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Discussion Starter · #1 · (Edited)
I am not a huge expert on speakers and cabs, really just starting to explore.

I've recently acquired a pair of mint 15ohm Celestion G12 Alnico Golds from a great GC member and just got a chance to install them into a custom cab that I acquired last year. The cab is 3/4" solid pine and the speaker baffle is 3/4" Baltic bitch plywood. The cab was originally set up as a large 1x12, but included a 2x12 baffle which I grill clothed and installed. I have not (yet) heard this cab with another speaker. On the pictured jack plate, double all impedances -- the fancy jack plate is only available labelled for a pair of 8ohm speakers.

The issue is that this setup is super (super!) bright. It is also very directional -- I can drastically change the spacial sense and sound by shifting my head a few inches when 6-10 feet in front of the cab. I am using the "4ohm mono" jack, which in this configuration is 2x15ohm in parallel so about 7.5ohm. I am using multiple amp heads on their 8ohm outputs. I have another 8ohm 2x12 cab available for comparison and it is completely different with all amps, in same space, at all volumes.

Any explanations or advice? Is this "normal" (not at all what I was expecting from this setup from my readings). Is open back the right way to run these speakers? Is the root cause the cab or the speakers? I don't think there is anything wrong with the speakers as they otherwise sound clear and look fantastic. Is this just the nature of efficient speakers?

Note that all of this testing is in a medium-sized basement, but it is finished, carpeted, with soft furniture, drywall walls, and plaster ceilings (no hard concrete surfaces) and I have turned it up for testing -- the brightness is there at all levels.










 

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Maybe. Golds are a bit bright, but usually nothing offensive. They do have a lot of upper mid as well that can get a bit harsh with certain amp/cab configurations. What amp are you using with it?
 

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Discussion Starter · #4 ·
I've tried three amps: Mesa Boogie V:25 on all power levels, 1967 silver face circuit Bassman, Peavey Classic 20MH on all power levels. All consistently bright (yes, the Mesa can sort of dial it out, but the settings are completely different from any other cab).
 

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Discussion Starter · #6 ·
I've heard of and understand the physics of break-in, but have never heard a before and after break-in to form any intuition.

I don't know about a previous cab: I got the speakers separately and have never heard this cab with another speaker yet.

I will be shuffling things around cabs to see what component the brightness follows, but thought I'd ask to formulate a starting hypothesis.
 

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Discussion Starter · #8 ·
Out of phase: that is an interesting idea, I will double check. That jack plate has a specific colour wiring (L- L+ R- R+), so it should be hard to get it wrong, but not impossible. Are the symptoms consistent for out of phase?
 

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You'd typically get a big loss of bass and volume and the cab would seem very thin sounding. An easy check- disconnect one speaker if it sounds much fuller then they're likely out of phase with each other.
 

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Discussion Starter · #12 ·
Let's save @greco's fingernails ...

... that was it, out of phase!

I got the right speaker backwards, it was a late night. It is still bright, but not ridiculous and actually quite dialable. Actually, I liked the sound of the single one quite a bit as well, might eventually do that instead as a 15/16ohms cab.

@gtrguy, if you were nearby, I'd buy you a beer, but as is, it will have to be a virtual one:



Awesome, thanks everyone! I'll leave the thread up as: a) monument to my stupidity, b) diagnostic info for future generations, and c) hey, NCD/NAGD :)
 

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good catch!

I always put a 9v battery across the speaker jack/cable with any new cab I get or wire...you will see if all the speaker cones move in the same direction. easy to check phase

sometimes speaker tabs are coloured wrong too! always good to verify using the battery
 

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Well, now you know what an out-of-phase cabinet sounds like. It'll be quicker to sort it out next time.

And don't worry about the 15 ohm nomenclature. If you've ever seen an impedance graph, you'd know that neither 15 or 16 is that precise, it is supposed to be the lowest impedance throughout the frequency range and might be for only a very small part or two of the speaker's operating range. The difference is not really worth thinking about. Think of them as 16 ohm speakers.
 
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Just a note, if you ever want to use the left speaker in mono by itself, you can just plug any cable into the right mono jack without connecting it to something else. (if you decide you like running one speaker at a time, then you can at least use them evenly) It doesn't even need to be a cable, just the plug will work too.
 

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Nice catch indeed. Nice cab too.
To get still better low end, closing the back will get you more umph out of those speakers. Easy to do by adding a plank in the opening.
 

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Discussion Starter · #19 ·
@troyhead: Yap, that's how I did the original out of phase test. Those jack plates are pretty nice and the price really wasn't crazy. Only annoyance is the labelling, but I'll just use a label maker label on top. Oh, and the series jack is never to be used with two 15/16ohm speakers, so need a dummy plastic filler plug to reduce risk. Thanks for the original recommendation on that jack plate.

@BGood: I thought Alnico Golds were specifically recommended for open back? But I probably will try the filler at some point. Although I don't think I could ever match that tolex exactly if I ever wanted to keep it that way. It might make sense to try an entire full back in a contrasting tolex instead. Hobby projects ... probably no actual time.
 

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@BGood: I thought Alnico Golds were specifically recommended for open back? But I probably will try the filler at some point. Although I don't think I could ever match that tolex exactly if I ever wanted to keep it that way. It might make sense to try an entire full back in a contrasting tolex instead. Hobby projects ... probably no actual time.
Ah ... right ... didn't think about matching Tolex.
I have to say I don't really care how things look, especially from the back. As long as it sounds the way I want.

Guitars are another matter, you hold them in your hands, caress them. Cabs are on the ground, over there in the back.

These are two of my home made cabs. No Tolex, no dovetail assembly or fancy grill. 2X12" has window screen to minimally protect the cones. 1X12" has chicken wire. Jack plates are made from recycled metal parts.

Even my pedal board is a recycled pine plank, with pedals tied down with Tie-Wraps, no expensive Velcro needed and much more stable.



 
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