How much boost?

[toecheese]

My IB sub has amazing clarity- but it doesn't kick me in the rear. I have plenty of power to feed it, but don't know how much I should.

Ideally, I'd add more drivers, but a buddy of mine has a graph that shows doubling my drivers just adds 3db (hmmmm. Makes sense, doesn't it).

I've been playing around with my BFD and REW and gave an 8db boost at lower frequencies. Finally- a kick in the seat.

But, am I screwing up by doing this? How much boost should I feed in? What is my limit?

[brucek]

How much boost should I feed in? What is my limit?

I depends on several things. There are frequencies in a room (that usually show up as a dip in the response) that can be fed more and more power with very little positive results. These nulls aren't solved by adding power, but by repositioning of speakers or listening positions or sometimes treatments.

Generally, if we're not talking about these nulls, and the room accepts the boost, then you can add voltage gain to a system until the power amp clips its output or your drivers reach maximum excursion (before the power amp clips). Both these conditions are fairly obvious when they occur.

brucek

[toecheese]

Thanks, Bruce- that's what I was hoping to hear. I know about room nulls- figure easy enough to spot, but these low spots were at the low-range of my frequencies. Looking at some of the other charts, could see I wasn't the only one boosting there.

My amp is 2400 watts so I doubt it'll clip anytime soon.

As far as excursion limits- will I know it before I find a cone lying on the floor?

[brucek]

As far as excursion limits- will I know it before I find a cone lying on the floor?

This is something I have no experience with. Good question.

I have read that you hear a clacking sound that is unmistakeable, but it's never happened to me. Perhaps someone else can comment on this.

brucek

[Wayne A. Pflughaupt]

I know about room nulls- figure easy enough to spot,

Not necessarily. Some people have been led to believe that any low spot in their response is a null. This is not the case. You’ll find that most low response areas will respond to equalization, as you can see by looking at the before-and-after charts you can readily find in numerous threads on this Forum. As brucek said, you can recognize a true null by the fact that it will not respond to boosts in equalization.

As far as excursion limits- will I know it before I find a cone lying on the floor?

brucek is right, you’ll definitely know when it happens – it makes a lot of racket. However, if you have visual access to your drivers, you should be able to tell you’re “on the verge” just by looking at them. They’ll have some pretty violent cone movement. You don’t have to worry about permanent damage, though – i.e., one time overdriving them won’t damage most sub drivers, since they’re generally fairly robust. Just back down on the volume or EQ enough to make it stop.

Regards,
Wayne

[toecheese]

Wayne A. Pflughaupt wrote:

Not necessarily. Some people have been led to believe that any low spot in their response is a null.

I understand what you're trying to clarify- differences in speaker resonance, impedance, etc. at different frequencies can also cause nulls.

In my case, the low area I am referring to is the entire range below 35Hz or so, not a 'dip'.

[Danny]

Really you can probably safely overload your driver by twice. With mine it is rated at 300watts but I'm putting 600 through it without distortion. Speaker
distortion is easy to hear so if your hear distortion and its not your amp clipping then the driver is overloading.

Really anything below about 30Hz (depending on your age) is inaudible.