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How to sound deaden car doors

How To Reduce Sound In Your Car By Sound Deadening Your Wheel Wells

An excerpt from our Reference Information & Guide page

Wheel Well Sound Proofing

Added 11/13/2022

Supplies needed

   . ResoNix CLD Squares

   . ResoNix Fiber Mat 25 and/or 45 (depends on how much space you have and what you can fit)

   . Optional and preferred: ResoNix Barrier

 Note: ResoNix Fiber Mat is perfectly fine in this location and exposed to the elements. It will not hold water, it will not degrade, it will not grow mold or mildew. This is the very same material that is used in these locations by car manufacturers such as Mercedes.

Wheel wells are one of the most offensive sources of noise in a vehicle. Below is what I did in my own vehicle, a 2019 Volvo S60 R Design. Please note, that the exact approach will be different on every vehicle. This can be due to how much room there is to work with, moving parts, or more. Please, use your best judgement. We have   

First up is obviously removing the wheels and wheel liners. During this process you are going to want to evaluate what you can fit, what parts of the body of the vehicle are going to need the most attention, etc. Remember, resonant panels will need it most. Its crude, but a simple knock with your knuckle will let you know what parts of the body need treatment. More on this part below, but on this particular vehicle, the body was relatively non-resonant, and the wiper fluid reservoir blocked a lot of access on the drivers side. Due to this being planned as a few hour-long project and was recovering from a medical procedure, I did not decide to remove the reservoir and instead worked around it. While getting a closer look, I also noticed that I had gained access to the back side of the fender and the airspace behind it. I decided to also apply ResoNix CLD Squares to the back of the fender and apply ResoNix Fiber Mat 45 on top to fill the airspace. 

Next up, treating the wheel liners with ResoNix CLD Squares. Before you do anything, you should clean the liner with isopropyl alcohol thoroughly. In some cases, it is even recommended to sand the plastic with a low-grit paper to encourage the best adhesion possible. In my case, I didn’t feel it was necessary considering how well the ResoNix CLD Squares adhere to pretty much any material and surface you will find in a car. 

Once you have the panel prepped, apply full coverage of ResoNix CLD Squares. In the case of doing wheel liners, I wouldn’t recommend less since the liners are mostly decoupled from the body of the vehicle, so not only do you get resonance control of the plastic liners, but it also acts as a noise barrier. Remember, treat all panels in the largest pieces of CLD Squares possible.  

Note: We will only be treating the back side of the liner. Leave the exposed side untouched.

Optional: if you have the time and budget, I would also suggest a full coverage layer of ResoNix Barrier over the layer of CLD Squares for further noise blocking. In my case, I did not add this as I was restricted on time, and was recovering from a medical procedure and couldn’t afford the even heavier lifting that Barrier would impose.

Once the liner is fully treated with ResoNix CLD Squares, we can start our full coverage application of Fiber Mat 45. Remember, when it comes to absorption, more is merrier. Full coverage is highly recommended, and if you can fit, the more layers the better. Be sure to take note of suspension components, wiring, or any other parts of the car that may need to be worked around.

 Once the wheel liner is covered, that’s it. You’re nearly done and its almost time to re-install it. Before re-installing it, you should explore treating the body of the car with ResoNix CLD Squares. Once that is done, re-install the liner and enjoy 🙂

How To Sound Deaden Car Doors - The Right Way!

Here at ResoNix Sound Solutions, it’s no secret that end-result performance is our main priority. It’s also no secret that there is a lot of misinformation, poor advice, and marketing disguised as guidance that plagues the automotive sound treatment groups, threads, and discussions. The point of this article is to show you how we here at ResoNix sound deaden car doors for the best end result possible. This post is taken from the “Installing It: Doors” section of our Reference Information & Guide page. The installation is done in a Lamborghini Huracan Evo, but applies to pretty much any vehicle.


NOTE: This guide is for SOUND DEADENING your car door, not sound proofing. There is a difference. Sound deadening your door, which is what we are covering in this article, is the approach you would take when you want to treat the part of the vehicle, in this case the doors, for audio performance improvements only. Sound proofing is the approach you take when you want to reduce outside noise from entering the vehicle. The approach is similar, but there are some small differences. For the doors, the only difference would be a full application of ResoNix Barrier added to the inner door skin after CLD application.  

Installing it: How To Sound Deaden Car Doors

New Version. Written 12/17/2022

Hey everyone, Nick here. I finally have an updated guide for you on how to sound deaden car doors. This one being in a Lamborghini Huracan that we did at Vanguard Automotive Design. This new guide features almost everything you need to know and need to see to sound deaden a car door. I say “almost everything” because EVERY car, every situation, and everyone’s goals are different and may require some adapting to your specific situation. The best thing you can use going into sound treating your doors, or any part of your vehicle for that matter is the information provided in this entire article, but most importantly your own common sense. We have worked on many cars, but we may not have worked on your car. Considering this, I will do my best to lay this out and explain everything on how to sound deaden car doors as clear as possible, but your situation may have a portion that requires an additional step, or a different approach. If you feel this door installation guide, and everything else posted in this entire article do not answer all of your questions, feel free to reach out and we can help guide you, and even update the article to provide more clarity. Alright, so lets hop into it.. 

This 2020 Lamborghini Huracan came in with the request for a high-end sound system that could also get plenty loud, as well as a few other services, but there was one problem.. It’s a 1600hp, soon to be 2400hp track car. Since this is a track car, of course it has an ice box for the turbo system in the front trunk and a half cage that resides behind the seats in the cabin. This meant there was nowhere to install a subwoofer enclosure or amplifiers. Long story short, we got creative and came up with a solution to achieve high quality and relatively high-volume bass with good low frequency extension for this system. It was to install the Illusion Audio Carbon C10 Shallow Subwoofers in the doors. Normally, installing subwoofers in the door is a huge no-no, but there are a few details to consider in this case that made it work, and work well at that. First, the extremely low distortion of these subwoofers along with their low moving mass and low inductance allowed these subwoofers to not only play their typical 20-80hz range, but also extend up to 300hz no problem. The Lamborghini Huracan comes with an 8″ midbass in the OEM lower door location, and were sure we could fit this 10″ shallow subwoofer to use it as a subwoofer as well as a midbass and have it acoustically mate up to the 3″ midrange in the pillars. It ended up working very well, but for now, lets focus on HOW we got this to work so well. The careful and meticulous installation of ResoNix Sound Solutions sound treatment product offerings. 

You can see the rest of the entire installation here..

General Synopsis on How To Sound Deaden Car Doors

. Outer Door Skin (part of the door that is the outermost layer) 

100% coverage with ResoNix CLD Squares. This is used to damp mechanical energy that is caused by the speaker, and regular driving. ResoNix has the best performing Constrained Layer Damper on the market and is responsible for making the great end results that we achieved out of this install possible. Once we finished with the full coverage of ResoNix CLD Squares, we topped them with full coverage of BlackHole Tiles (now replaced by ResoNix Guardian), also supplied by ResoNix. ResoNix Guardian is a 12″ x 12″ x 1.375″ sheet that is constructed out of a 1/4″ Hydrophobic Melamine foam layer, a MLV noise barrier layer, another layer of 1″ Hydrophobic Melamine foam, and a non-woven polyester acoustic facing that has a peel-and-stick adhesive and are naturally fully waterproof. The absorption properties of this product achieves a few things. First, and most important, it absorbs acoustic energy inside of the door cavity that is created by the rear wave of the speaker. Absorbing this rear wave will lower the amount of acoustic energy that can excite the door skins, and it helps reduce standing waves in the door cavity. Both help clean up the sound and improve transient response of the system. The other benefit of Guardian is it helps block and absorb any noise entering the vehicle from outside of the doors. Another small thing we did with the outer door skin was use ResoNix Rope in sections between the crash bar and the outer door skin. This helps stabilize the outer skin even further.

Note about Blackhole Tiles and ResoNix Guardian: These are NOT a replacement for a standard constrained layer damper. They are a supplement and help further enhance performance by a different means of acoustic suppression.


. Inner door skin 

On the inner door skin, we were pretty lucky. On the Huracans, the inner skin is thick and has 3 dimensional curves, which helps increase rigidity. The access hole is also not too large or complex in shape. We ended up doing as much coverage within reason with the ResoNix CLD Squares, and then using ResoNix Barrier to replace the flimsy plastic access panel cover. This ResoNix Barrier is secured over the access hole using stainless machine screws and provides a thin yet rigid plate that can seal off the access hole, yet still be serviceable when needed and is also thin enough and moldable enough to fit the curves and tight tolerances.


. Door panel 

The door panel is what I usually worry about most. There are so many plastic trim pieces, overlapping parts that aren’t fully secured, tight spots, flimsy material, etc etc. Thankfully, the Huracan door panels are very strong on the grand scale of door panels. We covered as much as possible in ResoNix CLD Squares, and also used ResoNix Fiber Mat 25 and Fiber Mat 45. The Fiber Mat products are exactly what they sound like. A mat that is constructed of a synthetic fibrous material. It is exactly what you see in some vehicles from the factory, but the car manufacturers usually use it sparingly, probably due to budget. The Fiber Mat product kills two birds with one stone. First, it is an acoustic absorption material. It is used to absorb outside noise when entering the vehicle, and to absorb acoustic energy behind panels. Secondly, it is an excellent decoupler. A decoupler is a product that is thick enough yet compliant enough, like a pillow, that can be placed between panels and prevent them from vibrating against each other by providing cushion between them. Many other companies only use closed cell foam for this, but to date, this is by far the best decoupling product we have used, and its great that it also acts as an absorber.


All of this combined, even after having a 10″ subwoofer in each door running on 300 watts each, there were no rattles in the doors. That speaks volumes to both the quality of the materials used, and the installation of them, no pun intended 🙂

Detailed Explanation

How to sound deaden car doors

First things first, we removed the door panels and inspected what we were working with. When removing the door panel. We find that the inner door skin (the metal part of the door that is closest to the interior of the cabin) has a medium-sized access panel/hole, and everything else is sealed and pretty sturdy. That said, there are still plenty of areas to treat. From here, we removed the factory 8” midbass speaker to assess the door cavity and outer door skin.

Once the speaker and access panel were removed, we were able to inspect the outer door skin and door cavity. Again, a relatively normal door cavity and outer door skin. Nothing different or unique to worry about. Just a flat outer door skin with a crash bar right across the middle, which is the case for pretty much any car we come across.

How to sound deaden car doors

First up with the sound treatment portion, applying ResoNix CLD Squares to the outer door skin. First things first, we cleaned all of the surfaces that would be treated with isopropyl alcohol and a rag to remove all dirt, oils, and grease. Once that is done, we can move on to installing the CLD Squares. Remember, it is VERY important to keep the pieces that we install as large as possible. We go over why in the CLD section of the Reference Information article. We ended up with about 4.5square feet of coverage (4.5 ResoNix Squares) on the outer skin. We went with full coverage to get the best performance possible and to not leave ourselves second guessing. That said, we understand there is the 25% coverage rule that floats around the internet. First, let’s make it clear where this 25% coverage general rule of thumb came from. It comes from someone who wasn’t doing car audio installations. He was doing general sound treatment for the sake of just lowering the noise floor of the vehicle. Frankly, 25% coverage is not what I personally would consider acceptable for a car audio installation that has a door-mounted midbass driver. In a general sound treatment installation to lower the noise floor of a car, sure, but not in a car audio system. Let me explain why.

As we know, a CLD’s job is to lower structure-borne resonance by constraining the substrate it is applied to and converting that mechanical energy into heat. When driving under normal conditions, the resonance of the door is purely caused by 2 things. Wind, and the mechanical transfer of energy from the cars wheels and engine into the body. That’s it. Not much resonance will be caused by this relatively speaking. Now when we add a high-powered speaker to the mix and the user wants to get great performance out of that speaker, the doors are getting sealed, and a lot of acoustic energy and pressure is now being created inside of that door and that positive and negative pressure is being applied rapidly to the door. Due to this, the inner skin, and especially the outer skin are resonating MUCH more aggressively than before.

 Now, in almost any sound system, we are hoping to get a door-mounted midbass speaker to extend down to at least 80hz (accounting for the appropriate crossover as well) without any acoustic low-end roll off, distortion, or resonance/rattles. We also should take note that the resonant frequency (or FS, where an objects natural resonance lies and will resonate the most) of most outer door skins just so happens to be around 80hz. This is unfortunate considering this is the frequency range we are typically trying to recreate in this location, but most doors are going to make that very difficult due to this. 

 Lets assume we want to do 25% coverage in this case. We now have smaller pieces of CLD that are placed throughout the area of the outer door skin. What this will do is definitely take care of most of the higher frequency resonance as well as some of the lower frequency resonance that will be centered around the panels resonant frequency. But, with that much area left uncovered, it will still allow the panel to flex and resonate at the lower frequencies near its resonant frequency. When doing full, or near full coverage, you are constraining the entire panel, therefor limiting the panel from moving as a while.

Anyways, onto the installation of the ResoNix CLD Squares on the outer skin..

How to sound deaden car doors

Once the application of the ResoNix CLD Squares to the outer skin was complete, we can move on to a quick and easy yet highly effective way of further reducing resonance of the outer door skin. What I am speaking of is using ResoNix Rope to couple the outer door skin to the crash bar inside of the door. Now, yes, sometimes they are already “coupled” with another type of adhesive or material from the factory. But it is usually a very light and ineffective material and is just used to provide very minor support. Using ResoNix Rope, you can use a proper material to couple the two together and use the rigidity of the crash bar coupled with the viscoelastic and adhesion properties of the ResoNix Rope to provide even more support and structure to the outer skin.

One thing to note, do not rip off the factory material to replace it with ResoNix Rope. Only use ResoNix Rope in conjunction with it. Another thing, more is always better, but we usually provide some gaps to allow for water drainage IF the factory adhesive also has gaps. If it doesn’t, you can go for full coverage. In this case, there was some adhesive gaps so we did the same.

How to sound deaden car doors
Next up, Blackhole Tiles (As of 1/30/2023 we suggest ResoNix Guardian instead of BH Tiles) for the outer door skin. As mentioned in the guide, what these do is absorb acoustical energy inside of the door. To quote the guide above..

“The main focus for absorption for automotive sound systems is most definitely going to be inside the doors if you have door-mounted midbass drivers. The purpose of absorption here is to do two things. Less energy makes it from the speaker’s rear wave to the outer door skin, and it lowers the energy that makes it back to the midbass drivers’ cone; both will reduce distortion. Unfortunately, you cannot just go and stick any old acoustic foam in your doors since it will hold moisture, grow mold, and prematurely rust your doors. You need something that can absorb AND is highly water-resistant or even fully waterproof. While our Fiber Mat products can work for this, I get nervous about window mechanisms interfering and causing issues. ResoNix Guardian is a safer bet to use here. ResoNix Guardian is a unique product, and there is nothing else like it on the market. We have managed to create a waterproof product that absorbs sound, insulates from heat, and even provides a noise barrier floating inside it. Now, most install this in a checker pattern in their doors, but if you go ahead and do full coverage, you can get some noise blocking and heat insulation out of them as well.”

So yeah, since we have a LOT of energy that will be produced in this specific vehicle, we opted for as much coverage as possible.

Something to note: If you are budgeting to only do partial coverage in your doors, definitely try to get 100% coverage in the area that’s directly behind the speaker and taper out from there.

Another note, since I get asked this more often than I would have guessed.. No, these do not replace a Constrained Layer Damper such as ResoNix Squares. They do two different things and are used in conjunction with each other to reach an end goal. If you had to use one, Constrained Layer Damping is more important.

Once this is done, the outer door skin is complete and we can move on to the inner door skin.

Moving on to the inner door skin. The most important aspect of treating the inner door skin is to seal the access holes using what many people would call a “block off plate”. Now, after enough time and experience in this field, I can say that while sealing these access holes is the most important part of treating the inner skin, it is highly recommended that you go about it in a way that is easily serviceable. There are many ways to go about sealing these holes. You need something that is solid and rigid. Being able to hold us to the elements is also highly recommended for obvious reasons.

The most ideal way is to use a relatively thick and rigid plastic, usually ABS, and cut out plates that can be secured to the inner skin around the perimeter of the access holes. This is only a good option if the inner door skin is flat and doesn’t have any meaningful curves to it. If it has curves, you are most likely not going to be able to use a thick enough material that will be able to both conform to the shape while also sealing the hole and being rigid and free of resonance. When using a plastic material to block off access holes, You will want to apply CLD to the plastic block off plate, and also provide a gasket for where the plastic meets the metal. I would suggest foam, such as ResoNix CCF7.

The second most ideal way, a way that yields, in my experience, no real audible differences from the first method listed above, is to use ResoNix Barrier as the block-off plate. Our Barrier product, while rigid and strong, is thin and moldable. This is an excellent option to use if your car has a three-dimensional shape to the opening and the block off plate needs to conform to this, or if you do not have the ability to make block off plates out of plastic, as you can cut our Barrier with heavy duty scissors. Using ResoNix Barrier is what we did in this specific install since the inner skin is curved and has a three-dimensional profile to it. In order to secure it, we use riv-nuts secured to the inner skin and machine screws with fender washers to hold it in place.

The third way, and least preferred way, is to just use CLD as your block off plate. While I would say this isn’t a terrible idea for small holes, this is not ideal for anything bigger than say 20 square inches for two reasons. One, it is not what I would consider rigid enough to act as a proper block off plate and cause resonance of its own. Same goes for using MLV for this task. They are just not rigid enough for the job. Another reason, serviceability. Once CLD is stuck on, it is NOT fun to remove. Don’t take that chance.


Once the block off plates are taken care of, you can apply your CLD to the inner door skin. I like to get the block off plates figured out first so I know where to not plate the CLD. You can see the CLD (along with the riv-nuts for the block off plates) installed into the photos above, along with the finished photos below.

Remember, as large of pieces as possible. Little itty-bitty pieces are damn near useless. If the area doesn’t have the ability to accept a piece that is at minimum, and I’m really going minimum here, 8 square inches or larger, do not bother. I typically do not do pieces that are smaller than 20 square inches for the inner door skin. For the door panel and other areas, this is not the case since not every panel is the same and CLD can be used for purposes such as holding two pieces snug together while damping them to prevent their contact rattles. You can see a few examples of this in the reference section above in the CLD installation photos. But if using it just to treat resonance, I tend to not bother with anything that wont take 20 square inches or larger.  Once the inner skin is sealed and treated with CLD, you can move on from here and treat any wires or modules that are mounted to the doors using CCF7 to decouple or use as a gasket, and you can use our VW/Audi OEM Non-Woven Tape to wrap any wire bundles to prevent any rattles or buzzes from them. Once this is done, it is time to move on to the door panels.

How to sound deaden car doors

Alright, now on to the most complex part of doing a door deadening installation, the door panel itself. This is the part of the doors I get the most questions about, and honestly, I cannot reliably answer most of them since EVERY door panel is different, and every door panel will require slightly different approaches to its spot treatment. I do my best to cover this in the other pictures below that are not of this Lamborghini and hope that is enough to help everyone out there. That said, our goals for the door panel include killing resonance, reducing panel on panel vibration (this includes both the door panel to inner door skin, and the overlapping layers of the door panel vibrating against itself), as well as acoustic absorption to reduce the amount of energy that makes it through the door panel cavities.

Lets start with step one, which would be all of the little spot treatment. Remember, every car is different and you will have to use the information here combined with your own common sense to figure out what parts of this door panel are going to vibrate against themselves and cause audible buzzes.

From our previous door guide..

“As mentioned previously, door panels can be made up of multiple different layers and pieces. If these layers are easily separated and you can hear then vibrate against each other when you knock on the panel, you will want to spot-treat the area where they meet with closed cell foam or even butyl rope. It’s also a good idea to hold door panel clips into place with our VW/Audi OEM Non-Woven Tape or butyl rope to prevent them from vibrating against their housing.

Below, you can see a door panel that we did for a 2014 Mazda CX5. Not only did we use CLD Squares on the large, flat surfaces of the panel, we also used the Non-Woven OEM Tape, ResoNix CCF7, and ResoNix Rope to decouple various parts of the panel from one another to prevent any audible buzzes or vibrations. If you zoom in on the second picture, you can see some of the areas that we treated circled in red.”

I prefer to treat this first, because once you apply the larger pieces of CLD Squares, you can no longer take it off and work on the small stuff underneath, so make sure all of your spot treatment is done before you start laying down your large pieces of CLD.

Note: why we used old pictures and other door panels for this is because the Lamborghini door panels are built very well from the factory and didn’t require much spot treatment. This 2014 Mazda CX5, different story.

How to sound deaden car doors

Remember, do not waste your time with super tiny pieces unless it is used to prevent two things from vibrating against each other.

How to sound deaden car doors

Once we are done with spot treatment, we can move on to resonance control of the door. This is when we install the larger pieces of CLD Squares. Remember, focus on the large, flat areas and use as big of pieces as you can to get the most constraining of the panel possible. Again, every car is different and will require a different approach. But my advice comes back down to focusing on the area around the speaker, and any large flat areas. Focusing on the area around the speaker should be obvious as to why, but in case it is not obvious, it is because this is the source of the energy in the door and its always best to stop it or reduce it as soon as possible, same reason why I suggest full coverage behind the speaker with ResoNix Guardian.

How to sound deaden car doors

Once that is done, it is time for Fiber Mat 25 or 45 (which one depends on how much room there is). One thing to note about Fiber Mat 25 and 45 is that you do not want to stuff it to the point where it is compressed. It absorbs best in its resting state, but there are areas of the door where it will need to be compressed, and is overall better serving the end result by doing so, as it is also acting as a decoupler for the door panel. As you can see, we didn’t just put one sheet of Fiber Mat over the door panel and call it done. While that is fine to do, when trying to get the most out of your install, it is best to fill all cavities and voids to get the most absorption possible (remember, fill, but do not stuff to the point where you really have to compress the material too much).

Thankfully, our Fiber Mat has an automotive grade peel and stick adhesive to make the installation easy.

How to sound deaden car doors

Once that is done, it is almost time to install the door panel. But first, the very last thing you want to do is seal the gap between the speaker and the door panel. ResoNix Strips are perfect for this. This couples the speaker to the door panel and prevents energy from getting into the area between the door panel and the inner door skin, and helps funnel that energy out of the door panel grille. Remember, you want your midbass speaker mounted close enough to the panel that the 1” thick strip will contact the door panel and provide a seal. If it doesn’t contact the door panel all the way around and seal the speaker, it isn’t really doing anything beneficial. In the first picture, you can see another Huracan that we did. Here, we used a baffle/speaker setup that allowed the ResoNix Strip to be placed onto the door panel itself. Sometimes its better to do it on the door panel, like in that particular case, but usually it is better to install it on the speaker, as seen in the second photo. We fabricate a ring that acts as a washer over the flange of the speaker and install the ResoNix Strip onto that, but that is a lot of extra work for those without the tools to make that quick and easy, so you can do it how you see fit. You can see the second photo of another Huracan that we did where we installed the ResoNix Strip onto the fabricated ring that secures the midbass driver down.

How to sound deaden car doors

Once that is done, install your door panel correctly and enjoy your silent doors.

How to sound deaden car doors

Tech Tip: Helix DSP Software Tech Tip - Setting Up Differential Rear Fill & Using Real Center

Helix DSP Differential Rear Fill is a commonly sought-after rear speaker setup for car audio hobbyists using any of the Audiotec Ficher DSP’s. It is used for its ability to help “enhance” the front speakers by simulating the late reflections of a larger room. Implemented correctly, this can result in a sound system that feels larger than the boundaries of the vehicle. How it works is simple. It is a Left minus Right/Right minus Left signal. This L-R/R-L signal is a sum of left and right, but the reversal of polarity of one side results in the cancellation of all of the correlated information and leaves you with only the left and right information. Once the signal is set, you can add extra delay (again, to help simulate the reflections of a larger room), adjust crossovers, equalize, level adjust, etc to fit your needs/taste. When equalizing differential rear fill you will either need to use uncorrelated (stereo) pink noise, or just temporarily turn off the differential signal as correlated (mono) signal will not play through the differential signal routing. 


Things To Note

. From personal experience, you want your rear speakers as high, wide, and far back as possible for this to work well. Down low in the rear doors does not work well, but can still be better than nothing for some.

. I recommend using 3″ or so wideband/full-range speakers. This allows for an easy installation that gets you the full 200-20,000hz spectrum needed.

. Before applying the extra delay, I still recommend setting delays to account for the path length difference to the listener.

. High pass this signal no lower than 250Hz or so. You do not want any bass or mid-bass frequencies in your rear fill as it is harder to de-correlate them to your front speakers. 

. Speaking of crossovers, if your front stage is a 3-way, it is best to just match your rear fill high pass filter to your front midrange high pass filter. This way you do not have to worry about possible phase issues and cancelation when playing with lower delay settings. Technically, the appropriate crossover to use would be 12db slopes, this only yields no issues if your front midrange crossover slopes are also 12db, or if there is enough delay applied to the rear speakers to decorrelate them from the front speakers. I personally use a 12db LR or 24db LR high pass, and a 6db BW low pass (if I decide to use a low pass at all).

. As you can tell, I am not speaking in definites. Nothing about differential rear fill is technically accurate to the source material. You are PURPOSELY adding something that was never meant to exist, so dialing this in by ear to fit your subjective wants/needs/taste is highly encouraged. As a starting point, I typically end up with at least 14ms of delay, usually more, and start by matching the high pass crossover to the front midrange, run the top end wide open, and go from there.


Things You Can Try

. Give Stereo Rear Fill a try instead of differential signal, with or without the extra delay. You might prefer it. I find these setups are better for those who prefer something that feels more “fun” and energized as opposed to perfect SQ. This is usually what I end up with when doing lower rear door speakers for customers.

. Instead of using Left minus Right/Right minus Left, you can use the Real Center and Virtual Channels of certain Audiotec Fischer DSP models to do Left minus Center/Right minus Center. What this will do is give you hard left on the left speaker, and hard right on the right speaker. With a traditional differential signal, you get left and right on both sides.



Speaking of Real Center..

In the vast majority of applications, only the sum of the right and left front channels is used to generate a signal for the center speaker. However, this means that the spatial stage image is restricted and the sound on the driver’s side ultimately only takes place between the left front speakers and the center speaker. The same applies accordingly to the passenger side, where the stereo panorama is reduced to the area between the center speaker and the right front speakers.

Audiotec Fischer’s proprietary “RealCenter” is a much more complex approach in which the center loudspeaker only reproduces the monophonic elements of the music, i.e. only the information that is simultaneously available on the right and left front channels. Stereophonic information that is only contained in the left or right channel is not fed to the center speaker.

The advantage: The width of the spatial stage image, which is generated by the stereophonic components, remains completely unchanged with the RealCenter, since these are still only reproduced by the left and right front speakers.

Without Virtual Channel Processing:
For a proper operation of the algorithm it is mandatory that the “Front Left” and “Front Right” signals must be present on channels A and B, as well as a sum of “Front Left” and “Front Right” on the actual center channel.

With Virtual Channel Processing:
For a proper operation of the algorithm it is mandatory that the “Front Left” and “Front Right” signals must be present on virtual channels “Front L Full” and “Front R Full”, as well as a sum of “Front Left” and “Front Right” on the virtual “Center Full”.

NOTE: Real Center is technically not an upmixer, but instead a center signal extractor. There is a difference. Personal experience.. while possible, it is NOT EASY to get a great sounding 2-seat system, but it does help with getting something that is definitely better than a traditional mono center. 

Be sure to check out our Audiotec Fischer DSP PC Tool Software Setup Part 1, here.


We also have a full automated tune video featuring Automatic Time Measurement, Tune EQ, & More, here.


If you have any specific requests on tech tips regarding the Audiotec Fischer DSP PC Toll Software, or anything else related to car audio or sound treatment, please email us with a request. Thank you!

ResoNix Sound Solutions Audiotec Fischer Helix Brax Match Differential Rear Fill How To

What Is Sound Deadening?

Sound deadening in cars is a process that involves the use of materials to absorb or dampen sound waves and vibration. This process can be applied to various parts of a car, including the doors, roof, trunk, and floor. The goal is to reduce noise and vibration that can be distracting, uncomfortable, or even harmful to your hearing. It is also used by many to improve the sound system in their vehicle.

There are a handful of main types of sound deadening materials for cars. Constrained Layer Dampers (commonly referred to as Sound Deadener) are by far the most common and widely known. There are also Sound Absorbers, Decouplers, and Barriers. Constrained Layer Dampers and are applied to the body and interior panels to reduce structure-borne resonance. This is arguably the first and most important step. Absorptive materials, such as Hydrophobic Fiber Mat, absorb sound waves and convert them into heat energy. Decouplers help isolate two panels to prevent them from rattling against each other. Barrier materials, such as ResoNix Barrier, block sound waves from passing through into the car’s cabin.

How Does Sound Deadening Work?

Sound deadening in cars works by reducing the transmission of sound waves and vibration through various materials. When sound waves or vibration hit a surface, they can be reflected, absorbed, or transmitted. The amount of sound or vibration that is reflected or transmitted depends on the density and thickness of the material.

Sound deadening material, constrained layer dampers specifically, are a vibration damping system. This system consists of a viscoelastic core sandwiched between a stiff outer aluminum constraining layer, and the panel it is adhered to. When the structure to which the damper is attached vibrates, the viscoelastic core of the damper dissipates the energy of the vibration by using its natural shear forces and converting the mechanical energy into heat. This reduces the amplitude of the vibration and, therefore, the noise and wear and tear on the structure.

Why Do You Need Sound Deadening in Cars?

Sound deadening in cars is essential for several reasons. First, it can make your ride more comfortable and less fatiguing by reducing road noise and vibration. This can make long drives much more pleasant and less stressful.

Second, sound deadening in cars can improve the sound quality of your audio system. By reducing background noise and vibrations, as well as resonance that causes distortion, you can hear your music or podcasts more clearly and at lower volumes, and have it retain clarity at higher volumes.

Finally, sound deadening in cars can help improve the resale value of your vehicle. A car that is quiet and comfortable to drive is generally more desirable than one that is noisy and uncomfortable.



Sound deadening in cars is a critical process that can make your driving experience much more comfortable and enjoyable, and drastically improve your sound system. Whether you’re looking to reduce road noise, improve audio quality, or increase the resale value of your vehicle, sound deadening materials can help. By understanding how sound treatment works in cars and why it’s essential, you can make an informed decision about whether it’s right for your vehicle.


If you have any specific requests on tech tips regarding anything else related to car audio or sound treatment, please email us with a request. Thank you!

Tech Tip: Helix DSP Software Setup, Part 2: Input EQ, Summing, Automatic Time Measurement, Tune EQ

This is our second post going over the Audiotec Fischer Helix, Brax, or Match DSP software. For this second video, we are focusing on the  Helix DSP software Setup, Input EQ, summing, Automotive Time, Measurement Tune EQ, and more!

Please note that the software used is the V5.00.05, so some things may change as they update the software, which they regularly do. 

Helix DSP Input EQ – The input EQ on the Audiotec Fischer DSP PC Tool software is the most powerful available. In this software version, it features up to 5 bands of parametric, shelf, and all pass filter equalization, as well as per-channel input delay.

Summing – Combining multiple inputs per output to acheive a full-range stereo signal and using the basic input RTA.

Automatic Time Measurement – In this video we go over how to use the Audiotec Fischer PC Tool feature that automatically and accurately sets time alignment for you.

Audiotec Fischer Tune EQ – We also go over how to use the Tune EQ automatic EQ feature. 

If you have any specific requests on tech tips regarding the Audiotec Fischer DSP PC Toll Software, or anything else related to car audio or sound treatment, please email us with a request. Thank you!

Be sure to check out Part 1, here.


If you have any specific requests on tech tips regarding the Audiotec Fischer DSP PC Toll Software, or anything else related to car audio or sound treatment, please email us with a request. Thank you!

ResoNix Sound Solutions How To Audiotec Fischer Helix Brax Match DSP PC Tool V5 Tune EQ Virtual Channels

Tech Tip: Helix DSP Software Setup, Pt.1: Initial Setup & Inputs/Outputs

This is going to be our first post going over your Audiotec Fischer Helix, Brax, or Match DSP product. For this first video, we are focusing on the initial Helix DSP software setup and configuring the inputs and outputs. Please note that the software used is the V5.00.05, so some things may change as they update the software, which they regularly do. 


Inputs and Output Menu: This will the first menu you have to set up in your Audiotec Fischer Helix, Brax, or Match DSP. It is also one of the most confusing for new users. In this video we go over how to use it, its capabilities, and more.

Virtual Channels: Virtual channels are essentially “a DSP within your DSP” and is another function of the Audiotec Fischer products that is often misunderstood.

Signal Management: The signal management tab is where you will designate how your input switching behaves.  


Part 2 can be found here.


If you have any specific requests on tech tips regarding the Audiotec Fischer DSP PC Tool Software, or anything else related to car audio or sound treatment, please email us with a request. Thank you!

Tech Tip: How To Use Winisd To Model, Simulate, & Compare Loudspeakers

What is WinISD? 

WinISD is a free software program designed for speaker design and optimization. The software allows users to create and simulate different speaker and subwoofer enclosure designs, and analyze their acoustic performance.

WinISD provides a variety of tools and features to help users create optimized speaker designs. For example, users can input the parameters of their chosen driver, such as the Thiele-Small parameters, and the software will calculate the optimal box size and port tuning frequency based on the selected design.

The software also includes graphical analysis tools, which allow users to see the predicted frequency response and impedance curve for their selected design. This can help users optimize their designs for specific applications, such as home theater or car audio.

In addition, these modeling softwares can simulate different types of speaker enclosures, including sealed, ported, and passive radiator designs. The software calculates the predicted performance of each design, allowing users to compare and choose the optimal design for their intended use.

Overall, WinISD is a powerful tool for designing and optimizing speaker systems, particularly subwoofers. Its flexible and user-friendly interface makes it an ideal choice for hobbyists, DIY enthusiasts, and professionals alike who are interested in designing high-quality and optimized speaker systems.


What can we use WinISD for in Car Audio specifically?

For my purposes of designing and installing high-end car audio systems, I use winisd for a few things. Using its many features, I can determine what I can determine which subwoofer and midbass drivers are best for a specific application. Or, I can simply figure out what size enclosure a driver needs and how much power it’ll be able to handle mechanically. The video below shows how I use WinISD to determine which driver is more suited for a specific application.


Things to keep in mind about modeling software..

Remember, WinISD is ONLY a loudspeaker modeling software. The way this software works is it uses the TS Parameters to mathematically plot its behavior in a theoretical anechoic environment. TS parameters will only tell you how a speaker behaves at and near its resonant frequency. Modeling software does NOT tell you how a loudspeaker sounds as far as its distortion performance or its actual frequency response caused other aspects of the speaker. It also does not tell you how it’ll behave in your given room. 

TLDR, do not use WinISD as an ultimate decider on what speaker is better than another. “Better” can have many different meanings. 



WinISD Alpha Pro (what I personally use)

WinISD Beta

Screenshot of myself modeling two subwoofers to check excursion limits.

How To Measure & Verify Phase Cohesion Through A Crossover Using An RTA

Hey everyone, I’m starting a blog to share various tech tips and useful information. For my first post, I decided to make an old video of mine available again. In this video, I demonstrate how to measure phase quickly and easily verify phase for maximum cohesion through a crossover. This is done using nothing but an RTA, All Pass Filters, and the Phase Slider on my Helix DSP. Additionally, I measure the results with Room EQ Wizard and a USB Measurement Microphone. Although I used a Helix DSP for this demonstration, it’s an older video, so some things may look a bit different. Furthermore, the video includes my old company’s intro.

Keep in mind: this method is only for even-order Linkwitz-Riley crossovers. A perfect LR crossover will be rolled off 6dB at the crossover point. The two will sum perfectly flat to 0dB. So, a perfect LR crossover will sum + 6dB. 90 degrees out of phase LR crossovers will sum 3dB. 135 & 225 degrees will sum with no change. 180 degrees out of phase will result in a null. With this simple process, you can measure and improve phase in your sound system.

Seen below is a more traditional way to measure phase directly, which can be much more complex and unnecessary to many.

Two traditional phase measurements are pictured below, overlaid on top of each other. If you’re trying to tune your car audio system using your DSP and a simple measurement setup, this could be too complex and might cause you to get lost in the sauce.