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SPL, Trouser Flapping and Driver Diameter

Emlin

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I often read (on other forums) that speakers with small drivers, however large the throw, do not create the same "visceral" effect as those with larger drivers at low frequencies, even at the same SPL for the same frequency. But surely, if the SPL is the same...

I may be being naive here, but doesn't SPL always equal SPL?
 

ernestcarl

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Well, 50Hz from my 5-inch Monitors sounds and feels different from the 50Hz from my 12-inch sub even at the same measued SPL... so clearly other factors do matter.
 

McFly

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Well, 50Hz from my 5-inch Monitors sounds and feels different from the 50Hz from my 12-inch sub even at the same measued SPL... so clearly other factors do matter.
Resonances and harmonics, perhaps?
 

LTig

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Well, 50Hz from my 5-inch Monitors sounds and feels different from the 50Hz from my 12-inch sub even at the same measued SPL... so clearly other factors do matter.
The reason could be that there is more power in the higher dynamics and hence less power in the fundamental for the 5" speaker compared to the 12" speaker when combined SPL is the same.
 

Juhazi

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Harmonics?
Harmonic distortion, I guess. A small diameter transducer must use higher excursion to make same spl, and this comes with higher distortion.

But 50Hz is easypeasy - 30-40Hz is where difference is much more evident. Typical hifi-speakers are reflex-tuned around 40Hz, and diameter of the reflex port is typically around 3" (smaller in bookshelve speakers)
 
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Mnyb

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Supose the small speaker really puts out more 2 nd harmonic (or a lot of ) than ther fundamental tone in the bass ie THD is more than 100% so the spl at 100Hz do fell and sound different than the same SPSL at 50Hz .

Or are speaker drivers better nowadays ? When i was young "doubling" was a real thing ie bass drivers did not handle themself well at high spl and low frequencies and did actually produce much more harmonics practically "doubling" the input frequncy ?

I'm still suprised by my current 15" sub how it does not really sound like anything at the levels i play at :) i compare to my cheapr HT sub in the HT room , that one really does have a sound to it
 

watchnerd

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I'm still suprised by my current 15" sub how it does not really sound like anything at the levels i play at :) i compare to my cheapr HT sub in the HT room , that one really does have a sound to it

Even if I'm standing right next to them, I usually can't tell if my subs are even playing music unless I go put a hand underneath them and feel the cone.
 

ernestcarl

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Yeah, harmonics and resonances contributes... and -- I would argue, more importantly -- I can definitely feel a breeze of air from the damned front ports of the KH120s! -- nearfield (0.8m)

Oh, one thing I did forget to mention is that the 12" sub is sealed.

I've yet to do single bass tone tests in my room wherein I could not tell the sound is coming from any of my bass limited, ported speakers vs my sealed sub. Maybe if I had the KH310s to test, it would be harder to notice a difference?
 

ernestcarl

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Even if I'm standing right next to them, I usually can't tell if my subs are even playing music unless I go put a hand underneath them and feel the cone.

With actual music, and the sub turned off, yeah it can be a guessing game.
 

ernestcarl

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Typical hifi-speakers are reflex-tuned around 40Hz, and diameter of the reflex port is typically around 3" (smaller in bookshelve speakers)

Unfortunately, I've only ever done such tests with the typical, reflex ported, bookshelf type speakers. The resulting difference may be less evident with large floorstanders or any one of those large 'bookshelf' type pro-monitors.
 

Kvalsvoll

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I may be being naive here, but doesn't SPL always equal SPL?

I see this and similar questions are quite frequent, so this must be something that many are curious about. And you should be.

If you open up a book about acoustics, the first thing you see is the wave equation - a differential equation describing how sound travels through air. For most us, this equation does not make much sense, since we do not have a solid mathematical background that enables us to understand how this relates to sound and how this works.

What we can see, is that sound is characterized by a pressure amplitude, and a velocity vector with direction, amplitude and phase related to the pressure. Measuring pressure only does not give a complete representation of the sound.

How this works, and how it relates to sound reproduction - especially in the bass range - has been discussed for several years now, but it is not well known outside some of the more obscure parts of the hifi-world.

Pants and clothes flapping happens when velocity is high enough, at quite low frequency. The mechanical impedance of clothing in air is such that it does not require high intensity (intensity == acoustic power), which again means phase and pressure amplitude is not important. To create such a soundfield, has more to do with room acoustic properties and placement of observer (the flapping clothes) and sound source. So a 5" can do just as good as 4x 18". Provided the necessary acosutic output from the source is present, and this is where size matters - a small speaker simply can not output enough sound pressure at low frequencies.

Close to an acoustic radiator, the sound field changes. So that the sound field can be affected both by size and principle. Close to a ported box, the velocity is much larger compared to a sealed box, and a horn with larger radiating area, will maintain this effect at a greater distance. This can be measured, it is not something obscure and mystical, it is very real.

At the listening position, there will usually be no measurable difference in velocity close to the floor, between say a small horn and a sealed system.
 

watchnerd

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Doesn't trouser flapping depend upon the fabric of which the trousers are made and the resonant frequency thereof?

Flapping denim jeans and silk pajamas is very different.
 

Mnyb

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High velocity close to the cabs I can believe in that :) walking past the bass cabs in some club can induce that...
 
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