StarCaptain Posted July 26, 2015 Report Share Posted July 26, 2015 I wont mention any brands in this for a few reasons. Let me just start off by saying my equipment is decent stuff and I had it tested after I bought it to make sure it is within it's 2% or less accuracy ratings. The sub is a brand I am not very familar with but came with a detailed T/S sheet and looks durable enough. It's no top of the line model, but it's not bottom of the barrel either. The amp is one of those off brands that claims massive power but is really light and fused very low. I've been an Audiophile for some years now and after a long hiatus I am getting back into it seriously. I have installed several systems in both my vehicles and friends based on what has shown to be quality stuff or what they specifically wanted. I never had a way to make sure it was working at max efficiency until recently. I finally purchased some decent testing equipment and have been brushing up on the new tech and techniques. I have a good voltmeter, good amp clamp, o-scope, and test tones on cd and iPod. So far I have tried to test amps that others have tested to see if I get the same numbers and have gotten close to theirs on most occasions. When I didn't, it was usually do to bad connections on my testing equip. or not getting good power to the amp.Here is my problem. A friend has a cheapy amp and wanted to know what it was pushing as the sub didn't sound right (ie muddy, not very loud). The sub was in the right size box. It's not ported (space limitations). It's rated to 1500w RMS and might handle it, it looks beefy enough. It's a DVC hooked up as a 2 Ohm load. His amp claims 1400w RMS @ 4 ohms. This seemed impossible due to its size and being fused at only 70 amps. He brought it in the vehicle over and I went to work. I checked the input voltage and wire size, found 14V DC and what was close to 2 AWG wiring. I clamped the positive speaker wire and hooked up my scope to the amp speaker terminals and put on a 40hz tone. I did this with the car running and had him keep the RPMS at 2000 to maintain the best voltage. I played the tone 3 times for 5 seconds and got these numbers just before clipping.38.6VAC 9.6 Amps @ 14.0VDC input38.8VAC 9.7 Amps @ 14.1VDC input38.7VAC 9.7 Amps @ 14.1VDC inputThis gives me roughly 375W RMS out of this amp. This is how I have seen it done by others. Obviously a static resistive load would be more accurate but I haven't purchased the parts to make one yet. My friend says I am doing it wrong and according to someone on the internet it should be38.8 X 38.8-----------2(resistance)which comes up to about 750 RMS. He showed this site and videohttp://www.mobileedgeonline.com/mobile-edge-tests-the-real-world-output-of-2-amplifiers/This looks sketch to me. I didn't watch the video as they wrote it all out and I can read faster, but the tester never mentions or doesn't realize that the Memphis rating is RMS and the Boss rating is MAX. I also have rarely seen car voltages in the 13.5 volt range unless the alternator was going bad, though I have never intstalled or tested a sytem of more than 1500W RMS. I countered by testing my own amp, one that has been tested by SMD, Sonic Electronix, and a couple of other independent testers and has proven to deliver around 960W RMS @ 2 Ohms. I got just over 60V AC and just over 16A for around 970W RMS pointing out to him that my equipment seemed overly generous. I also mentioned that by his method my amp produced 1800W RMS which is more than it is rated for @ 1 Ohm and as my sub is rated only to 1000W RMS it should have cooked some time ago.My two questions are1. Am I doing my testing correctly and is there anything or any tricks that would give me more accurate readings aside from the obvious(better/more equipment)?2. Is this volts squared a quick and dirty way to get within 15% of MAX watts and by extension half being RMS? I'm not finding to many testers using this method, though it obviously is part of Ohms law and the numbers do seem to work thay way. Link to comment Share on other sites More sharing options...
StarCaptain Posted July 31, 2015 Author Report Share Posted July 31, 2015 60 views 0 replies. Either I am doing it right or am screwing up so badly no one thought they could help me lol! Link to comment Share on other sites More sharing options...
reedal Posted July 31, 2015 Report Share Posted July 31, 2015 Voltage squared divided by resistance (your friend and that site's method) really only works for DC. In case you didn't notice, using that method for your results on your friends amp gives thousands of watts of output. And the way you're doing it really only works for DC. The entire power wheel (equations to find power, resistance, voltage, or current, given you have at least two of those variables) is for DC I believe, otherwise alllll of the amps in the world would be rated for way more than they are. VAC multiplied by AC current (your method of calculation by your example) does not give you AC power. You get AC volt-amps, and you need to know the power factor in order to find AC power. Here's a quick link to help you understand if I didn't explain it properly in a manner you understand. http://www.rapidtables.com/electric/Power_Factor.htm SMD Tool Map https://www.stevemeadedesigns.com/board/topic/193176-smd-tool-map-new-november-2014/ Build log https://www.stevemeadedesigns.com/board/topic/197217-reeds-03-tahoe-hat-sqaq-singer-xs-shca-cockbox-80prs/?page=32 Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted July 31, 2015 Report Share Posted July 31, 2015 Here is a video that will help explain it: "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
StarCaptain Posted July 31, 2015 Author Report Share Posted July 31, 2015 Ok. So if I understand the calculations correctly I multiply the VA by the PF. The PF can be found by getting the phase angle of the current and finding the absolute cos. However getting the phase angle appears to require an o-scope with more capabilities than mine and more expensive. All of this means I should just go buy an AMM-1 doesn't it? Link to comment Share on other sites More sharing options...
reedal Posted July 31, 2015 Report Share Posted July 31, 2015 AMM-1 will definitely give you real world results. And will also make you and your friend disappointed I think since there are so many factors that affect what an amplifier is putting out at the time of measurement. Best bet if you get one is to find where your lowest nominal impedance of the subwoofers in their enclosure is, and measure power out using a tone of that frequency that gives you the lowest impedance. The result being your amps maximum output in your situation given a presumably clean signal and constant environment. SMD Tool Map https://www.stevemeadedesigns.com/board/topic/193176-smd-tool-map-new-november-2014/ Build log https://www.stevemeadedesigns.com/board/topic/197217-reeds-03-tahoe-hat-sqaq-singer-xs-shca-cockbox-80prs/?page=32 Link to comment Share on other sites More sharing options...
TaylorFade Posted July 31, 2015 Report Share Posted July 31, 2015 You're doing it right. His amp sucks. Link to comment Share on other sites More sharing options...
StarCaptain Posted August 1, 2015 Author Report Share Posted August 1, 2015 Yeah it looks really cool though. If I use a dummy load it would also give me more accurate results right? If I read the page correctly and understood the video if you use a constant resistance source then the factor is 1 and the numbers you get are as accurate as the meter right? Link to comment Share on other sites More sharing options...
TaylorFade Posted August 1, 2015 Report Share Posted August 1, 2015 Yeah it looks really cool though. If I use a dummy load it would also give me more accurate results right? If I read the page correctly and understood the video if you use a constant resistance source then the factor is 1 and the numbers you get are as accurate as the meter right? Probably cheaper and easier to just buy an AMM-1 Link to comment Share on other sites More sharing options...
StarCaptain Posted August 3, 2015 Author Report Share Posted August 3, 2015 Yeah I did some shopping around on the net and and it looks like it would cost around 250 to $300 for 1000w RMS worth. Link to comment Share on other sites More sharing options...
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