Hello Clevor1
With such proportion, it is more a vibrating beam than a plate!
I don't remember having seen something close to that here. I have search a bit thinking somebody has already designed a narrow central channel but not found.
What sounds strange (I don't say it won't work) in this is the 15cm dimension :
- In DML, sound is emitted by both side like in an OB. Reducing the front to rear path length risks to increase the frequency cut off so that you won't reach the targeted bandwidth
- This short dimension risk to make the panel very stiff in this direction leading to a too high resonance frequency. A very light or even no suspension would avoid that.
I made some tests (not a full panel) gluing different materials like layers of different woods but not with real good results. The glue (white glue) add quickly weight and damping.
About the exciter, I have tested only one, the DAEX25FHE.
Christian
Homeswinghome
For adhesive, I plan on using 3M 77 adhesive spray, since it works on multiple surfaces and should leave little to no barrier between surfaces. That may help, not sure.
I plan on testing (by ear since I have no actual audio test equipment) some different combinations of materials, using these brackets.
So maybe I should change the dimensions? I also think that HDF peg-board would be interesting, with another material behind it.
Are the Dayton ones just better than the ones from Tectonic?
It may be a week or two until I can mess around with this though, got some other projects to wrap up, but like planning ahead!
For adhesive, I plan on using 3M 77 adhesive spray, since it works on multiple surfaces and should leave little to no barrier between surfaces. That may help, not sure.
I plan on testing (by ear since I have no actual audio test equipment) some different combinations of materials, using these brackets.
So maybe I should change the dimensions? I also think that HDF peg-board would be interesting, with another material behind it.
Are the Dayton ones just better than the ones from Tectonic?
It may be a week or two until I can mess around with this though, got some other projects to wrap up, but like planning ahead!
Hi Clevor1,
3M 77 was mentioned by Veleric in #4735, not for the exciter but between layers of a sandwich membrane (balsa).
Steve (Spedge) uses PVA glue. In #9923, Eucy describes his technique with masking tape.
I use simple double side tape (from my local DIY store). I have doubt about the performance in HF. You should find other techniques in the posts of this thread.
The brackets proposed by Dayton Audio are interesting. They were cited several time here but I don't remember seeing any results (FR). I have a doubt about the influence on HF because of the weight added at the voice coil.
From what I see HDF peg board is MDF. It is not in my "material list" : heavy, damped... Increasing the density reduces the efficiency. On that way, I wouldn't go higher than poplar plywood.
About DaytonAudio versus Tectonic : the question of which exciter has been opened quite often without final conclusion. Possible I miss some posts but my criteria for a wide range application remain low mobile weight, high force factor, low inductance. Every other factor equal a 8 ohms exciter might be better in HF (no evidence for that).
Christian
The space between the UST projector and the screen is roughly 8in so I want some room for mounting. I was planning on two exciters wired together as a center since I know that it will be a large panel. I already have a pair of RT16s for my L/R, so this would be a center channel with two exciters to keep up with them.
Are you thinking because the soundstage is so big that I should not make the panel as wide, because it may bleed into the L/R?
TY! And yes the 3M 77 is more panel-to-panel application. So I should find a that is not too dampened. My thought was that with the pre-cut holes, and from what I have read here, that may produce a better overall sound. I am trying to do the least amount of cutting as possible.
It sounds really nice! What was done to the center of those, specifically the one on the left?
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+ @clevor1
Hello,
Here is a quick measurement of a 15x38cm piece of cardboard (about 2mm thick made of 2 flute layers).
I'd say the low frequency roll off start around 500Hz (don't take into account the 50 and 100Hz which are I think electrical noise in my system).
For now, I haven't tried to link this high pass effect with the panel dimensions but i think it should be possible.
With a bit of EQ, it would be possible to go lower. Similar to OB application?
Hello,
If it can have an interest for somebody, here are the next steps of the DML posted in #10187.
Compare to the previous post, the exciter is now a 30mm and I wired a passive crossover to work with the woofer. The tweeter is not wired for now. The position of the exciter was also change compare to previous post to limit the hump which was at 300Hz.
The crossover is probably not optimized, made of parts I already have.
I just had some listening tests with one channel (second channel not wired for now). The results are encouraging.
Here is a measurement. The curve of the tweeter FT17H is here as a "reference" (HF and efficiency).
If it can have an interest for somebody, here are the next steps of the DML posted in #10187.
Compare to the previous post, the exciter is now a 30mm and I wired a passive crossover to work with the woofer. The tweeter is not wired for now. The position of the exciter was also change compare to previous post to limit the hump which was at 300Hz.
The crossover is probably not optimized, made of parts I already have.
I just had some listening tests with one channel (second channel not wired for now). The results are encouraging.
Here is a measurement. The curve of the tweeter FT17H is here as a "reference" (HF and efficiency).
Thanks jaxboy, I think they sound great too.
The frequency response on my screen was taken from my microphone 3m back into the room , which was shown in the video.
Obviously going closer to the speakers improved on this giving a fuller sound.
Which hopefully came through in the video also.
There are no problems with small panels in a normal sized room in the UK, volume wise 😀
Even more so if you raise the xo frequency to prevent low frequency problems.
Steve.
Hi Christian.
I am thinking of buying the 25HFE for testing heavier panels.
Referring to your two new plots, the hf on your last plot shows an early roll off above about 6k.
What is the material and its dimensions and thickness?
Your previous plot shows the usual peek at 10k ,which I have previously shown how to correct.
Hopefully this exciter will give a full frequency response on my panels under test?
Steve.
I am thinking of buying the 25HFE for testing heavier panels.
Referring to your two new plots, the hf on your last plot shows an early roll off above about 6k.
What is the material and its dimensions and thickness?
Your previous plot shows the usual peek at 10k ,which I have previously shown how to correct.
Hopefully this exciter will give a full frequency response on my panels under test?
Steve.
Hi again Christian.
I have mentioned before the two humps in the low frequency area which is quite normal depending on panel materials and exciter.
Also depending on if the panel can actually go that low.
I have shown many plots with these humps in place.
You also mentioned MDF , which I have tested many years ago using the same 6ftx2ftx 3mm size rigidly framed panel as the ply panels .
The performance was very similar to the ply panel , but I felt it had less colouration than the ply.
But it still suffered the same problems as all heavier panels.
Steve.
Use your screen as the speaker membrane. Because the screen size is usually quite large, you will have plenty bass.
Build the screen out of 3mm or 6mm plywood. Paint it with a titanium-coloured paint applied by roller. This should give you a nice neutral grey matt finish and will not show the hotspot from the projector.
Apply your exciters directly to the plywood screen on the rear side, left, right and centre. Fix the left and right channels 1/5th from the sides along the horizontal centre line, and the centre driver can be 2/5ths from the top or bottom. The DAEX32EP-4 Thrusters should be ideal.
Hello Steve,
With the 25HFE, I have quite good HF extension with my canvas panels and also with the plywood ones.
Those last FR are with a 30HEFS but I think this is not the origin of the roll off. the origin is probably in the material : a 3mm corrugated polypropylene with square flutes. I described the first test of this panel in #10187.
For this application, first intention was to use the 25HFE but due to the low HF extension of the material, I changed to the 30HEFS with a better power handling; those panels should be used in a (very) large room. They are also a pretext for testing new things.
Christian
I remember about those humps and also exchanges with Eric : the density of the first modes or let say the distance between them is too high so some valleys appear (mode 1,1, mode 1,3). After the density is better so the valleys are no more visible. In that case, I have doubt because the panel is small. I have had such humps at 50 and 100Hz in other measurements. I should think to a measurement with an other mic to be sure.
MDF seems to be in the range 600 to 800kg/m³ even 1000kg/m³ for what is called Isorel (don't know in English). I have in my notes 530kg/m³ for the poplar plywood. In addition the 3 layer plywood has different stiffness according to the direction which is described in some papers as an advantage to spread the coincidence frequency.
Christian
Plywood's are Typically made in two types of structure, one being a Cross Grain Orientation on each tier, this is the method used for producing the the most rigid structure for a board.
The other method is an in line Grain Orientation, this enables a board to have a flexion and is the board chosen for forming curves as it yields to applied force and can be steam treated to hold the form.
There are MDF Boards with a fascia that has a rebate cut into one fascia at equidistant dimensions, again to help create flexion.
This might prove useful if a Thin Thickness Board can be found with the rebate cuts.
A lighter Board will be one benefit and less rigid board might also be an advantage.
The other method is an in line Grain Orientation, this enables a board to have a flexion and is the board chosen for forming curves as it yields to applied force and can be steam treated to hold the form.
There are MDF Boards with a fascia that has a rebate cut into one fascia at equidistant dimensions, again to help create flexion.
This might prove useful if a Thin Thickness Board can be found with the rebate cuts.
A lighter Board will be one benefit and less rigid board might also be an advantage.
Because I can't find the model number
I searched carefully and found that the model number is "30HESF"
DAEX30HESF-4 High Efficiency Steered Flux Exciter with Shielding 30 mm Exciter 40W 4 Ohm
From the specifications, the high-frequency extension is not bad
Christian.
If you look in my gallery on the NXT Rubbish forum , you will see the low frequency humps in the 40cm 10mm panels and also the large 25mm panels ,and others.
Don't forget that these are free floating panels.
If you mount the panels using foam or other materials, and clamp them all around this will heavily damp and change these properties.
Similar to mounting the panels with foam willy-nilly (randomly 😀 ) around the panels, this also will change the properties to unknown frequencies.
Even if I were to mount my panels using foam I would try and find the best positions possible for the frequencies that I wished to use.
Using pink noise.
Trying to use the weights to change the random frequencies caused by the mounting method is not the best way to improve things.
I would find the spots that improve performance on the free floating panel first, then probably if possible use these points to mount the panel.
All these things should be done and listened to carefully, to make sure it sound better, rather than a flat frequency response , but hopefully if done properly they should both be good.
Steve.
If you look in my gallery on the NXT Rubbish forum , you will see the low frequency humps in the 40cm 10mm panels and also the large 25mm panels ,and others.
Don't forget that these are free floating panels.
If you mount the panels using foam or other materials, and clamp them all around this will heavily damp and change these properties.
Similar to mounting the panels with foam willy-nilly (randomly 😀 ) around the panels, this also will change the properties to unknown frequencies.
Even if I were to mount my panels using foam I would try and find the best positions possible for the frequencies that I wished to use.
Using pink noise.
Trying to use the weights to change the random frequencies caused by the mounting method is not the best way to improve things.
I would find the spots that improve performance on the free floating panel first, then probably if possible use these points to mount the panel.
All these things should be done and listened to carefully, to make sure it sound better, rather than a flat frequency response , but hopefully if done properly they should both be good.
Steve.