tolga7t
49 posts
Mar 01, 2010
5:22 PM
|
Hello everyone,
One thing I don't understand regarding amps is the wattage. How is this determined? Is it related to the speaker size? If not, can you use any size speaker with a certain wattage amp to make it louder? I don't understand even the basic technical stuff regarding amplifiers, so any info you can give me will be greatly appreciated.
Thanks
Tolga
|
jonsparrow
2464 posts
Mar 01, 2010
5:28 PM
|
its the power of the amp itself. an amplifier its just the part with the electronics inside the cabinet. like you can buy a half stack, which would be an amp an the cabinet separate. when buying different speakers you have to make sure the ohms match up. a bigger speaker will not make the amp louder.
----------
Last Edited by on Mar 01, 2010 5:29 PM
|
tolga7t
50 posts
Mar 01, 2010
5:31 PM
|
oh ok so it's all about the amp, nothing related to the speaker. And how would you determine the wattage of an amp if it doesn't say on a label somewhere?
|
walterharp
249 posts
Mar 01, 2010
5:34 PM
|
ask at the lone wolf harp forum with the name of the amp and maybe a picture of the circuit, if it is an old tube amp.
If it is a newer electronic amp google for a users manual and it should say in the tech specs.
|
jonsparrow
2466 posts
Mar 01, 2010
5:34 PM
|
it might say on the inside some where. or you could check online. but if you mean like hooking up a multimeter to find out how, i have no idea.
----------
|
Cisco
79 posts
Mar 01, 2010
5:54 PM
|
Wattage can be calculated by the manufacturer in several different ways and at best is a close approximation of what the amp can put out which is determined by the input instrument's impedance, the amp's circuitry and the room's dynamics. You will only find it in the owner's manual for the amp. Often the amp manual can be found online somewhere.
|
LeonStagg
148 posts
Mar 01, 2010
6:19 PM
|
A watt is a unit of power.
You use Ohm's Law to calculate watts.
Volts x Amps = watts
Example :
At 120 volts, a light bulb draws .5 amps, then it is a 60 watt bulb.
(If it is 3 phase power you multiply by 1.73 which is the square root of 3.)
|
MJ
126 posts
Mar 01, 2010
7:23 PM
|
you can get a 'ballpark' estimate by using the ac volts setting and a resistor that is same ohm load as your speaker. you cannot use a speaker for this because real impedance (ohms) of a speaker changes while it is playing and any numbers you get would be wrong.
1. disconnect the speaker and replace with resistor.
2. play music or test tone loudly.
3. measure ac volts at the speaker terminal.
4.the formula is voltage squared divided by the ohm load. say your amplifier makes 40 volts
40 x 40 = 1600 divided by the ohm load of your resistor.
|
Tuckster
416 posts
Mar 01, 2010
7:34 PM
|
As a general rule,the more output tubes,the more power an amp will have. 1 tube would be anywhere from 5 to 15 watts, depending on the tube. 2 output tubes 15-40 watts, very roughly.And the ear doesn't respond linearly to power. 3dB is considered the smallest change the general population can hear. A 3dB increase in level requires double the wattage. So for 3dB louder in a 5 watter,you'd now need a 10 watter. To be twice as loud as a 5 watter-a 10 dB increase-you'd need 10 times the power-50 watts.
|
Nastyolddog
342 posts
Mar 01, 2010
8:29 PM
|
Hi tolga7t check out this web page it's got some good info about amps in the Guitar menu .http://www.gmarts.org/index.php?go=210 or just Google GM ARTS it should help out..
|
congaron
597 posts
Mar 02, 2010
8:38 AM
|
You cannot use ohm's law with the information on the UL plate because it has nothing to do with the amplifier's output. Many things happen after the wall plug before the sound comes out. There is no correlation with the UL plate and the output in wattage, FYI.
|
congaron
598 posts
Mar 02, 2010
8:40 AM
|
If you are looking for more volume, the efficiency of the speaker has a great deal to do with what is available from any given amp. It takes a tenfold increase in wattage to double your volume, but a speaker with even just 6db greater efficiency will do the nearly same thing, as far as your ears are concerned. There are speakers out there with 103db/watt@ one meter efficiency. There are also some with ratings like 94db/watt@ 1 meter. The volume difference between these would not only be noticable, it would be striking. From your post, I sense the need for more volume? More speakers will also do this to a point.
For an example, I have two Jensen 12 inch speakers I can connect separately or together in the same cabinet. There is a measured 6 db difference in sound pressure level at 10 feet and almost 10 db at one meter off the cabinet when both are connected versus the one. The cabinet and the room affect all this, but I run them together most of the time for obvious reasons. The volume difference is so marked it affects the necessary volume control settings in a small room.
Last Edited by on Mar 02, 2010 8:49 AM
|
5F6H
2 posts
Mar 02, 2010
9:37 AM
|
"One thing I don't understand regarding amps is the wattage. How is this determined?" Wattage, when discussing guitar amps, is the maximum wattage the amp can still produce a clean signal (smooth sine wave) at. That clean signal is usually applied from a signal generator at much less voltage than you will usually encounter from a harp mic. MJs procedure is how the power is determined, using a true RMS AC voltmeter.
"Is it related to the speaker size?" Not in any way whatsoever. But more powerful amps sometimes require more speakers to spread the power out, in the old days 10" speakers may have only been a handful of watts each, so amps like the 4x10" bassman needed 4 speakers to stop the amp from tearing them apart under warranty. 100W amp with an 8" speaker is feasible, but probably wouldn't disperse the sound well. Conversely, a 5W amp with 4x15" speakers may struggle to efficiently move that amount of paper, voice coils & air. Speakers are typically rated at twice the wattage of a tube amp, because it is accepted that the amp will be operating at beyond its rated W RMS figure when overdriven.
Congaron is right that speaker efficiency is relevant, but with more efficient speakers comes more magnet strength, bigger magnets & voice coils and potentially more feedback on stage...it's swings & roundabouts, if your super efficient speaker feeds back long before an average speaker, you may not exploit the potential volume available.
2x12" may be better than 1x12", but four or six 12" would probably make it difficult to get anywhere near the amp before feedback.
That's the big thing with speakers for harp, balancing efficiency against feedback ceiling. Most of what determines a good speaker against a bad one is empirical testing & user testimony. The specific speaker in question is more important than speaker size per se.
The amp's voicing also dramatically affects percived loudness, a brighter voicing will be heard easier above the band, the trick is balancing that with a pleasant & useful range of frequency response...you still want low notes to come out with full harmonics, rather just strident higher harmonics with a thin, or sometimes missing altogether, fundamental note.
In short, W RMS is far from the full story when considering harp, as is whether you will exploit that rated W in a typical gig situation.
Is there a particular amp, or speaker you have in mind?
Last Edited by on Mar 02, 2010 9:55 AM
|
