project: Emperor L26ROY (tweeter + Yamaha JA-0801 + Seas L26ROY)

The nomogram image shows the relationship between a throat (plate thickness + hole size), depth of a chamber, and the percent of the open area. The goal is sorta trap a particular frequency by defining the open area of the plate. Energy is lost as heat in the throat. I used this site to find the spacing: https://www.perforated-sheet.com/calculation/how-to-calculate-open-area.html
I followed that link, scanned quickly other pages on that site. I still don't understand how a mostly solid plate can absorb or trap the dome tweeters back wave: the plate has the same acoustic quality -- mostly blocking or reflecting -- from either side. For trapping to occur sound has to pass through from the source side, then block reflections from inside the cavity from going back through to the back of the diaphragm. Can't see that happening. But I dunno...

Is there any commercial or other documented, successful application of this idea in loudspeakers?

KEF's metamaterals, OTOH, clearly works: it uses an array of tubes closed on the far end, tuned to different frequencies, to effect a broad nearly complete absorption (99% claimed) of the tweeter's back wave in their coax driver. Metamaterial is clearly marketingspeak. It generally refers to materials with properties that don't exist in nature. One source suggested this as a more accurate term: Broadband multi-resonance acoustic absorber.

My hope for the Yamaha BE mid dome is to smooth the low end & extend it if possible, and ditto the top end while reducing its distortion as @Patrick Bateman described for his meta-absorber modded sb26adc. I think different diameter/length straws glued/packed together into a conical back cover (like in the SBA mid dome) could be a meta-absorber covering 500~6000 Hz. Might even be able to 3d print it with some help. Or maybe a puck-style absorber PB created could be used. 💡‼️ I might even just begin with the one I 3d printed for the sb26adc.

Please see these threads:

https://www.audiosciencereview.com/...new-metamaterial-absorption-technology.15713/

https://www.diyaudio.com/community/threads/3d-printed-metamaterials.360739/page-5

https://www.diyaudio.com/community/...ordable-two-way-unity-waveguide.342019/page-5
 
Is there any commercial or other documented, successful application of this idea in loudspeakers?
https://timberix.com/perforated/

Here is a company selling something for walls.

I don't think I have seen it in a speaker. This is something usually used for highways and concert halls.

There is a paper on it that I can send you.

the plate has the same acoustic quality -- mostly blocking or reflecting
In my last version I did use a layer of melamine behind the perforated plate.

Yeah, blocking, reflecting, and some will pass through. Now imagine that there is a mid-point where a range of frequencies gets stuck or rings and that is how it works. Sound is not produced with a group delay of zero, the absorber has lots of chances to ring.
 
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Squeezed a bit of time this afternoon to mess with the 3D printed meta-puck ( :LOL: ) for the SB26 on the Yamaha BE mid dome.

PXL_20240104_001322182.jpg

Didn't trust myself to remove all the fiberglass out of the center hollow w/o damage to the dome so left it in place. Lined the edge of the meta-puck with weather stripping foam.

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Used duct tape to seal around the mating. Not perfect, but probably good enough for a quick test. (In the background, you can see the "traffic cone" used in previous tests.)

The results were not great. Fs went up in frequency to 405 Hz, and a secondary peak appeared at 90 Hz as well. Obviously, the resonant frequencies of the meta-puck are not ideal for the Yammy mid dome. Will have to ask @Patrick Bateman about the specifications of his SB26 puck.

And get one designed for the JA0801

JA0801-SB26metapuck.jpg
 
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Since I already had the back off this JA0801, I decided go all the way. Used 99% isopropanol to soften the seal around the grill, then pried it off, like this fella on youtube. The rest came pretty easily. I figure these pics will help anyone else who's pondering what to do with their JA0801 -- whether to repair or mod.

Used alcohol on a shop paper towel & cotton swabs to clean off grime on what must have been the top side of the dome. Still some left but... Then took the rest apart. A medium Philips head screwdriver was all it took.

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Several noteworthy items:

1. The diaphragm, VC, surround, faceplate & terminals are all one assembly. The dome is numbered. It is not the same number written on the faceplate.
2. Light fluffy fiberglass fills the entire cavity, including directly under the dome.
3. There's a foam ring glued on the underside of the dome, near the perimeter. That's starting to separate & fall away.
4. A single ~1/2 cm dot of the same foam is affixed to the center of the dome underside
5. The cylindrical cavity is tapered, getting smaller as it gets farther from the dome.

Tried gentle pressure on the dome to roughly gauge its excursion. It did not move much or easily. Not sure what that might mean about Xmax. Surround looks clever, like it should allow for some reasonable movement.

I didn't apply much pressure when I swiped the dome with the paper towel or cotton swab. A gentle but not butterfly touch. Tried even a bit of scrubbing motion on some of the sticky parts which did not come off. I did not feel I was risking damage.

Any thoughts on how to repair the foam ring that's slowly ripping off the dome? I don't think I'll try to replace it but maybe a few drops of super glue? Or runny silicone?
 
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@silent mike Neat! There is not much too these things.

I am sure on some level all of these different resonant plates/chambers/mazes work the same.

Today I am going to take the back off again and re-measure the cup for a small plate near the top or maybe inside of the magnet. Having it right at the top wont work with the hole size I am using.

If you don't mind a suggestion, save the measurements to memory in DATS or export them as text and import to REW so you can A/B in the same graph.


Any thoughts on how to repair the foam ring that's slowly ripping off the dome? I don't think I'll try to replace it but maybe a few drops of super glue? Or runny silicone?
There are some black rubber speaker repair glues.
 
If you don't mind a suggestion, save the measurements to memory in DATS or export them as text and import to REW so you can A/B in the same graph.
👍 Any data I post here is saved.

One thing I forget to mention in my list of notables is how surprisingly light the faceplate assembly is. I will weigh it today, but it seems lighter than it should be. Maybe it's the labyrinth/honeycomb pattern on the backside that's minimizes the aluminum material... and my expectation of greater weight given its perimeter thickness. The magnet structures seems to comprise ~90% of the total mass.
 
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Quick observations:

1. The stock 365 Hz Fs is pretty low, but impedance is higher than I'd expect. Perhaps it's because all current tweeters I've measured have ferrofluid.
2. Open back Fs is lowest at 235 Hz. This would seem the lowest Fs we can hope for when the back is closed.
3. With the 12" traffic cone over the open back, Fs rises, as expected, but only to 265Hz, which is less than I expected. Multiple aux peaks above & below look bad.
4. The poly fill helps tame the multiple peaks, brings Fs down to 250 Hz, but peak amplitude is only down a dB.
5. Long teased wool has similar effect to poly, but I did not weigh either, so it might not have been exactly the same amount.

The "seal" between the backside of the driver & the cone was far from perfect -- just placed with a bit of pressure.

Admittedly, a 12" cone on the back of a driver is impractical. I would probably reduce this down to maybe 8" if I decided to use an expanded cavity back.

The big question for me is what an array of varied length thin straws (1/16" to 1/8" depending on length) packed and closed at the far end in such a cone might do. Yeah, a broadband multi-resonant absorption array akin to KEF's "metamaterial".

That experiment will have to come later. Probably best when I have the JA0801 in some kind of viable speaker system.
Not sure am I right here, taking a page out of the latest revision of NS1000 mid and homoz(sp?) piping effect from a part expreess speaker project, I guess the whole tube can be shorten by a T shaped PVC tube. Getting 250hz range is like something ATC mid cant do
 
Interesting. I measured Fs on the JA0801's from my Yamaha NS1000's decades ago (early 80's) after buying them new. Fs was close to 260Hz on both units. Perhaps the suspension stiffens up after many years.

When last were these used? Perhaps a little 'burn in' will soften up the suspension?

When I sold the speakers, I thought they did not sound as well integrated as they used to. Perhaps the crossover transfer function changed due to a shift in Fs. I did not measure though.
 
Interesting. I measured Fs on the JA0801's from my Yamaha NS1000's decades ago (early 80's) after buying them new. Fs was close to 260Hz on both units. Perhaps the suspension stiffens up after many years.
That is contradictory to Yamaha's own spec. See the attachment on the 1st post by the OP. The impedance curve shown there indicates Fs somewhere 600~700Hz.

But the measured Fs of my unmodified JA0801 is around 360Hz, same as Headshake's
https://www.diyaudio.com/community/threads/headshakes-far-field-3way.382393/page-14#post-7434715
https://www.diyaudio.com/community/...maha-ja-0801-seas-l26roy.402637/#post-7554406

There might have been variances in different production runs over the years. They were in production for at least a couple decades.
 
It is not contradictory. The data sheet is for the JA-0803, which is a version used in the NS1000X, whereas the JA-0801 was used in the NS1000M and related models.
Right.

So @HeadShake & I both measured Fs @~360 Hz. I got this with the Dayton Audio DATS V3. You got 250Hz with a brand new JA0801 way back when. (Tested how?) Unfortunately I have not found any other JA0801 measurements or detailed specs, so it's hard to verify your conjecture that the suspension stiffened with age, leading to the >100Hz higher Fs. OTOH, I also haven't run into a single large mid dome with Fs below 300Hz. I think the lowest I've seen is for the ATC-SM75-150, which Troels G. found to have Fs= 307 Hz. http://www.troelsgravesen.dk/ATC-SM75-150.htm

Perhaps other NS1000 or JA0801 owners here can be persuaded to measure theirs?
 
There are some Yamaha NS-1000 measurements on Troels' website:

http://www.troelsgravesen.dk/Yamaha-NS1000.htm
Ah, I see the one graph showing impedance of all 3 drivers. Based on that, it looks like the mid dome Fs is just above 300 Hz, maybe 320.

It's cool in my studio -- rarely more than 16-17 C except in summer, so that could have an impact.

In any case, these Fs variations don't matter much to me. My aim is to reduce or eliminate the back wave from my particular JA0801 domes. P

I haven't done anything since the last post. I am thinking about using straws of different lengths in a conical back much like what @xrk971 used on the back of the Scan Speak 10F -- he called it dagger iirc.
 
Your project is interesting. FWIW, instead of trying to extend the mid's bandwidth downward, I would have added a good 6.5" to 7" midbass into the system. Something like SEAS Excel. You can get a lot of value out of using a driver over a limited bandwidth where it performs the best, especially if you are using DSPs.
 
Your project is interesting. FWIW, instead of trying to extend the mid's bandwidth downward, I would have added a good 6.5" to 7" midbass into the system. Something like SEAS Excel. You can get a lot of value out of using a driver over a limited bandwidth where it performs the best, especially if you are using DSPs.
The reason for all this work on the JA0801 is to make it as good as possible, for use in a big 3-way active studio monitor project, with Hypex plate amp, probably 253. My design reference is the Neumann KH420 or KH310. Not for me but for my musician friends.

Basic requirements are F3 = 35 Hz, excellent dynamic range, controlled but not narrow directivity, LR4 at 250~350 Hz & 3.5~4.5 kHz. Optimized for near field completely flat response, not the -6 to -8 dB downslope to 20 kHz that's nicer for standard commercial recordings.

The need for flat high frequency extension was made very clear yesterday when two friends tried recording in my studio, which has very good acoustics: the reduction in higher frequency energy between the live acoustic guitar vs the unedited recorded playback was so obvious; not useful for studio work. This through my LX521 clones which sound fantastic with most released music but must have the down sloping FR to sound realistic. (Makes me wonder why so much music is mixed so brightly.) I'm tweaking a new config file for the lx521 clones to get flat extension out to >15 Khz for the next time my musician friends come.

Other components will likely be a sealed 10" woofer, and either a proven metal dome tweeter like the SB26ADC or a suitable AMT/planar with wide directivity. The mid dome will be flush mounted onto a waveguide cut into the 1" thick BB ply; a dome tweeter will get the same treatment. It'd be nice to have the enclosure be smaller & lighter than a NS1000 but if that is what it take to create a high performance studio monitor for modest cost, so be it. Arranging the mid & tweeter like in the Neumann KH310 -- side by side when enclosure is vertical -- will help keep the size down.

It should be easy to integrate an 8-10" conical back for the JA0801, and I'll use a meta-resonance absorber if the SB26 tweeter is used.