ,well............"prototypes".

For me the best thing about quality DIY is that the guy down the street isn't going to be able to walk into a big box store and buy the same thing you have.

[OB_Newbie]

Same...  I'm more interested in the next build instead of finishing the existing design.  But that is where the fun is... fun to build and try different things.   

[captainjack115]

Same...  I'm more interested in the next build instead of finishing the existing design.  But that is where the fun is... fun to build and try different things.   

I found this photo of the Goebel crossover. Apparently it's not just for crossing over their bending wave transducer to their woofers. They mention that it's also for linearization of the bending wave driver.
To me that seems to infer equalization.

I can't help but wonder what Oliver Goebel's panel would do connected directly to a flat amplifier. They claim their bending wave device goes up to 29,500 hz. "Does it" or does it need some help?
Admittedly the fluted corrugated plastic I used is lossy, but high frequency EQ seems to work.

Jack

[Odal3]

Same...  I'm more interested in the next build instead of finishing the existing design.  But that is where the fun is... fun to build and try different things.   

What - I didn't know I was supposed to finish it before moving on to the next. Perhaps that's what my wife has been implying 

I like the look of the thinner ones as well