Non-linearity of air?

So i'm reading through one of my sound books and I came upon this:

High Performance Loudspeakers: 5th Edition wrote: Another potential source of distortion is the excessive compression of air in the box. If this exceeds 5% by volume, harmonic production from this source may be significant. In practice this is unlikely to occur as the ouput in the case of a medium sized enclosure would be approaching a very loud 120dB SPL at 1m. If greater levels are required, then it would be expedient to increase the box size. Sinse a larger driver with a high power rating will undoubtedly prove necessary, a larger box will in any case be employed. Incidently, such distortion is a problem with horn systems, particularly high output mid-range drivers where the effective air compression in the horn throat is considerable.

I was wondering how this affects the current drivers with high excursions and low air volume requirements?

I dunno try doing the math. Before anyone jumps down my throat, this would, of course, given parameters needed (which are not always provided honestly) and the shape of cones and what-not, a best guess sort of a thing. Take any particular woofer, and get ur xmax and your sd in the same units. Now multiplay them together and viola! Maximum volume displaced by the woofer. Now get your box volume in the same unit, and multiply by .05. If the volume displaced by the woofer is smaller than that number, then it shouldn't matter... according to your book. "I'm finished!" - Daniel Plainview

Ok thanks. Question: What's the recommend enclosure size for an Adire Brahma 15? The Total volume displaced by it = 124.2163in^3

OK... you asked for it...

Poormanq45 wrote: So i'm reading through one of my sound books and I came upon this: High Performance Loudspeakers: 5th Edition wrote: Another potential source of distortion is the excessive compression of air in the box. If this exceeds 5% by volume, harmonic production from this source may be significant. In practice this is unlikely to occur as the ouput in the case of a medium sized enclosure would be approaching a very loud 120dB SPL at 1m. If greater levels are required, then it would be expedient to increase the box size. Sinse a larger driver with a high power rating will undoubtedly prove necessary, a larger box will in any case be employed. Incidently, such distortion is a problem with horn systems, particularly high output mid-range drivers where the effective air compression in the horn throat is considerable. I was wondering how this affects the current drivers with high excursions and low air volume requirements?

Hmmm... interesting concept. The way I see it is this: 1 cubic foot = 1728 cu inches. 1728 x 5% = 86.4 cu inches. This is how much the box volume would have to be compressed (and/or rarified) to induce significant distortions of this type. 86.4 x 2 = 172.8 cu inches of displacement (total of ± 5%. A 5% compression or rarifaction relative to the "at rest" position of the woofer). The way to figure how much volume is displaced (or swept) requires knowledge of Sd (area of diaphragm) and Xmax. Multiply these numbers together. If this number (the swept volume) EXCEEDS 5% of your net box volume, you may need to go to a larger enclosure, or use a woofer with a shorter Xmax. My Eclipse SW9122 (a three inch throw woofer - 75.95 inch Sd) provides only 151.9 cu inches of displacement, linearly (easily, ±1 inch). If driven to it's non-linear range of ±1.5 inches (it's specified 3 inch X-max), it will provide 227.85 cu inches of displacement, but by the time I reach this range, I have a bit more than the non-linearities of AIR to worry about... I also would like to take issue with the assumption that the enclosure WOULD be producing 120dB at 1M. This seems completely wrong to me. I say this because as the frequency goes down, (longer stroke - more compression - lower frequency - less output) so does your output. If you have an enclosure that is producing a 40Hz tone, its excursion will be X and XdB, but at 20Hz, the excursion will be 4X, and the output will (likely) be XdB -6, the standard roll-off for a sealed enclosure being 6dB per octave. Also, WOOFER EXCURSION HAS LITTLE TO NOTHING TO DO WITH THE ACTUAL OUTPUT OF A SYSTEM. Frequency response, yes, output, no... If this were the case, then Eclipse and Adire woofers (as we all know, two exceptionally long throw, and equally capable woofers) would be capable of WAY more output than, say, a Cerwin-Vega or JBL Pro... An equally powered Eclipse or Adire woofer will NEVER exceed the output of either of these drivers. You'll notice I chose two relatively short throw woofers to compare with. This is to illustrate the fact that shorter throw will almost always equate to more output for a given input power. Output is SPECIFICALLY determined by rate of change - how fast can the woofer change direction? This factor MOSTLY being affected by 1) voice coil inductance, and 2) magnetic field strength in the voice-coil gap.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Nice post ham fist. I also took issue with the fact that the book specified an SPL. Oh and nice drivers you compared to there. Two of my favorites(CV and JBL)

Poormanq45 wrote: Ok thanks. Question: What's the recommend enclosure size for an Adire Brahma 15? The Total volume displaced by it = 124.2163in^3

i believe its 4.731 ft^3

Nice one, haemphyst.  That one gets saved into my list of explanations that I'll have to re-read over and over and over... Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Is he doing it again??? I mean just by the topic I knew who the author was.Certified Security Specialist

Always check info with a digital multimeter.

I promise to be good.

Tell Darwin I sent you.

I've been sick lately, sorry I won't be on much.

"did I do that...?" Now come on, am I REALLY that predictable? BTW, it wasn't me that opened the can...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."