Why do subs sound bloated or slow?

I agree with Plato. I also run two channel fronts and I have a Paradigm Signature Servo subwoofer. This Paradigm sub has its own Class D amp to power the woofer and three controls knobs to control phase, cut-off and loudness.

Because I only have one sub, I also bought a Paradigm X-30 crossover unit. The X-30 has the same controls and also allows me to combine left and right channels without shorting my pre-amp Mains. I feed my main fronts off the preamp's Main 1 output to the power amp. I run my fronts straight out. I feed the X-30 off of the pre amp's Main 2. output As stated, I use the X-30 to combine the two channels into one channel for the subwoofer.

My front speakers are Paradigm Signature 8 v2. The fronts roll off at roughy 35-40HZ. Of course room placement also affects base contour. However, as a general matter, I cross the sub over at 40-50HZ. Based on my ear, that sounds about right. Too high a cross-over and the bass sounds boomy. Too low, and bass is thin.

I also adjust phase by ear. I listen for the best sounding bass response. Loudness often varies by source material, but as I got used to working with the sub controls, I don't move the adjustment controls around too much.

I understand that Paradigm's current subwoofer line-up offers a bass adjustment kit which uses a small mike to sample bass contour, phase and loudness information directly into the woofer's self contained power amp. The sub's amp does all the work and makes the necessary adjsutments. That's about as good as it gets.

Anyway, I hope this helps. For those of you whose subwoofer doesn't allow cross over, phase and loudness adjustments, I suggest buying a cross over control box like the Paradigm X-30. It really works. BIF

Bifwynne, thanks for your insights... at last someone gets what I was saying.

I have one sub set up in a two-channel system with Magnepans and it works quite well and another in my Home Theater (previously mentioned).

They both integrate very well and add some punch and weight on the very bottom which is all they are meant to do.

It's great that sub manufacturers are finally finding ways to do the necessary adjustments automatically because most audiophiles simply don't understand how to make the appropriate adjustments. I think that's why so many people complain about bloating and poor transient response and so have negative opinions based on their own experience (and failure to get it right).

"Under many circumstances, optimizing frequency response and optimizing transient response is a zero sum game. In other words, getting one right usually means you get the other wrong."

Strongly disagree. When you get one right, you get the other one right at the same time.

Both the bloat and the slowness you describe are primarily frequency response problems; at low frequencies the ear has very poor resolution in the time domain so it doesn't really pick up the transient response in and of itself. The ear cannot even detect the presence of bass energy from less than a singe cycle, and it takes several cycles to determine the pitch. There is a correlation between transient response and sound quality at low frequencies, but that is because of the kind of frequency resposne curve that inherently accompanies good transient response. More on this later.

Now the ear is quite good at hearing the sort of frequency response anomalies rooms typically impose on subwoofer systems.

Given the wavelengths of bass energy and the time it takes for the ear to hear bass, by the time you hear it, the room has already very significantly altered the native frequency response of the sub. You have two primary mechanisms going on (really just different manifestations of the same mechanism): Severe peaks and dips imposed by room interaction, and a general trend of boosting the bass as we go down in frequency (room gain).

One effective solution is to use multiple subs. Each sub will interact with the room differently, and the sum of the two dissimilar peak-and-dip patterns will be much smoother than one sub all by itself. If you pay attention to internet posts where someone has gone from using one sub to using two subs, they invariably report more natural-sounding bass. So I believe that one of the reasons a lot of people prefer the bass of a good pair of speakers over satellite+sub bass is that the latter doesn't benefit from the smoothing we get from having multiple bass sources... unless of course you use more than one sub.

The observation that low-Q sealed subs sound tighter and more natural than vented subs goes back to room gain. Typical room gain is +3 dB per octave below 100 Hz. A low-Q sealed box rolls off at -6 dB per octave below system resonance, so combined with room gain that gives good extension without over-emphasizing the low bass. On the other hand a vented box is probably "flat" down to a much lower frequency before room gain is factored in. Suppose our vented box is "flat" to 25 hz; after room gain, it's now +6 dB at 25 Hz! That will definitely sound heavy and sluggish. As proof that it's the frequency response and not the transient response that matters, take both subs outdoors where there is no room gain, and the vented sub will sound tight and solid but the low-Q sealed sub will sound thin and anemic.

So to recap, audible bass anomalies arise primarily from frequency response problems, which in turn are primarily caused by room interaction issues.

Duke
dealer/manufacturer

i couldn,t live with my magnepan mmgs without dual 10inch velodybne subs. i hate boomy bloated sound. it takes some work and adjustment to get everything the way you want it. good questions and answers.

Duke, you make a great point. The room acoustics play a huge part in getting good bass and unfortunately the majority of rooms were not designed with any thought to good sound reproduction. Many rooms are just plain horrible for proper bass reproduction.

That said, mapping the room response and selecting a subwoofer with the best characteristics for that particular room will make more difference (in many cases) than simply throwing more money into a sub thinking that just by buying an expensive product your results should be much better (not always the case...).

I will also add that I've had better luck matching subs to mains that delve below 50Hz on their own, which could be a coincidence but it's been my experience.