A & B or B & B

KraftyBob

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First band practise with the new setup and it sounded amazing! Tight, enought low end and great dynamics. Love it! Still thinking about changing speakers to one of the cabs tho... always on the prowl for new music stuff : D
If you get the Greenbacks maybe try installing them in a cross pattern in both cabs instead of one cab of Greenbacks and the other T75’s. This way if you ever play a gig where you only need one cab you still have the mix of speakers.
 

Fernieite

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I don't have a preference, but I was surprised to find out that my 1965A (4×10) cab doesn't have a slant baffle like a 1960A!

It looks like a normal slant cab, but the speakers are actually on a flat baffle like a regular B cab. It has a piece of wood on the front of the baffle to make it appear that the two top speakers are pointed upward. (However, they are not)

So, technically my A & B 1965 stack is sort of a B & B. :)

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Seanxk

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There is a difference with the A & B cabs, the obvious is the forward projection of the A, but it's what's happening inside, with the A cab the internal bass frequencies of the top two speakers are projected down and into those of the lower two speakers, result, cancellation/loss call it what you will, technically the A cab is a sonic ( on paper ) disaster and an awesome looking cab, but it actually seems to work.

But does it really matter? I prefer the B cab though and the added bonus is my beer sits on the cab and not on my amp.

Now take a different Celestion like a 25M ( as opposed to a T75 ) and the difference is greater in either cab, or for an even greater change play a dry cab and a damp cab,.....'' a dry T75 will utterly out class a damp pre Rola 25M, Full Stop ''
 

Browneyesound

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I prefer the A cab with my JTM45, and the B cab with my superlead. So you need both.
 

william vogel

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Horse Hockey! You can't have an out of phase set of speakers running the same in phase speaker on the bottom cab. Two reasons, 1) the signal to the speakers would cancel out electrically, 2) the coils would likely burn out before you could say oops! not to mention the OT would melt!

Its equivalent to taking the positive or hot voltage from the wall AC and connecting it directly to the neutral.

You can have an acoustic difference of phase if that is what you mean. In this case some would amplify and some would partially attenuate. But you never get a full cancel because the air in the room has space to deflect from each other.
Please explain your theory of damaging the output transformer due to speakers being wired out of phase. There’s no magnetic or electrical coupling between the speakers. The acoustic cancellation would definitely occur but not silence as you said. The speakers unless possibly being dual voice coil and wired out of phase would be the only possible chance of any interaction that could cause problems with the output transformer. The individual speakers are going to move independently of each other and have no electricity effect to each other. In fact in a transformer that has multiple windings you can wire windings in series, phase correct to increase voltage and in series phase reversed to reduce voltage and no harm occurs. An example being taking the 5 volt secondary winding and series connecting it to the primary 115 volt phase correct. This will create a 120 volt primary and lower secondary voltage. Same scenario, hook the 5 volt secondary in series phase inverted to the 125 volt primary winding and it will bring the primary winding effectively to 120 volts vs 125 volts to increase the secondary voltage. I’m doing this with Hammond power transformers right now to get 120 volt primary from their 200 series power transformers because the primary is wound with a 115 tap on a 125 volt primary and my mains voltage is 121 volts. 125 winding makes the 6.3 low and 115 tap makes 6.3 ( and everything else) high. I don’t use the 5 volt winding because of solid state rectifier and this solution is perfect.
 

XTRXTR

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@william vogel
How can you have the bottom cab in phase and the top cab out of phase from the same OT two jack parallel output? e.g. two 16 ohm cabs, 1960A and 1960B opposite phase same OT on the 8 ohm tap. Is this not the same as connecting the two 8 ohm output wires (common to 8 ohm) to each other in a dead short? Tip to sleeve shorted?

What happens to the current inside the OT secondary 8 ohm tap then? What happens to the coils of the speakers?

Perhaps I have some misinterpretation of how it all works. From my point of view the AC power dissipation would collide inside the OT secondary heat up and melt the insulation to a short and perhaps the coils of the speakers if the primary becomes shorted from the heat as well sending DC to the speaker coils.

If am I wrong I would certainly listen to how and why.
 
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william vogel

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@william vogel
How can you have the bottom cab in phase and the top cab out of phase from the same OT two jack parallel output? e.g. two 16 ohm cabs, 1960A and 1960B opposite phase same OT on the 8 ohm tap. Is this not the same as connecting the two 8 ohm output wires (common to 8 ohm) to each other in a dead short? Tip to sleeve shorted?

What happens to the current inside the OT secondary 8 ohm tap then? What happens to the coils of the speakers?

Perhaps I have some misinterpretation of how it all works. From my point of view the AC power dissipation would collide inside the OT secondary heat up and melt the insulation to a short and perhaps the coils of the speakers if the primary becomes shorted from the heat as well sending DC to the speaker coils.

If am I wrong I would certainly listen to how and why.
It’s not the same as a direct short. Imagine hooking up two electric motors in parallel but on positive to positive negative to negative and the other positive to negative (the motor wire terminals) and negative to positive. We’ll use DC in this example and it will represent the positive flow of AC current. One motor will turn clockwise and the other will turn counterclockwise. They don’t represent a short circuit but they represent a load but their output is opposite of each other. With the speaker example and an AC waveform the correctly phased speaker cone excursion is correct and it’s cone travels outward away from the magnet structure and the reverse polarity speaker cone excursion travels inward toward the magnetic structure. This is the reason we have sound cancellation because the air displacement of one speaker is absorbed by the opposite displacement of the other speaker. The motor structure of a speaker has the same impedance whether it’s checked phase correct or reversed and checked phase reversed. The impedance’s are still present exactly as they would be connected in the circuit but the orientation of their output is opposite each other. If they were housed in the same sealed cabinet the speakers could be observed vibrating but sound output would be minimal because the internal cabinet pressure would be 0 and outside of the cabinet nearly no sound.
 

MoonKnighter

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It’s not the same as a direct short. Imagine hooking up two electric motors in parallel but on positive to positive negative to negative and the other positive to negative (the motor wire terminals) and negative to positive. We’ll use DC in this example and it will represent the positive flow of AC current. One motor will turn clockwise and the other will turn counterclockwise. They don’t represent a short circuit but they represent a load but their output is opposite of each other. With the speaker example and an AC waveform the correctly phased speaker cone excursion is correct and it’s cone travels outward away from the magnet structure and the reverse polarity speaker cone excursion travels inward toward the magnetic structure. This is the reason we have sound cancellation because the air displacement of one speaker is absorbed by the opposite displacement of the other speaker. The motor structure of a speaker has the same impedance whether it’s checked phase correct or reversed and checked phase reversed. The impedance’s are still present exactly as they would be connected in the circuit but the orientation of their output is opposite each other. If they were housed in the same sealed cabinet the speakers could be observed vibrating but sound output would be minimal because the internal cabinet pressure would be 0 and outside of the cabinet nearly no sound.
I apologize for the question a little ... naive ... but, at this point what would be the possible technical solution to solve this problem and ..... do not change / sell a 1960A cab (or in a 1960A style cab)??? All in order to make a Classic Stack 1960A + 1960B as efficient and with the best volume as possible?
 

william vogel

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I apologize for the question a little ... naive ... but, at this point what would be the possible technical solution to solve this problem and ..... do not change / sell a 1960A cab (or in a 1960A style cab)??? All in order to make a Classic Stack 1960A + 1960B as efficient and with the best volume as possible?
Just make sure all the speakers are wired in correct polarity. It’s easy to check. You use a 9 volt battery to energize the cabinet or each individual speaker with the back off the cabinet. Using a flashlight, observe the speakers. When you hook the battery positive to the speaker positive (tip) and battery negative to speaker negative (ring) all the speaker cones should extend.
 


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