"Fast" and "slow" subwoofers: can we put them to bed?

twelti

WBF Technical Expert (Subwoofers In Rooms)
Apr 29, 2011
38
0
0
#41
Huzzah Todd. The audio mafia in Detroit including Clark, Geddes The late Tom Nousiane and the rest of us no-names have been ROTFLOAO about "Fast bass" for years for exactly the reasons you stated. One of our jokes is: 'Fast woofer = midrange driver" ;-)
Ha! I still hear it frequently though!
 

twelti

WBF Technical Expert (Subwoofers In Rooms)
Apr 29, 2011
38
0
0
#43
One of the most serious problems with IB subwoofers is that they are kinda hard to relocate for better bass performance. No joke, one of my friends with a massive IB sub with 4 very robust 18 inchers ended up with a major hole @ 60 Hz at exactly his favorite listening position.
But was it a slow hole or a fast one??!
 
Aug 21, 2014
21
0
0
France
#46
I'm not aware of any "formal" definition of fast bass.
The fastest (double) bass I've ever heard (attack/decay) was during open air concerts. Absence of reverberation helps.
A slow bass could be something like this:
090701gent_evergem-002.jpg
(is there a way to resize images?)
 

Blazar

New Member
Oct 28, 2014
20
0
0
#47
The concept of bass being fast or slow is some sort of subjective interpretation. The question perhaps is not that bass is either fast or slow. The question is why humans seem to consider some aspect of the speaker's sound "fast" or "slow". Is this a lack of "tightness" of bass? is it someone standing in a null in the room and analyzing a sub? multiple subs that are not setup with proper delay settings? a subwoofer that is not time aligned well with the main speakers? poor crossover setup?

Is it possible that some very specific bass notes (specifically in a song that you like) might impact your opinion of a subwoofer?

I know that there are a few songs that as use as my "reference" since I like the bass section of the track. There is no doubt that some setups are going to augment those exact notes that I like and therefore color my subjective experience.

On the other hand, if you don't use a track that you know, how would you compare apples to apples when comparing subwoofers?

I now realize that a vast majority of sub's deficiencies that I have heard in the past were inadequate SPL at the frequencies that I cared about. Also sometimes it was me expecting my subwoofer to produce sound that would actually be produced by my main speaker. I was thinking that the deficiency was the sub when in fact it was my mains (frequency range).

Who is really testing their subs ALONE without the rest of their system interfering?
 
#48
Any driver that employs a voice coil: speed is dependent upon the inductance of the coil and all wiring to it from the amplifier. There was a whitepaper done on this a couple years ago. Inductance alone, was found to be the determinant factor in driver transient response.

The rate of change of acceleration IS the transient response - it's what dictates how fast the driver can change speed, which also means it dictates how fast the driver can move from position to position.

BLi = ma


So, the Motor Force Factor BL times the current i equals the moving mass of the driver m times the
acceleration of the driver a.

BL is time invariant, assuming small excursions
i is the current into the driver
m is mass.
a is the acceleration.

So, let's rewrite the equation, and replace the time-invariant parameters with a simple "C" to indicate a
constant (a parameter that does not change with time):


Ci = Ca (eq 3) or i :: a (eq 4)


This says that the change in acceleration of a driver - how fast it can change position - is
strictly a function of the current through the driver.

A loudspeaker is a coil of wire wound on a former that attaches to the
cone. The current flows through the coil, creating an alternating magnetic field that interacts with the static
magnetic field of the permanent magnet. So, what could limit current flow? Well, what does a voice coil
look like? How about an inductor?

So, what about an inductor will alter the way current flows? Well, inductors don't like to have the current
flowing through them change. They like to hold the current constant. They will allow you to change the
current flowing in them, but the bigger the inductor (or, the higher the measured inductance) the longer it
will hold the current before it starts to change.

It turns out that transient response of a woofer is not a function of the moving mass, as is commonly espoused (one of the most infamous audio myths). In actuality, it is based upon the inductance of the driver. And the greater the inductance, the slower the driver - the lower the transient response.
 

stehno

New Member
Jul 5, 2014
545
0
0
Salem, OR
#49
I find it interesting that some have difficulty with the concept of slow bass. There is such a thing as a fast and slow amplifiers, CD players, etc.. I've experienced a few myself. To the best of my knowledge it has much to do with the rise and fall time of a note. Which in turn is the result of design, quality of parts, as well as whether or not the distortions that plague our components have been addressed to some degree small or great. But then, it also has to do with quality of cabling too.

My first experience with a "fast" component was a Sim Audio Moon W-5 amplifier in 2001. It was also my first experience with what was known as a "sweet" sound. There are components considered "fast". One such "fast" component was the McCormack DNA-2 LAE (limited anniversary edition) which I also owned after the Moon W-5. Peter Moncrieff of Intern'l Audio Review, who some considered to be head and shoulders over most other reviewers, in 1998 rated the DNA-2 LAE as the most musical of all the solid state amps he auditioned and more than any other attribute he waxed eloquently on and on about its speed.

Around 2003 there was a Balanced Audio Technology (BAT) CD player I think, that was auditioned by TAS reviewers and several of them claimed the BAT was slow. It wasn't that the music was actually slower. A 3 min 47 second sound track still took 3 min and 47 seconds to play. It just sounded slower. What they were describing was a perceived slowness in the music's tempo. The beat of the music establishes the tempo. But when a component is induced with an abnormally larger amount of distortions that usual and/or inferior design, the notes can smear with one note running into the next. Rather than the music beats being quick and distinct, with fast rise and fall times, and significant impact, this all becomes smeared to the point all such distinction is nearly gone, thereby giving the impression that the music's tempo has slowed.

There's fast, tight, well-defined, and deep, tuneful, and natural bass. But then there's also sluggish, poor, ill-defined, sloppy, rolling earthquake, woolly, or slow bass too. Again, for the same reasons there are perceptively fast and slow components.

Some complain that it's difficult or even impossible to dial-in a subwoofer so that it compliments the main speakers. You often times hear complaints that the sub sounds disjointed from the mains. One primary reason for disjointed and/or sluggish or slow bass is that the industry taught us for years that since it's only low frequencies dedicated to a subwoofer's output, it mattered very little what kind of interconnects used for the sub.

So what often times happens is the enthusiast meticulously selects a superior interconnect and speaker cables for their components that to their ears generates the most musical presentation. But then because they bought into the rumor that subwoofer cables matter very little, they buy a POS $20 cable and when the subwoofer does not blend in with the mains or sounds slow they sell the subwoofer and do without.

In other words, to minimize a subwoofer's potential for disjointedness or sluggish or ill-defined bass, the first thing one should do when attempting to insert a subwoofer into their playback system is use the exact same ic's for the sub as they do for the main components.
 

bwraudio

New Member
Jan 24, 2011
54
0
0
#50
Any driver that employs a voice coil: speed is dependent upon the inductance of the coil and all wiring to it from the amplifier. There was a whitepaper done on this a couple years ago. Inductance alone, was found to be the determinant factor in driver transient response.

The rate of change of acceleration IS the transient response - it's what dictates how fast the driver can change speed, which also means it dictates how fast the driver can move from position to position.

BLi = ma


So, the Motor Force Factor BL times the current i equals the moving mass of the driver m times the
acceleration of the driver a.

BL is time invariant, assuming small excursions
i is the current into the driver
m is mass.
a is the acceleration.

So, let's rewrite the equation, and replace the time-invariant parameters with a simple "C" to indicate a
constant (a parameter that does not change with time):


Ci = Ca (eq 3) or i :: a (eq 4)


This says that the change in acceleration of a driver - how fast it can change position - is
strictly a function of the current through the driver.

A loudspeaker is a coil of wire wound on a former that attaches to the
cone. The current flows through the coil, creating an alternating magnetic field that interacts with the static
magnetic field of the permanent magnet. So, what could limit current flow? Well, what does a voice coil
look like? How about an inductor?

So, what about an inductor will alter the way current flows? Well, inductors don't like to have the current
flowing through them change. They like to hold the current constant. They will allow you to change the
current flowing in them, but the bigger the inductor (or, the higher the measured inductance) the longer it
will hold the current before it starts to change.

It turns out that transient response of a woofer is not a function of the moving mass, as is commonly espoused (one of the most infamous audio myths). In actuality, it is based upon the inductance of the driver. And the greater the inductance, the slower the driver - the lower the transient response.

Here is another explanation from Peter Moncrieff of International Audio Review Opposites in Reactance

Consider next reactance, as another example of opposite behavior. Conventional subwoofers have large reactance, plus severe reactance changes, at low frequencies. This reactance comes from the driver's free air resonance, compounded by the resonance of the enclosure volume with this driver, compounded by the resonance of the port or vent (if any). This reactance creates four huge sonic problems, which preclude correct bass reproduction. First, this reactance sets up a barrier fence at a certain frequency, below which the conventional subwoofer cannot go, to reproduce the full bass spectrum. Second, this reactance stores energy and then releases it much later in time (as bass overhang and ringing). This spurious delayed energy release not only creates a phony bass sound (boomy overhang), but also obscures subsequent musical information (of all frequencies) that happens to occur immediately after each bass transient. Third, this reactance robs energy from the initial bass transient (the energy contained in that delayed energy release has to be stolen from somewhere), so the initial attack of bass transients lacks sufficient dynamic impact. Fourth, this reactance grossly corrupts the time domain waveform put out by the conventional subwoofer, so that its contribution to the overall musical transient does not properly add up with and cohere with the waveform put out by the main loudspeaker for this same musical transient.
But again the new TRW subwoofer is just the opposite, of conventional subwoofers. It does not have any reactance at very low frequencies. Thus, the TRW subwoofer does not evince any of these sonic problems that reactance causes in conventional subwoofers. First, the TRW does not have any barrier fence precluding response to very low frequencies, and can happily reproduce the full spectrum at full amplitude all the way down to DC. Second, the TRW does not have any spurious delayed release of energy, so its bass quality is inherently correct and tightly defined, without any phony boom or overhang. And the TRW also thereby allows you to hear much more information immediately after each bass transient (e.g. the woody timbre of a sounding board), so everything from music to special effects sounds much more real. Third, the TRW does not steal any energy from the initial bass transient, so you get the full dynamic impact of each bass transient, again getting you much closer to sonic reality. Fourth, the time domain waveform put out by the TRW is inherently accurate, instead of inherently screwed up, so its waveform correctly adds up with and coheres with each musical (or sound effects) transient put out by your maim loudspeaker, to give you for the first time in your life a correct, coherent transient. This last point might seem to be the most subtle sonically, but it turns out to actually be the most pervasive, affecting more sounds and more of your listening than you would ever have suspected.

Having owned the TRW Rotary subwoofer for 6 years, I can say Peter is correct.
 

stehno

New Member
Jul 5, 2014
545
0
0
Salem, OR
#51
Here is another explanation from Peter Moncrieff of International Audio Review Opposites in Reactance

Consider next reactance, as another example of opposite behavior. Conventional subwoofers have large reactance, plus severe reactance changes, at low frequencies. This reactance comes from the driver's free air resonance, compounded by the resonance of the enclosure volume with this driver, compounded by the resonance of the port or vent (if any). This reactance creates four huge sonic problems, which preclude correct bass reproduction. First, this reactance sets up a barrier fence at a certain frequency, below which the conventional subwoofer cannot go, to reproduce the full bass spectrum. Second, this reactance stores energy and then releases it much later in time (as bass overhang and ringing). This spurious delayed energy release not only creates a phony bass sound (boomy overhang), but also obscures subsequent musical information (of all frequencies) that happens to occur immediately after each bass transient. Third, this reactance robs energy from the initial bass transient (the energy contained in that delayed energy release has to be stolen from somewhere), so the initial attack of bass transients lacks sufficient dynamic impact. Fourth, this reactance grossly corrupts the time domain waveform put out by the conventional subwoofer, so that its contribution to the overall musical transient does not properly add up with and cohere with the waveform put out by the main loudspeaker for this same musical transient.
But again the new TRW subwoofer is just the opposite, of conventional subwoofers. It does not have any reactance at very low frequencies. Thus, the TRW subwoofer does not evince any of these sonic problems that reactance causes in conventional subwoofers. First, the TRW does not have any barrier fence precluding response to very low frequencies, and can happily reproduce the full spectrum at full amplitude all the way down to DC. Second, the TRW does not have any spurious delayed release of energy, so its bass quality is inherently correct and tightly defined, without any phony boom or overhang. And the TRW also thereby allows you to hear much more information immediately after each bass transient (e.g. the woody timbre of a sounding board), so everything from music to special effects sounds much more real. Third, the TRW does not steal any energy from the initial bass transient, so you get the full dynamic impact of each bass transient, again getting you much closer to sonic reality. Fourth, the time domain waveform put out by the TRW is inherently accurate, instead of inherently screwed up, so its waveform correctly adds up with and coheres with each musical (or sound effects) transient put out by your maim loudspeaker, to give you for the first time in your life a correct, coherent transient. This last point might seem to be the most subtle sonically, but it turns out to actually be the most pervasive, affecting more sounds and more of your listening than you would ever have suspected.

Having owned the TRW Rotary subwoofer for 6 years, I can say Peter is correct.
Sorry for my delayed response as I just happened upon this thread again. Yes, it seems Peter is often times correct in his assessments. When he rated the top 30 or 40 SS amp back around 1999, I think I owned 3 of his 4 top picks and his assessments seemed right on the money with each of those amps. It seems Peter is one of those rare birds with extremely well-trained ears. I've even heard rumor that other reviewers sit around the campfire telling scary Peter Moncreiff stories.

So you're the proud owner of a TRW subwoofer, eh? I know nothing about them, except I experienced a few minute demo at THE Show in I think 2007. I think that may have been their debut of the subwoofer and I remember walking away impressed but I also think it was a deliberately light non-offensive demo so as not to instill fear into visitors. I've never bothered to read up on the TRW sub but it certainly seems an intriguing technology.
 

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