Weird sound from SB12+

[alzard]

Dear all,

I am new to this forum. I recently purchased a SB12+ and I love it. However, I experienced some strange behaviour from my sub, which doesn't happened in my previous Sunfire HRS-8.

I watched the first chapter of "The Dark Knight", there is a shot zooming from aerial view to a building, the glass wall was being shot from inside and make one deep "boom" sound. When I use my SB12+ now, when it operates at a certain level, the one "boom" sound becomes a short series of "bubububu" instead. This problem will not appear if THX mode is turned on in my receiver.

My friend of mine to me that it is protective circuit activates when the sub if feed with very low frequency. I would like to check how this problem can be prevented or any special configuration required on my equipment to resolve this.

Thanks in advance.

My receiver is Onkyo NR-906 with a Sony S350 as source.
SB12+ setting: X-over "By pass", LFE 80Hz (at AMP), Gain at 9o'clock, PEQ and Room Compensation are disabled.

[Jack Gilvey]

Hi!

From your description, it sounds like the sub is being overdriven on that bass peak. Is the sub calibrated to the system, what size room is this, and at what Master Volume level does this sound start to happen?

THX Mode often engages a low-frequency rolloff below 35Hz or so, so that could explain why it helps with the noise as it spares the sub the deepest bass. You can try the Room Comp control at various settings, starting at Large, and see if that helps. What the control does is introduce a rolloff of the deepest frequencies that can help add headroom if the sub is at its limit.

Another less likely possibility is that the subwoofer output from the 906 is clipping. A Gain setting of 9:00 is a bit lower then we recommend in most cases, and moving it closer to 1/2-way can allow you to recalibrate the AVR's own subwoofer output lower, which can make it cleaner.

[eaglerider94]

Jack I'm considering purchasing the New PB12 Plus. Can you elaborate a bit more what headroom is? I've read about it but must admit, am still a bit confused. Perhaps a brief description in layman's terms, LOL. I've been researching subs to death and have zeroed in on a SVS sub based on many of the positive posts at hometheathershack. Believe or not, I've explored DIY but the more I view the New PB12 Plus the more I love the Rosenut finish which I could never duplicate, oh and of course the performance the New PB12 Plus puts out.

[Jack Gilvey]

Hey Rick,

The term "headroom" simply refers to how much clean output a sub has left before it hits it limits, how much is left "in the tank" when operating at a given level.
In the SB12-Plus example above, while lowering the setting of the room comp control won't change the current volume of the sub, it will add more headroom since it will allow the sub to get louder on peaks (there won't be as much deep bass to deal with).

[eaglerider94]

Got it Jack, now I have a clearer understanding, thanks for the quick reply. Enjoy your Sunday!

[Ed Mullen]

Yep - sounds like you are bouncing off the limiter - it will engage/disengage like you are describing. The SB12+ is a good little sealed sub, but it has far lower limits than its larger vented brethren. The PB12-Plus will dominate over the SB12-Plus in any comparison of low-end output capability.

If you are routinely pushing the SB12-Plus to the limiter and you are into action/blockbuster HT, then you should have a PB12-Plus or PC12-Plus in your system instead - it would take about four SB12-Plus to match one PB12-Plus in <~40 Hz.

For the interim, set the room gain comp to Small, and (as Jack indicates), that will ease the low-end load on the subwoofer and lessen the chances of limiter activity.

[alzard]

Thanks for your prompt reply. I appreciate the response time from SVS as it is on Sunday.

As per Jack's advices, I tried to recalibrate my SB12+ with the following setting,
Gain: 1 o'clock
Room Comp: Small

Using Radioshack Analog SPL Meter, the volume of speakers are at 72-74db, whereas the subwoofer is in 78db (C-Weighting, Response Slow). I guess the calibration is pretty accurate here.

After running auto setup from 906, the LFE level is set to -12db, so I think the clipping from AMP can be eliminated. I tried the "Dark Knight" Chapter 1 scene again, the problem persists.
With Dynamic EQ: Master Volume -20db, a minor bottoming is heard
With MultEQ XT: Master Volume: -15db, a very minor bottoming is heard.

The result is similar to before.

Question:
Which configuration is better for clean bass?
1. Gain dail to 9 o'clock, LFE in receiver set to -6db
2. Gain dail to 1 o'clock, LFE in receiver set to -12db

Since there is another SVS user has this problem, and he definitely need to use his subwoofer more than -10db. What would be the best solution to his case?

[Jack Gilvey]

Hi,

Your original Gain setting is fine, #1 above.

From this info, it's clear that the SB12 is just being driven past its limits. The RS meter reads ~2dB low on sub tones, so if your main speakers read ~73dB and the sub reads 78dB, the sub is actually 7dB too high, very "hot". At a MV setting of -15dB, the sub itself is being asked to run at only 8dB below reference, and is behaving as expected. As noted, it's our smallest, lowest-output subwoofer. Wonderful little sub, but not meant for modern LFE approaching reference levels.


As Ed notes, you're really a candidate for one of our ported Plus models. At the very least, though, calibrate the sub lower (if the speakers are at 73dB, set the sub to 73dB max) and set Room Comp to "small" to add needed headroom.

[Ed Mullen]

If the subwoofer channel level is set to -12 after calibration, that means Audyssey ran out of travel range.

Set room gain comp to Small, set the subwoofer channel level to -5, run the subwoofer test tone, and adjust the gain until the subwoofer SPL reads 73 dB on the RS meter (C/Slow). Then run the speaker channel test tones and adjust them to 75 dB (C/Slow).

The subwoofer will then be calibrated flat/even with the speaker channels since (as Jack stated) the RS meter reads 2 dB LOW on the subwoofer test tone (meaning 73 on the meter is 75 actual).

After you made those two changes (RGC set to Small and re-calibration), you've given the SB12-Plus the best fighting chance to avoid limiter activity. But if you push the playback level hard enough, it will definitely still kick-in.

Also DEQ places a pretty large low-end EQ boost on the subwoofer channel, and this naturally will chew-up headroom too. So if you run DEQ because you like what it does for the surround channels, try reducing the subwoofer channel level from -5 to -10 to keep the sub from working too hard. Many users find DEQ to be too heavy on the subwoofer channel anyway, and it will probably sound pretty good there, but feel free to experiment.

[alzard]

Hi Jack and Ed,

Thanks for your suggestion. I will try to work on it again and see if this little sub can deliver the performance that I expected.

Update: I discussed with another SVS user and we would like to know what is the max SPL SB12-Plus can output. Since our sitting distance varies (for some users if their room is big, even though we set the SPL level accordingly from the previous post), it would be useful if we know the specification of this sub before we make judgement whether it is the suitable one for our audition area.