Acoustics - 80Hz loss in car!

Captain Jack Sparrow

Jul 1, 2007
Reaction score
Recently, I replaced my subwoofer amplifier to fix an unrelated issue, but this happened even with the previous amplifier. I wrongly believed that using a more powerful subwoofer amplifier, setting the crossover higher then 80Hz, and pumping more power would address this. I learned the hard way that sadly, bigger isn't always better. It didn't help, I guess my subwoofer simply isn't designed to do this. In fact, it muddied the vehicle's natural frequency response, and somehow made it sound even worse.

There's around an 80Hz cut when sitting in the driver or passenger seats. Although I appreciate that the cockpit of a vehicle is not the ideal acoustic environment, this still doesn't seem to be normal to me. I'd expect vehicle manufacturers to accommodate this, as 80-120Hz is an important frequency range for music (especially 70s - early 2000s music).

Audio equipment details
Below is the equipment in detail.

VehicleVolkswagen Polo 2003Type 9N (Mk 4), 5 doors
Head unit/stereoOEM VW 'Blaupunkt' Gamma V BVX radio/cassettePart number 6N0 035 186, 4 x 17W DIN at 4 Ohms, with pre-amp output (this SKU is designed for Polo Mk3 1995-2002)
Front speakers (L/R)OEM VW 'D&M PSS' 6.5" bass drivers, door speakersPart number 6Q0 035 411 A, 4 Ohms, 20W each speaker (OEM tweeters are part of the A pillar trim)
Rear speakers (L/R)OEM VW 'Blaupunkt' 6.5" full-range - dual cone, door speakersPart number 1C0 035 411 M, 4 Ohms, 25W each speaker (OEM 'tweeters' are part of the rear door cards, but these are useless. Full-range speakers were specifically chosen to compensate for this)
Subwoofer amplifierSony XM-GS100600W RMS (2 Ohms, 10-300Hz)
Subwoofer driverDayton Audio RSS265HO-44Sealed enclosure, tuned to 50Hz. Dual coil driver - 2 x 4 Ohm, connected in parallel for 2 Ohm load (see above)
Audio interfaceParrot MKi 9200Consolidates Bluetooth, 3.5mm line-in/aux and HDMI audio inputs via the head unit's CD changer analog input
Test audioRonan Hardiman - Lord Of The DanceWell-known composition for Michael Flatley's 'Lord of the Dance' performance. I chose this instrumental track because it has a balance of sub bass, mid-range and high frequencies. When testing, I use a lossless 16 bit, 44.1KHz track from Qobuz, thankfully the dynamic range hasn't been crushed. YouTube compressed version here: external link, YouTube

I admit that I don't know much about acoustics, so my theories are based solely on basic electronics and physics.

1. Your OEM VW tape deck stereo sucks
My stereo is the original OEM cassette player (yes, it's a tape deck). Initially, I thought it was caused by the stereo having a hard-coded OEM EQ curve. To check this, I took the stereo into the house and powered it from a spare 12V car battery. Then I connected it to the home theater speakers, so it was driving them directly. There wasn't any 80Hz loss, it sounded awesome, as it does with the regular home theater amplifier. I guess having bigger space minimizes frequency response anomalies.

2. You didn't install 'Dynamat' soundproofing in the doors
I've listened to an equivalent vehicle (VW Golf Mk4) that was fitted with 'Dynamat' in all 4 doors. It still suffered an 80Hz loss, although it boosted the sub 80Hz frequencies (this vehicle did not have a subwoofer). This was enough to satisfy the customer, but personally, I felt that having a subwoofer makes this redundant, and reduces load on the head unit's built-in amplifier. Maybe I'll get hate for this, but 'Dynamat' seems like snake oil to me, at least in VW cars.

3. The audio interface is applying its own EQ
I bypassed the audio interface by playing a FLAC file which was burned losslessly to a CD-RW disc. There was still an 80Hz loss, and I verified that the audio on the burned CD can correctly reproduce these frequencies.

4. The front and rear speakers are conflicting with each other
If you've read this far, wow. I think this is the most likely cause of the 80Hz loss. The eagle-eyed will have noticed that the front and rear speakers are not the same part number, the rear speakers are dual cone, full-range speakers. Originally, my car didn't have any rear door speakers installed. So I had to grab some replacement rear door cards from the scrapyard, these had integrated, non-replaceable 'tweeters'. They were terrible, and barely produced any usable sound. I specifically chose dual cone, full-range door speakers as a futile attempt to fix this. But maybe they're doing more harm than good, should I consider replacing the rear speakers with the same models as the front speakers?

So how should I troubleshoot this properly? Will I need some kind of professional audio spectogram device?
Last edited:

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question