Original 604-8K or GPA 604-8H-III

[stevenarrow]

Hello,

I am enjoying a new to me pair of 604-8k with a stock crossover in 620 enclosure. I am interested in possible upgrade. I was hoping someone with direct experience can relate the differences between the 8K and the current GPA 8H-III with GPA crossover. Is it worth the expense? I can always re-sell the vintage units to re-coup costs...

This is for home audio, music only.

Thanks,
Steve

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Any additional comments or opinions on these specific drivers / crossovers is welcome.

[Old Guy]

Later 604's used the EV magnet, which results in lighter bass. My understanding is the GPA reverts to the original magnet.

OTOH if you add a sub to the 604K you likely will have a better system than the GPA alone.

You should get better performance going either direction. You pays yer money and you takes yer choice.

RMH

[GM]

For sure some improvement from an upgraded 8k XO, but the III has a bigger horn with better acoustics to offset some of the 8k's phasing issues, so the III is at least theoretically worth the cost and just a couple of reasons why I only recommend it over all but the early 1 kHz XO'd duplexes, plus may want to remove the loading caps with either one: EarthLink(R) - Page Not Found............WTF ?! Posted three valid links viewed/copied from Jeff's site........Altec Lansing 604-8K................... Phase Correction for Altec Ferrite Duplexes.................. Altec Compression Driver Rear Loading Caps................Grrr........not showing paragraph separations or ability to modify text due to 'HTML' being 'off'?............ HB's way of saying 'donate'?

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For sure some improvement from an upgraded 8k XO, but the III has a bigger horn with better acoustics to offset some of the 8k's phasing issues, so the III is at least theoretically worth the cost and just a couple of reasons why I only recommend it over all but the early 1 kHz XO'd duplexes, plus may want to remove the loading caps with either one:

Altec Lansing 604-8K

http://home.earthlink.net/~jmarkwart/id16.html

http://home.earthlink.net/~jmarkwart/id21.html

GM

[stevenarrow]

Thanks for the info. I have pulled the trigger on a XO from GPA. I figure I will do this step by step to gauge the changes.

[GM]

You're welcome! Looking forward to your comparison.

GM

[stevenarrow]

New GPA networks installed. They dropped right in. The hardest part was actually getting the drivers out of the box; they were installed 35 years ago...

The sound opened up in a subtle way. It is not game changing but certainly an improvement. A little added separation between instruments, the sound stage got even bigger, and there is a sense of added smoothies (less grainy?).

Any ways, I'll be keeping the GPA XO in for a while.

Up next: a pair of Bison MLTL cabinets!

[Skip Pack]

New GPA networks installed. They dropped right in. The hardest part was actually getting the drivers out of the box; they were installed 35 years ago...

Up next: a pair of Bison MLTL cabinets!

I hope you build them quickly and love them!. I've got refurbed 604Cs and the Bison plans. I trust the change in drivers would not be very different in the same cabs. If you do the bottom port option, there should be good (not visible) tuneability. Your experience will influence my go/nogo decision.

Skip

[GM]

It's 10 + ft^3, so big enough for older drivers and tuned around 30 Hz IIRC, but if driven with a high output impedance, then best to tune each cab to the driver's actual Fs.

GM

[Skip Pack]

Thanks, GM! I expect my likely choice in amps' output impedance would be .5 to 2 ohms.

Skip

[GM]

You're welcome!

OK, combined with XO, wiring losses, 2 ohms [Qts'] is marginal with such a low Qts driver to benefit much from Fs tuning, so tune it to suit and only 'dig down' to Fs if not satisfied. Either way may need some baffle step compensation [BSC] if not near/at a wall to fill in the [mid] bass, i.e. more series resistance or proper filter if not digital: General Speaker Related Articles

In general, Qts' > ~ 0.32-0.38 [depending on the source] is where actual Fs tuning is a good plan: Qts' = Qts + any added series resistance: mh-audio.nl - Home

GM