One of the key upgrades with the coming of Surround Sound audio systems was the addition of the Center speaker; providing anchored sound centered right at the screen. For example, for dialog.
But it turns out Home Theater, Center speakers end up getting fried out of proportion to all the other speakers! The culprit is excess bass. In this post I'll explain why that happens, and what to do to protect against it.
Given space considerations and room aesthetics, Center Speakers are usually not very large. And they are not really intended for "full frequency range" playback. This is no problem at all for their primary function of serving up dialog. But there's a gotcha here:
The guidelines for creating multi-channel audio tracks for movies say the audio engineers must NOT assume the user will have a Subwoofer in their home system. This means all bass critical to the proper presentation of the movie must ALSO be included in the main speaker channels. That bass won't be as loud as bass mixed for the special, LFE channel (the ".1" of "5.1" or "7.1" tracks, for example), but it will still carry substantial energy.
TECHNICAL NOTE: The main speaker channels have no lower limit on how low they can be authored to go in frequency. The reason for the special, LFE audio channel is to provide a channel dedicated to carrying LOUD bass audio. This is accomplished by recording the LFE channel at -10dB attenuation compared to the normal speaker channels -- thus providing extra headroom for that LOUD bass. During playback, Subwoofer Boost is applied to get the LFE audio back up to the proper level to match against the audio authored for the main speakers.
Now, although there is no fixed rule for this, what USUALLY ends up happening is this main speaker, movie bass gets authored into the Center speaker channel!
The idea is the Front Left and Front Right speakers should be keep free for music in the audio mix. And the Center speaker is the most likely "next speaker" for owners to add when upgrading to Surround Sound.
TECHNICAL NOTE: These guidelines are for movies. There's no real consensus on how to handle this among folks who mix multi-channel music. But the problem -- the thing which stresses the Center speaker -- is typically the "effects" bass in movies.
There is an EASY, preventative step you can take to protect your Center speaker. Simply insure Crossover processing is enabled for the Center speaker!
For more details on Crossover processing, see my post on Choosing a Crossover Frequency.
There are multiple reasons folks might be tempted to configure their Center speaker as "full range" -- or "LARGE", in the typical parlance used in AVRs. First, when you've paid a lot of money for a speaker, you WANT to believe it is full range. And the Marketing prose in the brochure for the speaker may also tempt you in this direction.
But the main reason folks configure their Center as LARGE is they have not yet invested in a Subwoofer!
Even if you do NOT have a Subwoofer, you should STILL configure your Center speaker as non-full range -- or "SMALL", as AVRs would call it.
This will work with most every AVR out there, because if you do not configure a Subwoofer in your speaker setup, the Crossover processing in the AVR will, instead, steer bass from SMALL speakers to the Front Left and Front Right speakers.
Now, your Front Left and Front Right speakers may also not really be intended for full range operation. But odds are they are BETTER suited for that than your Center speaker! In addition, steering the bass to those TWO speakers means less bass energy is sent to each of them than would otherwise go to your single, Center speaker. I.e., they share the load.
So enable Crossover processing for your Center speaker, and help it have a long and happy life!