How "Fast" is your bass? Does your subwoofer have "Speed?"

[Flint]

I edited my original post without the haze of several adult beverages in me. This should be easier to read and understand now.

I've seen and heard the terms "Fast" and "Speed" used in relation to deep bass for years. But those words are terrible descriptors of what people are discussing. Literally, the speed of a driver is defined by the frequency response. Higher frequencies require higher "speed" from "fast" drivers or else those higher frequencies don't get produced. It isn't complicated. The amount of time it takes a speaker to produce a simple 40Hz wave is always however long it takes for a 40Hz wave to be produced, which means cycling 40 times per second. 80Hz demands double the "speed" of 40Hz. 160Hz is inherently four times faster than 40Hz. The math is simple.

So, all subs and woofers have the same "speed" and are all equally "fast." Those terms, when taken literally, are defined by their operating range and nothing else. So, we need to stop using them.

That said, there is a difference in how low frequency sound is reproduced which many people like to use terms like "speed" and "fast" to describe. A woofer's ability to response very quickly to the power input from an amp is one of those. Some woofer struggle with getting going - but those drivers are for the most part cheap crap as any decent driver these days responds quickly to input voltage stimulus. So, unless we are talking about very low dollar speaker systems, like cheap sound bars and White Van speakers, I cannot imagine one woofer being any better or worse than another at how quickly it responds to input.

At the other end of the stimulus timeframe, however, there are often considerable differences in how long it takes a woofer to stop producing acoustic energy after the amp stops sending voltage to it. Some woofer systems are poorly controlled and will continue to resonate long after the signal stops - often called ringing. There are several causes for ringing:

1. Poorly designed woofers
2. Using a woofer designed for ideal performance in a sealed cabinet in a vented cabinet
3. Poorly designed woofer/enclosure systems which are not air-tight, improperly tuned and/or dampened (Qtc is the value used to describe this aspect)
4. Using a passive crossover increases the likelihood over carryover from the woofer after the signal stops
5. Using an amp with very low damping, like a tube amp or badly coupled solid state amp

All these things, sometimes all present in one system, can result in an output which resonates several cycles beyond the end of the stimulus.

In general, a well made vented woofer system with an appropriate Qtc for the driver will not have ringing issues, but poorly made vented systems can ring and resonate for a long time and sound "loose," "boomy," and "floppy." This all too common issue contributes to many assuming sealed woofers are always "tighter" than vented systems. While that is true when the vented system isn't designed and built well, it isn't the case when the vented system is designed properly. That said, it is easier to make a cheap sealed woofer system to perform relatively "tightly" than a cheap vented system. If you looking at quality stuff, these issues shouldn't exist.

So, when referring the characteristics which often get referred to as "fast" or having "speed" in the bass, I believe we should be saying "tight" or "dynamic".

Because of the use of the terms "speed" and "fast", an entire mythology has been evangelized and promoted throughout this hobby suggesting that smaller woofers are inherently "faster" because they are smaller and lighter. That logic makes sense when using the term "fast". But if we use terms like "tight" or "dynamic", then the size or weight of the driver doesn't really apply. Instead, to get a "tight" or "dynamic" performance, we should expect well controlled driver/enclosure combinations which are not limited by driver size or vented/sealed enclosure designs.

Straight up, we should discourage the use of the terms "fast" or "speed" when it comes to bass.

There is much more to add to this specific topic to more fully understand it, but the basic concept that "speed" is a terrible descriptive word for the tightness of a woofer system. Take that term along with "fast bass" out of the lexicon.

 

[TitaniumTroy]

My old speakers had the Fastest bass in the land as they used planer woofers. Start on a dime and stop on one too. Just teasing you Flint with some Audio mythology, they did have great definition. Too bad about the limited dynamics and inability to play very loud.

 

[bmwuk]

My subwoofer requires several dates and courting. So probably not too fast.

I learn something every day here it seems.

 

[Randy]

Great explanation Flint those terms are pure conjecture and writin folks just need things to write about so they use inaccurate terminology to relay their message.

I was originally led to believe the myth of sealed boxes being tighter than vented boxes, until I was exposed to properly designed and built vented boxes and then I saw the light.

 

[Flint]

One of the problems with using inappropriate terms in hopes of better explaining what we hearing is that we are pretty smart people in general, yet most know almost nothing about the physics and mechanics of audio reproduction, so as smart people we start using logic from the knowledge we do have to conjecture that a speaker sounds "fast" because it is smaller and lighter. After all, in most aspects of our lives fast things tend to be small and light. So we start inventing theories that having four 7" woofers will inherently be better than one 15" woofer, even though that isn't a hard and fast rule by any means.

There are potential benefits to having four 7" woofers over one 15" woofer, but those benefits tend to be more about configuration options, lowering costs, or simplifying manufacturing and supply chain. I have long argued that if you shop for high quality woofers which operate very well from 60Hz to 400Hz, bigger is usually better. I've found that getting the same audible performance from four 7" woofers requires spending more money on those four woofers than you would pay for the one 15" woofer of equal or better performance. On top of that, smaller woofers all struggle to perform really well at lower frequencies, even when used in groups. So, you could pay less for a single 15" woofer and get deeper bass output and lower THD at those lower frequencies than you can get from four high quality 7" woofers.

Of course, that's just an example to make a point - there are so many variables anyone knowledgeable about speakers can find holes in that example.

So, we now have an entire swath of very honest and good people who want to enjoy great sounding music in their homes believing the nonsense about small woofers somehow being "faster" when use of that term was really meant to my "tight", "dynamic" and "controlled". That myth is just wrong.

 

[Flint]

Yo... I edited the original post to be much easier to read and understand.

 

[Haywood]

I really love these articles you keep posting. They are super informative.

 

[MatthewB]

I've always been intrigued by companies that use multiple smaller woofers to achieve the effect of a larger driver but that seems to go against the laws of physics. A 15" woofer to me seems like if designed properly would have no issues reaching sub 20Hz frequencies where a 8" woofer (no matter how many) seems like it could only get down to about 30Hz before dropping off. So in theory wouldn't having six 8" drivers in the same enclosure at best only get down to about 30Hz? Or am I missing something.

 

[Flint]

I've always been intrigued by companies that use multiple smaller woofers to achieve the effect of a larger driver but that seems to go against the laws of physics. A 15" woofer to me seems like if designed properly would have no issues reaching sub 20Hz frequencies where a 8" woofer (no matter how many) seems like it could only get down to about 30Hz before dropping off. So in theory wouldn't having six 8" drivers in the same enclosure at best only get down to about 30Hz? Or am I missing something.

You can make a smaller driver play lower by increasing the weight of the cone - that's the principle behind those car subs which have a 2 inch excursion. But, when you make the cone heavier, you then have to equally increase the motor strength, which means larger and stronger magnets - again, this is seen in those crazy car subs. You still have much lower sensitivity than a huge subwoofer because of the smaller cone area.

But, if you take enough smaller woofers with heavier cones to get the same lower free-air resonance of the bigger woofer, and you increase the magnet size and weight in order to maintain a nice, tight controlled motion, then you could get similar performance to a huge woofer. However, the cost of those smaller woofers combined will greatly exceed the cost of the larger woofer.

To give an example, I can buy four 8" woofers with similar low end extension and Qts as a high quality 15" woofer and get similar performance. But, each of the smaller woofers will cost about 75% of the 15" woofer, resulting in a speaker system which costs 3x more to make.