Oh! I did get some replies from Dave on the forums. This was after he watched the videos I made of the extreme excursion:
"There are basically two ways woofers produce sound, wavelengths that are within the piston range of the woofer, and wavelengths that are out of the piston range (shorter wavelengths). Within the piston range of a woofer, in order for the woofer to reproduce this - the cone most move forward and back no different than a piston. For shorter wavelengths - the woofer cone itself resonates (out of the piston range). When a typical transducer (a woofer, for example) produces soundwaves that are out of the piston range - these wavelengths become extremely directional (also known as beaming).
One of the major design goals of the Sierra Tower was to come as close as mechanically possible to matching the exceptionally wide and linear off-axis response of the 70-20xram ribbon tweeter, which is designed to easily handle a low crossover point (which we take advantage of). In order to achieve this goal, we used smaller diameter woofers with very high excursion and crossover points optimized to keep the woofers operating within their piston range.
The pro's to this are obvious, very wide and linear horizontal dispersion which is clearly visible in the horizontal polar response (no blooming, wide dispersion etc.). This is a key performance attribute.
The con's to this is that the woofers can exhibit a lot of excursion depending on the source material, especially at very loud volume levels. Is this harmful or will it shorten the longevity of a woofer - no, not in the least provided you are not bottoming the woofers. In fact, that movement is what helps keep the voice coils cool.
You will absolutely know when you bottom a woofer as you will hear a noticeable "bang" and these woofers are built for extreme excursion. Again, woofers are designed to operate like a piston, sometimes you will see a lot of movement depending on the source and volume level.
Pogre, from your video - everything looks completely normal to me - but this is obviously at a very loud volume level.
That said, if you are exceeding your amplifier's power specifications - and the amp is starting to clip - the distortion produced by this will produce transverse waves. (this may or may not be audible) These wavelengths are problematic for any speaker as they will cause excess movement - this is what destroys dome tweeters, tears up ribbon diaphragms and burns woofer voice coils.
With your amplifier, which is rated at 200 watts and considering your 15 foot listening distance, do not try and exceed 100dB from 1 speaker at your listening distance. 103dB from both speakers combined.
I have a hunch with that video, you are well over 100dB from that one speaker.
What device are you using to measure spl?
Also, Dolby Reference level is really just an arbitrary number and has no application for music. It was originally designed for movie theater volume levels - to attempt to achieve 85dB average listening volume at every seat in a theater and for this to become a standard at every theater. In this way, mastering engineers are able to set channel levels appropriately so that dialogue and effects are appropriately "leveled" on the mix so that the mix tracks well from one theater to another etc. It works very well for theaters but as Curtis mentioned, is not really appropriate for movies mixed for home theaters. Sometimes movies are re-mixed specifically for home environments, sometimes they are not.
Ever wonder why in some mixes for the home, dialogue is impossible to hear - or effects are much too loud? The intention was good, and it has worked very well for theaters, but it's been a disaster IMO for home theater.
I wish a new standard was developed for home theater mixes as most consumers unknowingly blame the speakers when they watch a movie and can't hear dialogue, or effects are so loud forcing someone to constantly adjust volume levels. They think something is wrong with the speakers...
To repeat, Dolby Reference level is 85dB average listening SPL from one speaker at the listening position. Dolby Digital mixes allow for a massive 20dB of headroom, this is where that 105dB "peak" reference level comes from. It has no bearing for music. Some music sources have as little as 3-6dB headroom (thanks to the damn loudness wars) - even a well recorded CD will never come close 20dB of headroom.
All that said, in a home environment - I would considering anything above 97dB to be too loud and potentially damaging to your hearing.
Hope this makes sense!"
Then he followed up with some more, responding to a post about crossover points/slopes:
"Yep - we use a shallow slope on the mid crossed to the woofers, and a steep slope on the woofers crossed to this mid. Plus that SVS Ultra tower has (2) mids, that automatically cuts the excursion requirements in half, plus they are larger woofers which increases efficiency - further reducing excursion requirements at the same volume levels.
Pogre, you really can't compare one speaker to another with regard to excursion, unless it is a subwoofer with the same size woofer and similar tuning, similar filtering and EQ. It gets complicated. Our Towers were not designed as SPL beasts but I have run ours in our demo room at 110dB for hours at a time, at a listening distance of about - 9 feet in a very well damped room. We have had customers turn up the volume to insane levels at times, often prompting me in the factory area to knock on the door and ask them to turn it down a bit. We have had these same towers in our demo room, which have been seriously abused and with many thousands of hours of listening time on them for close to ten years now. We have yet to have to swap out a woofer or the RAAL 70-20xr. In fact, I believe in an early demo of the towers - I believe Curtis and some other people accidentally bottomed the hell out of the woofers when Mike (I believe it might have been Mike but I could be wrong) played an insane Linkin Park track, full range at about 110dB.
Even more reassuring to you - in many thousands of ribbon towers sold, we have only had (2) customers damage the RAAL 70-20xram. One because the tower got knocked over and landed square on the face, basically shattering the tweeter - and another who used the towers outdoors at his own party, threw an insane amount of power into them and burned up every component, including melting the inductors and resistors in the crossover. That was an interesting situation, as the customer attempted to blame the speaker and fought with us over the warranty -- that was until his some dropped the speaker off at our facility, met Dina and Joe - felt bad and told us the truth as to what really happened"
Bottom line, I'm playing at much higher spl than I realized. I'm about to find out now since my spl meter just arrived...
