I bought some cheap used compression drivers on ebay. They are the eminence nsd2005-16. i chose them because they have a 2 inch diaphragm, a 1 inch throat and a factory fs of about 578hz. not to mention i bought the pair for $90 shipped. I'm not one to spend a fortune on audio and i figured it was a good place to start. Once ia recieved the drivers, i printed a horn to test them in; the ath a520g2 with extended throat. I also printed a couple metamaterial rear chambers and picked the best of the two. then i added aquaplas to the diaphragm wihich i also purchased from ebay for $23. here are the results.
factory rear chamber, no aquaplas
Metamaterial rear chamber, no aquaplas
metamaterial rear chamber, 1 gram of aquaplas
a lot of this is below the noise floor of my rather noisy ifi zen dac but its what i have at my disposal. i havent listen to music with these but the sweep itself sounded noticeably better. the only problem i see is a deeper/wider notch @ 14k. idk why this is. it could be that i dimpled the diaphragm while applying aquaplas. it popped back but this is a lesson learned. when i get around to the second one i will be more careful and hopefully it wont happen again. then we can see if there is a difference. otherwise i consider this a success.
factory rear chamber, no aquaplas
Metamaterial rear chamber, no aquaplas
metamaterial rear chamber, 1 gram of aquaplas
a lot of this is below the noise floor of my rather noisy ifi zen dac but its what i have at my disposal. i havent listen to music with these but the sweep itself sounded noticeably better. the only problem i see is a deeper/wider notch @ 14k. idk why this is. it could be that i dimpled the diaphragm while applying aquaplas. it popped back but this is a lesson learned. when i get around to the second one i will be more careful and hopefully it wont happen again. then we can see if there is a difference. otherwise i consider this a success.
This is the rear chamber i settled on. I just created a shape and used the hilbert curve infill at 30%. Yes it was that easy. There are many space filling curves out there, just do a search, but this is the one in orca slicer (maybe prusa slicer). The infill wraps around that inner ring to the outer area. The entire shape is 250 cubic cm but idk the actual airspace.
this is what the aquaplas looked like after i applied it. I tried to make it even as possible using a brush. This stuff is thick like whipped butter. It was recommended to dilute with water and spray on.
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The overall smooth response of the horn is impressive, as is the increase in sensitivity in the 600-1100Hz range of as much as +4dB due to the metamaterial.
The Aquaplas sensitivity reduction of -3 to over -6dB will require 2 to 4 times the power to get the levels similar.
After adding that much power to achieve similar SPL, the distortion differences won't be as much, but the reduction in dynamic range may be more noticeable.
I'd suspect the additional mass, and it's distribution has changed the modal response of the diaphragm, resulting in the -16dB null around 14kHz.
I'd be surprised if the second driver's response prior to damping is the same as the first 😉
Looking forward to your findings!
Art
unfortunately the other diaphragm is defective. Much worse and clearly audible distortion and much different frequency response.
I tried swapping diaphragms between motors mutiple times and the other one is obviously defective. Its odd to me because looking at it i cant see anything wrong with it. It looks brand new. What could be wrong with it?
After some research it sounds like the diaphragm isnt properly aligned. The distortion is very audible at the lower end of the sweep but the distortion is a mess all over the midband. Ive pulled it out and put it back in and it cleaned up in some areas but still terrible in others. Took it out again and it was the same results as before 😡 Hopefully i can figure this out because these diaphragms are apparently no longer being manufactured. Ive only found them in stock at 2 websites which ive never heard of: https://www.aallyandsons.com/horn-driver-coil-eminence-nsd2005-16dia/
And
https://www.alphaelectronics.com/pr...lHSg6OLULavHjlKNcg3EO7xHW3gQWds5CZY4Sa3fDDq5V
And
https://www.alphaelectronics.com/pr...lHSg6OLULavHjlKNcg3EO7xHW3gQWds5CZY4Sa3fDDq5V
Looking at the application of the aquaplas I noticed you did the surrounds as well. That might be part of the problem. If you "clog" the surrounds, you could be restricting the diaphragm movement in the lower end. Another potential issue doing the surround is messing with any tuning done for the secondary resonance by the surround forming process. Just looking at JBL use they almost never aquaplassed the surrounds. That could be your 14K notch.
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When doing your diaphragm coating, use a small rotating disc/table to spin it. And keep the pencil steady.
Will give much cleaner results, just do a few tries on fx. a coke can bottom first.
The coating looks a little uneven, too dry and grainy, and came onto the surrounds too. The dillution is a good idea.
The manufacturer of the original product (not named Aquaplas). Advices to use a airless spray system for good finishes, (media/paint fed from pump not air pressure).
Will give much cleaner results, just do a few tries on fx. a coke can bottom first.
The coating looks a little uneven, too dry and grainy, and came onto the surrounds too. The dillution is a good idea.
The manufacturer of the original product (not named Aquaplas). Advices to use a airless spray system for good finishes, (media/paint fed from pump not air pressure).
apparently these diaphragms are very particular about their alignments. I put the diaphragm back in its original motor and rotated it until it worked. Idk why but i figured they would be manufactured with higher quality control. I was wrong... These are also older obsolete drivers.
I couldnt imagine trying to use any airless sprayer im used to. It probably takes a quart to fill the lines before spraying anything. I have a nice hvlp cup gun with a turbine but i dont have a small cup setup. I thought about buying an airbrush. Also they told me to do the surrounds but im sure it affected compliance. I would be surprised if coating the surrounds caused the dip at 14k. I imagine these were tuned as a whole unit and adding anything to the diaphragm would cause some deviations in the frequency response.
Most are, though it seems many users are not 😉
You didn't mention measuring to determine whether the gap width is symmetrical, or cleaning the gap.
Both are critical steps in diaphragm replacement.
Too bad OEM diaphragms don't appear to be available.
Yes but your Aquaplas is available in 5 gallon buckets (or larger quantities like 520lbs drum), and used for larger surfaces as a damping compound (spray on). That is why it is prohibitive for single use on diaphragms where you need maybe 0.5 grams. And why one buys small 20$ jars on Ebay 🙂
It's called a liquid spray damping from the mfg.
The dillution will help.
Also those small jars if not properly vacuum sealed will make it's consistency change over time. They do not come like that from the Mfg.
1. Apply by spraying (air less preferable), trowelling or brushing. Do not apply if ambient temperature falls below 50°F.
2. All surfaces must be completely clean. Thoroughly degrease all surfaces to be coated. Loose scale or corrosion should be removed by sandblasting or wire brushing.
3.It is shipped at the proper consistency for application. If necessary, use only a small amount of water for thinning. Use no solvents.
4. When (air) spraying, feed line is 3/4”. Use a 1/4” round nozzle or equivalent. Atomizing pressure is 40 to 50 p.s.i. Keep gun in water when not in use. Clean equipment with water after every shift and before material dries.
5. On heavy metal products apply at 1 to 1-1/2 times metal thickness. Apply only 3/16” at one time and allow to set before additional coats. 1.5 lbs. wet will cover one square foot at dry thickness of 1/8”.
This is the measurement of the other driver once i got it working properly. this measurement is at about 2 meters. also i have no way to mount it properly so it was sitting in an office chair which impeded the bottom curvature of the horn. i dont know how much it affected the response im guessing not terribly but it would only be better in proper position. all of my measurements should be taken with a grain of salt because im an amateur and not good at keeping constants.
this project was simply to see what could be had at the $100 mark for compression drivers. once i print the other horn i will have to see how it compares to my meh horn. im not sold on this combo yet. increasing the volume to over 100db at lp increased the distortion to around -35db for a single horn. the lower end sounded a little "zippery" but i havent listen to any music with this yet so idk.
this project was simply to see what could be had at the $100 mark for compression drivers. once i print the other horn i will have to see how it compares to my meh horn. im not sold on this combo yet. increasing the volume to over 100db at lp increased the distortion to around -35db for a single horn. the lower end sounded a little "zippery" but i havent listen to any music with this yet so idk.
I tried to clean the gap but i didnt measure anything. These are the diaphragms that came with it so i thought they would be fine in either motor. I was switching diaphragms out of the motor rather than switching the driver entirely because it was quicker and easier. This was the problem. I thought they were exactly the same and i guess they are not.