[mzbrahce]

I have been interested in exciter based panel speakers since I started reading the thread, "NXT.....rubbish??...THINK AGAIN!" in the circle "Open Baffle Speakers" several years ago.  I spent most of my spare time for about a year experimenting with corrugated cardboard panels treated with shellac, trying different sizes, shapes, thicknesses and layers of cardboard, different numbers and types and mounting positions of exciters, etc. The end result, so far, is a panel about 2' x 3' of single thickness corrugated cardboard with a second layer added around the perimeter, powered by 2 exciters placed in the first 2 Monacor positions, suspended by cotton string placed through a hole in each upper corner of the panel.

Danny was willing to give these a listen and do his usual thorough job of testing them, so I packed up 2 panels and sent them off to GR Research.  One of the panels is just a single layer, the other has the double layer edge treatment.  To my ears, the added layer somewhat improves FR by increasing the bass and reducing the treble.

I am really interested to find out what Danny measures, and what he thinks about how they sound; I hope some of you will be, too.  These speakers are incredibly cheap (less than $20 in parts for the two panels I sent).  As I told Danny,  I think they have their good and bad qualities--I am amazed at how quick and detailed these funky cardboard panels are.  They are very efficient and play quite loudly, with big character.

We'll see what Danny says.....

[Danny Richie]

I have been interested in exciter based panel speakers since I started reading the thread, "NXT.....rubbish??...THINK AGAIN!" in the circle "Open Baffle Speakers" several years ago.  I spent most of my spare time for about a year experimenting with corrugated cardboard panels treated with shellac, trying different sizes, shapes, thicknesses and layers of cardboard, different numbers and types and mounting positions of exciters, etc. The end result, so far, is a panel about 2' x 3' of single thickness corrugated cardboard with a second layer added around the perimeter, powered by 2 exciters placed in the first 2 Monacor positions, suspended by cotton string placed through a hole in each upper corner of the panel.

Danny was willing to give these a listen and do his usual thorough job of testing them, so I packed up 2 panels and sent them off to GR Research.  One of the panels is just a single layer, the other has the double layer edge treatment.  To my ears, the added layer somewhat improves FR by increasing the bass and reducing the treble.

I am really interested to find out what Danny measures, and what he thinks about how they sound; I hope some of you will be, too.  These speakers are incredibly cheap (less than $20 in parts for the two panels I sent).  As I told Danny,  I think they have their good and bad qualities--I am amazed at how quick and detailed these funky cardboard panels are.  They are very efficient and play quite loudly, with big character.

We'll see what Danny says.....

Well, when they arrived it was evident that the little exciters pulled themselves off of the cardboard during shipping and were both laying in the bottom of the shipping box.

It took a little bit if time, but I was able to slice the little plastic pieces off of the card board and glue them back onto the exciters.

Then after the glue dried I glued them back onto the card board. So I got one of them back up and playing.

The measurements were not bad actually. They don't have much above 10kHz, but the rest was not bad at all. Off axis was not far off of the on axis too. So on axis or off axis was very consistent.

And they didn't sound too bad with some source material.

I'll try and post the measured responses later tonight when I get back home.

[Danny Richie]

I would also note that there are two of these little exciters in a solid piece of cardboard that is 22.5" wide and 32" tall.

Okay, here is the on axis response. This is actually a true 1 watt/1 meter measurement.



And as one would guess, the spectral decay is not real clean. There is a lot of mass there.



Here is the off axis response. 0, 10, 20, 30, and 40 degrees off axis.



And the impedance response.



I added a 39uF cap inline with it and it flattened out the response a little.



That is actually pretty accurate with the added cap value. Sure, it has no bottom end and the top octave is gone, but it is not bad through the range that it covers.

[mzbrahce]

Thanks, Danny!
I appreciate the extra effort you spent to re-attach the exciters.  Your results are pretty much what I expected.  No competition for you, but not bad for a piece of cardboard.  It is interesting how decent they can sound despite the restricted frequency response.  With its speed, low frequency percussions sounds are quite realistic, but there is no shimmer to cymbals.  They definitely have a lot of un-damped vibrations.  What would you estimate their efficiency to be?

[Danny Richie]

Thanks, Danny!
I appreciate the extra effort you spent to re-attach the exciters.  Your results are pretty much what I expected.  No competition for you, but not bad for a piece of cardboard.  It is interesting how decent they can sound despite the restricted frequency response.  With its speed, low frequency percussions sounds are quite realistic, but there is no shimmer to cymbals.  They definitely have a lot of un-damped vibrations.  What would you estimate their efficiency to be?

What you see on the first frequency response curve is a true 1 watt/1 meter measurement. Sensitivity is pretty high in the mid-range, but a little low elsewhere.

If you figured out a way to mount them by the exciter and used a small diaphragm on one for the higher frequencies and a larger diaphragm on one for lower frequencies then you might be able to balance out a response. It will take some time, but it might turn out to be pretty surprising.

[Folsom]

We've been chatting about these a little, and believe it might be possible to make an amp that would work better than many others with them, as opposed to dynamic drivers.

[mzbrahce]

I'm willing to keep experimenting.  These panels are insidious--just good enough "out of the box" to make you think there's got to be a way to make them better.  That's why the NXT string is so long--people have tried a lot of different things.  I'll work on a HF panel.  I've got a few ideas, but your insight is always welcome.
Folsom--I'm interested.  I've been using a 3116 chip amp for a lot of my testing.  I've purchased your boards, for amp and monopole, but haven't bought the parts yet.  I'll order within a week.  Looking forward to hearing it after all of the great feedback you've received.

[Folsom]

I'm pretty sure the demands for an amp for this type of exciter speaker are different. I'd probably create an EQ in it, and make it current based instead of voltage.