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I just purchased 4 Infinity Reference 6520CX components. When replacing the tweeters, do most people install the crossovers in the doors or just hook them straight up?
 

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Do you have the premium 10 speaker sound system, or the 6 speaker system?

With the premium 10 speaker system, the tweeters are amplified separately, and you will not need the external crossovers at all. The crossover is taken care of by the system internally. (I don't know if they use an active crossover pre-amplifier, or if it's a passive network post amplification though.) Note that the factory system's crossover point may not be optimal for your speakers, though in general with similar speaker sizes, the crossover points aren't likely to vary by much.

I would connect them straight in place of the existing one, and check them at very low volume, which will not damage the speakers even if the frequency range is inappropriate.

If you want to check, use a cheap full-range speaker, and connect it to each channel separately. The midrange/woofer outputs should be missing the high frequency information, and the tweeter outputs should be missing midrange and low frequency.

I believe that the premium system is actively crossed over pre-amplifier, but there are some setups that have a simple first-order filter on the tweeter output (6dB/octave) and no filter on the midrange at all, and simply allow the speaker's lack of response to filter out the high frequencies. In cases like those, I would disconnect the tweeter output, and use only the midrange output, using the passive crossover network supplied with the speakers. This might be applicable for the lower end audio system.
 

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Install them. One of a few things will happen, none are bad.
  • The factory had no crossover in-line, so you just saved your tweeter's life.
  • The factory crossover is set higher than the crossover you have, in which case your crossover is already in the crossed-over band and will make no audible change.
  • The factory crossover is set lower than the crossover you have, in which case you needed your crossover to protect your tweeters to Infinity's spec.
  • The factory crossover and your crossover are set at the same frequency, in which case the rolloff will increase and roll-off those unwanted frequencies at a steeper curve.
 

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If you connect the crossovers, you have to choose which speaker channel you connect both to, so you will probably be missing something from the summed output. Passive crossovers on just the tweeter channel can do some weird things to phase relationships which will have some weird effects to staging.

It is true, however that connecting in the crossovers will, at the very least not physically damage the speakers, but you might find that it's definitely not an upgrade. :)

@firebirddude: The 10 speaker setup has a separate amplifier output for the factory tweeters and midranges. The supplied crossover in the separate set assumes that you will have a single full-range signal to split to the woofer and tweeter, and compensates for phase correctness in that case. In order to use this, you'd have to sum the amplifier outputs from the factory mid and tweeter to the input of the Infinity crossover, which could damage the factory amplifier, as each channel would be pumping reverse voltage back into the amplifier output stage. Most amplifiers will reject this, but it is possible to present an effective short circuit to the amplifier devices this way, which will burn out the output devices.

If there is no crossover on one channel (Which would typically be midrange) then you can use that, and disregard the factory amplifier channel for the tweeter, however given the specifications for the DSP when I looked it up, it does appear that the factory system is actively crossed over, and that there is no proper input channel to feed into the passive crossover to split to the mid and tweeter.

You COULD use the passive crossover for just the tweeter, but that will have phase distortion effects on the tweeter channel, and make its slope and cutoff mismatch with the woofer. This will produce problems with the sound staging, and probably introduce interference issues with dead and loud spots in the speakers frequency response.

Separate speaker sets are always set up to be able to deal with a frequency response that is well outside of the supplied crossover range, so the factory crossover being a little different isn't a problem.

I do suggest that you test with a full range speaker, and try with an initial low volume test. Get a set of test tones in 1/2 or 1/3 octave steps from low to high, and see what comes out of each channel. Be careful to match the phase of the output, or you'll have weird dead spots in the sound output.

Overall, I want you to get the most out of your speaker replacement, and I'm hoping that it ends up being an upgrade and not a disappointment.
 

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Hi there guys. Hate to butt in but I have a query regarding the previous post, which mentions a feedback into the amplifier when signal summing.

My stock system is a SYNC1 Sony HU, on my Focus mk3 with 9 speaker system (European spec, pre-facelift Titanium).

There’s no amp or sub in the boot. I’ll be running a sub (undecided) and Hertz ESK 165 components from a Pioneer GM-9704 in 3 channel mode.

I plan to use a WAVtech LINK4; it provides exactly the functionality I need. AudioControl gear is hard to come by in the UK, and it’s very expensive. Is it safe for me to use signal summing on the front tweeter and woofer outputs by splicing into the back of the HU?

Cheers
 

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In that configuration, I would use hte rear outputs and connect your line level converters to that.

I believe that this will exclude things like warning chimes from being run through your amplifier, which is a good thing. It will also provide some level control via the fader.

For summing the tweeter and woofer channels, I would avoid this if at all possible. There exists some possibility for undesired feedback, even if it does not damage the amplifier output devices. Without spending some time studying a schematic for the head unit (Which is never going to be provided) I believe that the risk is unacceptable, given the cost of replacing. Almost all 12V amplifiers are designed to run in BTL mode, as opposed to a common ground. Good aftermarket "bridgeable" amplifiers usually run common ground, but this is almost never the case when the amplifier is integrated into the head unit, even in the best aftermarket units, and so far as I know, never in factory units. This makes any kind of summing of the speaker outputs risky.

I did not know that there was a 9 speaker version of the Sony sound system, nor that it was available with Sync1. I have the 10 speaker (North American) version with the sub and amplifier, and MFT setup.

There is one configuration that might be possible, and safe to sum the signals, and that is to use line-level converters on all 4 channels separately, then sum the high and low signals afterwards with a Y cable. Pre-amp signals are much easier to sum that way, and far less sensitive to feedback, since the output devices aren't dealing with much real power, and are generally very high impedance. This costs a little more, but think of it as insurance.

In this case, however, I believe that it might also be worthwhile to consider an additional, smaller amplifier for the tweeter signal. Run the mids and subwoofer from your 3 channel amplifier, and run the tweeters from a smaller 2 channel amplifier. Other people go to great lengths to get that bi-amped setup.
 
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