I too asked Pez and he said it would add a lot of weight to the fair, and becasue of the environment it's in it wouldn't do much when riding the bike. If you're only listening to it with the motor off then go for it. Most of use have aftermarket exhaust that can be loud, and when cruising down the highway wind noise becomes a big factor too.

 

Not so my friend

The best way to look at it, is like this: Breathing > Inhale - Exhale

The speaker (as we see it) is a cone that pushes air waves toward our ears. Those air waves are what our ears perceive as "sound"...well, technically it is sound, but sound is made of several thousand different frequencies, but I digress..
In order for the cone to move out, it has to move back at an almost equal distance. <remember, inhale - exhale>
This motion creates a sine wave. Sine waves are made of a positive motion and a negative <inhale - exhale>; we are hearing the different changes in air pressure.
Now, if you are sitting in front of a speaker and it's moving, then air is being pushed in your direction. At the same time, air on the back side of the speaker is doing the same thing, just opposite timing of the front, so remembering that sound is air that is moving, this means that sound is coming out of the back of the speaker as well.
The next time you have your fairing off, crank up some tunes and stand behind the speaker. I'll bet you a dollar to a doughnut that you'll hear the music...know why? Because you're listening to a speaker do it's thing...just 180° out of phase from the front.

In comes deadening material. There are two different front runners.

Dynamat - Is a deadener, but not as much absorbtion as the Dynaxorb. In it's non-porous state, Dynamat is best used to stabilize a surface.
Have you ever come to a stop light and have the opportunity to sit next to a car with a subwoofer in the trunk? If you hear rattling, then you are listening to body panels/parts being moved by those air waves. Dynamat adds a layer of stability to those body panels and decreases the flex of said panels, thereby decreasing what we hear sitting next to the unfortunate person that wasted their money on all that power.
Another thing Dynamat does, is add a layer of protection (deadener) to prevent the sound waves from penetrating the protected surface or getting all the way through the Dynamat barrier. It's not 100% effective, but it's significantly closer than without it.
Conclusion - Dyanamat on the inside of the outer fairing will add stability to the flexible body panel, that would otherwise be vulnerable to movement due to air pressure.
If there werent so many obstructions on it, then putting it on the inside of the inner fairing would suffice as well!

Dynaxorb - Is a porous material made to absorb sound waves. In our case, it absorbs sound (aka "back waves") in an attempt to prevent them from reverberating and interfering with the opposite movement of the cone. Have you ever been in a recording booth, or a recording studio? These environments are full of that egg crate looking foam, which is there to absorb reverberating sound waves...same thing that Dynaxorb does in our environment!

The more dead the environment that houses the speaker = less reverberation = tighter, cleaner sound waves and at the same time, the speaker is not having to work as hard, which is referred to as "efficiency".

Now to address the comment about the fairing not being fully enclosed, so the waves will go wherever they want...that's true...however, if there is absorbant material behind the speaker to catch those back waves, then there is less sound to go wherever it wants. There doesn't need to be a perfectly sealed environment in order for you to kill back waves. It helps, big time, but it's not necessary.

Inhale - Exhale

So, do you absolutely need to deaden your fairing; NO!
Will it make a dramatic difference if you know what you're listening for, uhh YEAH!
It may sound like a crock to you, but believe it or not it does make a difference.

Sorry for the long winded explanation, but audio and acoustics is not only my passion, it's my profession.
Admittedly, I have absolutely no clue what I'm doing when it comes to how my scooter works mechanically, which is why I'm here...to absorb some of the wisdom of those here, that are willing to teach me.
If you took this post as a dig against you, or an attempt to try to outsmart you, then I humbly apologize, as that is not my intention.
I just want to enlighten those that may not know (or care) as much about this particular subject as I do

 

to answer your question in short...no..lol

to get the best response from your speakers, you woulld have to completely seal off you inner and outer fairing, then, by adding the deadoning material, you may see a slight difference... but with a trained ear.. i would be hard to recognize, unless you are talking about very high end equipment...

again, no! invest in some very nice highs, and get that almighty arc amp for firecap...lol...

 

I really appreciate you taking the time to share your knowledge with us on this topic.

If you don't I'd like to pick your brain a little more...

So I've spent quite a bit upgrading speakers and amp on my Street Glide. I will be the first to say that is MUCH better then it was when completely stock. In addition to the amp and the speakers, I do have the dynamat squares in my fairing.

That being said...

I've noticed I get a lot less distortion at loud volumes when the bike is standing still vs when the when the bike is moving at highway speeds (70-85 MPH). I know there are a lot of outside forces in play when the bike is moving. But given your explanation above, I can't help but wonder if a lot of is it air pushing against the back of the speakers when going down the road.

I know the bat wing is not a totally air tight enclosure, but if air were making blowing into the bottom of the fairining, that might explain some of my "problem"

Thoughts?

 

Save your money for something else. That stuff makes absolutely no difference whatsoever. It WILL make your fairing heavier, though. I got sucked into that Dynamat/Dynaxorb issue and spent the money. I don't have a decibel meter but I can tell you there was NO improvement in the quality of the sound or volume. At first I thought there was, but after removing it (the Dynamat) I think the sound is actually better now that it's gone. I just got caught up in the "I spent lots of money so it HAS to sound better" thing.
Don't get me wrong. Dynamat/Dynaxorb is a great product (albeit spendy) when used for what it is designed. I've used it in my hotrod,etc. and it works great. It just makes no difference inside these fairings unless you've got a rattle you want to suppress.

 

You are correct in that the fairing is not a sealed environment, but I honestly couldn't tell you if air flow (while in motion) plays a factor in the distortion you're hearing.
My first thought would be to ask if you are 100% sure that you are comparing the same sound pressure levels...meaning are you sure that you're comparing the same volume sitting still, than you are while you're riding and hearing the distortion?

 

What I'm getting from this is....technically it will provide better sound under specific conditions. But the improvement is not worth the trouble, cost, and added weight.

 

I believe so. I'm using the stock radio and it does have a sound bar on it. So I set it to the exact same spot each time.

The problem could very well be the air that blows up behind the fairing from the bottom. It's not something that bugs me while I ride, (in fact, I can't think of a time I've felt it...) But I know there are several thread on here where people complained about the air flow that came from the ground up while moving... So perhaps that's the cause of the problem.

One other thing that could greatly impact the flow is that I use a short 6" windshield. So the "bubble" I sit in is really not all that tall...

 

basically... yes, the stuff is best used on metal, anyway... where the metal will flex/vibrate and the vibration sort of translates into sound, which could potentially cause more distortion, vs. plastic, not so much...

 

I really don't think it makes much of a difference.
I think the speaker enclosures would work better.