User:Denis Sbragion
From DRC
Contents |
A work in progress
My actual system isn't what can be called an High-End system. From an optimistic point of view I use to call it a medium quality well optimized Hi-Fi system. I will add more details and some picture in the future, in the meantime you can find a complete set of measures about it, both corrected and uncorrected, in the DRC manual at the following link:
http://drc-fir.sourceforge.net/doc/drc.html#htoc189
The system is composed of two main speakers from the italian manufacturer Chario, one home built vented subwoofer with two 10" Peerless woofers in a 60 liters box using a push pull configuration, an home built electronic crossover, two 50 W/ch. amplifiers, a Yamaha CDP Player working only as transport unit and of course a digital room correction system made out of an industrial "shoe-box" PC which works also as the DAC unit. The PC is equipped with a TerraTec EWX 24/96 soundcard and is used to run filters created, of course, by DRC. Everything is placed in a decent listening room and despite all the gear being now quite old, coming from a decade ago on average, it still show quite decent performance figures.
The electronic crossover is made using just a bunch of good quality operational amplifiers and some passive components, providing a simple 12 dB/Oct. Bessel cut at frequencies ranging from 30 Hz to about 200 Hz. The crossover cut-off frequencies are user selectable by a set of dip switches and some precision resistor ladders providing 64 different frequencies. I preferred the use of dip switches over potentiometers because potentiometers have quite big tolerances that makes almost impossible to get the same xover frequencies for both channels. The crossover settings are completely independent for each channel and each way, and now are set at 55 Hz for the sub and 115 Hz for the main speakers. The the sub level and crossover frequencies have been optimized using some acoustic measurements, way before I started implementing DRC.
The two 50 W/ch power amplifiers are made by Cabre (an italian manufacturer, no longer existing) and Akai. The Cabre amp is of pretty good quality (dual mono circuit, discrete oversized components, etc) and is used to drive the main speakers. The Akai amp is used to drive the subwoofer, and despite being of inferior quality with respect to the Cabre, it drives the sub without problems, mainly because the sub itself has been designed to be really easy to drive.
Silent convolver PC
I've just finished to make my "shoe-box" convolver PC completely fanless. I've used a big external heat-sink (these modern CPUs dissipates more power than a big class A amplifier!) and two heat pipes to connect it to the CPU. After a couple of days spent drilling and machining something to provide some good thermal conduction from the CPU to the heat pipes and finally to the heatsink the results are really good. Thanks to the oversized heatsink and to the heat pipes efficiency now the CPU run at no more than 45° C even under heavy load conditions. The external heatsink never gets more than a little warm. Most of the times the CPU is even colder than the motherboard. This way I have even some margin to put some faster CPU in the PC if needed, even up to a 1 Ghz PIII, which is the fastest processor supported by the small mainboard.
Of course the AC adapter fan was also an issue, but being a simple external AC adapter, much like that of a nootebok computer, I only needed to replace it with a fanless one. It hasn't been easy to find one rated at 120 W, but after a bit of searching I've been able to get an Ault PW122 AC Adapter from Allied Electronics. The efficiency of this AC adapter is quite impressive. Even after many hours of use, and despite the absence of any fan, it never gets more than a little warm. The previous AC adapter was smaller, but had a fan that turned on after half an hour of use or so, making quite an audible noise even after enclosing it into some furniture.
With these modifications, and switching the hard disk off after boot, which is quite a simple operation under Linux, the PC is now dead silent. The hard disk spindown is performed using few simple commands at the end of the /etc/rc.d/rc.local startup script:
# Mount the root partition read-only and switch the hard disk off echo "Hard disk spindown..." /bin/sleep 1 /sbin/hdparm -S 1 /dev/hda > /dev/null /bin/sleep 3 && /bin/mount -n -r / -o remount & /bin/sleep 10 && /sbin/hdparm -Y /dev/hda > /dev/null &
For these commands to work almost every service and program that uses the hard disk need to be disabled, so that the root partition can be mounted read-only, which also protects against filesystem corruption if the PC is turned off without performing a proper shutdown. After the hard disk spindown no operation at all has to be performed on the hard disk, else it gets turned on again automatically.
Remote serial line control
Using a switch connected to a serial line I'm able to switch between two different correction filters in real time, directly from the listening position if I use a long enough cable. More details about the configuration and the scripts used are available within the Brutefir section in my sample configuration page.
The filters, along with the Brutefir configuration if available, are loaded at boot time from an USB memory stick using another simple shell script that get executed from the rc.local startup script file:
#!/bin/sh # Try to mount the USB memory stick if mount -r -t vfat /dev/sda1 /mnt/ > /dev/null 2>&1 ; then # Check if some filters exists, set 1 if [ -r /mnt/lf1.pcm -a -r /mnt/rf1.pcm ]; then # Copy the new filters to their final place cp /mnt/lf1.pcm /root/bffilters/lf1.pcm cp /mnt/rf1.pcm /root/bffilters/rf1.pcm # Ensure that the right permissions are set chmod 644 /root/bffilters/lf1.pcm chmod 644 /root/bffilters/rf1.pcm fi # Check if some filters exists, set 2 if [ -r /mnt/lf2.pcm -a -r /mnt/rf2.pcm ]; then # Copy the new filters to their final place cp /mnt/lf2.pcm /root/bffilters/lf2.pcm cp /mnt/rf2.pcm /root/bffilters/rf2.pcm # Ensure that the right permissions are set chmod 644 /root/bffilters/lf2.pcm chmod 644 /root/bffilters/rf2.pcm fi # Check if a new BruteFIR configuration exists if [ -r /mnt/bfcfg ]; then # Copy the new configuration to its final place cp /mnt/bfcfg /root/bf/bfcfg # Ensure that the right permissions are set chmod 644 /root/bf/bfcfg fi # Unmount the USB stick umount /mnt fi
With this set of scripts and the configuration used I'm able to perform a basic reconfiguration of the convolver PC without the need of a keyboard, a screen or a network connection, so effectively turning the PC into a "convolver black box".
The future
Actually I'm starting to prepare for my future system in my new house, where I have a dedicated room designed from the ground up for audio use. There I will place probably a pair of Genelec 1038B Studio Monitors along with an IB subwoofer using eight 15" Dayton Titanic MKIII high excursion drivers powered by a couple of QSC RMX1850HD power amps, giving a combined power output around 3.6 Kw.
The system will be able to deliver 120 dB SPL from 10 Hz to 20 Khz and coupled with digital room correction and passive acoustic treatement should be able to provide quite an accurate reproduction. With the new system I plan to experiment with stereo dipoles and PanAmbio, creating combined room correction/xover cancellation filters using DRC.
More to come...
