help me calculate box rise?

[Robby Holmes]

just getting into the technicalities of boxes,

and am trying to get the box rise of my box

whats the formula?

and also, can i get a definition of it also?

[matt402]

Quote:

Originally Posted by

KikiTheCat

you need an AC clamp meter and a dmm. You will need to measure the AC voltage output going to each of your subs or if they're bridged just the wires going into the amp. Once you get the AC voltage you will need to find the AC current. You do this by clamping the negative wire going to the set of speakers. I'll give you an example.

You clamp your wire and get 38.6 amps of current

You probe the + & - wires and get 61.7 volts

Next you would take the 61.7 volts and multiply the 38.6 by it to find your MAX power which would be 2381 watts

Next to find out your impedence rise you would divide the voltage 61.7 by the amperage 38.6 which would be 1.59 ohms

So if you were to have a nominal or starting resistance of .5 ohms you would have a rise of 1.09 ohms, but would have an overall reactive load of 1.59 ohms

this is the only real way to do so.. now measure at different output/input and you can see how power compression affects output to some extent(losses affect it so its hard to tell but it gives you a ruff idea)

if you look over @ termpro someone tested the DDz 18 in his extreme install capable of doing over 180DB if i remember correct power compression was detected with around 1800 watts.. pretty damn high considering most 3" coils start around 750-800 watts with really high power coils around 1200..

^quote from www.caraudioforum.com

[Robby Holmes]

Quote:

Originally Posted by

KikiTheCat

you need an AC clamp meter and a dmm. You will need to measure the AC voltage output going to each of your subs or if they're bridged just the wires going into the amp. Once you get the AC voltage you will need to find the AC current. You do this by clamping the negative wire going to the set of speakers. I'll give you an example.

You clamp your wire and get 38.6 amps of current

You probe the + & - wires and get 61.7 volts

Next you would take the 61.7 volts and multiply the 38.6 by it to find your MAX power which would be 2381 watts

Next to find out your impedence rise you would divide the voltage 61.7 by the amperage 38.6 which would be 1.59 ohms

So if you were to have a nominal or starting resistance of .5 ohms you would have a rise of 1.09 ohms, but would have an overall reactive load of 1.59 ohms

this is the only real way to do so.. now measure at different output/input and you can see how power compression affects output to some extent(losses affect it so its hard to tell but it gives you a ruff idea)

if you look over @ termpro someone tested the DDz 18 in his extreme install capable of doing over 180DB if i remember correct power compression was detected with around 1800 watts.. pretty damn high considering most 3" coils start around 750-800 watts with really high power coils around 1200..

^quote from www.caraudioforum.com

thank you!!

i gotta get some help with clamping my amp xP

[matt402]

also...

Your wiring is not causing the impedance rise

What you need to realize is that contrary to what you might think, resistance and impedance are not the same thing. Resistance is merely a part of a system's overall impedance. When your sub is just sitting there, it has an impedance of one ohm per coil.

That

number is a resistance. However, as soon as you start feeding your sub a signal that isn't just DC, aka, a music track with different frequencies, you start dealing with not just the resistance of the coil, but impedance of the coil which is taking into account capacitance and inductance.

Here, the main culprit is inductance. Basically all a speaker voice coil is at rest is a resistor with whatever resistance is stated on the side of the box. Under a signal, it is behaving more like an inductor (aka a low resistance coil which stores energy in a magnetic field), meaning that the current flowing through it is creating a magnetic field, which when interacting with the polarity of the motor, creates the excursion. At the system's resonant frequency, which is far more a factor in ported enclosures than sealed, the impedance is naturally going to rise for reasons I won't bore you with. Note that it's impedance, NOT resistance, so changing your wiring out won't make a single difference.

The way to "fix" it is to make your resonant frequency higher, aka, make your box smaller. However, for obvious reasons, you still need an audio setup that works the way you want it to, thus people factor in the rise in impedance as part of the design so that they know how to get the most out of their amplifiers. I hope that helped

http://www.sears.com/shc/s/p_10153_12605_03482369000P

[bkolfo4]

When your sub is just sitting there, it has an impedance of one ohm per coil. That number is a resistance. However, as soon as you start feeding your sub a signal that isn't just DC, aka, a music track with different frequencies,

Overall good post, but this is not quite correct.

The DC resistance vs. the AC impedance has nothing to do with the sub "just sitting there". It is DC current vs. AC current applied.

When DC current is applied the sub cone will move to a certain point based on the voltage level, and the resistance is constant. This is the DCR rating of the sub - the 0.7, 1.4, etc that people confuse with impedance.

When AC current is applied, the impedance varies with frequency due to many factors. Inductance, resonant frequencies, etc.

The only way to truely know the impedance of your system is to measure 1 frequency at a time through the entire usable frequency range and plot it. A ported system has peaks that you will never be able to control. If you are looking at the impedance in one of these peaks, you will just have to live with it if you are playing music.

Your best option is to design the box based on your performance goals. If you need every last 0.1 dB, buy more power than you need. . .

[siucsaluki11]

also...

Your wiring is not causing the impedance rise

What you need to realize is that contrary to what you might think, resistance and impedance are not the same thing. Resistance is merely a part of a system's overall impedance. When your sub is just sitting there, it has an impedance of one ohm per coil.

That

number is a resistance. However, as soon as you start feeding your sub a signal that isn't just DC, aka, a music track with different frequencies, you start dealing with not just the resistance of the coil, but impedance of the coil which is taking into account capacitance and inductance.

Here, the main culprit is inductance. Basically all a speaker voice coil is at rest is a resistor with whatever resistance is stated on the side of the box. Under a signal, it is behaving more like an inductor (aka a low resistance coil which stores energy in a magnetic field), meaning that the current flowing through it is creating a magnetic field, which when interacting with the polarity of the motor, creates the excursion. At the system's resonant frequency, which is far more a factor in ported enclosures than sealed, the impedance is naturally going to rise for reasons I won't bore you with. Note that it's impedance, NOT resistance, so changing your wiring out won't make a single difference.

The way to "fix" it is to make your resonant frequency higher, aka, make your box smaller. However, for obvious reasons, you still need an audio setup that works the way you want it to, thus people factor in the rise in impedance as part of the design so that they know how to get the most out of their amplifiers. I hope that helped

http://www.sears.com...05_03482369000P

you don't have to bore him with the reasons, but if you care to explain, or have links to areas that could explain, either post them up here, or send me a PM, I'm an audio nerd, and I've wonders what all goes into box/imp rise. I knew it occurred at res freq of box, but i didn't know the reasons behind it, and have always had it in the back of my mind.

[bkolfo4]

Loudspeaker Design Cookbook 7th Edition Book

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=500-035&utm_source=googleps

[siucsaluki11]

I've been meaning to buy that, but life keeps getting in the way....have too much shit to read for school at the moment to pick that book up and learn more shit...maybe next time i have a break ill get it.

[RAM5493]

also...

Your wiring is not causing the impedance rise

What you need to realize is that contrary to what you might think, resistance and impedance are not the same thing. Resistance is merely a part of a system's overall impedance. When your sub is just sitting there, it has an impedance of one ohm per coil.

That

number is a resistance. However, as soon as you start feeding your sub a signal that isn't just DC, aka, a music track with different frequencies, you start dealing with not just the resistance of the coil, but impedance of the coil which is taking into account capacitance and inductance.

Here, the main culprit is inductance. Basically all a speaker voice coil is at rest is a resistor with whatever resistance is stated on the side of the box. Under a signal, it is behaving more like an inductor (aka a low resistance coil which stores energy in a magnetic field), meaning that the current flowing through it is creating a magnetic field, which when interacting with the polarity of the motor, creates the excursion. At the system's resonant frequency, which is far more a factor in ported enclosures than sealed, the impedance is naturally going to rise for reasons I won't bore you with. Note that it's impedance, NOT resistance, so changing your wiring out won't make a single difference.

The way to "fix" it is to make your resonant frequency higher, aka, make your box smaller. However, for obvious reasons, you still need an audio setup that works the way you want it to, thus people factor in the rise in impedance as part of the design so that they know how to get the most out of their amplifiers. I hope that helped

http://www.sears.com...05_03482369000P

You just took me back to my physics and EE classes... i hated them soooooo much lol... Thanks for the info, makes a lot of sense and now I understand a lot more

[TexasJesse]

also...

Your wiring is not causing the impedance rise

What you need to realize is that contrary to what you might think, resistance and impedance are not the same thing. Resistance is merely a part of a system's overall impedance. When your sub is just sitting there, it has an impedance of one ohm per coil.

That

number is a resistance. However, as soon as you start feeding your sub a signal that isn't just DC, aka, a music track with different frequencies, you start dealing with not just the resistance of the coil, but impedance of the coil which is taking into account capacitance and inductance.

Here, the main culprit is inductance. Basically all a speaker voice coil is at rest is a resistor with whatever resistance is stated on the side of the box. Under a signal, it is behaving more like an inductor (aka a low resistance coil which stores energy in a magnetic field), meaning that the current flowing through it is creating a magnetic field, which when interacting with the polarity of the motor, creates the excursion. At the system's resonant frequency, which is far more a factor in ported enclosures than sealed, the impedance is naturally going to rise for reasons I won't bore you with. Note that it's impedance, NOT resistance, so changing your wiring out won't make a single difference.

The way to "fix" it is to make your resonant frequency higher, aka, make your box smaller. However, for obvious reasons, you still need an audio setup that works the way you want it to, thus people factor in the rise in impedance as part of the design so that they know how to get the most out of their amplifiers. I hope that helped

http://www.sears.com...05_03482369000P

Sorry to bring up a 2 month old thread, but please correct me if I am wrong or I misunderstood what you said, but I thought larger boxes were more efficient, hence being able to feed less power to subwoofers in a larger box and more power to the subs in a smaller box. I always like to build my boxes to their optimal (Maximum) recommended volume requirements. So if that is the case, then I will get more box rise than if I were to build the box at, for example, their minimum box requirements?

I have 4 SA-8 V.2 Stock SPL version 8's. Stock SPL versions include a different voice coil and an extra spider to handle more power. I lose a little bit of bottom end, but gain some upper end. They require .5-.75 cu ft of airspace net. I built my box @ 3 cu ft net ported to 31hz, with 2 subs wired to 1 ohm each with each pair wired to my Audiopipe 18001D. So I have two AP18001D's which are rated for 1800wrms @ 1 ohm @ 13.8 volts. I have read that the AP series of the Audiopipe amps can do a tad bit more than they are rated for, which are CEA-2006 Compliant, so they do atleast their rated power. I am a big fan of Audiopipe and have ran several of their amps and never had a problem. I also have installed several of their amps and no one has had a problem and they seriously beat. People bag on these amps because of their low price, but they are legit. I have ran DD, Sundown Audio, Zapco, etc... high end expensive amps and these hang with the big boys. Jacob did a test on the normal production SA-8 V.2's and the test resulted in him stating that the normal production SA-8 V.2's can handle 800wrms daily without a problem. Since I have the Stock SPL versions, they can handle a bit more than that. I want to send 1000wrms to each 8, which I believe they will take them in stride. I have had these subs since March, yet I haven't had them hooked up yet and Im dying to hear them. Alot has happened over the past several months so I have been unable to hook them up. So my next setup, I am thinking of wiring each of my amps to a .5 ohm load to achieve a 1-1.5ohm load. I also have a brand new Audiopipe AP30001D, but decided to go with more power so I bought two AP18001D's to achieve 900wrms. But with box rise, I guess Im probably only sending them roughly 800wrms, which is what the normal production SA-8 V.2's can handle so since I have the Stock SPL versions, I'm positive they can handle anywhere from 900-1000wrms.

I definitely wont be able to hear them for a while, now that I totaled my truck on Tuesday morning. A lady pulled out in front of me while I was going 65mph with a distance less than 50 yards. So it was either swerve to miss her or hit her, which more than likely would have killed her and possibly would have injured myself even more. A 7000 pound 4 door 2008 Sierra vs a Ford Taurus with her going 5mph and me slamming on my brakes which would have ended up me hitting her at probably 55mph from rear-ending her. So I dont know what I am going to do about a new vehicle, whether it be another truck, always been a pickup person, or a car. But anyway.

So in order for me to get the least amount of box rise, I would need to build a smaller box? I am just now diving into this part of car audio. I have been into car audio for over 10 years and haven't learned this aspect of car audio yet. You guys and other forums have really helped me over the 10+ years in educating me which has turned me into someone who knows quite a bit about car audio. This is just one thing I dont know about yet and want to learn more. I am going to check out that book that was previously mentioned.