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Subwoofer Integration: Bass Management and Distance Settings Explained

by June 05, 2016
Goofy Home Theater Set Up

Goofy Home Theater Set Up

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:

Denon X5200 Bass Mgmt.jpg

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.

AT 4400 LCR.jpg
 

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.

SB13U FR.jpg

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.

XTZ Room Analyzer.jpg

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.

Confused about what AV Gear to buy or how to set it up? Join our Exclusive Audioholics E-Book Membership Program!

 

About the author:

Steve Munz is a “different” addition to Audioholics’ stable of contributors in that he is neither an engineer like Gene, nor has he worked in the industry like Cliff. In fact, Steve’s day job is network administration and accounting.

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Recent Forum Posts:

RF2000 posts on February 26, 2018 09:54
aarons915, post: 1146127, member: 63086
This is a great article the only thing I would add is the importance of your speaker having a 4th order high pass to blend with the subwoofer. 99% of receivers/processors use a 2nd order high pass filter and most speakers these days are ported so they don't work correctly. So you really have 2 choices, one is to get a processor or receiver capable of a 4th order high pass filter on the mains, I use an emotiva UMC 200 to achieve this but there are other ways. The 2nd way is to bung your speaker in order to give it a natural 2nd order acoustic high pass filter which combines with a 2nd order high pass for your 4th order total high pass filter.


I think this would only matter if your crossover point is set to where your mains are acoustically rolling off. If you are far enough above the acoustic rolloff of your speaker and you use a 2nd order high pass there shouldn't be a need for a 4th order low pass.
aarons915 posts on July 16, 2016 18:04
This is a great article the only thing I would add is the importance of your speaker having a 4th order high pass to blend with the subwoofer. 99% of receivers/processors use a 2nd order high pass filter and most speakers these days are ported so they don't work correctly. So you really have 2 choices, one is to get a processor or receiver capable of a 4th order high pass filter on the mains, I use an emotiva UMC 200 to achieve this but there are other ways. The 2nd way is to bung your speaker in order to give it a natural 2nd order acoustic high pass filter which combines with a 2nd order high pass for your 4th order total high pass filter.

And to the people who think it doesn't matter much, I've confirmed with measurement equipment that the difference between 2nd order and 4th order high pass when crossing to the sub is pretty drastic, with a 2nd order high pass without the ports sealed you'll get a large dip or peak at and around the crossover frequency which won't be as seamless a blend between the mains and sub. Just my 2 cents.
qwsa posts on June 09, 2016 18:56
Hi,Gene
Did you mention what level should we set our (Master volume) when setting each speaker level to (75dB)?
(0dB) is too loud (unbearable) for my room size? (15x12)
To use (0dB) for Master volume as Reference should one not have a minimum room size requirement for this?
My room main seating is about 10 feet away from the main speakers and the subwoofers
I have the (Master volume) set to (-10dB) when I set the speaker levels to around (+44/+45dB)
Regarding subwoofer distance, not quite sure… but I think (Auto EQ) set my subwoofers to (40 feet)

Should I leave it at that distance or take out the tape measure?
GarryP posts on April 30, 2016 18:46
Surprised that there are no replies to such an easy tweak, so anyhow here is my experience.

Equipment is dual SVS SB2000 subwoofers in front corners, Oppo BDP-103D, and Anthem MRX-510. Initially running ARC gave surround speakers (bipoles) a xover of 120Hz, fronts (floorstanders 160mm drivers) 60Hz, and centre (MTM 160mm drivers) 90Hz. Power amps are Rotel 120W per channel. The distances were all checked via tape measure first. Listening levels are what I would call normal ie adjusted so speech level sounds just right.

Manually changed the xovers to all being 120Hz and played some bass heavy movies such as Battle Los Angeles and Edge of Tomorrow. The subjective result was a smoother, more even bass that sounded as if it had more dynamic range. Speech also sounded clearer. I haven't the equipment to do before and after measurements so this is just my impression over the past two weeks using a variety of media - BD, CD, and DTV.

"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."

Thank you for this article Audioholics, as this is something that I wouldn't have thought to try otherwise.
shadyJ posts on April 18, 2016 15:48
Nice article Steve, but I always thought of the sub as a linebacker rather then the QB! QB = center speaker; a central player that gets all the attention, but it is nothing without a good team. A good home theater is a team effort from all components!
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