Nostromo

Ah, so you're saying the B9 had 4 wires? It's trying to drive 2 voice coils at 8ohms a piece?

James Cole

Yes exactly, B8 had only two.

Nostromo

Found a JL shallow mount sub that is dual 8: 10TW3-D8

But looks mostly discontinued. A couple on ebay for $300

James Cole

I will let you know a little secret.

I had a 17 S3 with B&O and MIB2 Amplifier...

The sub the car had was 8 inch DVC 8ohm and made a lot of mechanical noises (rattles) at mid volumes, so I replaced it with an 8 inch kicker free air DVC 4ohm DVC...

Did the amp blew up? NO it worked perfectly and had more power and bass extension without the rattles.

The amp ran a bit warmer and was constantly monitored by me (its under the seat for the S3), but I decided to go a step further and contacted a guy that fixes this kinds of amps specialized Bose and B&O that comes with audi vehicles, he told me that running 4ohms instead of 8ohms was not a problem since the resistors (or circuits) could handle a 2.8ohm load, that gave me peace of mind + there are some B8 owners running at 4ohm load their subs with no apparent issues.

I might give it a show... OEM bass is adequate but the rattles kill it for me...

Hope this is helpful to you.

JC

Nostromo

That's very helpful! I do know those threads about the guys running a 4ohm load... it does make me slightly nervous though.

I shoved some foam between the deck and the card, solved a lot of rattles for a quick fix. But subwoofer still sounds like a boomy mess. Not tight and seems to struggle to get those low tones out.

Bobby Kinstle

Sorry for the necropost but I've been exploring this exact problem. I did some math and I've come to the following conclusions:

Stock 8ohm coil, lets assume 100W per coil is the amp's maximum output. This means each channel is driven at about 28V at 3.5A average current. Most class D sub amps are 90% efficient at high output levels so this means each channel should produce at least 9.2W of heat, 18.4W total for both channels. Now lets swap in our 4ohm DVC sub and see what happens when we drive it at the same power of 100W per coil. Voltage drops to 20V, current increases to 5A, and heat output increases to 10W per channel. This is only 1.6W total heat increase. Given the currents involved here are generally small I'm not terribly worried about blowing a fuse or overloading any wires and lets be clear, we are talking about a ridiculous loudness level in these examples. With only 8% increase in heat at equivalent listening levels (SPL efficiencies not withstanding) I say go ahead and do it. Even running the amp at full power into a 4ohm load would be 7.5A of current going to the speaker and only add 2 more watts of heat on top of the equivalent load (or 3.6W on top of the factory configuration at absolute maximum theoretical output levels)

About the only thing I can think of going wrong are over-saturating an inductor in the output path (would sound bad but not break anything), or perhaps blowing the fuse supplying the amp. If you want a boomin system, add an amp. Otherwise, drop in a good 4ohm DVC sub and go to town. I've also been doing T/S calculations on subwoofers and I think the best fit is the Kicker 44CWCD104 followed by the Polk Audio DB 1042 DVC. I do not think the JL TW3 will perform well below 40Hz and when I asked JL about it they gave me a rather generic "Don't do it" response.

markjohnsonii

Our A4 B9 uses the Audi 8W0-035-465 Amplifier. I can't find anything on the technical aspects of it so if anyone's got more info on it, please share!

jschrauwen

I've been using a JL10W0-4 for 3 years. Plenty of umph from the oem system to meet my needs.

Bobby Kinstle

I ended up putting a Kicker CompC 10 DVC 4 ohm into mine and the factory amp powers it without difficulty or any signs of overheating. I'm still going to add an amp because I also replaced the front door woofers and now the sub and woofers overlap in the 45-70hz range and the easiest way to solve the problem is with an amp with a low pass filter.

https://www.audiworld.com/forums/s4-...e-b-o-2972479/