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

[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"

[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.


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

and more

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.

[toddalin]

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

[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!