speaker loads

[Sgt.]

I was reading in one of the trade mags. recently and the article was talking about an older Fender, I think a blackface with twin 8 ohm speakers, right, and an 8 ohm external speaker. The gist of the article was that the amp was louder with just the twins in parallel making a 4 ohm load and losing some power with an additional external cab plugged in ... can anyone figure out the approx. load with the twin 8 ohm speakers and the external 8 ohm speaker? It was somewhere between 4 and 8 and the question was why does it sound louder WITHOUT the external cab attached? You'd think it'd be more volume with the additional cab. It also mentioned that old Fenders (usually 8 ohm speakers) can tolerate the mismatch better than Marshalls ... it warned ... Marshalls DON'T LIKE MISMATCHES!!!!

Why Marshalls? Why? How come Marshall amps won't tolerate mismatch like a Fender? Does that mean you MUST match the speaker impedance exactly to the amp like 16 ohm to 16 ohm for example and Fender can tolerate the reduced impedance you get when adding additional cabs (even thought they'd all be 8 ohms)?

I wondered about this logic that the overall volume was reduced with the more as many cabs you ran from the amp. Seems to me I run two separate 1x12" 8 ohm cabs in parallel from an Ibanez TSA15, two 8 ohm cabs makes a 4 ohm load. It seems to me that the overall volume is louder when just one of the cabs is plugged in ... now I may be a big dummy, considering that one speaker is 80 watts and the other just 30, and the 80 alone sounds louder, but ... I would think together they'd be a little louder than just the 80 watt, not so.

[rct]

Basically:

 

The output transformer on an amp determines the impedance, or resistance it would like to see. We measure that impedance in ohms.

 

The transformer has taps on it. 8, 16, 4, sometimes 2. From this tap goes the speaker out.

 

The cabinet shows the transformer the correct resistance. Incorrect resistance, over a period of time, can wreck the transformer, usually in the form of heat building up.

 

When I was a kid, Marshalls had fairly crappy transformers, and we did blow them up, even with the right resistance in our silly stacks o' doom. Fenders generally speaking had better transformers in them, and stood up to slight errors in impedance.

Traynors had good transformers, we used them too.

 

Most amps, most of the time, can tolerate impedance mismatch pretty well, for the average gig, for a whole lot of average gigs, provided the mismatch isn't too great. I use a Princeton Recording amp these days, it expects to see 8 ohms. I use the speaker in it and an 8 ohm 2x12 cabinet with a y cable, so it is a mismatch. But I don't care, I won't kill it.

 

And finally, adding speakers will not add volume, it will add pants flapping air movement, and it will add perceived size of sound. Your 15 watt amp I'm assuming by the name of it will not get louder with more speakers, but will move more air and create the impression of bigger sound, especially standing right in front of it. The wattage of the speakers doesn't mean much in all of this, only that it is better to over drive them than to under drive them for the most part.

 

I'm not an engineer, so someone will help fill the holes I've left. Meantime, there are pretty good books about it all, and there are websites that help explain it. Is Gerry Weber still around? Send him an email, he'll tell you more than you'd ever want to know about speakers.

 

If you want more volume, get more amp. If you want more space, get ore cabs and move them apart. If you want good small venue sound, get a decent amp, don't need much more than 30 watts or so, point from the side at you across the band, stick a decent mic in front of it for the PA out front. As you age you will be more and more amazed at finding the perfect volume, it usually isn't nearly as high as you once thought it was.

 

Good luck bro. It's a long road and often confusing.

 

rct

[Sgt.]

In a perfect world I could mismatch speakers, an 8 ohm and a 16ohm and it would work ... it doesn't and a tube smoked out! ha ha. I asked Fender expert about matching an external speaker to a 4 ohm Champion 600 and the best advice was that most of the Fender cabs were 8 ohm and that was a good match. I may be theoretically loopy to a real electronics guy, but we all have our own thinking ... I would never match a 4 ohm speaker with a higher rated amp ... melt, but matching a higher rated speaker to a lower rated amp, for example a 4 ohm amp to an 8 ohm speaker, I would think that a perfect match 4 ohm to 4 ohm would be letting the full power through the speaker, an 8 ohm driver only half power (as we perceive it, hear it), and a 16 ohm a quarter. Really I wanted someone to tell me that plugging in a 16 ohm cab and an 8 ohm cab would just mismatch but it smoked a tube. Maybe I plugged them in to the wrong amp holes, I've got 1 for 1x16 ohm, 2x16 for an 8 ohm load, 2x 8 for a 4 ohm load, or 1x4 ohm. Generally by trial and error (obviously I had to satisfy my own curiosity one rainy afternoon) you must match speaker impedances. The othe question arises (that was covered in another thread) is why we have different impedances? Why don't we just have a standard 8 ohm? It was answered that the windings on the 16 ohm speaker are more and thinner and therefore sound brighter. So there is a choice.