Fitting an aftermarket Sub-Woofer - bass roll-off and signal sources

[mgrobins]

Hi,

I'm looking at fitting a sub to my 2014 GTI. I've been examining different options from underseat (front passenger) to a boot install under the floor which I tend to leave in the upper position (gives 90mm of space + wheel well).

I have 4 main queries at this point:

1. Can a line level signal be taken from the head unit between it and the amp or am I stuck with high/speaker level (most folks use the rear speakers it seems but given I often have them near off I'm not sure that would be my best choice).

2. Does the head unit force bass roll-off? I'd like to know if I need something like the Audiocontrol L2Ci to undo that.

3. I see people turn the bass way down on the head unit and then up the gain on the sub amp. I assume this is to improve the dynamic range of the door speakers by decreasing the head unit/amp effort producing bass. Would it also increase the noise on the bass signal (relative to SNR) in any meaningful way?

4. I was going down the path of building a custom box to fit in the spare wheel and storage area, and likely use 2x 8" woofers, however am now looking at the Pioneer TS-WX710A (TS-WX710A Space-Saving Flat Amplified Subwoofer (200W) - Pioneer Car Speakers, Sub) which would fit in that area quite nicely.

I need to find out if it will be sufficient for a car of this size. Anyone have experience and able to advise?


Lastly.... I've seen installs using only one channel for the sub (eg R rear door speaker line). Why would you not take the other channel and ensure you get full stereo bass expression?

I have a background in design and work with Home Theatres and Audio.... just not a lot with car systems so I'm coming to grips with the limitations of the system. I'd rather a simple addition of a sub than going the path of a multi channel amp, equalization etc at this point .

[DV52]

Hi,

I'm looking at fitting a sub to my 2014 GTI. I've been examining different options from underseat (front passenger) to a boot install under the floor which I tend to leave in the upper position (gives 90mm of space + wheel well).

I have 4 main queries at this point:

1. Can a line level signal be taken from the head unit between it and the amp or am I stuck with high/speaker level (most folks use the rear speakers it seems but given I often have them near off I'm not sure that would be my best choice).

2. Does the head unit force bass roll-off? I'd like to know if I need something like the Audiocontrol L2Ci to undo that.

3. I see people turn the bass way down on the head unit and then up the gain on the sub amp. I assume this is to improve the dynamic range of the door speakers by decreasing the head unit/amp effort producing bass. Would it also increase the noise on the bass signal (relative to SNR) in any meaningful way?

4. I was going down the path of building a custom box to fit in the spare wheel and storage area, and likely use 2x 8" woofers, however am now looking at the Pioneer TS-WX710A (TS-WX710A Space-Saving Flat Amplified Subwoofer (200W) - Pioneer Car Speakers, Sub) which would fit in that area quite nicely.

I need to find out if it will be sufficient for a car of this size. Anyone have experience and able to advise?


Lastly.... I've seen installs using only one channel for the sub (eg R rear door speaker line). Why would you not take the other channel and ensure you get full stereo bass expression?

I have a background in design and work with Home Theatres and Audio.... just not a lot with car systems so I'm coming to grips with the limitations of the system. I'd rather a simple addition of a sub than going the path of a multi channel amp, equalization etc at this point .

mgrobins; hi-sounds like a really good project!
Not sure what system you currently have, but I suspect that your car isn't fitted with "VW's Digital Sound Package". VW call this the "J525" module and in NAR models it's normally fitted to a Fender sub woofer that's installed in the spare wheel well (together with the space saver spare wheel)

Anyhow, the reason that I'm telling you this is because it explains my answer to your first question -which alas is No. The way that the mk7 provides "line level" audio and video signals to other components in the car (like the J525 module and in Japan, a TV tuner) is via optical fiber cables.VW calls this their MOST 150 (short for Media Oriented System Transport operating at 150 Mhz/sec) bus which uses a type of ring topology network. So alas, the only alternative is to source your audio signal from speaker level signals.

As to your question about roll-off, I always get confused about this topic because ithe term is often defined differently by different folk. I've not seen the circuit diagram inside the J794 control module (i.e. The discover media unit), so I' m only guessing, but there are no external cross-over components in the mk 7 and I very much doubt that the j794 has active cross-over circuitry. I did provide a few posts to a fellow forum member on the Golfmk7 site and he used an LC2i in his project (he had the j525 module in his mk7 version car). Why don't you take a look at the Golfmk7 thread - it could provide you some ideas for your project. The link is HERE

When I find the diagram, I'll post up a pic of the speaker pin-out for the discover media unit - it might be of interest to you.

EDIT: Finally found it! Here's my PIN_OUT diagram for the speaker pins on the Quadlock connector on the rear of Discover Media unit.



And here's a video (from a crowd called "JustAudioTips") that describes how to physically remove the J794 module from the glove-box so that you can get to the Quadlock connector pins shown above

[Fixxxer]

DV52 sounds like he knows his stuff. There was a thread I found (maybe on UK forum) that showed a step by step with photos how to install an underseat sub/amp combo. He used the rear speaker high level inputs at the back of the CD/SD card area in the glovebox (mk7 R).

The pioneer unit looks like it would be great for a gti, pretty sure someone in Aus just did this using this sub. Check the forums. The underseat/boot subs will fill in the sound nicely and be enuf for most people, but obviously wont kick as hard as a proper (larger) sub install and amp that can deliver some serious power. The underseat versions seem to max out at 150wrms and 8" woofer.

I'm currently deciding between these underseat versions and puting in my old amp and 12" sub/box in the boot, so i'm interested in this thread. This combo worked great in my golf mk5 gti running off high level inputs. I'm leaning towards the 12" and extra power as I like it to thump - I dont use the boot much and could remove the box easily when it was in my mk5 gti. I might see if I can hide the amp under boot floor, or under dash for cleaner look and no probs if I need to lay down the back seats (amp was mounted to seat-back).

Good luck, hopefully others will chime in.
Fixxxer

[kaanage]

3. I see people turn the bass way down on the head unit and then up the gain on the sub amp. I assume this is to improve the dynamic range of the door speakers by decreasing the head unit/amp effort producing bass. Would it also increase the noise on the bass signal (relative to SNR) in any meaningful way?

With a sub/sat speaker system, the overall power handling can be high, relative to the power handling of the satellite speakers since the bass signal is filtered away from them - if this was not done, then they would distort and be damaged at only moderate volumes. The same principle can be applied to car audio.
The noise increase from padding down the bass and then reamplifying will mainly be in the higher frequencies which would not be reproduced by the subwoofer (especially since the sub amp will run the signal through a LPF).

Lastly.... I've seen installs using only one channel for the sub (eg R rear door speaker line). Why would you not take the other channel and ensure you get full stereo bass expression?.

Most music is mixed realistically so the bass signal is mono. A very artificial mix could have the bass signal completely in one channel at times so a dual channel source is preferable but most time, you wouldn't notice.

I'm currently deciding between these underseat versions and puting in my old amp and 12" sub/box in the boot, so i'm interested in this thread. This combo worked great in my golf mk5 gti running off high level inputs. I'm leaning towards the 12" and extra power as I like it to thump - I dont use the boot much and could remove the box easily when it was in my mk5 gti. I might see if I can hide the amp under boot floor, or under dash for cleaner look and no probs if I need to lay down the back seats (amp was mounted to seat-back).

Just wire it so the sub can be removed in a few seconds. Then you can enjoy the bass for the 95% of the time you don't need the boot space. I have my amp mounted on the sub but you could just run the cabling from the amp to the sub with connectors.

[mgrobins]

Thanks for the response guys.

When I mentioned Roll-off I wasn't talking about cross-over topology or function but a "room curve" - or in this case a bass curve designed to protect the stock speakers as volume increases. In vehicles it presents as a non-linear increase in bass frequencies as volume increases c.f mid'/upper freq's (both in db and also considering actual loudness and perception by the human ear). The use of the L2Ci as demo'ed in the linked thread is to restore that linearity or an alternative custom curve so that bass presence is consistent as volume is raised.

Interesting comment regarding the lack of cross-overs. I thought a passive cross-over was in use. The stock head unit for us in Australia has the amp mounted in the glove box unit behind where the SD card reader is. I hadn't checked the wiring in detail yet to learn how it links to the head unit or what speaker level signals are output.

With the back floor in the 'upper' slot I should have enough room for the pioneer sub to be hidden away permanently. Still have to make a choice as to going this path vs building my own box (custom MDF and fiberglass).

[Matt P]

The other option you could approach is something like this

MATCH by Audiotec Fischer

I have the PP52DSP and one of their subwoofers. If i had my time over again, i'd still get one of the amplifiers but would do my own sub/amp off of the PP52DSP.

Not a cheap setup, but it will all "plug and play" with no wire cutting etc..

[mgrobins]

THanks Matt,

that setup certainly looks like it would be worth investigating. I do agree the subs would not be ideal for me as I don't want to lose the spare and the round one is about 30mm too high I think.

I'm certain though that building a passive sub enclosure would be quite achievable - especially if I go a sealed box and avoid the port tuning.

THe active sub like the pioneer would feel like an over-spend I think as it's active and I'd be doubling up on channels.

May I ask where did you have the amp installed in the vehicle - passenger footwell area or elsewhere? Just wondering how things go with a dongle (I assume they have one that inserts between existing connectors to split the wires off from the stock unit and then back to the speakers?)

Importantly, does it sound better than the stock Au install?

Are you willing to divulge approx. cost for the change over?

[Matt P]

My setup is the amp as above, all wiring looms to suit the GTI 7 and a PP8E-Q subwoofer, all pro installed by a shop for $1400. Amp is under the passengers seat.

sound is significantly better even without changing speakers. Next step is to have my rainbow germanium components fitted and i expect to go up another level again

[mgrobins]

I think there is a 4 ch version of the amp you have which has a sub out as well. I'd consider the amp and perhaps the Pioneer Sub (WX710A) with its integrated amp to go under the boot floor.

Just need to see where I can source parts I guess .

[Matt P]

see if you can have a listen to the pioneer sub first. I found most of those super tiny ones a bit boomy for my liking. OK if its in the boot, but if they're in the cabin it might not sound the greatest. If you can, i'd still load a 10" into the boot in a hidden enclosure or something.

Your thread has made me search around again, one of the things my installer told me is that the tweeters for my rainbows were too deep. I dont want to start having to play with custom mounts so i started looking at the GLADEN ONE 165 GOLF 7-SQX. From what i can see, i can probably pick up a set for $500 and potentially self install (although not looking forward to pulling the a-pillars off).