Stacking subs?

[dodger]

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On 2/21/2005 4:03:15 PM Mjaudio wrote:

Thanks for clearing that up for me DrWho.

Since you seem to know what your talking about could I ask you about adding a Parametric Eq to the sub or subs. I was thinking about adding a couple of Art 351 or a BEHRINGER DSP1124P since they are now only $99 new at parts express.

Is this a complicated process and are the benefits worth the expense and time?

I know I would need to measure first since I could be lucky and already have a flat response. In this case an EQ would seem to be useless if there are no dips or peaks to correct.

Do you know if there are any resources online that could explain the process in the easiest possible manner? I already have a Radio Shack SPL meter and a copy of Avia like a respectable HT nut should have.

Any comments would be greatly appreciated.

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If you have the room and patience, some of thse valleys can be corrected by placement.

Some are truly surprised what a 4 inch, 8 inch, 1 foot change in placement can achieve.

Text books and papers are useful, but it's worthy to note who, or what comapny is paying the expert.

Try a Google search and you will see what I mean The same "expert" recommending several different placements. The best is to experiment yourself.

One thing to note for all subs if utilized at a higher volume. House Construction. The low frequencies do have an effect on things like drywall nails, the vibrations can cause minor gaps around windows, etc..

I'm not saying your house will fall down. But use of caulks that can expand and contract, drywall screws, a light bead of glue on floor joists - new construction helps.

For older homes if the plaster has cracked there is a spackle that is flexible for the repairs.

[DrWho]

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On 2/22/2005 8:44:43 AM dodger wrote:

In order to get the full 6 db of extra bass, one would need 4 subs, thus two stacks.

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This is true when you don't take into account the boundary effect...I'll make a simple scenario.

Let's say you have one subwoofer sitting in the middle of an infinetly large plane. This would be called half space because the subwoofer now has half as much space to fill than if there was no plane. Now put an infinetly large vertical plane behind the subwoofer. Now the subwoofer is in quarter space. The reason I bring this up is that everytime you halve the space, the output increases by 3dB (aka it doubles). So let's call half space a reference of 0dB, which means quarter space is +3dB, and 1/8th space (like a room corner) is +6dB.

So let's go back to half space and put one subwoofer in it. Now instead of adding another wall, let's add another subwoofer and put it beside our first subwoofer. Right away, we get an increase in 3dB because we've doubled up on speakers. However, we get an additional 3dB increase because each sub is now in a quarter space scenario. The extra speaker is essentially acting like another infinite plane due to the way the wave patterns interact. You get the exact same effect with electricity and magnetism. I'll see if I can't find some literature to support myself and maybe explain it a bit better. I know I'm not completely off my rocker because I've measured it in my room (others on the forum have measured the +6dB difference as well).

[dodger]

Hi Dr. Who:

There's plenty on Google, including sections of three of my text books.

Oops: EDIT:

One can actually get a dip by the addition of a second sub.

The boundary effect can help give you a hump, which is why some of the better subs have the boundary effect switch.

But the field effect also comes into play with 2 subs.

END EDIT

[dodger]

Boundary effect is a term that is loose.

If you use a Parametric equalizer, the corner is actually the best placement.

If not an option, the near field - closest to listening position is optimal as it allows the sound to reach the listener before reflections and other detriments reach.

The far field would be the placement of the sub in the center of the wall behind the listener.

Standing waves - which just about every room has, can possibly be minimized or eliminated by a placement in the center of the standing wave.

The boundary effect is akin to the drawing of the light bulb in a corner in the "Dope From Hope" Papers.

The placement of a second sub next to the first can actually create a dip, granted it may not always be large, but it has been proven and does show up in many discussions, some white papers. But we think alike in an area which you have touched but not yet voiced, note who wrote the paper and who is paying the person.

As I said to one member yesterday - I have no disagreement with you - at first your style was a little in your face - but that's the way we sound people have to be - but you have come to know the people and become friends with some. If there is a disagreement now it is not me.

We have different sections that we look at. But Though I post, I have nothing to gain, nothing that I need to prove to myself or others.

At 52, I have devoted 37 years into sound. You are ahead of many I know that are 30,35. So at this point if there is a disagreement it is only on one side.

dodger

[sfogg]

"we get an increase in 3dB because we've doubled up on speakers. However, we get an additional 3dB increase because each sub is now in a quarter space scenario."

I don't think that is accurate.

Two subwoofers do give around +6dB but it isn't from a difference in boundries as most subs aren't large enough to make an appreciable difference there.

The first +3 dB comes from doubling the cone area. I don't think there is a disagreement there.

The other +3dB comes about from effectively doubling the available amplifier power of the system. Either by having a second amp in a powered subwoofer or by halving the impedance of passive subs wired in parallel to a single amp.

Shawn

[Olorin]

I was wondering when that would finally get said. Shawn, you get the Occam's Razor "Close Shave of the Day" award.