Guitar Cab Help

Trooper46

Member
2008-08-22 4:12 pm
Hi,

I am in the process of building a ax84 P1, and i am going to need a cab to accompany the head. I play almost everything, but i find my self playing more 80s rock and metal than anything else. (Van Halen, Dio, Priest, Dokken, Etc..) I would like to build a 1x12 cab to start off with and maybe add a second 1x12 cab later after i get out of appartment life. Kinda like a mini stack. I am looking at the Eminence Red Coat Lynch Super, the Man-o-War, and the Black Powder for speakers. But I have no idea where to start designing the cab. Are there any calculators where I can just plug in the TS parameters and get a good starting point?

Any help would be great!

Thanks!
 

wakibaki

Banned
2008-01-08 11:51 pm
Most guitar cabs have an open back. Bass is a bit different.

An open back cab is effectively an open baffle. The most basic open baffle is just a flat sheet with a hole for the speaker. It prevents cancellation taking place between the sound coming from the back of the speaker cone and the front.

The frequency at which cancellation starts is the frequency whose wavelength can creep round the smallest dimension (measuring from the speaker to the edge) of the baffle. Circular baffles have octave resonances which are problematic, and rectangular baffles are often used. Open-backed boxes are often treated as folded open baffles.

An open-backed box will give you a sound probably best described as 'classic'.

For a more complete treatment of the theory of open baffles see this page:- Electro-acoustic models and others at Seigfried Linkwitz' site.

You can get some other info by googling 'open baffle speaker design' or 'open baffle calculator'

Since guitar cabs are often placed without regard to the sound (the cabs sit on the floor, which has an influence, and near walls, which have an influence), I would not be overly concerned with the exact dimensions of any open back cabinet I built, concentrating rather on convenience of transport and storage and robust construction without any rattles or buzzes, although many might disagree with this. To a certain extent, bigger is better (more extended bass response, although this will be limited by the driver anyway). You could take a tape measure to the local music shop and copy something there...

There are many other enclosures which can be used, basses often use ported boxes and may have tweeter reinforcement. You can find a number of enclosure design programs, having a look at these will give you a bit more grounding in the subject generally. google 'WinISD' which is free or simply 'speaker design software'.

w
 
Hi,

Here's what I'd try to bear in mind in your situation.
- the dimensions of the head. Do you want the amp to be smaller, wider, or the same width as the cab?
- how loud? Given a set wattage (assuming the speaker can handle it), a more efficient speaker will play louder.
Here's what I did when making my 1x12" cab...
Made it the same width as the amp driving it; looked at the frequency responses of speakers known to sound good (in my case, I was using a combo with 1x10", so I chose a 12" with similar response); I made the back removable, so I could experiment with sealed vs open backed (I preferred open back).
When an open backed cab is being used, most manufacturers will put boards across the top and bottom. Perhaps trying those would help?
100_0847 - My Photo Gallery

Might give you more to think about, though I would be jealous if you got the Man O' War.

Chris
 
Ya don't stress it too much, I settled for a comprimise, I built an open back ontop of a closed back ;) Just make some removable panel(s) if you are concerned.


When I was building my first amp years ago, I tried My 2 12" Celestions on a slab of 2'x4' plywood. Sounded great! lol. It only sounded slightly better in the finished box (3/4 closed back)

When I say "better" I mean it sounded more like what I was aiming for, very subjective.
 
Here's a peek of my newest one.
 

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Apologies for the terrible typos in my previous post!

I ended up trying the XF212 after I built a pair of the O10's and T24's. They sounded so good, I knew I couldn't go wrong. Once complete, the drives did need to be run in for 24+ hours though. The more I use them, the better they are sounding now.

Regards,
Robin.
 
Most guitar cabs have an open back.
I have to disagree with you there. Most combo amps have open or semi open backs. Nearly all guitar cabinets that are not homemade have closed backs. Closed backs with no ports.

I would not be overly concerned with the exact dimensions of any open back
MAYBE that is true for open back cabinets. I don't know. But the dimensions are extremely important for closed back cabinets. For example you may have seen a Marshall stack before and maybe the top cabinet was what they call a "slant face" and the bottom cabinet a "straight face". Well the straight face cabinets sound a lot better because they have more space inside (cubic inches). I know of a couple of bands who like the open back sound. The Allman brothers are one. They use closed back cabinets but they take the backs off for the gig. The vast majority of guitar players use closed back cabinets including myself.
 
Hmmm... I'd disagree about the "vast majority" bit.

Most Fender amps are open backed, as are most Vox amps. Some Marshall are closed, some are open. By open backed, I mean the driver is visible from the rear, so there's dipole radiation.

Sure, given sufficient cabinet volume, I'd expect that a closed back cabinet could sound okay (or even good), but when a single 12" driver is sat in a very large box... I'm sorry, but I'd have 4 of them, open backed. It's (IMO) better use of all that space.

Chris
 

bigbeck

Member
2010-01-17 3:57 am
An open-backed box will give you a sound probably best described as 'classic'.


I would not be overly concerned with the exact dimensions of any open back cabinet I built, concentrating rather on convenience of transport and storage and robust construction without any rattles or buzzes, although many might disagree with this.

Sound advice;) Maybe make a 1/2 back panel for it to sort of mimic a combo amp. I have 5 speaker cabs all with open back or half back. I never liked sealed back.

I also built a few AX84 single ended amps. The HO, SEL and P1EX. I've also built versions with parallel power tubes. After I built my first push pull amp, I gave up on SE.

Don
 
Most guitar cabs designs don't futz around much with "hi-fi" details like TS parameters. If you like the 80s classic rock sound, thats frequently gonna be a Marshall 4 X 12 cab loaded with Celestions. The parameters to design that cab were largely "how big does it need to be to cram 4 X 12" speakers in there?". Given what you like, I'd suggest looking around on the net at some of the commercial offerings (like Avatar, Marshall, etc.) and just plan to borrow some measurments from one of those for your cab. Some "higher end" designs to look at would be the TS designed Mesa cab, the Port City cabs, or the Hermida cab.
Unless you just want to build a cab, its hard to beat used prices - look around on Craigslist, Ebay, and pawn shops.
 
I bet you can't find one single picture of a guitar speaker cabinet that is open back (a closed back cabinet with the back removed doesn't count) and not homemade. Especially by Fender. Combo amps do not count. I already said they are almost always open back or semi open back.

But, if you can it will be the first one I have seen.
 
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Here ya go, Peckerwood:

MESA Boogie 1x12 Compact Guitar Cabinet

PRS 4x10 Open Back | Sweetwater.com

No Fenders, but I didn't want to waste more than 5 minutes of my time.

Admittedly open back extension cabs or stacks are the exception, but they do exist. I would propose that combo amps DO count, as generations of guitarists have happily wailed through them for more than half a century, they are clearly an open back design, and many seem satisfied with the sound quality they produce.
 
Admittedly open back extension cabs or stacks are the exception, but they do exist. I would propose that combo amps DO count, as generations of guitarists have happily wailed through them for more than half a century, they are clearly an open back design, and many seem satisfied with the sound quality they produce.

For guitar it doesn't really matter - they don't go low enough for cabinets to be a problem, unlike bass guitars of course.

As it doesn't matter, it makes sense to fit a back to protect the drivers, it's usually valve combos that don't, so it's easy to change the valves.
 
Well by definition a combo amp is not a speaker cabinet. I will give it to you that you were able to find a couple of open back speaker cabinets though. Those are the first ones I have ever seen.

Open back cabs do sound quite different though. I don't like them. You might like them better but whichever kind you like better you would be able to hear the difference. Like I said before the Allman Brothers run their cabinets with the backs off and they get a distinctly different guitar sound then other bands.