First attempt at quasi fiberglass sub, almost finished (pics) - diyAudio
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Old 23rd April 2004, 01:13 AM   #1
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Default First attempt at quasi fiberglass sub, almost finished (pics)

**apologies in advance for huge pics**

... it is my car woofer that I talked about here before advice needed- lightest, loudest, lowest sub

Wanted to post it in this forum cause this gets alot more coverage then the car audio section, and this is still a 'loudspeaker' hehe. This was my first attempt at fiberglass. I started the molding back probably in October but here in the mideastern USA it started getting COLD out so I really lost the motivation to work with the stuff. That and I really didnt like to use that sticky and itchy fiberglass stuff. So....now that its spring time again I have some extra time on my hands I decided to finally finish my project.

The woofer is the parts express close out woofer, that is a TC Sounds made Kove Audio Z15D. I've been using my sonotube enclosure in my car but it rolls around, so here my progress on my latest fabrication.

My requirements were: must be able to still stow the top of the car in the hatch; must be able to use at least 15" woofer in car, must be lighter then what I had before (so 50-60 lbs max);must have the potential to look 1/2 decent; have cubic volume of 2.0-3.0 cubic feet, must be easily removed if I need it to be.

With these requirements in mind I came up with this- the top and exposed pieces are MDF, for their ease in straight lines and right angles. The bottom is fiberglass for its moldability and light weight, not to mention my first attempt at fiberglass I dont care how ugly the bottom turned out cause it would not be seen, as long as it was strong and did not leak.

I first was planning 2 15" woofers in a 4.0 cubic foot enclosure that took up all 3 storage wells in the rear but realistically that was too heavy, not to mention expensive and it was hard to stow the top.

So here it is After many hours of using the jig saw, circular saw, drill, angle grinder and sander, its finally coming to an end. a 2.5 cubic foot (estimated by filling the FB part with water, and doing calculations of the MDF part) enclosure that will house a 15 AND be able to stow the top. Now I have no clue how its going to sound when the top in place and the woofer firing directly into it. This will eventually be a ported design, so I may have the 3.5" ports coming out the side.

its almost done and ready to be used. Ive test fitted everything NUMEROUS times. It fits snug in the rear hatch well, but there still should be enough to do some sound dampening. It also should not have any trouble sliding around in the back cause of how well it is molded to the contours of the car, but at the same time it is easily removed. With the rear parcel shade on you cant even tell that it is there.

In a few hours, I just have to cut the hole for the wire connections, caulk the inside of the main baffle, fill the box with polyfill and put the woofer in. At first I am going to try it with no ports, to see how it sounds and check for airleaks. I dont anticipate there being any leaks cause I water tested the fiberglass and made sure it was not leaking AT ALL.

Weight isnt too bad, the entire enclosure is about 25 lbs. The woofer weighs more then the box at 30-35 lbs. Total I think the entire package is about 50-60 lbs or so, so that was right at my targeted weight limit. Definately a learning experience though. Unfortunately I wasted alot of fiberglass cause originally I was going to have the box much larger then it actually became. The fiberglass is messy, its expensive and it takes a while to build up.

I eventually plan to carpet it with OEM carpet, but this is definately not a "show" piece by anymeans.

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Old 23rd April 2004, 01:55 AM   #2
Bose(o) is offline Bose(o)  Canada
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Nice work so far! My friend has a Neon and those don't have much room, so a Shiva as such in an enclosure that is based on similar building blocks is in order. Thank you for posting, keep up the good work!

Oh and, how do you plan on finishing this beast?
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Old 23rd April 2004, 03:40 AM   #3
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I've been planning to install a sub in my car that's flush with the floor. I have a 94 escort with a really large spare tire well. I just can't justify getting rid of the spare for the sub...
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Old 23rd April 2004, 05:22 AM   #4
Eva is offline Eva  Spain
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Sorry to say that I think such a bad configuration doesn't deserve so much work

In a car you should NEVER radiate any sound into the trunk, otherwise you will excite trunk standing waves and all mechanical resonances and get awful response inside the cabin

The air volume inside the trunk acts like a 2nd order lowpass filter with high Q [peaks around 30-45Hz depending on car model] and only allows very low frequencies [distorted] and all the standing waves and mechanical resonance frequencies [80-200Hz] to pass to the cabin. The walls of the trunk also provide some atenuation so in some cars with metal walls you get as much as 20dB of attenuation and ridiculous SPL

What you get in the end when you turn up the volume a bit?

A lot of 35-45Hz awful rumble [even worse for ported subs] with nothing above except lots of noise in the range 80-200Hz [or even higher frequencies, no matter if you use 4th order lowpass, the sub will still radiate some midbass and the trunk cavity will amplify and resonate this midbass before passing it to the cabin]

In the other hand, you can get clean low frequency extension by using 4th [or 6th order] enclosures properly designed to have -3dB at about 50Hz [depending on car size] and rolloff at 12dB/oct below that, as long as you place the ports in such a whay they radiate directly to the cabin [placed airtight so no radiation escapes to the trunk] and adjust their tuning manually since formulas are not valid when there are surfaces near the ports [using same lenght you usually end with up to 50% more diameter than predicted to reach the desired tuning inside a car]

This rolloff below 50Hz compensates for cabin gain and markedly reduces required Xmax of the driver. I've succesfully used 8" drivers with +-3.5mm Xmax to get pretty decent listening/feeling levels [150W@35Hz-100Hz range] in small enough cars

This method allows to succesfully extend the LF response of even 4" front drivers using bandpass 'subs' [actually working as sub+midbass] with front chambers tuned to 100Hz that have clean output up to even 500Hz due to high port diameters and small chamber volumes

Bandpass also allows to tailor the frequency response of the driver, so you may make a 15" sound 'fast' [mid-bass enhanced and intentional but not excessive LF rolloff] or a 8" sound 'slow' [LF enhanced and intentional mid-bass attenuation]

That kind of bandpass designs provide front imaging even if you let them radiate reasonable amounts of SPL at 250hz since that radiation is 'clean'. Those standing waves and awful trunk resonances that produce that characteristic rear-coloured awful sound are simply absent

Anyway, this is only a suggestion, so if you like 'trunk sound' go ahead and have fun
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Old 23rd April 2004, 05:47 AM   #5
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Quote:
Originally posted by Eva

Anyway, this is only a suggestion, so if you like 'trunk sound' go ahead and have fun
Or if you actually drive your car, and need something that is better than nothing and also convienent. Or if you also realize that a car period is not the "ideal" place to have a speaker.


Other than that good work. Looks like you were able to keep the mess contained. I'm sure you'll enjoy it.


The only thing I'll add that is negative is.......put some clothes on that thing, because my god that thing is ugly
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Old 23rd April 2004, 07:00 AM   #6
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To all, thanks for the replys.

Quote:
Originally posted by Bose(o)

Oh and, how do you plan on finishing this beast?
I'm going to go to a junkyard and get OEM carpet, like the stuff you see around the hatch area. That way, the teture and grain will match perfectly. As you can see, my car has alot of flat area, so carpeting it to the flat area box will not be a problem.

Quote:
Originally posted by nicksmurf
I've been planning to install a sub in my car that's flush with the floor. I have a 94 escort with a really large spare tire well. I just can't justify getting rid of the spare for the sub...
In my old old car, I thought about cutting a hole in the spare tire well and doing a humongo infinate baffle setup with a weather resistant 18" PA woofer. but I couldnt find anything that was affordable, and Macauley was the only one I couldn find.


Quote:
Originally posted by Eva
Sorry to say that I think such a bad configuration doesn't deserve so much work

In a car you should NEVER radiate any sound into the trunk, otherwise you will excite trunk standing waves and all mechanical resonances and get awful response inside the cabin

The air volume inside the trunk acts like a 2nd order lowpass filter with high Q [peaks around 30-45Hz depending on car model] and only allows very low frequencies [distorted] and all the standing waves and mechanical resonance frequencies [80-200Hz] to pass to the cabin. The walls of the trunk also provide some atenuation so in some cars with metal walls you get as much as 20dB of attenuation and ridiculous SPL

What you get in the end when you turn up the volume a bit?

A lot of 35-45Hz awful rumble [even worse for ported subs] with nothing above except lots of noise in the range 80-200Hz [or even higher frequencies, no matter if you use 4th order lowpass, the sub will still radiate some midbass and the trunk cavity will amplify and resonate this midbass before passing it to the cabin]

In the other hand, you can get clean low frequency extension by using 4th [or 6th order] enclosures properly designed to have -3dB at about 50Hz [depending on car size] and rolloff at 12dB/oct below that, as long as you place the ports in such a whay they radiate directly to the cabin [placed airtight so no radiation escapes to the trunk] and adjust their tuning manually since formulas are not valid when there are surfaces near the ports [using same lenght you usually end with up to 50% more diameter than predicted to reach the desired tuning inside a car]

This rolloff below 50Hz compensates for cabin gain and markedly reduces required Xmax of the driver. I've succesfully used 8" drivers with +-3.5mm Xmax to get pretty decent listening/feeling levels [150W@35Hz-100Hz range] in small enough cars

This method allows to succesfully extend the LF response of even 4" front drivers using bandpass 'subs' [actually working as sub+midbass] with front chambers tuned to 100Hz that have clean output up to even 500Hz due to high port diameters and small chamber volumes

Bandpass also allows to tailor the frequency response of the driver, so you may make a 15" sound 'fast' [mid-bass enhanced and intentional but not excessive LF rolloff] or a 8" sound 'slow' [LF enhanced and intentional mid-bass attenuation]

That kind of bandpass designs provide front imaging even if you let them radiate reasonable amounts of SPL at 250hz since that radiation is 'clean'. Those standing waves and awful trunk resonances that produce that characteristic rear-coloured awful sound are simply absent

Anyway, this is only a suggestion, so if you like 'trunk sound' go ahead and have fun
I appreciate the input, very interesting indeed, infact when I had a sedan I always thought about a bandpass box that fired its ports directly into the cabin. However the car I'm working with right now is a coupe. There is NOTHING between the rear of the car and my head. Infact due to the shape of the glass, it helps to hornload the bass slightly (although the horn flare is going the wrong way). Also I have no clue how this is going to sound, but its pretty much the only option I have.


Quote:
Originally posted by Hybrid fourdoor


Or if you actually drive your car, and need something that is better than nothing and also convienent. Or if you also realize that a car period is not the "ideal" place to have a speaker.


Other than that good work. Looks like you were able to keep the mess contained. I'm sure you'll enjoy it.


The only thing I'll add that is negative is.......put some clothes on that thing, because my god that thing is ugly

Haha, yeah I'll put some OEM carpeting on it to make it look stock, but custom. But first gotta see how the woofer performs in its nakedness
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