1/4 Wave Therory

[southside connections]

hello,i'm new to the forum,my name is kris and i have been admiring the work posted on this website

now i'm an spl competitor in my country-Trinidad and Tobago,and i need a few questions answered if you all don't mind, thanks

well i very well acquainted with 1/4 wave theory and straight transmission line boxes and i was wondering if a 1/4 wave corrects the rear wave of a speaker from 180degrees to 270degrees(90degree shift),because from what i've seen, 1/2wave correction will give me a full 360degree shift and ,is it possible to correct to half wave,bringing the rear wave fully aligned to the front wave of 0degrees?, and so if this is done what could be the benefits of it?

thanks in advance,

krystian seunath

[jack]

hello,i'm new to the forum,my name is kris and i have been admiring the work posted on this website

now i'm an spl competitor in my country-Trinidad and Tobago,and i need a few questions answered if you all don't mind, thanks

well i very well acquainted with 1/4 wave theory and straight transmission line boxes and i was wondering if a 1/4 wave corrects the rear wave of a speaker from 180degrees to 270degrees(90degree shift),because from what i've seen, 1/2wave correction will give me a full 360degree shift and ,is it possible to correct to half wave,bringing the rear wave fully aligned to the front wave of 0degrees?, and so if this is done what could be the benefits of it?

thanks in advance,

krystian seunath

if you can acurately line the front and rear wave off the subs then you will have zero cancellation and will have a higher reading on the sensor

[banginAltima]

[Derrick824]

if a 1/4 wave corrects the rear wave of a speaker from 180degrees to 270degrees(90degree shift),because from what i've seen, 1/2wave correction will give me a full 360degree shift and ,is it possible to correct to half wave,bringing the rear wave fully aligned to the front wave of 0degrees?, and so if this is done what could be the benefits of it?

This has got to be a joke.

[Boon]

Theoretically if you build a hybrid half-wave t-line/6th order series tuned bandpass (where the back half is the t-line instead of the ported section with the sub in it) then you'll get perfect phasing in the front chamber of the bandpass for a THEORETICAL 3dB gain (doubling of wave = double pressure change = 3dB)

Got to move a lot of air to make it work as well, it's inefficient with low cone area.

However it's only really possible in an extreme car I suspect, where you can control all the little variables.

A normal ported box has massive phase shift anyway...

[southside connections]

This has got to be a joke.

what is the joke?i'm just asking if i am correct

unlike the usa, my country does not have much pure spl vehicles,at present theres only 2-5 cars at most,and information is very limited since no one wants to teach anyone, they all just keep to themselves

so if i offended you guys and this forum,i am sorry and will not post again. i guess it will be fair to you guys

so i am sorry for the inconvenience to you all

yours respectfully

krystian seunath

[Colin - STAPUFT]

Check out this older thread. Lot's of stuff these guys know... could help.

http://www.stevemeadedesigns.com/board/ind...?showtopic=1828

[deafyT]

Welcome to the site. 1/4 wave theory is an old school idea that has been debated, tried, proven many many moons ago. Although, I think some intents were a bit difference than yours.....

There is a formula that takes the distance from the mic to the sub and gives you your theoretical peak frequency. At that frequency you're supposed to see a nice spike on the meter. It most definitely worked for some people on the old mics.

Call it coincidence or just a fluke, but after being skeptical I did the measurments, crunched some numbers, low and behold, according to the math, my peak theoretical frequency was 64hz. This was in my old car that used to peak at 63 lucky as hell on box placement and pretty damn close if you ask me. There is no other explanation as to how 3 sealed w6 12"s did over a 151 (legal on the old mic) from the trunk.

This is a question that will dig some OG heads out of hiding. Register to www.termpro.com, search in the archives and repost this thread. You'll find an abundance of info there.

Good luck to you.

[LSN2meBoom916]

what is the joke?i'm just asking if i am correct

unlike the usa, my country does not have much pure spl vehicles,at present theres only 2-5 cars at most,and information is very limited since no one wants to teach anyone, they all just keep to themselves

so if i offended you guys and this forum,i am sorry and will not post again. i guess it will be fair to you guys

so i am sorry for the inconvenience to you all

yours respectfully

krystian seunath

No worries bro-it's "above" a lot of folks out there to even consider such things, so if they don't understand, don't take it personally...this place is exactly where you should be asking this Q.

PM forevrbumpn...he authored the following mentioned thread on transmissionline boxes

Check out this older thread. Lot's of stuff these guys know... could help.

http://www.stevemeadedesigns.com/board/ind...?showtopic=1828

And Deafy seems to know wassup a bit, so please don't stop posting on this thread.

[Forevrbumpn]

I try and base every box I build on quarter wave theory, wether its ported, or transmission line, I measure distances from box to windshield, box to ear, box to where SPl mic would be placed on the windshield, get an average number, and work from there

Even tho the average car has a SQ peak cabin gain of about 34-35 hz you have to think the next octave up from there, and down from there .That number will be a good cabin peak that wont sound like total ass, when the next octave up 68-70hz will be louder than that 34hz . Every car will have a good listening peak, and a SPL peak, its not theory, watch when people run a Termlab mic, and you see the RTA, you see peaks at Your peak, and every octave up from there

If at all possible, always to do the math first, then RTA second- You want to know the numbers, and then see them on a computer screen and see how accurate you were, and learn from there

Another thing to think about, OFCOURSE location of box...

What Boon said was pretty accurate too,

if you can combine the front wave of the speaker, and rear wave of the speaker, and combine them in a Bandpass manner, you CAN, and WILL gain effeciency/SPL

the way worded may be kind of akward if you never heard it said that way, you just got to think of the front wave, and back wave working together IN PHASE and you will see some pretty impressive numbers from even small subs, 8"s and 10"s sounding like any other Joes 15s and 18s

Sick96vtechaccord (dunno if thats right) just built his first 1/4 wave box, and told me in PMs how he is amazed how just a simple change in box design can change so much in output