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Backwoods

Real wattage to subs, Impedance rise and frequency.

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I know there are older threads about this, but instead of resurrecting a really old thread i figured we could start a new one and discuss... 

 

So, i did a clamp test on my sfb1K today... It was eye opening and a good learning experience... My amp puts out the most wattage at 30hz, and only put out 602 watts.... At 40hz, even though that sounded noticeably louder to my ears, the amp was only putting out like 400 watts according to my calculations. Now i may not of done things perfectly, and the clamp i used was a real cheap one... But i was really surprised how much less i was getting under rated power, and how frequency also determined how much wattage the subs got.

 

A couple questions, how does frequency change the power actually sent to the subs? And how does box tuning affect this?

 

Setup. Sfb1K amp on 2 SA dual 4 ohm 12s wired to 1 ohm, My box is 3.7 cubes net ported and tuned to 32-34hz.

Electrical is all stock, and sat at 13.1-13.2 volts during the test. 

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I do understand my amp is rated for 1K at 14.4 volts, so at 13 volts I'll see less. And do understand impedence rise a bit... But don't really understand how wattage changes with different frequencies.

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24 minutes ago, CstrokerV said:

Unless you count for phase your numbers are off also Go to https://damoreengineering.com/ he has a couple of videos watch them

 

 

I'm looking on that website but I don't see anything about how to account for phase?

 

I watched a couple of youtube videos on clamping amps to figure out real wattage, accounting for impedence rise, and just copied them... DMM on speaker outputs, clamp on speaker positive close to the amp, playing sine waves and multiplying the 2 readings.

 

How do you account for phase, and what does that mean exactly LOL 😆

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I found the videos... Holy crap bro... Cosign tangent power factor squared... My brain hurts. :D

 

 

But according to all that... It seems like I would need a 10K amp to get 1K.

 

He says in video 7 if you clamped the way I did and get 707 watts, you really only get 200 real watts... So in that case my 600 watts clamped would be even less.

 

So again... I'll never understand why manufactures say to match amps and subs by RMS.

 

If your subs can really handle let's say 1500rms, after impedence rise and losses you would need at least a very efficient 5K to ever even get a little close to that 1500. 

 

Edited by Backwoods

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42 minutes ago, Backwoods said:

I found the videos... Holy crap bro... Cosign tangent power factor squared... My brain hurts. :D

 

 

But according to all that... It seems like I would need a 10K amp to get 1K.

 

He says in video 7 if you clamped the way I did and get 707 watts, you really only get 200 real watts... So in that case my 600 watts clamped would be even less.

 

So again... I'll never understand why manufactures say to match amps and subs by RMS.

 

If your subs can really handle let's say 1500rms, after impedence rise and losses you would need at least a very efficient 5K to ever even get a little close to that 1500. 

 

There must be some truth to that because switching from an alpine mrv1200 on my single p3 vs a taramps smart 3k made a huge difference. The sub really has come alive, and its only keeping a stable "3k" from 1-2 ohms.

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18 minutes ago, Stefanzoh said:

There must be some truth to that because switching from an alpine mrv1200 on my single p3 vs a taramps smart 3k made a huge difference. The sub really has come alive, and its only keeping a stable "3k" from 1-2 ohms.

Yeah that 3K is probably delivering less than 1k to your sub according to all this. But if that sub is rated at 600rms then you are probably getting close to it's rated RMS finally, and with the old amp was probably only getting half, or less, of what it's rated at after losses and impedence rise.

 

 

Crazy stuff. More and more I'm wishing I went with a 3K amp for my 2 Sundown SA 12s instead of the 2K... But they were rated at 750 each... I figured 2K for a little head room... Now I'm thinking even the 2K won't push them to their full potential... Hell a conservatively set 5K even.

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If it’s to your liking it’s fine... I put 2 dc lvl 3 m1’s they are 600 a piece putting 1300 well why amp says it’s rated and it loud and gets down so I wouldn’t necessarily put more on them unless I was trying for numbers

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So here's a related question....

When a sub woofer company says a sub can handle, lets say, 1600 wts RMS (like my 18" ZVX) do they expect it to usually get much less because of impedance rise ?

 

OR, when guys say a sub is WAY underated, is this because it takes a 2500 watt RMS amp to even get close to an actual 1500 watts ?

 

I was concerned about running my 2400.1 (bench tested at 2630 wts) to my 18" ZVX.... Until I figured this stuff out... And also one member here (Gigawatt)  said my 2400.1 should be perfect for my 1600wt ZVX, and he was totally right 👍

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Just to be clear, a 1500 watt amp should output 1500 watts, if it doesn't its a shitty amp. A 1500 watt subwoofer should be able to handle 1500 watts continuously without an issue. 

 

There are a few reasons subs are "under rated" though.

-Part of that is because of impedance rise and the dynamics of music. Because of those an amp won't output full power all the time. Your 2500 watt amp might average a 1500 watt output and your 1500 watts subs will probably be fine. Most quality speakers can handle burst wattage quite a bit higher than RMS ratings. But if you start playing tones for a long time (which would be weird but hey) and if you happen to be near your rated impedance level and are shoving 1k extra watts into a system that wasn't designed to handle that much extra continuous power then you might run into a problem. Not a very typical scenario though, most people don't blast tones continuously. 

 

-Part of it is some people really know what they are doing when it comes to design of the system and use of the system. Just because some people can run 2x power to a sub doesn't mean everyone can do it. I tend to stick pretty close to RMS ratings though. I'm pretty good at paying attention to how hot my subs get and the smell, but I am terrible at enclosure design. I build within manufacturer's specs for enclosure and stick to RMS ratings of the sub. Not exact ratings mind you, but close. I ran 1.5K to my 8s that were rated at 600 each.

 

-Part of it is manufacturers rate a subs RMS based on how most people will use the equipment. Again, just because some people can run 2x power doesn't mean that works for everyone. RMS ratings are safe for what most people are going to do. 

Edited by MrSkippyJ

 

F150:

Stock :(

 

2019 Harley Road Glide:

All Rockford Fosgate

Amp: TM400Xad - 4 channel 400 watt

Fairing (Front) 6.5s -TMS65

Lid (Rear) 6x9s -  TMS69

 

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