How Do i Protect My Subwoofer

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[MikeMiesen]

This will probably take a little clarification, but I've already blown the driver in a Yamaha 18" sub, and I don't want to do it again! I am looking at a DBX 166a on CL for $75. Is this the type of equipment that would protect the sub? A little history...I used the preouts on the DVD to a mixer, then to the amp(no idea where to set the amp levels), then on to the sub. Everything was great until an explosion on loud boom, and I could hear the sub slap, which fried the coil. I am looking for any guidance so I don't do this again...thanks.

[cinepro]

Probably not going to save you any more than setting the sub woofer up properly in the first place. Movies are mixed with a wide dynamic range, when setting up a sub its important to remember that some scenes can be vastly louder than others. Its when the bombs explode or the plane takes off, the scene in the discoetc, thats when you may do damage to your speakers. When setting up your subwoofer, select your reference scene (the familiar movie you know) at its loudest scene and then set your sub level from a low position so that there is no peak light or distortion and mark the setting. Never turn the sub up past that point again.

[ArniePye]

Mike,

Play some music you know well through your system and set the sub level so you have a nice full sound without the music sounding too boomy.  You now have a rough balance between your main L/R speakers and your sub(s).  When you play your movie, resist the initial temptation to raise the sub level until you get through some scenes that you know have real boom-boom.  Then tweak to taste.  Listen carefully for those mechanical slapping or popping sounds.  If you hear them, turn it down!   

A compressor set with a high ratio (< 8:1) is a great way to protect your sub but it takes a bit of skill to dial it in properly.  You can very easily suck all the dynamic range out of the low frequencies.  We can get into the details a bit more if you like. 

It's worth noting that most powered subs have some type of preset limiting and amp protection built in.     

[MikeMiesen]

Thanks for the great tips, but as always I have a one more question. Do you recommend turning the amp all the way up, and adjusting with the gain on the mixer? The amp is a Crown XLS602, 1200w bridged mono..the sub I think is rated at 500w pgm?

[ArniePye]

Mike,

Turning the amp all the way up and controlling with the mixer is fine as long as the mixer is putting out a decent level.  However, with the amp all the way up if you are only tickling the meters on the mixer that is not optimum.  You want to maintain a good signal to noise ratio in the mixer by making sure your levels are around 0dB but not so loud that they run into clipping.   

The level controls on a an amplifier only attenuate the signal.  You can still drive the amp to its full output with the level controls turned down.

I would put the amp controls in a repeatable location (12 o'clock, 3 o'clock, etc.) and fine tune at the mixer. 


AP

[MikeMiesen]

Thanks for taking the time for the explanation, I'll give it a try tomorrow. Oh, I am really confused by the part where you can turn the amp all the way down, and still put out full power?

[ArniePye]

Mike,

I know the concept can be a little confusing.  Take your amp rated at 1200w - if you turn the level controls down halfway (12 o'clock) it does not limit the power to 600w. 

There is a certain voltage that drives your amp to full power (for the XLs 602 it's 1.25V).  Let's use easy numbers as an example.  Say 1 volt drives the amp to full power.  If you turn the amp level controls all the way up then 1V out of your mixer takes the amp to full power.  If you turn down the amp the equivalent of 6dB then your mixer needs to to output 2V to get the same power.  The level controls are actually input attenuators - they are only capable of turning down the input - and all the way up let's the entire signal through (no attenuation).

The bottom line is that turning the amp down will not prevent you from toasting your sub again.


AP

[tscoff]

I work at a school district and we bought that DBX compressor/limiter to protect the speakers at our stadium because the coaches let students play with the sound system.  For the first time ever, the kids haven't managed to blow out the amplifier over the course of a single school year......twice in a row.