What does subwoofer level table mean?

[Marti]

I am an audio neophyte - I just know I LOVE my iFI!!!

I see in the manual that various lights come on with various movements of the volume indicator to indicate something on the subwoofer, but I don't have the foggiest idea what "+/- 00" or "+1/+2", etc. means!!

Could someone give me a VERY simple explanation?

Thanks in advance!

Marti

[Jay481985]

plus minus 0 is basically flat, that is when you hit the subwoofer and it has two amber bars in the middle. +1 +2 -1 -2 is 1 decibal louder, or minus etcA decibal is about the smallest a human can differentiate in sound difference. When someone says turn it up a bit it mostly means around 3 more decibals.

Also when you get three more decibals you doubled the wattage. Think 1, 2, 4, 8, 16, 32, 64 watts etc.

[Marti]

Thanks, Jay. I understand that the setting affects the relationship between the subwoofer and the satellite speakers. Do the "plus" numbers mean the subwoofer puts out "more" (more what?) than the satellites and the "minus" numbers mean the subwoofer puts out less than the satellites?

Why would I decide to use a particular setting?

[Jay481985]

The plus means 1 db louder relative to the speakers. The ifi was matched from satellites to subwoofer. But subwoofers do vary output in rooms. Contrary to Bose's ideology of placing the sub anywhere and out of site, placement in the room is important. Just try it, place the sub in the middle of the room and then play some music. Then walk around the room and listen to it getting louder in some places and not in others (those are nulls) Then place it near a wall but not in a corner (it should be louder) then place it in a corner and it should be even louder. That is basically 1/2 space (no walls boundary but floor. Well not exactly as you are still in a room and its really meant for outside) 1/4 space (floor and wall) 1/8 space (floor, and two walls) and each gives +3 more decibels per each movement. It really is how much you like your bass. I leave it on middle. Though its fun to have some bass on some songs.

[Marti]

Thanks much - I'll have fun experimenting!

[Andy W]

Jay, Marti,

Adding a boundary will increase the output by a theoretical 6dB, just as adding another identical subwoofer will add 6dB. (In practice you usually get slightly less than 6dB.)

In the case of a boundary, imagine that each boundary is a mirror. When you go from full-space to half-space imagine placing the subwoofer on a mirror, and you now see the sub and its reflected image. Your eye sees two subwoofers. Place another mirror (quarter-space) with the sub in the corner and you will see a 4 subwoofers. Place a third mirror (eighth-space) with the sub in the corner (like in the corner of a room) and your eye will see eight subwoofers (imagine eight subwoofer cubes stacked in a cube).

The reason you get a 6dB increase by adding another subwoofer is that a doubling in power gives you 3dB. (If you add another subwoofer you have added a second amplifier and driver which doubles the acoustic power that is radiated into the space.) Adding the second subwoofer also cuts the acoustic load in half (each sub is now moving half as many air molecules) so you get another 3dB increase. 3+3=6.

I have attached a simulation of a fictitious 6" driver and cabinet. The bottom curve is anechoic, and each successive curve adds a boundary (half, quarter, and eighth space). You'll notice dips in the higher frequencies in the two corner loading scenarios (1/4 and 1/8 space). This is because the source of radiation (the woofer) is not 'in' the corner but is facing the room, thus the direct sound and the reflected sound (bouncing off the wall behind the subwoofer) are out of phase and partially cancels. It does not cancel fully (null) due to the difference in the total distance to the microphone (the sound bouncing off the wall travels a longer distance so its magnitude is lower). If you turn the sub around to face the wall the cancelation will be reduced, but since the distance to the microphone is also increased, the magnitude will be reduced slightly.

The smaller the box is the less this effect will be noticed. (FYI in this simulation the port is on the rear of the box -- in the corner, like the iFi would be.) If the box is very large this can start to be a concern and is the reason why, on the RSW-15, that the passive radiator is on the front and the driver is in the back. Since the passive radiator only produces the lowest frequencies, it can't cause large cancelations.

At any rate, at subwoofer frequencies, this is not a huge concern anyway. It matters, but not much.

[Jay481985]

then why do the rw class subwoofers have the port in the front with the subwoofer? Or the KW120? I know the KW120 is meant to be flush for that installed look but now the port and cone are in the front? Is that a concern due to the smaller box nature?

Also the 6db theoretical is the best answer I could give as it is detemined by room etc so I went with the 6 db naturally.

[Andy W]

[]

Like I said it's not a huge difference. In the RSW series you have an active and a passive, and you can't fit both of them on the same panel, so you have a choice. Given the choice you put the driver on the back and the passive in the front.

The RW series has the amp panel on the back and the driver is in the front. The amp is ugly, the driver is pretty, so the decision makes itself. The port comes out the front because it doesn't fit the other way, so that decision makes itself too. Also yes, it's kind of "install friendly" that way.

The iFi has the amp in back/driver in front for the same ugly/pretty reason The port is kinda ugly too so it goes in the back.

But there are other reasons to put the ports in the back.

[Jay481985]

[]

Like I said it's not a huge difference. In the RSW series you have an active and a passive, and you can't fit both of them on the same panel, so you have a choice. Given the choice you put the driver on the back and the passive in the front.

The RW series has the amp panel on the back and the driver is in the front. The amp is ugly, the driver is pretty, so the decision makes itself. The port comes out the front because it doesn't fit the other way, so that decision makes itself too. Also yes, it's kind of "install friendly" that way.

The iFi has the amp in back/driver in front for the same ugly/pretty reason The port is kinda ugly too so it goes in the back.

But there are other reasons to put the ports in the back.

Put the rw woofer on the side?? hmm []

and those reasons are??? please Andy explain yourself instead of leaving us wondering!

[Andy W]

To get rid of the dust bunnies behind your sub! LOL.

[Jay481985]

To get rid of the dust bunnies behind your sub! LOL.

Why do I get the run around feeling []