Extra speaker cabinet

[blackwood]

Hi!

A friend of mine asked me to build him 2 extra speaker cabinets for the band.
No woodworking problems, just a few questions.

Here's the deal.
Engle amps, combo, both 50 watt, with 2 x 8 ohm and 2 x 16 ohm outputs.

He wants a cabinet the size of the combo, with 1 x 12" Celestion, 60 watt, 8 ohms.

1) should I make an open-back or a closed one? they need it for some extra volume and the combo boxes are both open-back.

2) if I build a closed cabinet, should I cut a hole on the front panel, something like a 4" circle? is the plastic tube a MUST or can I just leave the hole as it is?

3) connecting the speaker - do I simply use one jack, solder those 2 wires to the speaker and plug in a cable from one of those 8 ohm outputs?

4) if so, should I use shielded cables INSIDE the cabinet (jack-speaker)? would it be OK if I include an ON/OFF switch?

5) do I need to use any isolation inside the cabinet? all the cabinets I've seen are just plain, old plywood on the inside..

Anyone?

Thanks!!
Igor

[Earl Norton]

1. An open back will be brighter and more omni directional. I have used an open back combo with a closed and sealed extension for years and love it. YMMV.

2. For a spanish guitar, tuning the cabinet does not get you very far. But try it if you must.

3. make sure the polarity is the same as the combo you use it with. Check it with a battery to make sure the cones jump in the same direction when touching the same connections. You'll get the drift if you do it.

4. Do not use an on/off switch (Why?). Do not use shielded cable to connect speakers. Use stranded zip cord (lamp cord)

5. Most closed cabinets are filled with insulation for damping and to increase the percieved volume of the cabinet. Fender used fibreglass.

[blackwood]

That's what I was thinking, a combination of an open-back combo and a closed cabinet giving it a thighter feel with more bass.

Maybe it's my english, but I don't quite understand the part about a spanish guitar and tuning the cabinet I mean, the air has to come out somewhere? Or not? Doesn't that put a lot of stress on the cabinet itself?

An ON/OFF switch, why not?

Insulation.. Can I use something else?

[Earl Norton]

The lowest note on a spanish guitar (six string) is 80 hz which is well above the resonant freq of a common musical instrument speaker. The purpose of a port is to tune the cabinet to lower the usable frequency response of the whole system. In other words the point becomes moot because the spanish guitar does not go so low.

A sealed cabinet provides the best damping charateristics. Roadies are a lot more stress to the cabinet...take good drugs.

OK. Try an on off switch if you want. I can't think why, however.

You could stuff the cabinet with pillow stuffing, foam rubber, silicon breast implants or just about anything with similar characteristics. Let me know how the implants work out.

[blackwood]

OK. No holes or ports or whatever. Even better.
Yeah well, roadies? That would be me.

Foam rubber it is, I don't want guys trying to seduce my speaker cabinet when they find out it has implants

Thanks for helping out!

[TD_Madden]

I used 2-inch batting I found at a fabric store inside my bandmaster cabinet...works great and no itching like you'd get from fiberglass.....

[blackwood]

I used 2-inch batting I found at a fabric store inside my bandmaster cabinet...works great and no itching like you'd get from fiberglass.....

A few days ago I read an article about guitar speaker cabinets and it says they don't need any acoustic wadding??

In fact, the article is from the Celestion homepage!
"Do not use internal acoustic wadding, it is inappropriate for guitar cabs, reducing sparkle and life."

??

[Brad1]

Bottom line is that you won't know what sounds best to them unless you try everything.
Build the cab as a fully closed back. Try it that way. Pop the back off, and try it that way. Perhaps even have some extra wood to try it as a half-back. (Perhaps bottom half covered, top half not, or 1/4 each top and bottom). Try it with a back and no batting. Staple some batting in, and try it that way. You can always remove it.
I think I would avoid the on/off switch. I'm not sure why, but I would get the willies kicking the speaker in and out. I think I would be more comfortable at least putting the amp in standby before changing the load. At that point, I'd just unplug it from the amp. But, that's just me. I would be more comfortable using a proper speaker switching device designed for that purpose.

I dunno about the foam rubber thing. Foam rubber has a tendency to deteriorate, especially if it gets hot then cold, humid then dry, etc. Deteriorating foam rubber in a closed, vibrating cabinet may cause quite a mess.

Once the cabs are built with all these options in mind, it should be easy enough to test all the variations in a couple of hours of evaluation with the full band, and individually. You may even find one guy likes his a certain way, and the other likes it another.

Brad1

[petemoore]

open it up?

Closed back cab's project more sound foreward, and tend to have a different 'more' bass definition or response..tend to..oversize enclosure will tend to get the extreme of what's possible cabinet resonance wise, if the wood sound is what you're after and the material is thin enough to do that...and that takes more messing with and tuning than just a more solid enclosure, which will have good bass just different.
Bass doesn't necessarily get lost with open back, and depends on...other stuff [ot].
Open back cabinets in a band may allow the drummer to hear the guitar straight from the back of the cabinet.
I tried open back and closed back for 5e3 2x12'' oversized 'resonant' cabs [one is plywood the other is antique pine, both use ~1/2'' for the sides, thicker up to 5/8th's for longer spans and baffleboard. A little extra added to dampen the top too...just right..lol, and the plywood one has two 4'' holes in the back, the Pine has a slot down each side, about 2'' wide, these ports opened the cabinets up [we think] and still retain some nice bass resonance.