Building the enclosure to the vehicle...

[dwright27]

are you wondering like port forward or port back or subs forward stuff like that?

I think he's more referring to like matching the quarter wave and such... That being the case I'm going to sit back and take notes. It's always interested me, but I'm not enough of

an SPL guy to go out of my way and learn; but since he asked, I'll learn. Lol

1/4 wave and resonant frequency go hand in hand in a way. The quarter wave helps you find the resonant frequency of the portion of the vehicles cabin that's gonna be pressurized and aids in that "magic" loud peak note.

As least from my understanding of it.

[Supercharged DCs]

Mainly testing.

Resonant frequency of the vehicle ( peak ) and just general knowledge of boxes, power applications etc. Usually in my experience at least, boxes peak 4 - 8 hz above tuning frequency. There are exceptions sometime where the box can peak lower then the tuning frequency, but not as common.

and most people think their box peak is their

cabin peak. 90% of time isn't the case. Only way to really know is to get a sealed box, and test.

Thanks for the information Dustin, I never considered using a sealed enclosure to find the resonant frequency, I would have just used a ported box which, as you mentioned, would probably have it's own peak.

Any more information (or links to sources) about 1/4 wave theory?

[dwright27]

Also, with the sealed box, I believe ( someone correct me if I'm wrong ) that you have to make it so it sees the same amount of cabin space as it would in your finished application. So if you're building a wall, you would want to have your sub in a sealed box, with a big giant trim panel around it. I coul e wrong but it makes sense to me because with the larger cabin area it drops the resonant frequency ( maybe it raises it? ) can't remember which.

[dwright27]

http://www.decibelcar.com/menutheory/55.html

http://www.canadiancaraudio.com/showthread.php?t=242315

Maybe those can help?

There is also a 1/4 wave thing in the subwoofers/enclosures section pinned iirc

[nCOMP1337]

the 1/4 wave thing in the enclosure section at least what i assume your talking about is about 1/4 wave tlines, i havent seen anything in that section referring to the 1/4 wave theory in reference to box positioning and tuning and peak frequency

i actually had a decently convo with ray few months back i chat about the 1/4 wave theory being used with the enclosure, though i dont remember most of it, lol

iirc, it has to do with finding the 1/4 wave of the box from the baffle to the windshield, or ive been told firewall as well. i think that distance times 4 then divide that by the speed of sound and you get the 1/4 wave frequency, then i assume if you can get that to match up with vehicle peak, it will be great for SPL

then people would try to tune their box to this, to get peak output, it does sort of go hand in hand a bit with how a 1/4 wave tline works i think

its not really as useful in normal applications but it can be very useful when getting all the SPL out of your system you can

when ray talked to me about it it was when he was testing those 12s in a suburban or something and kept finding out best place to put them, best positioning for everything in the car, etc. he ended up breaking 150 i believe too

that snot all of it but that may help you, its all i can remember

Edited August 9, 2011 by kynto

[dwright27]

^^

DBDon asked for 3 measurements.

Door panel to door panel, roof to floor and firewall to back of enclosure.

[Supercharged DCs]

Kynto, that's the kind of information I'm looking for (technique as opposed to just trial and error.) Wish Ray could chime in.

I understand what your saying Dustin, would I also test the resonant frequency with certain things postioned for optimal scoring on the TL? (Like seats forward/visors down [shit like that]?)

Going read through those links now.

[nCOMP1337]

^^

DBDon asked for 3 measurements.

Door panel to door panel, roof to floor and firewall to back of enclosure.

he mentioned firewall to me, but not the others, good to know

[LoudBurp]

If I may chime in... I know I am still technically a forum "noob" but I do know about 1/4 wave. I am a Radio Frequency Technician in the Air Force and this is one of the many things we have to learn about. Next time I am home I will look for my training books that explain everything, and try to post stuff that is relivent to the car audio world, but for now I will let you know some of the stuff I know that would be somewhat easy to explain.

1/4 wave is actually 1/4 of the waveformat to be examined. When talking about your car radio, your antenna is ~1/4 wavelenth of the radio station frequency your listening to (it is known as a marconni antenna). Its not perfect, because there is more than one station that your radio can tune to. So, they come up with the average frequency of the entire bandwidth, figure out how long one wavelenth of the average frequency is, and divide it by 4. There are also many other types of antennas too, such as half-wave dipoles, full-wave and even 2 wave. All of these propogate differently.

When dealing with fractional waves, you have to understand that they are always in refrence to the original format (it sounds weird but I will touch that in a bit). When some thing is 1/4 wave it could be said that it is 90 degrees (1 full wave lenth = 360 degrees). This also relates to your phase.

From my understanding the perfect box, is one that has an infinate baffle and infinate volume. This makes the sound waves from the front of the woofer not interact with the sound waves from the back. (they are 180 degrees out of phase(they cancel each other out)) This would allow for the waves off the front to move through space uninterupted. BUT, as we all know this is completely impossible. SO, the sealed box was conceaved. Now, when you start to add a port you kick it up a notch. Tuning the port to 1/4 wavelenth, actually takes the sound wave and slows it by 90 degrees. So at this frequency you have now brought a canceling wave into one that now complements the one from the front of the woofer. Which is why you see better gains, and why you see that "peak" frequency.

Now some might argue that it has to do with the speakers resonant frequency, the vehicals frequency..... It does! What I just described was with a theoretical woofer that is perfect in every way. When you put woofers in a car you have so many reflected waves and resonance it is just crazy. This is why you can see differences with seats up, down, forward, back.... everything matters. Now with what was said by people before me, you can find the "perfect" position for everything by finding 1/4 wavelenth of your desired frequency and tune towards it.

So, I hope I helped in answering some questions you may or may not have had and I hope it was easy to follow. I know I am not a professional builder, but this information is just stuff I learned about. Hope you get the answers your looking for, and if you need clarification on anything I said, send me a PM and I will try to get you the best answers that I can.

[Bacy2k]

i too was wondering about this and wondering ricks methods on the subject. one thing that i was wondering, and i guess you may be too (or not, just something to throw in there), is how/why he came up with the size of the box that he did for the woofers. it was larger than spec for each sub, and from different companies. wondering the reasoning for THAT SIZE enclosure for a particular vehicle