What happened to the loudness control?

Eldarford: In the example I gave you, I used 100% of the volume control simply because there wasn't enough gain in the system. During that period, my volume control would be at max most of the time, not at 90% or any other setting.

Tell me how your loudness control compenstates for the roll off of your subwoofers? They certainly aren't flat nor do they have uniform output as the volume drops.

However, you have piqued my interest in loudness control circuits. I think I will revisit the current thinking of circuit topology and see if anything new has been done in the last few years.

Spatialking...If your volume control is always at the same setting, whether that is 100% or 60%, a Loudness control has no relevance. In this situation, if you don't like your sound, what you need is some kind of fixed equalization. Loudness controls are not intended to correct equipment/room frequency response problems, like the SW roll off that you mention. As to your suggestion that a SW efficiency (dB/watt) varies with SPL (watts), I have heard this suggestion before, but it is not true at all for my particular custom built subwoofer system. (I have actually made measurements to investigate this).

Eldarford: Really? You have consistent efficiency in your subs across the entire voltage input range? I would be most interested in your studies. Many, if not most, subs or speakers for that matter, have consistent efficiency across their entire voltage input range.

My comment above was spoken in the context of linearity, rather than efficiency. It seems in general these days, if your speakers efficiency is off across the input range, it is acceptable for the amplifier to make up for it. There is an arguement that consistent efficiency, as well as higher efficiency, results in better sound but I don't take a side on that one as I have heard bad and good systems at both extremes.

I am still very interested in seeing your test results. If you don't want to publish your results here, please email me directly.

Thanks,

Spatialking...First let me point out that my subwoofers are a custom design, and may not behave like your off-the-shelf subwoofer. Each of my three front speakers (Maggie 1.6) has its own subwoofer system in a 7 cubic foot sealed enclosure embedded in the wall behind it. Each SW system consists of a 15" driver and a 12" driver, each driver powered with it's own amp rated at 600 watts (CarverPro ZR1600). This gives a relatively large radiating area, especially when you consider that there are three of these systems in the room, so that no extreme cone excursion is necessary.

I have a spectrum analyser. When I play a noise test signal the frequency response, which is (with equalization)quite flat from 20-20KHz does not change with SPL. This suggests that if there is any loss of efficiency at low levels it is the same for the Maggies and for the subwoofers.

I had a discussion with Sean (of fond memory) about this subject and the following is a report of the tests that I ran for him.

SOME DATA

Signal......SPL
..-67.......50
..-52.......55
..-45.......60
..-40.......65
..-35.......70
..-30.......75
..-25.......80
..-20.......85
..-15.......90

Both the electrical signal and the SPL were measured, in units of dB, using my two Behringer DEQ2496. The SPL at 60 and 80 were crosschecked with my Radio Shack meter, and agreed within 1dB. The signal was white noise from a DVD player (used for channel balance). The measurements were RMS. Because this bounces around a bit, some estimation was necessary to get an average value. I set the SPL using the preamp volume control, and then read the associated electrical signal. The speaker measured was one MG1.6 backed up with a subwoofer, and the mic was about 4 feet from the MG1.6. I could not go higher than 90 dB because my preamp volume control maxed out using the DVD player signal. 90 dB RMS is pretty loud, and there is no indication of compression.

A plot of the data shows that at low volume below 60dB the SPL does not increase as steeply as it does over the rest of the range. However, I do not think that this reflects the kind of low SPL inefficiency which Sean suggests, because the background noise of the room ranges between 45 and 55 dB, as a function of traffic on the road outside. This background noise is pulling up the SPL data for the lowest two points. Late tonight, when background noise is low, I will make some more measurements.
Eldartford (Reviews | Threads | Answers)

03-30-05 El: thanks for taking the time to not only perform the testi ... Sean

03-30-05: Eldartford
Sean....I did not get to rerun the test last night when background noise was low. Maybe tonight. I am quite sure that the background noise is the reason that the plot becomes nonlinear at low level. By the way, the data looks too perfect over much of the range, and you might be suspicious, but that is exactly what I read from the instruments. It surprised me.

Per you suggestion I will run a test using only the dynamic cone subwoofer with a warble tone as a signal. This will cover the range 22.5 to 250. The warble will come from an Audio Control Richter Scale equalizer, and it is only as good as it is. One problem I anticipate here is that if I go to any loud SPL all the windows and doors are going to rattle, and screw up the measurements.
Eldartford (Reviews | Threads | Answers)

03-30-05 If you are going to test a sub, try to get the meter as clos ... Sean

03-30-05 I loved that audio control richter scale and the sweep it ca ... Cytocycle

03-30-05: Eldartford
MORE DATA

Signal..SPL
..NONE...40 to 55 background noise
..-80....42
..-75....46
..-70....50
..-65....53
..-60....58
..-55....63
..-50....68
..-45....73
..-40....78
..-35....83
..-30....88
..-25....93
..-20....98
..-15....103
..-10....108

The signal was white noise, as before, but limited to frequencies below 400 Hz, and reproduced by my subwoofer system. (Easy to do. I just muted the HF and adjusted the X/O frequency up to 400 Hz). From prior experience I know that the warble tone would have rattled things. The mic was positioned about one foot from the 15 inch driver.

This time I set the signal level using the preamp volume control, and read the resulting SPL. When reading the SPL for the range below about 60 dB I took the lowest of rms indications over about 30 seconds, which corresponded to a lull in the traffic (background noise). For the higher SPL readings I took the average, as before.

Plot the data and you will see that there is almost no suggestion of decreased sensitivity at low SPL, which I attribute to the greater care that I took to minimize error due to background noise. And anyway, the SPL range where the data is not perfectly linear (for whatever reason) is so low as to be almost inaudible, so it wouldn't matter anyway. I am particularly happy to see no compression for high SPL, which would be a worse problem.

All of this is for my speakers :-). Maybe yours are different :-(
Eldartford

Eldart does it again...