Dedmans 1x12 speaker cab

[Dedman]

I built this today, I didn't have a plan. Plans are for people who know what they are doing!

So yes , it is big for a 1x12 . The back can be either open or closed back and there is space inside for a 6m speaker lead and and Orange Micro Terror Not that it's going in there but the space is there oh no, that's going on the pedal board that I also don't have a plan for but I may put a little shelf in there for it.

So I just need to finish off the speaker hole (its a bit wobbly) and do some filling and my favourite thing of all SANDING!
Then stain and clear coat (satin). Going to try the printing onto grease proof paper thing for some logo's on the front panel. I have black hessian for the front. It will end up looking like a perfect match for my GD-1

oh speaker is 8ohm Celestion Greenback

[wazkelly]

Now who has been a busy bee then?

Fairly tall and upright looking and based on the size of the cut speaker hole the dimensions look to be about 600mm x 600mm x 300mm? Are you going to put any sound insulation stuff inside?

I did this sort of thing with making stereo speakers when I was a teenager and the sound insulation stuff was just like a thin fibreglass insulation batt. It made a little bit of difference but I was itchy for days after installing the stuff and reckon high density foam would be the better way to go nowadays. There is probably some science on it to be found on the internet but it will need something to stop the timber vibrations resonating out of control.

[Simon Barden]

Fairly tall and upright looking and based on the size of the cut speaker hole the dimensions look to be about 600mm x 600mm x 300mm? Are you going to put any sound insulation stuff inside?

I did this sort of thing with making stereo speakers when I was a teenager and the sound insulation stuff was just like a thin fibreglass insulation batt. It made a little bit of difference but I was itchy for days after installing the stuff and reckon high density foam would be the better way to go nowadays. There is probably some science on it to be found on the internet but it will need something to stop the timber vibrations resonating out of control.

The 'sound insulation' stuff inside Hi-Fi speakers and a lot of PA speakers (and the occasional guitar speaker, though this is pretty rare) is there for absorbing some of the upper mids and high frequency sounds within the enclosure. This is an attempt to stop standing waves building up inside the enclosure at the cabinets' resonant frequencies, (as determined by the size of the enclosure) and colouring the sound produced by the speakers.

A small Hi-fi speaker may have internal dimensions say of 28cm (h) x 18cm(w) x 20cm(d). The fundamental frequency of a standing wave is determined by the distance between two parallel surfaces; For any standing wave, the fundamental wave and all its related harmonic frequencies have zero amplitude where the wave touches at the sides. Points of zero amplitude on a wave are called nodes.



This is exactly the same principle as fretting a guitar string, where the string can't move at the saddle or where it's fretted, but the rest of the string is free to vibrate.

And standing waves are like feedback on an electric guitar. If the volume/gain is enough, the sound will vibrate the strings, but frequencies close to, or the same as, the fundamental or harmonics of un-damped strings will cause those strings to vibrate in sympathy at those frequencies, resulting in a build up of sound that may or may not be wanted.

The worst type of enclosure for standing waves is a square box, with all three sets of enclosure walls parallel and the same distance apart, as all three sets of walls have the same resonant frequencies. With parallel sided enclosure construction, you really want all the distances between sides to be different and also not multiples of one another e.g. a 80cm x 40cm x 20cm enclosure would still have lots of resonance issues, despite the distances not being the same.

Ideally, all three sets of the enclosure walls would be non-parallel, but practically this is hard to achieve and be both aesthetically pleasing and sturdy. But it is why the majority of portable PA speakers these days have non-parallel sides and tops/bottoms, with only the front and back being parallel (although internally the faces are rarely smooth which all helps).

So if a parallel-sided speaker is reproducing a wide range of frequencies (i.e. playing back music), it's exciting the air inside the speaker enclosure and it will cause standing waves within the enclosure. These will reinforce the sound produced by the speaker at those particular frequencies, and so 'colour' the sound reproduction.

Because most h-fi speaker enclosures are relatively small, the wavelengths are small and the frequencies quite high. We can convert wavelength into frequency by dividing the speed of sound by the wavelength. The speed of sound varies with air temperature and pressure, but it's around 343m/s at 20°C at sea level.

So our example hi-fi speaker has it's longest wavelength at 0.28m, and 343/0.28 = 1.225kHz. That's a pretty high pitch to start with, and harmonics will be whole-number multiples of those wavelengths i.e. 2x = 2.450kHz and 3x = 3.785kHz. 1.225kHz is around a D#6 on a piano.

It takes a lot of mass to absorb or damp out low frequencies, but as the frequencies go up, it takes less and less mass to do so. That's why carpets, curtains and fabric-covered furniture are so effective at reducing the amount of higher frequency reflected sound in a room. It also helps that fabrics and carpets have a fairly open texture. Closed texture surfaces reflect sound. When it's open texture, the sound waves can pass through and bounce around, loosing energy with each internal reflection (turning it into heat).

So to absorb sound, you need an open textured material or open-cell foam, with lots of internal surface area. Because speakers can get hot, especially if pushed too hard, you also want it fireproof. This is why glass-fibre strands are so often used. Glass fibre (with no resin) is a very effective sound absorber, though for use within a room it needs to be enclosed within open-weave fabrics to stop the fibres getting out.

Because the amplitude of standing waves is zero at the very sides of the enclosure, Ideally you mount your absorbing material away from the sides so that a) the amplitude of the sound wave is greater, and so it can absorb more energy and b) the wave passes through the material (loosing energy as it does so), hits the side and reflects back through the material again, loosing even more energy. Practically, it's easier just to staple it to the sides and hope for the best.

It really isn't there to damp the enclosure wall vibrations, though by absorbing some of the sound energy that hits the walls, it does have some effect. To stop the enclosure walls resonating you really either need a) a lot of mass b) a lot of cross-bracing c) curved sides that have a structure that isn't prone to vibrating or d) a combination of two or more of a) to c).

A couple of of DIY hi-fi speaker chaps I know use very thick marine ply, along with cross bracing and line the insides with lead (high mass) to reduce cabinet vibrations .

Some of the studio monitor manufacturers (e.g. Genelec) now use moulded high-density resin-based materials to create internal enclosures with no parallel surfaces but use rounded sides with a constantly varying radius.

But when it comes to guitar cabs, really anything goes. It's not there to reproduce sound, it's there to create it. The floating baffle (loads of resonance) on the earlier Fender amps was as much a part of the overall sound as the amp circuitry. According to an old bass-playing friend (who also had a company sub-contracting in the amp build for H&H and some other long-gone UK manufacturers in the '70s), the older Trace Elliot bass cabs relied much on cabinet resonance for their sound. With guitar cabs, if it sounds good, it is good.

[Dedman]

I've noticed commercial open backs and combo's don't have any insulation. I used that horrible fiberglass in hi fi speakers too never again! I have some 50mm wool insulation if I find it needs it
you are pretty right on the dimensions, I didn't have a drawing but the ply on the front was 600 wide :P

[wazkelly]

Big enough for a 15" then if you ever think of upsizing to Bass?

Know what you mean about open back cabs and personally not a fan as too much sound going in the wrong direction, backwards. Only upside is you can crank it up a bit more before getting too loud all over.

[DrNomis_44]

That 1 X 12 Cab is looking great so far Dedman, should look awesome when it's all finished with the black hessian in place, and I reckon your Micro Terror should work great with it too, I'll have to get cracking and start doing all the prep work for building a 2 X 12 for my Peavey Renown amp, but since my Marshall is up and running, the 2 X 12 speaker cab project isn't such an urgent project so it's on my waiting list for the time being, my Pedalboard build is the project that's next up for me to work on, I have finally got all the FX Pedals I need for my Pedalboard, just waiting on an FX Looper pedal to turn up in the post.

[Dedman]

Thanks guys, yea, the idea is that in the future if I wanted to make it a 15 or a 2x10 I could and also it's been made to fill a spot in the cave as a piece of furniture. I'm planning a pedal board with a cover that will also hold the little Orange amp and the whole lot will basically be tidy and not recognisable for what it is when not being used

[Fretworn]

If you are going closed back you might want to consider holes on the front to port out the bass tones from the back of the speaker.

[Dedman]

I've been thinking about that Fretty, I have a set of old Ultra Linear hi fi speakers built that way, the main driver is 8inch and there is 2inch hole next to the tweeter for the speaker to 'breathe". I'll see what size hole saws I have I prefer it closed to keep the dam gecko's out

I stained, aged and clear (mat) coated the cab today. I tried the "printing onto grease proof paper and ironing on to wood" trick and it does work!. The smoother the wood the better the image, as I was going for the barn find look I didn't sand much and was rewarded with a well worn look. Pretty happy with that!

All that remains is to put the cloth on and wire it, which brings me to my question.
Can I use an ordinary guitar jack for the input or do I need a special one?

[DrNomis_44]

I've been thinking about that Fretty, I have a set of old Ultra Linear hi fi speakers built that way, the main driver is 8inch and there is 2inch hole next to the tweeter for the speaker to 'breathe". I'll see what size hole saws I have I prefer it closed to keep the dam gecko's out

I stained, aged and clear (mat) coated the cab today. I tried the "printing onto grease proof paper and ironing on to wood" trick and it does work!. The smoother the wood the better the image, as I was going for the barn find look I didn't sand much and was rewarded with a well worn look. Pretty happy with that!

All that remains is to put the cloth on and wire it, which brings me to my question.
Can I use an ordinary guitar jack for the input or do I need a special one?

Yep, a standard guitar jack will work fine for the input provided that the wood used for the back of your speaker cab is thin enough to allow enough threads for the small nut that holds the jack in place, if the wood is a bit too thick you might need to buy one of these from Jaycar Electronics:

http://www.jaycar.com.au/search?text...6-948350295c33


If you buy one of those, you can also buy two of these:

http://www.jaycar.com.au/search?text...6-948350295c33


And about a metre of this wire:


http://www.jaycar.com.au/search?text...6-948350295c33


And you'll be able to make a custom speaker lead for your speaker cab and Micro Terror.