SB ACOUSTICS SB34SWNRX-S75-6
The Active Subwoofer uses an SB Acoustics SB34SWNRX-S75-6, a 346mm (12-inch) driver plus a built-in 200W class-AB amplifier module that can deliver up to 180W of continuous output power in this application. It is designed to match the Active Crossover Amplifier and Active Monitor Speakers, described over the last two issues. However, it is a very high-quality sub that you could use in any application. It will provide high power, extremely low distortion bass for the lower octaves. Subwoofers are all about moving large volumes of air. The deeper you go into bass frequencies, the more of a challenge that becomes. For true high fidelity, we want a -3dB point well below 30Hz and to achieve solid output to 20Hz. Unfortunately, we also need to consider practicalities like the physical volume req
The Active Subwoofer uses an SB Acoustics SB34SWNRX-S75-6, a 346mm (12-inch) driver plus a built-in 200W class-AB amplifier module that can deliver up to 180W of continuous output power in this application. It is designed to match the Active Crossover Amplifier and Active Monitor Speakers, described over the last two issues. However, it is a very high-quality sub that you could use in any application. It will provide high power, extremely low distortion bass for the lower octaves. Subwoofers are all about moving large volumes of air. The deeper you go into bass frequencies, the more of a challenge that becomes. For true high fidelity, we want a -3dB point well below 30Hz and to achieve solid output to 20Hz. Unfortunately, we also need to consider practicalities like the physical volume required. That requires us to set aside exotic approaches such as infinite baffles or horn loading. After modelling quite a few similar drivers, I settled on the SB Acoustics SB34SWNRX-S75-6. Mounted in an 50-litre enclosure tuned to 25Hz, it gives a -3dB point at 25Hz and is only 8dB down at 20Hz in free space. This enclosure is modest for such a hefty driver and for operating to such low frequencies. I could have opted for a much larger enclosure and tuned it lower, but I feel that the increase in size and porting difficulties are not in line with most people's needs. This is a serious subwoofer. Witt the amplifier running flat out, delivering close to 200 watts, this driver operates entirely within its linear region right down to 20Hz. I have built a lot of subs, including professional audio products, and this is an outstanding result in comparison. Driven at this power level, the Sub will produce over 110dB SPL (sound pressure level) right down to 30Hz and over l00dB SPL at 20Hz. Those ligures are for free space; in the real world, there is a floor and usually a wall or two, which will increase them by up to 6dB. The fact that we are in a finite volume room means the Subwoofer basically produces a flat response to close to 20Hz. The voice coil on this driver is 75mm in diameter and 28.5mm long. That is a very long voice coil, required to achieve lhe linear excursion mentioned above. One consequence of this is that much of the voice coil is outside the magnetic air gap, which is 6mm high. That significantly impacts driver efficiency, which is the price we pay for achieving high output at low frequencies. It can be driven from a home theatre amplifier's subwoofer output or an active crossover. I recommend that the Subwoofer be placed not too far from your main speakers, but somewhere that your family members will accept. If cost is no object, two subs are always better than one. I would place each Subwoofer in the general proximity of one main speaker. To be honest, though, it is not likely that a single active subwoofer will ever 'run out of puff'. The fantastic thing about this Subwoofer is that the very expended frequency response does not come at the expense of power handling, and you can safely drive it at very high levels right down to 20Hz. Yes, it is a significant investment to achieve this, but in use, it is truly impressive. Vented or passive radiator, I have opted to use a slot vent in our Subwoofer. Passive radiators exist that can be paired with the Subwoofer, bul they are pretty expensive, and you need two of them! The port is as large as I could fit and has flared ends to minimise 'chuffing' at high outputs. It is made with stacked layers of MDF cut to form flares at both ends, resulting in a 48-50mm high, 180mm wide port. The vent configuration is shown in the 'X-ray' style overview of Fig.1, along with the amplifier and enclosure. If you are not expecting to drive the Subwoofer at high levels or very deep, a single 10cm diameter round port of 41cm length will suffice. Still, with the investment this Subwoofer represents, I feel that compromising on the port is missing the point. Silicone-Chip January 2023
- Our OEM 12" SBA Tiga Kit uses 2x passive radiators
- This cabinet uses a port instead to reduce costs
- Any Plate Amplifier over 200W would be suitable
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