Lowering the crossover point.

[aditya]

This is good work .
The second reading seems to be nearer.
When are you going to measure up the 'C's ?

[VolvoHeretic]

Um, that would be me. I would build a couple of wood rings and epoxy them to the inside of the cut end of the barrel halves so that they don't fall apart when you start shaking them. I'ts going to take a lot of glue to hold them together, although, if they work out nicely, I would fiberglass up the insides into one strong solid mass.

Edit: I mean a hollow ring at the open end and a solid one at the closed end where you are going to cut in the speaker to hold the multi-piece lid together (I think that it is multi piece) and then cut out the speaker hole out through both the lid and the reinforcing ring. Kind of hard to describe without pictures.

[VolvoHeretic]

Glad I made sence CD. The fiberglass would be for the inside. If it where me, I would have the outside sandblasted, wood and metal, then stain if so inclined and then clear coat for a nice rustic weathered look. Brushed or 36 grit coarse sanded with the wood grain would look better, but I don't know how you could get it uniformly even with the metal rings in place.

[GM]

Finally I found one page...........

Attachment 1482

For some unknown reason, these specs don't quite jive, i.e. Sd, Cms, Mmd, BL, Re won't calculate the listed Fs, Vas, Qts, though 'in the ballpark' for general comparison and basic cab alignments.

GM

[GM]

Cut a hole in the small end.........

Be sure and offset the driver some golden or acoustic ratio as a circular baffle has the highest amplitude eigenmodes of any shape.

GM

[GM]

Okay, Measured up a 604C today.

Don't see the Vas for the Es. The C has stiffened up a bit as Fs is high and Vas low, which I imagine is due to the spider, though sometimes the surround goop can too. Acetone will loosen the latter up, but unless GPA knows a trick or two, might be SOL on the spider.

GM

[VolvoHeretic]

GM, what's with the "Golden Rule"? Is the inside of my speaker doing the same thing as the inside of my listening room with nulls, nodes, voids, and/or standing waves (and evidently eigenmodes) being created by the sound waves bouncing back and forth off of the top/bottom, side/side and front/back panels and you don't want the speaker positioned in the dead center of the front baffle and having any frequencies canceled out?

[GM]

Correct, the cab is a miniature building both inside and outside, so adheres to the same acoustical physics. Note that peaks/nulls can't be cancelled out, only averaged out by shifting them to many more smaller amplitude ones that will in turn decay away more rapidly due to being lower in energy.

Inside the cab can be damped of course, but always best to keep it to a minimum IME, so while using an offset is primarily for the exterior, you 'kill two birds with one stone'.

Making as many different path-lengths to the various boundaries as practical does this. A circle with a sound source dead center will radiate in a virtually infinite number of peaks/nulls all at the same frequencies, so with a large baffle this can be quite audible as they comb filter with the driver's output.

GM

[aditya]

For some unknown reason, these specs don't quite jive, i.e. Sd, Cms, Mmd, BL, Re won't calculate the listed Fs, Vas, Qts, though 'in the ballpark' for general comparison and basic cab alignments.

GM

Yes GM, the BL data particularly seems to be in what unit, W/M ? Re seems to be the Zmin at around 11 ohms, at around 400 HZ, and not the usual Rdc. Cms, and piston dia seems to be ok. I accepted Qts at the specified value of .264, and after playing around got the BL at 21.48 N/A. Vas, Le and Fs stayed the same. 'n' is also pretty close.

Actually these readings were taken at around the same time when Thiele's papers were published in the AES journals, and I am sure but not able to recollect now, that these measurements were taken either by Thiele himself or somebody pretty well known in the industry. I am still searching for the source where I had found it.

[aditya]

Okay figured out the VAS problem, It helps if you put 12.75 in the piston dia instead of 3in...I thought they meant VC dia. Turns out there's a big difference.

Put the piston dia at 12.58 inch. And repeat the Vas measurements with different weights, and note the results. Choose weights to shift Fs between 15% to 40%, and note the changes in the readings. It takes some effort to get the correct data for Vas.

Also take a 'in-box' impedance reading. This will help.