4ohm or 8ohm subs?
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=48416
Printed Date: May 29, 2024 at 12:23 AM
Topic: 4ohm or 8ohm subs?
Posted By: Sharp21
Subject: 4ohm or 8ohm subs?
Date Posted: January 23, 2005 at 7:57 PM
im gonna build a self contained unit with deck, amp, 2 8's & 2 5.25's. ive found a pair of rockford 8's on cardomain.com & they come in 4 or 8 ohm. what would be better for this application? i intend to run them in seperate sealed boxes. they are rated at 150rms & my amp is a 2 channel running 180rms @ 4ohms or 425rms bridged to one channel @4ohms so 2 4ohm subs, one to each channel, will put out 180w to each channel @4ohms correct?
Replies:
Posted By: haemphyst
Date Posted: January 23, 2005 at 8:40 PM
Please elaborate... WHAT are you doing?
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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: Sharp21
Date Posted: January 23, 2005 at 9:06 PM
i am building into ONE box: a headunit an amplifier 2 8" subs 2 5.25" speakers & one powerpack to convert 110v to 12v. i am then going to put it in my workshop, plug it in, & listen to bumpin tunes while i work on my next project. https://www.layitlow.com/forums/index.php?showtopic=153046 that should give you an idea. except im not gonna use a battery, & im gonna have the speakers properly enclosed.
Posted By: Sharp21
Date Posted: January 23, 2005 at 9:09 PM
one more question. im trying to keep the size fairly compact. would it be alright to have the 5.25's fire into the same enclosure as the 8's? ie. have one 8 & one 5.25 in the same sealed compartment?
Posted By: haemphyst
Date Posted: January 23, 2005 at 9:19 PM
OK, got it. Your amp will make the most power into the 4 ohm woofers, but this will also require a larger power supply. How big is your 120 to 12 volt adapter (hereinafter referred to as the "power supply")? What amp are you thinking about? What head unit? We really still need more information.
Otherwise, NO, do not run the coaxes in a common enclosure with the woofer.
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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: rcallon
Date Posted: January 23, 2005 at 10:21 PM
I would go with Single Voice Coil 8 Ohm Subs, or Duel Voice Coil 4 Ohm subs. This way, you can have both subs bridged without messing up on your ohm load. Check out this site:
https://www.jlaudio.com/tutorials/wiring/
This will give you all the info you need. Good question, hope this helped.
--Robb Callon
Jett Audio
Posted By: Sharp21
Date Posted: January 23, 2005 at 11:18 PM
i will be using this head unit https://www.audiovox.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10001&storeId=10001&productid=13666&langId=-1 & this amplifier https://www.audiovox.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10001&storeId=10001&productid=13682&langId=-1 & im looking at these subs, which come in either 4 or 8 ohms https://www.cardomain.com/item/ROCP18S42PAK in addition ill run 5.25's or 6.5's if i can fit them off of the deck. if i got 2 4ohm subs & plugged one into the left channel & the other into the right channel, wouldnt that result in a 4 ohm load @ 180w? the subs are rated for 150rms so thats pretty close isnt it? or am i missing something? i dont need to max out the power, i just want to match up the subs with the amps output.
Posted By: Sharp21
Date Posted: January 23, 2005 at 11:21 PM
oh & as far as the power supply, im not sure yet. im still in the info gathering stage. i figure ill need a 12v 5amp power pack.
Posted By: haemphyst
Date Posted: January 23, 2005 at 11:50 PM
OK, while that deck will output nowhere NEAR 200 watts, it will still pull about 100 watts from a power source, as a minimum. The "360" watt amplifier, also excessively overrated, should easily pull 300 watts from a power source (allowing around 50% efficiency for the deck and amp). Now 300 + 100 = 400 watts. 400 watts / 12 volts = 33.3 amps. A 5 amp power supply will BARELY power those two components ON, let alone have any significant output. Otherwise, I stick with my previous recommendation of using the 4 ohm drivers.
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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: Sharp21
Date Posted: January 24, 2005 at 2:20 AM
should i just wire one 4 ohm sub to each channel?
Posted By: Ravendarat
Date Posted: January 24, 2005 at 3:14 AM
No man, buy the 2 subs at an eight ohm impedence and wire them in parallel and bridge them to the amp. Quick, simple and easy. For the power supply, this is easy. Look at the deck and look at the amp, what size of fuses are in them, add hose to fuses together and get a power supply that is that big or larger. so if the deck is 10 amps and the amp is 20 amps then make sure you have at least a 30 amp supply although I would always suggest haveing a little more that whats absolutly nessasary. Make sure the 5 1/4 are in seperate chambers from the 8s. That would be a small catastrophy to have them in the same air space (I know I spelled that wrong but is 3 am and I just dont give a sh*t). I think I covered all your questions, if not, sorry.
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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer
Posted By: Sharp21
Date Posted: January 24, 2005 at 4:24 AM
no that makes good sense. add the fuses from the amp & deck & make sure the power supply is equal than or greater too. wire two 8ohm subs in parallel & bridge the amp so that the final impedance is 4ohms. i knew id get cancelling waves & whatnot by having different speakers in the same airspace. ive done a bunch of drawings already & think ive got it figured out. just dont want to end up with a hulking box! one thing, wont that overpower the subs? they are rated at 150rms. the amp when bridged mono is spec'd to put out 345W RMS x 1 (Bridged Mono) into 4 ohms. does that mean that each sub would be receiving 345w or that they would eack be getting 345/2 = 172.5w? https://www.audiovox.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10001&storeId=10001&productid=13680&langId=-1 thats the amp spec incase youd like to look at it also, ive started looking at power supplies & am having trouble finding one that is reasonably priced! any ideas?
Posted By: Sharp21
Date Posted: January 24, 2005 at 4:27 AM
Posted By: Ravendarat
Date Posted: January 24, 2005 at 4:27 AM
power supplies arent cheap, but you can use a battery charger as well on a high charge mode. They are a little bit better in price. As for the amp, If it did put out 345 watts rms then the subs would each be getting 172.5 w rms which is not gonna be a problem, however that amp is over rated and is probally not gonna put out that kinda power.
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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer
Posted By: Ravendarat
Date Posted: January 24, 2005 at 4:28 AM
still not gonna be to much cause it aint gonna put out that much power in a realistic world, but just make sure its set properly and youll be fine anyways.
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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer
Posted By: Sharp21
Date Posted: January 24, 2005 at 5:52 AM
sorry, do you mean i can use a battery charger & feed the positive & negative directly to it? ie. no battery, just a charger? & that will make enuff power?
Posted By: jeffchilcott
Date Posted: January 24, 2005 at 6:23 AM
here is something along the lines of the power supply I think you should be looking for
https://etronics.com/product.asp?stk_code=pyrps52kx&store=&catid=4071
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