QuestionQUESTION: I recently pulled my after market equipment and re-installed it in a new GM vehicle. The quality was outstanding before and now sounds muffled or filtered no matter what I do. I'm running 4 Polk 6 1/4's in the doors and 2 10 " subs in a custom built box. It's powered by two separate amps. The new vehicle has a navigation system and I'm being told that I need to replace the head unit for better quality. Is there any way around that option?
ANSWER: Hi Chuck,
I'm wondering how your after-market equipment is connected to the factory audio system. Are you using basic line output converters? High-level inputs on the amplifiers? Some sort of summing device? Also, was the factory system a Bose package?
When you're using after-market equipment with a factory source unit, one potential problem is that the factory audio system may use built-in equalization and crossovers designed for the factory speaker system. This often causes sound quality problems when you're not using the factory speakers any more. The solution is a summing device/processor such as Rockford's 3Sixty.2, JL Audio's Cleansweep, or a variety of products from AudioControl.
Hope this helps!
Brian
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QUESTION: Yes I used high level inputs and it is a Bose system however I
have no summing device.
ANSWER: Chuck,
There's quite a bit of variation in the Bose systems found in different GM vehicles, so it's hard to say exactly what you're dealing with in yours. However, there are two things that often cause problems with after-market gear wired to a Bose system.
First, the Bose amp often incorporates crossover filters on the various speaker outputs. That means the door speaker, for example, may carry only midrange frequencies, while the treble is sent to a separate tweeter. If your high-level inputs are connected to speaker wiring that only carries the midrange, then that's the frequency range that will be reproduced by your after-market amp; and that's the frequency range that will be played by your new speakers.
Second, Bose systems almost always include built-in equalization settings to get the most out of the Bose speaker package. When you install a new speaker system using the high-level inputs, you're still using the Bose EQ curve; and it might not sound nearly as good with an after-market speaker system.
I used the term "summing device" before, but that's kind of a catch-all phrase for a wide variety of OEM integration products. A true summing device is designed to connect to separate low, midrange and high frequency speaker outputs, and combine them into a single full-range output for the after-market amp. Another type of device is an OEM signal processor; this is specifically designed to remove the factory EQ curve, so your after-market amps start out with a clean, linear source signal, which can then be adjusted to your preference.
Many devices, such as Rockford's 3Sixty, combine the summing and processing features. You might also look at JL Audio's Cleansweep products; these include the CL441-dsp signal processor, and the CL-SSI summing device. Depending on your vehicle, you might be able to use the low-level outputs from the Bose head unit to feed a signal processor, instead of the high-level outputs from the Bose amplifier. This would eliminate the need to use a summing function, because the head unit outputs will be full-range. You can't use a passive device like a line-output converter with the head unit outputs, but they'll work with a more sophisticated interface like the CL441-dsp. However, some Bose systems use a data-controlled amplifier, and fixed line-level outputs from the head unit; in this case, your only option would be to use the Bose amplifier outputs for your signal source.
Hope this helps!
Brian
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QUESTION: One more thing Brian. I keep getting different views about using any type of processing device. One question I have is will they work if the signal from the head unit is digital? Also would it by easier to just replace the head unit?
AnswerChuck,
If you have a "premium" Bose system in a newer GM vehicle, then the output isn't digital. It's a fixed left and right analog output. The amplifier is controlled by a digital signal, but the actual audio signal remains analog. It comes down to the same thing, though, because the factory head unit's volume and fader controls don't actually affect the pre-amp audio output, so it's useless as a source for a processing device.
If you have this type of system in your vehicle, then you wouldn't be able to use the output directly from the head unit. You'd have use the outputs from the factory amplifier. That means you'd need the "summing" functions, to combine all the various outputs into a single full-range signal; and you'd need the processing functions, to remove the coloration from the factory equalization. However, if you pick the right processor, then you should end up with a clean, full-range output that will work perfectly with your after-market amp and speakers.
Would it be easier to just replace the head unit? Unquestionably. This would simplify things quite a bit. However, you might have to give up some of the advantages of the factory system. If you have Onstar, steering-wheel controls, an XM radio tuner or other external source unit, rear seat audio controls or rear seat entertainment options, then you it might be more expensive or impossible to keep them working with an after-market head unit.
Hope this helps!
Brian
