Car Audio & Electronics

Decided to make this page a speaker building resource since it often comes up in online discussions when i’m chatting with others in the hobby. Besides owning Mountain View Carpet home hi-fi and car audio has been a hobby of mine since i was a teenager. Over the years i have watched many changes happen in the industry. Back in the early 90s, before i could even drive a guy who lived down the street from me owned a business called the speaker clinic. That particular person went on to be an engineer at Phoenix Gold here in Portland and is probably most responsible for my development in the hobby. When i was 15 i met the now legendary Vance Dickason and at the time didn’t even realize who he was. For those of you who still don’t know; Vance is probably the most well known loudspeaker engineer in the DIY and even parts of the professional community authoring titles like “the loudspeaker cookbook”

Now on to the nuts and bolts of things. Winisd is my favorite free resource for car or home audio DIY subwoofer projects. http://www.linearteam.dk/?pageid=winisd from the linear team in Finland is one of the most bug free and easy to use box designers a person can freely download. If you’re like many people and assembling an upgrade for your car or truck you really have a couple choices. Take it to the store and hope they know what they are talking about. In our area that very short list is Mobil West on MLK or Stereo King on 82nd or Aloha. Mobil West does most of the higher end installs and between the two service is pretty good. Stereo king is however easier to wheel and deal with if you’re after good prices. The one place i would avoid at all costs is Car Toys. There is nothing you will get there the previous two won’t do better. More worrisome is how many stories i have heard of things gone wrong.

Now on to choice number 2. the DIY option. This is in my opinion where it gets fun. You obviously save money on labor via the install but even better, you learn about what you like and how it works. There is about a 98% chance you won’t have an optimal system if you just build subwoofer boxes to spec and toss mids in your door blindly. First i’m going to address the subs and a few discrepancies. For examples sake i’m going to use JL Audio drivers but this really applies to any brand.

case study number 1. the 10w3v3, the first thing i typically check is what’s called the efficiency bandwidth product. to find this you simply take FS/Qes in the case of the 10w3v3 we have an FS of 31.49hz and a Qes of .523, 31.49 divided by .523 = 60.2. What is this number and what does it mean? typically drivers under 50 greatly prefer to go in sealed enclosures, between 50 and 100 can go either way and above 100 will really want to be ported. now on to box design. First up, the sealed enclosure. the JL spec is .625cuft which is noted on the purple line below. the yellow line is 1cuft. there are a couple of sonic differences that happen here first we have what’s called total Q or Qtc. Qtc Denotes the enclosures ability to control the driver response at resonance. Qtc = 0.707 is the optimum value for sealed enclosures, providing flattest response and {sometimes} highest SPL for deep bass extension. Enclosures for this value are often rather large. Lower Qtc can give even better transient response, down to a Qtc of 0.577 for the best damping and transients. What exactly do i mean by sometimes? a sub may actually get louder in a higher Q smaller box but will require more power and will not perform as well going lower. That pesky resonance also can be a problem. Now on to cabin gain in the car and the where and why of small sealed enclosures. One reason there is no perfect answer in a car is because speakers will perform differently in a small hatchback vs a large SUV. through personal experience and experimentation i can tell you that if the sub is in the cabin with you there is a good chance the larger enclosure will sound better. in the example of this 10w3v3. theoretically F1 or 1db down happens at 59hz in the smaller box but 65hz in the larger one. this is the beginning of rolloff. when we get to 35hz however that larger box is 1db ahead of the smaller one and will require less wattage to hit xmax. that’s a nice free gain in the low end but the real key here is resonance. when a speaker produces sound sound waves are produced coming out the front and out the back. the sound waves coming out the back smack into the rear of the box, resonate and bounce back through the cone. if you have ever been in a car that has subs that kind of hum or seem to just play 50hz very loudly chances are they are in too small of an enclosure. acoustic foam on the back of the box or really on all sides inside the box helps with this but it still won’t cure the resonance small enclosures and higher Qtc designs produce. another note about overall system Q. it changes when you add polyfill or foam and it changes when you go in car. in my opinion, in most cars rap, edm, bass, alternative and dubstep will sound the best with a qtc of .700 to .720. rock music can go higher up to .800 as it’s more of a midbass and the smaller boxes sometimes work pretty well, especially with trunk enclosures or smaller vehicles that produce a lot of cabin gain. in a small to large suv that 10w3v3 will produce a more pleasing sound aligned in .9 to 1.0 cuft sealed as you will virtually eliminate the resonance problem and you get a free 1db bump at 35hz.
10w3v3 sealed

now on to ported.

In a ported enclosure we are faced with similar choices to sealed. larger box and flatter response or smaller box with a bit more of a peak and less low end. the yellow line is ported in 2cuft and the purple line is JL spc at 1.125 cuft. the larger box gives us a much better bottom end and a much flatter frequency response. peaks like you see on the purple line are often amplified due to cabin gain in the car. ever hear someone say “ported subs sound boomy”? well this is why and this isn’t even one of the worst offenders. the 13w7 is much more peaky than this ported to spec vs ported properly. the 13w7 ported to JL spec is designed to get loud but it does so with a major peak at 45hz. it is not sonically accurate aligned that way even though it could be in the right box. it is however very loud and people will hear your coming for blocks with just one of them. back to the w3. it depends on how much space you have in your car and it depends on your musical preference. in the larger box our 3db down point is 24hz with a flat response the whole way up. this is home theater status. in the smaller box there is roughly a 1.5db peak from 45 to 60hz and we are 3db down at 31hz. will this sound more boomy and not dig as deep? yes ! but it will also handle a bit more power and it’s 1.125cuft not 2.0 which can be a big deal in a car. you really have to ask yourself how big of a perfectionist you are and how picky you are with sound. the larger box will blend MUCH easier with your mids and tweets and sound much more accurate. the smaller box will get loud, it’s small and that’s about all. the 1.5db peak at 45-60hz may not sound like a lot but it can give the feeling of a lack of low end as that frequency is often the loudest. in my opinion i would always use the larger box IF i could fit it. it’s more efficient requiring less wattage and i can actually make a ported sub in car sound musical. this of course brings up another argument of “what can i fit in less than 1 cubic foot” again, just speaking JL the answer is a sealed 10w6 or 10w3, a sealed 8w7 or ported 8w3. there are pros and cons to all of those. if you’re a basshead go ported, if you want to get loud, go ported. if you have a lot of space and like accurate music you can go ported. that said, for a lot of cars, sealed is still the way to go simply because it’s easy, requires small boxes and gives you a rolloff on the lows not peaks that stand out ala small ported enclosures. did i mention small boxes? this is seriously the number 1 concern of many shoppers.
10w3 vented response