AV RECEIVER TECH

If you were ever curious as to why a source unit would offer bass management and not leave that duty to the processor, the answer is simple: In the vast majority of cases, the 5.1-channel inputs on a receiver or pre/pro bypass the unit's internal processing, equalization, and crossovers—which, of course, means the processor's bass management is bypassed. Naturally, if you're using the 5.1-channel analog inputs, the receiver or pre/pro knows that the signals have already been processed in the source unit; all it needs to do is pass them along untouched. There are a few receivers and pre/pros that will let you use bass management with the 5.1 inputs, but most will not. With the release of the multichannel audio formats SACD and DVD-Audio, this issue has become a hot button. At this point, because of copyright and piracy issues, you cannot pass the high-resolution signals from an SACD or a DVD-Audio disc through the digital outputs, so the signals must be internally processed and sent to the receiver or pre/pro via the player's 5.1-channel analog outputs. If your player does not have internal bass management, you will either have to use an outboard bass-management system or go without, based on the aforementioned fact that most receivers' and pre/pros' 5.1-channel inputs bypass their management systems. Surprisingly, there are many SACD and DVD-Audio players that don't offer bass management, so make sure you know what a player can do before you buy it, especially if you have bass-limited speakers anywhere in your system. Sending a full-range signal to a speaker that isn't full-range (i.e., almost all center-channel and surround speakers, plus a surprising number of front speakers) can obviously have disastrous results.

While it's not as detrimental to your system's performance as not employing crossovers at all, making sure you don't employ multiple crossovers is also an important consideration. Whether to use the crossover system in your processor or your sub is a debate that must wait for another day (it essentially boils down to your equipment's capabilities), but the first step is making sure you use one or the other. If you have a crossover system in both components, you need to find out if either one has a bypass option. In the processor, this will usually be a setting buried somewhere in the menu (consult your manual). On the sub, the bypass option is usually in the form of either a separate set of inputs (labeled bypass or something of the sort) or a switch that will tell the sub to forego the crossovers for the main input. If you engage both crossover systems simultaneously, you'll run into a situation called cascading crossovers. This, in effect, is what happens when you employ multiple circuits in the signal path next to one another, which multiplies the effect that a single circuit would have produced. The result can be serious phase anomalies, drops in level (usually around 6 dB), and other noticeable problems.

The bottom line is to do your homework. The SACD and DVD-Audio formats have helped bring the bass-management issue to the forefront, and there's more information out there about it than ever before. Read the literature carefully for the gear you already have and make sure you ask the right questions about the gear you're looking to buy, including some of the issues that I've raised here. Not only will proper bass management help protect your system from damage, but it will improve your system's performance in ways you may have never thought possible. A proper investment in time and, in some cases, money to get your system's bass management right is an effort that will always provide positive results.

Although the masses have spoken and the situation is becoming rare, there are still SACD and DVD-Audio players on the market that don't offer proper bass management—and let's not forget about the earlier players, of which there's an even higher percentage that don't have it. As some of you who own these players may have already learned the hard way, virtually all receivers' and pre/pros' multichannel inputs bypass any bass management they offer. However, all is not lost if you find yourself in this situation. External bass-management systems are already showing up on store shelves, such as the LFE-3 unbalanced ($399) and LFE-4 balanced ($899) models from M&K and the ICBM-1 ($249) from Outlaw. True, these components require an extra outlay of cash and some extra cabling; however, when you consider the alternative, investing in them is a wise move. If you continue to run your system without proper bass management, you may very well end up spending a lot more to replace your speaker system, not to mention the fact that your ears may never forgive you.