# Building a 4x8" Guitar cab (beginer some help needed)



## Dragonrose (Dec 29, 2009)

Just stumbled across this site whilst searching google for some answers, looks like this is the place to get them 

Im taking the plunge and building my own guitar amp cab, as a cheaper way of achieving a good bedroom use amp and getting the best features in the cab i can with the money i have. I have the cab built, and tolexed, handles fitted and castors fitted. I still need to caulk around the handles on the inside of the cab and around the baffle board so its fully sealed. The cab is slanted and closed back, im aiming to put Eminence Alpha 8A speakers in it (these came recommended to me by some other guitarists who have used them in custom cabs) 

I have some questions tho on a few little things, woofer tunnels/speaker ports, if i was to fit 2 on the rear of the cab what size would i need? 3 inch or 6 inch ones, or is there a way of working it out along with there positioning?

Ive seen in some speakers and noticeably another persons diy guitar cab (here on this forum) that some people use a grey foam on the sides and bottom of the cabs, what does this add/take from the sound? or whats its use?

The speakers have these specs:
Resonant Frequency 76dB
Magnet Weight 0.57kg
Impedance 8 Ohm
Sensitivity 97dB
Power RMS 125W
Frequency Response 65-5000Hz
Diameter 203.2mm 

Would i be able to wire it so it has 3 input jacks on the rear pannel, which allows for using the cab in mono at 4ohms or stereo at 8ohms?

Thanks


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## StereoClarity (Apr 22, 2008)

That driver is an excellent choice. For a single 8" driver there is no way you'll need a 6" port. I think a single 3" port would be just fine. 

How large is the enclosure you built? You said 4x8 but there is an important 3rd dimension that you left off so I'd need that to figure out the volume of the enclosure. From modeling I'd think that a tune of 45-50hz would do best in your situation. I've not tuned many guitar cabs though so I don't know what response is really intended to go to on those. The driver doesn't have much of a low end range.

The other important question is....What kind of guitar?


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## Dragonrose (Dec 29, 2009)

Hi thanks for the reply, sorry i think i may of mis-worded my title a little, the '4x8"' is the number of speakers x speaker size. So my cab has four 8' speakers, all four are the Eminence Alpha 8A models. The actual cab dimensions i will take down and post. And its going to be used for electric guitars, with various solid state and small valve heads.


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## StereoClarity (Apr 22, 2008)

Ahhhh, ok. So you said you already have the cab built correct? What's the interior volume? That will determine the vent length. For 4 8" drivers I'm thinking dual 4" ports would work or a single 6" for sure. 

The gray foam inside helps break up standing waves inside the cabinet.


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## soho54 (Jul 22, 2006)

Are you trying to create your own custom sound, or are you just wanting a PA cab?

If you are after a PA type of cab (i guess you are with the 8A) that just plays whatever you put into it, build it like a normal speaker. Seal it and add stuffing, or port it to ~30Hz and line the insides.

If you are after a personal sound, anything goes.

If you want to play with porting remember a low E is ~80Hz, Drop D is ~73Hz, and if you go really low Drop B is ~61Hz. 


"*Would i be able to wire it so it has 3 input jacks on the rear pannel, which allows for using the cab in mono at 4ohms or stereo at 8ohms?*"

You could get mono 8ohm, or stereo at 4 or 16ohm. You would also need a way to disconnect the un-used jacks while not in use. I would build a removable panel and use some jumper wires. You could also use some extra 3pole 1/4" jacks, and make an external jumper.

Edit: just caught a math error.


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## Ricci (May 23, 2007)

Go for a 60hz tune. That way you'll hit the drop B 7 string type sound easily if that sort of thing floats your boat.


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## StereoClarity (Apr 22, 2008)

^gets my vote. Make it fun or don't make it I say!


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## Dragonrose (Dec 29, 2009)

StereoClarity said:


> ^gets my vote. Make it fun or don't make it I say!


Exactly why im making this, i don't wanna just buy a generic cab and i already have a 1970's 4X12 cab for bigger stuff, this is purely for bedroom use and to be the best of its kind. Which is why i want the mono/stereo switch, and to know as much as i can about possible features it can have.

Ill be getting the internal dimension measurements tonight and posting them later, ive been looking at eggcrate foam (or acoustic foam, seems to have quite a few names) to line the cab with, ebay seems to be the best supplier so far for me (in the UK)

What feet options are there? I have casters on it which are easily removed when the cabs not been moved around, so would having rubber feet produce a better sound then casters? Or ive seen some with a spring foot ?


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