Making a 416 out of a 421

**magnarc** · August 9th, 2011, 03:39 AM

Originally Posted by Old Guy

A 416 kit does fit into a 421. GPA has done it before. However the 421 has a back vent so must have a front cap with no vent hole..

In the case of spec sheets though, you can certainly believe when one has a ceramic and the other Alnico, that they aren't the same magnet.

OTOH I do not know if the later 416 with ceramic uses the 421 mag. Good chance, but just plain dunno.

OK Thanks for that.

**les winter** · August 16th, 2011, 07:28 AM

Hi GM. I'm in forward progress. I got my first 421 and a 416 recone kit in hand. I stripped the 421 and cleaned it. This unit has two screens. One on the magnet rear, and one under the dust cap. The one under the dust cap has what appears to be metal spatter; not so as to completely block it off, but there is some. It doesn't come off when I dab it with adhesive tape or shoot it with compressed air. Should I leave it in place? Do you have a recommendation for how to block off the back vent?

Thanks.
Les

**Old Guy** · August 16th, 2011, 08:44 AM

Altec glued a metal disc over the hole...at the end some of those came loose, Altec's QC was deteriorating..

EV used a tapered foam plug to block back vents...I would be tempted to do something like that...and just put a permanent adhesive Mylar label inside and out...circular labels are a stock item...but I would also ask GM's opinion of that before I did it...

**les winter** · August 16th, 2011, 04:19 PM

Well the excitement never ceases. I reconed the 421, left the screens in, taped up the back vent, and measured it using WT3 with the speaker laying on its back.

Ugh.

QTS measured 0.75. I let it run in for a while with low frequency signals. Got worse. I called Speaker Exchange where I got the recone kit: they never measure driver Q so they don't know if it is normal or not.

Inspiration. I propped up the speaker vertically. Bingo (kind of). QTS measures around 0.4. Seems like the new suspension is very limber and maybe, the coil was out of the gap in the when the speaker was lying on its back. Does this make sense? VAS was around 30, but that was measured in a box with the speaker facing down.

Any wisdom out there?

**Earl K** · August 16th, 2011, 07:07 PM

- What Fs did you measure ?

FYI :

- A cone kit that's not broken in yet will have a stiffer suspension leading to a higher than normal Fs, as well as a higher than spec., Qts ( Vas will be smaller ) .

- A really well used woofer may have a suspension that's half in the bag .
- One consequence of a loose suspension will be a lower than normal Fs, as well as a lower than normal Qts ( Vas will be larger than normal ) .

- I just measured ( with WT2 ) one of my 416-8Cs that has a Fs of @ 22 hz & a Qts of @ 0.18 ....

cheers <> Earl

BTW ; You ought to be measuring a woofer hanging in the air ( suspended from a strong pipe with strong sash cord, etc ) / hanging off the ground by a few feet ( & away from flat reflective surfaces ) .
- Doesn't WT3 provide instructions for all of this ?

**Panomaniac** · August 16th, 2011, 08:27 PM

Right-O! You can not get a proper reading with the woofer on its back. I clamp mine into a bench vise. Suspending them would be even better. Or holding it straight up at arm's length, if you're man enough.

Originally Posted by Earl K

I just measured ( with WT2 ) one of my 416-8Cs that has a Fs of @ 22 hz & a Qts of @ 0.18 ....

Arrrgggg...... I hate you! I can not get a 416 with a Q below 0.4 no matter what I do. The flabby 416 curse is upon me.

**Altec Best** · August 17th, 2011, 03:05 AM

Originally Posted by Panomaniac

I can not get a 416 with a Q below 0.4 no matter what I do.

Or you can get a pair from a friend that has a good pair ! Curse defeated !

**les winter** · August 17th, 2011, 05:40 AM

Hi Earl. The Fs was 19. I should check the WT3 instructions again.

**les winter** · August 17th, 2011, 02:09 PM

OK, so after much fooling around, I've determined that the qts is 0.45, the vas is 40 ft^3 and the fs is 18.5 . This is driving me towards a very large sealed box to get the system Q down below 1. Any suggestions on altering the vas? I'm figuring if I really stuff a 5 cubic foot box, the stuffing will drop the system Q. I would really like to get this into a 3 ft^3 box but I don't see how. Maybe applying some kind of goop to the spider?