Originally Posted by
captain_video
Interesting. So you're both saying that I should leave the capacitor off the center speaker and let the head unit provide the correct frequencies? I have often wondered why the tweeters had caps and the center speaker didn't. I only added it because that's what others had done before and I went with their recommendations. What you're saying about the speakers being connected in parallel and using a capacitor makes perfect sense. I'll give that a try and see how it goes.
FWIW, the crossover frequency that was measured by another user for the center speaker indicates a bandpass filter from 500 Hz to 12 kHz. Apparently all three speakers in the dash for the B&O system are midrange speakers, with the two outer speakers using a high pass filter at 250 Hz. The tweeters are located in the sail panels at each side. The non-B&O system has two tweeters at the outer edges of the dash and a midrange in the center, but no tweeters in the sail panels. Looking at photos of the B&O center speaker it does not appear to have a capacitor connected. I have one of the outer midrange speakers and it doesn't have a capacitor either. So far, the only dash speakers that I can confirm having capacitors are the two tweeters in the non-B&O system, and they both have the 10 uF caps. The more I get into this, the more confusing it gets. I'm starting to wonder if any of the speakers other than the non-B&O tweeters require a capacitor.
The main thing about the cap is that it prevents low frequencies that would damage the tweeter from entering the driver. Since larger drivers don't need to worry about normal bass frequencies (obviously a small driver will over drive if played too hard and too low) they don't face instant death like a tweeter does. Combined with that many larger speakers naturally fade off and stop playing frequencies above a certain point, car companies often omit the low pass filter to save cost. This isn't always a good thing for issues like phasing as I mentioned before, but it can also be a very bad thing because many larger speakers do have a high frequency response that it highly distorted or peaking at certain harmonics above it's rated "usable" range. This is especially true on paper speakers. Another problem with not using a low pass inductor is that the entire frequency range of power is flowing through the driver. Even though it can't play those frequencies, the electricity still flows through it which steals power from the tweeter, and puts a heavier load on the amplifier.
So if the tweeter doesn't have a cap on it, don't add one because it will change its behavior. Sometimes caps exist also just to block DC if the amp has a loud thump when you turn it on or off. If the speaker does have a cap you should use one, but you have the opportunity to change it's behavior to something you want.
The 3rd case is the midrange speakers. You can add a cap to limit the lower frequency response, but I would only do so if it's a problem. IE it's too loud in the bass range, or it's buzzing badly, or being overdriven. If the dash speaker is being driven on the same channel as another speaker, it's often a good idea to filter it above the point where the impedance starts rising so you don't put too much load on your amp.
Regarding the frequency response of the center, I measured 250 to also around 12K, but that was for BOTH the tweeter and midrange on at the same time as it was more trouble than I was willing to put forth to isolate them from each other.
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