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Old 19th February 2010, 01:16 AM   #11
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Location: New Zealand
I recommend the following paper:
Hearing at low and infrasonic frequencies
H Moller, CS Pedersen
Department of Acoustics, Aalborg University, Denmark

It can be read online (text only) at:
Hearing at low and infrasonic frequencies Moller H, Pedersen CS - Noise Health

You need to subscribe to download the PDF with figures. (It used to be free download, so you may find PDF copies elsewhere on the Web.)

Searching in Google with the article title will produce many hits, and related papers.

As for Michael's question about "linear loudness" effect, take a look at the latest "equal loudness" curves (ISO 226:2003 standard). They are quite different than the old Robinson-Dadson and Fletcher-Munson curves. The curves progress reasonably smoothly from "log loudness" at 1 KHz to almost "linear loudness" at 16 Hz. The infrasonic research paper I referred to indicates that the curves continue to trend closer together as the frequency decreases further.

URL for a summary of the standard:
http://www.sengpielaudio.com/Acoustics226-2003.pdf
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Old 19th February 2010, 01:34 AM   #12
oublie is offline oublie  United Kingdom
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Thanks Don,

I'll Have a good read.
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Old 19th February 2010, 02:08 AM   #13
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Hi there Don: Thanks for the ISO equal loudness curves. From the curves I now realize the need for much more SPL ( if listening at home 95db at 1000hz, 120db at 27.5hz would be needed ) to be able to hear the lowest frequencies you regularly encounter in a concert hall. Even lower frequencies from pipe organs would be way beyond that SPL level.
...regards, Michael
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Old 19th February 2010, 04:00 AM   #14
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Bear in mind that, for orchestral music in particular, the lowest frequencies are rarely as high in level as the midrange. (The reverse is usually true for rock etc, and even more so for HT.)

I've been thinking about the problem for a while. Check out this thread:
http://www.diyaudio.com/forums/multi...s-control.html
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Old 19th February 2010, 08:59 PM   #15
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in my findings i have found that most sound below 30-25hz tend to excite other objects in a room into resonating new sounds(unwanted noise). room vibration, furniture/windows/doors rattling, even dished or circular objects creating higher harmonics.

of course proper damping helps, but at higher spl's you cannot stop everything from resonating. room tuning becomes even more of a challenge than speaker building after a while.

many times we hear the high harmonics that accompany the lower hz sounds and our brain combines the two fooling us into thinking we can hear that low. upper distortion and spacial delays can play a big part of what we perceive as sound.

phasing will become more of a room thing than a speaker one. experimenting in placement will be the final judge. the reads on the lower the hz the less we can hear them is valid and a consideration with your final outcome as we all are looking for different things.
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Old 20th February 2010, 01:08 PM   #16
MaVo is offline MaVo  Germany
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Quote:
Originally Posted by oilcanracer View Post
in my findings i have found that most sound below 30-25hz tend to excite other objects in a room into resonating new sounds(unwanted noise). room vibration, furniture/windows/doors rattling, even dished or circular objects creating higher harmonics.
That may differ with the room. In my room, for example, things get noisy in the upper bass range of about 50-100hz. Below this, only the doors shake slightly, which doesnt make a sound any more after i put a little damping material between door and frame.
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Old 20th February 2010, 03:55 PM   #17
oublie is offline oublie  United Kingdom
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I've read through don'ts suggested links and there is one thing that strike me.

Why do we model flat for subwoofers?

I can understand the reasoning behind flat to say 200hz or so but if we are actively compensating for music or movies in the bass and sub bass regions should we model for a rising efficiency as frequency drops?

What i mean by this is if we design a sub that has it's peak efficiency at say 20hz rolling off as the frequency increased we are in effect building in a certain amount of equal loudness level contour?

I did a bit of modeling and rethinking and arrived at a sub design with a peak spl of 135 db at 20hz rolling off to 125 db at 70hz if this was more accurately modeled to roughly follow my normal movie or music listening spl wouldn't it be flatter from a human perspective?

I know it wont be a perfect curve for all listening levels nor will it compensate for in room response but why isn't this done?
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Old 28th February 2010, 11:29 AM   #18
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As I understand it, we model flat because that's what sounds right and natural. If you just look at the curves, you would thnk that you should be progressively boosting all the way down from 1 KHz.

You've started me thinking about non-flat alignments to get more output at the lowest frequencies though, for example the QB5 alignment is useful for the satellite parts of sub-sat systems. Take a look at this:

Satellites and Subwoofers

It may be useful for subs as well, but I think the box sizes will work out to be prohibitive.
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Old 28th February 2010, 07:37 PM   #19
MaVo is offline MaVo  Germany
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Modelling subs with a falling response is a suboptimal approach, because the mechanical properties of the woofer define its maximum low output. If you put it into an enclosure which lets its frequency response fall with rising frequency, the low end max spl is the same like a flat response enclosure of similar type. You just sacrifice the higher frequencies but gain nothing. And tailoring a sub to the room is not to be done with the enclosure design, but with proper EQ.
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