Can Technology Produce Small Subwoofers With Big Bass?

Andrew Welker explains the progression from table-sized subwoofers to small subwoofer enclosures, how amplifier power figures in, and DSP technology.

Can Technology Produce Small Subwoofers With Big Bass?

I recently did a video talking about why speakers morphed over the years from being fairly wide and shallow to becoming narrower and deeper and some of the reasons, at least in my opinion, that that transition has occurred over the last 40 years or so.

Somebody commented on that video and said, "Wait a minute. You didn't see anything about subwoofers. What about subwoofers? They seem to have gotten smaller. Why is that?" And it's a really good question, and I didn't even think to talk about it in that video, so hence, I'm going to speak, in my opinion, in today's video why subwoofers have gotten smaller.

Now, first of all, have they really gotten smaller? Now, many people will think that subwoofers are a newish thing that came about just in the days of the advent of home theater, but they've been around way, way before that. And many of them were large. I remember subwoofers by some manufacturers that doubled as equipment stands they were so big. They were built into something that was an actual coffee table or end tables to try and hide them, but they were large. And part of the reason I believe that subwoofers have become smaller and smaller over the years ... In most cases, not in all ... Is an aesthetic one. As I mention in that previous video about when we came to the advent of multi-channel home theater and we had now to have, instead of a pair of stereo speakers, we had a pair of speakers, a center channel, a pair of surround channels, and probably a subwoofer, and just the visual impact on big boxes all over let's say a regular or normal sized living room or family room would be just too much.

And one thing that came about in that advent of home theater was the fact that people wanted really small. There was this thing that was all the rave in the '90s and pretty much into the early 2000s called the sub-satellite system, where you had either five identical or four identical plus a little center channel, all very small, and then a smallish subwoofer to provide the bass that all of those satellite speakers couldn't. But why did we go from subwoofers that were coffee table-sized into some that are very, very small? You've probably seen some of those small little cube subwoofers, maybe one foot cubed. Talking about all these performance things, plays down to 18 hertz, et cetera, et cetera.

Well, on the technical side, subwoofers, I believe, have become smaller. The push for aesthetics, yes. But what's made that possible is modern electronics and driver design. What I mean by that is with the advent of cool-running high power in small packages, Class-D amplification, and DSPs, or digital signal processors, allowing all kinds of exotic tailoring and EQ of driver response and specifically limiting and compressors that you could accurately put the brakes on things before you blow up woofers and things like that. Those were two very important advents that allowed us to make subwoofers smaller.

I think the aesthetic demand, people love to have stuff, a small little cube in the corner that it's unobtrusive and get great bass out of it. But why did we need Class-D amplifiers and DSPs for these small subwoofers? Well, from a technical standpoint, if you think about it, making the cabinet volume smaller and smaller and smaller means that the natural amount of bass, so the bass that a driver in a particular box can produce without any equalization, so it's natural response we usually call it, means that it's not going to have much bass. It's going to be significantly rolled off because of that small cabinet volume. What can you do in that case? Like how do you get good bass performance when you have very little cabinet volume?

And the only way to do that, really, is with equalization. We now boost those frequencies that are missing, and now you can get a flat response, and you can get a small little cube box that will play down to 18 hertz. Well, the problem is is that equalization consumes a massive amount of amplifier power. And also what it means is that this drive unit is operating in a small volume of air where there's massive pressures acting on it. And so the driver, the woofer needs to be built in a very robust way so that the surround doesn't collapse because of the changing air pressure. And you need a lot of motor strength to overcome that pressure.

Here's what you end up with. It's almost like the law of diminishing returns. You want a subwoofer in a small, small box, but the woofer itself, the motor, everything has to be so overbuilt that you suck up even more of the internal volume, and you have less for the driver to operate with. That's a really, really interesting thing.

How are we overcoming this? Well, like I said, we just need gobs of amplifier power to apply that EQ and to overcome the very low efficiency of those systems. If we have to really beef up a woofer and make things heavier and surround stiffer and all of those things, guess what? The natural efficiency of that woofer starts quickly going down, so we've got now a worst case scenario really from an engineering standpoint. We have almost no cabinet volume to deal with. We've got an inefficient woofer working inside it, and we want decent output level and actually some bass so it performs like a subwoofer and not a little bookshelf speaker. So we throw masses of amplifier power. And you've probably seen some of these small subwoofers claiming 1500 Watts or 2000 Watts or whatever of amplifier power. And in many cases, that will actually be true, and they have to sink a ton of power to overcome all of those limitations because the laws of physics can't be broken.

There is no such thing as a free lunch in subwoofer design, like pretty much everything else in life. And we just have to realize that everything in subwoofer design is compromised. If you want a small, small cabinet, there's going to be some major trade-offs. And I would say that an average size subwoofer like this EP125 or a medium-sized subwoofer is likely in most cases going to outperform one of those tiny little micro-cube subwoofers.

One other thing to mention about those small subs is, in almost every single case, you'll find that it's a sealed box, or it's a woofer plus a passive radiator. You will never see one of those small cubes ported, as a ported system like many conventional subwoofers. The reason why? There's nowhere to put a port of sufficient size to tune that cabinet properly. Plus, because of those massive air pressures in that small volume that I was talking about, all you would get is port noise and whistling and wind noises, and things wouldn't sound very good.

I hope that's cleared up that question. I do believe that, overall, if we look going back to the earliest days of subwoofers to today that they have, on average, becomes smaller and smaller. Although many subwoofers are still large, many of them have become smaller. And the reason was two-fold. One, it was an aesthetic and a demand from the customer base to make smaller subwoofers. And on the engineering side, the advent of things like Class-D amplifiers and DSPs to allow us to actually try and break the laws of physics and get a massive amount of bass output out of a small cabin.

I hope that answers that question. Again, thanks for watching. Thank you very much for all of your comments. As you can see, like in today's video, it's from those comments that I get ideas for new videos, and I'm happy to answer your questions.

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