It's all about the bass

“It’s all about the bass”… we hear that a lot.

Last week we posted a blog on the bookshelf vs floor stander dilemma. We briefly touched on bass management and by golly did we open a can of worms!

The amount of questions we received about digital bass management is dizzying – and it certainly can be a confusing subject. But you know how we tackle problems like that: we write a blog and explain a little further.

Remember that all questions are good questions and we are more than happy to explain further if you get stuck with your set-up.

As we mentioned in last week’s blog, digital bass management is pretty important and incorrect settings in the AV receiver can result in poor sound quality, and in some cases can even damage the loudspeakers.

The fundamental principle of bass management (also called LFE Crossover; ‘LFE’ stands for ‘Low Frequency Effects’) is that bass content in the incoming signal, irrespective of channel, should be directed only to speakers capable of handling it, whether that be the main system speakers or one or more subwoofers.

A Blu-ray DVD typically contains seven discrete speaker channels, and also a Low Frequency Effects channel. The LFE channel is an independent channel and has no effect on the other speaker channels. The information that is in the LFE channel extends up to 120Hz regardless of whether you have bookshelf speakers or full-range super tower speakers. It is important to distinguish between the LFE channel and what goes to a subwoofer. The LFE is a production channel, whereas the subwoofer is a playback channel. The sound engineers determine what goes to the LFE channel, and the users of the home-theater systems determine what ends up coming out of the subwoofer.

Another popular misconception is that the LFE channel is the only channel on a DVD which contains deep and powerful bass. In reality, depending how a given DVD is mixed, there can also be deep, powerful bass in any of the speaker channels.

In a modern Home Theatre system, the speakers are typically not designed to handle deep bass. The goal of proper digital bass management is to ensure all of the deep bass present in the DVD is directed to the subwoofer, which leaves the speakers to handle the mids and highs.

AV receiver settings can be confusing or misleading, because speakers are often labeled ‘Large’ or ‘Small’, and in reality these terms have little to do with the actual physical size of the loudspeaker itself.

A Small setting doesn’t necessarily mean the loudspeaker in that channel is physically small – it just means the bass below the crossover frequency specified by your AV receiver is redirected to the subwoofer. While historically a Small setting typically meant a crossover in the 80-100 Hz range, modern AVRs now commonly offer crossover frequencies as deep as 40 Hz, which covers even physically large and bass-capable speakers like towers.

For reasons mentioned before, with the possible exception of truly full-range tower speakers, a Small setting is recommended for all speaker channels, since this will ensure that the speakers are not sent bass which is below their safe and effective limits. This improves the sound quality of the speakers, and it also frees up additional power in the AV receiver, thereby improving overall system dynamics.

A Large setting means that speaker channel will receive a full-range signal from the AV receiver. (Again, with the possible exception of truly full-range tower speakers, a Large setting is generally not recommended, since it might overload and/or damage the speaker, and it also can consume additional power from the AV receiver, thereby reducing dynamic headroom.)

Crossover

The optimal crossover frequency for each speaker channel varies with the bass extension and dynamic output capabilities of the connected speaker. Below is a general guideline for recommended speaker/subwoofer crossover frequencies:

Tiny ‘satellite’ speakers: 150-200 Hz.
Small center, surround, bookshelf: 100-120 Hz.
Mid-size center, surround, bookshelf: 80-100 Hz.
Large center, surround and bookshelf: 60-80 Hz.
Very large center, surround, bookshelf: 40-60 Hz.
Tower speakers with 4”-6” woofers: 60 Hz.
Tower speakers with 8”-10” woofers: 40 Hz or Large (i.e., full-range).

If you are unsure of the best crossover frequency for each speaker channel, you should double check with the speaker manufacturer

There are several types of bass management systems that can exist.

Here are the most common:

Fixed: These systems merely ask you whether your speakers are Large or Small and do not offer the option to change the frequency of the crossover point. There is a crossover frequency (usually 80 or 90Hz), but is it not changeable by the user. While this is simple, it may not be right for your individual set of speakers. Being the highly engineered products that they are, with AV receivers you generally get what you pay for. As a logical consequence, it is the budget AV receivers that would offer this bass management option.
Variable Crossover: These systems offer you the ability to set your speakers to Large or Small, but also offers to alter one global crossover frequency which applies to all channels being bass managed. This one-for-all crossover frequency may not be optimal for all the speakers, particularly if you have a mixed speaker system and there are tower speakers in the system. This type of crossover system is found on most modern receivers and preprocessors.
Multiple Variable Crossover: There exist a few companies that allow a crossover frequency to be assigned to each individual speaker channel that is being bass-managed. This is a nice feature because it allows the crossover frequency to be tailored to the bass extension and dynamic output capabilities of each individual speaker. On the downside, this is a little more complicated to set-up and if not done right can make things worse instead of better. The new Anthem MRX AV receivers fall into this category, as well as the top of the range Yamaha RX-V1079, RX-V2079 and the RX-V3079 AV receivers.

So we clearly are in a little bit of a pickle here: on the one hand there is the reality that most of us have an AV receiver with variable crossover bass management; on the other hand, there is the issue that most of us also have a mixed speaker system. And as we have just stated: that not the ideal situation.

Here’s what to do:

With an AV receiver which can only apply a variable (not multiple) crossover and large floor standers for the main channels, there are two recommended set-ups to try:

Option 1: Set the main tower speakers to Large, the other speakers to Small, and crossover to 80 Hz. Usually when the mains are set to Large, there will be an option for sending a duplicate signal to the subwoofer, so the sub works on 2 channel sources – this will typically be called double bass, extra bass, plus or sub+ mains (see below in Subwoofer Mode Menu Options).
Option 2: Set all speakers to Small with an 80 Hz crossover.

Generally speaking, in this kind of set-ups, most people prefer option 1.

But wait, there is more…

You may find your AV receiver also has a Subwoofer Mode menu option, which will vary depending on the sophistication of the bass management circuit, and also the speaker size selected. Below is a description of common AV receiver subwoofer modes:

LFE (aka Normal)
- The LFE channel is sent to the subwoofer.
- The redirected bass from all speaker channels being bass-managed (Small) is sent to the subwoofer below the specified crossover frequency.
- The bass from any speaker channel being sent a full-range signal (Large/Full-Band) is not sent to the subwoofer.

LFE+Mains (aka Double Bass, Plus, Sub+Mains)
- The LFE channel is sent to the subwoofer.
- The redirected bass from all speaker channels being bass-managed (Small) is sent to the subwoofer.
- The bass from any speaker channel being sent a full-range signal (Large/Full-Band) is duplicated and also sent to the subwoofer. The cut-off frequency for this duplicate signal depends on the sophistication of the AV receiver bass management circuit.

The AV receiver subwoofer menu may also have setting called ‘LPF for LFE’.

LPF stands for Low Pass Filter, which blocks high frequency signals above the cutoff frequency and passes low-frequency signals. Low-pass filters are generally used on subwoofers to block high frequency signals that they cannot reproduce.
The LPF for LFE setting controls the highest playback frequency for the LFE (.1) channel before being cut-off (low-pass filtered) by the AV receiver.

This setting should be adjusted to 120 Hz, which is the default setting in most AV receivers, and also matches best practices/standards for encoding DVDs.

Nearly all modern AV receivers offer an auto-set-up routine with a plug-in microphone and easy to follow steps.

The four core functions of the auto-set-up routine are:

Level matching the speaker channels and the subwoofer so they all play at the same relative volume, which results in a balanced sound field.
Time-aligning the speaker channels and the subwoofer so they all arrive at the listening position at the same time, which is important for convincing panning effects across multiple channels.
Equalizing the speaker channels and the subwoofer for the best sound quality.
Selecting the best digital bass management settings for each loudspeaker channel and the subwoofer.

Auto-set-up routines occasionally make non-optimal choices (or even outright mistakes), particularly in the digital bass management settings. For example, an AV receiver might assign a crossover frequency which is too deep for a given loudspeaker, or it might even set a loudspeaker channel to full-range when it should be bass-managed instead. So check whether the auto-set-up is to your liking, revert to the basics and consult with your speaker and subwoofer company if you are not happy or unsure about the result.

There’s a whole lot more to this topic, however this should really drive home how important these settings are to a system. Now that you know a little more about it we hope you’ll go to your receiver and re-check your settings to optimize your speakers and system to operate at its optimal potential. We highly recommend beginners making their lives a lot easier by setting ALL of their speakers to SMALL and using their AV receiver’s bass management (80Hz crossover) to route the bass info to a powered subwoofer. This will almost always give you a great result to start from without manual tweaking to optimize the performance.