Perfect cabinet size for GPA 604-III...9 cubic feet?

[atilsley]

I built a Stonehenge V cabinet earlier, which was slightly under 9 cf...say, 200 liters. (See attached pic...thanks Todd W for your help on this :-))

GPA suggests 255 liters, 9 cubic feet (tuned to 45 Hz) for the 604.

1. Is there any benefit in going larger? (for normal mid-sized room listening.)

2. Is the x2 5 1/4 inch di ports the best option? (I will probably put these in the floor of the cabinet and raise it approx 4 inches using corner stands/feet).

3. What would be the best one or two tweaks you'd make to the standard GPA cross-over for this two-way? (I will use a SET amp...eg 300B...so no bi-amping at this stage.)

4. Any special bracing you'd suggest? (I was going to fit two one-inch cross-braces 1/3 way down the cabinet running front to back, plus side to side. Also, the front baffle will have an additional 1-inch panel running on the inside for additional strength...so the entire front will be 2 inches.) (Cabinet to be constructed in 25mm [1-inch] MDF.)

5. What special sound deadening would you suggest? (I was going to line 3 non-facing internal walls with 1.5 inch accoustic foam, like this.) Alternatively/additionally, I will add a couple of flat panels at odd angles to minimize any standing waves.

Thanks

Andrew

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[Ronald Lee]

When I built my enclosure, I read the following Altec publication which found handy suggestions:

1974 Enclosure Manual

[Cal Weldon]

1. No, you'll start losing the perceived bass as the system Q goes down.

2. If that is what is recommended then stick with it. It's a true bass reflex. No silly port there to add unwanted chuffing.

3. It's their modern XO so I would leave it alone. One thing I have found with the 604's is they require an EQ or at least the dual attenuator XO that came out with the 604-8H model, especially in smaller rooms.

4. Shelf bracing is the most effective and you can use cheap old MDF for them. Make sure you do not space them equally as you wish to have different free panel areas to reduce the amount of exciting that occurs at any given frequency.

5. Linoleum stick-on tiles and then sheep's wool. Don't be afraid to do all panels. Fiberglass works fine too. The stuff you show seems rather expensive considering what it's doing.

Good luck with the project.

[atilsley]

Thanks Cal....very helpful.

Can you comment on the use of sheep's wool vs the acoustic foam (with its peaks and troughs)? I've bought some of the 1.5 inch foam for this project...so interested in opinions re the use of another type of product.

An idea, line three internal walls with acoustic foam, then the other panels with an alternate product. Would this not better help minimize unwanted frequencies floating about?

Andrew

[Cal Weldon]

Sure. If you wish to use the foam then why not, it probably works great. Better than fiberglass? Who knows, I've never been one to lay out the money in areas like that as I feel it's just not necessary. It's another example of something coming along that's going to take over the industry and it will either fade away or become a niche item. When I talked about the linoleum panels it has to do with panel damping which is at least as important as wave damping. Also keep in mind that the material will only be useful in the higher frequencies and that it's effectiveness goes down with the frequency, so it all depends on the actual purpose intended as to what the best material is likely to be. I think the egg carton pattern is more for the buyer than the standing waves.