Trying to understand speakers

Coma

Coma

Well-known member
Can anyone direct me to a good introductory source? I'm trying to just learn the basics of speaker power rating and resistance (impedance?). If you've got a 4x12 loaded with G12H speakers, and each speaker is rated for 20W output, why aren't they blowing up when played through a 100W tube amp?

And are there factors beyond ohm to take into account when matching cabs and amps (beyond preferences in tone)?

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Re: Trying to understand speakers

Let’s say you’re playing your amp really, really loud and it’s delivering 100W. If you have four identical speakers in a balanced load configuration, they will all be getting the same amount of power. In this case, 25W per speaker. That might be too much for a 20W speaker — it depends on frequency content and duration of the signal.

But consider this: You can play this combination stupid loud using just a fraction of the 100W available. Let’s say you’re using 50W. Each speaker is getting 12.5W. That shouldn’t blow anything up.
 
Re: Trying to understand speakers

Let's start with the basics: Sound comes out of speakers.
 
Re: Trying to understand speakers

Little Pigbacon said:
Let’s say you’re playing your amp really, really loud and it’s delivering 100W. If you have four identical speakers in a balanced load configuration, they will all be getting the same amount of power. In this case, 25W per speaker. That might be too much for a 20W speaker — it depends on frequency content and duration of the signal.

But consider this: You can play this combination stupid loud using just a fraction of the 100W available. Let’s say you’re using 50W. Each speaker is getting 12.5W. That shouldn’t blow anything up.
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Ok, to continue down this path.

One of my cabs is loaded with 4 speakers. Each rated at 8 ohm. But cab is rated as 16 ohm. If I remember my 8th grade electronics correctly, wiring the speakers in serial would give you 32 ohm of resistance. So how are those speakers wired?

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Re: Trying to understand speakers

Coma said:
Ok, to continue down this path.

One of my cabs is loaded with 4 speakers. Each rated at 8 ohm. But cab is rated as 16 ohm. If I remember my 8th grade electronics correctly, wiring the speakers in serial would give you 32 ohm of resistance. So how are those speakers wired?

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Are those manufacturer’s ratings? Usually when you have four of the same speaker in a cab, the result is either the same as the impedance of each speaker, or one-quarter of it.
 
Re: Trying to understand speakers

Because:
1) 25% over isn't quite so extreme as to immediately blow
2) rated power is how much the manufacturer felt they could stand behind, for heavy duty service, without angering people
3) actual output wattage is more related to how far your gains and volumes are cranked

Don't push it, though.... and if you've got an amp circuit where you can pull one pair of power tubes, read up on how that works and do that instead. Or, for Mesas or other amps whose manufacturer says they hold up to impedance mismatch, wire the cab 8ohm and plug into an 4ohm tap, or wire cab 16ohm and plug into a 8ohm tap.
 
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Re: Trying to understand speakers

Coma said:
Ok, to continue down this path.

One of my cabs is loaded with 4 speakers. Each rated at 8 ohm. But cab is rated as 16 ohm. If I remember my 8th grade electronics correctly, wiring the speakers in serial would give you 32 ohm of resistance. So how are those speakers wired?

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Impossible.

8ohm speakers in a 4x12 always makes 8 ohms for our purposes (because 2 ohms or 32 ohms, the other options for wiring a quad of 8 ohm speakers, don't work with guitar amp applications)

Now 16ohm speakers, those can be wired for 4ohms or 16ohms (or 64 ohms, but again, that doesnt work with guitar amps)


Best guess? Your cab is labelled wrong, reloaded, or, if you're actually reading ~16 ohms tested (around because the 8 or 15 or 16 you see on speakers are "nominal" ratings, not actual measured numbers), then you only have 2 speakers wired up
 
Re: Trying to understand speakers

Here's the manufacturer's info page. Maybe I misread it?
fd745faa003b48c4646e8732d90bd2d3.jpg
 
Re: Trying to understand speakers

Maybe they’re 16ohm speakers (15ohm)?
 
Re: Trying to understand speakers

Coma said:
Here's the manufacturer's info page. Maybe I misread it?
fd745faa003b48c4646e8732d90bd2d3.jpg
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Your quads should read ~6.6 ohms for 8ohm nominals, or either ~3.0 or ~12.1 for 16ohm nominals... not actually 16 ohm, well, ever.

Get a tester and see what's what.
 
Re: Trying to understand speakers

The general specifications state that the speakers you can purchase are either 8 or 15 ohms, NOT what your actual speakers are. You need to open up your speaker cab and read or measure which impedance factor of each one of your speakers are and observe how the speakers are wired. A digital multimeter will indicate whether the speaker impedance is closer to 8 or 15 ohms, they may not be exact.
 
Re: Trying to understand speakers

Remember also that the rated nominal impedance of a speaker is the sum of the DC resistance and the reactive impedance (a function of the speaker’s inductance, the frequency being measured, and a certain amount of magic). Your meter in DC resistance mode won’t be able to see the frequency-dependent component of the impedance, so you’ll probably be measuring something at least a few ohms lower than the rated impedance.
 
Re: Trying to understand speakers

Sounds like TS is mostly concerned with electronics and loading schemes -but after everyone finishes elaborating on the other important factors such as the magnet size, coil size, sensitivity, range, material, impedance and power rating of a speaker etc etc (which is a lot to learn)......then you can throw in the stiffness of the speaker suspension and the type of enclosure which will then render everything you thought you knew up to that point pretty moot or incomplete

I used to work for the highest end of studio reference monitor companies and did R&D -some daysI would test individual raw speakers in an anechoic chamber and match then -what fun looking back

it's a bottomless worm hole!
 
Re: Trying to understand speakers

Adieu said:
Because:
1) 25% over isn't quite so extreme as to immediately blow
2) rated power is how much the manufacturer felt they could stand behind, for heavy duty service, without angering people
3) actual output wattage is more related to how far your gains and volumes are cranked

Don't push it, though.... and if you've got an amp circuit where you can pull one pair of power tubes, read up on how that works and do that instead. Or, for Mesas or other amps whose manufacturer says they hold up to impedance mismatch, wire the cab 4ohm and plug into an 8ohm tap, or wire cab 8ohm and plug into a 16ohm tap.
Click to expand...

My Mesa manuals say the opposite. “Safe mismatch” is when speaker load is greater than the output tap - so, you’d run a 16ohm cab off an 8ohm tap, or an 8ohm cab off a 4ohm tap.


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Re: Trying to understand speakers

VinceT said:
My Mesa manuals say the opposite. “Safe mismatch” is when speaker load is greater than the output tap - so, you’d run a 16ohm cab off an 8ohm tap, or an 8ohm cab off a 4ohm tap.


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Why not to just match the impedance?

I've never understood the whole "Safe mismatch" thing. It's very simple and easy to fix the impedance right. Running mismatched impedance is just careless stupidity in my opinion.
 
Re: Trying to understand speakers

Jacew said:
Why not to just match the impedance?

I've never understood the whole "Safe mismatch" thing. It's very simple and easy to fix the impedance right. Running mismatched impedance is just careless stupidity in my opinion.
Click to expand...

Agreed. I was just pointing out what Mesa say in their manuals.


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Re: Trying to understand speakers

Mesa mentions the impedance mismatch thing in the manual for my Blue Angel. It basically says that it isn't very sensitive to mismatches (4 or 8) and use what sounds best. I am guessing delivering too much power causes some element of speaker break-up, but I don't play that loud. So, I just keep it on the matched setting.
 
Re: Trying to understand speakers

To add: speakers are a hugely important part of your rig... YUUUUUGE.

They are the final "EQ filter" when playing "live" (not mic'd up or DI'ing, etc).

Speakers apply a hi and lo pass to your amp's signal; along with their own individual (per model) speaker "EQ".

Change a speaker and your tone can drastically change even if you're using the exact same gear for the rest of your rig.
 
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