Raising the While Flag on 604 Project

[GM]

I was going to mention that about the stuffing. One can change the amount to change the finger rap on the cone from a thump to more of a whack....you have to try it.

A port firing down into the floor, especially hardwod makes no sense to me.. In a box that large, firing forward makes more sense.

Right, one way to ~critically damp the cab by ear.

Why? Acoustically there's no difference until the down firing port is close enough to the floor or other boundary to mass load it to a lower Fb except when there's padded carpet underneath, then it absorbs any out of BW noise that it may be pumping out.

GM

[mah]

This GPA 604 project had to deal with 'shoutiness'. It might be helpful.

6moons audio reviews: Steph?n's Altec 604 Dream Speaker

Cheers, Marshall.

[Seadweller]

This GPA 604 project had to deal with 'shoutiness'. It might be helpful.

Thanks mah...I actually traded several e-mail's with Stephaen, and he was kind enough to give me some advice, and send me the schematic of the 4th order crossover he currently uses...I had it built and tried it, but the sound is very dark and subdued...In all fairness, he warned me this would be the case...

[Seadweller]

You're welcome!

Which can be caused by a leaky cab rolling off all the bass.........

GM

The only possible leaks would be at the removable XO panel on the back of the speaker, or the driver itself...I do not have a gasket behind the driver, although I've seen cork gasket sets on eBay...

The driver and XO panel fit extremely tight to the cabinet, and the XO panel is actually secured by 10 screws...Could a very minute amount of leakage in these areas impact bass response to this degree?

[GM]

Are you saying there's no sealant between the driver or XO and mounting surface? If so, I'd be very surprised if there's no leaks and based on your various observations WRT vent lengths, various XO woes, etc., it would explain them all except maybe some portion of the high intensity beaming which can be dealt with by adding a foam insert, but that comes under the heading of fine tuning.

AFA how big a leak it takes to basically delete the vast majority of box loading it's as little as air leakage around the mounting bolts and T-nut threads, but an air leak around the driver ~completely negates any box loading.

GM

[Art J.]

Hi gang. In my absence, I had to catch up on 11 pages of this subject.
The last time I saw a project go this bad, the problem ended up being the CD player.
Didn't you say it's 20 years old? Is it your only source?
I've heard them shout when they fall out of specs.

[Seadweller]

Hi gang. In my absence, I had to catch up on 11 pages of this subject.
The last time I saw a project go this bad, the problem ended up being the CD player.
Didn't you say it's 20 years old? Is it your only source?
I've heard them shout when they fall out of specs.

Funny you mention this, as it is my only source...This was on my list of suspects, but quite frankly, I never tried another source, because every time I inquired, folks said that it would not be possible for the CD player, being digital, to impart its own sound...

[Seadweller]

Are you saying there's no sealant between the driver or XO and mounting surface?

AFA how big a leak it takes to basically delete the vast majority of box loading it's as little as air leakage around the mounting bolts and T-nut threads, but an air leak around the driver ~completely negates any box loading.

GM

Thanks GM....No, there is no sealant around the XO panel or the driver....The XO panel and cabinet mating surface were milled so they basically seal, but I guess without a gasket of some sort, it would not be completely air-tight....I'm sure there's leakage around the driver as well, but it never occured to me that such a minimal amount of leakage could impact the loading of the cabinet to this degree, particularly with such a big cabinet, and large driver...

If a small amount of leakage can impact things so drastically, I think my initial steps at this point will be to install a gasket in the XO panel, and a gasket behind the driver to make sure the cabinet is sound...Then I'll get an amplifier and different CD player to rule out the obvious...

From there, I guess it's back to the XO...

EDIT: I may have to correct myself, but I'm on my way to the airport, so I'll have to validate this weekend...It's been a while since I installed the drivers, but something tells me that GPA shipped a neoprene-type gasket set with them...I'll pull the driver and see if they're installed...

[Todd W. White]

OK - time to jump in again.

1. Digital electronics, especially older digital electronics, does, indeed, impart it's own "contribution" to the sound of the audio passing through it. It just can't help it - unlike tube-type systems, which respond in what I call a "harmonic" manner (even-order harmonics), digital audio has more odd-order harmonics in it which gets added into the mix and does (believe me) sound harsh.

This is why I recommended originally getting a recording of music that you are familiar with that was recorded LIVE - not mixed down in a studio (many of them are all-digital now) - and see if the problem goes away. While I was thinking about the recording itself, it could be your problem lies in the playback equipment, at least in part.

2. As far as the GPA 604's go, I have the following to say:

A. They are excellent drivers that measure extremely well. I have seen the TEF measurements and they are amazing - the best of any of the 604's ever made. The "shoutiness" that some folks get with them would show up in the TEF response curves and waterfall plots if this problem was inherent to the speakers themselves. It's just not there. Period.

B. The stock crossover from GPA was developed by Jerry Hubbard, who was HEad of Acoustic Research at Altec for many years. His designs are straightforward, simple, and effective. He does extensive real-time testing to assure they are correct. That said, one also has to keep in mind that his design was done with these products installed in a correctly designed and built enclosure - as several have pointed out here in this discussion, when the enclosure leaks, is the wrong size, isn't properly damped, is damped too much, if the crossover is changed, etc., all these things can alter the sound coming out of the speaker, and the 604 will pain the audio picture of those changes, "warts and all."

C. With regard to the man who was disappointed in the GPA 604's at the Colorado audio show - having not attended (I will this year), I can't comment on the system that was used there. That said, I can tell you that when I demonstrated the 604-8H-II's in Stonehenge V-type boxes at the Great Plains Audio Fest in Tulsa a few years ago, using the stock crossovers, no one heard what you're talking about or complained of listener fatigue. The only person who did complain was Earl Geddes, who was yelling at me about the size of the horn being too small, but he was mad because his new, amoeba-shaped speaker was getting bested by the 604's, according to the comments of the attendees.

I was using a newer CD player and a vintage Altec 714A Receiaver (30-watts) from 1964 to power them - no eq, no L-pads. Just straight. We also auditioned some tube amps and other recordings, all of which, except one of the recordings, were well received.

D. My suggestion is:

1) Build one Stonehenge V-type enclosure with proper bracing, properly sealed, properly tuned, and properly damped. If you need drawings, dimensions, etc., I have the hand-drawn ones I made for my cabinet man to use when he built them for me. They're not pretty, but the design works.

2) Install the stock GPA crossover & connect the speaker to the amplifier.

3) Set your amplifier eq settings (aka tone controls), if it has any, to flat.

4) Find a live recording (we used to call it direct-to-disc) of music that you are familiar with, or, perhaps, totally unfamiliar with. Maybe more than one - some with vocals, some without.

5) Borrow a high-end playback unit from someone, if need be, for playback. Do not use the one you've been using. The newer digital units have been "tamed" somewhat.

6). Take the speaker outside and listen to it as it sits on the grass with no reflective surface nearby.

7) Listen to it. See what happens. Make specific notes as to what you hear on what recordings.

8) Now take it inside and repeat #7.

Let us know what happens.

Ultimately, my guess is you'll find that you've been chasing rabbits - the real problem is, I think, that you've been trying to treat symptoms that have been caused by symptoms, rather than the real problem, adding "fix" upon "fix" upon "fix", and muddying the waters even further.

As Chief Engineer Montgomery Scott, after assisting Admiral Kirk In StarTrek III in stealing the Enterprise from Spacedock and the Excelsior was unable to pursue, when handing the computer chips from the Exclesior's TransWarp Drive computer to Dr. McCoy, he said, "The more they overcheck the plumbing, the easier it is to stop up the drain."

These speakers are excellent performers - the problem is not in them. It is elsewhere.

[nullspace]

A. They are excellent drivers that measure extremely well. I have seen the TEF measurements and they are amazing - the best of any of the 604's ever made. The "shoutiness" that some folks get with them would show up in the TEF response curves and waterfall plots if this problem was inherent to the speakers themselves. It's just not there. Period.

Hi Todd,

Could you share the off-axis measurements? The on-axis TEF measurements I've seen are indeed impressive, but "shoutiness" is sometimes apparent only when looking at the power response/ range of on- and off-axis measurements.

C. With regard to the man who was disappointed in the GPA 604's at the Colorado audio show - having not attended (I will this year), I can't comment on the system that was used there. That said, I can tell you that when I demonstrated the 604-8H-II's in Stonehenge V-type boxes at the Great Plains Audio Fest in Tulsa a few years ago, using the stock crossovers, no one heard what you're talking about or complained of listener fatigue.

I heard what I heard. And, I'll suggest that my impressions seem to echo some of the feedback received at Tulsa, as seen here: PIC'S OF ICONIC'S DEMO ROOM @ GREAT PLAINS AUDIOFEST IN TULSA! and further discussed by GM and joyspring later in the thread.

I have no doubt that the 604s are excellent performers, and that I am in the miniscule minority that is perhaps hyper-sensitive to these kinds of issues. But that doesn't mean I'm nuts, either.

My apolgies for taking the thread so far afield; I'll restrain any future comments to only address Seadweller's journey.

Regards,
John