how to stop inpedence rise

[csu87 10+ year member]

thanks for the info guys. most of it went over my head but i think i caught the jist of it. very good work. should be stickied

 

[80INCHES 5,000+ posts]

So in the quest for supreme knowledge, I wanted to post the list of impedance sources (according to the loudspeaker design cookbook):
1) DC resistance of the coil and tinsels

2) Real part of the voice coil inductance

3) Imaginary part of the voice coil inductance

4) "Inductance" of the moving mass (cone, dust cap, coil, former, surround, spider)

5) "Capacitance" of the compliance/stiffness of the woofer (suspension, cone, air)

6) "Resistance" of the damping of the woofer (spider, surround)

7) Impedance due to sound waves in the box's air

8) Impedance due to sound waves in the car's air

In an impedance curve, the impedance grows steadily as a woofer goes to higher frequencies, and generally has a peak at Fs.

Fs - Speaker's free air resonant frequency. It is attributed to 4) and 5) (mass and compliance), mostly.

1), 2), and 3) are coil related, while 4), 5), and 6) are soft parts related. To change any of these would require a recone, or a different woofer.

1), 2), and 3) change with different voice coil configurations. This is why the T/S specs are slightly different for different coils in the same woofer. Changing coils will change the way the driver uses the available BL. Generally the higher ohm woofer will have a higher Fs (1 or 2 Hz), lower Qms (-5%), and dramatically higher Qes (10%).

Assuming you like your woofer and coil configuration, and only want to change the box, what are effective ways to decrease the impedance caused by 7) and 8) ??

simple...build a bigger box..the bigger the box your rise wont be so bad..the smaller the box watch ur rise jump up like mexican jumping beans

80

 

[csu87 10+ year member]

Smaller

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 //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

simple...build a bigger box..the bigger the box your rise wont be so bad..the smaller the box watch ur rise jump up like mexican jumping beans
80

they say smaller

 

[tinmanchris217 10+ year member]

So after rereading PV's post earlier. He said that "at resonance, the imaginary parts go away." That would be #3 on my list above.

So, if you burp at your resonance frequency(all else ignored), it leaves only the real part of the voice coil's impedance. This is why the impedance rise levels becomes constant.

2 Questions:

1) Does impedance rise change with power level? I imagine it does, though 1,3,4,5, and 6 don't change, while 8 shouldn't change much.

2) Does this mean that burping far from your resonant frequency will cause an impedance oscillation?

 

[tinmanchris217 10+ year member]

If we can get all the ideas together, I'll work out a "Unified Theory of Impedance Rise" for a Sticky.

Right now, it's still unproven that small box decreases rise. Not saying it's false, because I know quite well it's true... but it may not be the only way. Does anyone know WHY, though?

 

[michaellane 5,000+ posts]

im soo lost...so even tho when i use a dmm and my final load reads 1ohm when im playing music it will possibly be up to 2ohms that my amp is seeing? is this right? and if it is could i wire my amp to a .5ohm load (final load shown by a DMM) since when playing music my amp will see around 1 ohm?

 

[michaellane 5,000+ posts]

anyone?

 

[kingkongjr 10+ year member]

definately should be stickied. alot of good info here..now what crossed my mind, but could be figured out down the road- would the box make that much of a difference IF only changed .5-1.5 cu/ft total. OR would using different size ports/flared ports reduce 'rise' any. of course it would change #7 & #8, but would that be enough to see a difference. maybe ill throw a box together for myself to see if i can notice a differnce and help this out. cause i know that im suffering from impediance rise.

 

[csu87 10+ year member]

im soo lost...so even tho when i use a dmm and my final load reads 1ohm when im playing music it will possibly be up to 2ohms that my amp is seeing? is this right? and if it is could i wire my amp to a .5ohm load (final load shown by a DMM) since when playing music my amp will see around 1 ohm?

when you wire your subs to 1ohm, thats the starting value. all the things the guys in here said then contribute to the impedence raising. ive seen from .3ohm rise to 4-5ohm rise. the only way to know is to measure it

 

[michaellane 5,000+ posts]

when you wire your subs to 1ohm, thats the starting value. all the things the guys in here said then contribute to the impedence raising. ive seen from .3ohm rise to 4-5ohm rise. the only way to know is to measure it

well what im asking is if your amp is not .5 stable can you have a starting value or ohm ,load of .5 since with music and all other factors it will rise??

 

[csu87 10+ year member]

well what im asking is if your amp is not .5 stable can you have a starting value or ohm ,load of .5 since with music and all other factors it will rise??

possibly but then it would all depend on how much rise you get on music. music is dynamic and rise will vary throughout the song. i know that when i burp a 43hz tone i get a rise to 1.5ohms from .5, but with music i rise anywhere from .7 to 2ish

atleast that is my understanding someone correct me if im wrong

 

[michaellane 5,000+ posts]

possibly but then it would all depend on how much rise you get on music. music is dynamic and rise will vary throughout the song. i know that when i burp a 43hz tone i get a rise to 1.5ohms from .5, but with music i rise anywhere from .7 to 2ish
atleast that is my understanding someone correct me if im wrong

this is what im understanding as well and if this is true then i dont see why it would be a problem. i mean your amp will only see .5 maybe once im guessing and the entire time your listening to music it will be anywhere from

.6 and up....so how could this be a problem for a decent amp that is stable at 1ohm?

 

[marcotheclepto 10+ year member]

im enjoying this thread very much. thanks to all posting info. of course some of it goes over my head, but i get most of it.

 

[tinmanchris217 10+ year member]

Music is dynamic, and rise will vary throughout the song. i know that when i burp a 43hz tone i get a rise to 1.5ohms from .5, but with music i rise anywhere from .7 to 2ish...

When you wire your subs to 1ohm, thats the starting value. All the things the guys in here said then contribute to the impedence raising. I've seen from .3ohm rise to 4-5ohm rise. the only way to know is to measure it

Exactly. Nominal impedance is the initial value. The final value is usually 2-3 times more when burping, in a well designed box. On music, it varies. Off resonance, it can either be higher or lower impedance rise.

@Michael - You can run a 1/2 ohm nominal load on a 1 ohm stable amp, but it's not a good for daily. Some people design boxes or port placements, to add "box rise" so that a 1/2 ohm setup behaves like a 1 ohm... but again, I wouldn't recommend it (ever).