Altec 604 D Enclosures

[GM]

The 6 Moons and SS MLTLs are based on a private design I did for Jay Fisher, who shared my PMs with them without bothering to tell me, though he did ask me some technical Qs for a 'friend'. I had to learn about them both from others some time after the article was published. For sure, I never would have approved of any of my PMs being published verbatim, especially partly out of context as was done in the 6 Moons article nor willingly helped a 'for profit' venture who later claimed he changed it enough to make it 'his' design.

Don't recall any updates, the design started out as one of my default floor loaded MLTL alignments and JF shortened it and relocated the offset driver a bit differently than I recommended due to WAF? considerations. I used MJK's software to alter the vent length, made some bracing, damping, driver support, floor spacing recommendations and AFAIK, that's what was built. If there were other changes, I'm not aware of them nor care to be.

GM

[charly1944]

Sorry GM,
My message to David where i said i was looking for your guidance went through just before i could read yours. Let me make sure that i understand your comments(Dont forget that i am French and although my English is decent i tend to miss some subtleties of your language and certainly miss a lot when it comes to technical terms).I understand that there is nothing fondamentally wrong with my friend's enclosures and that improvements can be achieved.Do you mean that optimally i should get those reconed drivers measured in terms of impedance and TS parameters in order to adjust the dimensions of the enclosures and the vent.If yes this is a bad news because i will need a lot of help to measure those drivers.But i am ready to go for it. Few questions:
If we are making the assumption that indeed those reconed 604 D dont have the 604 E characteristics,i guess we have to use the trial and error approach rather than any approach based on modelling.What elements could we easily and reversably change to lower the tuning ;Ex:If i have to reduce the vent,should i make drastic changes and is there a formula to help me in doing that.Same thing with the feet :to day,2 inches.Should i change that and by how much .The dimensions of the enclosure without changing the volume:Higher,deeper? Sorry if my questions dont make sense but i badly need specific(and if necessary ,iterative) recommendations to make progress.
Thanks in advance.
Charles.

[Altec Best]

If your dims are correct ? 11.3 cubic ft. Is a very large cabinet for the 604.You would typically see like a 9 cubic ft cab for the 604 (620 A or B) being considered a large cabinet.Also sounds like those cabinets could use some stiffening/bracing.If you like those cabs you could add some length to the vents to lower the tuning.

It doesn't surprise me though that the new recones/remag's sound better.I had a similar experience with my 416-8B's.The surrounds and or spiders are the issue.They either stiffened up or they loosened up/sagged.When that happens the sound quality suffers.

One other thing if you build something similar I would go with round ports as they are easier to add length to then square/rectangle IMHO.

"Sound is Round"

[Altec Best]

That's an older review I think GM has done some updates since then.Dunno ? Hopefully he can confirm this or not.

[David Yost]

Here is some info on yet another 604 MLTL: Serious Stereo Ultimate Transmission Line Speaker. The ultimate High Efficiency Speakers found anywhere

[GM]

Restricting the vent via boundary loading creates a form of band-pass loading [think R-J style reflex loading] and while I'm sure that the wave equations can optimize the gap for 'x' amount of gain, I've never seen it published and even if I did, don?t have a clue how to manipulate it, so I have to find the amount I want empirically. Basically, it lowers tuning due to air mass loading, so can either shorten a vent or increase its area [Av] for a given Fb same as a vented TL [MLTL] does.

I worked up a simple way to find a minimum gap before it begins to audibly affect speaker response that?s based on speaker base area from empirical data and should have ?run the numbers? before posting as I get a pretty high minimum, so in theory there is some loading going on, lowering tuning [Fb], but would have to be measured or at least listen to test tones to find out how much.

Then again, this much vent area Vs cab base area makes it almost a simple TL, which by itself would be tuned to ~78.5 Hz, so ignoring floor gain, around 70 Hz may not be that far off. In retrospect, considering its age, I wonder if it?s not tuned same as an early A7, which puts it around 65 Hz, not a high tuning for the early ?50s/604D. This would imply a fairly significant amount of floor gain.

GM

[charly1944]

Thanks David,
It looks interesting but probably difficult to implement for me.Is the MLTL solution considered as the state of the art solution for a 604? I look forward to getting some guidance from GM.