oad presented to amp (this is embarrassing to ask)

[garfa]

hi guys,
I have just lost the crewin vega (400Wrms, ported just a mid-range model) sub I was testing (the bloke wanted $150 or more) so I was thinking of purchasing a couple of jaycar carbon 12inch subs. whats the SQ like? sealed i was think of going, i want the kick!
They are a DVC 4 ohm 150Wrms per coil sub. Now my jaycar 400Wrms monoblock has 2 speaker outputs and at 2ohm will put out 700Wrms. The part I am confused about is if its possible to wire each coil to the other coil of the sub in parallel and then wire the subs up to the amp as 2 separate 2 ohm loads. does the amp just think it has a 4ohm load connected instead or 2x2ohm loads?
Seems kind of trivial but I never wondered about this before. This will seriously effect my decision on if I buy these subs or not because i will be hugely underpowering these subs otherwise.
also the CV sub was 94db/Wm efficent and the jaycar is 88db/Wm. i am concerned about this, should i be?
should i be looking at other subs? recommendations?
thanks, garth.

[StoneX]

The two terminals on the amp are just one channel but in parallel. So if you hook two 2 ohm loads up, they will be 1 ohm overall. The same as if you connected them all to the one set of terminals.

If you wire them as 1 ohm, the amp can produce up to 820Wrms.

Why would you be concerned about the efficiency? Technically, if you have two of the Jaycar subs, you're up to 91dB/Wm efficiency. With the CV you could give it 400Wrms, with the Jaycar's you could (in theory) give them 820Wrms which is double the power so you add another 3dB. You're back up to 94dB/Wm efficiency But in a car there is so many variables that will affect the output anyway and 3dB is not much when listening to music.

[garfa]

well how did you work out that 2x12' jaycars will be 91db/wm efficent? this is where my limited knowlage is limited!
how badly will the sq be effected from driving a 1ohm load over a 4 ohm load?
will i be able to notice the difference with my $300 jaycar subs?

[StoneX]

If you double the surface/cone area, the intensity increases by 3dB. If you double the input power, the intensity increases by 3dB. I couldn't find a link to prove the surface area formula, but that's what I was taught in Audio class and commonly known in car audio. In theory it is correct, but in practice, there can be cancellations and other problems that may not allow a full 3dB increase.

Manufacturers don't always measure the efficiency by the same method, so that spec can't be used accurately between brands. Your box will make the biggest difference between sound output.

I don't know how much difference the lower impedence will cause. I've run my old dual 2 ohm sub at 4 ohm (without knowing) and 1 ohm and didn't notice any difference.

[garfa]

ahh i thought there might have been more than just that.
thanks stone.
i just bougt the suckers. so 2x12' seaker sealent and foam ect... all for $325.
cheap.
not the best but for $300 it will do!

[azzfox]

id like to know how they go, good luck

[Tasmaniak]

yers.....what stone said is completly true..also to the point that I couldn't find a link to it either.

But a lot of people don't subscribe to the theory of doubling your conal area increases your volume by 3dB

I personally subscribe to the theory that it *CAN* increase your SPL by 3dB.

Note: The SPL and not volume was used.

[garfa]

hang on so i am lookign at a 6db max increase in spl? hmmm... why didnt i stick to 1 sub?!
yeh it should be good, i am just realising i ****ed up and dont know shit about how to use a box calculating program.
i am thinking i have a damn steep learning curve ahead. any help would be great at the moment!
i am so ****ed...
if possible could some one have a talk to me on msn if they know much about creating a box?

[StoneX]

I don't know alot about speakers so this is limited info i've READ on forums and other websites, so I don't know it's accuracy.

The efficiency rating does not always relate to the output in a car... The efficiency(from what i've read) is tested in a 1cu ft sealed enclosure with 1W from 1m distance. That might not be the optimal enclosure for the speaker, so when you do put it in a properly designed enclosure, the output will be much better. Also, the output SPL won't neccessarily be even between subs as the volume is increased certain speaker parameters can cause output increase to be limited compared to another speaker. That is a pretty vague sentence because I forget the terms used to describe the effect. It's something like "power compression" or something. A quick search found this just search for "power compression" and it has a brief description.

So in the end two Jaycar's in properly designed sub boxes MIGHT be alot louder than the one CV, and they might not be aswell.

This gives a quick idea of what type of enclosure suits your subs. If you got the Jaycar CS-2228 model, then they appear to suit sealed enclosures better anyway, due to the Fs / Qes rule.

Are you able to build the enclosures easily? If so, i'd build a temporary box the size Jaycar recommends (45L), listen for a week. Then add about 15L of bits of wood to each chamber, listen for a week and keep changing the volume until you're happy with the sound that you get. Then build a permanent box the volume that you liked the sound of best.

[edit] I was looking at a different model, but the theory is still the same.

[StoneX]

hang on so i am lookign at a 6db max increase in spl? hmmm... why didnt i stick to 1 sub?!

That is exactly why people "in the know" always recommend one good sub over two average ones