master the art of timing


Everyone wants the best sound but is your system delivering it?

Despite moving speakers around, problems can remain with the focus and soundstage width, a muddy bass, or flat and piercing digital highs. And there's no sense of ‘being there’.

Even after balancing your audio or AV system through careful component choice, cabling and setup, it can still get better. However, the good news is that even if you’re not equipment-centric, your sound can be drastically improved.

What’s the biggest problem in achieving great sound?
As hard as it is to believe your speakers introduce more forms of errors and distortions to the audio signal than every other audio component in your system and the entire upstream recording, production and media distribution process combined! Typically ten-to-a hundred times more frequency-response, time and phase errors cause a massive loss of resolution. Speakers can’t help themselves; they’re electro-mechanical devices using uncompensated analog crossovers.

Can high-power DSP resolve analog sound?
DEQX processors and preamp processors are thoroughly-engineered, analog-sounding DSP processors packed with innovative, patented speaker and room compensation technology. DEQX-Cal™ software runs to nearly half-a-million lines of code refined by award-winning DEQX engineers over fifteen years of development that distinguishes DEQX from other processors and crossovers on the market. The notion of digital or analog sound doesn’t exist in the DEQX Universe; we let the music, soundtrack or even gaming to speak for themselves by fixing the Best-Kept Secret in Audio!

What’s DEQX do?
DEQX uses high-power DSP to measure your speakers: looking for timing and amplitude distortions at hundreds of different frequencies. Only after calculating the linear-phase calibration filters needed for your speakers DEQX compensates for the relatively minor room interaction problems.

In addition to frequency-response errors DEQX’s biggest strength is restoring phase and time-domain coherence by delaying faster-arriving frequencies until slower-arriving frequencies catch up for a coherent Impulse-response. DEQX even corrects timing delays in frequency groups within the drivers themselves rather than just time-aligning one driver to the next. Restoring the group-delay accuracy of the original makes the sound jump off the speaker grills and into your room in a focused, vivid and exciting way.

How good does it sound?
We know you’ve read the word “spectacular” many times in describing small sonic improvements. But you may find Stereophile Editor John Atkinson’s report of the 2012 Rocky Mountain Audio Fest of interest: “I’m gobsmacked and you can quote me on that!”, or CNET’s Audiophiliac Steve Guttenburg: “If I hadn't heard it with my own` ears I wouldn't have believed such as thing was possible” (link to reviews), or Positive feedback online editor Dave Robinson: “I went, I listened, I was amazed … DEQX is real”
Gob-smacked by DEQX | Stereophile.com

Audio reproduction basics

Why do you need DEQX?
DEQX works directly on audio reproduction fundamentals so it’s helpful to review the basics. The recording, production, distribution and reproduction of audio are based on only two variables, amplitude and time. Even after amplification the audio signal from front-end components usually has good resolution and very high accuracy with regard to amplitude and timing at all frequencies.

Speakers do their best to convert the voltage representing amplitude to a precise air pressure arriving at our ears at any given instant in time. Compared to the upstream electronics that drives them loudspeakers must integrate several uncompensated mechanical transducers (bass, midrange and tweeter drivers) as transparently as possible and it’s very difficult to get that exactly right.

Audiophile loudspeakers reproduce about ten octaves: Three decades of bass (20-200Hz), mids (200-2kHz) and highs (2k-20kHz) usually requiring a suitable driver for each. The midrange driver plays frequencies we hear the most, just where we’re most sensitive to any timing (phase) and amplitude anomalies. The 3.3 octaves of midrange frequencies are typically delivered by a 5” or 6” diameter drivers. For bass a 10” to 12” woofer is typical whereas a 1” tweeter is the most popular for the highs. In practice designs vary considerably regarding the number and types of drivers and choice of crossover frequencies.

Every speaker driver introduces errors to varying degrees whereby the sound they produce differs from the signal driving them at certain frequencies or frequency groups. Some frequencies will play slightly louder or softer than specified (frequency-response errors) and be variously delayed compared to others (group-delay errors). Together these errors are characterized by the speaker’s impulse response that contains the amplitude and timing accuracy at all frequencies.

The best speakers, particularly with regard to their phase/timing accuracy, sound more engaging, musical and realistic. These tend to be the most expensive speakers due to the high level of engineering, component matching and other issues that are unable to be compensated in analog speakers because it’s impossible to look-ahead and correct timing of delayed frequency groups!

The good news is that frequency-response and group-delay errors are consistent for every model of speaker except for manufacturing variations. After DEQX measurements these errors are corrected by precisely compensating the audio signal prior to amplification.

Adjusting the phase/timing and amplitude differently for hundreds of specific frequency groups simply can’t be achieved using analog electronics. DEQX adds a brief window of time that allows earlier-arriving frequency groups to be delayed so late-arriving frequencies caused by loudspeaker mechanics and crossover filters can catch up.

This process of speaker calibration using Low-Latency Impulse Response Convolution was pioneered by DEQX in the 1990s. Normally, this high resolution Impulse response convolution adds around a quarter second (250 milliseconds) to process, so synchronizing a ‘corrected’ sound track to video for example is a problem to say the least. DEQX maintains high resolution adding only around 5% of the time usually taken, or about a quarter film frame’s delay of the audio that’s not noticeable.

DEQX’s look-ahead control over audio’s amplitude and time fundamentals realizes the potential of HD Audio more effectively and affordably than at any time before -- at any price!

How does DEQX improve the audio experience?
DEQX makes anechoic measurements (without room reflection interference) of your speaker’s performance and calibrates it with your room’s subsequently measured behavior. This integrated approach improves accuracy and provides a better, more holographic soundstage as a result of not damaging the integrity of the audio source.

Some DEQX models such as the HDP-4, PreMate and Express II also provide preamp functionality including the DEQX 3-Band Forensic Tone Control with settings that can be saved via the remote. All models can seamlessly integrate one or two subwoofers.

HDP-4 and Express II models also provide DEQX’s industry leading linear-phase active crossover option that improves speaker dynamics and minimizes dynamic distortion thus improving resolution and volume capacity while allowing more natural dispersion – all combined with individual driver Impulse Response calibration!

High-order (steep) crossover filters are required to maximize resolution (minimize distortion) by quarantining driver to their comfort zone. Normally only the lowest-order (single-pole 6dB/octave) very shallow crossover filters maintain linear-phase, resulting in high levels of congestion. Given its control over time and phase DEQX provides very high-order crossovers that maintain linear-phase allowing the highest resolution. That’s why some of the world’s leading loudspeakers use DEQX for calibration. See Going Active Q&A section below.

DEQX calibration involves what’s called convolving the audio signal with the calibration template filter computed from your speaker’s measured errors. This essentially cancels the errors all speakers introduce including phase errors that cause timing delays to some frequencies (group-delay errors), and amplitude errors at some frequencies (frequency-response errors).

How does DEQX improve resolution?

Loudspeaker distortion reduces their resolution in several ways. DEQX directly corrects phase/timing and frequency-response errors, the linear distortion that speakers always make to varying degrees.

DEQX reduces other forms of distortion by ensuring drivers only operate in their most linear frequency range where they perform at maximum resolution. Adding subwoofers for example can reduce the main speaker’s intermodulation distortion at lower frequencies. If practical, implementing DEQX’s linear-phase active speaker architecture provides ultimate resolution capability. See Going Active in the Q&A section below.

How can I be sure that DEQX works in my system?
A significant improvement is yours with any DEQX installation. The actual degree of the improvement is related to how accurate your system is to begin with and how many DEQX features it’s practical to use.

DEQX is used to calibrate professional studio monitor speakers and top-flight active audiophile speakers costing hundreds of thousands of dollars. One early installation was at Abbey Road Studios where DEQX ensured the accuracy of classical recordings in surround.

DEQX processors are equally at home improving performance of low-cost and classic speaker designs so they perform like audiophile systems especially with linear-phase active crossovers.

Is DEQX like other DSP equalizers, room calibration systems and active crossovers?
It’s difficult comparing DEQX with other DSP processors that provide equalization and/or room calibration, more rarely speaker calibration or active crossover control because DEQX provides enhancements to all these features in one integrated solution. There are similarities but most DSP solutions are best suited to commercial audio applications. DEQX is designed for audiophile applications where “first do no harm” is the priority.

In the digital domain DEQX uses powerful 32-bit floating-point processing with added SRAM and FLASH memory. High-resolution asynchronous reclocking and sample-rate conversion is used to minimize jitter. The level of detail in phase and amplitude calibration that DEQX provides can’t even be contemplated in the analog domain. The process adds no noise, distortion or phase corruption, where in the digital domain THD+S/N measures in the order of -140dB or about 20dB better than the best analog designs!

However DEQX’s fourth-generation HDP-4 and Mate processors provide that very-much-sought-after analog sound. To get there we use Cirrus Logic’s highest end pro-audio reference ADC (Analogue to Digital Converter) and Burr-Brown’s reference 32-bit DACs. Each DAC’s I/V stage incorporates video-speed 300V/usec slew rate conversion followed by Burr Brown’s new-generation differential driver stages. Main power supply rails are at near zero source impedance to eliminate digital high-frequency noise incursion.

The hundreds of thousands of lines of software code constantly refined since 1997 established DEQX’s status as the pioneering reference for speaker and room calibration for consumers and pro audio.

I play vinyl more than digital so will DEQX affect the analog experience in any way?
Successive generations of DEQX processors have focused on heightened transparency so the joys of analog are unaffected by DEQXification, not a trivial matter. But there is no analog or digital sound in the DEQX Universe, just the sound of your system set free and making music! The HDP-4 is the top performer and thus sounds very analog closely followed by Mate and PreMate models. Many happy DEQX users play vinyl and use tube amps!

My expensive speakers already sound very good, how can DEQX speaker and room calibration help?
Speakers introduce a suite of errors, even in expensive models where diminishing returns sets in as engineering costs rise dramatically for an increasingly marginal benefit. DEQX provides excellent value because even low-cost speakers demonstrate dramatic improvements. There is no speaker on the market that doesn’t benefit from DEQX calibration, subject mainly to the accuracy of the measurement on which its calibration is based.

Speaker measurements corrupted by room reflections can make the speaker sound much worse which is why DEQXpert installation service is recommended to ensure anechoic measurement accuracy. A simpler installation might only make use of DEQX’s room calibration features.

The degree of speaker calibration required is normally less for very expensive speakers but integrating DEQX speaker and room calibration always provides obvious improvements that better resolve the soundstage, bass coherence, dynamics and overall balance.

Which DEQX product is right for me?
Speakers are normally supplied with internal passive crossovers that only need a stereo or one monoblock power amp per side allowing consumers to mix-and-match amplifiers and speakers. The DEQX Mate and PreMate are ideal for such systems while the HDP-4 provides slightly improved transparency.

Increasingly high-end consumer speakers and virtually all professional monitors use active mode where each driver (bass, midrange and tweeter) has its own power amplifier so two or three power amp channels are required for each speaker side. Active crossover filters benefit greatly from the high-caliber DSP available in DEQX processors when operating at preamp signal levels rather than about 100 watts of amplified power.

The HDP-4 and Express II provide up to 3-way active crossover filtering using DEQX’s patented low-latency high-order linear-phase filters. The MATE provides up to 2-way crossovers to correct passive full-range speakers and optionally integrate them with one or two subwoofers that can also be corrected! The HDP-4 and Express II can also accomplish this.

The HDP-4 is the flagship DEQX Preamp Processer provides the highest level audio quality plus preamp functionality with remote control. It provides balanced and unbalanced analog outputs as well as digital outputs enabling external DACs to be used. If you are contemplating going active now or in the future the HDP-4 is the choice to make.

The DEQX PreMate provides the same functionality as the HDP-4 except it doesn’t provide the option to go fully 3-way active.

The DEQX Mate is suggested for those looking for a set-it-and-forget-it solution for speaker and room calibration -- plus you can add one or two subwoofers. It has balanced and unbalanced analog inputs and outputs but no digital inputs or outputs. The Mate is intended for users who already have a preamp although we feel obliged to point out the Mate comes with a remote for volume and the DEQX 3-Band Forensic Tone Control with 99 preset EQ memories for media calibration! The Mate uses the same high quality electronics, chassis speaker and room calibration features as the HDP-4 with a new zero-earth-leakage switch-mode power supply instead of the HDP-4’s linear power supply.

The Express II uses commercial/pro-audio-grade audio-quality components, chassis and power supply while still providing the same preamp and crossover functionality as the HDP-4 but limited to unbalanced analog outputs.

Do I want flat frequency-response for both speaker and room calibration?
Yes and no … DEQX speaker calibration always targets flat (accurate) on-axis frequency and time response subject to the frequency extension of the speaker. This is the same target curve used by all loudspeaker manufacturers that are trying to accurately reproduce audio.

Some designers don’t aim for accurate response although that’s increasingly rare. However, DEQX allows limiting the degree of calibration towards flat over user-selected frequency ranges. The overall calibration window is also limited with regard to the bass extension of the speaker and the measurement’s bass extension resolution.

The speaker shouldn’t color the sound but any variation from flat is actually coloration that’s subject to the speakers’ integration with the room. But the need for accuracy is essential to realize the exciting sense of dynamics and being there that DEQX achieves. And if a speaker’s on-axis response isn’t accurate it’s rarely capable of achieving this as in-room reflections make it worse.

DEQX room calibration doesn’t necessarily target flat response at the listening position. In a typical listening room using 1,000Hz as the reference point bass below 100Hz may be raised by several decibels whereas high frequencies towards 10kHz typically may be attenuated by as much as 3 to 6dB.

This is normal behavior from a psychoacoustic standpoint because what you hear at the listening position is a mix of direct sound from the speaker and reflected sound from all the room’s surfaces. Since highs reflect less efficiently than bass and midrange frequencies the balance of bass is slightly higher, and balance of highs is less at the listening position. While this may be taken into account by mastering engineers you may still benefit from calibrating an unusually dead or live room, or to personal taste.

Of course DEQX allows you set virtually any balance of bass, mid, highs and anything in between using its preference settings that can be saved to several profiles. However, you probably won't do so once your system is “calibrated to accurate”!

Correcting existing (passive) speakers

How does DEQX measure a speaker’s timing and amplitude errors without interference from room reflections?
Speaker designers use anechoic measurements to evaluate their speaker’s accuracy. Anechoic means non-echoing so an anechoic chamber doesn’t reflect any sound from wall, floor or ceiling surfaces. You can measure speaker performance in fine detail this way because no echo is present to mix with the speaker’s direct sound and throw off the measurements.

Several calibrations can be made based on different measurements made from different horizontal on-axis or off-axis locations. A slightly off-axis measurement is usually recommended because it compensates for the speakers directional response at the ideal listening position.

DEQX speaker calibration -- as distinct from room calibration -- employs software that facilitates anechoic measurements in typical listening rooms. It focuses on correcting phase/timing and amplitude errors from the upper-bass through the critical midrange and high frequencies where we’re most sensitive to timing errors. An outdoor measurement, or measurement in a very large room, typically provides more bass resolution. Normally bass issues are especially room related and are dealt with by DEQX room calibration measured from the listening position.

Why are different measurement techniques required for speaker and room calibration?
Although simpler to perform, a room measurement can’t know the native behavior of the loudspeaker because it’s corrupted by reflections from all the room’s surfaces. This is why room calibration systems alone can’t perform speaker calibration which requires an anechoic (no echo) measurement technique such as DEQX provides.

Can I use the measurement of one speaker to correct the other speaker?
Yes, the majority of errors are consistent for all speakers of the same design and model. This means a filter designed to correct any speaker of the same design will also correct about 90% of errors in other speakers of the same model.

However there are always small manufacturing differences between similar models so measuring and correcting each individual speaker ensures the acoustic output of each is matched regardless of manufacturing variations. A solid, dynamic three-dimensional soundstage relies on well matched speakers.

What is impulse response and what does DEQX do with it?
A speaker’s impulse response refers to the reaction of its drivers to an input as a function of time. One of DEQX’s main features is providing low-latency impulse response correction. This new generation of low-latency FIR/IIR digital signal processing was actually pioneered by DEQX for speaker calibration in the 1990’s.

The speaker’s measured impulse response defines its timing/phase and amplitude accuracy at any given frequency. DEQX uses Convolution FTT to redefine the speaker’s impulse response to correct the relatively dramatic errors it introduces compared to the more subtle errors of other component your system.

The audio signal is processed prior to the power amplifiers that drive the speakers so it is connected like a traditional equalizer but that’s where all similarities end. DEQX compensates for the errors measured in your speakers! This is very different from traditional equalization that’s unable to correct critical phase errors at different frequencies.

Can DEQX correct planar, electrostatic, omnidirectional and ribbon speakers?
Absolutely, many DEQX installations include various forms of flat-panel, bipolar and planar designs and even full-omnidirectionals like mbl speakers. A pseudo-anechoic measurement is often used in these cases whereby some degree of rear-room reflection is incorporated into the measurement.

Can I measure a bi-amp passive speaker with DEQX?
Yes as DEQX allows separate speaker measurements for bass and mid/high combo drivers where typically the bass is separately driven from the mid/highs. In this case one DEQX option is to provide further crossover filtering in addition to the existing in-speaker network.

Why do some audiophiles think flat-measuring speakers don’t sound very good?
This is often due to misinformation because virtually no Hi-Fi loudspeaker is in fact flat i.e. accurate. It’s very difficult to make traditional passive speakers with accurate (flat) on-axis frequency and phase response. The average frequency response achieved is within a range of 6dB (+/-3dB). This 6dB range is the same difference in volume we hear driving a speaker at 25-watts as against 100-watts. Professional monitor speakers usually achieve +/-2dB while DEQX typically delivers +/-1dB or better.

Since speakers are judged by their measured frequency response accuracy flat seems best. However some designs achieve their frequency response accuracy by using traditional analog or digital EQ in addition to their crossover filters to compensate for more serious errors. Since most EQ isn’t linear phase it causes more timing incoherence (group-delay errors) so the cure is often worse than the disease. Flatter frequency-response reduces tonal coloration but often at the expense of timing coherence.

Group-delay errors can be considerable in passive designs and are more difficult to quantify and correct than frequency-response (tonal) errors. DEQX frequency-response calibration is precisely applied to the thousands of frequencies that require it in fraction-of-decibel increments. This process doesn’t introduce further group-delay (phase) errors and in fact corrects existing group-delay errors.

Is frequency-response calibration related to phase/timing calibration?
The precise phase/timing calibration that DEQX pioneered goes hand-in-hand with its frequency-response calibration where frequency-response errors imply group-delay errors. Traditional EQ provides frequency-response compensation with a broad brush adjusting all frequencies in the vicinity whether they need it or not, nor does such EQ maintain linear-phase.

DEQX corrects phase and frequency response at thousands of frequencies only to the extent specified by the anechoic speaker measurements while maintaining or correcting phase accuracy. This simply can’t be done in the analog domain.

Why not use speaker designs and drivers that don’t need calibration?
Compared to a quality audio signal arriving at any loudspeaker’s terminals the measured output from the speaker will be between ten-to-one-hundred times worse in all relevant measurable categories depending on the loudness and complexity of the music being played.

Hopefully good passive speakers fall into the “only” 10-times worse category but even that’s based on static measurements that can’t measure dynamic degradation due to intermodulation distortion at higher volumes especially with complex orchestral music explaining the size and cost of the most expensive speaker systems.

The ear is sensitive to less than 1dB of volume at different frequencies yet a 6dB window is considered acceptable for a passive crossover speaker. We also detect timing inaccuracies on the order of microseconds that sound unconsciously unreal to us. An exciting you-are-there audio experience requires minimizing subconscious cues that tell us what we’re hearing isn’t real. All speakers benefit from active compensation such as DEQX provides as it minimizes the need for subconscious psychoacoustic reality checks.

Integrated room calibration and setting preferences

How does DEQX correct the room?
After the loudspeaker calibration phase is completed one or more room measurements are taken from the listening position to compensate for room acoustics. Multiple measurements are made to average calibration over a wide listening area, or a single sweet spot measurement provides reference-quality results for an audience of one or two. Four presets allow a variety of configurations to be saved.

If the bass is independently amplified, as is the case with powered subwoofers or bi-amplified speakers, it can be measured for speaker calibration from the listening position that provides better results as it includes room acoustics without compromising midrange clarity.

After speaker calibration is completed only minimal room calibration is required and that focuses mainly on bass frequencies. DEQX’s multiband minimum-phase parametric EQ can be automatically or manually set or manipulated for personal preferences. Four profiles can store different preferences for recall via the remote.

Can I add personal EQ preferences?
Yes, the multiband minimum-phase parametric EQ used for room calibration is semi-automated and works in real time. Several EQ preference settings can be saved for instant recall. One setting might be for a narrower but very accurate sweet spot listening position, while another may be wider for family and friends’ enjoyment.

Can I add personal equalization preferences for specific recordings?
Absolutely, three bands of minimum-phase equalization can be set by ear using the remote control. The Low and High bands of the 3-Band Forensic Tone Control default to traditional bass and treble controls except the slope and frequency points can be adjusted. The Mid band is fully parametric allowing any frequency between 20Hz and 20kHz to be selected and any Q (bandwidth) to be selected from one semitone to four octaves wide. Up to 99 presets can be stored and recalled from the remote.

Installation

Can I install DEQX myself?
If you have DIY experience with loudspeakers, or a reasonable understanding of the principals discussed here and can use Windows software (or run Windows on a Mac), then the DEQX-Cal measurement wizard and calibration software is not overly complex to use. Installation manuals are available on request.

While many DEQX users have a DIY bent we recommend the use of our online DEQXpert installation service where qualified DEQX installers provide the fastest and surest route to great results. There’s minimal effort on your part other than connecting the DEQX to your system (which we will explain how to do) and then setting up the DEQX-calibrated Earthworks microphone. As an alternative to purchasing the microphone it is possible when using the DEQXpert service to hire the measurement kit including the calibrated microphone for a nominal fee. A typical calibrating DEQXpert session will run two or three hours.

What is DEQXpert installation service?
DEQX processors are incredibly powerful tools and much of their development has focused on ease of use and speed of operation. For best results a familiarity with PCs, general acoustic principals, and an adventurous spirit helps. However if time, uncertainty or unwillingness to go through the installation manual is an issue we can do most of it for you online using our DEQXpert installation service.

The DEQX-Cal software runs under Windows (or Windows on Mac) and your notebook computer connects to the DEQX processor via USB for setup. Four wizards divide the process into logical operations that can each be performed independently.

1) The speaker measurement wizard measures passive, bi-amped active or tri-amped active main speakers and subwoofers.

2) The calibration wizard takes the measurements above and using many typical default settings allows you to confirm the frequency zone you want to correct and set maximum and minimum degrees of calibration in decibels. If you’re setting up an active bi-amp or tri-amp filter set this is also where you choose the desired linear-phase crossover frequencies and slopes that are incorporated into each driver’s calibration filter.

3) The configuration wizard sets up your particular speaker configuration. This might be for two main passive speakers with optional mono or stereo subwoofers, 2-way active main speakers (bi-amped) with optional mono or stereo subwoofers, or 3-way active main speakers (tri-amped). You can then set timing delays (in milliseconds or distance) for main speaker time-alignment with subwoofers, and you can set high-pass and low-pass filters to crossover the main speakers with subwoofers.

4) The room measurement wizard measures the final in-room result from the main listening area and other positions, although the sweet-spot is often sufficient. Room measurements are displayed for each speaker on the multi-band parametric EQ display. If frequency-response and group-delay issues have already been addressed using speaker calibration the degree or room calibration necessary is usually limited to reducing three to six of the main natural room resonances lying below about 400Hz.

The DEQXpert service manages all of these processes on-line, where you help set up the measurements, play music when all is done, adjudicate results and set any preferences. DEQXpert can also provide you with one on one software tutoring.

Subwoofer integration

Can adding subwoofers increase resolution?
Intermodulation distortion occurs as the driver’s cone is pushed towards its excursion limit (X-MAX) where lower frequencies require correspondingly longer excursions. For every octave of bass extension driver excursion increases four-fold.

While the main incentive for adding one or two subwoofers may be to extend the bass DEQX integration tends to reduce upper-bass and midrange distortion as well. In the case of a 2-way passive bookshelf speaker DEQX’s high-pass crossover filter significantly reduces distortion from the typically 6” bass/mid driver.

If two subwoofers are added for bass below 100-Hz DEQX’s steep high-pass crossover filters remove most frequencies below 100Hz from the main 6” driver. Where previously it was near its excursion limit at 50Hz the excursion is now reduced by around 75% keeping the driver well within its comfort zone even on loud complex transients so resolution is indeed increased.

What’s the advantage of corner-loading subwoofers?
Subwoofers placed in the corners of the wall behind the speakers roughly double their efficiency and help clarify phase/timing coherence. Normally uncorrected corner-loading isn’t recommended because most of the time it sounds bloated and out-of-control. DEQX speaker and room calibration easily compensates for that while taking advantage of efficiency and coherence benefits.

Ideally subwoofers should be as high resolution as possible so that leads to smaller drivers in the 8” to 10” range rather than 12” to 18” designs. The lower surface area of the smaller drivers is compensated by efficiency gains of corner loading.

Can I add subwoofers without bloated bass?
DEQX processors allow mono or stereo subwoofers to be added and time-aligned with the main speakers. To solve bass bloat low-resolution subs are filtered so they don’t output upper-bass frequencies that muddy cleaner bass from the main speakers. Low distortion <1% THD subwoofers can often cross over to the main speakers at frequencies as high as 200 or even 400Hz.

Removing bass room resonances with DEQX processors applies to full-range speakers as well even when subwoofers aren’t employed.

How do I time align subwoofers with my main speakers?
When subwoofers are located at a floor-to-wall boundary or room corner to raise efficiency the main speakers should ideally be three or four feet away from the rear and side walls. Sound travels about one foot per millisecond so the sound produced by the main speakers must be delayed by three to four milliseconds.

Delay can be calibrated into the main speakers in real time using steps of about one millisecond. The wavelength of 80Hz is about 14 feet so this adjustment is not as critical as the time-alignment between the midrange driver and tweeter where at 2kHz the wavelength is only 7”.

However delay can be set in much greater detail within the crossover filter settings. To achieve the most precise alignment the impulse response measurements from both the subwoofer and the main speaker can be compared using the DEQX-Cal Viewer. A misalignment will be visible by the two impulses starting at different times and the time difference can be adjusted to correct it.

Going active

What are active speakers and what are their advantages over passive crossovers?
Speakers are normally supplied with internal passive crossovers that only need a stereo amplifier or one monoblock power amp per side allowing consumers to mix-and-match amplifiers and speakers. An active loudspeaker uses line-level active crossover filters that drive separate power amplifiers for each bass, midrange and tweeter driver.

Active mode allows more accurate analog and DSP filtering, the very reason pro audio monitor speakers are almost exclusively active. In comparison almost all consumer speakers are designed with passive crossover filters inside the speaker so that only one channel of power amplification is required.

Consumer passive crossovers must be designed to handle whatever power the amplifier delivers but they’re inefficient because of component losses – the more complex the crossover the greater the losses -- plus they destroy phase accuracy (linear-phase) in any crossover greater than 1st order. The upside is they’re relatively inexpensive to manufacture and allow easy access for consumers who aren’t concerned with multiple amplifiers per side or the external active crossovers needed to drive them.

Active speakers use separate amplifiers for each bass, mid and tweeter driver but the amplifiers only have to supply the frequency requirements of each respective drive unit. Bass requires very high power at moderate resolution, mids require good resolution at medium power, and highs require the highest resolution but at lower power. Where practical to do so, best performance is more likely and cost effective using three amplifiers each suited for their limited frequency range compared to very high-end amplifiers that can deliver all 10 octaves perfectly. Even identical amplifiers operating over limited frequency ranges perform better.

Another advantage of active mode is each power amplifier’s output stage connects directly to its respective driver yielding tighter damping control. A passive crossover acts like a buffer between the amplifier and each driver diluting its ability to dampen unwanted movement (overshoot) of each cone.

Ideally active speakers confine each driver to its respective frequency range using high-order crossover filters that maintain linear phase. Typically active speakers use steep crossover filters on the order of 24-48dB/octave (4th to 8th order) that don’t maintain linear phase although other advantages of active mode apply like louder volume with lower dynamic and crossover distortion, more natural dispersion -- drivers aren’t allowed to beam unwanted high frequencies on-axis -- better damping, easier amplification, and better active crossovers then their passive equivalents.

DEQX’s steep 8th order linear-phase filters are a popular choice (max 50th-order) that provide excellent protection for the tweeter from midrange and bass frequencies and similar protection for the midrange driver from bass frequencies. Both drivers can then play at higher volumes without the usual loss of resolution (compression) that transient volumes usually imply. The steeper crossovers also stop the bass and midrange drivers from beaming on-axis and at much higher distortion levels lowering resolution and compromising dispersion.

Does DEQX provide fully active crossovers?
Yes they can resolve normally-associated problems with any speaker crossover design, passive or active. The HDP-4 and Express II provide DEQX linear-phase active crossovers combined with DEQX-Cal’s integrated measurement and analysis software.

Despite the overwhelming advantages of the active speaker architecture it’s been impractical for consumers to know what active crossover filter parameters are required for their particular speakers unless it’s supplied by the manufacturer. And that’s assuming a quality active crossover was available for it in the first place or that the user has access to the same measurement tools used by the speaker designer and knows how to use them, all rather impractical.

DEQX address all of these concerns with integrated professional measurement and calibration tools not previously available for active speakers used for professional monitoring. Steep linear-phase active filters allow superior driver integration with minimal crossover distortion (comb filtering) than normal active crossovers, thus maximizing resolution. DEQX high-order filters maintain linear phase because DEQX’s big advantage is managing the time domain.

Maintaining phase coherence over the crossover region is normally only possible using shallow first-order (6dB/octave) crossovers. However, timing coherence is so desirable that many audiophile speakers use single order crossovers despite their minimal quarantining of unwanted frequencies in their respective bass, mid and tweeter drivers. In these designs extremely robust drivers are needed to minimize intermodulation distortion and break-up distortion as drivers are pushed well outside their comfort zones. A delicate 1” tweeter filtered only by a single order 6dB/octave high-pass filter (reducing bass frequencies) is barely protected from the upper-bass or midrange frequencies, so compression sets in easily.

Similar problems occur for the bass and midrange drivers where the crossover’s bass driver’s low-pass filter (reducing high frequencies) should ideally be steep enough to stop midrange frequencies from beaming compared to its lower intended frequencies. It is also likely that these higher frequencies contain higher harmonic distortion resulting in lower resolution of course. DEQX’s steep linear-phase active features resolve these problems.

Can I upgrade my passive speakers to active?
Yes, in fact virtually any speaker can be converted to run in active mode. However if you have expensive name-brand speakers under warranty that you may want to sell in future then modifying them to bypass the internal crossover filters may void the warranty and lower resale value. So care should be taken to allow the speakers to be returned to their original state. Going active may also require adding more speaker terminals to the rear of the speaker cabinet to allow individual connection to each driver.

You will need some DIY skills or know someone who does. But depending on your location it may be possible for a DEQXpert engineer or DEQX dealer technician to provide on-site modifications.

You might also consider designing your own speaker from scratch and DEQX is the perfect tool to get the most out of any speaker design as it provides state-of-the-art measurement, analysis, calibration and crossover tools. There are many DIY speaker kits available on DIY sites where DEQX will provide extraordinary performance compared to its recommended, typically passive, crossover design.