Ported box size vs power handling

[soundbit]

Ok I just came across something on another forum that I am pretty sure it BS but I can't say as I have ever heard it before.

Can a larger ported box handle more power than a smaller ported box? I say NO due to the fact that the less air to control the come movement. We know sealed enclosures can handle more power than ported due to box size and lack of cone control below tuning freq. But what about 2 ported boxes? Can a larger ported handle more power than a smaller ported? HMMMMMM...

[nutxo]

Ok I just came across something on another forum that I am pretty sure it BS but I can't say as I have ever heard it before.

Can a larger ported box handle more power than a smaller ported box? I say NO due to the fact that the less air to control the come movement. We know sealed enclosures can handle more power than ported due to box size and lack of cone control below tuning freq. But what about 2 ported boxes? Can a larger ported handle more power than a smaller ported? HMMMMMM...

NO,. Kinda. Depends on the ports efficiency. Also need to remember box size may compensate for mechanical issues but can do nothing to help with electrical. You can still cook the woofer even though you arent snow coning or blowing the thing apart.

[Eric D]

I would guess port tuning is more critical than overall box size, as far as power handling is concerned.

A small box tuned for 45Hz, playing at 35Hz likely has less power handling than a large box tuned at 30Hz, playing at 35Hz. Below the tuning the woofer unloads, and will over extend.

[soundbit]

That makes sense. Assuming you have a 3 cu. box tuned to 32hz playing 40Hz. and a 4cu. box tuned to 32hz playing 40Hz would the larger box have any better power handling characteristics?

[Eric D]

That makes sense. Assuming you have a 3 cu. box tuned to 32hz playing 40Hz. and a 4cu. box tuned to 32hz playing 40Hz would the larger box have any better power handling characteristics?

I am going to guess worse actually. Above tuning the box is acting more like a sealed box, where the air spring characteristics come into play. A bigger box would likely mean less air spring, and therefore more excursion, which would be less mechanical power handling.

If you take your example and move it out to the extreme, say a 50 cu. box tuned to 32Hz playing 40Hz, then for all practical purposes the speaker would be playing free air (infinite baffle), at which point there would be very little control over it, and very little power handling.

But, as with everything, there is always a catch. IB designs don't have much power handling, but can have excellent sound quality.

This is off topic, but still interesting none-the-less...

http://www.linkwitzlab.com/woofer.htm

I built one of those years back, and was very impressed with its performance in a home audio environment. This is what is called a dipole design, but it is basically an IB speaker setup with some amount of material in place to delay the out of phase back wave of the woofer.

[audiophyle_247]

First we need to remember that the power handling of a sub (rms/peak ratings) is a thermal matter before mechanical. A sub's voice coil can only dissipate so much heat before glues start to melt and shit shorts out. So instead of looking at the enclosure, we need to look at impedance curves of speakers, and what enclosures do to them. (c'mon Eric, this is your specialty )

Perry says it best here
http://www.bcae1.com/spboxad2.htm

Essentially the ported enclosure puts the highest impedance at the woofers tuning, and the impedance curve can actually be higher than that of a sealed enclosure, but it is over a much narrower range of frequencies.

This means if you played a sine sweep at 100w, the ported sub would see the least amount of that power at the tuned freq (peak of impedance curve), even though it's at it's loudest point.
If you factored in exactly what the impedance was at the tuning point, you could calculate out exactly how much power you would need for the sub to actually reach its power limit at that point, which would most likely be much higher than what a sealed sub's would be at its peak impedance. That's part of why you see spl setups burping 2~3 x's a subs rated power without them melting down instantly.

The issue comes with everything outside of that peak, and on a daily system listening to music & not tones, you could destroy that ported sub very quickly at any freq outside of that tuning area.
So in theory, I think yes a ported could handle more power but in reality the odds of it being beneficial are slim.

Anyone correct me if I am wrong here.

[Mr. Wild]

It all depends. If we compare a small and large box tuned to the same frequency we will find:

In the larger box the driver will hit its excursion limit sooner than in the smaller box. But it will make more SPL with less power while doing it which is a good thing.

Then again the drivers thermal (RMS) limits might be hit sooner than its excursion limits. It depends on the driver, tuning frequency and box size.

A larger box can house a larger port so it may have better power handling if port noise is the determining factor.

In other words there are no general rules such as smaller boxes have better power handling.

Only general rule here is that larger boxes are more efficient than smaller boxes.

I must correct you, Audiophyle on the topic of impedance curves. In a vented box there is a dip in the curve at the tuning frequency, not peak. In other words the driver draws the most current and power at tuning frequency. Add to that the minimal excursion and thus minimal voice coil cooling at tuning frequency and we are in thermal power handling crisis if the burping goes on for long.

2-3x rated power burps are possible only because they are short lived. The voice coils thermal mass is what absorbs that extra power.

[audiophyle_247]

You're right Mr Wild, don't know how I mixed that up (wtf was I on)