BURN-IN MYTHS
First of all I want to offer a big thanks to Speaker City and Madisound for sending woofers on request. One call to each of them and a small sampling of woofers were sent without hesitation.
Woofers used in this series of tests were the Dayton Euro woofer model 295-350, Seas CA18RNX, Peerless P832513, Peerless 830875, Peerless 830860, Peerless 830875, GR Research M-165X and GR Research M-130.
All woofers were new and fresh from the box to the best of our knowledge except for our M-130 woofer. As a control it was removed from an A/V-1 speaker that had at least 200 hours of play time on it. I asked for new woofers but can not guarantee that they had never been played before at all.
Each woofer was measured under the same conditions using a Clio 7.1 measuring system.
A 40Hz sine wave was played through all the woofers at once and at a level that pushed them to at least half of their rated X-Max. They were always allowed to cool for about 2 hours after each period of play to allow for them to return back to room temperature. Measurements were made fresh out of the box, after 1 minute of play, after 5 minutes of play, after 1 hour, after 10 hours, after 20 hours, after 40 hours and after 80 hours of play. Playing the drivers this hard with a 40Hz sine wave works them out more that typical music playback and will accelerate the burn in process. So under normal playback conditions this level of compliance change could take longer to reach.
The results address several known Internet based myths that include the following:
1) Speakers don’t burn in its your ears that burn in.
Obviously, as a woofer is played over a given time period the suspension compliance changes. This objective data showing changes in the T/S parameters as the suspension loosens up does not prove noted subjective differences in the perceived output, or how a speaker sounds, but does prove that there is something more taking place than getting used to the sound.
2) What break in does occur in a driver occurs within the first few seconds of opperation.
Clearly changes in a drivers compliance continues to change with extended play time well in excess of the first few seconds of play.
3) Within just a few minutes of the stimulus being turned off, most if not all of the change in compliance will completely recover and the parameters will reverts back to the original specifications.
Since the drivers were allowed to cool for several hours between taking the measurements we can clearly see that at no time did they revert back to previous measurements.
4) Drivers whose parameters change over time are defective.
All drivers will show a softening of the suspension when played over a given time period. Some will change more than others.
Below is a summary of the changes in driver compliance during the burn in process. Changes can be seen in Fs, Vas, and Qts parameters so those are all that are shown to minimize redundancy.
There are several things to note. As a woofer goes through the burn in process the Fs will drop, Vas parameters will increase, and Qts parameters will decrease. Vas will tend to have a small amount of variance between measurements and will bounce around a little in some cases but it will generally and always increase in value.
Temperature can and will effect these measurements. All drivers shipped in had set in the measurement room for several days to adjust to room temperature with a couple of exceptions.
The already burned in M-130 woofer that was removed from an A/V-1 speaker was stored in an area that was slightly colder than the measuring room. Even though it showed less change to from the burn in period than other drivers since it already had time on it, it had showed more change than it might have since it was not allowed enough time to completely warm up to room temperature.
The M-165X woofer was fresh out of the box that was from our storage area. It was quite a bit colder than the temperature in the measuring room and caused the greatest amount of change in initial measurements compared to the other drivers. The colder temperature causes the Fs to be higher, Vas to be lower, and Qts to be higher.
I have no data on two of the Peerless drivers from when they were fresh out of the box. This is because later recorded data was accidentally saved in the same file folder under the same name. So the later recorded data saved over the initial data (replacing it). After the driver had time on it then it was impossible to get a new measurement on it when it was fresh. Sorry about that.