Subwoofer Integration: Bass Management and Distance Settings Explained

If you’re a regular reader of the site, you’ve probably seen us claim that subwoofers are one of the most important pieces in an A/V system. To qualify that statement, one should consider that a great subwoofer is a lot like a great quarterback. Not only do they do their job well, but they have the potential to significantly improve the performance of their supporting cast as well. Of course, there’s one small catch. To live up to these lofty expectations, your subwoofer has to be properly integrated with the rest of your system. Today we’ll be going in depth for two settings that can make or break that process: bass management and the distance setting. Failure to get these adjustments right can adversely impact the sound quality of your home theater and its ability to reproduce the rumbles in action sequences of blockbuster movies. Let us show you how to ensure you get the BIGGEST WOW effect! 

Please check out our recently added YouTube instructional video that gives you step by step on how to configure your bass management settings before reading this article.

 How to Set Up an AV Receiver Bass Management, HDMI and More YouTube Instructional

Bass Management: Isn’t that part of the US Fish & Wildlife Services?

In simple terms, bass management filters out the low bass that would normally be fed to your speakers, and redirects that content to your subwoofer. In modern A/V receivers and pre/pros, this is accomplished via the use of digital high pass and low pass filters. The most common configuration is the THX standard, which specifies a 12dB/octave high pass filter at 80Hz for your speakers, and a 24dB/octave low pass filter for the subwoofer. With the pair of filters in place, you theoretically get a smooth transition through the crossover region (assuming your speakers also exhibit a 12dB/octave natural rolloff), as seen in this example:

Bass management of the Denon AVR-X5200W in action
Note: levels were not matched while taking this measurement

So set the crossover in your receiver or pre/pro to 80Hz and you’re all set, right? Not quite. When it comes to bass management, there’s no such thing as a one-size-fits-all solution. With respect to the THX standard, 80Hz makes a lot of sense when you take into consideration their entire ecosystem of hardware. Glancing at Atlantic Technology’s website, one can find several THX certified systems, ranging from their beastly THX Ultra 2 certified System 8200e down to the petite THX Select certified System 4400. Even with the less costly System 4400, you’re looking at L/C/R speakers boasting dual 5.25” woofers in a relatively large, sealed cabinet; that’s a pretty beefy speaker compared to your average mini-monitor. Now consider this system is only certified for smaller rooms up to 2,000 cubic feet. Suffice it to say, it takes a lot of speaker to get a lot of output with an 80Hz crossover, even in a smaller room.

 

The THX Select certified Atlantic Tech 4400 L/R speaker is a pretty heavy duty piece of equipment for a <2,000 cubic foot room

Turn It Up

So what happens if we bump up the crossover frequency? If you recall our article on the laws of the decibel, you’ll know that extending system response by an octave requires four times the driver displacement, or corresponding contributions from a port/passive radiator. In the case of a relatively modest bump in the crossover point from 80Hz to 120Hz, you’re still cutting driver displacement by more than half. This a huge deal: the implication is that instead of needing a pair of 5.25” woofers as seen in the aforementioned 4400 L/C/R speakers, you could get by with a single woofer assuming its power handling was up to snuff. With any given speaker, this also means that you potentially net an additional 6dB of displacement-limited output versus an 80Hz crossover frequency, as well as lower distortion at any given volume. Not too shabby for a setting that takes a second or three to switch.

A Word On Ports: As mentioned, ported speakers will tend to throw off the math a little bit. A port functions as a Hemholtz resonator, adding output over a relatively narrow bandwidth. If the port is tuned relatively low (<60Hz), the port contribution at 80Hz will be negligible, so the math still works pretty well.

Unfortunately, there are a few downsides to raising the crossover frequency. Not all subwoofers offer enough top end extension to allow for a 120Hz+ crossover. In addition, as the crossover frequency goes up, it becomes easier to locate the subwoofer by ear. As far as the subwoofer goes, we like to see a smooth response up to at least 200Hz to ensure a smooth blend between it and your speakers, even if users opt for a higher crossover setting. An example of such a subwoofer is the SVS SB13-Ultra, and you can peruse our full list of reviewed subwoofers to see how they all stack up in this respect.

Frequency response for the SVS SB13-Ultra

While getting a subwoofer that extends to 200+Hz isn’t a major challenge, the topic of subwoofer localization is a bit more complicated. We’re aware of at least one AES paper on the topic, #6431 “Detection of Subwoofer Depending on Crossover Frequency and Spatial Angle between Subwoofer and Main Speaker.” That paper has several useful conclusions to keep in mind. For the tested listeners and samples used, 120Hz (with a 24dB/octave slope) was the maximum crossover they could use without anyone detecting the subwoofer. However, approximately half the listeners couldn’t detect the subwoofer at the maximum crossover frequency tested (227Hz). The practical meaning of this is that a crossover at or below 120Hz is a relatively safe bet, but it can be worth experimenting with a higher crossover to see what works for you. In addition, it is our experience that good placement as well as running a dual-subwoofer setup can also help reduce the effects of localization, particularly if those subs are adjacent to your main L/R speakers.

Last but not least, any discussion of bass management has to include taking measurements. While the combination of high and low pass filters utilized in bass management theoretically results in a smooth response, in practice the actual results can be anything but. In this respect, experimenting with different crossover points can have a significant impact upon your system performance, above and beyond the benefits already mentioned. The key is being able to measure those different responses with a tool like Dayton Omnimic, XTZ’s Room Analyzer, or REW. These tools allow you to see in real time if you have any significant peaks or dips around the crossover point, and find the crossover frequency which yields the smoothest transition.

For optimal performance, you need a measurement system like XTZ’s Room Analyzer II.

Distance

Seriously, how important can this be? You let auto-calibration take care of this for you, or if you’re feeling particularly hands on, you might whip out the tape measure, right? A word of wisdom: don’t underestimate the power of the distance setting in your A/V receiver. Obviously the primary job of the distance setting is setting a delay relative to your other speakers. Note, the distance reported by your receiver’s auto-calibration will be inclusive of any delay caused by signal processing happening inside the subwoofer (EQ, low pass filtering, etc.), which can add several feet to the distance per your tape measure. Above and beyond this, the distance adjustment functions as a phase control of sorts. Adding or subtracting a couple feet from the distance of your subwoofer is a viable way of getting rid of an ugly peak or dip around the crossover point. Again, to make the most out of this tool, one does need the ability to take measurements. Still, who would have ever thought such an innocuous setting could have that kind of power?

Summary

Got small speakers and a desire for bigger, better output? Experimenting with your receiver’s bass management and distance setting could be just the ticket. Obviously no bass management or distance settings will turn a junk speaker into a great one; however, when considered in the context of overall system design, they can help create a system that is something more than just the sum of its parts. Have you already played the game of crossover roulette? Make sure to report your experiences on our forums.