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Big power cables in footwell area? (Car Audio)


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My newly-acquired 987 Cayman is causing me grief at the moment. The standard radio was terrible so I've installed a Pioneer double-din head unit in the dashboard and an older 4-channel amplifier in the front boot. Head unit is new, amp is old but known to be good. I'm running it active - i.e. with two channels on the amp to the mid range speakers in the doors and two to the tweeters in the dash. I've run the RCA cables and speaker cables through the bulkhead in front of the passengers and then again through the bulkhead beyond the battery into the front boot to connect to the amp. 


I am having the most enormous problem with interference from the engine; there is a whine whenever the engine is started. And it's most annoying. I've done or observed the following: 


- Good amp and HU connections. HU now connected to it's own custom loom straight to the battery

- No whine with RCA's disconnected. Whine occurs only when both sets of RCA's are connected

- Whine seems to be related to the position of the RCA's and I think there may be a source of interference in the footwell, somewhere near the centre console. Such is the design of the car then routing the RCA's via any other path would be difficult. 


Has anyone else installed an amplifier in the front boot and if so then where did you run the RCA cables? 


Thanks for your help. 

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I'm a bit confused! 😲


Surely the tweeters are connected to the door mids by crossovers? Why would you power them separately? :35_thinking:

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If you control the signal that goes to them before it is amplified then you have much more control over what frequencies they play and what frequencies they don't play. It's called an 'active crossover', as opposed to a 'passive crossover' which splits the signal once it has been amplified. 


The downside of an active crossover is that you need an amplifier channel per speaker, so a four-channel amp to do two mid-range speakers and two tweeters. And two sets of RCA cables. 


Back to the original question. :) Does anyone know of anything that may cause a LOT of RF interference in the footwells, somewhere near the centre console. Thanks! 

Edited by zcacogp
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I've always used a "passive" set up. Never tried "active" tbh.


Found this linky that may help but sounds as though you're more up on car HiFi than I lol




Edited by Mavrik
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Thanks for digging that up for me - it's appreciated. It's a good guide but I am having severe weirdness hence this thread! The whine doesn't seem to be being caused by any of the usual things and I'm confused. Normally HiFi systems whine because the earth connections are poor or the RCA cables run too near to the amp power cable. Mine is (I think) fine on both fronts. However the whine doesn't follow any sort of logic and seems to be in some way related to the route that the cable takes through the footwell, hence my question about whether there is something that causes a lot of interference in there. The chunky cable from the alternator to the battery +ve terminal seems to run through the passenger side (if you follow it from the battery it goes to the nearside of the car) but there is a thick black cable of some kind that appears behind the pedals and I don't know what it does. It could be a vacuum line from the engine but I'm not convinced. Given that I am currently stumped by it then I am seriously thinking about relocating the amp to under the passenger seat and taking the RCA cables elsewhere entirely. This will be a lot of work but the whine is intolerable. 


Thanks again for your help. 

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An update on this: it was the RCA cables. changing them for some KnuKonceptz Krystal RCA cables (better quality and very shielded) almost entirely solved the problem; when first installed they were substantially better than the previous cables but I had to do some more work on the routing before they were entirely silent. There is still something down in the footwell which makes a load of electrical noise and I've had to keep them away from that area.


I'm very happy that I now have a car whose radio can be listened to without a bad headache. I was despairing of ever achieving this! for reference, should anyone else try to install a separate amp and head unit then it's worth spending money on good quality interconnects. I skimped slightly on the sets I was using and wasted a LOT of time chasing down the problem. 

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