Car Audio, Custom Fabrication, Mobile Electronics

LIS Audio How-To: Properly Planning Your Sub-stage

Introduction

When it comes to planning out the sub-stage of a vehicle there are a few things you may want to consider, or questions to ask yourself before purchasing. These simple questions can help guide you in the direction of what maybe the best next sub-stage installation or upgrade whether you’re a seasoned enthusiast or a new comer.

First, lets consider these aspects…

How much power can your vehicle currently handle?

Have you had a subwoofer in a vehicle before, and if so, do you want more bass than you had previously?

How much available air space does your vehicle offer for the subwoofer enclosure?

How much storage space are you willing to give up for some additional bass?

Lets start simple, with demands. The amount of space you would demand to retain for storage and the demands the sub-stage could have on the vehicle electrical system. It is important to know what your future plans are with loading and unloading your vehicle on occasion. So, we’ll start with what to look for when taking measurements and deciding the proper size enclosure for your application.

Storage Space Demands

Here we will use basic geometry and algebra to factor exactly how much space we have available for a subwoofer enclosure after deciding how much space we are willing to lose. Keep in mind, many enclosures can be built to be easily removable, some are built to be permanent in order to match the proper air space demands. Grab a tape measure, painter’s tape (white masking tape will work), paper and a pen/pencil if you have some handy.

Go to the trunk, hatch or area behind a seat where you would like to store the sub or subs. We will measure height, depth and width in inches. If you are working with a large open space like a trunk or hatch and plan to store things in this area for trips, work or what have you then tape off the area which could be consider the portion you will us for storage. From here you should be able see how much depth and/or width you have available for the sub enclosure.

When storing the enclosure in a confined space it is easy to discern the height due to the fact that the storage area itself most likely limits it. When the area is open or has lots of upward space then decide just how high you would like to measure. You can even add a piece of tape to the panel or seat near the height measured that is sufficient for reference. Decide if at that height whether the enclosure would or would not block window views, seat mobility, speaker projection, or if the enclosure would be easily removable at that height. Decide the best height for your demands and then take a measurement and write it down.

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The next thing we will touch on is the math and exactly how to factor the volume of the enclosure space you have just created. The formula to factor the volume of a square or rectangular prism is Height X Width X Depth = Volume. Say the area chosen has a depth of 15”, width of 20” and height available to be 14” tall. Our formula would look like 14” X 20” X 15” = 4,200 square inches. This lets us know the outside volume of the enclosure, which we can then factor our wood thickness against to determine inner air space.

Height X Width X Depth = Volume

Lets say that we are building this enclosure with .75” MDF wood and we need to factor the wood thickness to determine the accurate inner air volume. We simply subtract 1.5” from each measurement taken to factor this, i.e. 12.5” X 18.5” X 13.5” = 3,121.875 square inches. So now lets move onto turning inches into feet.

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The conversion for inches into feet is 1728 divided by the sum of our measurement because there are 1728 cubic inches in one cubic foot. The volume of an exact foot squared is 1728 inches, which is factored by 12” X 12” X 12” = 1728^3. We divide our previous volume sum by one foot squared in inches, in order to properly convert inches to feet. Example: 3,121.875 / 1728 = 1.806^3.

Using this formula to convert the internal and external volumes you can subtract the two numbers to see how much mass the .75” MDF is taking up altogether. Example: 14” X 20” X 15” = 4,200”^3, 12.5” X 18.5” X 13.5” = 3,121.875”^3 internal, and 4,200” – 3,121.875” = 1,078.125”^3 difference. The means there is .62 cubic feet taking up air space inside this measured area. Leaving us with 1.806’^3 of inner air space for our subwoofer and taking up 2.43’^3 of net space.

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Now, some enclosures may need to be form fitted to a specific shape to tuck the enclosure out of the way of moving parts, or stored objects. This is common when a client of ours wants to have a factory looking system that has an aftermarket sub-stage. This becomes a bit more complex when it comes to figuring the amount of air space available but there are a few tricks to make it easier, which may require a bit more research on your part to learn.

There is also the option of replacing or adding a center console with a custom center console that is built to hold a subwoofer. This is a great alternative to traditionally enclosures when it comes to single cab trucks and other vehicles with extremely limited storage space for a subwoofer. We have many different builds on our website you can see in the “Gallery” tab to get a better idea of how some of our custom enclosures come together: http://www.lisaudio.com/gallery. For now, lets move on.

Electrical Demands

When it comes to the demands of the vehicles electrical system there are a few things to consider. Is the factory electrical system completely stock, or have any upgrades already been made? How big of an alternator did the vehicle originally come with? What other additional electronics like lights, air horns, or outlets do we plan to add later on? We will need to know the total demand overall to decide what is the best fit for our sub-stage, as to not overdraw the electrical systems capabilities and cause other components to suffer.

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This may mean adding more wire to the entire charging system under the hood (The Big 3 Upgrade), upgrading the starting battery or even upgrading the alternator to an aftermarket High Output alternator. The full demand of the electrical system is what will determine this. A good rule of thumb for most vehicle electrical systems is that they may be able to handle 500 to 1000 Watts of additional power. Now, keep in mind, energy is not created it is merely moved from one point to another. The vehicles motor, which produces mechanical energy through combustion, converts the energy to electricity using the alternator.

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8, 4, 0 and 00 Gauge OFC wire lined up.

Knowing vehicle electrical system demands is important because we need to be able to match the amplifier to fit our application, while knowing the electrical can survive with the power additional demands. So, lets talk about power verses air space, briefly. Many subwoofers have different power ratings. The key is choosing the subwoofer, or subwoofers, that will meet the demands of the additional power we can afford to give up while also fitting inside of our designated measured area.

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At his point it would be good assemble all of the components together and add up the power ratings to figure the total load. When we are looking at the total load or demand, that we plan to add to our electrical system, we will want to look at the Watts. The specification sheet online, in the box or on the box of the components will offer these measurements. Be sure to look at the “RMS” or “Power Handling” Wattage ratings, as these are more real world numbers. Ignore the “Peak” or “Max” Wattage ratings.

Here is an equation that will help you convert different electrical ratios. The formula is Amps X Volts = Watts. If we want to know how much power total our alternator will be able to produce it would look something like this; 140A X 14.4V = 2,016W. So, if we install a 240A alternator the math would look like this; 240A X 14.4V = 3,456W which means we now have an additional 1,440W we can use for our system with little to no effort from the alternator. Granted our wiring is sufficient. You can read up on wiring capabilities and the specifics of conductive surface area in our LIS Audio blog, How-To: Choosing The Proper Wire.

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Individual subwoofer impedance (Ohm load) and final amplifier load are what we will take into account at this point. When reading our LIS Audio blog you will see that I mention that electricity through a wire has more resistance the lower the impedance. This means the capability of more heat being introduced, which can translate into distortion and box rise. Knowing the impedance you want the sub-stage to play at and the final load impedance the amplifier you choose can handle is also important. Contact an expert if you have more questions on this subject. Lets move on to subwoofer sizes.

Choosing Subwoofer Sizes

Choosing the size of the subwoofer is mostly subject to the airspace allowed with storage area demands and the amount of air space a given subwoofer may demand to perform properly. Here are some extremely loose examples of amounts of inner air space found for many popular subs and sizes on the market today. Remember that in some cases it maybe better to use multiple subwoofers to occupy the given air space…

6” Sub .25ft – .5ft
8” Sub .2ft – .75ft
10” Sub .75ft – 1.25ft
12” Sub 1ft – 1.75ft
15” Sub 1.2ft – 2.75ft
18” Sub 2.5ft – 5ft
21” Sub 5ft – 10ft

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As stated above, different subwoofers have different specifications and will require slightly different sizes of air space. DO NOT use this table as a reference to building a to spec enclosure. This is merely a simple guide to what subwoofer sizes might or might not fit the air space you have allotted, without having to scour the entire Internet for the specifications of every single sub size available.

One extremely common question that is asked in car audio I will address now. Can I mix subwoofer sizes? The fact is yes, you can. Will you see a greater benefit from using multiple sub sizes over using the same sub sizes? Most likely not. Getting different sized subwoofers to perform in the same environment together without cancelling each other out at specific frequencies is no small feat, in most cases.

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Different size, and even series, of subwoofers perform better and less efficiently at different frequencies. This is mostly due to the subwoofer design and can also be attributed to enclosure tune or signal filtration. When it comes to properly setting up a system that has multiple sub sizes it will include some sort of multi-band signal processor to separate each set of size as to play their own independent range.

The subwoofers may also be chambered differently from, or into, the environment of the system to avoid wave cancellation. There are a bit more details we can go into on this subject but we’ll keep it short for now. Just know overall it is much more painless just to stick to one consecutive design and size of subwoofer for the entire setup.

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When we are deciding on what sub to run we should take into account whether we want the enclosure to be ported, sealed or possibly use a more advance enclosure alignment. We will cover the benefits of the different types of enclosures in the next section. Just be sure to keep this in mind when reading up on the subwoofer you plan to purchase next. What type of enclosures are they recommended to efficiently play in?

Acoustical Preferences

In this section we will cover the basics of sub-stage preference and subwoofer positioning. I will give you a short overview of the advantages and disadvantages to subwoofer positioning. What we will want to consider first in this area is, what type of vehicle is the subwoofer going to be installed in. Due to the fact that there are so many different variables, and I don’t want to spend most of the time in this section, I will touch on the most important aspects to take into account.

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When it comes to a coupe, or a sedan that has a trunk with a seat separating the cargo area from the cabin, we will need to consider the fact that the seat may separate the listener from the sub-stage. Some vehicles have fold down rear seats, which will allow a bit more bass to pass into the cabin, when folded down. A prefabricated subwoofer enclosure is a less expensive but also less efficient alternative to having a custom enclosure built. At LIS Audio, we don’t use prefab enclosures often at all due to the fact that they are built around very general specifications and are not ideal when trying to get the most out of your new subwoofer.

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Due to the fact that a hatch vehicle has more direct open space to the listener, and cabin gain, a hatch almost always has an advantage over a trunk sub-stage. There is almost always more room in a hatch due to the fact that a larger box can freely slide in and out of the opening and more enclosure height maybe available. A hatch vehicle also reverberates the bass differently and gives the effect of what we refer to as “cabin gain.” Which means, the sub-stage appears to play louder with the exact same setup that you would hear in a trunk car.

{Cabin Gain – Also referred to as the “transfer function,” this is the build up of long pressure waves (bass notes) inside of the vehicle in which the music is playing. At sea level the speed of sound is 1127 ft/ per second, which at 40 Hz means the wave is approximately 28 ft long, since the typical vehicle cabin is near 12 ft in length (give or take depending on the vehicle) than it is possible to gain 12 dB’s simply from this function. The less air space inside of the vehicle cabin occupied by the subwoofers and enclosure will give the vehicle more cabin gain, and vice versa.}

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In these types of vehicles it is pretty easy to position the subwoofer enclosure, depending on how larger, in many different positions and facing different directions. The most common firing directions are forward, backward, to the side, down-fire and up-fire. The direction the enclosure the subwoofer faces can make an audible difference in how it sounds from the listening position. The direction a port is aimed in conjunction to the surface the subwoofer is mounted to can also make a difference.

If you are not seasoned in knowing how a subwoofer might sound due to its directionality, attempt to utilize a setup that will allow you to easily move and shift your enclosure to see just how you might like the sub-stage to be positioned when all said and done. Keep in mind, having the amplifier installed on a surface other than the subwoofer enclosure will allow for more mobility of the box and less problems from vibration to the amplifier. Adding sound deadener to dampen the sheet metal of the vehicle can greatly improve the sub-stage as well. Read more on sound deadener advantage in my blog, The Benefits of Auto Sound Deadener.

Enclosure Types (Alignments)

The most commonly used subwoofer enclosure alignments for daily driven applications are sealed, ported and passive. Most commonly found in SPL Competition is 4th order, 5th order and 6th order. This section will cover the different types of alignments in a bit of detail to help you decide what may work best for you and your application. Take note that if you have a daily vehicle and plan to utilize a more detailed enclosure like a 4th order or above then make sure the subwoofer is capable performing in that style of enclosure.

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Sealed (Acoustic Suspension) – The interior of this enclosure has a completely air tight seal from exterior environment. A sealed enclosure alignment can be tuned by adding or subtracting to the internal air space, which will change the frequency response of the driver installed in the enclosure. This design is best for Sound Quality (SQ) as it provides a very accurate and tight response, but lacks a bit in output. Sealed alignments are one of the most commonly found enclosures in car audio due to their ease of design and petite size.

Passive Radiator – This alignment uses a passive radiator to tune the enclosure. The passive radiator provides dampening to the compression of the enclosure. These designs are most commonly found in all-in-one stand-alone home stereo systems and portable stereo devices, there is very rarely seen in car audio applications.

Vented (Ported or Bass Reflex) – This design of enclosure is very commonly found in the car audio industry. It allows the ability to tune the enclosure close to a specific frequency. Changing the diameter and length of the port against the amount of the internal air space is how to tune the enclosure. Vented enclosures are more ideal for output than quality, which is why they are also commonly found in Sound Pressure Level (SPL) audio systems.

Infinite Baffle (Free Air) – This setup is essentially a driver mounted to a baffle (or wall) with a nearly open space directly behind it and in front. It is most ideal to isolate the front wave from the rear wave to achieve decent output and sound quality. This alignment is mostly used with full-range speakers and commonly found in home audio or extreme Sound Quality (SQ) car audio applications when used with subwoofers.

Semi-Closed Aperiodic – This design is seldom seen in car audio applications, if at all. The enclosure design is of a typical sealed enclosure but the rear wall is replaced with a “leaky” dampening material instead of a rigid material that would typically be found. The internal air volume as well as the thickness and density of the dampening material used is what determines the enclosures tune, or the frequency response of the subwoofer.

Single Reflex Band-pass (4th Order) – This enclosure alignment brings together the two sealed and ported designs together offering the best of both worlds, and some additional draw backs, like being nearly twice the size of a traditional ported enclosure. The subwoofer is buried inside the cabinet to the baffle, which is the dividing wall between the two chambers. One chamber is sealed and tuned for accuracy while the other chamber is typically tuned toward output or high-end roll off. This enclosure is found in many large Sound Pressure Level (SPL) competition car audio systems.

Dual Reflex Band -pass (6th Order)- This design is similar to that of a single reflex band-pass enclosure but both chambers are vented. The two chambers must be tuned 180 degrees out of polarity from each other and must be tuned at least on octave apart to avoid cancellation issues. Dual reflex band-pass low frequency systems generally exhibit a roll-off of about 18-24 dB per octave on the high pass and 12 dB per octave on the low pass. The biggest benefit to a 6th order enclosure is amazing bass from smaller drivers, but they can be very difficult to design and build correctly.

Transmission Line Enclosure – Also referred to a Quarter Wave Design, a transmission line redirects the standing waves away from the rear surface of the driver reducing the chance of standing waves interfering with the primary waves.

Aperiodic – Refers to a type of bass-cabinet loading. An aperiodic enclosure type usually features a very restrictive, (damped), port. The purpose of this restrictive port is not to extend bass response, but lower the Q of the system and reduce the impedance peak at resonance. Many restrictive ports are heavily stuffed with fiberglass, dacron or foam. This design is also referred to as push-pull.

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There you have the definitions for the common and somewhat uncommon style of subwoofer enclosures used in car audio. As mentioned before, the most common are sealed and ported enclosures, which are found in daily driven vehicles. This is due to the ease of design and sometimes space restrictions. There are also more complicated designs that I will not break down in this blog.

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Utilizing a sealed enclosure will give your sub-stage tight and accurate bass with very smooth roll off. These enclosures are more ideal for sound quality applications. You will see ported/vented enclosures incorporated into audio systems where the listener prefers a bit more volume output on the sub-stage but at more specific frequencies. The maximum output of the bass will typically be around the tune of the enclosure, whether it be tuned lower for music like Rap or Dubstep, or higher for music like Country or Rock.

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The resonance of the subwoofer at different frequencies will change once introduced into the vehicle. The same sub, in the same box, on the exact same power will play frequencies slightly differently from being placed in a sedan to a SUV. You see, the vehicle itself creates a different environment for the subwoofer that can either help or hinder its performance but will most certainly change the way the bass is reproduced. Be sure to do some more research into this if you plan to be installing a Sound Pressure Level (SPL) competition sound system.

Where to Buy & Install

When it comes to buying product, it always come down to customer preference. Do you prefer the convenience of buying online? Would you prefer to buy in person so you can see, feel, touch, smell and hear the product? Is having a reputable shop to install and recommend other facets a necessity to you? In this section I will merely give you the pros and cons that I see daily when it comes to consumers buying product new and used in the 12 Volt Industry.

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The reality of buying any technology in the 21st century means looking for one or more of three things in everything, quality, convenience and price. Many other reasons for buying can be debated effortlessly but these are the most common things people seek out when shopping. How cheap can I get it? Is it close by or can I overnight it? Is the quality worth my time, effort and money? Hopefully I can give you somewhat of a reference guide here of what to look for in each area.

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When it comes to buying I will always recommend buy your audio products new. When we buy new most quality mobile electronics come with a warranty of some sort. This just isn’t in the budget for some of us, so I will break down buying used just a bit. A good rule of thumb when buying or selling used car audio, you can hardly expect the product is worth half of what it was new. Extremely rare and very high-end audio can be found used at high dollar amounts, but not traditionally.

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When you go to an expert shop to buy, you will also receive guidance in your purchase. Sometimes this can even help you eliminate full components that you thought you might need to get the job done but simply don’t. Look for shops that have technicians that are MECP certified or that are a part of the Mobile Electronics Association, as they must hold themselves to a specific standard. Top 50 Retailers and Top 50 Installer shops are always great to have on your list for shop references as well. Just be sure they still hold to the same standards and principals.

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What we most commonly see from clients buying product online verse in store is trouble with the warranty process. Some sellers online are private and may not have stock enough of the product that was just purchased months prior to replace it in a warranty. Many of them may also not be dealers with the brands that they at a cheaper, which means the warranty process is on customer contacting the manufacturer directly.

In other cases we will not be able to warranty a clients product through our shop so we will then have to charge them to remove the components, let them send it in with a wait time, and then charge them to reinstall the component. This would play out a bit different for the DIY or more installation savvy buyer. There are also a few manufacturers that will not hold to the warranty on items that were not installed by an approved dealer. Make sure you ask about and read your warranty before purchase. It can save lots of money and effort when it comes to buying car audio.

In Conclusion…

Hopefully now you have a better idea of how much power your vehicle can handle and what to look for when deciding on your total system power consumption. You will know how much space you would like to give up and how much space the sub, and/or subs, you want to add may take up. Then, also a general understanding of just how much bass you want and can realistically have with the space offered.

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Remember that a lot of your sub-stage will be built on preference. Preference of the product used. Preference of amount of bass delivered. Preference of the amount of money spent. Preference of enclosure alignment due to the music you listen to. Preference of the shop or person you allow to perform the installation and final system tune. Preference of direction you may like to face the subwoofer in the vehicle. Many of the preferences we have covered up to this point.

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I hope this helps you see the advantages and disadvantages of each type of scenario when designing your sub-stage. Using the information in this blog will help you to determine a good general direction to head when planning your sub-stage out but is also subject to change with preference. If your build goes beyond that of a daily driven vehicle, which means its limits surpass that which has been mentioned here, there are many people on social media you can contact willing to give further guidance. Reach out to myself, or our shop, if you have questions or would like to be directed to a credible shop near you.

Thank you for reading our How-To blog! Make sure to follow the LIS Audio Blog to see what we will feature next!! Find us on InstagramFacebook and YouTube!!

Contact LIS Audio if you have any questions…

Call: (913) 912- 6990

E-mail: info@lisaudio.com

Website: http://www.lisaudio.com

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