Reverse of the old Loudness Control

[panomaniac]

never mind.

[jamikl]

Pano ? Did I miss something?
jamikl

[Don Hills]

I've done some searching.

Loudness controls were briefly discussed here in diyaudio back in 2006:
Loudness experiences?

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.

[Don Hills]

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.

[pheonix358]

Make a little sub-chassis, put three dual gang pot on it, connect them with small gears, they will work in harmony. Cut off the shafts you don't wont after the gears.

Terry

[Don Hills]

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...

[panomaniac]

Originally Posted by jamikl

Pano ? Did I miss something?

No, sorry. Made a post without fully reading what someone else had said. It pays to read the whole post.

[Don Hills]

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?

[panomaniac]

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:

• 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?

.

[jamikl]

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