I tried using two vintage Coral (I got several more in stock somewhere) to increase the sound level in the HF. As they say the older you get specially male species like us the more you loose your hearing ability to hear HF notes. No wonder, there are some guys who needs increase HF level to enjoy. If I am not mistaken our ears started to go at age 30. And we start blaming the drivers rather than our ears. Hehehe.
LOL. I also had the experience ridding on the jeep and observed those jeeps really have kilansing (in a distorted way and not ideally soothing to the ears) only to find out that if I were in the driver seat you don't get to hear that much kilansing!!! Nor the bass!!! Or even anything decent. Take note he needs to be aware of the "para" and "ito po ang bayad" or "mama sukli ko" With all the noise out there and the speaker position was more for the passenger rather than the driver, the driver has no choice but to turn it up to his satisfaction but to the lost of the eardrums of the passengers. Ideally dapat isang set of speakers position para sa driver tapos another set of speakers sa mga pasahero. Assuming they tamed the speakers kasi ang ginagawa nila gaya gaya lang ng crossover circuit. Audiophile Jeep!
That experience made we aware to set up(tone and balance control) the sound system in my car if i have passengers. Try listening to the music as a passenger you'll see or hear what I mean.
Any way try the Pioneer imitation ojofool is offering. If its a piezo its not imitation that is it, Motorola made in whatever country. Try taming it or use two pairs baka ma mellow down the harsness and if it won't work try out different pairs of different brand. It's all part of the hobby. ENJOY!