Watts, Ohms... what? - Jemsite
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post #1 of 4 (permalink) Old 10-17-2003, 07:02 PM Thread Starter
Join Date: Jun 2001
Posts: 344
Watts, Ohms... what?

I'm really quite ashamed of myself here, but i don't know anything about watts, ohms, and all that jazz. What i mean is, i'm getting a Rocktron Chameleon preamp, a power amp, and a 2x12 cab. The power amp i'm getting will either be a Peavey Classic 50/50, or a Rocktron Velocity 300. While shopping around online for cabs, i've found a lot of things like 'such and such cab is rated at 100 watts at 8 ohms' and things like that. What's this all about? What do i need to know about this electrical jargin? Please speak in layman's terms, i know nothing!
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post #2 of 4 (permalink) Old 10-17-2003, 09:52 PM
Join Date: Apr 2001
Location: Minneapolis MN
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100 watts at 8 ohms, I would take that as it is an 8 ohm cab and can only handle 100 watts from an amp without farting out or worse. any watt rating on a cab is how much it can take, like my Marshall 1960's are around 300watt. you want to match the cabs ohm rating with the power amp or amp. if the one you get is 8 ohms, you would make that selection on your amp. on the amp side of things, using a lower number ohm, like 4 which is about the lowest the go(except that PV 50/50 in mono will do 2 ohms) will draw the most power out of the amp.
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post #3 of 4 (permalink) Old 10-18-2003, 12:19 AM
Join Date: Mar 2001
Location: Va Beach, VA
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Watts equals power rating, ohms equals resistive load. They are two different things entirely and you have to pay attention to both when selecting an amp and speaker cabinet match.

The power rating is easy enough to get. Your 50/50 is either run 50 watts per side in stereo or it can bridge to 100 watts in mono. You need a cabinet that can handle it. Typically speakers are rated very conservatively.

Ohms is the measure of the resitive load placed on your power amplifier. Especially in a tube amplifier, matching the ohm rating of the power amp output to the speaker cabinet is critical to maintaining optimal tone and life of the power amp. Mismatches are permitted but only by running a cabinet with a higher resitive load than the amplifier. For example, it is safe to run a 16 ohm cabinet out of the 8 ohm output of an amplifier.

Conversely, it is not safe to run a 4 ohm cabinet out of the 8 ohm output of the power amplifier. This situation may fry your output transformer...a pretty expensive problem.
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post #4 of 4 (permalink) Old 10-18-2003, 07:21 AM
Join Date: Feb 2002
Location: Portland, Or
Posts: 223
Hi! Ok, layman's terms! Woohoo!

Think of it this way: Watts are not linear to db, which means that if you have a 50 watt amp, it will be loud (if you hook speakers up to it ). A 100 watt amp will not be twice as loud tho. When an amp is run toward or at it's highest output level (volume, like 10, or 11, if you have one), tube amps have been known to exhibit certain qualities that some people like. IE, smooth distortion. With a solid state amp, this "pushing hard" or "strain" tends to produce a harsher, brittler sound that most do not like. So, with a 50 watt tube head, you could get closer to the full volume output in order to obtain that "smooth sound" of AMP gain without being as loud as it would take with a 100 watt tube amp, or higher. However, even 50 watts on anything but a large stage (or an iso room) is completely ridiculous, and hance the reason things like the "hot plate" and "power soak" exist; these allow you to turn the volume of the amp (head) all the way up, or at it's sweet spot, and use the controls on the "device" to control the actual "loudness."

Next up is Ohms. Ohms are good for many things. If you dont know what they are, and end up mis-matching gear and blowing something up, they are a great way to keep from getting too angry. Simply sit down cross-legged, and close your eyes, and repeat after me: Ohhhmmmmmmm....Ohhhmmmmmmm.....Ohhhhmmmmmm...
Monks do it, and I think Ghandi did also. YMMV.

OK- seriously now. Thinks of Ohms as being a damn. Now think of the AMP as being a bunch of noobies wearing roller skates, at the top of a very, very steep hill. Now, the "rating" of just HOW bad these skaters are, and what rating of "damn" is needed to keep the skaters from plummeting too quickly and getting seriously injured, is called Ohms. An amp that says it puts out 100 watts at 8 Ohms means that one must provide a "damn" of at least 8 ohms, or the skaters get injured, cause if they are allowed to go down that hill any faster...well, you know about Jack n Jill. Now, since a bigger damn would still keep them safe, but they wouldn't have as much "fun," cause they wouldnt be able to go as fast, but they wouldn't get injured, it will still work. In reality, hooking a 16 ohm cab to this amp will have a more "tame" sound to it, due to the bigger damn. As always, there are exceptions! Some amps LIKE to have less of a damn, and seem to be fine with the lower ohm cab's being hooked up to them. Since the damn is smaller tho, things "move faster," producing "friction," and thus more heat. Good ventilation is a good idea obviously. Some people will "mod" their equipment to work "harder" than the original specs, and with tubes, the result is a different "smooth" or "brown" sound, to quote some guy who had a problem with certain M&M's. With solid state amps, things are a little different, but not much. If you let the "skaters" go down the hill too fast with a smaller damn, sometimes death will result. Overheated chips smell funny, and then cook, and once baked, they are useless for the most part.

Smaller wattage speakers hooked to higher, or matched, wattage amps tend to "break up" sooner, and produce a sound some people like. A speaker's wattage is basically how much you can "pour" into it before it starts to crack, and eventually burst. So a 50 watt amp into a 50 watt speaker is leaving very little breathing room when the full 50 watts is allowed to "pour" into the speaker. But since the speaker has enough "room" for the full 50 watts, it probably wouldn't "burst," but the sound it would make when it starts to "break up" is desireable by some, for certain sounds. For a cleaner sound, high wattage speakers will allow far more wattage to be "poured into them" before even thinking of breaking up, and thus one can obtain a clean, and more accurate, sound. Further, if the "amount the speaker can hold" in watts is not high enough, say a 50 watt amp into a 30 watt speaker, and the amp says it is ok for the skaters to plummet as long long as an 8 ohm damn is there, but the speaker only has a 4 ohm damn, then not only would the skaters run the risk of flying down the hill too fast, but when all 50 watts worth of those skaters go plummeting at too fast a speed into a container that isnt big enough for them...well, you get the idea I hope.

Always be sure that phase is matched when using multiple speakers, unless you want the "out of phase" sound. Usually, it is noticeable as being out of phase because the low end just about disappears. To check phase, easiest way is to grab a good ole 9 volt, and place it across the terminals of a speaker for a sec, and watch how the speaker moves. If the cone "extends," or moves away from the magnet, then the positive terminal is the one that the positive tab of the 9 volt is on. Mark it with a red sharpie, or nail polish, or something. If the cone moves in, then the 9 volt positive is on the negative, or ground, side of the speaker, and obviously the other one is the positive. Most speakers are marked, but if you get one that has been reconed, it may not have a marking left from years of use. Some manufacturers mark them differently, and not knowing this and mixing two different speakers (or more) could result in problems. Better safe than sorry, I always check 'em, even new.

That is the basic idea in a (big) nutshell. Deviating from what you are and are not supposed to do has resulted in good things, and bad. Be careful, have fun, and if you have the $$$, experiment a bit. Always be sure things are grounded properly. Don't push a 1/4" jack too far up your nose, or in any other orifice it doesn't belong in. Hope that helps a little. Bit long winded, but it is late, I just woke up, and am out of it. Nikki
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ohm cab , ohm cabinet , ohm output , peavey classic , power amp , rocktron chameleon , rocktron velocity , solid state amp , solid state amps , speaker cab , tube amp , tube amps , tube head

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