posted
hey, i was curious if someone could model my subs on their enclosure modelling software and tell me what the plot looks like (or a chart or a pic of the plot would be nice too )?
i'm using two shockerII 15's in a ported wall. enclosure volume is 6.34ft^3 after port and sub displacement (i think). dimensions in the box are 22" X 26" X 20.5" and the ports are 7.5" X 6.5" X 10"...
i'm tuned to 30Hz for daily driving and 45Hz for comp and was mostly wondering what the impedance is from 45-60Hz mostly so i could possibly drop the impedance on my amp from 2 to .5 ohms for burps only.
------------------ Team "Under Pressure"--now in Minnesota for the summer with the stroke of a cone, i can make you moan wall w/two shocker15's and a cadence a7hc, soon to be 2 class D's
posted
That's a good question with a bad answer. Basically, subs specs vary, enough to make your useful impedance plots useless. The best cheap test I have seen and used so far is to put an 8 ohm resistor in series and test voltages across the resistor and speaker and all frequencies, blah blah blah. Rspeaker = R resistor * V speaker / V resistor. It's not the most accurate, but it'll do fine. If you don't mind me asking, why do you need a plot of the in-box impedance? Sure, once you know it, you know what frequency gets the most power, but you can't really use it to change the sound.
------------------
Posts: 768 | From: Ottawa, On, Canada | Registered: May 2000
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posted
emu, the plot is handy because say your peak freq is 53hz or something, and your impedance jumps from 2 ohm nominal/coil (my dd9515b 2/2) upto around 7 ohms/coil so normally your gonna run something like a memphis 1000d or similar to the paralleled coils (nominal 1 ohm) or a US Amps 2000x with the coils in series.. BUT at 53hz you'd be safe paralleling the coils and using a US Amps 2000x since your actual impedance is around 3.5 ohm, this can make a VERY big diff in the lanes because a 2000x at 14 ohm mono (actual impedance at 53hz assuming your just playing a tone) the 2000x is gonna make between 650 and 850 watts, but at 3.5 ohm mono it's gonna make ALOT more (I don't know what one actually puts out) but 2500 at that load is probably a very safe estimate. so compared to the coils in series 650-850 watts, you may get 2500 watts, now that's probably a good 4-6db in the lanes, so in my personal opinion this is one of the MOST usefull pieces of info you can get your hands on.
------------------ Digital Designs 9515b -- Memphis 1000D -- Panasonic source -- MB Quart fronts -- ADS power plate -- RW Audio LD4.12MBR -- 149.3 & climbing -- Member of Team Hertz Canada -- robin@rwaudio.com
Posts: 735 | From: Calgary AB | Registered: Oct 1999
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posted
RWAudio...thanks for explaining that for me
anyway...the main reason i'm asking for someone to model this is because whenever i test the impedance myself (check amplifier AC voltage out, then check output current and use ohm's law to find the impedance) i get really wacky numbers.
since my coils are about 2.2 ohms each when checked at rest that means with both subs wired in a parallel/series i should have about a 2.2 nominal impedance. and since the airspace for each sub is so large (6.4 cubes after displacement for daily driving, 6 cubes for comp due to larger ports) i thought that the impedance rise would be fairly minimal.
so when i measure the AC voltage and current i get large impedances around 10Hz above tuning. i do my testing at low volumes due to neighbors and whatnot but i was told this shouldn't matter much. the first time i checked impedance i got a minimum of 8 ohms, last time i checked it came out closer to 11 ohms. these impedances seem REALLY high for my subs and enclosure combination.
could this be due to the fact that my ports for daily driving are tuned to 30Hz but only have 30in^2 of port area thereby not allowing the air to move smoothly and raising the impedance? on the other hand, if these numbers are right i can rewire my A7 to a .5 ohm load for competition
-------------------- "Those who give up liberty for the sake of security deserve neither liberty nor security" - Benjamin Franklin
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Elemental Designs
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posted
Impedance matters not in the lanes. If it was that important, they would measure amp output at your burp freq and then judge you with that. What they're really interested in is SPL. You're better off doing a RTA or spl sweep( just invented the term, i guess).
High impedance is not dangerous to amps, and it usually indicates a high effeciency region such as Fs.
If you have to, take the measurements yourself and trust them, don't trust my computer genrated plot.
Posts: 768 | From: Ottawa, On, Canada | Registered: May 2000
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posted
emu...impedance matters ALOT in the lanes. reread RWAudio's reply...
and yes, they are looking for SPL in the lanes...how do you get more SPL? usually by adding more power or more subs. in this case it's adding power.
if your amp puts out 1000W @ 1 ohm and you measure the in-box, in-car impedance of your sub at the frequency you burp at and it's 1 ohm then you're fine. however this is rarely the case...
as was stated the impedance of a sub can vary greatly throughout it's frequency response. if i remember correctly the JL Audio 15W3 had an impedance range of almost 80 ohms...i think it peaked at 79 ohms at um, i dunno what frequency. but think about that...
say that 79 ohms was at the note you burp at...that means that you're getting almost no power out of your amp. even if it is efficient at that impedance to make up for the lack of power...just think what you could do if you could drop that 79 ohms to a lower impedance. you would get more power and still have the efficiency.
so in my case my amp puts out max power at one ohm. but i can only wire for .5 ohms or 2 ohms and my amp is not .5 ohm stable. and my subs are two 2 ohm DVC's wired for a 2 ohm load...not getting full power from amp.
so i check my in-box impedance at my sweet note and find it to be high enough to allow me to rewire to a .5 nominal impedance. even tho my nominal impedance is below spec, when the sub is burped the impedance will rise to a "safe" level. this will allow me to get more power which should transfer to more SPL. follow me?
i think RYAudio did a simpler job of explaining than me hehe...
-------------------- "Those who give up liberty for the sake of security deserve neither liberty nor security" - Benjamin Franklin
DiRtY SoUtH DEAF SqUaD
Elemental Designs
To cheat is to admit defeat
--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist.
posted
Just a note, the larger your box, the higher the in-box impedance of your subs.
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
a larger box means a higher impedance? i thought it was the other way around. why is that?
and the more port area the less impedance?
-------------------- "Those who give up liberty for the sake of security deserve neither liberty nor security" - Benjamin Franklin
DiRtY SoUtH DEAF SqUaD
Elemental Designs
To cheat is to admit defeat
--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist.
posted
I'm not sure how it may relate to box vol.. car vol.. port whatever, but when I did my impedance measurements my numbers were close to double with the hatch open (sub/port facing up in the hatch) IE I got 7ohms/coil at 50hz hatch closed and 12ohms/coil at 50hz hatch open.. someone might find that info handy/usable
-------------------- Beyond Audio Inhuman 12 (x2) -- US Amps 2000x -- Pioneer DEH-P9300 -- MB Quart components -- Orion xtr 500.4 -- RW Audio LD6.24MS"burp" -- 151.3 & climbing -- Member of Team Hertz Canada -- robin@rwaudio.com Posts: 735 | From: Calgary AB | Registered: Oct 1999
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posted
ok.. finally found the url for one of the sites for impedance testing.. (I had another better one but can't find it) http://www.installer.com/tech/sit.html
-------------------- Beyond Audio Inhuman 12 (x2) -- US Amps 2000x -- Pioneer DEH-P9300 -- MB Quart components -- Orion xtr 500.4 -- RW Audio LD6.24MS"burp" -- 151.3 & climbing -- Member of Team Hertz Canada -- robin@rwaudio.com Posts: 735 | From: Calgary AB | Registered: Oct 1999
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posted
Is there anyway (besides accumatch) to lower your impedance if you are using an amp per coil? I have a feeling since my box is sooo big I am not getting the full potential out of my amps.
-------------------- Scottie Johnson Sound Pressure Technologies
posted
Alaska, When I get a chance I'll run my DD's through Leap software and look at impedance Vs port area and see what effect it has. Bigger boxes definitely correlate to a higher impedance. But the subs are more efficient the higher there in-box impedance.
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
That's why using a speaker with 1 ohm coils won't blow an amp designed to run at 2 ohms...it really isn't 1 ohm, but not 2 either...
-------------------- Team Image Dynamics/Zapco/Werewolf/JK Lab Team Kinetik Sick Bastard Audio SQ Who feels it knows it Posts: 7866 | From: Charlotte,NC USA | Registered: May 1999
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It really doesn't matter if a sub's impedance varies. Higher impedances are safe for transistor amps. low impedances are not. Nominal ratings do serve some purpose and generally, they're a good guide to go by.
Even if you have a 1 ohm speaker playing 1 ohm in box impedance at say, 60 Hz, on a 2 ohm stable bridged amp. It's not safe, it doesn;t take that long to blow the amp. especially at comps where the notes are maxed and sustained. Bass notes by nature are sustained long enough to fry the amp eventually, and eventually isn't that long.
Posts: 768 | From: Ottawa, On, Canada | Registered: May 2000
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posted
thx mr. dank...gonna see how she does tomorrow at this USAC comp. didn't get to finish building my competition ports so i am going in armed at 30Hz ehheh
-------------------- "Those who give up liberty for the sake of security deserve neither liberty nor security" - Benjamin Franklin
DiRtY SoUtH DEAF SqUaD
Elemental Designs
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--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist. Posts: 4136 | From: Lafayette, LA | Registered: Sep 1999
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posted
EMU, Im confused about what you said. I think Winslow is saying that if you take a sub rated at 1 ohm and stick it in a big ass box, Your amp will see a 2 ohm sub. Or more accuratly, the lowest impedance you see is 2 ohms. So the amp will run ok without blowing.
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
I'm not sure on the relationships between box size and impedance but I doubt an IB will show any considerable impedance rise. As for in box, unless you've measured the impedance as being safe for a 2 ohm amp, it's probably not.
Posts: 768 | From: Ottawa, On, Canada | Registered: May 2000
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posted
ok...i finally think i got the right measurements cuz with the subs in ~6.4 cubes of airspace after displacement and only 30in^2 of port area tuned to 30Hz i had a calculated impedance of 3.5ohms at 45Hz. from 38-45Hz the impedance kept dropping from over 6 ohms to 3.5 ohms. that would make sense due to the 45Hz being above tuning where the impedance plot should be decreasing. so i guess i will be safe dropping from a 2 ohm to a .5 ohm nominal impedance.
gonna find out at the USAC 3X here in Oct....if i'm gonna blow something i wanna do it at home
-------------------- "Those who give up liberty for the sake of security deserve neither liberty nor security" - Benjamin Franklin
DiRtY SoUtH DEAF SqUaD
Elemental Designs
To cheat is to admit defeat
--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist.
posted
emu..what hes tryin to do is get all his amps power to the woofers..becouse as you know when it burps the ohms rise..so then hes not gettin full power...like if you have a amp that does 1000w at 4ohm...and you woofer set up has a 4ohm rise..you would wire a 1ohm load on the amp..so when you burp it, it hits tha amp with a 5ohm load..so the sub will be gettin almost full power..verses if he had a amp that did its power at 1ohm and wired it to 1ohm, when it burped and the ohms rose..he woulnt get hardly half the power....i know of some one with a set simular to this..( ithink) hes got his amps wired at 1ohm..couse his box rises to 5ohms..he got amps that make pwer at 4ohm so hes gettin almost full power to his woofers..
-------------------- Alan Hall Broken Silence CC 2007 usaci mod 1001-2000 champion 163.6 2003 usaci mod151-300 legal record holder 4th 2002 usaci finals mod 0-150 6th 2003 usaci finals mod 151-300 4th 2004 usaci finals prostock 1001-5000 4th 2005 usac finals mod 301-900 Posts: 667 | From: Troy IL | Registered: Apr 2000
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posted
Don't worry, I build amps. A few things to remember is that sound is measured logarithmically, by ear and by competition mic. You have to double the power to get a 3 dB increase. Even if you manage to drop the impedance in half, you'll get a theoretical 3 dB boost but what i'll effects will you suffer from the new box design. Frequency response is what counts, not impedance. dB's matter, not ohms, not power. Proper utilization of cabin gain will get you a higher score than putting more power.
Once you've tweaked everything that you possibly can, people start doing weird things becasue it's all they have left to bring up the score. If you erally want max power, make a bigger port to get more power.
Really, the only way to know if you can increase your score by using the freq with the lowwest impedance is to try it. Best thing to do, if it's ported, tune it to the resonant frequency of the car. You'll have a nice low impedance at tuning, but I can't guarantee you any trophies.
Posts: 768 | From: Ottawa, On, Canada | Registered: May 2000
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posted
well..i didnt think we were talkin about building a new enclosure...itwas once we had a good enclosure to basically get lower impedance to make up for the ohms rise...and if less say you got only a 2 db gain...at finals..i havent checked but i bet 1st-4th was less than a 3db gain...in classes like 1-2 ss???
-------------------- Alan Hall Broken Silence CC 2007 usaci mod 1001-2000 champion 163.6 2003 usaci mod151-300 legal record holder 4th 2002 usaci finals mod 0-150 6th 2003 usaci finals mod 151-300 4th 2004 usaci finals prostock 1001-5000 4th 2005 usac finals mod 301-900 Posts: 667 | From: Troy IL | Registered: Apr 2000
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posted
emu...which amps do you build? just wondering... and you said frequency response is what matters and you also said to tune to the res. freq. of my car so i get a lower impedance at that note. well...if freq. response is what counts then from my experience and what i've read from others the max output (i.e. peak in freq. response) is about 10Hz ABOVE tuning...not AT tuning (unless it's a huge box and you're using a DD or something).
i think you're confused as to what i'm doing...my amp is rated 800W @ 2 ohms and 1200W @ 1 ohm...a 400 W difference which when divided between 2 subs is about 200W more each. that would seem to me to be a nice little gain in power which could correspond to more SPL. how much more SPL i dunno...but any is better than none. every little bit adds up...
SPL Magician is right...i am tryin to lower the impedance my subs see so i get more power from my amp using my current box.
-------------------- "Those who give up liberty for the sake of security deserve neither liberty nor security" - Benjamin Franklin
DiRtY SoUtH DEAF SqUaD
Elemental Designs
To cheat is to admit defeat
--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist.
