Open Back Cab vs Closed Back

[Tonray's Ghost]

Title says it all. Any particular preference or is one preferred over the other in certain circumstances ?

If one buys an open back amp combo, would closing it require any special porting (for bass response) or can you just Tolex a piece of plywood to the back and be done with it ?


https://www.laney.co.uk/blog/open-back- ... ifference/


Never mind...this answered it for me

[toomanycats]

I'll mainly limit my response to open back vs closed back combo amps, as that seems to be what you're angling at. That being said, my preference is a 4X12 closed back extension cab loaded with a pair of Greenbacks and a pair of V30s. That's my idea of rock & roll heaven, as it's loud, warm, deep, woody, articulate, wide, and can rattle your bones.

But if we're talking combos then tube vs solid state is an important factor.

Most every tube powered combo amp I own has an open back, which I'm assuming is necessary for heat dissipation. Even that doesn't seem sufficient in some instances, such as with my Crate VC30, which can get alarmingly warm under heavy use. The only tube combo amp I own with a closed back is my VOX AC4. A pair of 12AX7 tubes can be sufficiently cooled with the air vent on top of the amp. It's a great sounding low watt tube amp with a good amount of low end projection, some of which is no doubt attributable to it's closed back design.

When it comes to solid state combo amps I own examples that are both open back and closed back. Solid state amps are less forgiving regarding the heat issue and I wouldn't worry too much about experimenting with the porting on the back of the amp. A quick and easy test for an open backed amp would be to play it backed up directly against a wall vs a few feet away from of the wall. You'll hear the difference.

EDIT: The Vox AC4 has a single 12AX7 preamp tube and a single EL84 power tube. I was thinking of my Marshall DSL 5, which does have a pair of 12AX7s and is, incidentally, open backed.

[Tonray's Ghost]

I'll mainly limit my response to open back vs closed back combo amps, as that seems to be what you're angling at. That being said, my preference is a 4X12 closed back extension cab loaded with a pair of Greenbacks and a pair of V30s. That's my idea of rock & roll heaven, as it's loud, warm, deep, woody, articulate, wide, and can rattle your bones.

But if we're talking combos then tube vs solid state is an important factor.

Most every tube powered combo amp I own has an open back, which I'm assuming is necessary for heat dissipation. Even that doesn't seem sufficient in some instances, such as with my Crate VC30, which can get alarmingly warm under heavy use. The only tube combo amp I own with a closed back is my VOX AC4. A pair of 12AX7 tubes can be sufficiently cooled with the air vent on top of the amp. It's a great sounding low watt tube amp with a good amount of low end projection, some of which is no doubt attributable to it's closed back design.

When it comes to solid state combo amps I own examples that are both open back and closed back. Solid state amps are less forgiving regarding the heat issue and I wouldn't worry too much about experimenting with the porting on the back of the amp. A quick and easy test for an open backed amp would be to play it backed up directly against a wall vs a few feet away from of the wall. You'll hear the difference.

When I really think about it, any amp I buy is going to sit very nearly with its back up against a wall anyway as that's the only location that makes sense. I was just watching some videos of that AC4C1..looks great I just wish it had onboard reverb. I keep telling myself that my ultimate setup would be an AC15c1 and also a Fender Princeton to cover all based. Both too loud for my space when using power levels that they need to make them sing..although many folks have stated they use both successfully at home, although using an overdrive pedal is necessary for the crunch at reasonable volume. Sigh...we'll see..well see

[Tonray's Ghost]

Wow..I'd better start saving for that AC15

This is a guy whose opinion on amps is pretty trustworthy

[golem]

It depends on the space. I don't have a strong enough opinion on this I like both.

[tonebender]

The position of my amp was normally in front of the drummer about even with the kick. This could make hearing the guitar difficult if I used a closed back cab and was not mic'd up so he could get it in the monitor. So for me it was about mic'ing up or not. A small place where we would not mic up, I would usually use and open back combo or cab so he could hear it. Bigger place or outside and mic'ing up I could use either but I would also be able to use a closed back cab. I have had a kajillion different cabs over the years but these days I have two. A closed back and an open back, both run V30's.

[BatUtilityBelt]

Apparently there's one more reason for closed back.

[Tonray's Ghost]

Apparently there's one more reason for closed back. Closed Back.jpeg

I'm more worried about geckos getting in to the main board and frying the amp or fouling the speaker..bastards are always in the house

[andrewsrea]

It truly is a preference thing and I like both for certain applications. That said I gravitate to closed-back more than open-back for two reasons: consistency of the note (tone) and tightness (punchy) of the low end.

Open-back will fill a stage, or a room in your house. It is omni-directional. The bigger the area the better, because of phase cancellation and volume wars with bandmates. An open back can sound horrible in a small room because the sound from the back of the amp bounces off of walls and recombines with the sound from the front of the amp in various phases. Some frequencies are completely out of phase and it sound like something is missing (like turning up the bass and it doesn't get deeper - just farty) some are degrees out which will make they sound thin or pokey and some are in-phase making those frequencies overbearing. Related, you can dial in a great tone in one position, move the amps in the same room and no longer can achieve that tone. You also get Doppler effect from the back of the amp. Last, a combo amp speaker is basically free floating and mechanically compliant with only its components. Energy causes the speaker to move forward until the limits of its spider and surround are reached and likewise in reverse. In as such, more amp energy is required for the speaker to reverse direction and some amps don't have enough, which creates distortion (some good, some bad). IMHO, open back has too many variables to deal with.

Closed back cabinets do not reintroduce the completely out of phase rear speaker sound to the listener. It only projects forward and is directional (sometimes very much so). And because the back is closed, the movement of the speaker creates a mechanical compliance, compressing the air when it is moving backward and creating a vacuum when moving forward. It takes much less amp energy to change directions and the amps 'energy demand' is aligned with the efficient in-motion cycles of the speaker. The result is louder, more efficient, purer note and tone. If you dial in a fantastic tone in your bedroom, it is just a few tweaks away from the same in a rehearsal room. And for stage volume wars, your amp will be much less likely to be causing your bandmates to be turning up. The downside is you may be deafening the folks sitting in the front rows in the path of your speaker's projection.

I am looking forward to other's preferences and why.

[Tonray's Ghost]

It truly is a preference thing and I like both for certain applications. That said I gravitate to closed-back more than open-back for two reasons: consistency of the note (tone) and tightness (punchy) of the low end.

Open-back will fill a stage, or a room in your house. It is omni-directional. The bigger the area the better, because of phase cancellation and volume wars with bandmates. An open back can sound horrible in a small room because the sound from the back of the amp bounces off of walls and recombines with the sound from the front of the amp in various phases. Some frequencies are completely out of phase and it sound like something is missing (like turning up the bass and it doesn't get deeper - just farty) some are degrees out which will make they sound thin or pokey and some are in-phase making those frequencies overbearing. Related, you can dial in a great tone in one position, move the amps in the same room and no longer can achieve that tone. You also get Doppler effect from the back of the amp. Last, a combo amp speaker is basically free floating and mechanically compliant with only its components. Energy causes the speaker to move forward until the limits of its spider and surround are reached and likewise in reverse. In as such, more amp energy is required for the speaker to reverse direction and some amps don't have enough, which creates distortion (some good, some bad). IMHO, open back has too many variables to deal with.

Closed back cabinets do not reintroduce the completely out of phase rear speaker sound to the listener. It only projects forward and is directional (sometimes very much so). And because the back is closed, the movement of the speaker creates a mechanical compliance, compressing the air when it is moving backward and creating a vacuum when moving forward. It takes much less amp energy to change directions and the amps 'energy demand' is aligned with the efficient in-motion cycles of the speaker. The result is louder, more efficient, purer note and tone. If you dial in a fantastic tone in your bedroom, it is just a few tweaks away from the same in a rehearsal room. And for stage volume wars, your amp will be much less likely to be causing your bandmates to be turning up. The downside is you may be deafening the folks sitting in the front rows in the path of your speaker's projection.

I am looking forward to other's preferences and why.

Excellent explanation.. thanks

[mozz]

Probably not viable for you due to shipping or a home project but................

You can always get a convertible cabinet. I had Tim make me one years back. That way you could buy the head of your choosing and favorite speaker.
http://www.trmguitarcabs.com/

[glasshand]

You also get Doppler effect from the back of the amp.

I agree with 99% of what you said but I don't think you mean Doppler effect. The Doppler effect is what you get when the source of a sound is moving relative to the listener. Think of how a passing sports car sounds higher-pitched as it's approaching you and lower-pitched as it's moving away.

[toomanycats]

You also get Doppler effect from the back of the amp.

I agree with 99% of what you said but I don't think you mean Doppler effect. The Doppler effect is what you get when the source of a sound is moving relative to the listener. Think of how a passing sports car sounds higher-pitched as it's approaching you and lower-pitched as it's moving away.

Example of doppler effect, courtesy of Larvell Jones in Police Academy.

[tonebender]

I cut the back panel in half on one of my old Marshall 4x12 cabs years ago and would open it up when needed.

[andrewsrea]

You also get Doppler effect from the back of the amp.

I agree with 99% of what you said but I don't think you mean Doppler effect. The Doppler effect is what you get when the source of a sound is moving relative to the listener. Think of how a passing sports car sounds higher-pitched as it's approaching you and lower-pitched as it's moving away.

Thanks and yes, I meant Doppler. If you are the audience listening to only an open back amp, the Doppler effect is present because of the sound from the front of the amp combining with the out of phase in the back of the amp, which changes with distance. Accordingly, as the listener moves, so does the tone of the amp. Now if that movement was as fast as a moving ambulance, that change would be more dramatic. But same physics involved.

[Rollin Hand]

Interesting discussion. WRT closing the back of a combo, I would make sure that the cooling needs of the amp get considered, because I'd bet the designers were counting on that air getting in.

I have run my Peavey Classic 20 with its back against the wall for years. One night, I took it somewhere to play, and in an open area, it had WAY more mids than normal. The wall focused things and made it sound fuller and bassier. Without the wall, I had to cut the mids in half.

And my phone replaced "mids" with "kids" in this post, which made it read really weird.

[mozz]

Cut the kids in half is a NJ duo band.