We’ve recently had a couple ZOwners comment on the new ZO’s sound quality in regards to bass. So we decided to break out our test equipment and run some frequency response plot comparisons on ZO, ZO 2.1, ZO 2.3 & ZO FS under various loads (which represent common headphone/IEM loads). Check out the results below.
ZO Bass Frequency Response Plots under Various Loads
Note: these plots have been normalized to 1kHz.
First thing you’ll notice is that ZO FS gives significantly more bass (in particular, sub-bass), especially with lower impedance headphones. Second is that the ZO FS’s bass response is much more consistent across various loads. So what makes ZO FS’ bass perform better than in previous ZO models?
Faster, More Unrestrained Power
To get detailed, fast and well-controlled bass, you need the right kind of raw power. If you’re familiar with ohm’s law, you may already know that power consists of both voltage and current. Most headphone amps (particularly those of the portable kind) are designed to deliver large voltage swings. Thing is, good sounding bass requires lots of current, not voltage. A high impedance headphone (like the HD600) only needs around 2.3V to reach painstakingly loud levels! So an amp designed to deliver upwards of 10V may make your headphones louder (especially for the midrange and treble), but if the proper amount of current isn’t there, your headphones’ voice coil won’t move enough (or have enough displacement) to produce deep bass! So what excellent bass reproduction comes down to is this… it’s not how much power you have, it’s how much of the right power you have that matters.
No Output Capacitors
The second major improvement to ZO FS’s bass is a consistent low frequency response across various loads. This is because the ZO FS doesn’t use output capacitors in the audio signal chain. Output capacitors have a tendency to alter the frequency response when paired with a load (such as your headphones), which results in the bass getting cut. Capacitors also become part of the load, which takes away from the power needed for delivering strong, punchy bass (which we explained earlier as being SO important).