8 ohm sub w 4 ohm amp?
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=26626
Printed Date: May 13, 2024 at 9:20 PM
Topic: 8 ohm sub w 4 ohm amp?
Posted By: dontnojack
Subject: 8 ohm sub w 4 ohm amp?
Date Posted: February 17, 2004 at 8:41 AM
I have a sony explode XM 2165 GTX 1000 watt amp with 165 per channel RMS @ 4 ohm. I also have a rockford fosgate 10" sub in a 1cu. ft. sealed enclosure. The sub isan HE-RFP4810,
8 ohm sub., with 50-200watts max RMS / 400 max peak. How should I wire this in? details please. new to this. I am running off of a pioneer 40w x 4 CD player using rca outputs. thanks.
Replies:
Posted By: DYohn
Date Posted: February 17, 2004 at 10:26 AM
A power rating on an amplifier lists its output into the MINIMUM ohm load it can handle. Any load greater than this (such as 8 ohms) is perfectly safe and fine. Just wire your sub up to the amp.
Posted By: forbidden
Date Posted: February 17, 2004 at 1:19 PM
Dyohn is bang on as usual, it will work fine. The only concern you need to be mad aware of is that an 8 ohm sub on a 4 ohm load will only deliver half of the rated power of the amp. I personally would take the sub back and get a single 4 ohm version instead to get all that I paid for in the amp.
-------------
Top Secret, I can tell you but then my wife will kill me.
Posted By: Thack79
Date Posted: February 17, 2004 at 1:37 PM
Or you could get a third a run it at 2 ohm if your amp can handle it
Posted By: Thack79
Date Posted: February 17, 2004 at 1:38 PM
Or you could get a third speaker and run it at 2 ohm if your amp can handle it
Posted By: aggie altima
Date Posted: February 17, 2004 at 1:51 PM
Just to clear things up, two 8 ohm subs in parallel would deliver a 4 ohm load, while three 8 ohm subs in parallel would deliver a 2.67 ohm load. To reach a 2 ohm load, you would actually need four 8 ohm speakers.
Posted By: dontnojack
Date Posted: February 17, 2004 at 3:07 PM
So if I used this sub and amp combo, if Best Buy doesnt take it back because it was on the sale rack, I would only be putting about 82watts to a speaker that can handle up to 200w RMS? The amp as stated above has only 165RMS watts per channel @ 4 ohms. The speaker is 50-200wRMS @ 8 ohm.
Posted By: DYohn
Date Posted: February 17, 2004 at 3:10 PM
That sounds about right. It will work and should sound fine, but it certainly does not realize the full potential of the equipment.
Posted By: dontnojack
Date Posted: February 17, 2004 at 3:31 PM
what if I were to add another identical sub to a bigger box for example, and make sure the box is to specs, what would happen. It seems like that amp would then have to handle 2 subs instead of one and would be worse. Is this correct? all assuming I am using the same amp. BTW, where in the hell does Sony get off calling this amp a 1000watt amp??? when it only puts out 200wattsRMS?
Posted By: DYohn
Date Posted: February 17, 2004 at 3:40 PM
Question one: adding a second 8-ohm sub will let the amp "see" a total 4-ohm load. So, the amp will put out power at its 4-ohm rating of 200 WRMS (or whatever it is.) The amp will be performing at it's peak capacity. Each sub will see exactly HALF of the available power that the amp is producing. This will be "louder" than one sub by itself by approximately 3 db, or about 1/3 louder to your ears. Question two: Sony gets off calling it that because, in their tests in their labs under ideal conditions, that amplifier produced a momentary peak output of 1000 watts without self-destructing. This is why you should never use the peak ratings listed for amps, and always look at the RMS output ratings. Even these are often exagerated, byt the way, and Sony is not known for being conservative in their ratings. I would be willing to bet that, tested under real-world conditions with full musical program material, that amp will sustain about 140 to 150 watts RMS per channel within its distortion limits.
Posted By: dontnojack
Date Posted: February 17, 2004 at 3:42 PM
RMS Power Output:
165 watts x 2 into 4 ohms (20Hz to 20kHz, 0.1% THD)
200 watts x 2 into 2 ohms (20Hz to 20kHz, 0.15% THD)
400 watts bridged into 4 ohms (20Hz to 20kHz, 0.15% THD) This is the specs on the amp. How could I wire it bridged to get the most out of the amp. again..bear with me. I'm learning because of nice people like you! and I'm not just typing post after post: I am going thru searches finding info on these topics. Thanks, Justin
Posted By: DYohn
Date Posted: February 17, 2004 at 3:53 PM
If you bridge this amp into your single 8-ohm speaker, it would produce about 200 Watts. If you add a second 8-ohm speaker, each speaker would use about 200 watts (the amp would operate at the 4-ohm rating.) If I were you, I'd go ahead and install the system, using your single speaker connected to the amp in bridged mode. Run the same input to both channels (the RCA level signal from your head unit) and see what it sounds like. This speaker might just be fine for you with this amp. The only way to get "more" would be to upgrade to a larger amp (if your sub can handle more than 200 watts) get a different sub, or add a second equal sub.
Posted By: forbidden
Date Posted: February 17, 2004 at 3:54 PM
The problem here is your sub, your amp is designed for maximum output into a 4 ohm load when it is bridged. Here is some basic math for you to help understand 8 ohm sub on a bridged mono amp that produces 400w rms @ 4 ohms, you get 200w 4 ohm sub on a bridged mono amp that produces 400w rms @ 4 ohms, you get 400w 2 ohm sub on a bridged mono amp that produces 400w rms @ 4 ohms, you get 800w Your amp is not capbale of 2 ohm mono, so disregard it, it is there to show you how ohms relate to power output. Your sub, the Rockford 8 ohm that you have is the first example, thus it is not a good match to the amp. To get the most from the amp, you connect the + speaker lead from the sub to the + bridged output on the amp, then do the same for the negative speaker lead. Usually the amp has markings on it to show the bridged terminals, does your amp have these markings? And are you going to return the sub for a 4 ohm version? this would be your best bet. ------------- Top Secret, I can tell you but then my wife will kill me.
Posted By: DYohn
Date Posted: February 17, 2004 at 4:04 PM
Rob is correct, you will only be using about half the capability of this amp, but the sub you list is rated for 200 watts RMS, so it will receive exactly the max power it needs and you will realize the max the sub is capable of. I'd still try it and see if you like it....
Posted By: dontnojack
Date Posted: February 17, 2004 at 4:20 PM
I was just going to say that. My sub is only rated at 200 watts RMS, so it should actually work fine. I will try it and if I'm not happy I should be able to make something else work thanks to you guys. I really do appreciate the help you are giving me, and the other potential viewers that may find this post in a search. I am usually on a forum for boats or snowmobiles, and had no idea that there was a car audio one like this. Thanks GOOGLE! Thanks again. Justin
|