SPL Questions

devious wrote:

hell i dont know what 1/4 wavelength is and im a physics major or at least trying lol. cause the 1/4 wavelength of a 70 hz note would actually be somewhere around 100000 meters. so nothing adds up here.

At around 69-70hz the peak to peak of the wave would be roughly 4 feet. I would start with the tune a bit high and then lower into the sweet spot till it stops gaining. You could go a little over on port area and tune and start filling port to lower tune. Using a mic till it stops gaining.

jonatan wrote:

explain tline for us that dont know please and if we do we might call it something else or nothing at all

It a transmission line enclosure. basically a ported box where the entire enclosure basically is a maze port. Figured with 1/4 wave formulas for tuning.

fritosaregood wrote:

James Reed wrote:

You measure from wave path from the sub to the mic position. Using that measurement you can then figure the 1/4 wavelength. Im sure you know 1/4 wave well from your t-lines you have done frito.

and you tune to that freq?

I think kyle told me something about someone doing that before.

Thats actually how we figured his peak and then tuned for that with the enclosure. It was confirmed with the mic shortly there after. If we went with a SPL area port to get there. He would be in the 150s already, but he wanted it to be good musically so port area was sacrificed.

ok after reading a little im still confused on how to find the 1/4 wl but i think i have some idea of what i need to do.

speed of sound ~1130 feet per second
divided by
frequency

then you get the length of that sound wave in feet

divide that by 4 to get the 1/4 wave

ok lets see if i got this 1130/37=30.54/4=7.64 correct

yep

thinking about it


i usually have a peak at 45 then another peak at 22

makes alot of since having a 45hz 1/4 wave and a 22ish hz 1/8 wave

[url=wave length chart]http://www.installer.com/tech/freqandwave.html[/url]

ok all cleared up now ok how bout this question wouldnt this be more determinate on the type of surface you were bouncing the waves off of
and to my first question how would you figure out what wattage your amp is pushing

fritosaregood wrote:

thinking about it


i usually have a peak at 45 then another peak at 22

makes alot of since having a 45hz 1/4 wave and a 22ish hz 1/8 wave

At least you know why now Im sure you have seen changing position also changed where it peaked due to the wavelength being changed.

James Reed wrote:

[url=wave length chart]http://www.installer.com/tech/freqandwave.html[/url]

great site thanks

devious wrote:

ok all cleared up now ok how bout this question wouldnt this be more determinate on the type of surface you were bouncing the waves off of
and to my first question how would you figure out what wattage your amp is pushing

Maybe in Pro Mod. But you cant really do much in stock classes. The wall should be strong anyway. Anything vibrating is wave energy being lost and being absorbed to a point. That why i say to just measure to the mic placement. All you can really do is make sure it is right to that point from its point of starting.

im getting lots of help here tonight yay glad im starting a new build wednesday anyone wanna help lol im in between searcy and pagburn.

fritosaregood wrote:

thinking about it


i usually have a peak at 45 then another peak at 22

makes alot of since having a 45hz 1/4 wave and a 22ish hz 1/8 wave

22 is probably your 1/4 45 is probably more 1/2. My navi is 43 1/2 wave. I would take a look and see if slightly raising tune would help you. 48ish or so. Or maybe do a port with more area a higher tune to close into the point. 45 just seems to low for that length just by looking.

ok more for me tom night guys thanks for the advice

devious wrote:

ok all cleared up now ok how bout this question wouldnt this be more determinate on the type of surface you were bouncing the waves off of
and to my first question how would you figure out what wattage your amp is pushing

a way to check if the amp puts out rated power without clipping you can use an oscope and adjust the gain to right before you see clipping on the oscope wave. then see what voltage is coming out.

to find power form that take you voltage and use V^2 divided by R and youll get Power
for example if you get 60 ac volts before clipping youll do 60^2 / 1 ohm and you get that your amp puts out 3600 watts of clean power at 1 ohm

to find you actual output after rise
you can only find it using tones
you have to use a DMM to measure ac voltage and a clamp meter to measure the current through the speaker wire

if you multiply your ac voltage and the current youll get the wattage output.

if you divide the ac voltage by the current youll get what your resistance is rising too.

James Reed wrote:

fritosaregood wrote:

thinking about it


i usually have a peak at 45 then another peak at 22

makes alot of since having a 45hz 1/4 wave and a 22ish hz 1/8 wave

22 is probably your 1/4 45 is probably more 1/2. My navi is 43 1/2 wave. I would take a look and see if slightly raising tune would help you. 48ish or so. Or maybe do a port with more area a higher tune to close into the point. 45 just seems to low for that length just by looking.

I tried that today and it only lower my score

So you were louder at 45hz then you were at the 54hz with the 153.x?

ok

James Reed wrote:

So you were louder at 45hz then you were at the 54hz with the 153.x?

I was louder at 54hz and my score got lower as i closed off the port area to lower the tune

but did you go larger then needed on port area so when your getting into the tune you want it is large enough?

it was 120 sq inches of port

my last box was only at 80 and it was really close to the same score

if i shrunk the port i have now to 80 it would be tuned to about 48.

do you have room for 120 and keep net where you need it to tune in for a peak at 45-48?

I might be able to get that port area and tune if i went back down to 5 cubes.

but with this box i was trying to get the most port area with a decent tune and keep the port straight

ive got some more testing with some other things, but i havent got around to it today.