Insane Amounts of Sub-20 Hz bass

[Sasha_G]

We did an analysis of the Saint-Saëns Organ Symphony that is included on our Test CDs.

First, here are some background notes:
Boston Civic Symphony conducted by Max Hobart, James David Christie, organist. Two AKG 414 ORTF cardioids, about the third row in Boston’s Jordan Hall, spring 1983. This was one of the last times that the Jordan Hall organ, already showing signs of serious asthma, was heard in a public performance. [Micha Schattner]

This recording has the strongest and cleanest 16Hz of any recording I have come across. It’s ideal for showing off the TN1220HO. [Dr. Hsu]

We did a "peak hold" audio spectrum analysis of it to show the loudest parts in the song, and the the numbers show what one must experience. As you can see in the chart, the loudest bass is at 17.5 Hz with plenty of bass at 16 Hz and 19 Hz as well. Such low bass filling the room is considered by some a spiritual experience. The air all around you is shaking, as well as the walls. No wonder you often find these super-sized organs in churches.

To avoid confusion, this is a chart analyzing the CD track by itself and no subwoofer was involved in its measurement. It's just a chart of the song.

A subwoofer would need to reproduce the 17.5 Hz bass at around -10 dB from the level the volume was set at. Oh, and by the way we include this song with all our subwoofers.

[Lwang]

Where does that 17.5hz sound come from? I thought the organ has a 16hz fundamental.

How does this relate to the overall level? It is a little hard to tell with music since there is no reference level etc. How many SPL would that be if the system is played at live level?

[Sasha_G]

I'm not sure why it came out as 17.5 Hz. Dr. Hsu also doesn't know. Room resonance is probably not the factor because the Concert hall where it was recorded is so big, Dr. Hsu says.

The level will be relative to wherever the volume is turned. The way I understand it, 0 db would be the loudest possible level, so if that was set to 115 db max, the loudest bass in this case would be -10 from this at 105 db. But it all depends on where the 0 db level is set on the system. Since all recordings tend to vary in volume, most people simply adjust the volume depending on the source.

It might be nice to include reference level in the graph or something, assuming a 115 dB peak. More information about reference levels can be found here:

http://www.hometheaterhifi.com/volume_7_2/feature-article-misunderstood-lfe-channel-april-2000.html

Keep in mind that this graph was taken directly from the recorded source with no mics or speakers involved, except for the mics used to record it in the concert hall.

[Lwang]

The absolute volume level on a -10dBFS would apply only to HT situations where the speakers are calibrated to 75dB when the signal is -30dBFS (or -40dBFS for LFE) and playback is suppose to be heard at the "reference level" setting.

But for music, the level is all relative. Some labels would push the avg volume to as close to full scale as possible to increase the S/N (or just to make the CD sound loud), while other sets the level pretty low so as to give the recording as much dynamic range as possible.

[Sasha_G]

So, let's say someone calibrates their home theater system to have 105 dB peaks (115 on the LFE "boom track"), and puts a dot or mark on their volume knob. If they then turn the volume to that dot, and put in this track, it should reach 95 dB.

Without using the dot, it would totally depend on where the volume knob was.

How they set the dot on the volume knob for 105 dB peaks would depend on which test tones were being used.

BTW, from:

http://www.prorec.com/prorec/articles.nsf/articles/EA68A9018C905AFB8625675400514576

"the “dBFS,” which stands for “decibels full scale” -- a kind of dB designation created especially for digital gear.

This one is a little strange because, unlike all the other dB varieties, the reference level isn’t at the bottom, or somewhere near the middle, but at the very top possible measurement. This means that “0 dBFS” designates the highest possible level, and that all other measurements expressed in terms of dBFS will always be less than 0 dB -- in other words, a negative number. This is why, on digital gear using VU meters (where 0 dBVU means 0 dBFS), the “0” is at the top of the scale, and the meter can never read higher than that."

So, the graph above really isn't relative since I copied the track directly off the CD using Exact Audio copy without normalization, compression, or any other processing. It really is in absolute dBFS then.

Exact Audio Copy:
http://www.exactaudiocopy.de/

[Lwang]

Originally posted by Sasha_G
[B]So, let's say someone calibrates their home theater system to have 105 dB peaks (115 on the LFE "boom track"), and puts a dot or mark on their volume knob. If they then turn the volume to that dot, and put in this track, it should reach 95 dB.

Without using the dot, it would totally depend on where the volume knob was.

How they set the dot on the volume knob for 105 dB peaks would depend on which test tones were being used.


I presume you are describing how loud the bass would be if one turned the volume knob to the above prescribed position. (Also, I think it would be 101dB of sound pressure instead of 95dB, assuming the bass is pretty much the same in the L&R channel, and the sub would sum up the 2 signals, giving 6dB increase in SPL.)

The question is what was the SPL level of that 17.5hz tone at the microphone when it was recorded? Was it 95dB? 105dB? I guess in some way, it would depend on one's actual experience in organ/church settings. Since I've never heard organ's going full blast in a church (I don't think hearing organs during wedding precessions counts), I won't be able to determine how loud it should be. (an example in the opposite direction would be if this was a solo xylephone recording with some of the tones at -10dBFS. If I play it with the volume know at reference level position, it would be way too loud).

[Sasha_G]

Interesting quesion. I think that Micha Schattner who commented on the track would know better than I. We'll have to track that person down to know how loud it actually was. I know it would depend on where you were sitting, for one thing. They build those organs to fill up the entire room, so if you were several feet away I can imagine it hurting your ears, but if you were in the center of the room it could be less if you crossed a room mode the wrong way.

[Sasha_G]

We put the chart of a 16 Hz test tone along side the Saint-Saëns Organ Symphony and indeed, the measurements were quite accurate in revealing a 17.5 Hz peak. Strange considering that the organ was tuned to 16 Hz. Keep in mind that the chart does reveal quite a bit of 16 Hz bass, it is just that the peak is slightly higher.

[haionlife]

Sasha, you mentioned in the first post that you include this track with all your subwoofers...Well I fear I may out of luck! I just bought the 2 1220's at the SF show and didn't get the disc :( Any chance you could mail me one????

Thanks! and I'm glad y'all enjoyed the Ray Montford CD :)

Mark Valade