Based on the table I have created earlier, it appears that the output voltage improvement at high frequencies is not as good as the lower frequencies. So, it would appear that adding a choke or inductor in series with the large capacitor (270uF in series) will have higher impedance at higher frequencies (Xl - Xc) but with minimal effect at low frequencies. However, total impedance (LC-RsCs) will be lower. So, we can achieve the results we're seeing at the lower frequencies. Based on iteration of various inductance values, a 100nF inductor or choke will achieve similar improvement at low and high frequencies.
Using Pronine Electronics air core choke calculator with magnet wire from AWG #18 to AWG #30 and, using an ordinary pencil (diameter = 0.8cm), 6 turns are required to achieve 100nH. To achieve this, we will need 7 inches of magnet wire. For this, I'm using AWG #19 magnet wire. You can use ordinary wire AWG #18 to AWG #30 if you don't have magnet wire (however, magnet wire is best). Please refer to below pictures:
We will have to connect the air core choke or inductor this way
We need 7 inches and a pencil with diameter of 0.8cm (this is the typical diameter of most pencils)
Winding the choke (I have already removed the enamel coating at both ends)
Adding the air core choke to a previously modified PC speaker
How does it sound? Well ... buo na mas may buhay