Real Fiero Tech

OK, i built a fiberglass box a while back to go under my hood, i removed the AC crap and made the washer fluid bottle smaller as well as a few other things i had to do in order to get the required air space for the subs. now i got the box as big as it needs to be and am ready to port it into the cab, but i dont know how. any ideas?

Also, can i sound deaden the inside of the box? or would that be bad? i have some deadener material (like dynamat) left over from something else, and i figure that might help it get to the cab a little better?

subwoofer info:
http://www.flashinstall.com/catalog.php ... egory%3D19

more specs:
FX-10W
• 1600 Watts power handling
• 800 Watts RMS
• 160 oz. magnet
• 2.5" BASV voice coil
• SPL 91dB
• Fs: 40 Hz
• Vas: 0.58 cu.ft.
• Qms: 5.58 • Qes: 0.63 • Qts: 0.566
• Xmax: 10mm
• Sealed box: 1 cu..ft.
• Ported box: 1.5 cu..ft.
• Tuning: 39 Hz.
• Port size: 4" (dia) x 13.6" (Length)
• # of ports: 1
• Mounting Depth: 6.2â€

Is it bandpass or just a ported box?

It's common to put damping material inside boxes. This helps them "appear" acoustically bigger to the woofer without unloading the cone at low frequencies.

The installs I've seen have piped the ports into the footwells via flexible ducting (like flex-pipe for exhausts).

as of right now, its just a sealed fiberglass box.

heres how it sits right now:

High resonant freq and pretty stiff suspension (Qts > .50)... those are going to like ported boxes best. I wouldn't even use one in a sealed box, much less one as small as 1 ft3.

You are aware that you're going to be using a big chunk of your power to rattle the front lid, right? If you can seal the front compartment reasonably well, you *might* be able to get a half-way bandpass effect out of that volume, but I don't think it will be worth much.

13.6 inches ought to be enough port to duct to the footwells. there's really no other place to bring a port into the cockpit without cutting up or sacrificing other systems in the car.

yeah, i made the box a little bigger than 3 cu. ft. (yes i figured in the area of the subs themselves) as i planned to port it, i just didnt want to cut anything until i knew for sure what i was doing.

so basicaly i just want to run a 4" "duct" of sometype into the cab that is close to 13.6" long??

Jinxmutt wrote:http://www.crutchfieldadvisor.com/ISEO- ... fiero.html

yeah, ive seen that about 1000 times, but it doesnt help me at all.

slow'n'steady wrote:so basicaly i just want to run a 4" "duct" of sometype into the cab that is close to 13.6" long??

Two. One for each woofer volume.

The box is all wrong. The box you built is a ported box. The port size is designed to compliment what is coming out of the woofer hence the port is tuned to produce a specific 1/4 wave frequency. To build a ported box and then just use the port for the sound will decrease sound quality. You would only be using the 1/4 wave part of the sound, your bass will sound "muddy" and have a decreased volume.
If you look at the Crutchfield link you will notice you cannot see the speaker. This is because he built a single reflex bandpass enclosure which is designed to seal the rear of the woofer and take the sound from the front of the speaker via a port. This takes all the sound and passes it thru a tuned port. Which is what you want to do to your car.

For subwoofer box designs check out this link:
http://www.the12volt.com/caraudio/boxes4.asp

The box isn't ALL wrong... it's just wasting a lot of its energy.

If you think about the funcitoning of a ported box vs bandpass, you'll see that the output of the port on a bandpass box is the response of the woofer as installed in the sealed volume filtered through the ported volume. The response of the port from a ported box is the infinite baffle response of the woofer filtered through the ported volume.

Obviously that's a simplification, since the ported volume affects the response of the woofer due to the two having similar impedances for sound propagation...

So he won't get sound that's THAT strange out of the port. It'll just waste a lot of energy rattling the hood.

The original "bandpass under the front lid" build was at a website called "Luna Park's Thrill Ride", but that has been taken down. It was a NICE build that featured a fully custom interior with D'apollito mids/tweets in the dash.

being that you are using the port for sound, you dont want to put any dampening material in the box. also, dampening is for when the box is to small, and you need to "fake" interior volume. PVC makes for a easy way to make the duct/port to the cabin. use at least as large pipe dia as the voice coil.

The Dark Side of Will wrote:The box isn't ALL wrong... it's just wasting a lot of its energy.

If you think about the funcitoning of a ported box vs bandpass, you'll see that the output of the port on a bandpass box is the response of the woofer as installed in the sealed volume filtered through the ported volume. The response of the port from a ported box is the infinite baffle response of the woofer filtered through the ported volume.

Obviously that's a simplification, since the ported volume affects the response of the woofer due to the two having similar impedances for sound propagation...

So he won't get sound that's THAT strange out of the port. It'll just waste a lot of energy rattling the hood.

OK so his box isn't "wrong" he is just using it in the wrong application.

Not only is he losing energy, but also 3/4's of the sound wave. Ported boxes have the port setup to take the 1/4 wave of the resonate frequency. Bass-Reflex boxes have the port designed to use the full wave of the resonate frequency. Just using the 1/4 wave will make his bass sound like a muddy, distorted drone.

Obviously he has spent some time and money because he wants to make his stereo system sound nice. Why give him poor advice on using a box in the wrong application instead of showing him the proper box for what he wants to do?

Ok... dumb idea

i need a "bandpass" style enclosure, soo If i where to seal the front compartment, and leave the box sealed, could i just port from the compartment to the cab? (so basicaly the open area outside the box will act as the front ported section of the bedpass box and the actual box will be the rear ported section.?)

Also i didnt spend any money really, i had the subs from an old project i sold and decided to keep them. I had all lthe fiberglass laying around as well as the MDF (MDF was from an old box i tore up). i was cleaning the garage gettin ready to throw it all out and decided i might as well use it. Only thing that is going to cost me money are the component speaker system and the wiring/ Orion D1200 amp.

well, since you have most the work done already - how about just mounting the speakers in the boxes backwards, and continue with port tube?

I dont know much about box design either...

Pyrthian wrote:well, since you have most the work done already - how about just mounting the speakers in the boxes backwards, and continue with port tube?

I dont know much about box design either...

you mean mount them with the magnets facing up/out? trying to fit such a big amount of box area into a small space was a bitch! i had to make the box as big as possible and while doing so i left only enough room for the subs full range of motion. only way i could do that would be cut a couple huge chunks out of the hood :bootyshake:

Mastermind wrote:Not only is he losing energy, but also 3/4's of the sound wave. Ported boxes have the port setup to take 1/4 of the resonate frequency. Bass-Reflex boxes have the port designed to use the full wave of the resonate frequency. Just using the 1/4 wave will make his bass sound like a muddy, distorted drone.

The port and woofer share a much more complicated relationship than that. At the resonant frequency the woofer cone is heavily loaded and the transfer of energy from the cone to the box is very efficient. The woofer cone is barely moving and most of the sound comes from the port. This is why a bandpass box is a bandpass... it has ONLY the sound of the port.

slow'n'steady wrote:i need a "bandpass" style enclosure, soo If i where to seal the front compartment, and leave the box sealed, could i just port from the compartment to the cab? (so basicaly the open area outside the box will act as the front ported section of the bedpass box and the actual box will be the rear ported section.?)

It would be blind luck if the remaining volume of the front compartment were correct to make a decent bandpass ouf of that box. Also, the hood and front bucket are NOT stiff enough to make decent boxes.

If you don't have any money in it, tear it down and build a bandpass. However, due to the high Qts, those woofers are probably not well suited to making compact sealed/bandpass boxes that actually sound good.

The Dark Side of Will wrote: The port and woofer share a much more complicated relationship than that. At the resonant frequency the woofer cone is heavily loaded and the transfer of energy from the cone to the box is very efficient. The woofer cone is barely moving and most of the sound comes from the port. This is why a bandpass box is a bandpass... it has ONLY the sound of the port.

Not exactly, The port on a bass-reflex bandpass box will put out the sound of the tuned cavity thru the port. Not the "sound of the port". Both need to be tuned. Yes it is a complicated relationship and a bass-reflex bandpass box is more difficult to setup/tune. The sound is from the tuned cavity not the port.

On a regular ported box, the port is setup to use the 1/4 wave of the resonate frequency. So this is where you want only just the "sound of the port" and why just using the port as the bass source would make for a poor quality sound.

Mastermind wrote:On a regular ported box, the port is setup to use the 1/4 wave of the resonate frequency.

You've used this terminology multiple times. You must know what it means, but you need to explain it better because it's gibberish.

I guess I should have written "sound FROM the port". You're right, the port by itself doesn't make any sound (unless it's too small for the application). It only acts in conjunction with the compliance of the ported volume.

Sealed: Best cone control, least power efficiency, best space efficiency(but depends on driver), most accurate sound reproduction

Ported: trade-off of cone-control to regain some efficiency--but not as huge as a bandpass. Decent sound reproduction, but can tend towards "peakiness" as well as problems with vent noise.

Bandpass: Good cone control, very power efficient, requires lots of space, sound reproduction is OK--but ONLY within the passband.

Ported and Bandpass both sound like complete and utter SHIT unless the box is made "just right." Of all the enclosure designs, sealed is the most "forgiving" in terms of size, but the box must be very well sealed.

I've got a program that'll give you the appropriate volumes and port length, but it's at home.

The Dark Side of Will wrote:

Mastermind wrote:On a regular ported box, the port is setup to use the 1/4 wave of the resonate frequency.

You've used this terminology multiple times. You must know what it means, but you need to explain it better because it's gibberish.

Gibberish?? Have you ever built subwoofer boxes?
To build a ported box you need the Theile/Small parameters for the driver.
Then take these parameters:
Vas = Equivalent air compliance (litres)
Qts = total Q of the driver at its resonant frequency
Fs = resonance frequency of the driver (Hz)
Dv = internal diameter of port (cm)

To calculate the box parameters,

Vb = 20*Qts^3.3*Vas
Fb = (Vas/Vb)^0.31*Fs
F3 = (Vas/Vb)^0.44*Fs
dBpeak = 20*LOG(Qts*(Vas/Vb)^0.3/0.4)

where,

Vb = net box volume (litres)
Fb = box resonant frequency (Hz)
F3 = -3dB frequency (Hz)
dBpeak = maximum peak or dip in system response

The port length is then calculated with Lv = (23562.5*Dv^2*Np/(Fb^2*Vb))-(k*Dv)

Dv = port diameter (cm)
Fb = tuning frequency (Hz)
Vb = net volume (litres)
Lv = length of each port (cm)
Np = number of ports
k = end correction (normally 0.732)

Giving you a port designed to use 1/4 of the sound wave (the peaks of the Fb's sine wave) at the boxes resonate frequency (Fb) which gives you the greatest sound pressure out of the port.