BoB- So "co-located" means stacked?

And, if you extrapolate the "1/12th octave 'notes'. The western musical scale, from A (27.5 Hz) to Middle C (261.63)" slightly below 20 Hz, what would the freqs be? (I'm still trying to figure out if ETF will allow me to define the freqs the test uses.)

I did try L & sub, and R & sub separately and there were some differences, but still the nulls were there. One thing I need to look at further, is increasing the 60 Hz crossover to 80 Hz. For the few tests I did last night, it *might* have looked better.

KCB,

No, side by side.

A 27.5
A# (yikes, can't read my notes)
B 30.87 (low B of a 5 string bass)
C 32.7
C# 34.63
D 36.71
D# 36.75
E 41.2 (Low E of a 4 string bass)
F 43.65
F# 46.25
G 49
G# 51.88
A 55 (next open string of a 4 string bass)
A# 58.25
B 61,74
C 65.41
C# 69.25
D 73.42 (next open string of a bass)
D# 73.5
E 82.41
F 87.31
F# 92.5
G 98 (last open string of a 4 string bass)
G# 103.75
A 110
A# 116.5
B 123.47
C 130.81
C# 138.5
D 146.83
D# 147
E 164.81
F 174.61
F# 185
G 196
G# 207.5
A 220
A# 233
B 246.94
C 261.63 (Middle C)

Boss- How about a few pts below 27.5 Hz ?

That's not necessarily the case. With the subs' crossover settings at 60 Hz, you will likely influence the the nulls upto 120 and, maybe, 180 simply due to overtones and room coupling. If you're using RTA software, it'll be helpful to find the optimal crossover point to mate the subs with your mains.

I do hope you are using pink noise and RTA software to do your measurements. Discrete tones used to test in-room frequency response are all but useless and bear very little relation to what the ear hears. Using either pink noise or warble tones is really the only valid way to do these tests.

Going down in frequency:

A 27.5
G 24.5
F 21.83
E 20.6
D 18.35
C 16.35*

*This is a 32' C pipe of a pipe organ, and none of these notes are associated with music, other than a pipe organ that's that big, so accuracy down in this realm is of no concern to me.

That's why I use the standard 1/12th octave sine wave disc for the LFE sub.

The RB, or music sub, was designed to play flat to 30 (-3dB@25, and with a second order roll off from there), which is at the actual low end of instruments, and to have extremely low group delay (5ms@30Hz) and have immense headroom for transients and to have adjustable damping (Q of .5 to 1.0) for personal taste.

I've been saying this for 2 years now, largely onto deaf ears, but summing the LFE channel with the redirected bass is the culprit in FR problems at the listening position.

When you design a sub that has to withstand the signal that all redirected bass+LFE+10 represents, you have a sub that's capable of subsonic reproduction at high levels.

Many of your favorite music discs were never monitored with subsonic capability and, therefore, include subsonic artifacts (yes, digital sources too) that a good music sub will discard, without the use of a subsonic HP filter, which causes phase shift problems that need adjustment when the filter is engaged.

A good RB+LFE+10 sub will not only reproduce those artifacts, the room it's in will grossly distort them as much as double or more. It's also almost always a ported or passive radiator design (and is BIG), and increasing order of subwoofer box design equals increasing group delay.

To those who argue that 20-30ms of time smear isn't audible down low, or if you tune a 4th or 6th order sub low enough, the group delay spike moves into the inaudible frequency range, I say..."Lay $1,000 on the table and subject me to a blind test, if I guess right every time, I get the dough."

The whole 'music vs movie' sub thing pretty much proves my theory. Contrary to lots of manufacturers claims, no one sub design does both exceptionally well. So, the answer to that is simple...have one of each kind of sub.

A smaller, sealed, high-quality sub that's flat to 25 Hz allows for it to be so much easier to reintegrate the redirected bass back into the soundfield from which it was taken, in any room, than a big, subsonic 'summed, single digital signal' subwoofer.

The LFE sub can be run hot, is silent during stereo playback, can be governed by any filter corner and slope, without affecting the RB sub and can be attenuated or even shut off when playing MC audio sources.

Otherwise, there is no tweaking required when switching back and forth from movies to music.

Keep in mind that movie discs are soon to have lossless soundtracks with much more headroom and accuracy of the signal, making multiple subs an even better idea.

Just an opinion.

SH,

Please explain why that is?

It's all about averaging.

A static tone will dwell on the peaks and dips produced by natural room modes, and the resulting measurements will read exaggerated peaks and dips in response while pink noise or warble tones do not stay on one particular frequency long enough to directly excite these modes. In other words, pink noise and warble tones average out the effects of these irregularities in response, and the resulting curve matches how the ear perceives these irregularities in response better than when discrete tones are used.

Measurements made in anachoic chambers that are used at speaker manufacturers (such as at Altec and JBL), do use discrete tones and sweeps but the difference is that an anachoic chamber does not reflect back sound from it's walls - it is essentially the same thing as doing measurements outdoors. They therefore are plotting the response of the speaker only, not the effects of the room.

This ear/measurement correlation is why we use logrithmic scales when referring to sound pressure and other audio measurements instead of linear scales. If we used a linear scale, the measured curves and how those curves are actually heard by the ear wouldn't match. A linear speaker frequency response curve for instance would look far worse than the ear would hear it.

My "Organ Demo CD" is loaded to the gills with strong 16Hz organ pedal tones. I'm very concerned with them....



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The Soundhound Theater

Thanks for the scoop on test tones, and please forgive the lapse of memory RE: the largest selling pipe organ disc in History.