Altec 604 D Enclosures

[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

[David Yost]

Charles,

Are you able to take advantage of the room corners? In other words, might you be able to "build-in" large floor to ceiling corner IB boxes canted approx. 30 degrees towards the listening position? If so, this would be my first choice and you could add eq or series resistance to balance the system. This layout also gives you maximum boundary reinforcement while minimizing diffraction and creating a pseudo early-reflection-free zone, not to mention using the minimum floor space. Also, if your corner walls are sufficiently rigid, you may be able to get by with building just a well reinforced front baffle screwed and sealed to wall, floor and ceiling furring strips -- it doesn't get much easier than this. A 4' wide (standard for plywood in the USA) baffle set at 30 degrees will yield about 25 cubic feet.

Building a large enough closed box will also mean that you can stop agonizing over your speakers' TS measurements -- they are what they are, and as long as the pair are more or less the same, you will be in business.

Best wishes,
David

[Panomaniac]

As for Open Baffle, here is a pair of 605As that I showed at the Lone Star show. The helper woofer is an 18" pro model with its own amp and active crossover.
Lone Star Audio Fest 2010, Dallas Texas | Hifi Zine

[cradeldorf]

As for Open Baffle, here is a pair of 605As that I showed at the Lone Star show. The helper woofer is an 18" pro model with its own amp and active crossover.
Lone Star Audio Fest 2010, Dallas Texas | Hifi Zine

OMG!!! That's you??? I was totally checking the links out that you posted on Audio Circle Last night. I wondered if that was you and wanted to ask you about your comment that you made about OB crossovers being totally different than the bass reflex crossovers. I was wondering what the differences would be? But maybe we can start a new thread instead of hijacking this one. Nice OB design BTW.

[Panomaniac]

Yeah, that's me. And yes, we should start another thread about Open Baffle design.

[charly1944]

Thans Panomaniac,
Very interesting indeed and not too bulky.The only problem i have with this system is that it uses a helper woofer + an extra amp + an extra active crossover.I really want to keep my system very simple for two reasons:
1.Space in the room:I already have two preamp(one per channel)and two monoblocks amplifiers(300B),on top of a tuner,a turntable which takes space,a CD player.I dont see myself adding an amp and an active crossover to all that.
2.Apart from the space i have a tendency to try to go for simple systems with no subwoofer.I dont mind sacrificing part of the low end(and by the way the upper end of the spectrum that i hear less and less) and i am more and more striving for systems which are musical ,lively and natural.
Thanks again for the suggestion;
Charly.

[Panomaniac]

Il n'ya pas de quoi!

The helper woofer is silent on some tracks, you won't hear it on "girl with guitar" tracks, but it really helps when you need it. The bass amp need not be complicated. A simple plate amp will do, you can even run the subs mono from the plate amp without too much penalty. Use your 300B amps for the 604s.

Otherwise, I'd try to get the T/S parameters and work with GM to design a nice MLTL box. You can start with what he's given you and work on the ports.

[charly1944]

Il y a de quoi,Panomaniac,
Let me know wether we should go on in French!Actually,your suggestion to go for an MLTL solution guided by GM after measuring my speakers is probably the more reasonable one.But it implies that i equip myself with measuring devices (an adapted mike and a sound card i guess), that i learn how to properly use them, and that when the measures are done, GM agrees to help me and has enough time to guide me in the design and the buiding process.He will tell me wether this is the case but i understand he his pretty busy with his house .So all that may take time.
Meanwhile i am tempted to try to improve my friend's enclosures by two combined approaches:
1. Reduce the size of the present rectangular opening empirically, the way Altec Best recommended ,and test the impact on the performance,simply by listening.This will be done on monday on my friend's speakers.
2.If that works,Change then the dimensions of the enclosures while keeping the same internal volume in order to get the height of the speaker more in line with my ear level .So increase the height of the boxes and reduce the width and the depth accordingly.My challenge here is to select a good a ratio to reduce resonances and minimize damping.They are many golden/desirable ratios published and i have no clue wether some have proven better than others.Help is welcome.
This will cost me around 400 USD and allow me to listen to music while preparing the MLTL solution if i am not totally happy with what i have.
Any thoughts,monsieur ?

[Panomaniac]

Reston en Anglais, pour nos chers Anglosaxophones.

Good idea to get something going for right now, your approach seems reasonable. Measuring the T/S parameters can be done fairly cheaply with a volt meter and some resistors, but it's tedious. I use the little WT3 from Parts Express, but the original Woofer Tester II (WT2) is supposed to be even better. They make measuring the drivers a snap. Once you get accurate T/S parameters for your drivers, then GM can proceed, if he has the time. You'll want to define your maximum dimensions before he starts, tho. That way he won't go to the trouble of designing an optimum box, only for you to find it too big. Figure out how big you can go first, then see if he can do something with that. Right, GM?

I think you'll be very happy with a reasonably sized MLTL for the 604s. I had a pair here in giant boxes, and they were among the most dynamic drivers I've ever heard. They were GPA recones and new diaphragms, BTW. Next step is crossover. Have a good look at Jeff Markwart's designs.

FWIW, even tho I had been listening to big Altecs since birth, I didn't know anything about them until I moved to Paris and got tangled up with the Revue de l'Audiophile crew - many years ago. Sure opened my eyes and ears! Now I'm an Altec junkie and find myself in good company here.

[charly1944]

David,
The only corners i could use are covered from floor to ceiling by bass traps(minichunks) made of rockwool and covered by 5 thin panels of wood of 2'x2' for each corner not to deaden the room.I would have to remove 3 of them in each corner to allow enough space for the two 604 and enough air around the drivers.I will then have in each corner one covered bass trap of 2'x2' at floor level and another one at ceiling level ,leaving enough space in between for a baffle about 3.5' wide 6.0' high ;I dont know wether this is enough to do the trick. If i get rid of the 2 bass trap together,i dont know what kind of impact it will have on the acoustic of the room which i spent months to treat acoustically with decent results for a relatively small room. By the way,when you refer to" Eq or series resistance to balance the system" ,how do you achieve that?
Any way we have got a potential option that i could work on with some additional guidance.
Regarding closed boxes not to have to worry about measures of the speakers,how big is "large enough"?I have to tell you that the 11.3 cb feet of my friend 's speakers are the maximum size i can accomodate .Actually i would prefer taller but not as wide boxes.
Thanks again for your input David.
Charly.