AC30CC2 Closed back?

[Robmosis]

Hey guys I have a AC30CC2 with the wharfdale speakers.
I am going to upgrade with a combination of a greenback and a G12h-30.
My question is has anyone tried to close the back on their AC30?
My concern is that the amps run so hot and how much effect does the open back have on cooling.
Any opinions would be greatly appreciated.
Rob

[Robmosis]

Anyone have an opinion on this?
I know it is a simple question but It has caught my curiousity.
Please share your opinions, I will be greatfull.
Rob

[trevorus]

My AC30CC doesn't have any ventilation in the cabinet. I don't think it would hurt anything to make it a closed back, but my question is what are you trying to achieve with a close back, and is it outside the normal realm of the tone of an AC30?

[Robmosis]

I want to preserve the sound of the ac30 as much as possible, but I was thinking of experimenting with a removable close back to tighten up th bass a little.
I do not know how this will ultimately effect the tone itself but I was thinking of trying it.
Rob

[Robmosis]

by the way trevorus, what kind of beer is that?
Its hard to tell in the pick.
Heck it might not even be beer.

[Jag]

by the way trevorus, what kind of beer is that?

So ... you're a drummer?

[Robmosis]

No, Just an -->uninteligent<-- blues guitarist!!!

[trevorus]

That's actually a can of cheapo ginger ale. You'll have to let me know if you do the closed back thing. I have an AC30 with a stock Wharfedale, and a Vintage 30. I wonder how it would sound with a closed back.

[Robmosis]

I will let you know how it works.
I was actually thinking about putting a greenback and a G12H-30
in my vox.
I am looking for that green sound with more of a bottom edge.
Anyways, how does the vintage 30 sound in the amp?
Does the fact that its rated at 60w make much of a difference?
Just curious how the Wharf at 30w and the vintage react with each other?
I am not sure what the sensitivity of the Wharfs are, but I know that
the greenback is 97db and the G12H-30 is 100db, but this is a common
combination and it has good results.
Let me know how the vintage sounds with the Wharf though. I am very curious.
Peace and Great Tone, Rob
P.S what tubes do you use? I use a balanced EH in the phase inverter, tungsols in other 2 pre amp spots, and Mullard reissue EL84's in the output.
Right now I have some JJ Tesla's in the output to try them out and see how they sound when broken in a bit.
I like the JJ's but I will put the Mullards back in. I love the sound of the Mullards to much to let them sit out of the amp.
I'll keep the JJ's as a good backup.

[trevorus]

I currently have a Tung Sol 12ax7 in V1, an EHX 12ax7 in V2 and an old USA GE 12ax7 in V3, and for power tubes I am running a quad of Sovtek/Mesa relabels. It's all my local retailer had, and my original tubes were about done after 6 months of hard gigging all summer. I need to buy some JJ's and get a new rectifier. The original rectifier started arcing internally, so I borrowed a used one from a friend, a Ruby GZ34. the Vintage 30 has a bit more mid presence than the Wharfedales, but they oddly complement each other well, to my ears. It seems to give it a more dimensional sound overall. The Vintage 30 is a bit louder than the Wharf, but I think that's due to the difference in it's response curve, as I really don't know the sensitivity specs on the Wharf.

Eventually, I want to try a Weber Blue Dog Alnico, because I have heard they are a good Celestion Blue approximation. I just thing the Celestion is so overpriced.

[Robert M. Martinelli]

Anyone have an opinion on this?
I know it is a simple question but It has caught my curiousity.
Please share your opinions, I will be greatfull.
Rob

Hi Rob,
I never tried such a thing, but I think closing the back should "help" the frequencies around 500 Hz ( mid-bass ) and should "damp" the frequencies around 750-800 Hz ( mids ) IMHO.

The rationale for this :
Let's work with a sine wave and analyze the fundamental only to make things easier on my poor brain; the speaker moves back and forth, and if you close the back, when the speaker moves back the sounds hits the closed back ( about ) 0,65 milliseconds later, then it gets reflected towards the speaker and reaches it after another 0,65 milliseconds, this means that the "returning" wave will be in perfect phase opposition with any signal having a period of 1.3 milliseconds, thus "damping" it.

If the returning wave is in phase with the next "forward" wave ( thus having a period 1,5 times*1,3 milliseconds = 1,95 milliseconds ) then it will "push" the speaker to reproduce that frequency ( around 510 Hz ) with more "strength".

Hope this helps

Best regards

Bob