In-Depth: Subtonic CTRL Crossover

Crossover CTRL In-Depth STORM

Welcome to our "In-Depth" blog series, where we take an insightful dive into the intricacies of our IEMs. In this article, we go in-depth into our CTRL Crossover, the industry's most complex crossover system.

What is a Crossover?

When two or more drivers are used, their frequency response range will cause an overlap. The frequency bands in which they overlap produces a louder volume due to the shared band range. 

Crossover filters can be applied (with the use of capacitors, resistors and inductors) to reduce the range of overlap, ensuring that only the frequencies range the driver is best at is reproduced, and to minimize overlap/bleeding between the drivers.



With bass woofers, you want to tell it to only let bass frequencies pass. We call this a low-pass filter.

With tweeters, you want to tell it to only let treble frequencies pass. We call this a high-pass filter.

With midrange drivers, you want to only let midrange frequencies pass, by telling the bass and treble frequencies not to pass. We call this a band-pass filter.

Using an analogy, you can think of crossover filters as a traffic light controller. Crossover filters tell the driver which frequencies are allowed to pass, and which frequencies are not allowed to pass. 


Number of Ways?

The number of “ways” the IEM has directly equates to how many times the sound signal is split between the drivers. The greater the number of “ways”, the smaller the frequency range in which every driver reproduces, which is the ideal situation as it allows for precise sound sculpting and better sound quality.

A simple 3-way crossover splits the sound into 3 bands to be handled by the drivers
A complex 7-way crossover splits the sound into 7 bands, so that each driver can handle a specific frequency band

Crossovers in today’s IEMs

Crossover designs of today tend to be overly simplified, where some drivers play full-range without the use of a crossover filter. Band-pass on midrange drivers are also often skipped due to greater cost and slower assembly speed efficiency.

Hence, it is not uncommon to find a 10 driver, 3-way crossover IEM with no band-pass, for example. This crossover simplicity causes drivers to have a lot of overlap between each other, negatively affecting sound quality.


Subtonic CTRL Crossover

The CTRL crossover is a sophisticated solution to allow for very minimal overlap between the drivers. Every driver has a crossover filter applied so they play in the frequency range they are best at. We go as far as to band-pass midrange drivers to enable optimal midrange sound quality. STORM has the industry’s most complex passive crossover, where the sound is split into 7 narrow bands and layered in an intricate manner to maximise coherency. 

Using the CTRL crossover allows us to squeeze the most out of the drivers and create an environment where the EST can thrive in like never before. One of the main benefits of CTRL is the fine control over tuning it offers, as narrower frequency band can be tightly controlled. This extra control means that the acoustic dampers that simpler designs use to control resonance is no longer needed in the mid-highs of the STORM.

As damping is one of the biggest detriments to driver resolution, the damper-less mid-highs of the STORM allows us to pull far greater resolution over traditional BA implementations. CTRL also allowed us to select one of the fastest BA drivers for the mids and mid highs, while still attaining the required tonal response, which would not be possible without the fine control offered by CTRL due to the uneven native response of the drivers.

Combined with the beneficial effects of limiting stress on the driver due to driver only playing a narrow band, transient speed and true resolution is also greatly increased over traditional BA implementations. This also allows for more coherent bridging to the ESTs, which traditionally have struggled with coherence due to the ESTs being much faster than BAs.

CTRL has allowed the potential of both the BAs and ESTs to be fully realised for the first time. This means that STORM doesn't just sound like conventional EST hybrid or tribrid IEMs, which only offer marginal improvements over IEMs without ESTs. Instead, STORM sounds more akin to a full-sized speakers, breezing through complex music and effortlessly weaving through recordings.


Enabled With Top-Grade Components

Low quality electrical components degrade sound quality by introducing distortion in the signal path. To enable Subtonic’s high resolution sound, we adopt automotive-grade inductors, capacitors and resistors that contain very low internal resistance (ESR), virtually removing any distortion within the signal path. Where the industry uses components that cost cents (and have high ESR), we opt to use premium components to attain maximum resolution in the pursuit of excellent sound.

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