Altec 604 D Enclosures

[charly1944]

Hi everybody,
I received from GPA my pair of 604 D.They remag. them and changed the LF cones.I also bought from them their N1600-16 crossover.After a pretty long breaking in period,i tried them at a friend's place.He has got a pair of 604 E with original cones ,a pair of "interesting" enclosures.So we could compare the two pairs of speakers in the same room and the same enclosures using the GPA crossover.The first conclusion is that the 604 D reconed by GPA sounded much better than the 604E with their original cones.Our best guess is his speakers probably need a remag.and may be a change of surround to perform optimally.The second obvious conclusion is that GPA did a very good job and that people should not hesitate sending their Altec to GPA for reconing.
Now come my questions regarding the enclosures.My friend has a pair of BR enclosures with the following external dimensions in feet :Height 3.05;Width 2.13;Depth 1.48.
Internal volume is about 11,3 cubic ft (from which one has probably to deduct the volume of the driver).The cabinets are bottom vented and the vents are actually two rectangles(1.0x1.5 feet) cut in the bottom of the enclosures and facing the floor.The 4 feet are 2 inches high.The walls are made of pretty thin(O.6 inch) and light plywood(Density about 0.5 when Baltic plywood is 0.7).No braces.The only internal damping consist of thin felt covering the internal walls. Those speakers are driven by high quality SE 300 B amplifiers.I was expecting from those speakers a lot of disturbing vibrations but actually they sounded pretty good and the only limit i could find was that i would have preferred the bass to go lower.So should i simply copy those light,inexpensive ,easy to built enclosures for my 604 D or should i try to improve them and in this case how?Charly 1944

[GM]

For real?! That puts the tuning up around 72 Hz whereas a typical Altec tuning would be around 40-42 Hz.

GM

[cradeldorf]

I had an E and a C, the C was way better sounding than the E, It dawned on me that the E crossover is supposed to be 1500 and I was running it with the same GPA N-1600 crossover your using. Not sure if that's why it didn't sound as good, but it could have been. The cabinet you described reminds me of my ex brother in laws Klipsch Cornwalls. When I saw the insides of them all I remember saying is they look like wooden bird cages. they were very light in weight. I was about 14 at the time so....yeah.
I'm glad to hear you got them back and that they sound great. I can't wait to see what cabinet design you go with but there are some real beauties out there.
These are my favorite for looks.
http://www.jacmusic.com/Yamamoto/Spe...604/YS-604.htm
These seem pretty cool too.
http://www.audiocircle.com/index.php?topic=54147.0

[omodo]

For real?! That puts the tuning up around 72 Hz whereas a typical Altec tuning would be around 40-42 Hz.

GM

GM, how does floor loading, especially in this case being only 2"/50mm off the floor, have an effect on port calcs/sizing?

[charly1944]

For real?! That puts the tuning up around 72 Hz whereas a typical Altec tuning would be around 40-42 Hz.

GM

Thanks GM,
Pretty high tuning indeed.No wonder that i found it could have gone lower in the bass.What options would you recommend to go for.I dont mind wether it is an OB (provided it is not too big) or a BR solution.Thanks.
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"

[David Yost]

I think GM has posted a MLTL box design for 604s on this site or perhaps AA High Efficiency, but it should be easy to find. I don't know if anyone has built it.

Here's another one: 6moons audio reviews: Steph?n's Altec 604 Dream Speaker

[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