# Turning my trunk into a subwoofer bandpass box



## chucked1 (Mar 2, 2016)

So i have a 10" pioneer subwoofer in a sealed enclosure (about 1.4 cubic feet i think) in my trunk of my 1997 miata. its a big help, but im hoping to improve it. 

im in the planning stages of trying to turn the whole trunk into a bandpass box that ports into the 'cabin' with a port that runs along the driver side tunnel.

im planning to cut a hole in the sheetmetal besides the driver and put a tube into the tunnel and remove the panel that separates the tunnel from the trunk. if i can fit some port flares great, but not crucial right now. i dont yet have a clear prediction of the diameter and length of the port until i work through the math. 

im working with my friend whos a speaker designer for a large PA company.

has this been done before?

im using this calculator to determine the size of the port that i want. 
mobileinformationlabs#com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201#htm

(cant post links yet so i replaced periods with # )

my goal is to add SPL on the cheap(esp below 40hz)! i think it will be quite easy, take carpet off, cut a big hole with a dremell or something, shove tube in and seal with epoxy.

other perks im hoping for, reducing the amount of force the trunk lid experiences, and therefore hopefully be a contributor in my rattle reduction strategy

reducing the impact that top down speed has on sound quality (i currently have to adjust my EQ and amp settings as i increase my speed, esp above 90)

im a big bass freak and love spending time in front of massive WALLS of 21" PA subwoofers at desert/underground music festivals/gatherings, i love the feeling of organ rattling bass and hair moving wind currents. im hoping to be able to feel a decent amount of wind with my hand/elbow when i put it in front of the port, to better connect with the low low bass that i love so much but will never really get out of a 10" (and yes i usually wear ear plugs, lets not get hung up on this)

no impact on trunk space


for reference, my system consists of a pioneer HU, pioneer gm-d1004 power pack amp giving 90w rms to front polk db6501 component speakers, 3.5" coaxial cheap headrest speakers (powered by HU), 10" subwoofer powered by 300 w rms soundstream amp (in passenger tunnel), 2 dayton bass shakers in each seat powered by cheap BOSS amp in passenger tunnel (in progress).

thanks for the help, i will do a lil writeup with some pics and results once its done


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## maggie-g (Aug 20, 2014)

is this a build log? What does this have to do with home or pro audio. This thread confuses me?


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## chucked1 (Mar 2, 2016)

maggie-g said:


> is this a build log? What does this have to do with home or pro audio. This thread confuses me?


not a build log, but ill post results once its done.

nothing to do with home audio or pro audio, just mentioned i was working with my speaker engineer friend to help people understand that we arent new to this and are taking it seriously and nerdily. 

im not finding anything about this approach on the internet, but wanted to check with you guys in case youve 'been there done that' and could share some knowledge and insights.


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## maggie-g (Aug 20, 2014)

I only asked because you posted this in the DIY home audio and Pro audio section of the forum.


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## Focused4door (Aug 15, 2015)

The trunk will leak air to much to work well. Build a proper bandpass box.


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## chucked1 (Mar 2, 2016)

Focused4door said:


> The trunk will leak air to much to work well. Build a proper bandpass box.


thats certainly one of my concerns. 
its hard to quantify how much leaking can be tolerated to still get significant positive gains. 

can i maybe strategize ways to make the system more tolerant of small leaks? (maybe a bigger port works better for this?)

ill do my best to find and seal the leaks with silicone or something, but it will never be perfect. but perfection is clearly not what im going for here. 
fun project with noticeable low bass SPL sensitivity gain with an added challenge of radical frugality 

best way to hunt leaks? im thinking putting a ton of smoke machine in the trunk and them pumping the system hard and looking for smoke around and under the car lol


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## gijoe (Mar 25, 2008)

chucked1 said:


> thats certainly one of my concerns.
> its hard to quantify how much leaking can be tolerated to still get significant positive gains.
> 
> can i maybe strategize ways to make the system more tolerant of small leaks? (maybe a bigger port works better for this?)
> ...


Sealing the trunk will be very important. You aren't going for perfection, but have you ever heard a sealed box that wasn't actually sealed? It sounds awful. If the part of the enclosure is intended to be sealed, it needs to be completely sealed. I don't think there is a way to seal it to a satisfactory level, I suspect that even the rubber weather strip for the trunk will leak enough air to ruin the response. 

You could always try, but I think there is a good reason you can't find examples of people doing this.


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## chucked1 (Mar 2, 2016)

gijoe said:


> Sealing the trunk will be very important. You aren't going for perfection, but have you ever heard a sealed box that wasn't actually sealed? It sounds awful. If the part of the enclosure is intended to be sealed, it needs to be completely sealed. I don't think there is a way to seal it to a satisfactory level, I suspect that even the rubber weather strip for the trunk will leak enough air to ruin the response.
> 
> You could always try, but I think there is a good reason you can't find examples of people doing this.


well im currently pumping into the trunk which then leaks everywhere else, so i really think that adding this port will help my SPL as well as sound quality. 

i think that the better i seal the trunk after that the more optimal the gains will become. 

im tempted to try a port with adjustable length so that i can just tune it by ear and SPL meter since the leaks in the trunk will make hard to calculate and predict the optimal port specs. i could use PVC piping with a 3 different length sleeves that slide over the initial inner section to get a big range of length attempts. 

i agree that the total lack of mention of anything like this anywhere on google is a bit surprising given how simple it can seem to be (cut a hole!) , but then again ive previously done lots of audio projects before that werent at all (or barely) discussed on the internet (such as lots of different types of bass shaker installs more than 12 years ago). theres a lot of us that do cool **** and dont post about it online, im only here now because i dont have anything better to do at my office, and i enjoy the mental masturbation lol.


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## Focused4door (Aug 15, 2015)

gijoe said:


> Sealing the trunk will be very important. You aren't going for perfection, *but have you ever heard a sealed box that wasn't actually sealed? It sounds awful.* If the part of the enclosure is intended to be sealed, it needs to be completely sealed. I don't think there is a way to seal it to a satisfactory level, *I suspect that even the rubber weather strip for the trunk will leak enough air to ruin the response.
> *
> You could always try, but I think there is a good reason you can't find examples of people doing this.


A leaky bandpass box will be worse than a leaky sealed box. 

I suspect the weather strip will be the worst leak in the car, and the hardest to deal with.

If you want more volume and to save the trunk space, infinite baffle is the way to go. Lots of infinite baffle drivers to choose from if the pioneer doesn't work infinite baffle (I have no idea if it does or not)


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## XSIV SPL (Jun 24, 2014)

I've never seen a trunk successfully turned into a predictable and reliable band pass enclosure, but hey... I'm subbed!


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## chucked1 (Mar 2, 2016)

XSIV SPL said:


> I've never seen a trunk successfully turned into a predictable and reliable band pass enclosure, but hey... I'm subbed!


i agree that i dont think my system is predictable, which is why my current plan is to install a 6" pipe and use trial and error of different length until i find something that works best.

if somehow everything i try ends up worse than it use to be, ill remove one of the semi-useless panels that separate the trunk and cabin, and that should remove any pressure/bandpass effect and give me a more direct connection to the sub.


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## gijoe (Mar 25, 2008)

chucked1 said:


> i agree that i dont think my system is predictable, which is why my current plan is to install a 6" pipe and use trial and error of different length until i find something that works best.
> 
> if somehow everything i try ends up worse than it use to be, ill remove one of the semi-useless panels that separate the trunk and cabin, and that should remove any pressure/bandpass effect and give me a more direct connection to the sub.


Changing the port won't fix the lack of a proper seal to the part of the enclosure that needs to be sealed. You can't fix the leaky part by changing the tuning of the port. Go IB, it'll be half the work, and will give a very predictable and flat response.


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## chucked1 (Mar 2, 2016)

gijoe said:


> Changing the port won't fix the lack of a proper seal to the part of the enclosure that needs to be sealed. You can't fix the leaky part by changing the tuning of the port. Go IB, it'll be half the work, and will give a very predictable and flat response.


i cant go IB, nowhere to put a sub. also the cost is huge (compared to cutting a hole and gluing a tube)

i cant fix the leak, but i can find a tube length that works WITH the leaks to result in something decent (hopefully!)


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## gijoe (Mar 25, 2008)

chucked1 said:


> i cant go IB, nowhere to put a sub. also the cost is huge (compared to cutting a hole and gluing a tube)
> 
> i cant fix the leak, but i can find a tube length that works WITH the leaks to result in something decent (hopefully!)


No, you can't. That's what we are saying. The port changes the tuning frequency, it will not make up for the fact that part of the enclosure that is supposed to be sealed isn't sealed. I don't understand why you don't have room for IB but you have room for a poorly done bandpass box. Where are you planning on mounting the sub right now? IB will take up less space than your current sealed box.


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## rton20s (Feb 14, 2011)

I think you may want to take into consideration that everyone who has responded so far has given you similar advise and attempted to dissuade you from pursuing you initial plan. 

I would suggest researching the use of a different driver that will perform to your liking with the selection of the correct enclosure type and size as well as sufficient power.

Just my 2 cents.


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## chucked1 (Mar 2, 2016)

gijoe said:


> No, you can't. That's what we are saying. The port changes the tuning frequency, it will not make up for the fact that part of the enclosure that is supposed to be sealed isn't sealed. I don't understand why you don't have room for IB but you have room for a poorly done bandpass box. Where are you planning on mounting the sub right now? IB will take up less space than your current sealed box.


i CURRENTLY have a 10" in a sealed box inside the trunk. since i have a sealed box inside of my leaky trunk, i effectively ALREADY have turned my 'system/trunk' into a 4th order bandpass box, its just that currently the 'port' is a combination of all the leaks in the trunk. 

by adding a semi-calculated big port that feeds near my seat, i have a good chance of getting better bass and less rattles. and at effectively zero cost. 

if it doesnt work, ill have lost some time, but will have tried and failed a fun project and learned some lessons along the way. 

im not currently interested in buying a different box or driver.


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## gijoe (Mar 25, 2008)

chucked1 said:


> i CURRENTLY have a 10" in a sealed box inside the trunk. since i have a sealed box inside of my leaky trunk, i effectively ALREADY have turned my 'system/trunk' into a 4th order bandpass box, its just that currently the 'port' is a combination of all the leaks in the trunk.
> 
> by adding a semi-calculated big port that feeds near my seat, i have a good chance of getting better bass and less rattles. and at effectively zero cost.
> 
> ...


Knock yourself out. The difference is that your current sub is in a properly sealed enclosure, you new plan won't be.

Do you're thing though, just don't expect much help. Very few people are interested in helping someone with a bad idea.


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## chucked1 (Mar 2, 2016)

gijoe said:


> Knock yourself out. The difference is that your current sub is in a properly sealed enclosure, you new plan won't be.
> 
> Do you're thing though, just don't expect much help. Very few people are interested in helping someone with a bad idea.


youre not getting it. im NOT touching my current sealed subwoofer. all im doing is making the leaks of the trunk bigger and aiming them towards me. and hopefully tuning them to achieve a slight sensitivity gain down low.


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## truckerfte (Jul 30, 2010)

Guys, it sounds like the man has made his decision. Let him do it, and post his results...


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## gijoe (Mar 25, 2008)

chucked1 said:


> youre not getting it. im NOT touching my current sealed subwoofer. all im doing is making the leaks of the trunk bigger and aiming them towards me. and hopefully tuning them to achieve a slight sensitivity gain down low.


I understand, but I don't understand how you think that is going improve things.


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## danssoslow (Nov 28, 2006)

Op, have you ever read that, at the tuning frequency, that the pressure inside of a ported enclosure is greater than that of a sealed enclosure?

Think of it this way, if you were to substitute the port with a passive radiator, do you believe that you could create the pressure in your trunk to get the PR moving effectively? The exact same situation will be involved using a port. 

Now, if you could seal the trunk; fill small crevices with foam, glass the outer surfaces, come up with some way to seal the trunk lid (maybe use some mdf, attach it somehow around the trunk opening, which creates a lip for you to attach a removable wall for access purposes, dunno), it would seem that making it a bandpass would be a simple as throwing a sealed enclosure into that sealed and ported space.

Nothing is impossible, but it surely doesn't sound easy.


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## chucked1 (Mar 2, 2016)

danssoslow said:


> Op, have you ever read that, at the tuning frequency, that the pressure inside of a ported enclosure is greater than that of a sealed enclosure?
> 
> Think of it this way, if you were to substitute the port with a passive radiator, do you believe that you could create the pressure in your trunk to get the PR moving effectively? The exact same situation will be involved using a port.
> 
> ...


thank you for an insightful and helpful post. you've redeemed my experience with this thread today. 

thinking of trying to move a passive radiator with good force has put a useful perspective on this. 

im going to go forward with my plan of putting a smoke machine in the trunk and pressurizing the system best i can (ideas for this? im thinking a paintball co2 bottle that purges into the trunk) to find ans seal leaks with silicone. and then using a large port and trying to tune the length to until i get something useful.


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## danssoslow (Nov 28, 2006)

I don't think the co2 would work at pressuring the trunk, I wouldn't waste the $15 to find out. Do the smoke, and plan on sealing everything regardless, I would seal to prepare for the pressure, rather than testing with it. How much pressure would be necessary? If you plan on using the same enclosure and sub you have now, try cranking some bass while you use the fog machine.

Befriend a person working at a packaging place, have them fill the trunk with peanuts, and calculate the trunk volume. From there, you can use a box bulging program to calculate the port.


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## Viggen (May 2, 2011)

:lurk:


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## danssoslow (Nov 28, 2006)

Since the trunk is an unwavering constant here, the sub will have no choice to change if it does not play nice; but I'm not certain how forgiving bandpasses are with ts params.

It's definitely an interesting proposition.


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## XSIV SPL (Jun 24, 2014)

chucked1 said:


> thank you for an insightful and helpful post. you've redeemed my experience with this thread today.
> 
> thinking of trying to move a passive radiator with good force has put a useful perspective on this.
> 
> im going to go forward with my plan of putting a smoke machine in the trunk and pressurizing the system best i can (ideas for this? im thinking a paintball co2 bottle that purges into the trunk) to find ans seal leaks with silicone. and then using a large port and trying to tune the length to until i get something useful.


Oh my...

I hate to say this, but your entire trunk area will become a non-mass-loaded passive radiator before it will become a useful enclosure.

(Watching, but with trepidation)


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## Focused4door (Aug 15, 2015)

danssoslow said:


> I don't think the co2 would work at pressuring the trunk, I wouldn't waste the $15 to find out. Do the smoke, and plan on sealing everything regardless, I would seal to prepare for the pressure, rather than testing with it. How much pressure would be necessary? If you plan on using the same enclosure and sub you have now, try cranking some bass while you use the fog machine.
> 
> Befriend a person working at a packaging place, have them fill the trunk with peanuts, and calculate the trunk volume. From there, you can use a box bulging program to calculate the port.


The packing peanuts isn't a bad idea, but honestly I would probably just bust out a tape measure and call it close enough. If you use a PVC pipe for a port, it is cheap and likely be buying 8-10 ft of it anyway, so plenty of it to test different lengths. Just start on the long side and cut it down until you cut it to short, then grab some of the leftover and cut to the desired length. 





danssoslow said:


> Since the trunk is an unwavering constant here, the sub will have no choice to change if it does not play nice; but I'm not certain how forgiving bandpasses are with ts params.
> 
> It's definitely an interesting proposition.


Bandpass aren't as forgiving as other box types, and it can be kind of interesting to plug in variances on parameters to see the effects. It's been a long time since I have done that, so can't recall what parameters have the biggest impact.

I still think the trunk seal is going to be the biggest problem, and likely to be inconsistent in leakage. Might have some differences with temperature changes as well due to the gasket seal.


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## XSIV SPL (Jun 24, 2014)

As I said earlier, I doubt that you'll successfully convert your trunk into a usable band pass enclosure, but if I were trying to evaluate a car with a trunk full of styrofoam peanuts and it sounded great, I'd say run with it


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## chucked1 (Mar 2, 2016)

packing peanuts are a good idea, as there are some seriously hard to get to areas of the trunk where a tape measure would not work. 
though depending on how much stuff im carrying the volume will change a lot either way.

im thinking that i can use the spare tire and let it leak out with a trunk full of smoke to hunt down some of the major leaks.


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## XSIV SPL (Jun 24, 2014)

Well, good luck with this


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