Raising the While Flag on 604 Project

**SD-50** · February 18th, 2010, 10:39 PM

Originally Posted by Todd W. White

The 604K's, almost without exception, have the wrong magnet on them - after EV bought Altec, they forced them to consolidate on some standard magnets EV was already using, and they made Altec use the DH-1A HF driver magnet, if memory serves, for the 604 and the 515.

The result in the 604-8K was the midband got too much energy. It wasn't that the bass was suffering - it was still there, just like always - but the midband was getting too much magnetic energy. Jerry Hubbard figured this out and fixed it - the GPA 604's don't have this problem.

I have a pair of 604-8ks waiting for cabs and this is the first I've heard of this problem. Is there a solution to correcting the midband by replacing, or modifying the stock XO?
Cheers

**Tom Brennan** · February 19th, 2010, 03:16 AM

Maybe the speakers just aren't for you, especially if you're fighting their basic nature so to speak.

**vuki** · February 19th, 2010, 03:28 AM

In my expirience problem with the bass is in the lowpass part of the crossover. Due to the rising response of the 604's bass/midrange driver, low pass crossover should be done so that it compensates it otherwise 604 speaker would have "no bass" and "shouty" sound.
Seadweller: try it with the crossover I posted

**Todd W. White** · February 19th, 2010, 05:09 AM

SD-50 -

The only real solution I ever had work for me was to eq the things way more than I'd like - I'm a "Cut Only" type guy and don't liek to use much of that, even (I probably get that from Don Davis and the AcoustaVoicing training), so I've used 1/3-octave units on it, as well as parametric's on them (used to own the Altec relabeled Dynacord parametric - it was NICE!). The parametric's were really nice, because I could dial in the correction, but, that said, you can do it with a 1/3-octave equalizer, especially if the filter skirts are constant-q, rather than variable-q. I like variable-q for live-sound eq, but not for this application.

The other solution is a custom crossover with eq built into it.

We used to have all kinds of problems with the acoustical consultants not allowing 604's because "they don't have any bass" back in the "K" years, when, in reality, as we later found out, the bass WAS there, but it was being overwhelmed/covered up by the midband...kind of like adding two dozen trumpets to your concert band, but not increasing the number of low brass players (tuba, baritone, trombone) to compensate and balance them out - the group will sound "shouty" and "harsh", not because the bass isn't there, but because the other guys in the trumpet section are playing TOO LOUD.

Does that make sense?

Oh - and thanks to all the other fellows who echoed my advice to take them outside: I remember years ago talking with my friend the late Dr. Paul Veneklasen about his experiences in measuring the Altec speaker systems out at the RKO Ranch in the late '40's: he said they had to get the speakers way up off of the ground to minimize LF reflections, but they still had to EQ the curve to compensate for them.

That said - even though he might get some bass boost from the ground reflections, he's still got a way better chance to hear what they're really doing without the interference one gets from the reverberant field...

**SD-50** · February 19th, 2010, 04:34 PM

Thanks Todd.
Gustavo Fitzwilliam

**Seadweller** · February 19th, 2010, 07:39 PM

Originally Posted by vuki

In my expirience problem with the bass is in the lowpass part of the crossover. Due to the rising response of the 604's bass/midrange driver, low pass crossover should be done so that it compensates it otherwise 604 speaker would have "no bass" and "shouty" sound.
Seadweller: try it with the crossover I posted

I had a suspicion that the "shoutiness" was coming primarily from the woofer, and not the horn...I disconnected the horn and confirmed this, but it's hard to tell just how much the horn itself is contributing.

Is it possible to install an L-Pad in a crossover that would lower only that range of frequencies? I have to imagine that a 16" driver would have a difficult time with midrange frequencies. Doesn't a driver of this size start to "beam" at higher frequencies? Is it possible to drop the level with some sort of notch filter?

**Seadweller** · February 19th, 2010, 07:41 PM

Originally Posted by Panomaniac

Yes, with an active crossover you will need 4 channels of amplification for your speakers.
The amp to run the horns does not need much power, a watt or 2 will do, but more is of course OK.

Thanks...So, does the active crossover allow you not only to set the XO point and slopes, but also adjust specific frequencies, similar to an equalizer?

Seems to me that XO's are more than just slopes and crossover points, that there are notch filters, uplift circuits, and other circuits that manage the drivers output.

**Panomaniac** · February 19th, 2010, 08:04 PM

Yes indeed, all that can be part of a crossover. Or the crossover can be very simple.

The nice thing about a digital crossover like the DCX2496 is that it allow you to do so many things. Most active crossovers have fixed filter types and don't allow to adjust each section independently.

But of course that comes with a price. Tweaking can be endless, if you let it.

**Steve Mac** · February 19th, 2010, 09:58 PM

Originally Posted by Panomaniac

...
The nice thing about a digital crossover like the DCX2496 is that it allow you to do so many things. ....

Yeah I agree...and if you are an analog purist...it's still the best way to quickly determine the response you want...and THEN emulate the curves in the analog world!

**NKF** · February 19th, 2010, 10:07 PM

I have a pair of the GPA 604 H-3's in a six foot box. I also use a small band pass sub with the speakers. I love the sound and the sub helps. Very good bass.

Nick