I’m working on some sealed woofer cabinets that have been sitting for a few years. Some of the fibreglass stuffing became slightly compressed while stored in a bag. The woofers have been stored mostly upright as they would be in the enclosure.
I reinstalled the wool liner, fibreglass stuffing and the woofer this weekend. Acoustic and impedance measurements revealed unexpected results.
Prior to disassembly, the bass extended to 40Hz and the impedance had a sharp peak at 41Hz, 26 Ohms.
Now the bass is down -6dB or more at 40Hz and extends to just 45Hz, with a rounded peak fundamental impedance resonance at 45Hz, 18 Ohms. I had a sharp dip in the very tip of the impedance peak prior to adding the wool liner to the inside of the cab walls, so damping is playing a part.
I removed the woofer and it’s free air Fs was the same as it was years ago, 26Hz.
If the woofer’s free air Fs is unchanged, can other T&S parameters change somehow? Or, Is this a case of flattened fibreglass stuffing no longer doing it’s job of creating a virtual larger enclosure volume?
I reinstalled the wool liner, fibreglass stuffing and the woofer this weekend. Acoustic and impedance measurements revealed unexpected results.
Prior to disassembly, the bass extended to 40Hz and the impedance had a sharp peak at 41Hz, 26 Ohms.
Now the bass is down -6dB or more at 40Hz and extends to just 45Hz, with a rounded peak fundamental impedance resonance at 45Hz, 18 Ohms. I had a sharp dip in the very tip of the impedance peak prior to adding the wool liner to the inside of the cab walls, so damping is playing a part.
I removed the woofer and it’s free air Fs was the same as it was years ago, 26Hz.
If the woofer’s free air Fs is unchanged, can other T&S parameters change somehow? Or, Is this a case of flattened fibreglass stuffing no longer doing it’s job of creating a virtual larger enclosure volume?
The latter, so personally would cut/pull it apart into pieces to damp the bottom, one side and back panels to 'taste'.
Thanks GM. These sealed cabinets are fully stuffed, but some of the stuffing is flattened enough to leave voids in the upper cavity above the bracing. I'll add some stuffing when time permits, but in the meanwhile here are some measurements.
Black is the left woofer in 2021, 23Hz, 87 Ohms free air.
Grey is the left woofer in 2024, 23.8Hz, 83 Ohms free air.
Red is the right woofer in 2021, 25.5Hz, 79 Ohms free air.
Pale Red is the right woofer in 2024, 26Hz, 75 Ohms free air.
Below, the woofers compared when loaded into the same enclosure, 2021 vs 2024. This is where something seems off, as the impedance peak is 45Hz, rounded and flattened. The acoustic output suffers as a result.
Black is the left woofer in 2021, 23Hz, 87 Ohms free air.
Grey is the left woofer in 2024, 23.8Hz, 83 Ohms free air.
Red is the right woofer in 2021, 25.5Hz, 79 Ohms free air.
Pale Red is the right woofer in 2024, 26Hz, 75 Ohms free air.
Below, the woofers compared when loaded into the same enclosure, 2021 vs 2024. This is where something seems off, as the impedance peak is 45Hz, rounded and flattened. The acoustic output suffers as a result.