Broke down. Got a duplex.

[Alien_Shore]

WT2 is more reliable than WT3/DATS ( different maker with a different way of measuring ) .
REW has a TS parameter measurement area ( you need to wire-up a small box ) that uses the same method as WT3 .
Personally, I wouldn't bother GPA with this type of thing until you've gotten similar measurements from at least one other measuring program.

Thanks Earl. I wanted to talk to Bill again simply because when I spoke with him just prior to GPA shipping the speaker back to me, he indicated that they used 16 ohm parts for the re-cone and new 'phram. I have been looking at some of these time-aligned crossover designs for the 604, so I'll just need to adjust for 8 ohm voice coils.

- Every once in a while it is worth the diy hobbyists time to check ( recalibrate ) the validity of ones measurements by using another method ( really , it's simply part of the scientific method ).
- For TS parameters ( when checking these "all-in-one" devices ) one can use the old standby method outlined here !
- I believe that verifying Re, Fs & Qts ( Qms, Qes ) is enough to know where ones device stands .

Totally agree, and while I have no reason to doubt the accuracy of DATs, I will perform a validation/calibration on one of my drivers to be sure.

[Alien_Shore]

Been out of town the last week or so, but will try to get back on track this week.
While the electrical investigations continue, I'm trying to move the cabinet research forward as well.

GM often relays the opinion of the MLTL being the best design for the 604 for home listening.

There's the
GM MLTL
Bill's Corner cabinets, and
6moons

upon a quick search...

[gortnipper]

Hey Mike - I built these cabs that GM sim'd for Jay Fisher - which is a variant of the 6moons build and am well pleased with them - Yet again, another 604 MLTL...

I ended up pulling all the stuffing for a raw 1" BB ply cab, putting a piece of ply painted to match the carpet under them (essential, since they are bottom-firing) and with 3R on the woofer xo, and am very well pleased with them. They sound very nice with 3 watts!

In retrospect, the only thing I would have done different is make them wider and less deep on the cross-section, as they are a bit too 3:2 and could use a bit more baffle and would sit a bit more nicely in the room.

[Alien_Shore]

Thanks 'nipper.
Did you do plans for your build? In retrospect, what would you change? Would a forward-firing port be better (e.g., to avoid the need for the reflective plywood on your floor)? Do you have a schematic for the crossover you used?

[gortnipper]

GM did the original sims, and I got plans from Jay, which I slightly modified for size. If you want, send me a PM with your email and I can send you an info pack I have sent a few others on the build.

A couple good related threads:
Ping GM!
GPA 604 and Hiraga

Like I said, I would make them slightly wider across the front and less deep (keeping the same x-sectional area). I would also offset the drivers L/R in the baffle, since I neglected to do that. I would definitely not do the build like the 6Moons one - where they used the narrow edge of the box.

If I did it again, I might make some of the changes discussed in this thread with GM, Scooter, and RC Daniel:
GPA 604-8H-III Build - Sneak Peak

I dont have a schematic for the xo, but it is described by the builder, Rick Craig, as thus:

"I didn't really pay any attention to the stock crossover or specifications when creating the new design. The drivers were tested for frequency response and impedance and then everything was imported into our software optimization program.

This combination presents a difficult challenge in that there's very little overlap of the driver response curves due to the fairly small horn and large diameter woofer. The woofer has a significant breakup in the 1.8K-3K area The tweeter also has resonance issues in the 1-2K area. The shaping of the filters around the crossover point is critical and choosing the place to cross isn't easy.

I started first with a lower parts count crossover and experimented with different topologies. The objectives were to maintain good phase response in the crossover region, minimize the resonance and frequency response issues, maximize horizontal dispersion coverage, and provide plenty of headroom to keep the horn distortion low.

The crossover's acoustic slope target around the crossover point was 24db/octave. There are different ways to achieve this and a third order electrical filter was implemented for the tweeter. The woofer filter is a first order combined with a parallel resonance trap. Both are far from textbook values and designed to work in tandem with the driver responses to achieve the desired acoustical transfer function.

I also added a conjugate filter which creates a smooth system impedance. This is important for tube amps, in particular SET designs which typically have high output impedances. The less reactive load will provide better results and insures compatibility with virtually any tube amp."

The full post is here: GPA/Altec 604 Series 3 Crossover

As I have said elsewhere, this xo is far superior to the GPA one (which I also have) and Rick's build is competitively priced to the GPA xo.

But you have a 604E, so this may not be so relevant. Have you looked at this? http://home.earthlink.net/~jmarkwart/id22.html

[donaldpatten]

Mike

Calibration of your test equipment is a great idea.
The impedance curves can be verified by testing a resistor in place of the speaker; try an 8 or 10 ohm .
This should produce a flat line at that value.

Don

[Alien_Shore]

OK, performed an impedance curve using a calibrated Vac test rig, and it tests out very close to the DATs test...



I didn't test 1 Hz intervals so the peak at Fs isn't as high with this rig, but this confirms that DATS is working well!

[donaldpatten]

Mike
What is the freq of the peak on the horn T/S curve? The blue line
Thank you
Don

[Alien_Shore]

Here's the T/S measurements and free air impedance sweep on the HF horn:



If you can't make it out from the pic:
Re = 6.5471 Ohms
Fs = 1832 Hz
Qts = 1.412
Qes = 2.217
Qms = 3.886
Le = 0.122 mH

At Fs, impedance is right at 18 Ohms.
At 1500 Hz, impedance is 13.21 Ohms.

[cradeldorf]

Hows the project coming?