Sublime Acoustic K231 User manual

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Stereo 3-Way Active Crossover
User Manual
Model K231
Sublime Acoustic, LLC
Features
•Stereo 3- ay Active Crossover for driving separate sub oofer, midrange and t eeter amplifiers
•Link itz-Riley crossover circuits, 4
th
order 24dB/Octave or 2
nd
order 12dB/Octave filter slope
•For Bi-Amping or Tri-Amping your sound system, or to add a sub- oofer to vintage audio systems lacking LFE outputs
•All analog design employing only the highest quality audiophile grade components:
•Burr-Bro n audiophile grade op-amps
•Metalized Polypropylene Film capacitors
•Metal film resistors ith 1% and 0.1% precision
•ALPS metal film potentiometers
•Crossover frequencies are selected through pluggable 'XO Frequency Modules'
•Wide range of XO Frequency Modules are available to support any crossover frequency (see list belo )
•High, mid and sub channels are phase aligned to ithin fractions of a degree to eliminate distortion at the XO frequencies
•Stereo or Mono Sub oofer Output - Optional Sub oofer channel L/R mixer
•Supports Balanced and Unbalanced audio input and output signaling
•Sub, Mid and High output gain level front panel adjustments
•Baffle Step Compensation, Adjustable Gain, Selectable baffle size ranges
•Silent On/Off circuit – No loud ‘Thump’ hen po ering On or Off
•Can be configured for 3- ay or 2- ay active crossover operation
Specifications:
•Total Harmonic Distortion (THD): Better than 0.0005%
•Total Harmonic Distortion + Noise (THD+N): Better than 0.0028%
•Intermodulation Distortion (IMD): Better than 0.0058%
•Signal-to-Noise Ratio (SNR): 120dB
•Channel Crosstalk: Less than -83dB
•Frequency Response: Linear from 10Hz - 250KHz
•CMRR (balanced inputs/outputs): Better than 70dB
•Input Impedance: 20K ohms unbalanced, 40K ohms balanced
•Output Impedance: 200 ohms, AC coupled
•Input Signal Max: 5.5V
•Insertion Gain: Adjustable Sub, Mid and High channels -9dB to +8dB
•Filter Topology: Link itz-Riley, Constant Voltage, 4
th
Order 24dB/Octave, 2
nd
Order 12dB/Octave
•Enclosure: Black Aluminum Extruded Chassis
•Dimensions: 6.5”W x 6.5”D x 2.5”H
•Shipping Weight: 3 lbs
Inputs:
•Stereo Balanced: ¼” TRS Jacks
•Stereo Unbalanced: RCA jacks
•Po er Supply: Wall Mount AC adapter, 100VAC to 240VAC input, 24VDC 500mA output, 12W
Outputs:
•Stereo Balanced High, Mid, Lo : ¼” TRS Jacks
•Stereo Unbalanced High, Mid, Lo : RCA Jacks
We support the follo ing Crossover frequencies:
•Any multiple of 10Hz from 60Hz-200Hz (e.g. 60Hz, 70Hz, ... 200Hz)
•250Hz, 275Hz
•Any multiple of 100Hz from 300Hz-4000Hz
•Any multiple of 500Hz from 4500Hz-7000Hz

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K231 Stereo 3-Way Active Crossover Overvie
The K231 Stereo 3-Way Active Crossover significantly improves the audio quality of sound systems by separating the lo , mid and high
frequency sounds using ultra lo noise, high precision active filter circuits. This allo s the use of a separate po er amplifier dedicated to
each speaker driver. These functions result in greatly improved clarity and lo er distortion of the sound that is produced.
The block diagram belo sho s the primary functional blocks of the K231. The line-level audio signals, either balanced or unbalanced,
enter from the left and are received and buffered by the ‘Balanced/Unbalanced Input Stage’ circuits. Note that the balanced and
unbalanced inputs are both al ays active. Whether your inputs are balanced or unbalanced is selected simply by hich jacks you plug in
to. The balanced inputs are ¼” TRS jacks, and the unbalanced inputs are RCA jacks. Since this is a shared circuit bet een balanced and
unbalanced input jacks, only one or the other can be connected at any given time.
After the input stages, the signal is processed by the ‘Baffle Step Compensation’ circuit, or BSC. This is simply a configurable stereo lo
pass shelf filter ith adjustable gain that compensates for the ‘Baffle Step’ effect. See belo for a more detailed description.
Next in the signal path is the Sub oofer crossover. This is a 2- ay crossover that splits the sub oofer frequencies from the mid and high
frequencies. Any frequencies belo the ‘Sub’ XO module setting are sent to the Sub output. The lo output can optionally be mixed into
a mono sub oofer signal via a small slide s itch that is accessible through an access panel on the bottom of the chassis. The high output
of this crossover gets passed on to the mid/high crossover.
The mid/high crossover, as the name implies, splits the mid frequencies from the high frequencies. Any frequencies above the ‘Mid/High’
XO module setting goes to the high output. Note that since the Sub crossover has already removed the sub oofer frequencies from the
mid/high signal, this makes the mid filter into band pass filter, hose frequency is bounded on the lo end by the Sub XO module setting
and on the high end by the Mid/High XO module setting.
All of the crossover circuit outputs then go to six identical ‘Balanced/Unbalanced Output Stages’. Again, both the balanced and
unbalanced outputs are active at all times. But, again, this is a shared circuit bet een balanced and unbalanced outputs and only one set
or the other should ever be connected at any given time.
Figure 1. K231 Block Diagram

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What is an Active Crossover and Why Do I Need It?
All speaker systems employ an electronic circuit called a crossover to split the sound into frequency ranges; it sends the lo frequency
sounds to the oofer, and the high frequency sounds to the t eeter. This is important because each of the loudspeakers is built to
produce certain frequency ranges, and they don’t sound very good, or may even be damaged, if run outside of their proper range.
Loudspeakers can actually distort ithin their natural frequency range if they are also presented ith frequencies outside their natural
range. In other ords if you send lo frequencies to your t eeter, the high frequency sound reproduced by the t eeter ill be distorted
by the presence of the lo frequency signal.
Most speaker boxes you see employ passive crossovers, hich are made up of large inductors and capacitors that filter the lo
frequencies from the highs. But passive crossovers have a number of very significant dra backs. One big problem ith passive
crossovers is they don’t have a very sharp roll-off. This means that some of the bass frequency energy ill still reach the t eeter, and
some of the treble energy ill still reach the oofer. Another major disadvantage ith passive crossovers is efficiency; they aste a huge
amount of the po er you’re amplifier is providing. High frequency sounds are prevented from going to the oofer (and lo frequencies
prevented from going to the t eeter) by essentially just shorting them out; so po er is asted in the form of heat dissipated in the
crossover components. In some cases up to 50% of the amplifier’s po er is lost to heat.
But by far the biggest problem ith passive crossovers is that they significantly degrade the quality of the signals that pass through them
by introducing distortion in the follo ing ays:
•Intermodulation Distortion (I D): Intermodulation distortion is a type of distortion that occurs hen the passive
crossover is tasked ith producing t o or more frequencies at the same time. The intermodulation bet een each
frequency ill produce additional frequencies at the harmonics and at the sums of the original frequencies that are
not part of the original signal. This is most pronounced hen simultaneously reproducing very lo and very high
frequencies. This type of distortion leads to a muddying of the sound created, making it harder to distinguish the
individual instruments across the sound stage. Active bi-amp’d or tri-amp’d systems are much less susceptible to
intermodulation distortion because the oofer and t eeter channels are driven by separate amplifiers.
•Loss of Damping: The caps and inductors placed in the circuit bet een the amplifier and the speaker coil cause a loss
of damping, meaning that the amplifier is more isolated from the driver and has eaker control over the motion of
the loudspeaker cones. The result is a muddier, less precise sound. In a bi-amp system the amplifiers are connected
directly to the speaker coils ith no capacitors or inductors to get in the ay of the amplifier’s ability to precisely
position the cones, hich gives you dramatically higher sound definition and vibrancy.
•Back-E F Distortion: Back EMF, or back electro-motive force, is the voltage created by the speaker inding hen the
momentum of the cone causes the inding to continue moving relative to the speaker magnet. This voltage,
particularly from the oofer, flo s back ard through the crossover to ard the amplifier and into the t eeter
channel. The massively chaotic interactions these voltages can cause are far too complicated to even begin to
calculate. But they do cause a great deal of distortion of the sound. Active bi-amp systems are not in any ay
susceptible to back EMF distortion.
•Channel phasing: Once a passive crossover splits the audio signal, the oofer and t eeter signals can be out of phase from
each other ( hich means one leads or lags the other) due to loose component tolerances or temperature related variations in
these large discrete components. This causes distortion at and around the crossover frequency because at these frequencies
both the t eeter and the oofer ill be driven, but each ill be in a different phase. At various points of time in the ave the
oofer and t eeter ill be either fighting one another or re-enforcing one another. This leads to a muddying of the sound
definition.
All of this adds significant distortion to the final sound created. Audio engineers for decades have tried in vain to come up ith ever more
complex passive filter arrangements to try and resolve, or mask, these inherent problems.
Active crossover circuits, like those used in the K231 , on the other hand, are built from the highest quality operational amplifiers (op-
amps) and the filter functions are applied to the line-level preamp input signals instead of the high voltage amplifier outputs. These
active filters are designed to be many orders of magnitude cleaner and more precise than the passives. Active filters have a much
sharper roll-off, 24dB/octave, allo ing each of the loudspeakers to perfectly focus on producing only the frequencies they are designed
to handle. Active crossovers are also more efficient from a po er standpoint because of the fact that the filters are applied in the line-
level audio input signal; only the energy meant for a particular driver is sent to the amplifier that drives it, so there is no asted energy.
But the biggest advantage of active crossovers is the sound quality. A vanishingly small amount of noise and distortion is introduced in
the op-amp filter circuits, on the order of 0.00005% total harmonic distortion. All of this results in extremely clean, precise, and ell
defined audio output to your amplifiers.
To learn more about the many advantages of active crossovers over passive crossovers, please read our paper on the subject:
https://www.xkitz.com/blogs/making-the-case-for-active-crossovers-vs-passive

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Front Panel
The front panel contains four control knobs; One for BSC filter gain, and one each for High, Mid, and Lo output channel gains. The panel
gradients for the BSC knob are marked off in dB, from 0dB in the counter-clock ise position to 6dB fully clock ise. This allo s you to
control the gain of the BSC lo pass shelf filter (see the BSC section for more info). The High, Mid and Lo knobs have a small circle that
indicates the 0dB gain point for each of these channels.
Back Panel
The back panel contains the po er input jack, the main po er s itch, a green po er indicator LED, and all of the audio input and output
jacks. These are all fairly self explanatory. As previously mentioned, for any given audio channel, only connect a balanced source OR an
unbalanced source, but never both at the same time.
3-Way or 2-Way Active Crossover Configuration
The K231 is primarily designed as a 3-Way crossover, but it can be configured as 2-Way crossover by plugging in a Sub- oofer XO module
in the 12Hz range. This channels all frequencies above 12Hz (meaning all audible frequencies) to the Mid/High crossover. In this
configuration your oofers ould be driven from the Mid channel outputs and your t eeters from the high channels. The ‘Sub’ outputs
ould be left unconnected and the ‘Sub’ knob on the front panel ill have no effect.
Input / Output Signals – Balanced or Unbalanced
There are t o basic systems used to connect the audio signal on consumer and pro audio equipment; unbalanced signals and balanced
signals. Unbalanced signals use one ire for signal and the other for the shield ground. Balanced signals, on the other hand, have t o
signal ires and a shield ground ire. These t o signal ires both contain the same audio signal, but one is 180 degrees out of phase
ith the other (in other ords, they are differential signals). These are the (+) and (-) signals.
Unbalanced signals are most common in consumer grade audio, and are generally much more susceptible to audio noise like 50/60Hz
hum than are balanced signals. Unbalanced signals ill pick up any electro-magnetic noise in the nearby environment (such as
computers, cell phones, micro aves, etc.) and add it to your audio signal, making it audible in your speakers. Unbalanced signals can also
lead to ground loops, hich are the major source of 50/60Hz hum in any sound system. Ground loops arise henever there is more than
one path from any piece of audio equipment to earth ground. Your equipment ill al ays be grounded through your AC line. Adding
another path to ground through your unbalanced audio cable adds a second path to ground, and this can cause audible 50/60Hz hum.
Balanced signals are more common in high end consumer and professional audio systems and are much less susceptible to noise.
Balanced signals allo you to run very long audio cables ithout allo ing electro-magnetic noise to couple into your signal. They’re also
not susceptible to 50/60Hz hum; there is no connection to ground in the audio signal cable (ground is only in the shield), so they can’t
create ground loops in your sound system. Since the signals are differential, and signal receiver circuit only measures the difference
bet een them (not the absolute voltage), any noise that may couple into the signals ill couple equally on both the (+) and (-) signal
ires. They’ll both contain the same (common mode) noise, but the difference of the t o ill remain the same and not contain the
noise. In other ords, the noise ill be canceled out and on’t be audible in your speakers.
Another very significant advantage of using balanced mode is you ill get an extra 6dB of dynamic range, hich gives you a lo er noise
floor and t ice the sle rate of your signal for greatly enhanced signal definition.
If you have the choice, you should always choose balanced mode over unbalanced!
Both the balanced and unbalanced inputs/outputs are al ays active. There is no s itch to select one or the other signaling mode. You
select balanced or unbalanced mode by the jacks you choose to connect. The RCA jacks are all unbalanced signals, and the ¼” TRS jacks
are all balanced signals.
Figure 2. Balanced ode signal Input and Output ¼” TRS Jack Wiring

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Configuring the Crossover Frequencies
The sub oofer and mid/high crossover frequencies are controlled by the values of t o ‘XO Modules’ inside the K231. These are
accessible through an access panel on the bottom of the chassis. Normally these ill be pre-installed at the factory and you may never
need to do anything ith regard to the XO modules. But you may ant to experiment ith other crossover frequencies, and this can be
easily accomplished ith the K231. The XO modules are nothing more than small PCBs that are inserted into t o card slots labeled ‘Sub’
and ‘Mid/High’. Changing the sub oofer or mid/high crossover points is as simple as replacing the XO module(s) ith ne values.
Additional XO modules can be ordered from Xkitz.com.
12dB Crossover Filter Slope and Channel Phasing
If you’re using XO Modules that are set for 12dB per octave filter slopes, the resulting ‘Mid’ output channels ill be 180⁰ out of phase
from the ‘Sub’ and ‘High’ outputs. This is a normal attribute of 12dB filters. To compensate for this you ill need to s ap the speaker
ires on the speaker that is driven by the ‘Mid’ output channels to put the output channels back in phase. If you’re using 24dB/octave
XO modules, then all the outputs are in phase ith each, so no speaker ire s apping is needed for 24dB modules.
Sub oofer Output – Mono or Stereo
The sub oofer output can be configured to be either stereo or mono by setting a small slide s itch marked ‘Sub:’ behind the access
panel on the bottom of the chassis. When set to stereo, both sub oofer L and R jacks are active. When set to mono, the L and R
sub oofer channels are mixed into a single channel hich is available on both Sub output jacks. When set to mono mode, you can plug
your sub oofer amplifier into either of the Sub output jacks.
Baffle Step Compensation (BSC)
Baffle Step Compensation, or BSC, allo s you to apply a lo pass shelf filter function to the audio signal to compensate for a
phenomenon here sounds above a certain frequency (determined by the size of the baffle, or the front of your speaker box) are
actually reflected by the front of the speaker enclosure. Sounds that fall belo that frequency do not get reflected, but instead rap
around the back of the speaker enclosure and are attenuated to a certain extent. This has the effect of reducing the magnitude of the
lo er frequencies. Your ear hears the primary aves plus the reflected aves on the highs, but only the primary aves of the lo s. The
BSC circuit, by applying a lo pass shelf filter, ill roll off some of the highs to restore the overall sound to a more natural, linear state.
There are a number of good articles on the eb ith much more in-depth descriptions of BSC.
The knob on the front panel labeled ‘BSC’ allo s the BSC filter gain to be adjusted. Turning this knob fully counter-clock ise reduces the
BSC filter gain to the point of being entirely disabled. Turning it clock ise increases the BSC magnitude to a maximum of 6dB. In other
ords, it increases the amount of attenuation of the higher frequencies to 6dB belo the lo er frequencies. This compensates for the
theoretical 6dB attenuation of the lo frequencies due to the baffle step effect.
There is a small slide s itch that is accessible through the access panel on the bottom of the chassis labeled ‘BSC:’, and each position is
labeled ‘1’ through ‘3’. The position of this s itch controls the frequency of the lo pass BSC shelf filter. Set this s itch to best match
your speakers’ baffle size (use the smaller of the t o speaker height and idth dimensions).
Table 1. Baffle Step Compensation – Recommended Switch Setting
Baffle Width (in Inches) Baffle Step Freq. BSC Switch Setting
Less than 9" 507Hz 3
9" - 13" 350Hz 2
Greater than 13" 253Hz 1
Initial Po er-up and Calibration
Ideally you should use a hite or pink noise generator and a spectrum analyzer to accurately balanced the High, Mid, Lo and BSC
settings, but you can just as ell balance your system ‘by ear’.
To balance your system, first set the Sub, Mid and High levels to unity gain by setting the knob indictor lines to point to the small circles
on the panel gradients. For simplicity, set the BSC to fully OFF, or counter-clock ise to start ith. Turn on the po er to your system and
the K231. The initial sound ill most likely be ay too bright, as t eeters often have a higher sensitivity than oofers. Drop the level of
the ‘High’ knob until you get to a natural mid/high balance. Then balance the ‘Sub’ channel (assuming you’re running in 3- ay
configuration). Lastly turn up the BSC knob until the bass sounds natural.

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