Speaker power ratings??

APB_4

New member
I've got a couple of questions about speakers:
1. How does the power rating for speakers work? You're supposed to get the same or a higher rating than your amp right?
2. What should I put in an extension cab for a Marshall JTM30? How many?
 
Re: Speaker power ratings??

The speaker rating determinates the maximum power the speaker should be handling so it doesn't blow (most quality speakres handle a bit more than that tho... i think ;) )
Many guys say Greenbacks are the best choice for Marshalls... allthough it will depend on what music you like to play...
How many speakers does your cab have?
 
Re: Speaker power ratings??

Currently it doesn't have a cab, it's a 1x12 combo but I was just thinking about an extension cab that I might make or buy sometime in the future. I was thinking either 1 or 2, 10" or 12" would probably work best. It needs a 16ohm load and is a 30Watter.
 
Re: Speaker power ratings??

As far as what you're hearing is concerned, the higher the power rating on your speakers, the more headroom you have before they start to distort. In other words, if you've got a 30 watt amp, if you used a 35w speaker you may start to hear some crunch in the speaker with the amp cranked. If you used a 100w speaker, it'll ring just as clear as the amp will let it.

10s or 12s? If you use a 12, you'll potentially get a better bass responce but will lose some of the punch or attack of a 10 inch speaker. You could always mix and match them, too.

How many? Well, that depends on the impedance (in ohms) of the speakers and whether they're in series or parallel. Two 8ohm speakers wired in series will get you 16ohms. That's probably the simplest combination, but there are so many more you could use.
 
Re: Speaker power ratings??

Thanks for the info. How many speakers do you think a 30 Watt amp could push though? Presumably you start losing volume after a certain number of speakers.
 
Re: Speaker power ratings??

As long as you match the impedance of the speakers to the impedance on the amp, you'll have no problems. If you had an amp with a 100ohm output, you could connect 100 - 1ohm speakers in series and not lose anything (this would be ignoring the impedance of the wire, and that much wire would make a pretty big difference).
 
Re: Speaker power ratings??

Thanks Jackson, I was just looking through the manual and it says it will deliver 30 Watts into 1 or 2 16 Ohm speakers. Does this mean if I ran the internal speaker and a 2 speaker cab I would not get 30Watts of power going into each speaker?
 
Re: Speaker power ratings??

Are those the exact words it used? Unless it is automatically sensing the impedance of the speakers (or maybe it has a toggle switch somewhere) it wouldn't be advisable to do that way. I assume it only has one external cabinet jack.
 
Re: Speaker power ratings??

Yes just one external jack. Here is the entire 'Note:'
"The JTM 30 will deliver 30 Watts into either one or two 16 Ohm speakers, ie 16 or 8 Ohm total impedance. The unit should not be driven into a load of less than 8 Ohms."
 
Re: Speaker power ratings??

That is what I was thinking, about the last statement... 2 16 ohms could be 32 ohms... that is a HUGE difference and could cause problems...

I am in the same situation as APB4, but I am going a different route.. I have a 112 Fender Hot Rod Deluxe that REALLY sounds sweet, but loses some of the bottom end when I hit the Disto... I am desiging a 115 cab that will go directly under it to help in the bass department. I understand the properties of impedance, but would it be advisable to put a crossover in between to help the lows go to the 15 and the highs to the 12?

Hope I am not hijacking, just thought I'd piggyback this thread instead of starting a similarly new one!

Thanks,
Allen
 
Re: Speaker power ratings??

No problem gordon it's all good. The internal and external sockets on my amp must be connected in parallel which surely means as long as an external cab makes up 16Ohms it will match the impedance I'm just wondering whether there will be enough power.
 
Re: Speaker power ratings??

With two external speakers, there would still be plenty of power on tap. Look at it this way... Your output is not always 30 watts. At lower volumes, the output might be more like 5 watts. All that means is that there is less volume and a long way to go until you start to notice distortion from the speaker cones.

If the amp can run both 16 and 8 ohms externally, I think you'd be safer with a 2x12 cab with 2 8 ohm speakers wired in series for a total 16 ohm load. Amp is not going to care how many speakers you've hooked up to it so long as the loads are properly matched. In reality, you could run 4x12 (16 ohm drivers) with an output of 16 ohms and the amplifier wouldn't have a clue as to the number of drivers it was pushing.

Running multiple speakers will increase your cabinet's headroom and more than likely beef up your sound.
 
Re: Speaker power ratings??

gordon_39422 said:
I am in the same situation as APB4, but I am going a different route.. I have a 112 Fender Hot Rod Deluxe that REALLY sounds sweet, but loses some of the bottom end when I hit the Disto... I am desiging a 115 cab that will go directly under it to help in the bass department. I understand the properties of impedance, but would it be advisable to put a crossover in between to help the lows go to the 15 and the highs to the 12?

I am unfamiliar with the output of the HRD. Are you planning on replacing the 12" speaker as well? How are you proposing to wire this up? You could "win back" your bottom end and minimize the possibility of headroom loss at high volumes simply by changing the existing speaker. The issue could also be internal to the amplifier and not actually an issue with the driver.

Theoretically, you could place a crossover in front of the speakers in a 12 + 15 set up, but I'd be concerned with how that might affect the tone (although, it does seem that a tone change is exactly what you're after). Essentially what you are proposing is a componant set, and it would be interesting to see how guitar loud speakers react to that. I have no idea where you would begin to set the crossover frequency, either. My guess would be in the 150 hz area would be a good place to start, and work your way up from there.

Anyway, I'd recommend trying a different 12" driver in the combo first, then think about adding the 15" if that doesn't do it for you.
 
Re: Speaker power ratings??

Well said, Mike.

As for the crossover, I don't think it would be very beneficial. Your 15 inch speaker can handle some pretty good highs and your 12 can handle some decent lows (though not enough, obviously). But I don't have a whole lot to base that statement (not needing the crossover) on, so you might want to look into it more. I know Gibson combined speaker sizes in some of their cabs. ;)
 
Re: Speaker power ratings??

Just a few thoughts:
If you use a Passive crossover, you more than likely will lose a fair amount of power, passive crossovers eat a lot of wattage to operate.
One other note;
speakers are usually rated with a one watt @1 meter standard. In the case of the Celestion Greenback for example, 1 watt @1 meter equals 97db of sound. In order to increase db by 3, it takes twice as much power, so: 2watts would gain you 100db,4 watts=103db etc. The average rock concert is usually between 110-120 db.
 
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