Subwoofery: Trick or Treat?

Subwoofery: Trick or Treat?

Written by Jim Smith

Part 2 – “Fast” bass? Really??? …

… Just when I think some errant audiophile terminology is finally extinct, it rears its ugly head again.  I am still amazed when audio reviewers describe subwoofer bass as fast or slow.

First, let me get the most insulting statement out of the way: If a subwoofer could be described as very fast, it would be a tweeter!

When a subwoofer is described as slow, it’s nearly always poor integration with the main speaker.  Poor integration can range from wrong location (this is much more than simply finding where to put it) to wrong crossover implementation to wrong levels and more.  These factors can be just a bit off and still affect the sound – and they are inter-related.

If a sub can be described as fast, that’s also a problem.  You shouldn’t be aware of it – in much the same way that you never think about how fast or slow it is when listening to live music.

A relatively straightforward goal can be best described as never feeling the need to readjust the sub with different recordings or types of music.  When you get that aspect working you are done, or at least well on the way.

We will explore these topics and techniques later in this series.

However, there are some other pesky performance issues with some subs that can also contribute to the illusion of fast or slow bass:

(1)  The main issue about speed that I encounter isn’t how fast the woofer starts – but how quickly does it stop?  This issue can definitely contribute to the slow bass illusion.  It’s one reason why speaker manufacturers are continually looking for more rigid, but lower mass drivers.  Not for speed, but for control.

(2)  Cabinet resonances can also contribute to the slow illusion.  Although the sub may only be working up to 35 Hz, if its enclosure has a sympathetic (…what a weird adjective!…) resonance at 140 Hz, it can often be described by some as being slow.

(3)  An out-of-band subwoofer anomaly (fortunately this is rare) can also add to the illusion.  If it is flat to your 40 Hz crossover point, but it has a peak at 80, then here comes the illusion again (though it depends somewhat on the slope of the crossover).

To close out this section, let’s agree that we want the sub to disappear as an obvious source of the sound.  If you are aware of it, especially as to its speed, you probably have some work to do.  It’s not rocket science (sorry, couldn’t think of a better descriptor), and the rewards for your effort will pay musical dividends for years to come.

Part 3 – Finding the anchor point for the best Dynamics, Presence & Tone

This has to be my pet peeve when evaluating audio installations.  It is so very important – but rarely mentioned – and sadly, it is done even less.

First, a description of the issue:

Dynamics are essential in order to have the music “pluck your heartstrings”.  That’s why the current overuse of compression (of dynamics) in recordings is so damaging – but hey, that’s another topic…

Here, we are discussing the effects of bass peaks and dips in your playback system.  The peaks destroy dynamic range as they were never intended to be there.  They mask musical dynamic subtleties in the recording that are meant by the musician to be heard, but you can’t fully experience them, as they are overshadowed by the excess bass sounds.

The same lack of dynamics is true (but for a different reason) whenever there are dips in the bass frequency response.  These dips detract from the music’s intended impact and definitely diminish its intended dynamics, and sadly, sometimes in a major fashion.

I have heard too many systems that – depending on the frequency – were almost missing some bass notes, while other notes were booming away. Both bass anomalies detract from the music’s dynamic contrasts, with a potentially far greater effect than those that may occur elsewhere in the midrange and treble.

Please understand that we are not considering uneven speaker response.  We are concentrating on the room resonances that all rooms have, based on the room’s dimensions.  Peaks in bass frequency response are additive resonances and dips are subtractive.  Even though we are talking about subwoofers, we are still intensely concerned with all bass anomalies, in the boundary dependent region from 25-250 Hz.

Since all rooms suffer from these issues, how can we overcome them?  While some may wish to immediately employ electronic EQ and Room Correction (another upcoming topic in this series), I have found that it’s always best to first smooth out the bass response in an organic fashion (meaning working with the room rather than against it), rather than immediately resorting to using electronic EQ and/or Room Correction.

And since I’m up against my word limit, we’ll explore how to successfully accomplish our goal in the next issue.  Hint – it’s probably not what you’ve heard.  🙂

Still to come:

More on – Finding the anchor point for the best Dynamics, Presence & Tone

Part 4 – Why a RTA (Real Time Analyzer) is useful, even if you are not technical – and how to get a good one nearly free

Part 5 – Sub set-up info you probably haven’t seen (but you should)

Part 6 – X-over freq. vs. level; location, location, location

Part 7 – The role of EQ and Room Correction when working with subs

Part 8 – A true story about the musical impact of bass – with a good outcome and lots of documentation

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