# Foam Rings Around Door Speakers?



## xt577 (Apr 19, 2011)

A shop owner I know has been touting the use of foam rings that go around the circumference of woofers and sit between the inner door skin and the door panel. He is saying this improves sound quality by minimizing reverberations in the doors.

What do people think about this?


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## 94VG30DE (Nov 28, 2007)

The owner is correct, although this technique doesn't seem to be very popular for the aftermarket. It is almost always used from OEM though. Keeping the air moving straight through the door card instead of bouncing around between the inner door skin (metal) and door card (plastic, melanine, misc trash) greatly reduces vibrations in the door card. Doesn't 100% fix everything though, so you still generally want to deaden both surfaces somehow. 

But a properly sealed and aligned foam ring should go a long way...


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## Aaron'z 2.5RS/WRX (Oct 24, 2007)

That^^^


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## HondAudio (Oct 19, 2006)

94VG30DE said:


> The owner is correct, although this technique doesn't seem to be very popular for the aftermarket. It is almost always used from OEM though. Keeping the air moving straight through the door card instead of bouncing around between the inner door skin (metal) and door card (plastic, melanine, misc trash) greatly reduces vibrations in the door card. Doesn't 100% fix everything though, so you still generally want to deaden both surfaces somehow.
> 
> But a properly sealed and aligned foam ring should go a long way...


My door cards have a plastic ring that protrudes into the cavity between it and the inner door skin, and this ring couples to a thin (~1/4") circle of foam around the factory speaker. There isn't much in the way of vibration-deadening, but the pair serve as a conduit to direct the speaker's energy into a "tunnel" and through the grill.


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## 94VG30DE (Nov 28, 2007)

HondAudio said:


> [...] but the pair serve as a conduit to direct the speaker's energy into a "tunnel" and through the grill.


^ That is the effect you are trying to recreate. I think the reason it isn't often done in the aftermarket is because it's difficult to implement without some un-common measuring and marking techniques. 

I believe I have seen some commentary on best-practices for getting an aftermarket baffle to line up with the protruding plastic ring you mention, but it's kind of an ad hoc process for each car and baffle.


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## xt577 (Apr 19, 2011)

HondAudio said:


> There isn't much in the way of vibration-deadening, but the pair serve as a conduit to direct the speaker's energy into a "tunnel" and through the grill.


Yes, foam rings I was describing are flimsy and do nothing for vibration dampening of audible panel resonance. The technique is used to channel soundwaves into the cabin, and prevent them from becoming lost in the door cavity and adding unwanted harmonics.


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## 94VG30DE (Nov 28, 2007)

xt577 said:


> Yes, foam rings I was describing are flimsy and do nothing for vibration dampening of audible panel resonance. The technique is used to channel soundwaves into the cabin, and prevent them from becoming lost in the door cavity and adding unwanted harmonics.


I'm a little confused by this statement. If you can keep the air being moved by the speaker out of the door card, then that doesn't _dampen _panel resonance, it _prevents _it.


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## xt577 (Apr 19, 2011)

94VG30DE said:


> I'm a little confused by this statement. If you can keep the air being moved by the speaker out of the door card, then that doesn't _dampen _panel resonance, it _prevents _it.


A little foam might help reduce higher frequency harmonics in the door, but it won't stop lower frequencies from being transferred directly into the door (through speaker attachment points) and producing door skin and door card vibration. Also, what I'm discussing isn't a perfect seal by any means and air will still be moving in front of and behind the inner skin.


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## Van Wilder (Jun 6, 2011)

Without the foam being sandwiched between the driver and the door panel I don't see how you could get any type of major benefit. In the past I have used a thick foam gasket around the woofer that meets the door panel to help with panel vibrations simply by adding slight pressure to the rear of the panel... 

I think you would have to do a side by side comparison to get an answer on this one and unfortunately I would believe it to be very application specific...


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## Randyman... (Oct 7, 2012)

My assumption was the car designers/engineers use foam to couple the speaker to the door panel's opening because a) foam will flex and allow for some tolerance in fit while still "sealing" the speaker to the opening; and b) foam would not reflect upper-mids and highs like a solid ABS type material would (creating some nasty comb filtering in that region - like playing the speaker into a very short pipe - not quite a horn).

I'd also imagine once you consider the stock plastic speaker grille itself is likely reflecting a good deal of high-frequencies back into the cavity between speaker and grille, adding a solid cylinder as a coupler has potential to sound really nasty IMO. You want some way to keep the speaker directly coupled to the listening environment - and not to the area between the speaker and door-panel-opening - so foam seems like the best compromise...


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## Van Wilder (Jun 6, 2011)

There are going to be a handful of theories here but in my opinion it would prove to be nothing more than a placebo in most applications...


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## 94VG30DE (Nov 28, 2007)

xt577 said:


> A little foam might help reduce higher frequency harmonics in the door, but it won't stop lower frequencies from being transferred directly into the door (through speaker attachment points) and producing door skin and door card vibration. Also, what I'm discussing isn't a perfect seal by any means and air will still be moving in front of and behind the inner skin.


It doesn't have to be a perfect seal, but the better the seal, the more effective it will be. 
There is two ways vibration can be "induced" to the door card in this instance. 1. Direct contact (speaker basket to door skin) and 2. indirect contact through media (in this case air). 
The foam ring doesn't help with 1, but it does help greatly with two. A speaker is just moving air, there is no magic physics going on. Keep air out of the spot between the door card and door skin, and you have a happier day. 



Van Wilder said:


> In the past I have used a thick foam gasket around the woofer that meets the door panel to help with panel vibrations simply by adding slight pressure to the rear of the panel...


This effectively works to "deaden" the door, because you are making it less prone to vibration through pre-loading. A lot of people do this technique around the "Christmas-tree" clips that hold the door card to the door skin for the same reason. 



Randyman... said:


> My assumption was the car designers/engineers use foam to couple the speaker to the door panel's opening because a) foam will flex and allow for some tolerance in fit while still "sealing" the speaker to the opening; and b) foam would not reflect upper-mids and highs like a solid ABS type material would (creating some nasty comb filtering in that region - like playing the speaker into a very short pipe - not quite a horn).


A. is definitely correct. You will notice on a lot of cars, the foam ring is not perfectly concentric with the speaker basket, but still seals because it's a wide strip. Foam (automatically-adjusting media to expand to correct height) creates a variable seal to mate with the door card no matter where it is sitting within it's tolerance "range". 
B. is not really noticeable (outside of the baffle step behavior if you are playing higher frequencies out of that same speaker), but I like where your head's at. For the air space/restriction in front of a woofer to have a significant effect, generally you would have to have around 2/3 of the Sd covered. An open "tube" bigger than the Sd would never compress air, so it has no horn/bandpass behavior. It is good to think about that though. 



Van Wilder said:


> There are going to be a handful of theories here but in my opinion it would prove to be nothing more than a placebo in most applications...


Do you really think OEMs spend the money on the part for a "placebo effect" that no one would ever see?


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