how to fight box rise????

[sharkman]

No i understand about the box rise i just wanted to see if there was a way to keep it down. Im hoping to get the most out of my system for the money. Still waiting on getting an amp for my 18. Today i had time so i hooked up a few amps i had laying around. Only one that worked was a cheap power bank 1000w 2ch. It was ok but the amp was crap plus this was free air because my box isnt done

 

[nismos14 5,000+ posts]

No i understand about the box rise i just wanted to see if there was a way to keep it down. Im hoping to get the most out of my system for the money. Still waiting on getting an amp for my 18. Today i had time so i hooked up a few amps i had laying around. Only one that worked was a cheap power bank 1000w 2ch. It was ok but the amp was crap plus this was free air because my box isnt done

Well the more you understand it the more you don't fight it. It is what it is.

 

[hispls 5,000+ posts]

No i understand about the box rise i just wanted to see if there was a way to keep it down. Im hoping to get the most out of my system for the money. Still waiting on getting an amp for my 18. Today i had time so i hooked up a few amps i had laying around. Only one that worked was a cheap power bank 1000w 2ch. It was ok but the amp was crap plus this was free air because my box isnt done

This sort of crap is why I really wish people wouldn't just parrot catch phrases and clever sounding **** without knowing WTF they're doing.

"Box rise" is a misnomer. A woofer in an enclosure behaves as a rather complex electrical circuit with resistive, capacitive, and inductive components. Not only the electromagnetic component of the driver, but volume of air in the box, port(s), and even to some degree the acoustic properties of the room (vehicle in our case) the system is in all effect what the amp "sees" at any given frequency.

In short, at 40hz your amp may see a 20 ohm load, but at 25hz it may see only 1 ohm. The frequencies aren't so important, but the important bit is that at some point your amp very probably will see your nominal impedance. The only way to have a constant load at the amp would be to use a non-conventional speaker (like servo driven or perhaps planar transducer.... though I haven't really looked into planars enough to even say for sure there... but servo for sure).

So, if you plan to compete and your system is ONLY used to play one frequency and will never play anything else this is something you can try to play around with; if you plan to play music it's a red herring. Match your amp to your sub's nominal impedance and don't worry about it. Your quest to "get your money's worth" out of your amp will result in broken equipment long before you get dramatic audible gains.

 

[T3mpest 10+ year member]

This sort of crap is why I really wish people wouldn't just parrot catch phrases and clever sounding **** without knowing WTF they're doing.

"Box rise" is a misnomer. A woofer in an enclosure behaves as a rather complex electrical circuit with resistive, capacitive, and inductive components. Not only the electromagnetic component of the driver, but volume of air in the box, port(s), and even to some degree the acoustic properties of the room (vehicle in our case) the system is in all effect what the amp "sees" at any given frequency.

In short, at 40hz your amp may see a 20 ohm load, but at 25hz it may see only 1 ohm. The frequencies aren't so important, but the important bit is that at some point your amp very probably will see your nominal impedance. The only way to have a constant load at the amp would be to use a non-conventional speaker (like servo driven or perhaps planar transducer.... though I haven't really looked into planars enough to even say for sure there... but servo for sure).

So, if you plan to compete and your system is ONLY used to play one frequency and will never play anything else this is something you can try to play around with; if you plan to play music it's a red herring. Match your amp to your sub's nominal impedance and don't worry about it. Your quest to "get your money's worth" out of your amp will result in broken equipment long before you get dramatic audible gains.

The part I find most interesting is if you look at it, where boxes are most effecient is also where your impedance goes up the highest, it all works out pretty well.. Right at tuning your impedance may jump to 30ohms BUT you SPL is actually the same or higher there than anywhere else.. Also, since the cone isnt' moving at that frequency really throwing "rms" on it probably isn't a good idea. As others have said, don't fight impedance rise, just build the box to get a response you want and it is what it is.

 

[Adnan 10+ year member]

Interesting read I was always under the impression that impedance rise would cause your output to decrease as if you wired your subs to a higher load i.e: if your amp puts out 1000w rms at 1 ohm and 600w at 2 ohm, rising to 1.8ohm would give you roughly 600w...

if its rather irrelevant and does not affect output why is this term common amongst SPL guys? this term comes up a lot in conversations like this : "hey bro what numbers did you hit?" "i hit 153.2db with my 12"...not bad given box rises to 2.3 ohm and im only running like 6 batteries I needz moaar electrical"

 

[SounDrive Pro Seller]

Interesting read I was always under the impression that impedance rise would cause your output to decrease as if you wired your subs to a higher load i.e: if your amp puts out 1000w rms at 1 ohm and 600w at 2 ohm, rising to 1.8ohm would give you roughly 600w...
if its rather irrelevant and does not affect output why is this term common amongst SPL guys? this term comes up a lot in conversations like this : "hey bro what numbers did you hit?" "i hit 153.2db with my 12"...not bad given box rises to 2.3 ohm and im only running like 6 batteries I needz moaar electrical"

Because they don't know what they're talking about generally. If you're burping a single frequency though, you can figure out the box rise at that frequency and possibly wire at a lower impedance safely.

 

[brian84corvette 10+ year member]

ive read somewhere that box design can have a certan effect on "rise" where a larger box can have more rise vs the same sub in a smaller box

probably all false - as rise is just something that happens - nothing to do about it - like another poster above said - forget about it - its not something you can mess with

 

[Adnan 10+ year member]

good to know thanks

 

[T3mpest 10+ year member]

Interesting read I was always under the impression that impedance rise would cause your output to decrease as if you wired your subs to a higher load i.e: if your amp puts out 1000w rms at 1 ohm and 600w at 2 ohm, rising to 1.8ohm would give you roughly 600w...
if its rather irrelevant and does not affect output why is this term common amongst SPL guys? this term comes up a lot in conversations like this : "hey bro what numbers did you hit?" "i hit 153.2db with my 12"...not bad given box rises to 2.3 ohm and im only running like 6 batteries I needz moaar electrical"

Several reasons. One most of them don't know wtf they are talking about as SounDrive said. Secondly, they are only burping one note for about 3 seconds, so thermal limitations rarely come into play on a burst that short. Three, they are shooting for just that one note, so overall response is a complete no issue, if your only goal is to get loud on one note for 3 seconds, then knowing your rise can be somewhat helpful. Really though it's still just a game of throw power on it until it stops getting louder or breaks.. Anyways it still reinforces my point, they are hitting 150db with 600 watts after all their rise and lower scores where they are well away from tuning and actual impedance is close to nominal and have 3kw of input.. effeciency is a good thing and where your most effecient is also where you have the most rise.