LFE15 Subwoofer Explained
LFE15 DUAL-FORCE™ SUBWOOFER EXPLAINED
The LFE15 is a 15-inch dual-force subwoofer and Barefoot’s first LFE model. People have been asking for a Low Frequency Effects (LFE) channel for their surround systems from Barefoot, and we have finally delivered. It’s expected that everyone will be excited about it.
It’s a very powerful subwoofer with 1400 watts of power. It’s intended for Low Frequency Effects, but there’s also a cool feature called Boost Mode, which allows it to be used in conjunction with a stereo pair of monitors. The primary intention is for it to work as a Low Frequency Effects channel in surround systems—and that’s its main purpose. It has the classic Barefoot Dual-Force approach. The subwoofers are monstrous, with giant 2 1/2-pound slugs of neodymium in them.
Even with 1400 watts, they produce an incredible amount of power per watt. These are beasts. They will shake the listener’s guts in a normal-sized room, which is quite satisfying. People have been buying Barefoot surround systems but haven’t had a subwoofer that could keep up with them. This was the impetus behind designing this subwoofer.
It’s the full-bore Barefoot low-end approach, everything we do, everything we’re known for. It’s a sealed box with Dual-Force force cancellation, a huge amount of power, and a huge amount of excursion. The Dual-Force design makes the cabinet rock solid, with no vibrations transmitted to the floor.
One question that might arise is whether it is intended for 2.1 systems, and it is not. The Barefoot approach is to build subwoofers inside the monitors themselves, and we have focused on that approach.
If someone has a smaller set of monitors and wants more low end, it’s probably best to upgrade and buy a bigger set of Barefoots with larger inbuilt subwoofers.
Many people don’t necessarily want a monitor in 2.1 but want a subwoofer they can add when they’re composing, showing off a mix to clients, or just want the extra bump.
The LFE15 has a feature called Boost Mode, which allows the user to add the subwoofer and have it fully sum with the stereo pair without any cancellation that typically happens with normal subwoofers using standard low-pass filters. A chart can illustrate that effect.
Looking at the first graph, one can see the typical scenario. For example, if the LFE15 is in LFE Mode, it uses a typical 4th-order low-pass filter, usually at either 80 or 120 hertz—in the case of the LFE15, one can select between the two.
However, if this is added to a stereo pair, the sharpness and phase shift from the low-pass filter will cause phase cancellation as the low frequencies start to roll off into higher frequencies. Adding that in with the 4th-order filter results in a summed response with a notch right above where the subwoofer starts to roll off at high frequencies.
As the response goes down, they sum up together, and since the LFE goes much deeper than a typical set of monitors, there is a little sort of shelf down there because they’re no longer really adding up; it’s just the LFE working by itself.
In Boost Mode, shown in the second graph on the bottom, the 4th-order low-pass filter is replaced with a 1st-order low-pass filter, and the low end is bumped up. One can see it’s raised and has a sharper response down there.
What happens with that 1st-order filter is that it is minimum phase, so it integrates with the monitors without any cancellation. The summed response is just a nice, smooth shelf with no cancellation in the upper frequency area.
Again, it’s not a crossover. It’s just cutting out the high frequency of the monitors and replacing it with the LFE. This adds in without any cancellation, making the sound gargantuan.
The inputs are very basic. There are stereo inputs that sum, so if left and right are connected, they will sum together. If used as a single channel LFE, it can go into either the left or right channel; it wouldn’t matter.
There are throughs as well. Again, no crossovers, but simply a through that can be sent to stereo speakers. When in Boost Mode, the stereo speakers work, and the subwoofer can be turned on. There’s a remote foot switch for mute, allowing it to be turned on and off and added in at will.
There’s also a level control, and that’s pretty much it for the back panel. The front panel allows switching between LFE and Boost Mode, and there’s also a +10dB gain, which can be applied to either mode. That’s the typical 10dB sensitivity gain used in surround systems to gain dynamic range on the LFE channel.
In LFE Mode, one can switch between 80 and 120 hertz 4th-order low-pass filter, and in Boost Mode, one can switch between 60 and 80 hertz 1st-order low-pass filter.
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