friskicouple

a quick ?..... I have a Directed 250d. I had it hooked up to 1 Pioneer 12 (rated at 150rms) in a small truck box facing the hatch motor and it hit very hard, now i went to 2 MA Audio 12's in a Camaro/ Firebird box facing the window and I think that its not even half as loud as it was with the Pioneer...... Am I crazy or what??? Shoud I get rid of the MA's and go with 2 Pioneers or maybe 2 JL's? Or should I just get 1 dual VC 12 and face it to the back? Any advice would be great.....

AJ_92RS

If you had only one 12" sub bridged, then went with two 12" subs unbridged, the two would be getting less power (total) than the one 12" did.

The reason is, most amps are rated to put out a lot more power bridged, sometimes twice as much. But the fact that you have two subs doubles the cone area (duh) which would, or should make that a wash (i.e. break even).

That could be part of it.

The other reason could be the sensitivity level of the Pioneer compared to the MA subs. The Pioneer I have (TS-W33C) is rated at 91dB/1 watt. If the MA subs are rated at 88 dB/1 watt or lower (numerically) they won’t put out as much sound with the same amount of power.

Rule of thumb; For an audible difference to be audibly noticeable, you have to increase the SPL (Sound Pressure Level) by 3 dB. You can do that by either adding another sub of the same size and split the power between the two, double the power to the sub(s), or use a sub(s) with a higher sensitivity level.

For instance...
I have a sub with a sensitivity level of 91 db/1 watt @ 1 meter. That’s measured 1 meter away (industry standard). So basically I can run a 1 watt amp to the sub, put my head 1 meter away from it and I’ll hear 91 decibels of sound.

In order for me to be able to hear a difference I have to increase the decibels by 3. In order to do that I have to double the power to the speaker. So now I’m at 94 decibels by using a 2 watt amp, still 1 meter away.

If you do the math you can see the power needed doubles fast and quickly washes out the gains in SPL ....

1 watt = 91 dB
2 watts = 94 dB
4 watts = 97 dB
8 watts = 100 dB
16 watts = 103 dB
32 watts = 106 dB
64 watts = 109 dB
128 watts = 112 dB
256 watts = 115 dB
512 watts = 118 dB
1024 watts = 121 dB
(Keep in mind that turning up the volume increases the wattage to the sub.)

Of course that’s not including the cabin gain of the car. That’s a sealed or ported box with the internal volume that the speaker manufacture suggests is “optimum” for that speaker.

Now. Let’s say your MA subs are 88 dB/1 watt. Now the math looks like this (for one sub).

1 watt = 88 dB
2 watts = 91 dB
4 watts = 94 dB
8 watts = 97 dB
16 watts = 100 dB
32 watts = 103 dB
64 watts = 106 dB
128 watts = 109 dB
256 watts = 112 dB
512 watts = 115 dB
1024 watts = 118 dB

As you can see, you have to double the power in order to get where the sub with the higher sensitivity is.

But since you have two subs (doubling the cone area), that also adds ~3 dB. That will have the same effect as doubling the power. In actuality, it would be the same as the math in the first chart, all else being equal.

Now that you understand that, let’s go one to the bridged/un-bridged part of it.

We’ll say your amp is rated at (just an example) 100 watts x 2 into 4 ohms un-bridged, and 400 watts x 1 into 4 ohms bridged.

When you were using one Pioneer you were pushing 400 watts to that sub, and if it’s sensitivity was 91 dB/1 watt, then you’re somewhere in here...
256 watts = 115 dB
512 watts = 118 dB
Probably 117 dB total SPL, 1 meter away.

Now you have two 4 ohm subs with a sensitivity of 88 dB/1 watt, but now you only have 100 watts going to each one. For simplicity sake, I’ll combined the wattage to 200 watts total. That puts you somewhere around here (already adding in the 3 dB gain of using two subs, putting the total sensitivity at 91 dB again) ....
128 watts = 112 dB
256 watts = 115 dB
Probably 114 dB total SPL, 1 meter away.

You’ve effectively just reduced your SPL enough to make an audible difference. The same as either cutting the wattage in half or removing one speaker from your car. That could be why you “notice” a difference.

The effects of which way the sub(s) are facing does have some effect on it also, but in a 3rd gen it’s not nearly as noticeable as it is in a car with an actual trunk. The hatchback of our cars is pretty insensitive to sub direction. Our cars hatch design is similar to a megaphone. Just about any sound you produce back there will be amplified like a megaphone.

I hope that helps you, as well as others make good decisions about what subs to buy based on the total output of the amp you are going to use. It can make a huge difference.

friskicouple

Well, I did some research and found that my amp puts out 150 wrms at 4ohms x1, and 250 wrms at 2ohms x1. So I guess that each of my 12s are getting 125 wrms, correct? I think I'll be going back to the store on Monday, cuz they said that the Directed 250d will give each sub 250 wrms, that would be plenty to be loud and sound good. I'll be getting one 12 dual voice coil and it should be good again...... Thanks for the input...

friskicouple

Well, I went back and got 1- 12 JL and a new box and boy did it make a difference, only one bad thing, now I have to tighten my tail lights, cuz they rattle like crazy......lol, oh well, at least it sounds good.....