20 replies to this topic

[Beddo88]

Have just bought a 12" sub off ebay (It went for £3.20) and basically need an amp to power it. Havent seen the sub yet as i'll be picking it up next week, but the chap that sold it is also selling a vibe blackbox 1, which he previously used to power it.

Firstly, is that a good amp? It mentions bridging, which means nothing to me, short of passing over river valleys. Can someone explain this? I know i should go for a better RMS value and kind of ignore the peak power rated etc, but beyond that im a tad lost. Bought the sub as an impulse and didnt realise how confusing buying an amp could be!

Can anyone help? What should i be looking for?!

Cheers, Dan

[skaterava]

Ideally, you should be looking for a 1 channel amplifier with an RMS value precisely, if not very close to, the RMS of the subwoofer. Ensuring the ohm rating of the amp matches the sub also ensures a longer life for the sub.

[Beddo88]

Ok, so a single speaker output would be better than two bridged? There are a few on ebay, but as i havent seen the sub yet im not sure what sort of power it is, what do they normally run at? I'm very impatient with this whole waiting thing

[skaterava]

A single channel would be much simpler. What brand is the sub? 12" subs are usually between 400 and 1000W. Some of a high quality can be over 1000.

[Beddo88]

Its a soundstream, no idea whether they are good or rubbish. but for £3... does it really matter?

From the looks of the picture its an older model.

[skaterava]

Sounds like quitan obscure brand to me, but i've got some fairly unknown amps which do the job very well

[travellering]

If you can read the markings on the amp terminals, then a bridged amp install (positive feed from one channel, negative feed from the other channel) is no harder than a single channel. In a perfect world, you wouldn't have the speaker set up like this as any distortion introduced by the amplifier would be doubled, but in the real world, the difference between where a bridged amplifier and a single channel amplifier starts to distort noticeably is very slight, and even more slight on a subwoofer.
The only substantial installlation difference is that some amps will not have an input for bridged, so you might have to split a single channel of RCA output from the headunit (cd player/tape deck/ what ever else you have), but this can be acheived easily with "y" adapters that can split an RCA output.

Many single channel amps are more expensive, because they are built just to run subwoofer setups, and will be overbuilt for driving one four ohm subwoofer. For a single sub, a bridged amp may give equivalent RMS power for less money.

[carts60]

ok, so its all much simpler than you think.

Basically, the RMS's need to match each other from amp and sub - so a 350W sub, to be powered perfectly needs a 350W RMS amp

However, you also need to ensure that these RMS's are only the same at the same Ohm value:

Lets say your sub is rated at 250W at 2 ohms, then the amp must also be the same (not MUST but if its not either way then you'll get distortion somewhere along the line either by overpowering the sub or underpowering it)

If the amp you buy is rated at 250W at 4 ohms then it will deliver much more than that if its attached to a 2ohm sub, as your essentially halfing the load it needs to power.

Does that make sense? If i'v got anything wrong someone'll tell me im sure

Oh, and a Vibe blackbox is decent yes. I'v got a 1000 Watt Vibe A7 amp and its perfect for powering my two 10" Alpine subs

Edited by carts60, 31 August 2010 - 10:50 PM.

[Beddo88]

The vibe sold for more than i wanted to pay. so i didnt buy it! However i've got a couple of others im looking at, one is a kenwood. rated at 1x 120W RMS at 4 Ohms. So if that was going to power a sub, it would probably be weak? Unless its a 2 Ohm sub, in which case it should stand up to it a bit better?

According to Kenwood it is 2Ohm compatible and has a low pass fitler, which im led to believe is designed for use with subs?

Basically... im looking at the cheap end of budget for this, so anything that will likely suit the job is being bid on

[travellering]

The Kenwood will probably be a good bit less power than ideal. If you try to push a weak amp hard enough to drive a 12 inch sub, it can distort, and that will damage the sub faster than a too-powerful amp. In addition, it will make the amp run hotter, leading to thermal shutdown.
Not all amps will double their power into lower ohm subs. Some are regulated, so they put out less power if there is less resistance from the speaker, so they don't run as hot. (quick edit: and some will not even be designed for 2 ohms or less if you buy an older one off ebay, and they may fry completely if put on a lower load)
What is the RMS on your specific Soundstream sub? That may well help if anyone on here has suggestions for a reasonably priced amp.

Edited by travellering, 01 September 2010 - 12:42 PM.

[Beddo88]

I see... probably a good thing i'm being outbid then! I havent actually picked the sub up yet, so will find out at the weekend the specific model no. etc. As im only paying £3 for it i didnt really ask many questions. I'll keep looking for some more powerful ones then.

Cheers, Dan

[carts60]

Theres plenty of used amps out there (and subs for that matter).

To be honest mate, you just want a half decent amp that either drives equal or more than the sub. Then you can just push the sub to your hearts content, and even if it wobbles to pieces, you've only lost £3.

I had a 600W RMS 12" JL Audio sub in my boot which cost me £140 that an audio 'specialist' told me was being perfectly powered by the amp i bought off him (before i understood ICE), which was of a similar price.
This was totally wrong, as the amp was rated to 600W PEAK Power and only produced 325W RMS at the correct ohms.

It sounded abysmal and i ended up with a ruined sub, an amp that cooked itself alive and £250 out of pocket.

Thats when i decided to upgrade and do my homework before i splashed the cash, leaving me with a really good sound system in the end, but i learnt the hard way.

[Beddo88]

Cool. Well i've got a much better idea of what im looking for now guys, hopefully i'll be able to fidn something within my somewhat limited budget.

Cheers for all the help, much appreciated!!

Dan

[Watso]

http://soundstream.com/ - not bad stuff at all. There was a bloke in a past mini mag that used one of their 7 Channel "Da Vinci" amps in the boot of his mini to power an incredible system (it was literally the whole boot). Soundstream are quite renowned for producing some really good kit, so for 3 quid, you've got a bargain. Depending on what the subs specs were, the Blackbox 1 should be fine!

Watso

[Rich.]

Most of the advice is spot on in this thread.

The only this i would add is that in big end audio installs, and genrally any good installs, you genrally try to overpower the Sub with the amp, so you always have the potential to run the sub at its full potential without the possibility of an amp clipping, which is the overload kicking in as your asking too much of the amp. However this requires a careful ear, a driver dosnt mind being overpoered for a few seconds, as long as you act to tak the volume down slightly when you hear distorsion then you will always be able to get the most out of your subs.

If your driving round with a distorted sub becuase your overpowering it then you deserve to have it blow on you to be fair!

However, for a fit and forget system, when your not going to be needing every decibel the sub can produce, then a perfect match between sub and amp is a good compromise, as you dont have to worry about farting subs and the potential that you could blow your subs if you stop concentrating for a few seconds.

I come from a Large scale touring and concert audio background and was very suprised to learn that car audio entusiasts tend to match there amps and components or slightly over spec the amps, in the pro audio industry we generally go for double size amp racks compared to the line arrays power rating, although active/powered arrays are making life alot easier! Run a massive amount of mains to them and a single source then daisy chain them togeather and you can forget about amp matching, which is nice when yor concentraing on mixing a 20 piece band!

Not sure if my post was relevant or not but some useless info none the less!

Rich