Hot and Cold

Commercial subwoofers have volume limiting circuitry to protect the driver from overzealous mixing by some DVD producers, and from ham-fisted users.
In the DIY world, most of us are limited to plate amplifiers which don't have limiters, so we have to be a bit careful.
This page details which DVDs are mixed hot, and which are mixed cold, and covers a 16dB range.
It might just save you some grief.
When I first play a new DVD, I set the sub boost at around the middle of the range, say +6dB. When a loud section is encountered, I fine tune the setting. By the end of the movie, I've settled on a value for the highest safe boost. This is then written on a sticker for next time I play the movie.
These are all standard definition Region4 (Australia) releases, played back using the Dolby digital soundtrack, with all speakers set to small (ie Bass from mains redirected to sub in addition to LFE signal)

Wouldn't it be nice if DVDs had a sticker like this

You would know that you could set your sub 4dB higher than normal without running into trouble. In my library this sticker is on the "Pearl Harbour" DVD, with "Star WarsII" as the reference getting zero
Any takers for starting a "Subwoofer Safe" campaign?

These examples give an idea the challenges your sub woofer would face in each of the scenes
Here are two ways to visualise what the signal going to the subwoofer looks like:

Star Wars2 - Ch3 - Ship explodes on landing pad - 107dB

You can see why this is loud. Not only is it mixed the loudest, but look at the spread. No matter how good your sub is, this one has something for you

Pearl Harbour -Ch22 - Bombing of Battleship Arizona - 105dB

Something for everyone. Huge spread means that even those without subs will get a bang. Really good subs will find that ridge off to left which goes down well below 20hz

LOTR-Two Towers - Ch41 - Blocks landing after Helms Deep wall blown - 104dB

Strong component below 20hz. This is why some retailers demo their more expensive subs with this sequence

LOTR - Return of the King - Ch28 - Block lands from catapult - 104dB

Portion below 10hz probably an algorithm artifact. This is one of my favourites. Plenty at 25hz where my sub goes to. Lots more available for those with deeper pockets

James Bond Die Another Day - Ch4 - Hovercraft crashes into building - 106dB

Very little below 20hz, most from 30hz up. Would sound OK on most subs - mass market mix

James Bond Die Another Day - Ch1 - Surf sequence - 100dB

Good spread of frequencies will perform on all subs. Consistent level means I use this one for calibration

Star Wars I -Ch3 - Ship attacked in hold and explodes - 104dB

Woooaaah - reach for the checkbook. You want deep performance to get the best outta this one. Still, there's plenty for everyone!

Terminator3 - Ch12 - Crane smash - 104dB

Some signal below 20 but most above. Will render well with most subwoofers. Mixed with the mass market in mind

LOTR - Fellowship of the Ring - Ch29 - Troll first appears in Moria fight - 103dB

Some good 30hz bass. Something here for all subs

Earthquake - Ch8 - When quake begins- 96dB

Vintage film with nothing below 25hz. Not much of a challenge

Open Range

Opening Thunderclap


Thunder ("big un's coming...")


Gunfight

Comparison of selected scenes

This next graph has a lot of information. These curves are not an instantaneous snapshot - each curve is derived from the entire sequence using the Peak Hold feature. Each curve was individually snapped into Paintshop, so don't think you can get this graph without some work

The curves have been shifted vertically to remove the "boosted" settings, so this is what your sub will see with the volume controls left unchanged

Remember that the Threshold of Audibility increases as frequency decreases.
For most of these graphs to be 90db at 15hz, the SPL higher up in the spectrum would be threatening to your hearing, your house and your wallet!
For example, The Bond Hovercraft crash is about 70dB @15hz. If you raise this to 90dB in order to be audible, then the loudest part of the spectrum, around 40hz, will be a very loud 121dB

Just for fun - The best two films in each of my top 30 categories