My1999 XK8 convertible has the standard audio system with cd changer in the trunk. It's pretty pathetic sound wise and wondered if there is a signal at the cd changer to use for adding an amplifier and sub in the trunk and possiblly even amplifying the rear speakers or something.
Anyone tried something like this before?

 

Interested in doing similar to my coupe.

 

Forget about the sound system. Delete a resonator [or two] along the exhaust pipe. Much sweeter sounds from the V8 than anything from the headset.

 

I run a 5 channel amp in back, speaker level inputs so did involve some wiring though. Coupe with rear woofer.
l did notice what l think is the factory wiring for premium system present in back, if yours is same you might be able to utilise that in some way.

 

I ran a small sub in the trunk and the problem is the trunk is really well insulated in these cars! Could barely hear the thing. Between the carpet, rear seats and the fuel tank sandwiched between the trunk and the cabin, it won't help much. you could hear more bass outside the car than in it.

Instead I installed an amp and fitted these subs into the stock rear enclosures (they just fit and they are the absolute largest you will get in there) and I am very satisfied with the sound I get from them. Unless you are really looking for bone crunching bass, this should provide a significant upgrade over stock.
I've also seen installs where one of the rear seats is sacrificed for a subwoofer; human beings dont fit back there anyway.

 

I heavily modified my sound system in my 97 coupe, that had the most basic stereo system available. I added a custom box, sub and amp along with an aftermarket (older) alpine head unit, wiring, Bluetooth, upgraded all speakers and added tweeters in my dash. If you search my threads through my profile there are some useful things there. If you are trying to use the stock radio, there are ways too, but more involved for less effect. The stock location for a sub was in the rear deck lid but leaves little options for upgrade as you will need a very very shallow mount sub, one that’s rated for “free air” use (no box) and if car was not originally equipped with an amp an aftermarket one, although a stock subwoofer amp is probably going to be inadequate anyway.
then you need to consider this, if you upgrade the hell outta your bass, your mid and high ends if not upgraded as well will not be balanced, and even doing all that with the stock head unit will still not suffice. It’s no different than putting a cold air intake on and expecting night and day differences, without putting an exhaust system and cams and injectors and better cooling, fuel system etc etc.

start with identifying what stereo system you have, basic alpine, alpine six speaker, sub, or Harmon kardon 8/9 speaker. Then replace your speakers, if not satisfied then your head unit, and then do subs and amp if needed. Cheers!

 

Here’s a shot of my trunk when I first completed my sub and amp install. I removed the spare wheel, and customized this box to fit the way I wanted it in the spare wheels place. I installed some dynamat under box before securing to the floor of the trunk. Ran all the wiring to be as discrete as possible. I can still put the trunk carpeted spare tire cover in with no problem to look completely stock, for display purposes. The sub in the photo was actually four subs ago, I keep blowing them because I turn it up to 11, because I can! I have blown about a thousand dollars of vintage eclipse subwoofers, from composite cone to titanium cone ones. They’re
very hard to come by and expensive, but I like it loud! I even have installed a much upgraded amp that runs 1500w x1 (bridged)@ 2ohm stable, which needed 1/0 wiring and an inline 150amp fuse, and blew a 200 plus dollar eclipse 10” titanium cone dvc sub in 12 minutes, on the first ride! Hahaha I was bummed out but that 12 minutes was f——ing glorious! (My girlfriend would probably disagree!) but hey, you only live once. So needless to say but I went back to the smaller amp ☹️. Now I got four or five subwoofers to rebuild… 10/10 worth it, would recommend if you’re as dumb as me, but be prepared for catastrophic failure!!

 

A sub in trunk is more for the listeners along the way, than for you inside. It is all steel between trunk and cabin, plus the petroltank. Not worth it IMO
I have replaced the whole system with new Alpine HU and Alpine 8 channel amp with full DSP. Running true active x-overs and was really suprised of the sound from the original speakers in front (with a little EQ)
Changed the basspeakers in the rear and it is much better than before. Deep bass are nearly impossible in an open car anyways

 

Hey man to each their own, and if it’s not for you that’s all good. And not to start an argument, as you do bring up very excellent points about a sub in the trunk of these cars being inhibited by the separation of spaces, the insulation and the gas tank, but rest assured my car has plenty of bass inside the cab. And oddly enough, even to me, standing just outside the car it’s hardly noticeable, but definitely heard from a short distance away.
also…half the reason people do extreme bass systems IS to be heard by everyone around them…sorta the same way an exhaust system is heard inside the car but heard MORE by those around the car. Again, I do me, it’s my car, I can make my music and bass as loud as i want, no apologies, I was just offering some insight for those who asked for it. If you upgraded your stereo to your liking, who am I to **** on that? If it’s what you want, kudos to you! But why **** on me cus you don’t agree? No need for that man, it’s all love here. I’d love to hear exactly what you did to yours, as far as speaker sizes/brands/wattage handling, did you keep stock head unit or upgrade? Are your speakers amplified? What else did you
do? What year is your x100? I am a diehard bass head, can’t help it. But I love car audio and hearing what others have done, and their results. It only gives me more inspiration and ideas I haven’t thought of, hence the whole purpose of forums, to share info and help each other. Music makes the world go round, and I prefer mine my way just like you, so let’s share info and help the world jam out!

 

If it was my opinion that offended you, then sorry. I just wrote my experience on the topiq, regardless of what yours is.
You should read my lines and not so much between them. And please remember that I am Norwegian and my English is not that good. Maybe I write something that can be misunderstood

 

[size=16px]I can see the rear speakers in the space between the convertible top and the rear panel when the top is down. I might try to pull the speaker wires to use as a left and right signal to a 4 channel amp in the trunk and run the amplified signal back to the stock rear speakers and a pair of low profile kickers on the floor of the back seat area. Won't be ideal but should be much better I think.[/size]

 

Sounds like not a bad start. The oem head units (as far as I know, and at least definitely on mine) had no rca outputs for running a signal to an amp for subs or speakers. Almost all reputable aftermarket head units will have rca outputs, example mine has three sets, front, rear and subwoofer, but again, I have a (almost vintage) 2003 model alpine head unit, a cda-9813 that also has internal amplifier of 60w x 4 for front and rear speakers, and the sub rca have a 4v max pre-out which is not bad. It’s the second highest end model from alpine for that year. Only the alpine model cda-9815 is better then mine, having an internal switch for f/r/sw or “3way” x-over built in, a silver faceplate and surround vs the black mine has, and blue color led display and backlight buttons vs the green of my 9813. I chose the 9813 over the 9815 for the black and green to match the cars original interior coloration.

anyway… rca outputs from a head unit to an amplifier give the cleanest signal, simply put.

however, speaker line inputs CAN work just as well, given the amp is properly tuned to the output (speakers vs subs) and the amp has the necessary controls and adjustments needed.

for what it’s worth, I tried to tap into the signal from my stock head unit to the cd changer for a signal to an amp, and had no luck. The technology may exist out there but I gave up and upgraded head unit, after finding every one of my stock speakers were blown, and replacing/upgrading them, and then the head unit and then the sub box, sub and amp install I did. I’m glad I did because I had so many different options with setup using aftermarket head, and I even used the input for the cd changer for a wireless 5.0 Bluetooth to play music from my phone.
I guess it all comes down to down to your ultimate goal in listening experience, and moreover your budget, as well as look for what you can do.

 

I just realized after re reading the original post you have a convertible. However that’s some decent news for you, as the convertible cars had rear speakers in the same place as the coupes, but the speakers in the convertibles were installed into miniature “sealed” boxes. This in turn will (with no proof whatsoever) in my mind create a much better sounding bass from just speakers than a coupe would, with a lack of those sealed boxes.
Thinking about why they would do this I can only come up with one reason, as previously mentioned… in a convertible with the top DOWN, outside noises( wind, exhaust, road noises) would severely damper the audio system quality, and therefore the “sealed boxes” for the rear speakers would enhance the bass and total output for the rear speakers to counter act the outside sounds you would endure with the top being down.
My point being, if front and rear speakers were significantly upgraded, (especially rears) and an aftermarket amplifier was added(and properly tuned) the bass as well as the overall sound (especially from the rear) would be significantly improved, and possibly not needing a huge bass system upgrade…theoretically in my mind lol.

think of it like a home stereo setup we all had in the late 70’s to maybe early 90’s…. The subs, mids and tweeters were in sealed boxes, and rocked the whole house. Now, if you took the speakers out of the boxes, or took the back off speaker boxes, they sounded like —— and wouldn’t perform well. The “sealed boxes” for the rear speakers in the convertibles does this same effect, compensating for outside noise and lack of a roof to reflect and resonate the sound off of, perhaps the reason coupes did not have the boxes.

…..idk, food for thought I guess…..

 

IMO both the rear drivers and their enclosures in the convertible are too small to give convincing bass. Early convertibles had both a woofer and a midrange in each enclosure, but the latter driver was deleted with the change from Harmon Kardon to Alpine (MY2000, I think).

As with many things, there's a fair bit of science behind loudspeakers and enclosures (long):
https://sound-au.com//articles/enclosures.htm

Am I in a minority who think the coupé premium sound system is fine? Granted, it won't rattle your eardrums or shake your giblets, but I think it acquits itself pretty well. Bass is much better from the shelf-mounted woofer using the boot space as its enclosure.

 

The rear speakers in my 1999 convertible are not in boxes. I can see the speakers looking down through the space where the top folds down. I think I can actually get my arm down there to unplug the speakers. I suppose the boxes could have been removed by a previous owner. Maybe that's part of the reason the sound is so pathetic.