Making a 416 out of a 421

I'm starting the hunt for parts to build an altec pair for my home theater. I mostly listen to the opera via blu-ray. My main setup is a pair of clone model 19's. GM suggested using similar components for my HT set. So I am on the hunt for parts. Ideally 416's 811b's.

Because I lucked into a pair of $100 Valencias during my Model 19 build, I figured I could build my HT pair for a few hundred. Maybe not. 416's go for $325 or so on the 'bay. New ones from GPA aren't that far behind.

So I started considering 421's. Reconing kits are around $65 and busted 421's go for $24-$50 or so.

I have two questions:

1. any reason I cannot do the recone myself?

2. can I make a fair approximation of a 416 with a 421 reconed with a 416 kit? I notice the magnet on a 421 weighs the same as a 416 but it is not alnico, it's "ceramic ferrimag" per the GPA vintage catalog sheets.

thanks for any advice.
Les

Since you'll be using a sub system, you can use the 421 as is except swap out the 'chrome dome' for a 416's dustcap since you need neither the 416's low Fs nor extra Xmax.

GM

edit: you'll need to block off the rear vent also if it has one [can't remember if all models had one].

It works. I would use a hard paper dome instead of the chrome...just call bill at GPA he can do it. Or at least use parts he recommends.

I really would recommend getting 418 instead as it converts directly. Or 422, same core. Brother has a single for 25.

421 core is also same as 423.

418's actually work well if you have a sub...I cover the shiny dome with a felt one, bfish suggested vented paper instead....

Thanks guys.
The only thing about the 418 is that the magnet weight, per the catalog cut at GPA is 1/2 the weight of a 421 or 416.
OG I got email; thanks.

Just a little more info, please: If I substitute a 416 recone into a 421, do I get a reasonable replica of a 416? Any reason not to do this myself?
thanks again.

They are different drivers, and AFAIK, different VC and magnet structures.

Don't always believe the spec sheets either, you may find that the 418 is the same mag as a 416A, or 8-Z, but not a B or C.

There is nothing wrong with a 421. It is prob not the best unit for a M19 clone though.

I think you'll find a 416 kit will not fit into a 421.
A 420 tho, the biflex, is the same as a 416, and maybe a better go for a recone.

If you are careful, yes reconing can be done, search round for the ALtec tech letter on reconing techniques.

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.

Thanks O.G. Can I simply plug the back and use a screened cap (as on the 416) on the front?

As GPA instead of me if you want good advice. IMHO, 421 sounds better without the silver dome, and back vent increases power handling. I can't advise someone to do something I wouldn't do myself.

OK.
Thanks so much.
lw

Quote:

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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.

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OK Thanks for that.

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

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...

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?

- 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 ?

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.

Quote:

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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 ....

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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.

Quote:

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Originally Posted by Panomaniac

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

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Or you can get a pair from a friend that has a good pair ! Curse defeated ! :tongue2:

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

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?

Hi OG. what thickness and size do you recommend for the felt?
thanks
Les

Quote:

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Originally Posted by les winter

what thickness and size do you recommend for the felt?

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:confused: Not sure what felt?

You mean to convert 808's?

Quote:

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Originally Posted by les winter

I would really like to get this into a 3 ft^3 box........

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Go open back and adjust stuffing to get response down to ~80 Hz to XO to the sub system. Use tightly stretched double knit for a rear cover.

What makes vintage drivers such as the 416 special is its high Vas which allows better tracking of the signal at low input than modern day low Vas drivers [all else equal], so don't recommend altering the driver except through acoustic mass loading [stuffing]. Anyway, seems there's other ways: Modyfying the parameters of a 15" woofer - diyAudio

BTW, what are the rest of its specs?

edit: How come the embedded link isn't highlighted in some way?

GM

This started out as an inquiry about Model 15's over at the Audio Asylum. GM suggested that I consider building something like a small Model 19. So I got a pair of trashed 421's (one from Old Guy's Brother; thanks Old Guy) and a pair of 416 recone kits and off I went.

The lower cabinets are around 7 cubic feet and the upper ones around 3. Still to go: Mrs. Darst's foam (I hope) laminate the lower cabinets and cut the holes to connect the upper volume with the lower one. The crossover is a Model 19 clone. The horn is a 811B and the driver is a GPA 902.

Sounds pretty fair, even with an old Sony HT receiver.

Thanks for all the help I received.
Les

Sweet, looking good!