Any idea why a 50hz tone is recommended when setting gains using a DMM?

[quackhead 10+ year member]

It is possible an amp or processor or head unit has a bass boost or bass restoration circuit which can increase bass at some frequencies.
Yes, most DMM's are accurate at 50-60Hz since we usually measure AC voltage at that frequency. The meter should have a tolerance and frequency range listed, if not, you can't really trust it outside that range.

Note that there is an impedance spike at the woofer fs. That can affect the amp output voltage if the subs are connected and the tone is within an octave of fs.

Is it really necessary to judge other than by ear?..as you stated, once the resistor is hooked up(if you disconnected the subs for the gain set), the impedance changes according to not just the sub itself, but the environment it is in. I can understand using a DMM, if you are trying to set the gain on a amp that is rated to put out 3x the sub's rms rating. I usually try to find an amp that is rated for more than my subs rms rating..just a guess, @ 20% - 30% more and I have yet to clip one to death after setting the gains by ear, or a eyeballing the clip light..I am speaking in terms of most folks who come here looking for some bass..Competition is a whole nother topic.

 

[keep_hope_alive Premium Member]

In my experience, most don't know what clipping sounds like and people listen to massive distortion thinking its ok. We recommend the DMM method to force people to try to understand ohm's law and apply it. We also recognize that many people don't understand what a gain or input sensitivity adjustment actually does.

Setting by ear is a method used for decades. It is not scientific nor is it objective. It is just faster and doesn't require buying and understanding tools like a DMM. The end result is at the mercy of the person tuning it. And let's face it. If you have to ask, you don't know how. And learning something that complex over a forum is challenging. You have to care and most don't.

I suspect that People who use a DMM will end up with a lower gain setting that people who don't.

 

[RSDXzec 10+ year member]

Is it really necessary to judge other than by ear?..as you stated, once the resistor is hooked up(if you disconnected the subs for the gain set), the impedance changes according to not just the sub itself, but the environment it is in. I can understand using a DMM, if you are trying to set the gain on a amp that is rated to put out 3x the sub's rms rating. I usually try to find an amp that is rated for more than my subs rms rating..just a guess, @ 20% - 30% more and I have yet to clip one to death after setting the gains by ear, or a eyeballing the clip light..I am speaking in terms of most folks who come here looking for some bass..Competition is a whole nother topic.

Funny enough the sub I'm using is rated at 350wrms and the amp is rated at 1500wrms... so yeah it's handy. Only got that much power because I'll be throwing 2 more subs in there over the next couple of days. I like to set by DMM regardless because the theory makes sense to me, I am an electrical engineering student so ohm's law is second nature to me.

In my experience, most don't know what clipping sounds like and people listen to massive distortion thinking its ok. We recommend the DMM method to force people to try to understand ohm's law and apply it. We also recognize that many people don't understand what a gain or input sensitivity adjustment actually does.
Setting by ear is a method used for decades. It is not scientific nor is it objective. It is just faster and doesn't require buying and understanding tools like a DMM. The end result is at the mercy of the person tuning it. And let's face it. If you have to ask, you don't know how. And learning something that complex over a forum is challenging. You have to care and most don't.

I suspect that People who use a DMM will end up with a lower gain setting that people who don't.

I found it takes a while of listening to bass to be able to hear clipping. Six months ago I got my first sub system, and I couldn't tell clipping for the life of me, now I've come a long way and I can hear clipping a mile away. Really does sound horrible when you know what you're looking for.

I'm pretty happy a DMM will result in a lower gain setting, better to be safe than sorry imo.

 

[quackhead 10+ year member]

In my experience, most don't know what clipping sounds like and people listen to massive distortion thinking its ok. We recommend the DMM method to force people to try to understand ohm's law and apply it. We also recognize that many people don't understand what a gain or input sensitivity adjustment actually does.
Setting by ear is a method used for decades. It is not scientific nor is it objective. It is just faster and doesn't require buying and understanding tools like a DMM. The end result is at the mercy of the person tuning it. And let's face it. If you have to ask, you don't know how. And learning something that complex over a forum is challenging. You have to care and most don't.

I suspect that People who use a DMM will end up with a lower gain setting that people who don't.

This has been my reasoning for suggesting setting gains by ear on occaision, but that has depended on who I was speaking to. I have suspected setting the gain with a DMM without a load present is probably leaving 30% of available power on the table...but this is strictly a suspicion and I could be way off the mark.

 

[quackhead 10+ year member]

Funny enough the sub I'm using is rated at 350wrms and the amp is rated at 1500wrms... so yeah it's handy. Only got that much power because I'll be throwing 2 more subs in there over the next couple of days. I like to set by DMM regardless because the theory makes sense to me, I am an electrical engineering student so ohm's law is second nature to me.

Ohms Law is unwavering, no doubt. What amp/sub are you using exactly? Your amp is rated for 1500 watts rms at the load you are presenting to it? The gain on an amplifier is designed for one single purpose: to match the amplifiers' input section to the source unit maximum output voltage. So simple a concept, yet so misunderstood by people who have been insructed DMMing is the only way to set the gains. Using the DMM method is very confusing to many and masks the simplicity of the actual gain function. If one is determined to use this method, how do you confirm the input signal is void of any clipping? I totally understand why it is suggested... especially when it usually involves having to explain how power is distributed across multiple subs and how to wire said subs to create a specific impedance. All I am telling you is, don't let the simplicity of gain function prevent you from enjoying the potential of your system.

As an example, based on the info you provide: your sub is rated for 350 watts rms, and your amp is rated for 1500watts rms at the load your sub presents to the amp(?).

By using the gain function as a volume control and setting it to 350w max output, your subs will never see the 350w, unless you keep the HU volume at max(whatever reference you used when setting the gain is your max HU volume) ALL the time. If you ever play your system at 1/2 volume +/- a few notches, then you might be actually be using 75 - 200 watts on musical peaks, depending on impedance fluctuations and box design. I would suggest setting the gain by DMM at 500 watts, with the HU at 3/4 vol., therefore allowing your system the headroom required to use the sub to it's potential without damage...Especially if using a 50hz test tone and no load present when setting the gain with the DMM.

I found it takes a while of listening to bass to be able to hear clipping. Six months ago I got my first sub system, and I couldn't tell clipping for the life of me, now I've come a long way and I can hear clipping a mile away. Really does sound horrible when you know what you're looking for.
I'm pretty happy a DMM will result in a lower gain setting, better to be safe than sorry imo.

This so true.

 

[quackhead 10+ year member]

I should also state that not all "350w rms" subs are created equal, nor are all "1500 watt rms" amps....some produce and handle less, some more.

 

[keep_hope_alive Premium Member]

the biggest difference in amplifier power ratings is THD. an amp that can make 1000W at 10% THD is much cheaper to make than an amplifier that can make 1000W at 0.1% THD.

One common trick is to rate THD at like 20% of available power output, but rate power output at a high THD. So when you see the separate specs you are inclined to think they are relative when they are not.

 

[hispls 5,000+ posts]

so is that pretty much saying my amp is garbage?the amp is a ****** cheap class A/B amp so i wouldn't be surprised.

If output voltage is fluctuating you either are adding or subrtracting something from the signal elsewhere, or the amp is being driven beyond it's limits I suspect

I may be wrong but I was told by a tech that most DMM's are most accurate around 50-60cycles. The farther above and below that you get the bigger the error is in most meters, except high end meters.

That makes a lot of sense that cheap DMM is only really built to read 60hz AC.

 

[psych0ticnemes1 5,000+ posts]

Why do they suggest you turn your equalizer to flat when setting the gain with a dmm? Doesn't it make sense that when you turn it back to whatever setting you like, you're going to most likely change that gain setting?

 

[maylar 10+ year member]

I have suspected setting the gain with a DMM without a load present is probably leaving 30% of available power on the table...but this is strictly a suspicion and I could be way off the mark.

If the amp is actually capable of the power you're adjusting for, it doesn't really make a difference. The output voltage shouldn't change much under load except for IR losses in the wiring. It's when you're trying to extract every watt possible from an amp without clipping that you need a dummy load. And a 'scope...

Why do they suggest you turn your equalizer to flat when setting the gain with a dmm? Doesn't it make sense that when you turn it back to whatever setting you like, you're going to most likely change that gain setting?

Most folks here recommend setting amp gains with the EQ adjusted where it will be. A few clicks of the bass EQ can make a big difference in signal level.

 

[chillin 10+ year member]

If the amp is actually capable of the power you're adjusting for, it doesn't really make a difference. The output voltage shouldn't change much under load except for IR losses in the wiring. It's when you're trying to extract every watt possible from an amp without clipping that you need a dummy load. And a 'scope...


Most folks here recommend setting amp gains with the EQ adjusted where it will be. A few clicks of the bass EQ can make a big difference in signal level.

I've also heard many people say to set gain with eq flat and eq should only be lowered after, never raised.

 

[keep_hope_alive Premium Member]

I've also heard many people say to set gain with eq flat and eq should only be lowered after, never raised.

that is the best way to use an EQ, but not the way people usually use it.

 

[maylar 10+ year member]

I've also heard many people say to set gain with eq flat and eq should only be lowered after, never raised.

Yes, that's best practice. Unfortunately with a limited EQ like just a 3 band that's often difficult to do.

 

[kramer_212 10+ year member]

personally i use a 45hertz tone because that's what my bass boost knob is at.

and on my smd dd1 its a 40 hertz

 

[zako 10+ year member]

I suspect that People who use a DMM will end up with a lower gain setting that people who don't.

I understand the suspicion that a typical noob will try to turn the bass up as much as he possibly can, because he thinks this sounds uber cool or something. This is a good case for using DMM. However, people who are after SQ bass (e.g those into listening normal instrumental music, rock, etc, at healthy volume and without exaggerating any part of frequency range relative to the recording) can turn up the gain only up the the point where the sub stage blends well with the front stage, as suggested by ears using a good set of home speakers or headphones as a reference or by the means of RTA setup. This is how I set my gains. I suspect if I get the DMM and apply the DMM method, my subwoofer gain will be below that DMM says it could be.. I do have to try it some day. my 2c.