Silver Flute W20RC38-08
I have tried many woofers to get the bass that I want but almost all failed. The only one is my Peerless NE265W-04. It is a fantastic driver. It ranks amongst the best. If I’m designing a high-end speaker, I’ll have no qualms using the NE265W-04. The problem comes when I’m not designing high-end. When the midrange and tweeter are moderately priced, I need a woofer that doesn’t break the bank.
After numerous attempts, I finally found the right woofer. This came about from my earlier design using a Dayton SD215A-88 in a bandpass enclosure. The subwoofer is a compact 25 liters that doesn’t cost an arm and a leg. It gave me what I was looking for but I encountered an unexpected issue. The Dayton was bottoming out, even at low volume. I could hear distinctly the voice coil former hitting the back plate. I can’t explain why. Maybe it’s a manufacturing fault or something. Whatever it is, I didn’t have time to waste on it. I subsequently moved on to other projects.
When I bought a Silver Flute W20RC38-08, I replaced the Dayton SD215A-88 with it hoping that it’ll sound better. To my relief, it was exactly what I was looking for. A bass that’s tight, responsive and well controlled. There’s virtually no bloom in the bass notes. The overall bass character is one of detail and definition.
Fig 1 – Toucan-SF RAW response
Fig 1 is the RAW response of the Toucan-SF. For this measurement, the microphone was positioned at the mouth of the tuning port. No room reflections are recorded. What is measured is what is coming out of the port.
From the plot, the bandpass bandwidth is approximately 35Hz~170Hz. At the low end, there is a slight peak of about 2.5dB at 45Hz. I have absolutely no issue with this. Our hearing is rather deficient at low frequencies. A peak of 2.5dB at 45Hz may in fact work to my advantage. Moving to the right, we can see the bandpass rolling off at 170Hz. At 500Hz onwards, it starts to gain in spl. There’s a series of peaks brought on by port resonances before dying off at 5kHz.
I’m sure readers have come across articles saying no crossover is required when using a bandpass. Well, it all depends. From the Toucan-SF plot, the highest peak is at 1.5kHz, followed by 3kHz and finally 4.5kHz. Note the 1.5kHz peak is only -10dB below the fundamental of 100dB. The lowest 4.5kHz peak is -15dB. Playing music with the bandpass without any crossover, I could hear the midrange. It is not loud but it’s there. So if you’re not too fussy, yes a bandpass sub can be used without a crossover. However, if quality audio is your goal, a crossover must be used.
Fig 2 – Toucan-SF RAW and 125Hz Low Pass
The Red plot in Fig 2 is with my 24dB/oct electronic crossover set at 125Hz. The offending port resonances are completely gone. This demonstrates the importance of using a crossover. Now, what happens if I want to maintain the original bandwidth.
Fig 3 – Toucan-SF with 250Hz Low Pass
The Blue plot in Fig 3 is with my electronic crossover at 250Hz. At this setting, I retained the full bandwidth and at the same time, I still eliminated the port resonances.
Fig 4 – Toucan-SF at RAW | 125Hz | 250Hz
Fig 4 is the overlay of the responses at RAW, 125Hz and 250Hz. These plots are useful as they give me an idea of the behavior of the bandpass when it’s subjected to different crossover corner frequencies.
Fig 5 – Bandpass Simulation
The Toucan-SF bandpass simulation is in Fig 5. It is exceptionally close to the actual measured response in Fig 1. Even the bump at 45Hz is there.
In the Toucan-SF, I sacrificed SPL for bandwidth. If higher sensitivity is desired, I will have to increase the volume of the bandpass enclosure. This will obviously reduce the bandwidth. If I want to maintain the bandwidth and yet have a higher SPL, the only way is to use two 8″ Silver Flutes and do a triple chamber bandpass. The overall enclosure size of 50 liters is still manageable. I may just make one this coming spring.
As it stands now, this Toucan-SF is the best bass from all my woofers. It’s very reasonably priced and has excellent performance. At only 25 liters, it is wife friendly.
Before I forget, I lined the inside of the bandpass with 3″ rockwool. That helps to reduce the port resonances. If one is using an electronic crossover, absorption material may not be required because there are no midrange port resonances. I will need to test further. Thinking aloud, the bass should sound harder without absorption material.
March 11, 2020Projects