Dayton Audio DSP-LF: A Magic Box for Active Subwoofers

A Swiss pocket knife for less than 100
When paired with the iWoofer app, which can be downloaded to a smart device, the small DSP-LF is quite an advanced device for its size. Featuring simple 3.5-millimeter connectors, the box is easy to place almost anywhere, as it’s controlled via Bluetooth using the companion app. The basic version of the control app is free and available for Android and iOS devices. However, only iOS users can access the room calibration feature for a one-time fee of 4.99 euros. The reason for this is most likely that the specifications for iOS device microphones are more precisely defined and therefore more suitable for this type of task than the hundreds of different Android phone microphones.

But as mentioned, Android users can also access many of DSP-LF’s basic features, such as adjusting the crossover frequency and gain, configuring various filters and equalizer profiles, modifying playback delay and phase, adding synthetic subharmonics to the playback, and so on. In principle, the iWoofer app is relatively straightforward to a professional’s eye, but overall, the app does feel a bit rough around the edges. There are bugs as well as translation and typos, but they don’t significantly interfere with basic use. Furthermore, the DSP-LF is the kind of device that, once you take the time to fine-tune it, you probably won’t need to go back to the settings again.

One of the most powerful tools in the iWoofer (Pro) app, designed to control the DSP-LF, is a versatile equalizer that allows a skilled user to correct many playback issues. Automatic room calibration calculates the compensation response based on measurements taken near the subwoofer and at the listening position. It is recommended that measurements be taken multiple times to ensure the best results.

It works, but it takes some skill
DSP-LF and iWoofer (including the Pro version) are, in their own way, quite decent tools, but to get the most out of them, you need to know a thing or two about sound reproduction and know how to use your own system. In practice, the first step is to have some understanding of the settings for your amplifier and main speakers, since, for example, the crossover frequency between the subwoofer and the front channels is often adjusted programmatically in the AV receiver.

First, you need to know what settings are configured on the amplifier, since the signal from the amplifier goes to the DSP-LF in only one direction. In practice, the device and the app do not take the main channels’ playback into account at all, so you need to be able to set some kind of high-pass filter for them. On the other hand, as mentioned, there are plenty of tools available for adjusting the subwoofer.

However, automatic room correction, for example, may not necessarily yield groundbreaking results at the system level due to its limited scope. Although the iWoofer Pro takes measurements both near the subwoofer and at the listening position, thereby revealing the most significant room modes, we didn’t actually find the app’s compensated response curve for the subwoofer to be particularly groundbreaking on its own. And even though the actual measurement process went smoothly through its various stages, the app still froze while fine-tuning the compensation settings, requiring a restart (device: iPhone 13 mini, iOS version 15.5).

In practice, the most useful tool in the package—in skilled hands—is, for example, a versatile parametric equalizer that allows for as many as 25 adjustment bands with Q-value and level controls. In addition, more specific adjustments—such as stepless phase inversion—may be necessary, for example, when working with a subwoofer that has limited capabilities.