I’ve been trying to build a triple chamber bandpass sub for a long time but I couldn’t find the right drivers. Those that simulated well ended up with a size from 50 liters to 100 liters. That’s far too large for my taste. What I really want is a compact triple chamber sub. After all these years, I finally found the right drivers in the Dayton DA135-8. From my modelling, it has a small footprint of 8″x8″ and is only 23-1/2″ tall, exactly what I’m looking for. The height is important because it is meant to replace a speaker stand. A small 2-way can sit on top and you’ll have a 3-way.
Fig 1 – Palila Triple Cahmber Bandpass Modelling
Fig 1 is the predicted response of the Palila. Total internal volume is just 16 liters. The center chamber is 6 liters whereas the outer two are 5 liters each. The two drivers will be paralleled with their cones firing into the center chamber together. Bandwidth is about 50Hz to 150Hz.
Fig 2 – Palila Frequency Response. Mic at mouth of port.
The frequency response of the Palila (Fig 2) is exactly the same as in the modelling. Measurement was made with the microphone in the mouth of the port.
I played some music and was horrified by a distinct whistling. It originates from the first 2.5kHz spike in the port resonance. It was downright irritating. I concluded that a crossover must be used with the Palila to eliminate all the port resonances.
Fig 3 – RAW and 500Hz Low Pass Filter
I set my electronic crossover at 500Hz (24dB/oct) and did another sweep (Blue plot). Even at such a high frequency, it completely eliminated the port resonances. This means that if I choose to use the natural acoustic low pass of the Palila, which is about 200Hz, I can use a 500Hz low pass just to kill off the port resonances. This will be much cheaper than a passive low pass filter at say 125Hz.
Fig 4 – 100Hz to 500Hz Low Pass Responses
Fig 4 is a family of plots with my crossover set at 500Hz, 250Hz, 120Hz and 100Hz respectively. Notice how much the passband drooped at 100Hz. I recommend 120Hz as the lowest crossover frequency for the Palila.
Sound of Palila
This is the bass quality I’ve been searching for. The upper bass is tight and has a fast attack. The lower bass is there but not as deep as the Toucans. The Toucans use 8″ woofers but lack the attack in the upper bass. The Crows, with their 6-1/2″ woofers, lack the sensitivity. It needed two 5-1/4″ woofers to get it right.
In building the Palila, I lined the two outer chambers with R-13 fiberglass insulation. The center ported chamber has no insulation. You may want to experiment with different absorbent materials and even lining the center chamber too.
Lastly, make sure the DA135-8 are in parallel. Don’t depend on the woofer’s marking on the terminals. Measure it with a meter. It should read about 4Ω, not 16Ω. The reason I highlighted this is because believe it or not, one of my woofer’s terminal was marked incorrectly. The Plus was a Minus.
October 11, 2020HIFI DRIVERS, Projects