Gpa 416-8c

[VolvoHeretic]

It is illegal to put a 604 in a 1.5 cu ft box!

[Old Guy]

That's interesting. There's a 10dB slide starting at 900Hz and ending around 2300Hz. That's understandable. I wonder what accounts for the 9dB bump from 2300 to 2700?

A little phenomenon called beaming, and perhaps a bit of cone breakup overtones thrown in.

[GM]

GM - how do you think these would play in that big GPA 604 box.....

Using the measured plus derived specs [attached], it will need to be tuned lower [Fs] to get a 'close enough' similar response, so will probably need at least a 6? long vent.

GM

[gortnipper]

It is illegal to put a 604 in a 1.5 cu ft box!

10 cf box...

Using the measured plus derived specs [attached], it will need to be tuned lower [Fs] to get a 'close enough' similar response, so will probably need at least a 6” long vent.

GM

Thanks. And keep the 3.5R or no?

[VolvoHeretic]

sorry, last time I checied, 42.5 liters equealed 1,5 cubic feet.

[GM]

Thanks. And keep the 3.5R or no?

Hmm, IIRC, the 3.5 ohms was due to Jay's tube amp, so was tuned to the Iconic/GPA's Fs to maximize power conversion and you used it too.

Anyway, as a general rule for HIFI apps, I prefer/recommend an Fs or lower tuning and EQ if necessary to flatten it out in-room, but if you’re using a typical SS or tube PP amp, then try the cab as is first without any added resistance.

GM

[gortnipper]

sorry, last time I checied, 42.5 liters equealed 1,5 cubic feet.

Sorry, I copied out of GM's doc to Jay and L=Length of the internal longest dimension of the cab, not Liters. So, ~10.3 cu ft.

Hmm, IIRC, the 3.5 ohms was due to Jay's tube amp, so was tuned to the Iconic/GPA's Fs to maximize power conversion and you used it too.

Anyway, as a general rule for HIFI apps, I prefer/recommend an Fs or lower tuning and EQ if necessary to flatten it out in-room, but if you’re using a typical SS or tube PP amp, then try the cab as is first without any added resistance.

GM

OK, thanks again.

BTW - with the 604s in that box and my SE valve amp, I tried first w/o any added R and it sounded flat and thin. I then used a variable and found ~3R works very nicely so I added a fixed r.

[GM]

You’re welcome!

OK, then tune to Fs and experiment with up to 3 ohms if required.

GM

[Alien_Shore]

That's interesting. There's a 10dB slide starting at 900Hz and ending around 2300Hz. That's understandable. I wonder what accounts for the 9dB bump from 2300 to 2700?

Was this measured inside?

Yes, measured in my garage. This weekend, I'll take them outside, refresh the imepedance and T/S plots, and take another FR measurement.
That crazy FR rise at the end of the range is pretty typical woofer cone breakup; from what I've read*, paper cones and dustcaps (particularly lightweight ones) have exaggerated peaks like that.

*Some interesting references:
The Art of Speaker Design Part II
Cone Breakup Simulation
Woofer Design Tutorial

[cradeldorf]

shouldn't you measure them where they're gonna sit and then tune them to a flat response?