Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Cabinets-Speakers => Topic started by: jeff on April 02, 2011, 01:02:27 pm
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What are the pros and cons of using series/parallel VS. parallel/series?
Which is more common for guitar cabs?
Assuming each speaker is 25W does either way give a 100W cab?
Is there any advantage of one over the other aside from sound? As far as sound it seems easy enough to wire a switch that connects/disconnects the two wires that go from + to - between each speaker so I'll try that to see which I like better. If there is a significant difference in sound maybe a P/S S/P swicth could be a cool feature on a cab. Anyone ever try this?
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According to Gerald Weber, there's a difference- According to everyone else, there aint.
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The one thing I can see is if you blow one speaker, one set up you'll still have 3 going.
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IRRC I experimented with the alternatives in a Super Reverb build and I couldn't hear any difference between those two wiring choices.
I could hear a difference between speaker placement and pairing though (two Weber 10F150-T and two 10A125 speakers). Not a monumental difference, but I'm pretty sure I heard it :wink:
HTH
Chip
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The one thing I can see is if you blow one speaker, one set up you'll still have 3 going.
Yes. Ditto to Freshstart, operationally. But if operation partially fails, the wiring differences matter. According to Tom Mitchell, "How to Service Your Own Tube Amp": no one uses series or parallel-series in a 4 speaker cab (I'm sure he's exaggerating). The reason is as Jeff says above. The drawbacks are the impedance of the amp does go up, but only by a factor of 1.5X, not 2X. And the sole remaining speaker in the damaged pair will be working 2X as hard as the other 2 speakers combined; i.e., it will be doing 4X the work of one speaker. So it too is a candidate for failure. But this still is preferable to the other wiring methods.
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Hoffman recommends the series of parallel speakers if I'm reading his diagram right:
http://www.el34world.com/charts/Charts.htm (http://www.el34world.com/charts/Charts.htm)
Although if one speaker blows, it might well take its mate with it for the reasons JJ explained.
Cheers,
Chip
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I'm visiting my brother in TN right now but I want to try a SP/PS switch when I get home. It seems as simple as a stsp switch connection the two speaker sets together where they join in series. Since the ohms isn't really changing , 8 ohms either way, can this be switched while playing without hurting anything for A/B-ing?
The reason I really want to try it is maybe there IS something to it. I only think this because all the old Marshalls were wired series parallel. Wiring it the other way would save one wire and two terminal connecters. Not huge savings but multiplied by every cab they ever made would add up to some dough. I would think if it was the same either way, in mass production they'd do it the cheaper way. Something tells me there has to be some advantage to it. Maybe just protection as jjasilli stated but if it's so simple to try, why not?
-EDIT-After thinking about what jjasilli wrote some more, it makes sense. If you're going to blow your cab you're going to fry two speakers either way. One way, after the first speaker blows half the wattage is split between the reamining two. But the other way once one blows, one of the remaining three jumps on the grenade for it's buddies and takes two thirds the power giving the other two a break having to only handle one sixth.
So for example if you have 150W amp into your 100W cab, right away each 25W speaker is stressed out with ~37W. Once one blows either one speaker is disconnected from the circuit while two speakers get 75W, stressing them both out until another blows -or- one gets 100W and two get 25W, easing the strain on the survivors until the other speaker blows.(not taking into account the change in wattage due to the change in load)
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What are the pros and cons of using series/parallel VS. parallel/series?
I can't think of a legitimate electrical reason for a difference between them.
IRRC I experimented with the alternatives in a Super Reverb build and I couldn't hear any difference between those two wiring choices.
I think I also tried it after reading one of Weber's books back in the late 90's. I couldn't hear a difference either.
... One way, after the first speaker blows half the wattage is split between the reamining two. But the other way once one blows, one of the remaining three jumps on the grenade for it's buddies and takes two thirds the power giving the other two a break having to only handle one sixth. ...
No matter which way you slice it, if a speaker blows, its mate will be overstressed if you continue to crank full power through the cabinet.
It might be worth noting that in the Marshall 100w cabinets (at least the one I used to own, with "100" in the corner), they used 30w Celestions, not 25w Celestions. They probably wanted some breathing room to guard against blown speakers.
... all the old Marshalls were wired series parallel. Wiring it the other way would save one wire and two terminal connecters. ...
The way you have Series/Parallel drawn, it would take 4 wires, plus the two running from the speakers to the jack. Right-side negative runs to positive, ditto for left (2 wires). Now bottom negatives connected, ditto for top positives (2 wires).
Your drawing for Parallel/Series would require 5 wires, plus the two running to the jack. Top pair gets positives/negatives connected (2 wires), ditto for bottom pair (2 more). Now the top pair has to be connected in series with the bottom pair (1 more wire), then run wires to the jack.
So Parallel/Series actually takes extra wire. That's most likely the reason for Marshall's way. Your way might be different if the speakers in your cabinet were not equally spaced That is, you might find a means of arranging the speakers such that even with 5 wires, the total length of wire is shorter when wired Parallel/Series, and that would change your economic incentive to wire the other way.
My only problem with Weber is even when he's saying something true, there's too much voodoo and hype surrounding it. His books were very valuable to me when I was starting out (no Merlin, O'Connor yet, and the old books couldn't be found online or in stores/libraries). However, I had to grow beyond the things he says to really understand how amps work.
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I think I also tried it after reading one of Weber's books back in the late 90's. I couldn't hear a difference either.
That seems to be the consensus, but I'm the type of guy that won't be satisfied until I experience it myself. I have great respect for you HBP and learned much from you over the years. I fully expect not to hear a difference but I won't be satisfied untill I do it.
Is switching on the fly a problem, or should I shut the amp off when switching? I'm just connecting one wire from junction of two speakers of each set- 8 ohms to 8 ohms- so no variation in load as switch is thrown.
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...Is switching on the fly a problem, or should I shut the amp off when switching? I'm just connecting one wire from junction of two speakers of each set- 8 ohms to 8 ohms- so no variation in load as switch is thrown.
Check with the switch manufacturer, to see it switch is 'make before break' or 'break before make' type switch. There are both kinds available. You can't use a 'break before make' switch, with power on.
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Is switching on the fly a problem, or should I shut the amp off when switching?
There's no problem if you stop playing and no sound is going to the speaker when you switch. No need to turn the amp off. But there is a problem if you have someone else switch while you play, or use a footswitch while you play. Putting a switch on the cab to experiment can help you decide if there is a sonic difference that you can hear, but it may be an invitation to disaster to play with it.
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That seems to be the consensus, but I'm the type of guy that won't be satisfied until I experience it myself.
I'm cool with that. In fact, I encourage you NOT to believe me until you try it. It's the only way you'll really know, right?
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Check with the switch manufacturer, to see it switch is 'make before break' or 'break before make' type switch. There are both kinds available. You can't use a 'break before make' switch, with power on.
I don't understand. If I'm looking at this right I just need a SPST switch. Don't the terms MBB or BBM only apply to double throw switches, where for that split second the switch is being thrown, the commom is connected to A, disconnected, then connected to B(BBM) or connected to A, connected to both A and B, then connected to B(MBB)?
O=speaker _/ _=switch
+____________
| |
O O
|___/ _____|
O O
- __|_________|
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OK, I see what you're proposing now. There is no danger flipping that switch while playing to get and A/B sound comparision. And 'make before break' has no meaning to a SPST switch.
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OK thanks for all the help.
I'll try it as soon as I get back to MA. I doubt I hear a difference but I gotta try it. I'll use a stomp switch so I'll have no idea if I'm SP or PS to take the psycological switch up/down out of the equation. I think sometimes your eyes influence what your brain thinks/expects to hear.
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I'm back in MA. TN was great and we wound up stopping at the rock n roll hall of fame along the way. What a place!
Anyway I tried the switch and, just as predicted, couldn't hear any noticable difference. Seems so simple to wire up I don't know why I read alot of things saying one is darker than the other. Maybe perpetual superstition or overthinking, or irrational logic: Well the old cabs had a different sound and were wired different so It must be that(not the age/type of the speakers or type of amps) Or maybe that person didn't use a switch and compared from memory what it sounds like now to what it sounded like before he opened up the cab and added a wire? Or maybe my hearing isn't as good as theirs?
I don't know, but I tried it and couldn't hear a difference. Maybe there is a difference if you use mixed speakers, two of these, two of those, or maybe dogs can hear the difference, but I can't.
Thank for the help and I know, I should have listened, but with all the conflicting information I had to try it and see for myself.
Jeff
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I had to try it and see for myself.
And now you have an opinion that is based on something real, rather than just some mimicked hype. That's something you can take to the bank. I'm glad you shared 'cause I had no idea. Now I'm gonna mimic your opinion! :wink:
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I had to try it and see for myself.
And now you have an opinion that is based on something real, rather than just some mimicked hype. That's something you can take to the bank. I'm glad you shared 'cause I had no idea. Now I'm gonna mimic your opinion! :wink:
:l2: