New Product Development - 2402/075 - Can You Help?

[toddalin]

I will probably join the Urban Workshop this/next week and will have access to a Professional 3-D printer in ABS plastic. I've been learning CAD using DesignSpark and have some ideas for use with JBL products in mind.

I've already designed a set of tweeter stands and am working on a "slant plate" assembly for use with the 075/2402. 3D printing lets me create and test ideas that JBL could never have dreamed of with their technology of the time. And, with a couple keystrokes, we can change things such as the curvature of the slant plate and print a new set. This shows the slant plate and there will be an assembly that goes around the 075/2402 to mount it in front of the tweeter/baffle board (hence the rear cut-out that considers that the tweeter typically stands 1/4" out from the baffle board).

Anyway, this post is a request for a 2402/075 for disassembly and measurement. The unit doesn't need to work nor be in good condition so long as it is not dented or bent in any way. I may also try to cast the phase plug in clear acrylic tapped for the screw. (Why should 077s get all the ooohs and aaahs? How cool would that be???) I could also do this with the 2405 phase plug if someone has one "lying around" and of course they would get a pair and return of their plug if they wanted it back.

In exchange, I'll print you out a pair of stands, the slant plate assemblies, or what ever else I come up with, your choice.

Thanks

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_90_Jul_11_11_23.jpg
http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_89_Jul_09_17_53.jpg

[toddalin]

The missing piece. These should tame the 075/2402 a bit.

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_91_Jul_12_15_22.jpg

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_90_Jul_11_11_23.jpg

[toddalin]

The phase plug on the 075/2402 extends a bit beyond the perimeter so it was necessary to raise the face out a bit to compensate. Rather than just leave a "hole," I used CAD to blend the hole into the horizontal plane. I'll try to print out a set for initial fit and trial next week when I gain access to the $35K 3D printer.

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_92_Jul_13_17_37.jpg

[toddalin]

I made it a bit curvier and into two pieces so two will fit in a small "If it fits it ships box. ;)

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_93_Jul_15_15_38.jpg

[Horn Fanatic]

The missing piece. These should tame the 075/2402 a bit.

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_91_Jul_12_15_22.jpg

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_90_Jul_11_11_23.jpg
I'm curious as to what math you used to design your acoustical lens assembly.

[toddalin]

In accordance with the theory, the plates have to be less than 1/2 wavelengh spacing. I used 0.35", similar to JBL, that takes it over 19kHz..., higher than the 075 can go.

For the size, I used the HL-91 lens dimensions, but scaled them to the the diameter of the tweeter rather than the horn throat.

I did more "smoothing" of the "vane posts" at the throat.

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_94_Jul_15_18_50.jpg

[honkytonkwillie]

I may also try to cast the phase plug in clear acrylic tapped for the screw. ... I could also do this with the 2405 phase plug if someone has one "lying around" and of course they would get a pair and return of their plug if they wanted it back.


Turning a 2405 into a 077 is akin to alchemy. I think you have a money-maker here.

[toddalin]

We started the Urban Workshop last night with the laser etcher/cutter class and also have access to the 3D printer. The laser is great for working with acrylic, though you can/do get some minor burn spots along the edges.


Unfortunately, while use of the printer and laser are included in the membership, the media are not. For the laser, you just bring in what you want to cut/etch, if it is on the approved list.


For the 3D printer, they supply the ABS media in cassette spools. The media costs $10/cubic inch plus a $9 recycling fee on the empty cassettes! (I have no idea how far a cassette goes.) The pictured stands would use about 20 cubic inches of material EACH or about $200 just in materials.


For the slant plates, each plate is ~8" x 2.5" or 20 square inches. If each plate is 1/16" thick, it uses 1.25 cubic inches and the cost is $12.50/plate (x 8) or $100 per tweeter. The mount adds another ~5 cubic inches and you're up to ~$150 in materials alone per tweeter.


It is far cheaper (~$2/plate) to make them of 1/16" ABS. But ABS is not allowed in the laser cutter as it emits toxic fumes and the smoke clouds the lens. Acrylic works, but I want 1/16" and that typically comes in 1/8" and is not as strong as ABS.


We'll see what happens.

[1audiohack]

It's funny how 3D printing is always THE answer, until you actually get to it. Do they have value? Sure, but not for production.

Barry.

[toddalin]

But all is not lost. I've revised the slant plate to use laser cut acrylic, assuming the laser can cut down to 1/16" acrylic (the settings are provided for down to 1/8") and that the acrylic plates have enough strength.

The 3D printing may still prove beneficial in making "plate spacers" out at the ends because these would use little material. On the other hand, if I can go to the craft store and find the right kind/size beads to space the plates, that would be cheaper and easier.

[louped garouv]

very neat project --

Grainger or McMaster Carr (others) may also be a worthwhile source to check in with for any misc. fitments/gaskets/etc. that are necessary....

very neat project!

[toddalin]

"All of this and some of that's the only way to skin the cat." ;)


http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_106_Jul_21_14_32.jpg

http://www.audioheritage.org/photopost/data//500/ScreenHunter_107_Jul_21_14_33.jpg

[toddalin]

I was able to try the laser cutter/etcher today.

Look what I can do.

http://www.audioheritage.org/photopost/data//500/medium/Lasered_001.JPG

http://www.audioheritage.org/photopost/data//500/medium/Lasered_004.JPG

[Doctor_Electron]

Hello,Toddlain, welcome.

I have a few more questions. Is acrylic "A Go" for the slants?

Would using plate lenses in front of stock ring radiators produce a "compound dispersion" pattern as a result of the stock pattern response (may not be correct terminology lingo) but I think you know what I mean by that) of the stock signal being refracted again by the plate lens? If so, what would you expect as a result? Ring radiator experts, and we know you are here at Lansing Heritage, please chime in.

Will adding these to 2402's and 2405's alter their recomended low frequency cutoff values? New values?

I have one 2402 with dead alnico from which I could provide parts for measurement. I would need it back because the driver is now a display. (Prop). If interested please PM me with details.

Very interesting thread.

Regards, -de-

[toddalin]

Thanks,

Yes, the slant plates are a go. I have enough scrap 1/8" acrylic to make up a set of plates to test out. If tests go well, I'll try using 1/16" acrylic, which I have located in colors/smoked.

The acrylic mfg has a high-quality product that has a brown paper layer on either side to protect it. Though a bit more costly, this is is also the best stuff to use in the laser because the brown paper helps to keep the edges from burning as the laser cuts.

Once I've made a set, I can use a 6 mfd cap on an original 075 (never opened) and run pink noise though it. The 6 mfd cap is used in the 2400/2600 crossovers with the D130, so is the lowest recommended value for use with the 075. The 2600 actually pads the 075 down to avoid injury at this frequency, but I can keep the volume at a reasonable level for testing.

I have a 61-band RTA and can easily A/B the freq response with/without the lens. I also have professional sound level monitoring equipment (it's what I do), a protractor, and a piece of string 1-meter long so can measure off-axis response.

[toddalin]

Maybe not so classy as a 3D printed/injection molded stand, but this will work and carries the lines of the JBL original mounts. These will be 3/8" acrylic and I can do colors. Cost on these should be fairly reasonable.

http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_108_Jul_24_16_24.jpg
http://www.audioheritage.org/photopost/data//500/medium/ScreenHunter_109_Jul_24_16_25.jpg

[Doctor_Electron]

In accordance with the theory, the plates have to be less than 1/2 wavelengh spacing. I used 0.35", similar to JBL, that takes it over 19kHz..., higher than the 075 can go.

For the size, I used the HL-91 lens dimensions, but scaled them to the the diameter of the tweeter rather than the horn throat.

OK, the HL-91 or a flat-front biradial or a CD horn are the acoustic "transformers" to match, within physical constraints, (horn diameter and length) the diaphram's acoustical impedance with the air mass of the listening area.

For example, excluding the crossover network, the mid-range subsystem of the JBL 4350 Studio Monitor :

Midrange Driver: 2440 2" Compression Driver

Midrange Horn: 2311 2" Short Exponential Horn

Acoustic Lens: 2308 Slant Plate

Point being, in the midrange subsystem cited above, the 2440 compression driver "needs" the 2311 short exponential horn for impedance matching, and "needs" the 2308 slant-plate lens for impedance matching and to define the horizontal and vertical pattern characteristics.

But the 2402 and 2405 ring radiators are designed and manufactured with their acoustic impedance matching and pattern control built in, by way of their throat and phasing element geometries.

My question is, what will be the effects on the horizontal and vertical patterns due to the interaction of their intrinsic elements, and the slant plates? A lens is a lens. Something(s) will change. I know it can be worked out mathematically
and I wish I had those skills but do not.

How else could one predict the outcome? I think your RTA equipment will tell the tale. Ultimately, how will it sound ?

Regards, -D_E-

[toddalin]

Ultimately, the bean counters win out.

If the slant plates were truely "engineered" to the individual horn/driver combination, one would expect that the plates for the HL-91, 92, and 93 could all be optimized to that combination..., but they're not. Furthermore, each plate measures 10" across x 3" deep. Do you think that these values are based in "audio physics," or the ability to make them in production at some cost?

Similarly, the big oval horn came without a lens (Paragon) an BIG slant plate, like Keith Emerson used, a wavy slant plate (Hartsfield), and a midsized slant plate (maybe more?). If "one design" is superior for that horn, why bother with the others (maybe different throw for different venue?) BTW, the wavy plates were a nightmare, and I can't tell you how many were tossed out at VOX because of bends and dents.

Without the slant plate, the HL 91, 92, and 93 will have a circular dispersion pattern (like a ring radiator). I don't know how many degrees of coverage you get, and I've never seen a published number. I would expect the lens in front of a ring radiator would have a similar effect. We'll see.

[Odd]

If one wants to read up on the subject it is much and find here;

jbl acoustic lenses (http://www.lansingheritage.org/html/jbl/reference/technical/lens.htm)

and more (https://scholar.google.no/scholar?q=jbl+acoustic+lenses&hl=no&as_sdt=0&as_vis=1&oi=scholart&sa=X&ved=0ahUKEwjWx821oI_OAhWEIJoKHZwNAJcQgQMIHDAA)

[toddalin]

I was able to get on the laser today to try to make some parts. Between the four programs used in this, there was some rescaling, but I'm getting it figured out.

The stand.

I need to move the holes out about half a millimeter and open them up a bit more. Also, I'll redo the top angles just a bit.

http://www.audioheritage.org/photopost/data//500/medium/Laser2_002.JPG

The drawing file for the feet did not convert properly. The picture was not dead on center when the draweing file was produced so this displayed additional (background) lines in the final file that also cut and the foot fell apart from the extra cuts. I'll get it next time.

Oh, and the image on the left could look nice on there. Nah, I couldn't do that. ;)

http://www.audioheritage.org/photopost/data//500/medium/Laser2_001.JPG

This shows the slant plate assembly. Again, the sizes did not convert properly. The plates will actually be longer/deeper such that the portion that extends back hugs the outsides of the vertical stands. Also, the "backs" of the diagnol cutouts that hold the plates should be revised to be parallel with the back of the slant plate, rather than at 45 degrees to the back of the plates for a better fit/look.

http://www.audioheritage.org/photopost/data//500/medium/Laser2_004.JPG

[toddalin]

I got on the laser and made some parts today.

It took a few tries to get the flare "just right" (lower plate), but this is now very similar to the factory flare. The 1/8" plates show no sag or the need for spacers.

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Lens_006.JPG

Here you can see it assembled on a tweeter. The uprights will be 3/8" rather than 1/8" and will fill the void space and provide more strength.

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Lens_005.JPG

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Lens_004.JPG

[BMWCCA]

Very nice! It's really coming together.

[toddalin]

Voila!

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Stand_and_Slant_Plate_Assembly_012.JPG

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Stand_and_Slant_Plate_Assembly_001.JPG

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Stand_and_Slant_Plate_Assembly_002.JPG

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Stand_and_Slant_Plate_Assembly_007.JPG

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Stand_and_Slant_Plate_Assembly_008.JPG

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Stand_and_Slant_Plate_Assembly_010.JPG

[BMWCCA]

Very nice! :applaud:

[ivica]

...





Hi toddalin,


Nice work, my congratulations !
But I wonder, how such project would behave relative to the 2405 'slot horn' type "young brother", especially in F/R and off-axis response.

Regards
ivica

[toddalin]

We'll find out. I have some.

[toddalin]

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Slant_Plates_001.JPG

[grumpy]

Interesting look. Why stop at just the mini version? ;)

[audiomagnate]

So the size of the blades has no relation to the wavelengths of the frequencies the driver is emitting?

[grumpy]

If you were referring to my comment, I just meant why not laser beam out some 2308 replacements...

[toddalin]

So the size of the blades has no relation to the wavelengths of the frequencies the driver is emitting?


There is no mention that I recall in the JBL literature on the size of the blades. However, the spacing of the blades is addressed and our spacing is good to 20KHz (1/2 wavelength).

However, if the size of the blades does have a relationship with frequency, than we should be covered there too. The 075 is used from 2400 Hz up while the HL-92 is used down to 800 Hz. Our blades are ~20 percent smaller, but would not be expected to be used until over double the frequency. At double the frequency, the wavelength would be 1/2 as long and the blades would be half the size. But remember that the 075 and LE-85 have about the same top end extension. Also, the 375 used a world of different size blades, all the way from the rather small H-91 size to the ~3 foot across plates used by Keith Emerson..., so again, we should be good.

[toddalin]

Initial impressions with the RTA are that the lens does flatten out the peak and extend the lower range of the tweeter. On axis response seems to be down about 1.5 - 2 dBA overall, with most removed in the area of the peak, and volume actually increased at the lower end (<7KHz) maybe partly because of the blockage, but most probably because the energy is now spread over a wider area. The increase in dB at the lower end could be due to the "loading" of the horn. This may really help with the D130/075 systems.

I need to get some serious on and off-axis measurements and will probably even put the HL-92 lens in front of the tweeter to note what it does differently.

Is there anyone in the Orange County CA area that has the D130/075/N2400 load to "try this on" and offer impressions?

Thanks

[toddalin]

OK, did some on-axis comparisons including RTA pictures. Pink noise and graphic is from the Behringer Ultracurve 2496 using the Behringer ECM8000 microphone at a distance of 1 meter.

The 075 tweeter is totally original (never opened and hardly used back in the day) and works perfectly as designed and is representative of the line. The pink noise is passed through two 3 mfd caps in parallel (actual measured 6.18 mfd), and is representative of the 6 mfd caps used in the JBL N2400, N2500, and N2600 crossovers used with the D130 woofer and 075 ring radiator. The tweeter displays the typical curve inherant to this model. Three shots in rapid succession. Note that even though the crossover point is ~2,500 Hz, there is really nothing below 4KHz relative to the the upper range.

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Pics_001.JPG

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Pics_002.JPG

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Pics_003.JPG
http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Pics_004.JPG

Now we simply slip the slant plate assembly over the tweeter and repeat the process. I did turn up the volume approximately 2 dB to compensate for the on-axis volume diference, but the 075 has so much volume to spare. Note that the curve is much broader and flatter with usable volume all the way down to the crossover point. :applaud:

And this isn't even getting into the broadening of the horizontal plane (beaming). ;)

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Pics_005.JPG
http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Pics_006.JPG
http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Pics_007.JPG
http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Pics_008.JPG

[toddalin]

Further testing indicates that we can reduce that dropout above 4KHz by angling the plates outwards a bit more. Testing also shows that the JBL slant plate placed over the tweeter has similar effect, except that (interestingly) it doesn't provide as much boost between 2.5-4kHz, nor quite as much cut up around 10K. The JBL plates frequency response more closely resembles the tweeters without the plates. Also, the JBL plates are about 1 dBA louder than my plates, perhaps due to bleed through, and, the thinner plates block less of the opening. The dropout above 4KHz is still there, but not quite as much. Angling my plates out a bit brings the the volume to the JBL plates in that region, but retains the benefit of the increased bass and flattened highs.

I also think that perhaps with the JBL plates, the plates are half as thick so more sound actually goes through them, rather than around them, relative to my fatter plates and some of this "direct" path is getting through making the JBL plates a bit louder and more of the natural tweeter-like (hence turning my plates out a bit better simulates this "bleed through").

I've done another set of revised angles to hold the plates in CAD and need to cut them out and see the difference.

[ivica]

Further testing indicates that we can reduce that dropout above 4KHz by angling the plates outwards a bit more. Testing also shows that the JBL slant plate placed over the tweeter has similar effect, except that (interestingly) it doesn't provide as much boost between 2.5-4kHz, nor quite as much cut up around 10K. The JBL plates frequency response more closely resembles the tweeters without the plates. Also, the JBL plates are about 1 dBA louder than my plates, perhaps due to bleed through, and, the thinner plates block less of the opening. The dropout above 4KHz is still there, but not quite as much. Angling my plates out a bit brings the the volume to the JBL plates in that region, but retains the benefit of the increased bass and flattened highs.

I also think that perhaps with the JBL plates, the plates are half as thick so more sound actually goes through them, rather than around them, relative to my fatter plates and some of this "direct" path is getting through making the JBL plates a bit louder and more of the natural tweeter-like (hence turning my plates out a bit better simulates this "bleed through").

I've done another set of revised angles to hold the plates in CAD and need to cut them out and see the difference.

Hi toddalin,
Neglecting the thickness influences to the sound levels and internal reflections, You are aware that changing the plates angle, You are changing the delay of the sound, so You are changing the 'sound lenses' focal characteristics, and their off-axis dispersion...

regards
ivica

[toddalin]

Hi toddalin,
Neglecting the thickness influences to the sound levels and internal reflections, You are aware that changing the plates angle, You are changing the delay of the sound, so You are changing the 'sound lenses' focal characteristics, and their off-axis dispersion...

regards
ivica


Agreed. But I'm only looking at changing a couple degrees and if this provides sonic benefit, so be it. To my ear, frequency response is the primary focus, with such things as dispersion and imaging coming after, and if it can be bettered, so be it.

Also, don't think that JBL had a monopoly on using slant plates placed infront of their speakers. There are actually several manufacturers who put them in front of their tweeters with different shapes and angles.

[ivica]

Agreed. But I'm only looking at changing a couple degrees and if this provides sonic benefit, so be it. To my ear, frequency response is the primary focus, with such things as dispersion and imaging coming after, and if it can be bettered, so be it.

Also, don't think that JBL had a monopoly on using slant plates placed in front of their speakers. There are actually several manufacturers who put them in front of their tweeters with different shapes and angles.


Hi toddalin,

I have to agree with You, that You have to be the only respectable measure of Your taste.
I am only 'talking' about technical issues.
For sure JBL is not the only company using acoustic lenses of different kind.

Regards
ivica

[toddalin]

Today I got a nice pair of 3/8" clear stands cut. 3/8" acrylic is not easy to cut, even with a 50 watt CO2 laser, and it tooks some experimentation to get a nice cut. Then it takes several tries, with minor adjustments to the size of the piece, to account for the melting of the piece in the final product to get a nice tight fit, but not too tight.

I'll get some pics up in the next day or so and will offer these through the "For Sale" forum with pre-order sales through the forum getting a price break..., and as a bonus, if legal, a pair of JBL monogram coasters in 3/8" clear acrylic.

[toddalin]

Pics are up with a special price for JBL Forum members. These came out nice. Check them out in the "Lansing Product Marketplace" section.

Thanks,

Todd

[Ed Zeppeli]

Pics are up with a special price for JBL Forum members. These came out nice. Check them out in the "For Sale" section.

Thanks,

Todd

It's been fun watching their development. I hope you find a few takers.


Cheers,

Warren

[ivica]

Pics are up with a special price for JBL Forum members. These came out nice. Check them out in the "Lansing Product Marketplace" section.

Thanks,

Todd

Hi Todd,
Very nice, indeed, but what about 2405H (Ferrous magnet type, as is has larger diameter and weight).

Regards
Ivica

[toddalin]

Hi Todd,
Very nice, indeed, but what about 2405H (Ferrous magnet type, as is has larger diameter and weight).

Regards
Ivica

That's why the feet have the the contours to accomodate the ferrite magnets. Weight is not a problem. ;)

Today I made up a couple sets of the 1/16" slant plates for testing. Because these are thinner and more prone to flex, I also made some spacer/stiffeners that keep the plates from sagging out of position. I also made a couple different slope angles to represent the angle I used with the 1/8" plates, and one with a bit less downward slope, which showed response improvemements in the 4KHz range with the 1/8" plates.
It's getting there.

[toddalin]

This shows a pair of the slant plate assemblies hot off the laser. Note the protective coating on all pieces to keep them from scratching.

http://www.audioheritage.org/photopost/data//500/medium/Resized_Slant_Plate_Assembly.jpg

"Baby we were born to run." It would seem that the US Postal Service had us in mind when they designed their "If It Fits, It Ships" box. ;)

http://www.audioheritage.org/photopost/data//500/medium/Resized_Shipping_Box.jpg

A bit more testing for the better angle with the 1/16" plates and we should be good to go.

[ivica]

This shows a pair of the slant plate assemblies hot off the laser. Note the protective coating on all pieces to keep them from scratching.



"Baby we were born to run." It would seem that the US Postal Service had us in mind when they designed their "If It Fits, It Ships" box. ;)



A bit more testing for the better angle with the 1/16" plates and we should be good to go.

Hi Tod,

Very nice and profi work. congratulations !

Regards
Ivica

[toddalin]

I assembled a couple sets with the 1/16" plate material. I did one set in the original angle and another set with the angle raised about 4 degrees.
When I put them up next to the JBL plates, I found that my initial angle was about 2 degrees lower than the JBL angle, and the revised angle was about 2 degrees higher. This actually makes a difference in the overall sound, but changing from 1/8" plates to 1/16" plates made more difference.


With the 1/8" plates, the "swish" of pink noise became more of a "swoosh." The JBL plates didn't do this and the "swish" was still distinctly a "swish." The 1/16" plates, especially with the higher angle, left the "swish" a "swish" but added the lower range as the 1/8" plates did, more so than the JBL plates. The lower angle added a bit more in the lower range, but took out a bit more over 4kHz.


I've revised the angle to essentially match that of the JBL plates and will go with that. The overall frequency response improvement way exceeded expectations, and I've not even begun to look at the increase in horizontal dispersion.


http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Slant_Plates_0011.JPG

[ivica]

I assembled a couple sets with the 1/16" plate material. I did one set in the original angle and another set with the angle raised about 4 degrees.
When I put them up next to the JBL plates, I found that my initial angle was about 2 degrees lower than the JBL angle, and the revised angle was about 2 degrees higher. This actually makes a difference in the overall sound, but changing from 1/8" plates to 1/16" plates made more difference.


With the 1/8" plates, the "swish" of pink noise became more of a "swoosh." The JBL plates didn't do this and the "swish" was still distinctly a "swish." The 1/16" plates, especially with the higher angle, left the "swish" a "swish" but added the lower range as the 1/8" plates did, more so than the JBL plates. The lower angle added a bit more in the lower range, but took out a bit more over 4kHz.


I've revised the angle to essentially match that of the JBL plates and will go with that. The overall frequency response improvement way exceeded expectations, and I've not even begun to look at the increase in horizontal dispersion.




Hi Tod,

It would be interesting if You can make dispersion comparison of your lenses relative to the 2308 using "lower" and "higher" angled plates.
Here are JBL data for 2308 horizontal dispersion.

Regards
Ivica

[toddalin]

The higher and lower lens assemblies are not glued in place so measurements with the 1/16" plates and JBL lens have been done vertically (i.e., looking down at the assembly from above). At this point, I won't glue these in place intil the final angle is achieved, and that makes the comparison difficult.

[toddalin]

There is an old expression that goes something like:

"The angle of the dangle,

Times the heat of the beat,

Equals the mass of the bass"

http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Slant_Plates_002.JPG
http://www.audioheritage.org/photopost/data//500/medium/Tweeter_Slant_Plates_003.JPG

[toddalin]

I got the fit of the upright mounts just perfect and cut a bunch of lefts and rights today. While both sides should be identical, the laser "burn in" to the acrylic is a bit different than the "burn out." So if I make lefts and rights, they will be mirror images and the user can put whatever side (i.e., burn in or burn out) toward the inside/outside on both sides rather than have a burn in showing on one side and a burn out on the other. I do this with all parts that are in pairs. Also, I need to make the slots that hold the plates considerably smaller than the width of the plates, or there is way too much play in the fit, again due to the local melting of the acrylic. We work with it and we learn the limitations. http://www.audiokarma.org/forums/styles/default/xenforo/clear.png


Another aspect to deal with is the width of the cut relative to the thickness of the piece. A thinner piece cuts faster and as a result, makes a thinner hole/slot due to less melting of the surrounding acrylic. So while the vertical supports came out perfect, the fit of the thinner stabilizers is a bit tighter than I would like around the plates. While no glue is necessary for these as is, we don't need people breaking pieces trying to get them on or scratching up their slant plates. This is the last aspect to a completed product.


I have the laser reserved on on Friday and will have a set ready for listening shortly there after.

[Doctor_Electron]

If one wants to read up on the subject it is much and find here;

jbl acoustic lenses (http://www.lansingheritage.org/html/jbl/reference/technical/lens.htm)

and more (https://scholar.google.no/scholar?q=jbl+acoustic+lenses&hl=no&as_sdt=0&as_vis=1&oi=scholart&sa=X&ved=0ahUKEwjWx821oI_OAhWEIJoKHZwNAJcQgQMIHDAA)

Quite amazing that sound waves can behave as if they were comprised of photons. Is this true of all waves in motion, regardless of their frequency?

Regards, -D_E-

[Doctor_Electron]

Quote: " There is an old expression that goes something like:

"The angle of the dangle,

Times the heat of the beat,

Equals the mass of the bass"

- - - - - - - - - - - - - - - - - - - - - -

You could also factor in the Cube of the Tube...

[daveschott]

Quite amazing that sound waves can behave as if they were comprised of photons.


I think the analogy stops with sound waves sharing some characteristics with light waves. There is no 'carrier force' for sound!

[ivica]

I think the analogy stops with sound waves sharing some characteristics with light waves. There is no 'carrier force' for sound!

Hi,

Traveling through media where there is lower speed (as light), or passing longer path, in either situations would introduce a kind of delay so the wave front would 'bend', and that is a function of the lenses. Here (2308 lenses, or others similar) have 'hyperbolic' shape ("V") so it would behave as 'Plano concave' lens. Out of center sound path is longer than near the center so forming desired delay, and introducing sound wave front bend (curved).

regards
ivica

[daveschott]

Yep, wave behavior. It was a tongue-in cheek comment as introducing photons to a wave discussion is a stretch in this case. After all, photons are a particle...or are they? :)

[toddalin]

OMG!

In listening tests, these have surpassed expectations!

Listening to "Money for Nothing" it totally takes that "in your face harshness/fatigue" away from Mark Knofler's guitar. The results comparing the 2405 in the cabinet with the 075/slant plate on the cabinet (A/B/X with AlNiCo 2235/2420 on long horn, crossover at 800/7,500 Hz) is that the 075 now sounds like a "just a bit bright" 077, maybe with even better articulation. The tweeter is now far more listenable.

Further listening, and now the 2405 sounds a bit "veiled" next to the 075/lens combination. Voice is now a bit more natural (preferable) with 075/lens than the 2405.

http://www.audioheritage.org/photopost/data//500/medium/Resized1.jpg

[toddalin]

See the Marketplace for a video of the slant plates in action. :applaud:

[toddalin]

OMG! Check out the video in the Marketplace for use with the slant plate assembly and the N2400 crossover assembly. As I said, expectations have way been exceeded!

[Doctor_Electron]

After all, photons are a particle...or are they? :)

I think so.

But seriously, the thought of photonesque behavior occurred to me after reading the original acoustic lens article. At the end the author mentioned the possibility of using plate lenses with cameras.

I have a room with venetian blinds which form a perfect but inverted image of the back yard outside, on the opposite wall. Is this similar to the function of a pinhole lens, or an interference pattern-induced product with physics similar to those of a slant-plate lens?

BTW, is the Pauli exclusion principle still accepted in physics? It was 42 years ago when I attended college.

Particle board has seen widespread use in loudspeaker manufacturing. Wave board not so much.

Regards, -D_E-

[toddalin]

I took a pair of lenses down to San Clemente to listen with an AudioKarma member who had an interest. In the dining room, he has the D130/075/N2400 load in rather small/low cabinets. Unforetunately, the 075 is recessed up in the corner so the lens would not fit in the space. We put the baffleboard/075 on top and the improvement was there, and was easily demonstable with the RTA, but this is far from an ideal listening situation.

But, in the bedroom he has JBL cabinets (~4 cu ft) with LE15s with later foam edges, LE85, and 075s (with horseshoe mount on outside). Even with the horseshoe mounts on the outside the lens slipped right on with a nice friction fit.

Within the first minute of the first song (Stones "Monkey Man") he said,"Todd I think you have something here." I asked if I could quote him and he said "Oh Yes!" He said that he was able to hear Charlie Watts drums like never before. (Its that uncorrected ~9KHz hole/step followed by the ~10KHz spike that takes away from the drums and intelligibility.)

He had to have a set before the song ended.

Even if these things did nothing for the distribution pattern, if you have 075/2402s, the modifications to the frequency response alone are well worth the price of admission. It's hard to believe that JBL never came up with these. ;)

[toddalin]

Check out the Marketplace for new videos, for on- and off-axis RTA measurements demonstrating the slant plates. Unbelievable!