porting box to cab (built, just need port help)

[The Dark Side of Will]

Gibberish?? Have you ever built subwoofer boxes?

I'm quite familiar with the equations. Yes, I've built boxes. My current house subs are Jensen 10's in dual chamber ported boxes. They're big, but they give me pretty flat response down to 25 Hz. The dual chamber arrangement gives two resonant frequencies an octave apart and thus loads the cone and controls cone excursion over a wider range of frequencies than a conventional ported box.
I'm not using it right now, but I also built a "party box" using a pair of the original high efficiency Kicker XPL 10's. The box is a bandpass box tuned for high efficiency using a dual chamber on the ported side. The extra resonant frequency gives it an octave better high frequency range than a normal bandpass.

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.

This is what I meant by "gibberish". Are you trying to say that the port only radiates the upper 1/4 of the wave's amplitude? I can't evaulate the correctness of that because it doesn't even make sense. And it would generate a hideous waveform. Anyway, that's not how a port works.
A ported box is a helmholtz resonator. The compliance of the volume within the box acts like a spring and the mass of air in the port act like the mass of a spring-mass oscillator (google that). The woofer excites the air in the box at the resonant frequency and the box resonates. Because the energy transfer from the speaker to the air in the box is very good at the resonant freq, the woofer cone barely moves. It displaces almost no air in the room. It puts almost no sound into the room. The VAST MAJORITY of the sound the box makes at the resonant frequency comes from the port.

I have a pretty good (and pretty rare) book on the topic. I'ts packed up right now but I'll try to find it in the next few weeks.

[Mastermind]

Are you trying to say that the port only radiates the upper 1/4 of the wave's amplitude?

No it does not only radiate the upper 1/4 wave's amplitude, It is tuned to that point to increase the sound pressure level at the resonate frequency.
Which is the same as your statement "The VAST MAJORITY of the sound the box makes at the resonant frequency comes from the port."

The point was the port on a ported subwoofer box is designed to work at the resonate frequency, On the bass-reflex bandpass box the port is designed to pass a tuned band of frequencies. Hence why using just the port of a ported subwoofer box will sound like crap.

A ported box is a helmholtz resonator. The compliance of the volume within the box acts like a spring and the mass of air in the port act like the mass of a spring-mass oscillator (google that). The woofer excites the air in the box at the resonant frequency and the box resonates. Because the energy transfer from the speaker to the air in the box is very good at the resonant freq, the woofer cone barely moves. It displaces almost no air in the room. It puts almost no sound into the room. The VAST MAJORITY of the sound the box makes at the resonant frequency comes from the port.

A helmholtz resonator? I don't think so. Some of the priciples are similar but not quite the same. An acoustic guitar is a helmholtz resonator but not a ported subwoofer box.

[The Dark Side of Will]

Are you trying to say that the port only radiates the upper 1/4 of the wave's amplitude?

No it does not only radiate the upper 1/4 wave's amplitude, It is tuned to that point to increase the sound pressure level at the resonate frequency.

Oviously it doesn't actually do that. If that's not what you're trying to say, what are you trying to say? This may simply be a difficulty in terminology, but your terminology IS GIBBERISH. The term "1/4 wave" by itself is meaningless.

Which is the same as your statement "The VAST MAJORITY of the sound the box makes at the resonant frequency comes from the port."

What you're saying doesn't bear any resemblance to what I'm saying. What are you really trying to say when you say "1/4 wave point"?

The point was the port on a ported subwoofer box is designed to work at the resonate frequency, On the bass-reflex bandpass box the port is designed to pass a tuned band of frequencies. Hence why using just the port of a ported subwoofer box will sound like crap.

The port works in a frequency range around the resonant frequency. The response is a bell curve centered around the resonant freq on a log plot of frequency. This is why a bandpass cuts itself off at high frequencies. The port stops resonating (until the frequency gets up to integral multiples of the tuning frequency... which is one reason a bandpass still needs a crossover).

A helmholtz resonator? I don't think so. Some of the priciples are similar but not quite the same. An acoustic guitar is a helmholtz resonator but not a ported subwoofer box.

OK. What about a ported box makes it NOT a helmholtz resonator?

[slow'n'steady]

OK... since you seem to know you shit...

how do you calculate space needed for a bandpass box? also when building a bandpass is it considered sealed? as in i would only make it 2 cu.ft. instead of 3 (1 cu ft. for sealed box, 1.5" for ported)

I ask because i will be using the same subs in my trans am and would like to make a bandpass for it. i want the actual "box" to be in the rear well, then the front section to kinda come up over the rear are and have the port be right where the tops of the rear seats use to be (if you can fallow any of that)

[Mastermind]

Oviously it doesn't actually do that. If that's not what you're trying to say, what are you trying to say? This may simply be a difficulty in terminology, but your terminology IS GIBBERISH. The term "1/4 wave" by itself is meaningless.

Gibberish only because you don't know what it means.

Here is a quote from an article in Car Audio Magazine:

"The goal of designing the enclosure is to create the loudest peak possible near the 1/4 wave frequency"

Read the article at the link below.

http://www.caraudiomag.com/technical/02 ... rs_basics/

Note: I was mistaken previously, It is not the "peak", But 90* off of the peak of the sine wave.

OK. What about a ported box makes it NOT a helmholtz resonator?

The fact that a ported subwoofer box does NOT use an enclosed volume of air to act as a spring connected to the mass of the slug of air.

A Helmholtz resonator or Helmholtz oscillator is a container of gas (usually air) with an open hole (or neck or port). A volume of air in and near the open hole vibrates because of the 'springiness' of the air inside. A common example is an empty bottle: the air inside vibrates when you blow across the top.

A ported subwoofer box has a frequency driver (speaker/woofer) creating a sonic wave (sound wave) into a tuned cavity. The resonate frequency of the cavity is then outputted thru a tuned port to help produce an efficient flat frequency response out of the subwoofer.

The only thing that is the SAME is that loudspeaker enclosures often use the Helmholtz resonance of the enclosure to boost the low frequency response. But they are NOT "Helmholtz resonators". Even a sealed subwoofer box uses the helmholtz resonance of the enclosure to calculate it's Fb.

[The Dark Side of Will]

Gibberish only because you don't know what it means.

Here is a quote from an article in Car Audio Magazine:

"The goal of designing the enclosure is to create the loudest peak possible near the 1/4 wave frequency"

Read the article at the link below.

http://www.caraudiomag.com/technical/02 ... rs_basics/

Note: I was mistaken previously, It is not the "peak", But 90* off of the peak of the sine wave.

I don't know what you mean by it. That's probably because someone who doesn't quite get it is using the term incorrectly or out of context.
The mathematics associated with speaker enclosures is MUCH better done in the frequency domain. I suspect that someone is getting down into the time domain which is WAY too far into the weeds and does not readily facilitate a conceptual understanding of the phenomenon.

I'll read the article and reply in more depth later.

[Mastermind]

I don't know what you mean by it. That's probably because someone who doesn't quite get it is using the term incorrectly or out of context.
The mathematics associated with speaker enclosures is MUCH better done in the frequency domain. I suspect that someone is getting down into the time domain which is WAY too far into the weeds and does not readily facilitate a conceptual understanding of the phenomenon.

I'll read the article and reply in more depth later.

Sorry, I thought you had at least some knowledge of building subwoofer boxes for an application inside an automobile. Obviously you do not. I used the term correctly and in context. The thing being you never heard of the term and assumed gibberish is kind of an ignorant viewpoint on your part. You know it's OK to admit you are unfamiliar with a term instead of calling it gibberish.


Oh well, I've made my point that it whould have been better to advise the original author of this thread on proper application rather than trying to use a subwoofer box incorrectly.

Enjoy.

[The Dark Side of Will]

I've made my point that it whould have been better to advise the original author of this thread on proper application rather than trying to use a subwoofer box incorrectly.

No, you have NOT made a point.
You chastised me for not giving advice that was ideal for the application...
but then you link that article that gives setup advice for an SPL competition car. Talk about IRRELEVANT to the APPLICATION. That's like giving top fuel dragster tuning advice to a guy who asked how he could make his 2.hate faster.
"Hello, Kettle? This is Pot. How's every little thing? OBTW, you're BLACK!!!"

Second, you and the guy who wrote that article are both confusing transmission line enclosures with ported enclosures.
What he means by "1/4 wave" is that he's trying to set up a standing wave in the car. Since a full wave at extremely low frequency is too long to fit in the car, he selects a frequency that will fit 1/4 of a wavelength between the subwoofer and the microphone. By choosing a frequency that is an integral fraction of the fundamental in that space, he's trying to set up 1/4 of a standing wave AT THE PRIMARY FREQUENCY.

Now, what he is trying to do with the rest of the article is achieve a 180 degree phase shift in the back wave of the woofer. This is a separate endeavor. The only thing it shares with the 1/4 wavelength discussion is the primary frequency.
Using one of his drawings,
I will name a new term E = D - A. The way to achieve a 180 degree phase shift is to make B + C + E = 1/2 wavelength AT THE PRIMARY FREQUENCY. For 68 Hz as in the article, this total distance would be 8.3 feet. The enclosure would be roughly 4 feet deep. That's pretty big, but certainly not out of the question for an SPL competition car. At least that's what the author thinks is going on. There's a LOT more to sound propagation than ray tracing. Transmission line enclosures are parametrized by centerline distance, NOT raytrace distance, and the helmholtz characteristics of a ported box make it NOT a transmission line.

What does this methodology have to do with setting up a bandpass box in the front of a Fiero? NOTHING AT ALL.

The entire point of an SPL comp car is to make the max possible SPL at ONE frequency... it is NOT to reproduce music. The whole point of a sound system in a "normal" car is to reproduce music. This requires a reasonably flat frequency response that extends to as low a frequency as possible, which, as the article states is NOT the way an SPL comp system works.

So every technique in that article, including the famed "1/4 wave point" is ABSOLUTELY WRONG for a non-competition car.
You've also haughtily suggested a bandpass. Front/rear phase matching with a bandpass is IMPOSSIBLE because the rear chamber is sealed. All this information you've posted is IRRELEVANT.

[The Dark Side of Will]

OK... since you seem to know you shit...

how do you calculate space needed for a bandpass box? also when building a bandpass is it considered sealed? as in i would only make it 2 cu.ft. instead of 3 (1 cu ft. for sealed box, 1.5" for ported)

I ask because i will be using the same subs in my trans am and would like to make a bandpass for it. i want the actual "box" to be in the rear well, then the front section to kinda come up over the rear are and have the port be right where the tops of the rear seats use to be (if you can fallow any of that)

You can't use a standard sealed box formula to spec the sealed side of a bandpass and you can't use a standard ported box formula to spec the ported side of a bandpass. Each volume loads the sub in its own way and affects the way the sub interacts with the other volume.

In the past I've used Blaubox (formerly available from the Blaupunkt website) to calculate box parameters. However, I can't find it on the site now. Its primary virtues were simplicity and speed.
Putting "blaubox" into google brings up this page: http://diyaudiocorner.tripod.com/software.htm which reviews several programs for coming up with box specs.

Since there's some fudge factor in any box design, Blaubox fudges toward the small end for box volume. I used its volume, but filled the boxes with polyester batting and they work well. For my senior lab experiment I measured the frequency response of the dual front chamber bandpass I discussed earlier in this thread and it was exactly what I expected it to be.

I have not measured the freq response of the dual chamber ported boxes, but they don't have any obvious lumps when playing a sweep tone.

[Pyrthian]

well, either way you two: whats this guys solution?
at least I gave a half assed attempt by saying put the speaker in backwards, and use PVC for the porting, at min size being the voice coil size.
can a speaker be mounted in the front trunk area, and be succesfully ported into the cabin, and sound good? and, if so - any clue on how?
and, if neither of you can give a good answer - how bad is what he is currently doing gonna sound?

[The Dark Side of Will]

Your advice has already been addressed. He said that he can't put the speakers in backwards because they'd hit the decklid. That wouldn't do anything for the sound of the box anyway.

The specs he posted call for a 4" port. A port the size of the voice coil would be WAY too small.

I said that if he wouldn't be out any money, he ought to go ahead and tear the box down and rebuild it as a bandpass. That would be the best option.

As is now, he's going to be using a lot of his power to shake the hood.

[Mach10]

OK... since you seem to know you shit...

how do you calculate space needed for a bandpass box? also when building a bandpass is it considered sealed? as in i would only make it 2 cu.ft. instead of 3 (1 cu ft. for sealed box, 1.5" for ported)

I ask because i will be using the same subs in my trans am and would like to make a bandpass for it. i want the actual "box" to be in the rear well, then the front section to kinda come up over the rear are and have the port be right where the tops of the rear seats use to be (if you can fallow any of that)

Throw me your email address in PM. I've got something for yaz. :thumbleft:

[The Dark Side of Will]

I realized that after this "debate" about terminology, I didn't post up what the correct terminology is.

The term "1/4 wave point" has a meaning very specific to the article that Mastermind posted ( http://www.caraudiomag.com/technical/02 ... rs_basics/ ).
But in situations other than that desctibed by the article, the same effect could be achieve via a "half-wave point", a "full-wave point", or even a "6432 wave point".

The effect that he was actully trying to refer to was "constructive interference". In the case of the article, the system was designed to bring about constructive interference at a point in space 1/4 wavelength from the speaker. As I said before, 1/4 wavelength could be any distance as long as the sounf from the speaker and port arrived there in phase. The correct term is "location of constructive interference".

I hope that this was helpful and useful in your box design, slow 'n steady.