How to Improve OE Sub Bass Quality and Eliminate Vibrations

You guys are knocking it out of the park with this.

I did the subwoofer mod and it’s a nice improvement over the stock configuration. For the record I did use speaker grill cloth on the ports with no ill effects for those who may wonder.

I’ve been thinking about going further with the doors and doing more work on the cargo area, but since this isn’t my primary car, I’m on the fence about the work/reward ratio.

Nonetheless I really appreciate all of the contributions to this. Nice example of community effort and sharing.

supradupra said:

i wonder how much labor a stereo shop would charge if i printed out your install and asked them to do it......and perhaps dynomat and seal some stuff while they are in there.....like what ball park should something like this be from a shop?

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Labor shouldnt be that long but it really depends if they want to charge you a "Supra tax" definitely not difficult for anyone to do. I went back thru and laid some dyno mat down inside the rear hatch and near the battery. I am going to move onto the doors this weekend or next if i am free. I just need to find the instructions how how to disassemble the door.

2k20HTownMKV said:

.... I just need to find the instructions how how to disassemble the door.

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Door removal instructions:

Applied some Dynamat to cargo area floor to eliminate any further vibrations and reduce road noise...

I always try to use a dynamat (CLD) type material against metal frame surfaces to reduce vibrations and road noise...Noico foam is typically applied over CLD to suppress noise even further...

As far as applying Dynamat (CLD) to the rear cargo floor, I wouldn't say it made a "huge" difference....That said, it definitely made a difference in reducing road noise and helped to further reduce any residual low bass vibrational noise that can occur as your increase volume past ~60%...I find that the cleaner the sound (noise and vibration free) the greater I can increase volume (to a point)...Past 65~75% volume I'm finding that the amp is the limiting factor when it comes to distortions...



I also applied a few strips of Noico foam (lighter gray sections shown below) to some sections of the cargo floor panel that did not have any insulating material added...

Finally found the time to do this mod today. My wife sews a lot, so luckily for me we had all the supplies here at the house. Took me about 30 minutes, start to finish. The entire system sounds much better now! Thanks again for the write up!

Fast_Freddie said:

Finally found the time to do this mod today. My wife sews a lot, so luckily for me we had all the supplies here at the house. Took me about 30 minutes, start to finish. The entire system sounds much better now! Thanks again for the write up!

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Glad to hear it went smoothly ... crank up the music and enjoy!

Got a chance to do it thanks to Tom's guide. Now just need to Dynamat the floor and add a mesh around the hole.

For those wanting to add CLD / Dynamat. I pulled the car somewhat apart and the largest unreinforced areas without dampening or reinforcement were the roof and rear quarters. The doors have a mass damper on them and most of the floor and rear deck have reinforcing ribs or factory dampening. Dynamat helps on reinforced areas, but if you already are making the investment, getting to those areas isn’t difficult compared to the floor and firewall.

Summary and Final Thoughts:

It's been about a month and a half now since I made all the improvements outlined in the first post of this thread...I still remain extremely pleased with the results and currently do not feel the need to replace or upgrade the subwoofer system...

Surprisingly, the Harmon Kardon 8" Subs in the Supra are actually very good speakers once you correct some very basic design issues that were overlooked by Toyota... Without ports added, the bass exhaust energy was literally trapped behind the rear panel which created quite of bit of vibrational noise and also muddied bass response...

Adding exhaust ports to the rear panel along with lining the enclosure walls with wadding and insulating the space behind the narrow rear panel, essentially lowered the Q (damping effects) and resulted in a flatter / clearer bass response...The Bass is now deeper, punchier, and far less distorted and eliminated much of the vibrational noise heard...

For anyone considering installing direct replacement subwoofers as a knee-jerk reaction to improving sound distortions, vibrations, and rattles, these basic improvements should be seriously considered before replacing them...

And a big thanks to those that contributed along the way.... This was a fun and rewarding project!

stacyoz said:

@tada
I finally got all the parts to implement tada's subwoofer fix and just want to add an additional detail.

To modify the narrow rear panel, use the following drawing;

In the drawing you will note that the deck lid that covers the batter covers the bottom 1/2in of the panel. This is only important in locating the holes for the subwoofer ports.. I located the subwoofer port closer to the top of the panel so I would have about an inch clearance between the port and the deck lid. The rear narrow panel can take up to a 2.5in subwoofer trim piece, since the trim piece has a lip/rim.

I covered the narrow panel (carpet side) with blue tape, marked the two locations per drawing, and used a 2in hole saw to cut the panel. I used JB Plastiweld to secure the subwoofer port trim pieces to the narrow rear panel. This insures that the trim pieces will not pop out or vibrate.

This was a great DIY project which vastly improved the BASS. Thanks @Tada for posting this thread!

View attachment 26845

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Nice write up and detailed port location drawing...I added the drawing to the original post

Once I have the catless DP and tune done on my car, this is my next step. Thank you VERY much for this write up.

JakeM said:

Once I have the catless DP and tune done on my car, this is my next step. Thank you VERY much for this write up.

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I think you'll find it's a fairly straight forward DIY and you'll be very pleased with the results...

Finally got around to starting this mod. I tweaked it a little bit since I had the rear gutted last week. Decided to do both sound dampening and foam installation.

Stage 1: Adding sound dampening to: (1) Subwoofer Enclosure (2) Sub Port (3) Rear Lower Deck (4) Rear Trunk Latch Wall

(1) Subwoofer Enclusure: Dampened inside and outside to help cut down on vibrations and also help reinforcing and sealing the enclosure

(2) Sub Port:

Dampened all the inner walls of the sub port. Even added two sheets to the flat top side. You can't see it in the picture but I have circled the area in red.

This is a large piece of flat metal that gets alot of frequencies and air flow sent to it so I doubled up here with two sheets of sound deadening. There is a divider wall that is made of plastic that also got some dampening material. I made sure to not cover up any factory bolts in case access was needed to them at a later date.

TIP: Wear gloves when working in this area as it is tight and you can easily scrape your hand on the metal. You can also use pry tool to help lay the deadening down.