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Devialet Subwoofer Crossover
by ct_acoustic_frontierJuly 06, 2022
At Acoustic Frontiers we recommend that a two channel system always include subwoofers. Not only can you solve many room mode related acoustic challenges using subwoofers, but just handing off the bass from your main speakers to subs has other sonic benefits such as reducing distortion and increasing low frequency extension.
The challenge then becomes HOW to add subwoofers. As we explain in three ways to add a subwoofer crossover you should not run your main speakers full range. The bass to the main speakers should be rolled off at a certain frequency, summed to mono, and sent to your subwoofers.
Devialet have an answer
Devialet, the innovative French audio manufacturer, have an answer to the subwoofer crossover conundrum in the shape of their Expert range - the 120 (with the optional pre-out card installed), 200, 400 and 800. All of these models provide a highly configurable subwoofer crossover with ability to independently set frequency, slope, level and delay for the high and low pass sections. This is everything we need to properly integrate subwoofers.
The full crossover functionality was released via a firmware update (v8.1) in 2015. This is one of the great things about the Devialet Expert range, that it is an hardware platform whose functionality is software controlled, and that new features become available after you have purchased the unit!
Setting up a subwoofer crossover using the Devialet Configurator
All the setup is done through the Devialet Configurator, which is an online utility that can be accessed at http://en.devialet.com/configurator/advanced. If you haven't played with the Configurator then you should, to see how wonderfully flexible the unit is in terms of how you can set it up.
[caption id="attachment_3540" align="aligncenter" width="680"] Screenshot of the Devialet configurator for the 120.[/caption]
High pass setup
The high pass for the subwoofer crossover is setup by clicking on the icon with the down arrow under "Speakers". Through this screen you can setup different settings for Preout ON vs. Preout OFF (and whether the Preout is on or off can be set globally or per input). You can set the high pass frequency anywhere you want it, as well as set the filter order from 1st to 4th order (6dB / octave to 24 dB / octave). Critically this screen also allows you to delay the high pass feed to the main speakers, which is something very few products offer, but is normally critical to get the sub and main speakers properly aligned*. The delay is listed in us (microseconds) - to translate to the more normally used ms (milliseconds...sound travels 1.1ft in 1ms) simply multiply by 1,000.
* the reason for this is that subs are often placed behind the mains (i.e. further away from you) and also have additional frequency dependent delay due to phase shift related to EQ and porting.
[caption id="attachment_3541" align="aligncenter" width="697"] Devialet high pass configuration screen.[/caption]
Low pass setup
The low pass is setup by clicking on the arrow under the RCA jack icon second closest to the speaker binding post icons. You can then choose to setup the low pass as either a mono or stereo feed.
[caption id="attachment_3542" align="aligncenter" width="694"] Devialet low pass setup screen.[/caption]
Once setup as a pre-amplified output you can configure the low pass filter, and again you have a choice of frequency, filter order and delay. You can also change the relative output of the pre-amplified output (we've found this useful to keep the sub output consistent when going from the D200 to D400 in demo situations since the output voltage to the main speakers goes up when you make this change).
The Devialet subwoofer crossover in the Expert range works as advertised, and offers all the functionality you might need to set-up your subwoofers. It crucially allows you to digitally delay your main speakers so that you can perfectly align them with your subwoofers, something which very few other product offer.
One downside to the online configurator is the cumbersome process of making changes to subwoofer settings. Normally you'd need to experiment a little with the high and low pass settings (particularly delay) in order to get things perfectly integrated. With the configurator not being real time this requires re-downloading the configuration to an SD card, putting it into the unit and waiting for it to reboot. It would be nice to be able to do these changes "on the fly", perhaps via an iOS app.
Acoustic Frontiers is an authorized Devialet dealer and has the D120 w' pre-out, D200 and D400 available for in-home demo anywhere in the US.
Much confusion still exists about what a room correction product does, what problems it can (and cannot) solve and therefore its 'place' in a modern high quality sound reproduction system. Part of the challenge of understanding room correction is that it requires a reasonable level of understanding of sound quality, acoustic science, acoustic measurement and psychoacoustics (how humans perceive sound). The majority of the articles I have read online or in print magazines do not cover the fundamentals in enough depth to allow the curious and committed reader a chance to understand room correction on anything more than a cursory level. By the end of this article I hope that you will have learnt enough to judge for yourself what room correction can and cannot do and how best to apply it in the context of a world class music or home theater system.