I was on the verge of upgrading my stereo again, but because of some good advice I have received from a couple guys on the forum I decided to learn a little more before I make a final decision what I want. Currently I just have the stock 2011 FLHTK head unit with Boom! Speakers and it isn't enough. So, I have been thinking big power and speakers that will handle it but basically trying to decide between a plug & play or a car amp. Somethng dawned on me though and that is, for example, if I have an amp putting out 500W RMS and it runs at 50% efficiency then it consumes 1000W rms when you have it really loud. With just 12 Vdc powering it there is a lot of current draw. I was speaking to a young man I work with who has had an over the top stereo in his jeep. He tells me he had to install a 200 A alternator. So what happens with a bike stereo when it is trying to draw more power than is available?

 

A thousand watts continuous would consume a little over 83 amps at 12 volts or around 70 amps at 14.4 volts. You would need to add in the current load of all of your bikes other operating electronics to arrive at the total current load, then find or build an alternator that can supply that amount of current at minimum under engine idling conditions. You will also need a battery and wiring that can supply this kind of current draw too. If your supply can't deliver it then the amplifier won't run as efficiently and you won't realize anywhere near that power. A properly designed amp will automatically shut down when under voltage or under current conditions exist. A poorly designed amp will go into distortion or oscillate and possibly blow cheap speakers if the output power is still high enough.

 

however ,,, for the digital switching amps like J&Ms ROKKER XT series, even the 500w RMS amp, running at MAX VOLUME into 4 2-ohm speakers only draws an average of 8.5amps @ 13vdc ,,,,,,

it is because the software programed power supply looks at current demand a few hundred times per second and adjusts the current draw only to meet demand at a given time ,,,,,

this technology was not around for automotive type amps 15 years ago ,,,,,,,

J&M ROKKER XT amps can be found here http://www.jmcorp.com/SeeProducts.asp?PF=45 ,,,,,,,,

 

Da Shadow, don't be fooled by smoke and mirrors marketing techniques. You can't get something from nothing, the laws of physics have NOT been repealed. 13 volts multiplied by 8.5 amperes is still only 110.5 watts, not 500. Assuming the amp is 95% efficient (which is VERY generous to say the least) leaves a total power a little shy of 95 watts, again nowhere near 500 watts. In order to realize 500 watts RMS in an ultra efficient amplifier of 95% would require a current draw of over 40 amps at 13 volts.
If you were to sample the power supply at such an incredibly slow rate of only 200-300 Hz, and only provide those large 40+ amp current draws momentarily during large music excursions, a few things would happen. Number one is that you can no longer claim 500 watts RMS. It is now 500 watts peak for only a few hundred Hz, you can't lay claim to continuous power.
Second, Nyquist Theorem requires a sampling time of at least a minimum double your highest audio frequency. This means if your amplifier can reproduce sounds up to 16 kHz then your sampling frequency needs to be double that, or 32 kHz at a MINIMUM! If you're listening to music that's predominantly in the audio range of 300 Hz to 7 kHz then sampling and applying power a few hundred times a second (Hz) is not going to give the current pulses quickly enough to support those higher frequency notes. This is especially true if the note or notes are sustained for long durations of a few seconds or greater. As a matter of fact, sampling at only a few hundred times per second will either leave a nasty low frequency hum in your audio or completely collapse the amps ability to sustain 500 watts for anything more than a few milliseconds. And it will still demand over 40 amps from your power supply albeit for a shorter period of time, that's where the trickery comes in. Don't be fooled into believing you're getting a true 500 watt continuous power amp, you're not.
For more reading on the Nyquist Theorem and how it applies can be found here, http://en.wikipedia.org/wiki/Nyquist...mpling_theorem

 

You guys can use all the GORILLA MATH that you want, but ...... I run 2 of the Alpine PDX 4.150 amps, yes two amps that both produce more that 700 watts each.

I have been running the STOCK ULTRA charging system and battery for 5 summers with no incidences !!!

I'm sure what ever you have planned will be just fine !!!






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Ride-my-seasaw ,,,,,,,

no marketing gimmicks here ,,, sophisticated digital switching power supplies are different than what you are used to ,,,,,,

I have personally taken a simple amp meter, connected it in series with the J&M ROKKER XT 500w amp main power wire, and recorded the average current draw at that specific voltage & power output to the speakers ,,,,,,

I do know what I am talking about here ,,,,,,

below is a piece from this weblink http://en.wikibooks.org/wiki/Practic...ics/Amplifiers ,,,,,,,

Class G and H[edit]

There is a variety of amplifier designs that couple a class AB output stage with other more efficient techniques to achieve a higher efficiency with low distortion. These designs are common in large audio amplifiers since the heatsinks and power transformers would be prohibitively large (and costly) without the increase in efficiency. The terms "class G" and "class H" are used interchangeably to refer to different designs, varying in definition from one manufacturer or paper to another.

Class G amplifiers (which use "rail switching" to decrease power consumption and increase efficiency) are a more efficient than class AB amplifiers. The class G amplifier has several power rails at different voltages, and switches between rails as the signal output approaches each. Thus the amplifier increases efficiency by reducing the wasted power at the output transistors.

 

DITTO!

OP. the biggest difference between most car amps (especially the one(s) your younger counterpart is likely running in his jeep) is the Class of the amplifier. Class A, B, and A/B amps (used in car audio design) are power hungry amps and draw a lot of current but they are designed as such because they usually put out some very LARGE power even though rated at lower wattages and usually when you're talking multiple amps in a setup like this it will require the charging system in the car to be upgraded to handle it.

Class D, G, H amps are where the technology is for motorcycles. They are high power amps with very low current draw thanks to their switching power supplies and switching output transistors for each channel. For example. I have a SS PN4.520D and a SSPN2.350D (that's 870w max power) amp running my current setup. Running a 1000hz test tone through the system at full volume and full gains (no speakers connected obviously) with 4 ohm dummy load resistors the total amp draw is less than 10A. Now the way I tested this, NO ONE will ever achieve those types of current draws because you will toast either your amp or speakers long before you reach that point if not both.

Class D amps radiate EMI which could cause interference with FM reception so if FM is important to you, stay away from Class D amps although they are the obvious choice for better power.

GP and John are correct in their statements. RMSS is correct in what he states as well however WAY overthought. There's no need to inject all this technological BS in these basic audio setups on motorcycles. Now if you're talking a show-stopping audio setup that you'll use in a show type environment then I highly suggest you do this to your car and not your bike. Just my .02

 

Well this thread generated some great thought and knowledgable answers from all of you and I appreciate your continued patience with my learning curve. I have to tell you I am an engineer too thus the reason I am probably overthinking this. Other than trying to learn enough to rule out the ARC Audio kits I think I am zeroing in on MM651s and a J&M 360 four channel. I was looking at the J&M 500W but I don't think I need it. I understand the J&M are relabeled ARCs, that's ok with me. John has spent a lot of time answering emails for me so with all things equal I would prefer to give him my business. I am not sure I want the ARC speakers, the Polks seem to be about what I want. No competition stereo stuff for me I just love great sounding music and love riding my bike. Put the two together with a little gas money and I think I got it made.....

 

John, I'm very well versed on switching amplifier design since I've been designing class E amplifiers professionally since the 70's. Your cut and paste from a wikibooks link does not demonstrate your knowledge of the subject, it just serves to further prove my point. Take boosted rail technology, you are still switching a class AB amplifier. You claim your amplifier is doing it a few hundred times a second, we'll call that 300 Hz for arguments sake. How can you track and voltage boost an audio signal that's running faster than that, say 5 kHz? You can't. Certainly not at 300 times a second, being that the signal peaks you're trying to track and boost are running at 5000 times a second. That's where your claims fall flat. Yes, you can gain efficiencies by tracking and boosting the voltage rail during peak excursions, but what are efficiencies? In this case it's heat during the off cycles. You are not wasting energy heating up a class AB amplifier during the zero crossing or rise of the audio signals, only during the peaks. BUT this is still energy that has to come from someplace. You can't get more energy from less energy, if you could all the laws of physics would have to be rewritten. You simply are unable to read those quick momentary current draws with your ammeter.
If you're using an old analog moving coil type type ammeter there is no way the coil can swing the meter's needle fast enough to show the peak current draws. And if you're using a digital readout type ammeter, again the digital display itself can't sample much faster than a few kHz thus hiding your true current draw. Get yourself a FLUKE True RMS reading ammeter then come back tell us what you're REAL current consumption is. Bottom line is this, if your amp draws 8.5 amps at 13 volts then the absolute maximum 100% efficiency (lossless) is going to be 110.5 watts. To state otherwise is foolish. Just because your meter isn't fast enough to show you what's really taking place doesn't mean it's not happening. And it certainly isn't happening a few hundred times a second as you claim.

 

Ride-my-seesaw ,,,,,,

well then with your VAST knowledge on this subject (mine is obviously limited) how can you make the statement to SHADOW that a 500w RMS continuous power amp on a motorcycle would draw around 35 amps at 14.4vdc ?? ,,,,,,,

you have me totally confused ,,,,, (((and I thought I only used to be old & fat))) ,,,,,