This article aims to clarify some of the issues surrounding the use of Bass Management (or bass redirection as it’s sometimes known). This applies to all AV systems and should be considered as guidance when making installation decisions.
Some people advocate that differences in professional and domestic audio requirements dictate slightly different approaches to Bass Management. Wrong! For the recording studio or large broadcast venue to achieve the best audio in-room integration with accurate real-life sound the same principals apply along with the need to have the system, whether it be 2 channel or multichannel, set up correctly. The pursuit of audio excellence with a dynamic audio experience that mirrors closely the original recording depends on many factors that apply the same irrespective of domestic or professional requirements.
This article, however, focuses on the domestic user which after all said and done is the ultimate requirement for HiFi and the place where audio listening is enjoyed the most.
The primary function of Bass Management in Home Theatre or Multichannel audio only reproduction is to increase the dynamic range, or the total sound pressure (make it louder) that can be delivered by the speaker system. However, depending on the performance of the loudspeakers in use, this priority is not appropriate in the pursuit of HiFi and all situations where accurate music reproduction is desired. Who doesn’t want accurate audio reproduction? Isn’t that what we all want?
Switching off Bass Management in most AV Processors is simply a case of ensuring that the Subwoofer output is turned “ON” and that all satellite speaker size options are set to “LARGE”. This effectively tells the processor that all speakers are to receive a full range signal and that bass for each channel is to go directly to that channel without filtering. The subwoofer output is a channel of its own known as LFE (Low Frequency Effects).
The increased popularity of multichannel reproduction in the home has led to the desire for cheap speaker systems which can reproduce high sound pressure levels. Unfortunately, this requirement for cheap speakers is in direct conflict with quality audio reproduction. The simplest way of reducing the retail price of a product such as a loudspeaker is to cut back on the quality of the components and materials used. However, there is a direct relationship between the cost of a moving coil loudspeaker and its potential dynamic range. This can be attributed to a number of factors. For example, a speakers drive-unit metal parts act as a sink for the heat generated by the voice coil, so as the mass of steel used is reduced for cost-saving purposes, so the speaker’s ability to handle power is degraded, increasing compression and resulting in significant efficiency reduction. Magnet size and cone area also tend to be reduced in an attempt to cut costs. Again, the trade-off is efficiency and dynamic range, both of which suffer as the compromises are made.
A way of helping a low power system to deliver more sound pressure is to divert the low frequencies away from the speakers and into a subwoofer. Bass Management was devised to perform this task in the digital domain. It is a collection of filters and gain controls commonly provided as software settings in AV Processors or Decoders that can redirect low frequencies away from the satellite speakers (left, centre, right, surround left and surround right in a 5.1 configuration) and route it to the dedicated LFE (Low Frequency Effects) channel. Because the processing is accomplished in software it is attractive to those manufacturers who wish to increase the dynamic range of a cheap and inferior speaker system.
As described, Bass Management was devised for as a means of extracting more performance from cheaper speaker systems. However, in high-quality audio systems, it should be avoided. The improvement in dynamic range that may be achieved with Bass Management has side effects and in high-quality systems these side effects are significant. The reasons for avoiding its use in high-quality systems can be considered as follows: