Sonic Nirvana - How to Build Kick Pods in Classic Chevy Truck

[par4tom]

I've had a couple of requests in the past few weeks on how I built my kick pods for my 1961 truck (Took 2nd place at the 68th Grand National Roadster Show in January 2017), and thought I would share some thoughts on how to achieve "sonic nirvana" in your own truck...if there is such a thing!

I'll start with a photo of my driver side kick pod here, share some theory on what sizes will and will not work for speakers in kick pods and why, talk a bit about speaker placement and alignment and then finish with how I built my own kick pods. If I had known there was going to be so much interest, I would have taken more pictures while I was building them.

For you younger guys out there...I wish I would have had this information about 20 years ago when I was still competing in car sound...I've learned from some of the best minds in the world!

[par4tom]

Background -

I got into car audio back in the early 1980's and it has always been a favorite hobby of mine. Back in the day, 100 watt amps were a rarity and the "more is better" theory prevailed. "More" meaning, how many speakers and amps could you fit in your car or truck.

During the 1990's, my career had progressed and I was able to afford to do my first competition car audio car, a 1994 Acura Legend that actually was featured in a CES Booth for Zapco in 1998 or 1999. It was a rather simple system and went undefeated the year I competed.

Fast forward to 2014 when I started building my dad's old 1961 truck, I determined to push the cutting edge of car audio thought...just this time in a classic chevy truck.

So whether you're putting a system in an old truck like ours, or the latest sedan or coupe, the first rule of thumb is to:

Always build your system to your vehicle.Not vice versa!!!

Too many times I have seen guys (much like I did in those early days), cut holes in the wrong place or try to fit too large a subwoofer (or too many) into too small a space with very poor results and very empty pockets after.

When it comes to kick pods, I happen to be a very lucky guy because Steve Brown (who was an IASCA National Champion the year I competed) and later went to work to head the fabrication division for Alpine Car Audio, befriended me at a competition in Carson City, NV.

So you know, Steve was years ahead of his time when it came to those early days of fiberglass. He was also the only guy I ever met that was competing with fiberglass kick pods. And his were good enough to win a National Championship.

To make a long story shorter, I had Steve come up from Southern California to the Central Valley and put on a class on how to build fiberglass kick panels...which he did. After I watched him, I made my own set of kick panels. They weren't very good compared to his, but they helped me receive an invite to nationals in South Carolina that year.

With that said...I am not an expert...just a long-time hobbiest. And I've learned a few short cuts along the way...so here we go!

[par4tom]

Let's step back a moment and talk about what we are trying to achieve when it comes to accurate sound reproduction.

First and foremost, everyone of us has been to a concert at one time or another, and when we have been at a concert, the performers are in front of us and up on a stage. Notice what I am saying as this is a key point: The performers are in front of us, usually at eye level and up on a stage.

Therefore, the goal of car audio, is to try and replicate this "stage like" effect up in front of us...or in this case, over the top of the dash and as far forward in the vehicle as possible. In essence, we are trying to create an illusion of the performers up over the front hood of our trucks just as if we were at a real concert.

Which...creates a big problem already! There is no place for speakers on the front hoods of our trucks and no room for huge subwoofers anywhere in the truck except behind the seats. And subwoofers behind the seats already presents us with our first handicap since there are no performers in a front stage performance playing bass notes or drums from behind us!!! We're doomed before we start. Or are we?

To combat this problem, acoustical engineers have been playing with many different designs and remedies to this 'front stage" objective. This post is not going to go into too many of these complex issues, since all you and I care about is how to get decent sound out of our old trucks...specifically the kick pods.

Suffice it to say, speaker size, choice, location and alignment are critical in our quest for sonic perfection.

[par4tom]

Before I go any further, let's talk briefly about sub woofers. In small cab enclosures like our old trucks, subwoofers much larger than 10" in space are going to result in muddy, overhung base.

Granted...I get the whole thing with you younger guys liking to brag about having 4 12-inch subs behind your seats and blasting everyone out of the neighborhood. However, the problem with large subwoofers is that the require large amount of enclosure space in order to achieve acceptable results.

If you notice in my truck, I only have 2 (very good quality CDT Audio Subs) that are 8" each. I went this route because I could: a) Get them to fit behind my seat; b) get a big enough sealed-enclosure (in this case I built a .375 cubic foot enclosure for each sub) for accurate reproduction; and c) (which is probably the most important one), I was able to get them down and way from directly behind the seat so that all of the vibration from the subs wasn't pounding directly into my back, and ruining my first objective which is...you guessed it...create the illusion that all the sound was coming from in front of me and over the top of the dash.

Rule of thumb on subs - if you want to just be loud and proud, go with any size sub you want and how ever many you can fit. If you are looking for smoothness, bump, and accuracy, stay with a 10" or 8" sub. A pair is more then enough.

Trust me, I can get more sound out of a well designed pair of 8's then a lot of you guys can get out a pair of 10's or 12' in enclosures that are too small. I won't delve into the efficiency aspect of subwoofers, but will add that a lot of you are getting cleaned out by stereo shops that don't know what they are doing and paying too much money for poor results. Here are few photos of my own build...

Notice how far down and to the side each one of the subs is located. I moved them as far away from the back of my seat as possible.

[par4tom]

After that detour, let's get back to front sound stage issues. As I said earlier, our objective is to create an illusion of sound coming from over the top of the dash. And since 6 1/2 inch mids, or 5 1/4 inch mids won't fit on the dash, we are now stuck with a second dilemma what size speakers to buy and where to place them.

There have been many arguments over the years about what speakers are best, or which size speakers are best, and I won't get into that too much right here. Although I will say, buy good mids and tweets and buy as large of a driver as you can fit into the kickpod and still get acceptable performance.

Here is a very important point of speaker size:

1. If you are able to use the cowl vents as a type of infinite baffle (meaning the back of the speaker is vented out to the cowl vent), then going with solid pair of 6 1/2" midranges will work best. If you do not plan to use the cowl vents, DO NOT USE 6 1/2" drivers in a sealed kick pod. You simply will not get stellar performance out of this large of a driver.

Many people try to get around this by cutting the back of the kick pods out and venting the 6 1/2" drivers out into the cab. This is a huge mistake! There will be phasing issues and sound wave cancellation issues using this methodology.

Again, if you are stuck using the kick pod as an enclosure, you will actually get better performance and have fewer phasing problems and cancellations with a 5 1/4" driver or even a 4" drive. A good 5 1/4" driver or good 4" drive in a sealed enclosure, will outperform a 6 1/2" drive in a sealed kickpod.

In my application, I used the cowl vents with a good water shield in the vent to keep our rain and moisture and used a 6 1/2" drive. My crossover point is at 80 hz and is at a 12 db slope.

In the picture below you can see the first version of kickpod I made (I since redid them) showing a 6 1/2" midbass driver and a 2" mid/tweet driver down below it. I milled a Lexan beauty ring to hid the screws on the midbass driver.

[par4tom]

Speaker Alignment and aim - (Which direction to point the darn speakers!!!)

In the old days of car audio, there was a lot of trial and error with trying to achieve accurate sound reproduction. Mostly it was error...

Since then, several national champion competitors have spilled the beans with regards to how they achieved more consistent winning results.

I simply followed their leads...

In my truck, as a I've already mentioned, I used a set of CDT Audio drivers for the kick pods. A 6 1/2" mid and a 2" tweeter.

When it comes to which direction to aim the drivers, there is a very simple trick to follow that will help you achieve almost perfect results every time, while still being able to "trick" your mind into thinking the sound is coming from over the top of the dash.

To start this alignment process, have a friend outside the drivers side of the truck while you sit in the drivers seat. Have them look through the side glass and put a piece of blue tape directly opposite the opening of your ear. Again, sit in your truck. Have your buddy stand right outside and look through the glass, then stick a piece of tape directly opposite the opening of your left ear.

After this is done, take a tape measure from the piece of blue tape, measure 7 inches directly towards the front of the truck and then down 1 1/2 inches from that point and place a piece of blue tape at this forward aiming point.

This second piece of blue tape is going to be the exact point where you will be aiming the passenger side speakers.

Once you are done with the drivers side sitting position, go to the passenger side and repeat the same process you just completed.

You should now have two pieces of tape to aim your speakers at...one on each window.

Is this going to magically make your system sound amazing? Of course not! But it is going to give you the absolute best physical chance of achieving a good, stable and high front sound stage and that is the best that we can hope for in this imperfect environment.

Here is a picture of the tape on my window...it's a bit hard to see and is hiding part of the steering wheel. Anyway, I think you get the idea...

[88Stanger]

Originally Posted by par4tom

After that detour, let's get back to front sound stage issues. As I said earlier, our objective is to create an illusion of sound coming from over the top of the dash. And since 6 1/2 inch mids, or 5 1/4 inch mids won't fit on the dash, we are now stuck with a second dilemma what size speakers to buy and where to place them.

There have been many arguments over the years about what speakers are best, or which size speakers are best, and I won't get into that too much right here. Although I will say, buy good mids and tweets and buy as large of a driver as you can fit into the kickpod and still get acceptable performance.

Here is a very important point of speaker size:

1. If you are able to use the cowl vents as a type of infinite baffle (meaning the back of the speaker is vented out to the cowl vent), then going with solid pair of 6 1/2" midranges will work best. If you do not plan to use the cowl vents, DO NOT USE 6 1/2" drivers in a sealed kick pod. You simply will not get stellar performance out of this large of a driver.

Many people try to get around this by cutting the back of the kick pods out and venting the 6 1/2" drivers out into the cab. This is a huge mistake! There will be phasing issues and sound wave cancellation issues using this methodology.

Again, if you are stuck using the kick pod as an enclosure, you will actually get better performance and have fewer phasing problems and cancellations with a 5 1/4" driver or even a 4" drive. A good 5 1/4" driver or good 4" drive in a sealed enclosure, will outperform a 6 1/2" drive in a sealed kickpod.

In my application, I used the cowl vents with a good water shield in the vent to keep our rain and moisture and used a 6 1/2" drive. My crossover point is at 80 hz and is at a 12 db slope.

In the picture below you can see the first version of kickpod I made (I since redid them) showing a 6 1/2" midbass driver and a 2" mid/tweet driver down below it. I milled a Lexan beauty ring to hid the screws on the midbass driver.

"Water Shield"? What exactly is this?

[leonphelps]

what did you use for the adhesive with the vinyl?

[par4tom]

Good question...I use the vinyl top adhesive from a local upholstery supplier. They use to have a lot better contact cement here in California but the regulators have long since outlawed getting the good stuff here. If you live in other states, I think you can still get the good adhesive.

Weldwood Vinyl Top Adhesive. Available at any upholstery store. The adhesive in the spray cans will not work as they will not hold. Spray adhesive also will not hold if you live in a hot climate like I do here in Central California.

I should also mention another point...if you are going to apply vinyl, do not sand down your finished piece beyond 80 to 100 grit. The adhesive will tend to not stick. Also, I wipe down the piece really good with a tack cloth and Acetone to clean the surface and aid sticking.

To apply, I take a 2" chip brush and brush the adhesive onto the panel and also onto the vinyl. From there, you need to let it tack up to the point that the glue doesn't lift off when you touch it with the knuckle on your finger.

Originally Posted by leonphelps

what did you use for the adhesive with the vinyl?

[07SSSC]

I've been wanting to do this for years but didn't know where to start, great write up and I will surely try something along these lines this summer. I did a very crude setup using stacked rings on my kick panels that doesn't look very good.

Question for you though, I already have 6.5" drivers, no AC so I need my vents, what's you're suggestion in such a situation besides buying smaller speakers?

[par4tom]

Open up the back of the kickpods and let them vent out to the cab. You will lose a bit of snap in the snare drum and bass guitar, but you'll avoid a hump in the frequency response in the higher octaves...you can try and compensate for the loss in lower frequencies by lowering the x over point to around 65 hz, 6 db rolloff. Try 12 db roll off as well.
Posted via Mobile Device

[nsb29]

Originally Posted by par4tom

I've had a couple of requests in the past few weeks on how I built my kick pods for my 1961 truck (Took 2nd place at the 68th Grand National Roadster Show in January 2017), and thought I would share some thoughts on how to achieve "sonic nirvana" in your own truck...if there is such a thing! congratulations on 2nd place

I'll start with a photo of my driver side kick pod here, share some theory on what sizes will and will not work for speakers in kick pods and why, talk a bit about speaker placement and alignment and then finish with how I built my own kick pods. If I had known there was going to be so much interest, I would have taken more pictures while I was building them.

For you younger guys out there...I wish I would have had this information about 20 years ago when I was still competing in car sound...I've learned from some of the best minds in the world!

congratulations on 2nd place lets see sum pictures

[par4tom]

Here's a couple...

[par4tom]

And a couple more. This is my dad and mom holding the trophy. I hope they had as much fun as I did...maybe next year we can make a few upgrades and go back and win...

The guy behind me and myself, were the only ones to do almost all our own work. The guy in front of me dropped like $300k in his rig...a lot of nice rides!

[BIGglaSS]

Lots of great info here, thanks for sharing. Congrats at the GNRS, your truck looks great!

I have been planning my audio system to use 5.25"/1" silk tweets in the kick vents, and one down-fire 8" sub. I already bought a Zapco 5 ch amp (overkill). Way too many to choices. My head is spinning on what brand and type of components to use. Hope I'm headed down the right track.

[par4tom]

Look at a JL Audio 8w sub, I have heard great things in Hertz mids/tweets. Go listen to some at your local stereo shop and get the ones you like the sound of best. You'll probably end up spending between 300 to 400 of mids and tweets. Let me know if you have any questions along the way...

[BIGglaSS]

Originally Posted by par4tom

Look at a JL Audio 8w sub, I have heard great things in Hertz mids/tweets. Go listen to some at your local stereo shop and get the ones you like the sound of best. You'll probably end up spending between 300 to 400 of mids and tweets. Let me know if you have any questions along the way...

Thanks. I have looked at JL, JBL, Polk, CDT, Hertz, Alpine, Morel, Focal, Scanspeak.... Are you happy with CDT? I was looking at their CL series components.

[par4tom]

I do like the CDT...and if you need help with design or choice, call them. They were extremely helpful. I would buy the CDT again...

[JMC1965]

Just researching to do sound in my restoration. I'm continually impressed with art, mechanical, and engineering knowledge on the forum.

thanks for sharing. I see some of these kick panels in my future

[88Stanger]

Awesome write up, sorry to bring up such an old write up, but this is good info.