[SoundHound75]

Hello,

I have just installed my 2 woofers in my G31 with option S688A. I will explain the issues I encountered and how I overcame them. At the end, I will tell you my thoughts on the results .

Step 1: Removing the seats, that was easy, just remove the clips on the rails and loosen the 4 large Torx bolts.


Step 2: Position the seats as far back as possible and the backrest as far forward as possible, then tilt the entire seat back without disconnecting the connectors from the seat.

Step 3: Unscrew the cover of the woofer by loosening 4 Torx screws.

Step 4: Remove the original BMW woofers by loosening 4 Torx screws, use a flathead screwdriver to gently lift the edge of the woofer, and then you can easily remove it by disconnecting the cable. But for now, I left the connection intact.

Step 5: Here is where the first problem started. I had found on the internet that the amplifier is located on the left rear side of the car. I looked up the pinout of the amplifier, but the information I found was not correct. So, I started measuring all the thick cables for 4-8 Ohms and applied a 150 Hz sine wave to those cables. The thick cables arriving at the amplifier on the left rear are from the side panels! I couldn't find the woofers. Then, after some searching, I discovered that there is another amplifier behind the amplifier, dedicated solely to the woofer control.
After a few hours of struggling to try to remove the left side panels for easy access to that amp, I gave up and, based on the color code, started cutting the wires that I hoped were from the woofers, then stripped the wires, connected a function generator, and voila! Sound came from the woofers under the seats.

Step 6: Then, I connected the outputs of the original amplifier to the high voltage inputs ch3 and ch4 of my ESX QM500.4 amplifier. Ch3 and 4 have a bandpass filter suitable for woofer control.

Step 7: I connected the speaker outputs of ch3 and ch4 to the original wires going to the woofer.

Step 8: I connected the power supply of the amplifier to the main battery in the middle of the car. Don't forget to place the fuse as close as possible to the battery. First, loosen the GND nut of the battery cable, then connect the GND of the amplifier and screw the GND nut back securely. Then, disconnect the +12V from the battery, connect the 12V of the amplifier, and screw the nut back tightly.

Step 9: Disconnect the original woofers and connect the new Earthquake woofers. I do this via soldering to ensure no loose connections. The original air seal works fine to seal the woofer, and I partially filled the part where the wires come out with putty and made it airtight with hot glue.

Step 10: There is a thick putty under the carpet that I partially removed because the new woofer has a larger excursion than the original. By removing the putty, the new woofer doesn't have the chance to hit anything at high volumes.

Step 11: Secure both woofers firmly with the 4 Torx screws.

Step 12: Time for a test! Start with level setting of ch3 and 4 at minimum, middle control at 10Hz, and right control at 5kHz, X-Over LP/BP, AUTO turn-on on DC, and input level button on HIGH. I fired up some songs on Spotify, and voila! Only high tones were coming out, and the sound was terrible. It turned out that the amplifier manual was incomplete and forgot to mention that auto turn on only works on ch1. So, I paralleled the high-level input of ch1 with ch3, and voila, there was bass!

Step 13: Adjusting the levels, ch3 and ch4 levels had to be slightly higher than minimum, LPF set to +/- 25Hz, HPF set to +/- 300Hz.

Result:
There is clearly a deeper and more powerful bass, but I can't say the sound is better; it sounds more bombastic and less full than before. For now, I am not satisfied, and I hope that there are members who can provide tips on how to achieve a full, powerfull sound.


Thank you.

[SoundHound75]

Today, I conducted some additional tests, and it turns out that some music sounds fantastic while others don't.

The songs that sound great include Chris Isaak's "Wicked Game" and Chris Brown's "Gimme That." On the other hand, songs like Joe Cocker's "You Can Leave Your Hat On" and tracks by The Beatles sound terrible.

I believe this discrepancy can be explained by what I mentioned earlier – a portion of the frequency range is dampened. Some songs don't rely on this muted range and therefore sound good.

To investigate further, I downloaded a Tone Generator app from the App Store. Using it, I discovered that frequencies below 100 Hz are significantly louder than the range between 200 Hz and 1 kHz. The range from 100 Hz to 200 Hz is noticeably lower in volume, with the lowest point at 125 Hz.

My crossover bandwidth is set from 10 Hz to 1 kHz. Turning off the crossover, as the Harman Kardon amplifier already outputs filtered results (high-level signals to the original woofers), makes the sound even worse. However, enabling and adjusting the amplifier's crossover frequencies improves the sound.

Now, I'm wondering how I can make all music sound good. Would using a DSP (Digital Signal Processor) help? I'm aware that DSP amplifiers can be expensive. Is there a DSP that can modify the high-level output signals from the original HK amplifier to improve the sound quality?

Maybe adding something like this : https://rockfordfosgate.com/products/details/dsr1/

[WretchedRefuse]

Originally Posted by SoundHound75

T... frequencies below 100 Hz are significantly louder than the range between 200 Hz and 1 kHz. The range from 100 Hz to 200 Hz is noticeably lower in volume, with the lowest point at 125 Hz... Would using a DSP (Digital Signal Processor) help? I'm aware that DSP amplifiers can be expensive. Is there a DSP that can modify the high-level output signals from the original HK amplifier to improve the sound quality?
...

It sounds like your problem is equalization, not DSP. Either your new amp is putting out more power than the stock amp, your new subs are more efficient than stock, or both. Is it possible to reduce the output level from your amp, perhaps by playing with the input level control? You could also try a multi-band equalizer to tune the sound to your preferences.

[SoundHound75]

DSP provides me with a multiband equalizer. However, I find that the built-in HK (Harman Kardon) equalizer in my system lacks the sufficient number of bands to fine-tune the audio to my liking.
Therefore, I am considering purchasing a replacement DSP amplifier for my HK system. This would allow me to have complete control over all the speakers and access a broader range of equalizer settings for more precise adjustments. Do you have any specific type of equalizer in mind that you would recommend?