Subwoofer break in / burn in – Before and after
Do you have to break in your subwoofer?
Depends what you are trying to do. If you want to measure the T/S parameters of your speaker, then you must absolutely do it. The parameters change, quite significantly in some cases, and the correct parameters are those after the subwoofer break in. However, if you are going to make an enclosure for your woofer, and you are going to use the parameters provided by your manufacturer, there is little to be gained from this procedure.
Considering that you will use it few hours a day, it will eventually break in by itself. I always heard a noticeable difference after the subwoofer’s suspension has settled. This happens after few months of normal usage, it depends how long you use it daily and how high you crank the volume. However, artificially breaking in a speaker has some advantages. Stressing the speaker to force it to break in, will certainly reveal any suspension problems, if there are any. So, if you are starting a complex audio project, breaking in your speakers will save you some headaches, if you happen to have any bad speakers.
Subwoofer break in period and how to do it
To burn in the woofer, you have to secure it to some kind of frame. Do not place it inside an enclosure. I made some sort of improvised open baffle, to secure the woofer in place. The speaker I used is a Scanspeak 26w/8534g00, a 10″ woofer. The frame is made of 3/4″ MDF and it was sturdy enough by itself, not to vibrate while the burn in was in progress.
After I made the baffle and secured the speaker to it, I used a sine tone of the same value as the resonant frequency of the speaker in free air. Crank up the volume so that the woofer moves almost at Xmax. Since the frequency used as a tone was very low (23 Hz in our case), you don’t really hear the sound, but you do hear any motor noise, suspension tension and wind noise (if the speaker has a vented pole piece).
Of course, you hear these noises only if you push the speaker too hard, so make sure the speaker doesn’t make suspicious loud noises, because you will probably end up with a burnt speaker. After 12 hours of woofer pounding, the subwoofer break in should be complete. For good measure, I left it playing for 24 hours, though the sine tone can get quite annoying in the night’s silence.
First, I am going to quote the values which are given by the manufacturer :
- fs = 23 Hz
- Qts = 0.4
- Vas = 150 l
I know there are more parameters, but these are the important ones, which help you design the enclosure. Now that we got that out of the way, let’s move on to the measurement before the break in.
The parameters of the speaker before break in are :
- fs = 27.7 Hz
- Qts = 0.5
- Vas = 113 l
As you can see from the chart, my specific speaker had a slight bump in impedance near resonance. I’m sure that this is not the case with other samples, but mine had this anomaly. I’m guessing there is a stiffness in the suspension around 45 Hz, hence the little peak there.
After the 24 hour subwoofer break in period, I made another measurement :
The parameters of the speaker after break in are :
- fs = 24.9 Hz
- Qts = 0.45
- Vas = 139 l
As you can see we have gotten closer to the values quoted by the manufacturer, which is always a good sign. The hump in impedance has disappeared. Which makes me believe that the suspension has loosened up completely and that stiffness that was present before the break in, is now gone. To check the sanity of the woofer, the ratio fs / Qts, from before and after break in, has to match. The ratios are both approximately 55.4 which means the woofer is in perfect working condition.
I am going to model the response curve of 2 enclosures : one sealed with Qtc of 0.7 and a QB3 bass reflex box, using the parameters of the speaker after the break in. Using the same boxes I am going to model the response curves for the speaker before the break in, so we can compare them.
I went for a maximally flat QB3 design. The red line represents the speaker after the break in and the green line the speaker before the break in. As you can see the difference between them is minimal. The graphs mostly overlap, and there is a small 0.4 dB difference near resonance, but that is pretty much it. In real life there would be absolutely no audible difference whatsoever.
For the sealed enclosure I also went for a maximally flat response with a Qtc of 0.707. Now this is really difficult to tell any difference. Basically the 2 response curves are the same till the -5 dB point. Going downwards in frequency you can maybe see a 0.3 dB difference. There is barely any difference on paper, so in real life the difference will be impossible to detect.
The point I am trying to make is that even if the parameters look different the ratio fs / Qts is the same. If you design an enclosure for one speaker or the other, both will do about the same in either enclosure.
Subwoofer break in is not that serious when you are designing an enclosure. It surely won’t hurt if you do it, but it won’t make that much of a difference. It does not justify the effort. However, a thorough burn-in will reveal any flaws with the speaker, so you know you are starting your project with working speakers. This is basically the plus side.
The subwoofer will break in by itself, after sufficient daily use. From a subjective point of view, you can always tell there is a difference when the subwoofer has finished breaking in. As the suspension loosens up, you can tell it goes lower in frequency and hits “harder”. If you don’t want to wait for it to break in by itself, you can burn-in the speaker beforehand. Fiddling with the audio settings is best done after the speaker have broken in, so there is another reason to do it.
- Image source : link.