Altec 604 D Enclosures

[GM]

Thanks GM,

What options would you recommend to go for.

You?re welcome!

While OB, IB are theoretical ideals, there?s nothing intrinsically wrong with the existing cabs that maybe some additional damping, adding bracing and reducing vent area to lower tuning can?t solve and large enough to allow for an adequate amount of EQ/tuning options, though ideally we need their new GPA specs, especially since I seriously doubt they?re even remotely close to OEM.

Otherwise, at least as large an internal volume [Vb], though taller to make them an offset driver MLTL tuned around/at Fs and use some form of EQ to ?fill up? the cabs as required to tonally balance them in-room. This assumes of course the re-cones aren?t as ?weak? [high Qts] as some other recent GPA re-cones I?m aware of.

GM

[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]

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.

[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.

[charly1944]

Hi sorry i did get back to earlier and thanks for the pictures.I like the OB very much but i am wondering how big they are and how do they perform,specially when it comes to low freq.Regarding the difference of performance of your 604 E vs C,they are indeed different drivers with different surround and i doubt that the the GPA crossover is equally adapted to both of them.There is also a distinct possibility that your E and your C are not in the same"shape".Did you check the surrounds,the spiders and the level of magnetisation of both pairs?
Charles;

[David Yost]

Hi, GM

I didn't have any idea that Fisher had shared your design and PMs without permission, otherwise I never would have referred the OP to the sites. That really wasn't kosher for those boys to do that, and I hope it hasn't discouraged you from sharing your ideas with us DIY folk.

Best wishes,
David

[GM]

Greets!

No biggie, it's old news and no, for the most part it hasn't, though I now limit most help to on-line Qs.

GM

[omodo]

Charles, interesting to hear you are from France, are the enclosures based on Jean Marie-Piels speakers? I only have the following small picture from Revue Du Son No. 225 Dec. '98, but from what you describe they could be very similar. Unfortunately I do not have the article but would love to see a scan if you can locate a copy.

[GM]

Sorry GM,

(Dont forget that i am French


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:



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?

No apologies needed, it happens sooner or later to all of us.

No, I didn’t know you were French [or I forgot, a real problem for me now] as like so many Europeans, your English is as good or better than way too many public school educated locals, at least around me.

Correct, I’m really disappointed GPA doesn’t include as standard, or at least offer, the T/S specs for a reasonable price upon request. Actually, since they know the various specs of the sub assemblies [Mms, Cms, Re, etc.], they could easily calculate them in an Excel or similar spreadsheet ‘close enough’ for cab design.

The only real variable would be how well they drained, re-magnetized the magnets, but in a cab large enough to allow some tuning flexibility, this hopefully won’t be an issue, though again, there’s been some re-cones where the re-charge didn’t go well, which results in an unacceptably high Qts. Since yours sound good, odds are that they are fine.

Anyway, try to get them from GPA and if you can’t, then experimenting with vent tuning is easier than learning, doing T/S measurements if you have no one local to do it for you.

WRT tuning, the math is fairly intensive for other than a simple reflex, but I can sim different vent lengths close enough using MJK’s software and if you choose to use a bottom loading vent, calculate a minimum stand height.

Again, the cab would be taller with height typically based on seated ear height for an offset driver layout that requires the least amount of internal damping, so for ~38” it would be around 62” i.d. [inside dimension] for 11.3 ft^3 using 19 mm thick construction and assuming setting on the floor with the vent on one of the sides near/at the bottom. Width x depth would normally be an acoustic or golden ratio to minimize internal damping. Using the golden ratio, this would be ~22.58” x 13.95” i.d..


Anyway, just an example...........


GM

[charly1944]

Hi GM,
I dont know where you are located in the US but it seems to me that you are on the site either very early in the morning or very late at night!
Actually GPA told me that they are not used to measure the speakers as a standard service .Since i insisted to get my 604 measured after the reconing(i was advised by Jeff Markwart that it would be useful for cabinet and crossover design)they accepted to do it but then had no time to actually perform the measurements.I guess they had other priorities and actually i was not ready to wait for weeks.
For now and without measured elements to guide me ,i guess i have multiple options
1.To copy my friend's enclosure and to change(reduce) the dimensions of the vent and assess the results by listening.
2.To keep the same design (bottom vent boxes)but change the dimensions of the boxes and of the vent while keeping the total volume.In this option i noticed that for the width vs depth they are a lot of acoustic ratios published and none of them correspond to the golden ratio.So i am a little bit at loss when it comes to select one of those.Any recommendation?Regarding the height, my ear are at about 3 feet from the floor.So what could be the ideal dimensions of the boxes(without the stands).And what distance should i keep between the upper part of the speakers(rear mounted)and the upper part of the front baffle?Last but not least ,what should be in this set up, the dimensions of the bottom vent to get to an around 40 hz tuning?By the way,Altec Best suggested to go for circular vent rather than rectangular one.
3. to change the design and go for an MLTL( or a OB if the dimensions are reasonable in this relatively small room -12x16 feet).
What would you advise me to do .
GM,if i take too much of your time,let me know,i will understand.
Thanks,
Charles