The scope for DIY in Hi-Fi is enormous, and can provide an absorbing hobby as well as, hopefully, delivering quality sound. For a number of years I have been interested in widening the stereo field of stereo recordings. I always felt that a pair of speakers placed across the minor dimension of the listening room leaves something to be desired. Whilst, at the other extreme, AV surround sound just does not appeal to me for a variety of reasons. My objective is to produce a sixty degree wide stereo field in front of the listener.
You can widen the stereo field by simply placing the speakers further apart. However, the central images can become diffuse if the speakers are placed much more than thirty degrees apart. Indeed, this may be why, with two channel systems, the speakers ARE placed across the minor dimension of the listening room. So, instead, I connect the output of a stereo source to a multi-channel system. Having built a range of systems, I am confident that both four channel and six channel systems can support a sixty degree wide stereo field, with the step from two to four channels being quite apparent. The further benefit of using six channels is more subtle.
If anyone is interested in building a stereo field system, I would offer the following advice:
1. If you have an AV 5.1 or 7.1 system with an external RCA analogue multi-channel input and a separate stereo source, it is easy to set up a four channel stereo field system with just a few RCA Y phono cables:
a) Disconnect the centre and the surround-back speakers (if fitted).
b) Move the front and surround speakers into a line or arc, spaced apart by half the distance from the listening position. E.g. If the speakers are 2 metres from the listener, space them 1 metre apart.
c) Connect a male-to-male RCA Y adapter cable between the left channel output of the stereo source and the left front and surround inputs of the AV amp's external input.
d) Connect a male-to-male RCA Y adapter cable between the right channel output of the stereo source and the right front and surround inputs of the AV amp's external input.
e) Select "External input" (or some such) and adjust the AV amps channel volume controls to set the front channels to 0dB and the surround channels to -3dB. If desired, you may adjust the surround channels in the range +3dB to -6dB, to fine tune the width of the stereo field.
f) You may need to add a further RCA Y adapter to feed a subwoofer. If so, connect a Y adapter between one (not both) of the source channel output and the subwoofer input. Note: It is possible that this may affect the stereo balance. If that does occur, add an RCA Y adapter between the other stereo output and the centre channel input of the the AV amp. This may seem a strange thing to do, as the centre channel is not used, but it is purely to balance the load seen by the stereo source.
2. To reliably compare the settings you need a Stereo Field unit. This unit keeps the overall output constant whilst the settings are varied. The units are comprised of resistors acting as potential dividers, with no crossfeeding of the channels and less than 1dB overall insertion loss. The key factors in their design are:
a) The units must be matched to the input impedance of the multi-channel amplifier. Simpler units are designed to feed a fixed 47K Ohm input impedance. More complex designs can match fixed input impedances from 10K Ohms to 1M Ohms. Note: If the input impedance of the multi-channel amp varies (e.g. with the setting of the volume control) you may need to add a buffer unit to provide a fixed input impedance.
b) The designs have been optimised using a computer app. Those using switches to vary the stereo field are level to +-0.2dB, whilst designs using potentiometers are level to +-1dB (plus component tolerances). Note: The listening room and the placement of the speakers can have a significant effect on the overall level. So some experimentation with the layout may be needed to get the best effect.
Unfortunately, Stereo Field units are not available commercially. However, I can supply a link to a web site on which I have put instructions for how to build your own Stereo Field unit. As the units are purely passive, with no power supply, building one should be within the abilities of anyone familiar with using a soldering iron! Alternatively, I may be able to supply on loan a few Stereo Field units from the prototypes I have made. However, I would stress that these are constructed to "hobbyist" standards and lack the "feel" of professional units.
Please let me know if you are interested in any further information...
You can widen the stereo field by simply placing the speakers further apart. However, the central images can become diffuse if the speakers are placed much more than thirty degrees apart. Indeed, this may be why, with two channel systems, the speakers ARE placed across the minor dimension of the listening room. So, instead, I connect the output of a stereo source to a multi-channel system. Having built a range of systems, I am confident that both four channel and six channel systems can support a sixty degree wide stereo field, with the step from two to four channels being quite apparent. The further benefit of using six channels is more subtle.
If anyone is interested in building a stereo field system, I would offer the following advice:
1. If you have an AV 5.1 or 7.1 system with an external RCA analogue multi-channel input and a separate stereo source, it is easy to set up a four channel stereo field system with just a few RCA Y phono cables:
a) Disconnect the centre and the surround-back speakers (if fitted).
b) Move the front and surround speakers into a line or arc, spaced apart by half the distance from the listening position. E.g. If the speakers are 2 metres from the listener, space them 1 metre apart.
c) Connect a male-to-male RCA Y adapter cable between the left channel output of the stereo source and the left front and surround inputs of the AV amp's external input.
d) Connect a male-to-male RCA Y adapter cable between the right channel output of the stereo source and the right front and surround inputs of the AV amp's external input.
e) Select "External input" (or some such) and adjust the AV amps channel volume controls to set the front channels to 0dB and the surround channels to -3dB. If desired, you may adjust the surround channels in the range +3dB to -6dB, to fine tune the width of the stereo field.
f) You may need to add a further RCA Y adapter to feed a subwoofer. If so, connect a Y adapter between one (not both) of the source channel output and the subwoofer input. Note: It is possible that this may affect the stereo balance. If that does occur, add an RCA Y adapter between the other stereo output and the centre channel input of the the AV amp. This may seem a strange thing to do, as the centre channel is not used, but it is purely to balance the load seen by the stereo source.
2. To reliably compare the settings you need a Stereo Field unit. This unit keeps the overall output constant whilst the settings are varied. The units are comprised of resistors acting as potential dividers, with no crossfeeding of the channels and less than 1dB overall insertion loss. The key factors in their design are:
a) The units must be matched to the input impedance of the multi-channel amplifier. Simpler units are designed to feed a fixed 47K Ohm input impedance. More complex designs can match fixed input impedances from 10K Ohms to 1M Ohms. Note: If the input impedance of the multi-channel amp varies (e.g. with the setting of the volume control) you may need to add a buffer unit to provide a fixed input impedance.
b) The designs have been optimised using a computer app. Those using switches to vary the stereo field are level to +-0.2dB, whilst designs using potentiometers are level to +-1dB (plus component tolerances). Note: The listening room and the placement of the speakers can have a significant effect on the overall level. So some experimentation with the layout may be needed to get the best effect.
Unfortunately, Stereo Field units are not available commercially. However, I can supply a link to a web site on which I have put instructions for how to build your own Stereo Field unit. As the units are purely passive, with no power supply, building one should be within the abilities of anyone familiar with using a soldering iron! Alternatively, I may be able to supply on loan a few Stereo Field units from the prototypes I have made. However, I would stress that these are constructed to "hobbyist" standards and lack the "feel" of professional units.
Please let me know if you are interested in any further information...
