Thought I'd share this project I've been working on.
Background: As part of my PA system, I've been running some 15" ported subwoofers for a while. Beyma 15P1200Nd, compact boxes tuned to 40Hz. They've generally been good to me, but there are some problems in the construction (drivers hitting the grilles, stuff like that - mostly my own fault) that meant I was never 100% happy with them.
Drivers have moved on since those Beymas - more Xmax, more power handling. As an example, I happened to have accumulated 3x Faital 18XL1800 drivers, which feature an Xmax of about 20mm, and long-term thermal power handling of 1600W. Short-term, they'll take in excess of 3KW.
I have a good relationship with a local theatre director, and he'd hired me for a show called Into The Woods, which features (among other things) a giant. When I suggested that I build some subwoofers capable of strong very-low-frequency output for the giant's footsteps to be felt as well as heard, he was enthusiastic about the idea.
After some messing around with Hornresp, playing with cabinets of varying sizes and complexity, I decided on sealed boxes for these drivers. The reasoning is this: at 40Hz, they'll keep up with the previous ported subwoofers, which were usually loud enough. If I need these new subwoofers to go louder, I can raise the low-frequency cutoff, gain efficiency, and put out more SPL. Similarly, if there's plenty of Rig For The Gig, I can throw more power at them and get more LF extension. The cabinets would also be very compact, which is a Good Thing in the live sound world.
Side-note: it may be of interest to see what sort of performance an off-the-shelf product gives. Here's one: https://products.electrovoice.com/binary/EKX-18S_F01U308106.PDF
The venue in question is small (100 seats), so I decided to push for maximum LF extension:
I set off with a 12dB/octave lowpass filter at 18Hz (the red curve), which gave me a response that's pretty flat across the subwoofer range. Then, I decided to increase the fun-factor, and made it 18dB/octave (green). Afterwards, I increased the subwoofer level accordingly, so that the crossover to the main speakers (approx 70Hz) lined up well.
Power and processing was done by the rack of Powersoft T-series amps:
With the T602 bridged into two of the subwoofers, and the first two channels of the T604 bridged into the third subwoofer. Result: around 3KW per driver - enough to make use of the driver's generous Xmax for short-term peaks.
The giant's footsteps were played by timpani, as part of the show's pre-recorded music. Running that section through an RTA, the timpani had strong content down to 30Hz. While that's pretty useful (and would've been fine, I'm sure), these subwoofers can go lower, and I wanted to make use of that. Within the mixing desk, I took a digital split of the music input, applied a low-pass filter at about 80Hz, put it through an octave down, and mixed that into the subwoofer feed. The results were a lot of fun - even the lighting engineer was impressed.
This venue hadn't ever been subjected to a PA system like this, so all sorts of interesting rattles were apparent. By far the most distracting was a light fixture, so that one was removed entirely. With that gone, the quieter and more distant rattles contributed to the "there's something big coming this way" effect, so we decided to stop chasing perfection and have some food instead.
I found time to play a few bits of music (without the octave down), and the high output combined with serious LF extension was an excellent experience. Violence by Andy Stott was a good demo.
I think that about covers the story for the subwoofers.
A few other notes, if anyone's still interested:
In all, I've had a lot of fun here. It's good to be back.
Chris
Background: As part of my PA system, I've been running some 15" ported subwoofers for a while. Beyma 15P1200Nd, compact boxes tuned to 40Hz. They've generally been good to me, but there are some problems in the construction (drivers hitting the grilles, stuff like that - mostly my own fault) that meant I was never 100% happy with them.
Drivers have moved on since those Beymas - more Xmax, more power handling. As an example, I happened to have accumulated 3x Faital 18XL1800 drivers, which feature an Xmax of about 20mm, and long-term thermal power handling of 1600W. Short-term, they'll take in excess of 3KW.
I have a good relationship with a local theatre director, and he'd hired me for a show called Into The Woods, which features (among other things) a giant. When I suggested that I build some subwoofers capable of strong very-low-frequency output for the giant's footsteps to be felt as well as heard, he was enthusiastic about the idea.
After some messing around with Hornresp, playing with cabinets of varying sizes and complexity, I decided on sealed boxes for these drivers. The reasoning is this: at 40Hz, they'll keep up with the previous ported subwoofers, which were usually loud enough. If I need these new subwoofers to go louder, I can raise the low-frequency cutoff, gain efficiency, and put out more SPL. Similarly, if there's plenty of Rig For The Gig, I can throw more power at them and get more LF extension. The cabinets would also be very compact, which is a Good Thing in the live sound world.
Side-note: it may be of interest to see what sort of performance an off-the-shelf product gives. Here's one: https://products.electrovoice.com/binary/EKX-18S_F01U308106.PDF
The venue in question is small (100 seats), so I decided to push for maximum LF extension:
I set off with a 12dB/octave lowpass filter at 18Hz (the red curve), which gave me a response that's pretty flat across the subwoofer range. Then, I decided to increase the fun-factor, and made it 18dB/octave (green). Afterwards, I increased the subwoofer level accordingly, so that the crossover to the main speakers (approx 70Hz) lined up well.
Power and processing was done by the rack of Powersoft T-series amps:
With the T602 bridged into two of the subwoofers, and the first two channels of the T604 bridged into the third subwoofer. Result: around 3KW per driver - enough to make use of the driver's generous Xmax for short-term peaks.
The giant's footsteps were played by timpani, as part of the show's pre-recorded music. Running that section through an RTA, the timpani had strong content down to 30Hz. While that's pretty useful (and would've been fine, I'm sure), these subwoofers can go lower, and I wanted to make use of that. Within the mixing desk, I took a digital split of the music input, applied a low-pass filter at about 80Hz, put it through an octave down, and mixed that into the subwoofer feed. The results were a lot of fun - even the lighting engineer was impressed.
This venue hadn't ever been subjected to a PA system like this, so all sorts of interesting rattles were apparent. By far the most distracting was a light fixture, so that one was removed entirely. With that gone, the quieter and more distant rattles contributed to the "there's something big coming this way" effect, so we decided to stop chasing perfection and have some food instead.
I found time to play a few bits of music (without the octave down), and the high output combined with serious LF extension was an excellent experience. Violence by Andy Stott was a good demo.
I think that about covers the story for the subwoofers.
A few other notes, if anyone's still interested:
- The main PA speakers use a Faital 10HX230 per side. Ported boxes, tuned to 70Hz. I rather like those.
- The subwoofers have a port at the back, where a tunnel can be placed to vent the rear of the driver's motor. I plan on doing some thermal testing to see if that's necessary, but for now the vent is blocked and heat remains in the cabinet. Not a problem for this show - the duty cycle was very low.
- While the mixing desk and amp rack was placed side-of-stage, I mixed the show on a set of iPads from the control room. That kept the cable runs relatively short, and allowed me a good mixing position. During the more dramatic moments, the cupboards at the back of the control room were rattling.
In all, I've had a lot of fun here. It's good to be back.
Chris