Re: Ideas About An Inexpensive Sound System?
Sorry I do not know of a site that has all ftc power ratings and prices (there may be one...I just don't know about it). As for the 8 ohm rating, I like that even better, as long as the amp is rated at the load impedence you will be using it at. Decent quality power amps will almost double their power as the impedence halves, right down to the point that the amplifiers internal power supply starts to give up, or the output transistors cook. As an example, an amp rated at 100 watts per channel at 8 ohms, will put out close to 200 watts per channel at 4 ohms, some amps are rated down to 2 or even 1 ohms. I am not one to push a design to it's limits, so if I see an amp that is rated down to two ohms, I will only run down to a 4 ohm load on it. That kind of brings us back to some of the "power games" we talked about last night. For instance, lets assume that the amp you described that is 100 wattts per channel at 8 ohms, if it is rated down to two ohms, it will produce about 325 watts per channel at 2 ohms. Now if you don't know what impedence the power rating is at......your amp could be listed at 100 watts, while another amp is listed at 325 amps...you would think the second one is a larger amp.....that is why you need to know all of the specs. Now onto some more detailed things like bridging : Audio is Ac (alternating current) even if it is powered by Dc (direct current), because audio is Ac, that is the reason that a speaker cone moves in and out, the higher the frequency, the faster it moves in and out. In all designs, other than low power or very expensive audiophile equipment, there are at least two output devices (transistors) to move the speaker in and out, one transistor moves it out, the other moves it in. One transistor is reproducing the negative part of the AC waveform, the other is reproducing the positive side. What some manufacturers do to increase the power output on multi channel amps, is to give you the option to bridge the amp by flipping a switch, in that mode of operation, one whole amp channel will reproduce the positive part of the waveform and another whole channel will reproduce the negative part of the waveform, when an amp has two channels bridged, they will come close to quadrupling the output power into a single load. As usual, you don't get something for nothing, so while the amp is putting out more power while bridged, it cannot drive as low of impedence load as the individual channels can in the non-bridged mode. An amp capable of bridging, gives you more options as far as matching it to your speakers and how you want to set up your system. As an example, lets say that you had a four channel amp that put out 100 watts per channel at 8 ohms and a nice distortion rating of less than.08%,and lets say that the amp is rated down to two ohms per channel. Now lets say that you had two 6.5 inch, 4 ohm,full range speakers and a single 12 inch 8 ohm subwoofer. If the above amp did not have any bridging capabilities....you would kind of be screwed, or at least not able to balance things to well, in this case you would have two channels connected to your full range speakers(putting out almost 200 watts per channel) and a single channel connected to your subwoofer putting out 100 watts....and one channel not being used. That is a four to 1 ratio of high end to bass....not good. If you take the same amp, and add the capability of bridging any two channels....you would end up with channels 1 and 2 being connected to the full range speakers (200 watts each) and channels 3 and 4 being bridged into the subwoofer (400 watts)....2 X 200 watts for the high, and one 400 watt for the low....not bad at all. I will point out that some people would say "hey lets push that amp to the limit" they would wire two 4 ohm speakers in parallel on each channel (2 ohm load) for the highs, and use either a pair of 12" 8 ohm subs or a single 4 Ohm 12" sub on the bridged channels.....you can do this,and it will get louder....but to me, that is the same thing as using a 4 cylinder engine in the truck you use to tow your boat....it will get you there, but how hard is that engine working, compared to a big V-8 ?
