Bad sub response in 50-80hz region.

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I've recently finished building a sub using the Dayton Audio RSS390HF-4 driver in this sealed prebuilt 3ft^3 box and an external amp

The sub sounded just ok and seemed to be lacking something so I did some measurements with REW and sure enough there is a huge dip between about 50 and 80 hz. To confirm that there was no crossover trickery, which I normaly have set to 80hz, I hooked the signal directly to the amp and got the same results. The response drops between 50-80hz and then comes back up flat. The response below 50hz is good down to about 25hz.

Is this dip most likely coming from the fact that the box might be a tad small for this driver, or from the room, or what else might I be missing?
 
I've recently finished building a sub using the Dayton Audio RSS390HF-4 driver in this sealed prebuilt 3ft^3 box and an external amp

The sub sounded just ok and seemed to be lacking something so I did some measurements with REW and sure enough there is a huge dip between about 50 and 80 hz. To confirm that there was no crossover trickery, which I normaly have set to 80hz, I hooked the signal directly to the amp and got the same results. The response drops between 50-80hz and then comes back up flat. The response below 50hz is good down to about 25hz.

Is this dip most likely coming from the fact that the box might be a tad small for this driver, or from the room, or what else might I be missing?


Was it a close-miked measurement, or did you do the measurement from your normal listening position?
 
Was it a close-miked measurement, or did you do the measurement from your normal listening position?

I measured from a few different positions near the listening position with a Galaxy Audio CM-140 SPL Meter connected as suggested on the REW quick start. Also, not to complicate things too much but I actually have two identical subs positioned as stereo subs in the front of the room. The room is a 12x20x8 room. And both subs are being powered by a Behringer NU3000.
 
I measured from a few different positions near the listening position with a Galaxy Audio CM-140 SPL Meter connected as suggested on the REW quick start. Also, not to complicate things too much but I actually have two identical subs positioned as stereo subs in the front of the room. The room is a 12x20x8 room. And both subs are being powered by a Behringer NU3000.
 
I measured from a few different positions near the listening position with a Galaxy Audio CM-140 SPL Meter connected as suggested on the REW quick start. Also, not to complicate things too much but I actually have two identical subs positioned as stereo subs in the front of the room. The room is a 12x20x8 room. And both subs are being powered by a Behringer NU3000.

My guess is that it's caused by a room mode. Try repositioning your subwoofers.
 
Guaranteed to be room modes and/or boundary cancellations. Do a near field measurement of the sub and there will be no big dip in the response from 50-80Hz. (There is nothing you could do wrong in the design to cause one anyway)

If the sub is near the far end of the room the most likely culprit is the ceiling reflection, which if you work out the distances will be half a wavelength further than the direct path from speaker to listener, thus causing half wave cancellation.

Almost impossible to solve with a single sub, the only real solution to boundary cancelations and room modes is a distributed sub approach where you have 3 or 4 subs positioned in different widely separated locations around the room.
 
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+1 on the distributed subs. with what you have though, you also might try putting one out of phase. Then put the other one out of phase. Phase issues can show up in that region as well. You don't need high priced subs for room smoothing in the sub 3 and 4 position.
 
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