Vintage 10″ Pyramid Gold Compact 25L Bandpass Subwoofer

10″ Pyramid Gold 25L Bandpass Subwoofer

This Pyramid Gold is a 10″ car subwoofer that I bought way back in the 90s. It’s probably about 20 odd years now. All this while, I have never been able to get the bass I wanted out of this subwoofer. It just sounded blurry in a bass reflex. I even tried it in a sealed box but it was still unsatisfactory. 

When I started working on Bandpass Subs a few years ago, this Pyramid Gold subwoofer is the first driver that I tested. That was when I discovered that a bandpass enclosure can make a horrible driver sounds fantastic. I was utterly shocked when I got a punchy yet clear midbass that is so essential in music and it even went down to 40Hz.

10″ Pyramid Gold Frequency Response

Fig 1 – Measurements taken with the mic at the mouth of the port.

The Black plot in Fig 1 is the RAW response of the Pyramid Gold. It displayed a huge resonant peak spanning 700Hz~2.5kHz. The Blue plot is with an active Low Pass filter at 250Hz (24dB/oct Linkwitz Riley). The Red plot is at 125Hz and the Violet is at 95Hz.

The addition of a steep crossover is crucial otherwise the bandpass internal resonance will cause havoc in the midrange. The plots above are proof. All the garbage disappeared when the bandpass is low passed as high as 250Hz.