Hoerninger
09-19-2008, 12:28 PM
Some multichannel recordings made me wonder what is going on with bass. On the one hand it is sometimes overemphasized by the producer, on the other hand the bass had such a clarity and strength seemingly independend from room localisation not known from stereo reproduction before (all full range speakers).
I got in mind the paper "Multisubs" by Todd Welti (Harman International Industries)
http://www.harman.com/wp/pdf/multsubs.pdf
where he has proposed the usage of several subs, but:
"Based on the assumption of a rectangular room and a seating area in the center or center-rear of the room that there is no justification to use more than four (subwoofers). To the contrary, it was observed that the LF factor actually went down for larger numbers of subwoofers." (p.27) " Two and four subwoofers at the wall midpoints are still the best configurations overall." (p.26)
Read the paper for more details.
As I am mainly interested in multichannel audio reproduction and not in video. I have reread a remark by TELARC:
"Multi-channel surround sound for for audio playback for the home is a relatively new concept, and there are many variations as to how the systems can be set up. This disc ... was designed for optimal performance on a system that utilizes at least five full-range, and preferably equal speakers employed in a a left front, center, right-front, left surround, right surround configuration. There are mix components that require the presence of all five main speakers. A subwoofer is also recommended."
So I came up with my DIY idea.
The proposed circuit mixes the bass of six channels below ca. 80 Hz so it is mono. The mixing circuit does not restrict the frequency response in any way.
Each channel has a low path which adds bass to all other channels. In each channel itself some bass is subtracted. The mixing takes place in the middle of the circuit, not at the input or output.
The calculation of the resistors depends on the number of channels. In this design all six outputs are required. There may be less inputs. I have changed the filter from Butterworth 12 dB/oct to Bessel 18 dB/oct.
The analog approach makes sense as for SACD multichannel and DVD audio multichannel there is only an analog output signal available. My player delivers six analog channels and the receiver can handle them without digital gimmicks (as far as I have understood).
This circuit is based on a idea by J.P.Macaulay (Wireless World, Circuit Ideas, September 1979, "Rumble Cancelation Filter"). A simplified and improved version was published by Jens Langvad (Ring Instrument, Vanlose, Denmark) in Wireless World (Letters to the Editor, March 1980). A very similar circuit was published in Populäre Elektronik (March 1982, Germany).
All these circuits are for stereo.
The circuit in the attachment is needed six times. It is best to start with a six line bus and arrange the components adequately. You will need twelve OPs. One candidate might be the new LME49860 by National Semiconductors (dual, DIP).
http://cache.national.com/ds/LM/LME49860.pdf
____________
Peter
(dimensioning follows)
I got in mind the paper "Multisubs" by Todd Welti (Harman International Industries)
http://www.harman.com/wp/pdf/multsubs.pdf
where he has proposed the usage of several subs, but:
"Based on the assumption of a rectangular room and a seating area in the center or center-rear of the room that there is no justification to use more than four (subwoofers). To the contrary, it was observed that the LF factor actually went down for larger numbers of subwoofers." (p.27) " Two and four subwoofers at the wall midpoints are still the best configurations overall." (p.26)
Read the paper for more details.
As I am mainly interested in multichannel audio reproduction and not in video. I have reread a remark by TELARC:
"Multi-channel surround sound for for audio playback for the home is a relatively new concept, and there are many variations as to how the systems can be set up. This disc ... was designed for optimal performance on a system that utilizes at least five full-range, and preferably equal speakers employed in a a left front, center, right-front, left surround, right surround configuration. There are mix components that require the presence of all five main speakers. A subwoofer is also recommended."
So I came up with my DIY idea.
The proposed circuit mixes the bass of six channels below ca. 80 Hz so it is mono. The mixing circuit does not restrict the frequency response in any way.
Each channel has a low path which adds bass to all other channels. In each channel itself some bass is subtracted. The mixing takes place in the middle of the circuit, not at the input or output.
The calculation of the resistors depends on the number of channels. In this design all six outputs are required. There may be less inputs. I have changed the filter from Butterworth 12 dB/oct to Bessel 18 dB/oct.
The analog approach makes sense as for SACD multichannel and DVD audio multichannel there is only an analog output signal available. My player delivers six analog channels and the receiver can handle them without digital gimmicks (as far as I have understood).
This circuit is based on a idea by J.P.Macaulay (Wireless World, Circuit Ideas, September 1979, "Rumble Cancelation Filter"). A simplified and improved version was published by Jens Langvad (Ring Instrument, Vanlose, Denmark) in Wireless World (Letters to the Editor, March 1980). A very similar circuit was published in Populäre Elektronik (March 1982, Germany).
All these circuits are for stereo.
The circuit in the attachment is needed six times. It is best to start with a six line bus and arrange the components adequately. You will need twelve OPs. One candidate might be the new LME49860 by National Semiconductors (dual, DIP).
http://cache.national.com/ds/LM/LME49860.pdf
____________
Peter
(dimensioning follows)