I am about to make my first cabinets and I need to some clarification

[barrymclark]

I am planning on making a head and two separate single 12 cabinets open back.

My understanding is that, with open back, I will not need to pay much attention to sizing the interior of the cabinet for the speaker's sake.

The cabinet's interior as it stands is 18"w x 18"h x 10"d. Those numbers are fairly arbitrary. 18 was picked as a width because the amp chassis is 16" wide and I figured I would have a 1" strip of furring on either side for a very small amount of decorative back plating. It will only come down a few inches from the top and maybe an inch or so from the sides and bottom.

Is there anything I need to consider here? Do I need to dampen the interior at those back plate edges?

Thank you,

Barry

[soundguruman]

That is correct, however a ported cabinet built to the manufacturer specifications will result in more efficiency. There does not need to be damping.

[barrymclark]

That is correct, however a ported cabinet built to the manufacturer specifications will result in more efficiency. There does not need to be damping.

Thank you for your reply. When you say more efficiency, what exactly is that buying me? By ported, I assume you do not mean open back but mostly sealed but with a port of some calculated size.

Thanks again!

[soundguruman]

Thank you for your reply. When you say more efficiency, what exactly is that buying me? By ported, I assume you do not mean open back but mostly sealed but with a port of some calculated size.

Thanks again!

The speaker will be much louder with less power input, and it will sound better, much more even frequency response. It will also weigh more.
For example, a single EVM12L speaker in the correct cabinet will easily hold its own against a Marshall 4-12 cabinet in loudness, but will also sound better, take just as much power, and the speaker will be harder to blow.
Eminence Legend 1218 = 98.8 db 1 W 1 M
EVM12L= 100db 1W 1M
Celestion Rocket 50 12”= 95 db 1W 1M
(typical of stock speaker in many amps)
Peavey Sheffield 12” 97.8db 1W 1M
(typical of stock speaker in many amps)
JBL 2020H 12”= 103db 1W 1M
Jensen Alnico 12”= 95db 1W 1M
(typical of stock speaker in many amps)
However, the efficiency of many stock speakers is so low, they are not rated.

[barrymclark]

The speaker will be much louder with less power input, and it will sound better, much more even frequency response. It will also weigh more.
For example, a single EVM12L speaker in the correct cabinet will easily hold its own against a Marshall 4-12 cabinet in loudness, but will also sound better, take just as much power, and the speaker will be harder to blow.
Eminence Legend 1218 = 98.8 db 1 W 1 M
EVM12L= 100db 1W 1M
Celestion Rocket 50 12”= 95 db 1W 1M
(typical of stock speaker in many amps)
Peavey Sheffield 12” 97.8db 1W 1M
(typical of stock speaker in many amps)
JBL 2020H 12”= 103db 1W 1M
Jensen Alnico 12”= 95db 1W 1M
(typical of stock speaker in many amps)
However, the efficiency of many stock speakers is so low, they are not rated.

The speakers I am looking at are Eminence Patriot Canis Major (102db 1w 1m) and an Eminence Red Coat Private Jack (101db 1w 1m).

I'd certainly like to get the most of these speakers that I can. Do you know of a good calculator to use? I have used some in the past but they always seem to need a parameter I can't seem or have the experience to locate.

For this one, I wasn't able to locate the cone diameter. I also wasn't sure what to put in for port size and volume. Is this something I put in arbitrarily or do I base it on my desired dimensions?

http://www.webervst.com/spkrcalc/port1.htm

Thanks!

[olddawg]

This is all very subjective. Better means different things to different people. Personally I do not care for EV speakers and very much doubt that one loaded 12 will smoke a decent 4x12 cab. My suggestion is to copy the cab specs of a known good design that you like. The law of unintended consequences you know.

[cminor9]

It's rock n roll, not rocket science. Build your cab however you like it, just take the time to build it well and make it look decent. Reading stories of how Marshall and fender arrived at certain design conclusions is enlightening. The vaunted Marshall 4x12 cab came to be that size because it could be made with little waste, and it looked good.

Would a thiele cab sound better than an open back cab? Maybe. Would certain dimensions work better? Perhaps. But in the end you would be chasing trivialities. I'd argue that your choice of speakers is going to have more effect on your tone than your cabinets dimensions.

Sure, someone will tell you you should have done this or that. Someone's always going to criticize anyhow. Build something you like the sound of. Most people won't even notice, and those who do and nitpick, to hell with em.

[Chuck H]

It's worth noting that in soundguruman's example he DID reference a specific speaker appointment for the 4X12 cab. But I do agree that any single 12 in ANY cab won't do what a GOOD 4X12 closed cab will. It's just impossible, BUT, a single 12 EV in the Thiele (?) cab is said to be a pretty remarkable thing. I'd love to try one and eat my words.

As to the original post... There are many cab CAD programs out there. I don't use any of them because as it relates to guitar amps the listening is the real test. Even if you (or I) think that +3db at 80Hz is a good idea, we don't really know how it will work with a particular guitar speaker and a particular amp until we try it. It may end up "wolfy" or otherwise unbalanced, it might be the bomb. Just waaaay too many variables to try and do this sort of thing too predictably WRT overdriven tube guitar amps IMHE.

Also IMHE, the depth of open back cabinets does have an affect on bottom end that goes beyond sheer cabinet volume (volume as in air space, not loudness). I think 18x18x10 is a safe bet, BUT, if you really want to get big bottom end you may want to design the cabs such that you can make them closed back and port the baffle in case you don't have enough bottom end with the open back design.

JM2C

[barrymclark]

It's worth noting that in soundguruman's example he DID reference a specific speaker appointment for the 4X12 cab. But I do agree that any single 12 in ANY cab won't do what a GOOD 4X12 closed cab will. It's just impossible, BUT, a single 12 EV in the Thiele (?) cab is said to be a pretty remarkable thing. I'd love to try one and eat my words.

As to the original post... There are many cab CAD programs out there. I don't use any of them because as it relates to guitar amps the listening is the real test. Even if you (or I) think that +3db at 80Hz is a good idea, we don't really know how it will work with a particular guitar speaker and a particular amp until we try it. It may end up "wolfy" or otherwise unbalanced, it might be the bomb. Just waaaay too many variables to try and do this sort of thing too predictably WRT overdriven tube guitar amps IMHE.

Also IMHE, the depth of open back cabinets does have an affect on bottom end that goes beyond sheer cabinet volume (volume as in air space, not loudness). I think 18x18x10 is a safe bet, BUT, if you really want to get big bottom end you may want to design the cabs such that you can make them closed back and port the baffle in case you don't have enough bottom end with the open back design.

JM2C

I figured that the depth of the open back would have some affect on the sound of the amp. The design I came up with really is based on simplicity and room to fit everything. The open back served two purposes for me: no need to tune the cabinet and would cut back no the bottom end. Not a huge fan of BIG bottom in guitar. There's enough of a fight between guitar and bass. I don't wanna egg it on! haha.

[barrymclark]

This is all very subjective. Better means different things to different people. Personally I do not care for EV speakers and very much doubt that one loaded 12 will smoke a decent 4x12 cab. My suggestion is to copy the cab specs of a known good design that you like. The law of unintended consequences you know.

Where's the fun in that? haha.

[barrymclark]

It's rock n roll, not rocket science. Build your cab however you like it, just take the time to build it well and make it look decent. Reading stories of how Marshall and fender arrived at certain design conclusions is enlightening. The vaunted Marshall 4x12 cab came to be that size because it could be made with little waste, and it looked good.

Would a thiele cab sound better than an open back cab? Maybe. Would certain dimensions work better? Perhaps. But in the end you would be chasing trivialities. I'd argue that your choice of speakers is going to have more effect on your tone than your cabinets dimensions.

Sure, someone will tell you you should have done this or that. Someone's always going to criticize anyhow. Build something you like the sound of. Most people won't even notice, and those who do and nitpick, to hell with em.

Oh, I like this guy!

[Bill Moore]

I have mostly played in smaller venues, where the guitar amp was in close proximity to the rear wall. I personally think that this interaction will yield more low frequency emphasis. In larger stages, I have propped a rack cover behind the combo to project more of the sound toward the guitarist, (and the audience).

[Chuck H]

FWIW... My favorite amp (tone wise) for practice and small to medium sized clubs is a 1x12 open back combo that I built. The cab is 18x22x10. It's probably worth noting that it's made of poplar and has a "1/2" cabinet grade plywood baffle (1/2" in quotes because plywood never actually measures true. always less). I'm using a Vintage 30 in this amp. It was a little harsh at first, and took almost a year to break in in this 20 watt amp, but sounds fabulous now.

I expect the amp takes up enough room in the cab that you'll have as much or more interior volume as this cab with an 18x18x10 "speaker only" cab. After some experimenting I found that (for me) poplar and solid pine are good sounding woods for cabinets. I don't think pine has any tonal advantage but it's popular because many vintage amps were built with it. Poplar is easier to tool and work without tearouts and it's also easier to find good straight planks to build with.

JM2C.

[JoeM]

.... It's just impossible, BUT, a single 12 EV in the Thiele (?) cab is said to be a pretty remarkable thing. I'd love to try one and eat my words....
JM2C

I have a cab made to theil/small parameters for an EVM 12L. Compared with the same EV in a open cab, there didnt seem to that much difference. Maybe in the the lowest octave? Hi Fi speakers, where the lowest octave being flat is where I think the Theil/Small cab design might be the way to optimize the speaker, but guitarists arent generally concerned with a flat uncolored sound from the speaker.

[soundguruman]

If you look at the Marshall 4X12 speakers, they soak power and saturate. After about 45 minutes wide open, they are as hot as a toaster oven.
The EVM produces more SPL per watt with a lot less saturation. The speaker dissipates several times more heat than a stock Marshall speaker.
I don't think it's the same in any frequency range. But I do notice improved highs and lows with the cast frame speaker. It sounds Hi Fi to me, compared to stamped frame speakers.
So even though it weighs and costs much more, I would rather use the cast frame, and I think the difference is very noticeable.