setting gains

Using a multimeter to set gains, knowing what volts ac I want as i dont have an oscope, do I use 0db or a -dB test tone once my head unit is set at 0db 40hz for my subwoofer? Thanks.

Your ears are better at detecting clipping and distortion. A typical DMM won't - that's why oscopes are used. The DMM is only good if you know what voltage to set to, or have circuitry to isolate distortion & clipping.

Ok, I see what you mean, I was trying to make sure I didn't over power the sub as my amp is 500watts rms and my sub is 400w rms.

id say that difference between sub and amp power, 100w, is minimal. but with one catch, as long as your sub is decent quality. RMS basically means average power which means that you sub can usually take much more power than its rms rating but it just wont take it all of the time. i always set my gains by ear but it might take some tweaking later on if you end playing different music from what you used to set it, you might end up hearing something that you didnt hear when you set the gain originally. if im setting a gain for a customer then i usually under set it by maybe 15% to 20% if they plan on using their own box or a prefab box that i dont know the specs. if i personally built the box then ill set it at the best level to make most music sound its best.

It's a vibe a4 amp and a vibe slick slr 12 inch in an enclosed box, I'm no expert but I wouldn't say it's bottom of the line but it sure isn't the best of quality I don't think? Does anyone use the dd1 from Steve meade ? I have tried setting mine by ear but never done it before so not 100percent if I'm hearing the distortion with a test tone cd

Think I got that wrong, it's a non ported box.

distortion from a sub woofer is pretty easy to hear if you are listening to it directly, meaning you are pretty much right next to it. it is harder to hear if you are inside a car and the sub is in a trunk for example. if you are using a test tone then you will hear a noticeable shift from clean bass to distorted bass. my process that i use is basically to turn up your system to the max listening volume that you would normally listen to it, you should never set your gains by ear using a low volume because you will always end up clipping when you turn it up to a loud listening volume. if you insist on using test tones to set the bass then i would opt for a 40Hz tone because a sub is more likely to distort on lower notes and also the amp will tend to deliver more power to the sub at lower notes than higher ones. using a low tone to set your bass will protect your sub better when you switch to actual music especially if you listen to a lot of bass heavy music. like i said before, you should hear a noticeable difference in sound when the sub woofer starts to struggle to handle the power. and it isnt always about just power, the mechanical properties of the sub and the design of the box come into play. if the box is too large then your distortion point will usually be at a lower volume than if the box design is just right. this is why setting your gains by multimeter isnt that accurate overall. so as you listen, turn the gains up slowly until the sound starts to change from a clean note to a distorted note. once you hit that point then id back off until you get back to a clean note then maybe just a touch further to give yourself some head room. also it would be a good idea to turn the bass up on the head unit too. that way you can use the radio's settings to fine tune your sound in the listening position without the risk of hurting your sub by turning the bass up on the radio. this is a useful technique to basically idiot-proof your system against other people that might drive the car. i cant tell you how many times ive heard the story of somebody loaning their car out to a friend or family member only to get it back with blown speakers or subs because they played with the radio settings.

Thanks for your advice, I shall give a good go then. :-)

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Thanks :-)