Did you know that when you run a flat sweep tone into your speaker, you're actually feeding it a NON-FLAT power* response?! 

In a perfect ideal audio reproduction world, we expect:

1. the amplifier to drive a flat sweep tone, 

2. the speaker impedance to be flat.

3. and the power delivered to the speaker to be consistent

4. so that the resulting physical audio response is flat & perfect. 

Power* is the product of Voltage & Current.

Branded engineers in the market tend to build amplifiers based on numerical specifications. Even the major players, especially the modern ones, use these numbers as benchmarks to chase.

From an electronics perspective, they’ve created superb devices that perform well under ideal electrical conditions. 

But in the mechanical world, speakers are far from an ideal state, which makes it difficult for the amplifier to reach its desired optimum performance. 

I’m sure you’re familiar with the graph pattern shown in the attached figure. It represents a typical speaker impedance* & frequency curve found in most speaker drivers on the market.

Impedance* is how much the speaker resists motion at a certain frequency. The higher the impedance, the harder it is to drive the speaker cone. 

Observation 1: The FS (resonant frequency) occurs around 110 Hz, that's where you see a sharp increase of impedance at around 110Hz region.

Observation 2: The cone breakup happens between 1 kHz to 3 kHz. Cone breakup is a mechanism that the outer speaker cone can't catch up with the speed of the inner cone that attached to the voice coil. Which explains the noticeable frequency spike near that region, these spike causing harsh and ear piercing noises and this usually reduced with notch filter in the crossover.  

Observation 3 (Highlight):  The bandwidth, and the rolled off frequency. 

Now, let’s recall the basic Ohm’s Law:
V = IR, P = V²/R, P = I²R.

1. When the impedance increases, 

2. the current delivered to the speaker driver actually drops,

3. And when the current drops, the power delivered into the speaker dropped, 

4. when the power dropped, that’s where the roll-off begins.

We plug in a speaker equivalent circuit and simulate it under various conditions using SPICE. 

The equivalent circuit mimics how a speaker driver responds. The FS happens at around 50Hz, and the speaker impedance started to increased when the frequency start increasing.

Valve amplifiers are typically coupled with output transformers, which exhibit both inductive & resistive characteristics. While in contrast, modern solid-state amplifiers have extremely low output impedance (Zout). 

Let’s try to mimic the Zout of a valve amplifier. We simulate the output current response delivered to a speaker driver with different output impedances: 0.1Ω, 1Ω, 10Ω, and 22Ω. Interestingly, we observe that as the output impedance increases, the current response becomes noticeably flatter.

This leads us to an important conclusion: when using amplifiers with very low output impedance, especially modern Class D amps with extremely high damping factors, the bass and treble tend to roll off due to the impedance characteristics of the speaker itself.

At this point, we might begin to understand why some people complain that modern amplifiers sound "dull", "boring", or even "lifeless" compared to those that built in the old days.

Under High Zout:

Disclaimer 1: We are ignoring the electrical damping effect totally.

Disclaimer 2: We are ignoring the sensitivity totally.

To overcome this known issue, we have derived an God'AMP topology called C’Drive and integrated it into our Class A SS300B-25C.

The pink curve(SS300B25C) as you see in the highlights, its a mirror image of what the commercial amplifiers do in the market, we invert it, flip it, mirror it, reverse it, reflect it. No more early roll-off at bass & treble, anyone who hears it will be blown away by how insane it is, it just takes the sound experience to a whole new level like never before.