Why do higher rms subs get louder than lower rms subs with the same excursion?

[Beanz]

Good read krakin

[TRTC360]

Motor force is king.

[noobslayer77]

good read. thanks for the link.

[_paralyzed_]

S P L. Sound PRESSURE Level. One 10 inch 3000 watt sub with 15mm xmax sub will play about the exact same level as one 10 inch 200 watt sub with 15mm xmax in a cargo van. Change that to a honda crx and there might be a difference.

With multi woofer walled builds we are able to fill a vehicles interior with bass. (Pressure) The more bass, the more pressure. Once this is done, that bass pressure actually pushes back against the cones of the woofers and fights the bass response. To fight this phenomen you need MORE POWER.

So at some level the higher power woofers make no difference. I have no idea where that level is. Is it 2 12"s in a hatchback? Is it at least 8 15"s in a tahoe? There are so many variables. But there definitely is a place for the high power woofers.

[noobslayer77]

hmmm. that is interesting. that is kind of the same as needing more power in a small sealed enclosure to get as loud as a large ported enclosure with less power. Because the sealed enclosure's internal pressure works in the same way as a car filled with 8 12's. The pressure created by the subs is actually fighting back their movement at high levels. so you need more power.

[_paralyzed_]

hmmm. that is interesting. that is kind of the same as needing more power in a small sealed enclosure to get as loud as a large ported enclosure with less power. Because the sealed enclosure's internal pressure works in the same way as a car filled with 8 12's. The pressure created by the subs is actually fighting back their movement at high levels. so you need more power.

Yep. Sound is just moving air. Also, in a sealed box, a vacuum is created as the cone moves outward, so it has to overcome that force on outward strokes and resist pressure on inward strokes.

[SQL50]

Without being too technical about it. Motor force/magnet size, more powerful excursion movements. My 2 cents.

[jakmagic]

This may be completely wrong but on the subject of the sub fighting against its own bass/ air pressure in the cabin/ trunk, would the stiffness of the suspension come into play or no? Like the sub with the stiffer suspension with be able to combat the cabin pressure better. Just having random thoughts.

[iwannabeloud]

http://www.audioholics.com/loudspeaker-design/subwoofer-extension

[iwannabeloud]

http://www.ecoustics.com/electronics/forum/car-audio/599946.html

# 2 More xmax means more SPL

Subwoofer drivers really can be broken down in two categories: "Mass" controlled drivers and "compliance" controlled drivers. Mass controlled drivers tend to have low xmax and high sensitivity. These tend to be punchy and very loud and mostly used in live concerts for sound reinforcement or even car SPL competitions. Compliance controlled subwoofers which tend to be the majority of car audio subwoofers have high xmax, more weight, lower sensitivity, but more SPL in the lower frequency spectrum. Then there are of course hybrid drivers which are basically mixes of the two. Any driver in these categories can sound good or bad, but more important is being able to use the woofer where it performs the best. Using a low xmax woofer for subsonic content is probably not wise, likewise using a high xmax low sensitivity driver for sound reinforcement is not going to be very effective. In truth, there is no best driver and most drivers can overlap these zones with good results. We are not really used to the idea of a two way subwoofer, but as we demand more and more SPL and deeper bass, we may some day find that two different types of subwoofers used together are required to get the full reference SPL effect we all hunger for!

So yes, more specified xmax does mean more SPL but only for lower frequencies. Generally speaking, during lower frequencies, the driver tends to run out of usable throw (beyond xmax) before high thermal compression states occur and mechanical failure is a greater risk. 0-40Hz is primarily mechanical, 40-60 is in between) 60 and up is going to be more thermally limited. 0-20Hz is the subsonic content and in fact there are ]more efficient methods of producing bass in this spectrum rather than a regular piston based transducer. Surprisingly, even the largest drivers with high xmax and big voice coils can be bottomed out or run past a safe mechanical state with only a few hundred watts if the frequencies are low enough. Without a high pass (subsonic) filter, or in a low tuned system, bottoming out or breaking a driver could be a very real possibility without careful modeling and testing. The difference in displacement from 40Hz to 20Hz or rather half the frequency, or one octave, is quadruple! In the simple large sealed box example, that means if your woofer displacement is 1" peak to peak at 40Hz, you'll bottom out just about anything in existence by the time you dip below 20Hz without protection.

Often times when people want more SPL, they really need higher sensitivity in the form of higher BL product or less moving mass, rather than more xmax because 50-60Hz is really what they are after. This is a very sensual frequency range for humans and much of the bass in music content exists in that frequency domain.