Is it posible to make a filter, working off the volume control, which lowers the volume of frequencies below about 55Hz as the volume is turned up. This would allow me to use open baffles with boost on the low frequencies for quieter listening without using subs but If I listened at loud volumes I would turn on the subs and the boost on the open baffles would be reduced. I guess I am looking for a circuit to reduce boost with increasing volume but operated off the volume control so that two separate controls are not needed. This is to reduce xmax at high volumes. Thanks for any help, negative or positive.
jamikl
jamikl
Why not just use a low cut filter in the pre-amp section?
Most pre-amps and integrated amps used to have this function so I am sure there would be a circuit diagram somewhere or an alternative could be a low frequency parametric filter centered on : say 40 Hz, but with my limited knowledge thats as much a guess as anything
Most pre-amps and integrated amps used to have this function so I am sure there would be a circuit diagram somewhere or an alternative could be a low frequency parametric filter centered on : say 40 Hz, but with my limited knowledge thats as much a guess as anything
An alternative is a four ganged pot. Use two gangs for the volume and the other two for your contour.
Terry
What you are after I think is called a shelving filter with it's knee at 55 Hz. If you want the effect to be 'in' at 55 you may need to set the filter knee at 60Hz or so. I don't know how to design these but at least you know the name!
Terry
In my opinion, loudness compensation should be standard in audio reproduction. A glance at the equal-loudness contours shows that the subjective loudness at bass frequencies is much more compressed than at mid frequencies. A musical work is normally balanced to sound "right" at whatever SPL the mastering engineer listens at. You need to play back at the same SPL in your room to achieve the same tonal balance. If you play back louder than that, the bass is accentuated. If you play back quieter, the perceived bass is attenuated (relative to the midrange). Dropping the overall level by 3 dB may result in a perceived 10 dB drop at 20 Hz. This is the reason for the classical "loudness control", which progressively boosts the bass as the level is lowered.
The problem with the classic loudness control is that it is fixed relative to the position of the volume control. It only works well if your system's overall gain structure provides a reference level at the right position of the control. If not, it provides too much or too little bass boost as you turn down the volume.
What is needed is a progressive bass boost/cut control linked to the volume control, along with a gain setting control that lets you calibrate your system to the standard.
It would work like this:
At a reference position of the volume control, maybe at the "12 o'clock" or half-way position, the bass boost/cut would be "flat" (no boost/cut).
You set your volume control to this position, then adjust the calibration control for the music you want to play so that it reaches a specific SPL setting at your listening position. From that point, turning the volume control up or down will also adjust the bass level to provide a consistent tonal response.
The mastering engineers set their reference level like this:
Play pink noise at -20dB ref to FS, one channel at a time.
Using an SPL meter at your listening position, adjust the playback level for a reading of 83 dB, C weighted.
Repeat for the other speaker. Don't try to balance between the speakers, just measure the level of each of them and set the playback signal to the average. If there is more than a couple of dB difference, your system or room is set up wrong.
Having set the level, mastering engineers may then deviate from it quite a bit - for example, they may turn the monitoring level down by up to 15 dB if mastering heavily compressed music such as that by the Red Hot Chili Peppers or Metallica. The intention is that the average level in the mastering room will be 83 dB SPL per speaker, regardless of whether the music is high dynamic (classical music, jazz etc) or ultra-compressed (heavy metal, most pop).
For reproduction, the process is less complex - if you set your volume control so that the music averages 83 dB SPL per speaker, at your listening position, then you will be hearing the music as the mastering engineer heard it. The required gain setting will vary with the music type - you may need to turn your calibration gain down by up to 15 dB when playing Metallica compared with a string quartet.
A system using a "linked volume / tone control" would have two "volume knobs" (calibration and volume) and would be used like this:
Set the main volume control to the reference position.
Play the music.
Adjust the calibration control to provide about 86 dB C weighted at your listening position.
Adjust the main volume up or down to taste.
With practice, you will find that you can often calibrate by ear - a lot of music has a "right" setting, where it sounds natural and "life size".
This is no accident - the mastering engineer has optimised the tonal balance etc for this SPL.
Finally, getting back to the specific application under discussion, this system provides automatic bass management. If you raise the overall volume by 10 dB, the bass level may only increase by about 3 dB. This is obviously good for systems with limited LF capabilities, such as OB designs.
To match the equal loudness contours, the bass boost/cut should follow the standard Baxandall type response. A second section could be added to provide additional cut below, say, 55 HZ for OB systems on volume increase only, to keep excursion under control.
The problem with the classic loudness control is that it is fixed relative to the position of the volume control. It only works well if your system's overall gain structure provides a reference level at the right position of the control. If not, it provides too much or too little bass boost as you turn down the volume.
What is needed is a progressive bass boost/cut control linked to the volume control, along with a gain setting control that lets you calibrate your system to the standard.
It would work like this:
At a reference position of the volume control, maybe at the "12 o'clock" or half-way position, the bass boost/cut would be "flat" (no boost/cut).
You set your volume control to this position, then adjust the calibration control for the music you want to play so that it reaches a specific SPL setting at your listening position. From that point, turning the volume control up or down will also adjust the bass level to provide a consistent tonal response.
The mastering engineers set their reference level like this:
Play pink noise at -20dB ref to FS, one channel at a time.
Using an SPL meter at your listening position, adjust the playback level for a reading of 83 dB, C weighted.
Repeat for the other speaker. Don't try to balance between the speakers, just measure the level of each of them and set the playback signal to the average. If there is more than a couple of dB difference, your system or room is set up wrong.
Having set the level, mastering engineers may then deviate from it quite a bit - for example, they may turn the monitoring level down by up to 15 dB if mastering heavily compressed music such as that by the Red Hot Chili Peppers or Metallica. The intention is that the average level in the mastering room will be 83 dB SPL per speaker, regardless of whether the music is high dynamic (classical music, jazz etc) or ultra-compressed (heavy metal, most pop).
For reproduction, the process is less complex - if you set your volume control so that the music averages 83 dB SPL per speaker, at your listening position, then you will be hearing the music as the mastering engineer heard it. The required gain setting will vary with the music type - you may need to turn your calibration gain down by up to 15 dB when playing Metallica compared with a string quartet.
A system using a "linked volume / tone control" would have two "volume knobs" (calibration and volume) and would be used like this:
Set the main volume control to the reference position.
Play the music.
Adjust the calibration control to provide about 86 dB C weighted at your listening position.
Adjust the main volume up or down to taste.
With practice, you will find that you can often calibrate by ear - a lot of music has a "right" setting, where it sounds natural and "life size".
This is no accident - the mastering engineer has optimised the tonal balance etc for this SPL.
Finally, getting back to the specific application under discussion, this system provides automatic bass management. If you raise the overall volume by 10 dB, the bass level may only increase by about 3 dB. This is obviously good for systems with limited LF capabilities, such as OB designs.
To match the equal loudness contours, the bass boost/cut should follow the standard Baxandall type response. A second section could be added to provide additional cut below, say, 55 HZ for OB systems on volume increase only, to keep excursion under control.
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Thanks again, especially Don Hills. This is what I,d like to do and I'm sure that it would suit others with open baffles also. I would need to set the system for normal listening, whatever SPL that is and equalise the bass as much as possible
at that level. Turning the volume down would then give more headroom for equalising the bass in room and help the loudness contour. Turning it up louder than the set level would reduce the bass until the point came when the subs would have to be used.
I can"t afford the worlds best subs so I am looking for a way to get the best use I can out of the open baffle bass which will be two Eminence Beta 15s each side. Perhaps the T Bass circuit would help with this too but I don"t know enough to know if it will work for me. I think when the music becomes quite loud most times nobody will be too bothered about the purity of the bass so the subs should be OK.
jamikl
at that level. Turning the volume down would then give more headroom for equalising the bass in room and help the loudness contour. Turning it up louder than the set level would reduce the bass until the point came when the subs would have to be used.
I can"t afford the worlds best subs so I am looking for a way to get the best use I can out of the open baffle bass which will be two Eminence Beta 15s each side. Perhaps the T Bass circuit would help with this too but I don"t know enough to know if it will work for me. I think when the music becomes quite loud most times nobody will be too bothered about the purity of the bass so the subs should be OK.
jamikl
I seem to recall that many years ago a circuit was published for a Loudness control that varied with volume in perhaps Wireless World as it was then called. I don't know whose circuit it was, perhaps J. Lynsly Hood. This might well be what I need but I wouldn't have a clue where to find it now. Perhaps somebody out there remembers it.
jamikl
jamikl
I've done some searching.
Loudness controls were briefly discussed here in diyaudio back in 2006:
http://www.diyaudio.com/forums/solid-state/77599-loudness-experiences.html
Jamikl,
There was a loudness circuit published in Wireless World back in 1968:
Loudness Control for a Stereo System R T Lovelock Jun 1968 p148
The required loudness compensation appears to be in the order of 2:1. For example, if you decrease the midrange gain by 10 dB, you need to increase the bass by 5 dB at 20 Hz. Most simple tone control circuits max out at about 12 to 18 dB boost or cut. Matching this with a coupled volume control would result in a volume adjustment range of plus or minus 24 to 36 dB. The 36 dB figure would correspond to an in-room range from 50 to 122 dB, which is adequate.
I notice that THX specifies that the in-room level at 0dB reference should be 105 dB SPL. This is close to the 86dB at -20 dB ref calibration level suggested. This is probably not a coincidence.
Loudness controls were briefly discussed here in diyaudio back in 2006:
http://www.diyaudio.com/forums/solid-state/77599-loudness-experiences.html
Jamikl,
There was a loudness circuit published in Wireless World back in 1968:
Loudness Control for a Stereo System R T Lovelock Jun 1968 p148
The required loudness compensation appears to be in the order of 2:1. For example, if you decrease the midrange gain by 10 dB, you need to increase the bass by 5 dB at 20 Hz. Most simple tone control circuits max out at about 12 to 18 dB boost or cut. Matching this with a coupled volume control would result in a volume adjustment range of plus or minus 24 to 36 dB. The 36 dB figure would correspond to an in-room range from 50 to 122 dB, which is adequate.
I notice that THX specifies that the in-room level at 0dB reference should be 105 dB SPL. This is close to the 86dB at -20 dB ref calibration level suggested. This is probably not a coincidence.
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OK, I have a proof of concept design. It requires unobtanium, though - a 6 gang pot. That is, 3 stereo pots ganged together. Can anyone recommend an active (chip based) 3 terminal potentiometer equivalent? Something in the 100kohm range would be suitable.
I'll post a schematic of the proof of concept next time I'm close to a scanner.
I'll post a schematic of the proof of concept next time I'm close to a scanner.
I've seen such a construction, using small toothed rubber belts (Gilmer belts?). It does require a minimum level of mechanical competence and a source of gears, or pulleys and belts, in small quantities. Access to a junkyard full of dead laser printers and photocopiers would be helpful.
The circuit also requires op-amps, so given that there is electronic construction required anyway, I was hoping for an all-electronic solution. Hence my query about "pot on a chip" options. I'll Google it...
Keeping to the thread topic, having it all electronic would allow more complex control schemes. For example, at a given level the control could automatically cut the bass to the OB woofers further and bring in the powered subs. From late night lounge lizard to head banger's ball with one twist of the knob...
The circuit also requires op-amps, so given that there is electronic construction required anyway, I was hoping for an all-electronic solution. Hence my query about "pot on a chip" options. I'll Google it...
Keeping to the thread topic, having it all electronic would allow more complex control schemes. For example, at a given level the control could automatically cut the bass to the OB woofers further and bring in the powered subs. From late night lounge lizard to head banger's ball with one twist of the knob...
There are plenty of search hits for "digital potentiometer". For example:
Digital Potentiometers - Maxim
MAX5455 looks suitable, but one with +-15V supplies would be better.
Up/down stepping control is preferable to 8-bit control word type, because it is easier to interface in an audio application - the ganged digital pots can be driven by a digital encoder knob or by a simple feedback arrangement from a standard mechanical pot.
So, my current list of requirements:
- 100K ohm, 3 terminal.
- At least 64. preferably 256 steps.
- Non volatile setting memory not required.
- Up/down stepping, or voltage controlled.
- Preferably +-15 volt supply rather than +5V supply (supply voltage sets the maximum signal voltage allowed across the pot).
- Suitable for audiophile use (low noise and distortion).
If anyone has any candidates, I'd like to hear about them. Is there much audience crossover here? Or would I be more likely to get suggestions in one of the electronic construction forums?
Digital Potentiometers - Maxim
MAX5455 looks suitable, but one with +-15V supplies would be better.
Up/down stepping control is preferable to 8-bit control word type, because it is easier to interface in an audio application - the ganged digital pots can be driven by a digital encoder knob or by a simple feedback arrangement from a standard mechanical pot.
So, my current list of requirements:
- 100K ohm, 3 terminal.
- At least 64. preferably 256 steps.
- Non volatile setting memory not required.
- Up/down stepping, or voltage controlled.
- Preferably +-15 volt supply rather than +5V supply (supply voltage sets the maximum signal voltage allowed across the pot).
- Suitable for audiophile use (low noise and distortion).
If anyone has any candidates, I'd like to hear about them. Is there much audience crossover here? Or would I be more likely to get suggestions in one of the electronic construction forums?
I know that Jamikl was disappointed that this thread did not see more action. So I'll pick up the ball again.
Couple of questions:
Don is right on the money with his 1st post. It has to be calibrated - they rarely are. FWIW, I thought the level was 84dB in room with a digital level of -14dB. But whatever works.
Don is also correct that a calibrated and tracking loudness control is going to do at least 1/2 of what you want by turning down the bass as the level is turned up. That's going to help your x-max. Then it might be as simple as running your subs at the right level - let them fill in naturally.
Or somehow keep the subs OUT of the loudness control circuit. That way they would turn up and down in a linear manner with the volume control, but the OBs would get the loudness boost as you turn it down - and cut as you turn it up.
Does that make sense?
.
Couple of questions:
- Is the topic just your OB rig bass, or loudness in general?
- Where should a general loudness thread go? Here, the amp section, the source section?
- Do you want a simple analog circuit, or DSP?
Don is right on the money with his 1st post. It has to be calibrated - they rarely are. FWIW, I thought the level was 84dB in room with a digital level of -14dB. But whatever works.
Don is also correct that a calibrated and tracking loudness control is going to do at least 1/2 of what you want by turning down the bass as the level is turned up. That's going to help your x-max. Then it might be as simple as running your subs at the right level - let them fill in naturally.
Or somehow keep the subs OUT of the loudness control circuit. That way they would turn up and down in a linear manner with the volume control, but the OBs would get the loudness boost as you turn it down - and cut as you turn it up.
Does that make sense?
.
Thanks for responding again Pano and Don. I think your middle paragraph states what I am looking for. I guess maybe I should have put the tread in the amp section but as so many are trying open baffles now I thought this would be a good section to pose the question in. I am very interested in Don's ideas and am hoping something comes of it. I suppose more interest would help.
I am looking at this to help with the xmax issues when using open baffles with cheaper woofers but I guess if it comes about its use would be universal.
I was suprised when I bought a sound level meter just how loud a steady state of around 84 - 88 dB is. I don't think I could listen louder than that over several hours.
jamikl
I am looking at this to help with the xmax issues when using open baffles with cheaper woofers but I guess if it comes about its use would be universal.
I was suprised when I bought a sound level meter just how loud a steady state of around 84 - 88 dB is. I don't think I could listen louder than that over several hours.
jamikl
I'm of the opinion that SPL contouring is absolutely unnecessary and also detrimental. A live event does not control its SPL w.r.t. our sensitivity to loudness at different frequencies, nor does a microphone's frequency response vary with SPL. If loudness contouring is to happen (which it will, when we listen), then letting it happen naturally is the optimum solution - and the one that requires no work at all. Doing it before we hear it is only going to screw with our aural senses.
Quite completely disagree, I'm afraid.
Even live events are "mastered." Either by the musicians, the conductor or the sound engineer. Tonal balance is achieved right then and there.
That said, we are used to hearing the tonal balance change when we lower the volume - most of us. Usually we just accept it. Maybe we should not have to.
.
Even live events are "mastered." Either by the musicians, the conductor or the sound engineer. Tonal balance is achieved right then and there.
That said, we are used to hearing the tonal balance change when we lower the volume - most of us. Usually we just accept it. Maybe we should not have to.
.
I'm with Panomaniac on this one. At live events the sound engineers ride all the controls, massive mixing desks, in real time.
Most speakers like help to ensure they don't exceed xmax. It allows the speaker to play cleanly at louder levels. My preference is for a shelf filter on the bottom end.
If you have kids playing today's music, even softley some form of protection is essential. Your spiders will thank you.
Terry
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