Bass distortion before tweeter distortion with a monitor at high volume?
Thanks for all the interesting answers and differing points of view. I don't have the knowledge of many of the experienced posters here and it is nice to be able to take advantage of it. It seems it might be a good idea to look for a speaker/tweeter that has a lower THD? Are there any graphs or measurements available to show this and it be worthwhile? |
Here is the site I was referring to. In their distortion tests, they show the distortion as DB, not percentage. There are calculators if you want the actual numbers. In short, the number of db between the signal (top line) and distortion (bottom line) is what you are looking at. http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=941:nrc-measur... The takeaway from the KEF LS50 graph is that little mid-woofers are really pretty terrible at bass. I think it also dispels the myth that most subs aren't "fast enough" to integrate. Most subs have many many times lower distortion at bass frequencies. If you go to the Measurements menu and select speakers, there are quite a few speakers to choose from. For larger speakers, they do a test at both 90db and 95db. It doesn't look like most tweeters have significant measurable distortion at 95db. I can also tell you that if I plug the ports of my Revel M106s, the midrange clears up a good bit, so even limiting the woofer's excursion physically helps. Unfortunately, that makes integrating with a sub difficult because the sub has to play at a little higher frequency and I get localization of the sub's sound. |
The specific type of distortion likely to occur in a small but high-quality two-way loudspeaker driven hard is due to the woofer being driven beyond its linear excursion limits. Over-excursion results in what's commonly called "fartout" in the prosound world. Some motor designs go more gracefully into over-excursion than others, but eventually just about all of them will get there. In extreme cases, a woofer could be driven to its physical limits, which can result in the voice coil hitting the backplate with a disturbing machine-gun-like snapping sound. This causes damage to the voice coil and/or voice coil former, which may or may not kill the woofer right then and there. As noted by sboje above, cone excursion quadruples for each octave lower you go, for the same SPL. This would be true for a sealed box - for a vented box, it's more complicated. The backpressure from the port decreases excursion near the tuning frequency, but then excursion rises very rapidly below the tuning frequency. So if the small monitor speakers are ported, the main danger zone may be lower than you would have thought, but also more severe than you would have thought. In my opinion not only the highpass filter frequency, but also the highpass filter slope, comes into play if safely getting higher SPL out of a small speaker system is the goal. Steeper slopes do a better job. With all due respect to Richard Vandersteen, in this situation, imo first-order slopes may well be inadequate. |
| Post removed |
