Why do subs sound bloated or slow?

BIF - IME, the two simplest and most effective techniques for subwoofer placement that require no equipment other than a SPL meter are:

1. Optimizing frequency response by placing the sub at the listening position, then walking around the room and listening for the location where the bass is *consistent* across low frequencies. You can do this by ear with music, or you can use a SPL meter and low frequency test tones. Once you find the location in the room that has the smoothest frequency response, you place the sub in that location. Now the bass response at the listening position should be in pretty good shape.

2. Optimizing time alignment by maximizing constructive interference at the crossover frequency. This technique was described by Cbw in his post on 1/27:

You flip the polarity of either your mains or your subs (whichever is easier), then play a tone at the crossover frequency (e.g., and 80 Hz tone for an 80 Hz crossover). You then adjust the delay (or sub position) to *minimize* the SPL at the listening position. (You're effectively maximizing destructive interference.) When you're done, you flip the polarity back to normal, and you should be very close to time aligned.

Both of these techniques are simple and highly effective. Unfortunately, IME, they don't always give you the same answer about the best location for the sub (which is the point I've been trying to make throughout the thread). So, if I were you, I would start with the first technique to find a general location for the sub, then use the second technique to refine the placement.

Hope that helps.

Bryon

Personally, I'd recommend an RTA unit, preferably with on-board PEq.

Adjust the PEq and phase for flat on-axis FR at and around your usual listening position. There may be some variation as you move the mic, but -in my case- there was little since my room is set up for solo listening and "window" is narrow.

Screw around a bit with the PEq bands (i.e. use them as tone controls) and/or placement - changing one variable at a time - and try to note all correlations between audible results and the shape of the RTA's FR output. If you have control of the sub's Q, adjust that to different settings as well.

Eventually, you'll figure out what the best sound "looks" like on the readout, and you'll be able to re-locate the subs and dial in a close replica of your preferred response very quickly. Tweak from there by ear.

For me, the best SQ is yielded by flat (or flat to +/- 35hz with slighly and gently rising output below) with subwoofer Q set for medium damping. This has been pretty much true, regardless of where the subs have been physically placed.

I find the SQ remarkably consistent (and remarkably good) when using my Rythmiks/NHT and Velo SMS-1 when dialed in with this technique, which basically holds on-axis FR constant. I would, however, be the first to acknowledge that, for other listeners, differences may be more audible.

Marty

I agree with Marty that, for the greatest control over subwoofer integration, you will need some way of measuring and correcting the frequency response of the system. There are both hardware and software approaches to measurement/correction. Both can yield excellent results. Personally, I use a software approach to measurement, namely Room EQ Wizard, and a hardware approach to correction, namely Meridian Room Correction.

IME, the ability to measure and correct the system's frequency response dramatically increases your control over sub integration. But if your system doesn't allow for this, the techniques I described in my previous post will get you a good part of the way toward excellent bass.

Good luck.

Bryon

I rarely post on tweaks, but I just discovered one that is relevant to this thread: I placed 3 Black Diamond Racing Jumbo Pucks under my sub, which is resting on a three inch maple platform. This, in effect, replaced the soft feet of the sub with extremely hard feet. The result: An audible increase in bass articulation.

FWIW.

Bryon

04-21-11: Dbphd
One of the most reliable phenomena in psychoacoustics is what is know as the masking level difference (MLD). Present a mid-freuquncy sinusoid in correlated noise to both ears and adjust the level until it becomes inaudible; flip the phase of the sinusoid in one ear, and the signal pops up as much as 15 dB, depending on frequency.

Dbphd - My understanding is that BMLD is a measure of the difference between the thresholds of detection for…

1. Auditory stimuli in which the signal and noise are the same phase and level.

...and…

2. Auditory stimuli in which the signal and noise are different in phase and/or level.

It’s unclear to me how the existence of BMLD affects my observations about subwoofer time alignment. Maybe you can elaborate.

At the time, the data suggested the auditory system doesn't preserve timing as such up the neural chain, but may convey such information by the more central areas excited.

Again, it’s unclear to me how this bears on my observations about subwoofer time alignment. I’m not saying it doesn’t. I just don’t see the connection. Maybe you can say more. Having said that, I do have a few thoughts...

As you are probably aware, there has been a great deal of neuroscientific research over the past 20 years using fMRI and PET scans. Much of that research has been directed at correlating various brain regions with perceptual, linguistic, and motor abilities/deficits. A significant amount of that research has been devoted to auditory perception, including the brain regions that correlate with temporal processing and temporal resolution.

I’m under the impression that the neuroscientific research on temporal resolution has discovered a number of neural correlates for auditory temporal resolution, corroborating earlier measurements of temporal resolution obtained through psychoacoutic experiments (e.g. gap detection).

Here is an excerpt from an article in the journal Cerebral Cortex:

We used positron emission tomography to examine the response of human auditory cortex to spectral and temporal variation…Results indicated that (i) the core auditory cortex in both hemispheres responded to temporal variation, while the anterior superior temporal areas bilaterally responded to the spectral variation; and (ii) responses to the temporal features were weighted towards the left, while responses to the spectral features were weighted towards the right. These findings confirm the specialization of the left-hemisphere auditory cortex for rapid temporal processing, and indicate that core areas are especially involved in these processes.

Here is an excerpt from a paper by researchers at UCI and University of Toronto:

Our findings of M100 modulation by the shortest gap (2 ms) tested are also in good accord with animal studies of auditory cortical temporal acuity, where gap detection thresholds have been measured using electrophysiological methods to record activity in single or cluster units. A key result of those studies is that the firing patterns of neurons in auditory cortex reflect minimum detectable gap thresholds that are similar in scale (at 2-10 ms) to thresholds measured psychophysically in human [4, 5, 13]. Our MEG findings reported here provide evidence for a similar level of temporal resolution to brief (2ms) discontinuities in sounds in the synchronized neural response of tens of thousands of neurons in secondary auditory cortical fields [10], reflecting neural response properties at the population level in auditory cortex.

Research like this leaves me with the impression that human temporal resolution is highly sensitive, not only when measured psychoacoustically, but also when measured neurologically.

Of course, it does not *necessarily* follow that subwoofer time alignment is audible. But it does seem to indicate that my statements about subwoofer time alignment are not *disproved* by the current state of neuroscientific research.

Bryon