GPA 604-8H-III initial impressions...

[Todd W. White]

The reverse was the problem Altec had with the later K-series: the magnets were changed by EV, and, thus, output in the midband was increased.

As a result, the later K's seemed to lack LF performance, when it hadn't really changed - it only sounded like they didn't have any bass in comparison to the midband-heavy problem caused by the magnetic structure being out of balance.

Once the problem was discovered and solved by Jerry Hubbard, Bill implemented the correction in the 604-8H-II, and, of course, the III's.

I'm not sure why some folks are hearing "shoutiness" from the midband in either the 8H-II's or III's - I put an 8H-II in a Stonehenge V box side-by-side with a freshly rebuilt 604E with Hubbard-designed crossovers in the same design box, and the E sounded GREAT.

Until I switched over to the 604-8H-II.

Though the E sounded really good, it's midband was harsh and fatiguing to listen to over the 8H-II. Doing A-B listening, I found myself unable to leave the E on after a while. The 8H-II, on the other hand, I could listen to for days on end...which I did. Left it playing in the church auditorium for days, often spending hours just sitting there listening to different music through it.

Incredible!

My personal guess still goes back to this thing of our ears being prejudicial - we get SO used to hearing things they way they ARE, that we get to thinking that's the way they are SUPPOSED to be, even if their not.

This is why I listen to a lot of live-recordings when auditioning loudspeakers - so I don't hear someone else's idea of what the music was supposed to sound like: I just hear what went on at the concert.

I'm reminded of what happened one time when Don and Carolyn were setting up a new installed Acousta-Voice system in a large performing arts center.

Seems someone wandered in (I think it was my old friend Bob Thurmond), and, listening to the music being played back, was aghast at how thin, unnatural, and just awful the Altec system was sounding. This guy said he thought to himself something like, "Well, if THIS is what Altec is trying to peddle to us, no one's going to buy it!"

Then Don shouted, "OK Carolyn - turn on the Acousta-Voicing!"

All of the sudden, he recounts, the sound becsme full, and rich, and had a naturalness he'd never heard before!

Later, he said, he never realized how used to the older sound he'd become - and it took a while to get used to hearing what it was supposed to sound.

Perhaps this is what's going on, too, as I have listened to the 8H-II's using Jerry's crossover and love them.

[gortnipper]

Here are some pics...

[amandarae]

Very nice!! Congratulations! I too have the JEL OB's (604-8G's).

I dunno if it is the room, my amp, the XO or my sources but I have no complaints with bass. This is coming from an Orion Plus user for years (2 x 10" Peerless woofer in dipole open baffle H frame config per speaker resulting to a very potent bass response).


Again, nice stuff you have there!

regards,

Abe

[gortnipper]

Thanks Abe. You have a custom xo dont you?

As a guy pointed me on the AudioCircle OB forum, Jerry's xo is designed for a ported box, and that the GPAs "on a baffle that size will have a rising response, not a nearly flat one as it would in a box. So the crossover must be adjusted to match, or your tonal balance will be all wrong. On a baffle that size you will need a big iron core inductor, not that cute little aircore in the photo. Just a guess, you'll need to be at 24mH or more. And that means the 15s output will be pulled way down at the x-over point. So you will have to attenuate the horn even more - maybe as much as 10dB more."

Not knowing much about xo design, it intuitively makes some sense to me what he is saying, along with what Todd notes above about them sounding great in a Stonehenge cab.

David

[bfish]

As you already noted, your room is "hot" too. Reflected MF energy is additive, and the vocal band is exactly what comes off the back of the cone to be reflected (and added) back onto the room (the HF is sealed, and the LF cancels).

This is exactly (one of) my (theoretical) objections to Duplexes in Open Baffles, there's just too many things to "fix". Reviewing a driver that was designed and intended for a proper box in an OB app is unfair. Kinda like reviewing an electric hybrid on a racetrack... that wasn't what it was meant to do.

[GM]

Yeah, with OB you need an acoustic blanket over the rear of such drivers to attenuate the XO BW coming off the rear of the LF driver to preserve its co-axial (duplex) point source imaging/sound-staging.

GM

[amandarae]

Hello,

Sorry, but I have to go OT to respond.

bfish and GM know a lot more than I do with regards to the Altec's for sure and I will never question their expertise on this field. Having said that, I wish I can have you , both of them, or anyone using the 604's in OB to listen what my system can do regarding bass and I can have my Orion Plus side by side with the Altec's if necessary.

I am not saying that my set up is something unusual but I am not blowing smoke up your arses either

Maybe, and just maybe, this have some contributions to it

The top is the JM Xo, time aligned and such. The bottom is from a friend of mine. You can see the speaker wires and decide for yourself which one is being use most of the time.




Here is one of the amps I use. It is a 76/6SN7 cap coupled to a 2A3 operating at around 17-18 watts, SE using AC heaters and delivering a whopping 4.5 watts of pure SET magic It's, by all means, a Humprey of course! ( I meant hum-free!)

Here is the preamp


Using 6SL7 for phono and 76/6SN7 for linestage.

Here is my Orion Plus speakers

this picture was taken before I acquire the Altec's.


Here is a link to Youtube. YouTube - S.E.T. ATTACK and this one YouTube - Garrard 301 and SET and this one YouTube - Garrard 301 and Schick 12

Granted that the files are compress, but you can at least here the bass and have a basis of camparing if mine is really "less" compared to what you guys like.


I do not discount the possibility that our definition of "bass" in terms of quality and quantity differs from one another. If that is the case, then I will graciously admit that my requirements are not on par to what you guys have as a standard. To each his own.

regards,

Abe

[gortnipper]

Originally posted by bfish:
This is exactly (one of) my (theoretical) objections to Duplexes in Open Baffles, there's just too many things to "fix". Reviewing a driver that was designed and intended for a proper box in an OB app is unfair.

<font size="2" face="Verdana, Helvetica, sans-serif">I was semi-aware of the limitations of the OBs (in general terms), and it was never my intent to "fix" or properly review them for this application. It is just that they only took me one piece of ply and eight hours to make end to end to get them up and running, and I figured I would learn something along the way. Which I am, with all of your help. Muchos Gracias for that.

David

[bfish]

I understand completely David. My posts were meant to lend objectivity, not to be critical.

[gortnipper]

Yes, this is how I read it, so no worries there.