# JBL Infinity "DBO" bass boost/subsonic filter for dummies



## Brian10962001 (Jul 11, 2009)

I figured this would be worth posting considering I have seen 2 very wise users now mess this setup up. The confusion I believe comes from what JBL decided to do with these amps. If you look at the panel you'll see that you have a pretty basic looking center frequency and a boost frequency beside it. DBO however isn't just a boost center, it's also a subsonic filter.

I guess some people don't get this, it seems to me that the DBO sets the subsonic filter and boosts about 10hz higher than wherever the center frequency is, so when these guys had them set up at 60, 70hz, it basically killed their system's ability to go low.

So if you're using the DBO and not using any boost, set it where you want the subsonic filter to hit at. If you're using it for a bass boost, you're pretty much stuck keeping it low, like 40hz or so. I could really tell it was hurting performance if I tried to go anywhere near the 80hz mark. I don't see why JBL thinks this was a good idea. I guess that extra dial for subsonic is just to complicated.


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## TREETOP (Feb 11, 2009)

Brian10962001 said:


> I don't see why JBL thinks this was a good idea...


An infrasonic filter is usually best set about 1/3 octave below an enclosure's tuning frequency, JBL probably figured most people who would use a bass boost would boost at their tuning note for peak output. Just guessing though.


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## Hoye0017 (Mar 23, 2010)

TREETOP said:


> An infrasonic filter is usually best set about 1/3 octave below an enclosure's tuning frequency, JBL probably figured most people who would use a bass boost would boost at their tuning note for peak output. Just guessing though.


That was my initial thought after reading that. That's the best way to make a "one note wonder." Build a vented box tuned to a particular frequency with a sharp peak and a steep roll-off, use processing to maximize power at that frequency, and use a steep filter to make sure the sub/enclosure doesn't get fed frequencies below that point where it loses control. Interesting that JBL would combine those functions for that purpose if that is in fact why.


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## Brian10962001 (Jul 11, 2009)

I slightly edited my top post guys, I wrote it before I went to bed and got the center point backwards. JBL states that the center actually is where the subsonic is set, and the boost is applied 10hz above that frequency. You're correct in your assumption that they tell you to set your DBO to 10hz below the enclosure's tuning frequency basically making a nice one note wonder setup, but to the average consumer, that's loud. At least I assume this is the thinking behind it.

What they state gets even more confusing when you read some of the other manuals for amps with this feature. In the GTO amplifier flier they state that it's a variable Q high pass filter below 100hz (which is "well below regular bass frequency"...)


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