Why do subs sound bloated or slow?

Marty, I don't think the effect I described can be reduced to room interaction because, as I said in my earlier post, I can achieve the same result by adjusting the delay of the mains relative to the subs without physically moving anything.

Stringreen, sub level is certainly important for proper integration, but turning down the level on a misaligned sub won't solve the problem, it will just make it less noticeable (along with the bass).

Shadorne, I disagree "that you can't perceive accurately what is happening to the bass response except by what it 'masks' in the higher frequencies." If you consider a single frequency around the crossover frequency (say, 80 Hz), it is being played by both the mains and the sub(s). Those outputs will either sum properly, or not, and you can easily hear very small changes in delay. (As an experiment, try playing a constant tone and turning the phase knob on a properly-aligned sub while watching an SPL meter.)

But real signals are the sum of a wide range of frequencies, and the overlap between subs and mains is also across a range of frequencies. Properly aligned, the waveforms will sum together properly, but when misaligned they will smear out the low-frequency information. The effect is plainly audible, and can't be attributed solely to masking.

01-25-11: Martykl
There's an element of "When did you stop beating your wife?" to this discussion. It starts with the presumption of guilt (for subwoofers) and asks for proof of innocence.

Hi Marty - I regret the title that I chose for this thread for a variety of reasons, including the one you mention. It is was not my intention to imply that subs ALWAYS sound bloated or slow, as I mentioned in a post the same day I started the thread:

In the OP, I wasn't trying to suggest that all subs sound bloated or slow. I was trying to identify some reasons, WHEN subs do sound bloated or slow, WHY that is the case.

The principal reason I identified in the OP is a conclusion that I arrived at after extensive experimentation in my system and others, namely that optimizing frequency response often comes at the expense of optimizing transient response, since efforts to optimize frequency response usually include non-coplanar placement or EQ, both of which disturb the sub's time alignment with the mains, and hence the transient response of the system.

The use of the of the terms "bloated" and "slow" were not intended to be derisive, but rather descriptive. It seems to me that room modes often result in non-flat frequency response that can be described as "bloated," and that time misaligned subs often sound out of sync with the mains, which can be described as "slow." Having said that, I quite agree that bloated or slow bass is not a problem unique to systems with subs.

But what IS unique to systems with subs, IMO, is the "zero sum game" that results from scenarios in which efforts to optimize the system's frequency response disturb the system's transient response, and vice versa. The reason this is unique to systems with subs is that, for systems without subs, the time alignment of the system is determined almost entirely by the manufacturer, not the end user, for the simple reason that the woofers are physically attached to the same cabinet as the other drivers. For systems with subs, frequency response and transient response (for bass) are independently controllable parameters. Hence systems with subs have unique challenges, including, IME, the challenge of optimizing both frequency response and transient response. That was the central idea in the OP, and the idea I've been advancing throughout the thread.

Part of the confusion here might have been avoided if A'gon didn't limit my initial post to a little over 100 words. I have no idea why that is done, and I have seen many other threads in which the OP was far more than 100 words.

FWIW, I use a sub in my 2 channel system, and it sounds neither "bloated" nor "slow." But it took me literally years of periodic experimentation to arrive at that point. The reason, I believe, is the "zero sum game" I've been trying to describe.

Bryon

Cbw723,

You need to investigate further. If you can hear the difference caused by a time delay of 1 inch (roughly 0.1 msec) in a subwoofer then there is something seriously wrong. 1 inch is less than the distance between your ears - it is of the order of a very slight movement of your head.

Do you have a tool to ensure your head is within 1 inch of teh optimal positioning while listening?

Quite simply the highest frequencies of a subwoofer are normally around 100 Hz (max) before there is a steep roll off and this corresponds to a wavelength of around 10 feet.

Your observation suggests that your subwoofer is putting out significant sound at above 1 KHz - for example at 3 Khz a 1 inch movement can make a large difference on a pure tone (although it would very unlikely to be audible with music).

Scientists seem to agree that 1 to 2 milliseconds is the threshold of hearing a delay in sound - and this will occur at upper midrange frequencies and not at subwoofer frequencies which are omnidirectional to the ear/brain.

In essence, what you report suggests something else is going on.

Number one reason why subs, or for that matter any speaker producing frequencies below 80 Hz, sound bloated is the room. Adding a second sub will substantially help in reducing room mode peaks and nulls. That's why some people swear by using a full range pair instead of satellites and sub. Corner placement of a single sub is a guaranteed formula for exciting all your room modes to the max. It's impossible to hear whether or not the sub is doing its job correctly when the room is booming.