Altec 416-Z 48" 846B MLTL

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GM

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Joined 2003
Thread begun here: http://www.audioasylum.com/cgi/vt.mpl?f=hug&m=130139

Greets!

Again, using the horn mouth cavity and width, depth dims of the 846B shown here: http://www.lansingheritage.org/images/altec/plans/1974-enc-design/page22.jpg with a woofer layout same as the 846B, i.e. driver ~up against the inside bottom of the cavity, then assuming 3/4" (19 mm) thick no-void plywood such as 11 or 13 ply Baltec Birch (all dims i.d.):

L = 46.5"
W = 25"
D = 16.5"

vents = (2) 4" dia. with length varying from 0.75" to 5" depending on what works best in-room. I prefer the additional pipe loading that placing the vents near the bottom yields (3" up), but if you think you might ever convert to dual woofers, then placing them midpoint between them is better overall, or 26.25" down from the top. Regardless, place them 3" i.d. in from each side.

WRT bracing, either vertically oriented 'ventilated' plywood panels or 1x3 Douglas Fir (or stiffer) to both tie the parallel walls together as well as support/mass load the driver(s). Regardless of whether you design for the baffle or rear plate to be removable, I recommend industrial Nema 4 or 4x neoprene gasketing in lieu of the typical window sealing foam normally used to seal it.

WRT damping, Altec's standard of one of each parallel wall be covered with 1" acoustic fiberglass is more than enough, so top, back and one side, though rather than actually adding it to the top, making a hanging cradle of insulation that completely encloses the horn area is what I recommend.

I don't have a way to accurately sim how a high output impedance amp combined with the passive's and any wire resistance affects the frequency response and why you may need to experiment with different vent lengths, but it will be much flatter over a wider BW than shown.

The first sim is with 5" long vents positioned below the driver:

GM
 

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GM

Member
Joined 2003
If you're 'sure enough' these will remain single woofer speakers and they sound 'boomy' in-room, then sealing off the horn cavity to reduce the net Vb is an option. 6" vents positioned near the bottom:
 

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Thank You!

GM! I lost this for a while. Glad I recovered the link. Entire family was down with the Flu, twice.

I'll look over. Also looking into how to extend highs of the 806A or if I should replace with 902, etc. But, the 806s are so smooth...

Thoughts on amplification? Bi-amp with SS or PP down low and SET up top, or passive with SET or PP?
 

GM

Member
Joined 2003
Greets!

I wondered what happened to you. I sent you my ph# re the roof and never heard back either via email or ph call.

Anyway, hope all is well with the family, I've lost some friends/family to flu, so know how dangerous it can be.

Yeah, I saw your post on the AA forum, but since you addressed your Q to Tom I was going to wait to see what he posted. Anyway, while the 802-8G and most of the 900 series drivers has more HF extension at the expense of LF gain BW, with what you have all you really need is a bypass cap around the attenuator to allow the highs to come through unfiltered. Since the 806 has less highs than the 802, try a range of caps from ~0.5-3 uF.

If this fails to please, then you're either one of those rare folks that has good enough HF hearing and/or sit far enough off axis to require a wider sound stage than the 811 can produce, so will require super tweeters. Note that unless you listen alone, females (especially teenyboppers) should IMO decide what sounds best as their HF hearing acuity is often different enough to be the deciding factor of whether the speakers get a 'thumbs up' or 'move those big boxes out of the house, like yesterday!'.

I prefer all SS with active XO and passive response contouring of the HF, but most folks prefer using a passive XO and a high output impedance tube SET to both serve as amp and contour network, so as always YMMV. If either tube bottom end or only one tube amp is desired, then adjustable DF PP is the way to go since this is what Altec used to 'voice' all their designs through the mid '60s AFAIK.

GM
 
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