Boosting...Is it always bad?

[GregBe]

Here is my situation. I have a PB-10 in a pretty small room. I get tons of room gain from 18hz -30hz... I know poor me . I also get a peak at 63hz. I have a eD eQ.2 which has two bands to work with; one for below 50hz content and one for above 50hz content. Even with the full 15dB cut down low, I still get a rising response below 30hz, which looks great on paper, but still feels a little bass heavy. If I use the upper freq band to boost the 30-50hz range, vs cutting the 63hz range, I can get an overall flatter response down low.

I know boosting typically eats up headroom, but logic is telling me it might not be doing that in my situation. Here is my train of thought. If I cut the 63 hz peak, I then have to boost the entire subwoofer level (eating up headroom anyway) when I calibrate to get the 40-80hz levels even with the mains. If I boost the 30-50 range with eq, am I really boosting it any more than I would have done anyway by reducing the 63hz response. In fact, by boosting the 30-50hz range with eq, it would seem that I am also increasing headroom in the 18-30hz range, by essentially lowering those levels. Am I way off base with this?

Thanks
Greg

[brucek]

If I boost the 30-50 range

There's not a big problem boosting an area that isn't fighting the room, such as a sharp dip. In the case of a dip that is caused by a reflection, raising the level of the direct signal also raises the reflection, so there's no overall benefit - you could throw more and more gain at it, and nothing will happen.

In your case, if you have headroom, it should be OK.

brucek

[absolootbs]

from what i've read, the general rule of thumb is to keep it to around 3db gain or less. obviously that will differ depending on each specific situation, and how much headroom you've got on your signal and amp. i just recently set up a bfd on my bic h-100, where i boosted two different places by 3db each and so far i haven't noticed any headroom problems from doing so. and i watch most movies at, or just below, reference level. take it as you will...

[GregBe]

Sounds good. That is what I thought, but sometimes my logic is a little off.

[Wayne A. Pflughaupt]

GregBe wrote:

I know boosting typically eats up headroom, but logic is telling me it might not be doing that in my situation. Here is my train of thought. If I cut the 63 hz peak, I then have to boost the entire subwoofer level (eating up headroom anyway) when I calibrate to get the 40-80hz levels even with the mains. If I boost the 30-50 range with eq, am I really boosting it any more than I would have done anyway by reducing the 63hz response. In fact, by boosting the 30-50hz range with eq, it would seem that I am also increasing headroom in the 18-30hz range, by essentially lowering those levels. Am I way off base with this?

Sounds like you're on the right track (although it would be easier to visualize if we could see your REW graph).

Basically, there's no free lunch, equalization usually costs headroom whether you boost or cut. For instance, your situation, if you cut way down at 30 Hz and also at 63 Hz, you'll have to raise the volume of the sub to make up for the lost gain (as you've already noted). What has happened? Well, if you look at the EQ's electronic response (REW can let you do this, just check the "Filters" box), you'll see that you have a big peak between 30 Hz and 63 Hz - just like you'd have if you had used a filter to boost between 30-63 Hz and not changed the sub volume.

Regards,
Wayne

[GregBe]

Wayne A. Pflughaupt wrote:

Basically, there's no free lunch, equalization usually costs headroom whether you boost or cut.

I am definitely realizing this Wayne. I have been playing with this tonight, and am realizing that even though, I can get a near perfect response, I have to use too much eq, and it is eating up too much headroom. I have another spot, that is a little more uneven as a final result, but have a better starting point, thus I have to do less eq, have more headroom and have a smoother response across more seats.

[Andysu]

GregBe wrote:

Sounds good. That is what I thought, but sometimes my logic is a little off.

I think it boils down to reading a little understanding of what has gone before and applying this common sense of practice (to prevent a sub bass amplifier overload clipping issue from happening).

GregBe wrote:

I am definitely realizing this Wayne. I have been playing with this tonight, and am realizing that even though, I can get a near perfect response, I have to use too much eq, and it is eating up too much headroom. I have another spot, that is a little more uneven as a final result, but have a better starting point, thus I have to do less eq, have more headroom and have a smoother response across more seats.

I think more subs you, have equals a merrier possible uniform frequency response (that doesn’t come cheap). Well it’s doable.

This is why in think so many other subs fail at home because the user has pushed it into clipping due to lack of other portions of the frequency response not reaching his/her expectations (because they can’t see the frequencies that are missing or are even aware of the issues like “nulls” as their amp nears the critical level of breakdown).

[GregBe]

I think you are right. Without eq, my sub is fine for my room/listening level. When I apply judicious eq, I am just about right at my limits. If I apply too much eq, my sub goes into compression at my normal listening level with the tougher scenes.

[Andysu]

GregBe wrote:

I think you are right. Without eq, my sub is fine for my room/listening level. When I apply judicious eq, I am just about right at my limits. If I apply too much eq, my sub goes into compression at my normal listening level with the tougher scenes.

How many locations have you tried in the room including standing off the floor by any means possible will make a slight difference and even rotating it around also will be beneficial.

This is what I’ve done with the Eltax A-12R sub for LCRS sub bass extension to show you it only takes a mater of minutes to find anything (anything at all to raise it off the floor). Sometimes the floor is good spot other times it is depening on how its going to perform.

It’s good for a few frequencies on the floor at the left and right and few spots in the middle front. But with CRT standing in the way it does limit several inches at least 36 inches. Also I believe the CRT TV is bouncing off a few frequencies, (oh just a feeling I have).

So look around this afternoon for some first extra long cable first as you’ll need some cable for the audio a very long cable! Also power extension cable lead as the sub is going to be moved around and tried out. You do have REW? Getting up and running and conduct as many sweeps as possible.

Note the location that each sub was tested in on the floor and raised-up off the floor to see how it behaves. You might find a spot/location where it would be good for the what ever lowest possible range just above 80Hz or so?

So a small round table and stool is what it takes to raise it up as much as 43 inches. I won’t go right to the very top near to the ceiling but have since ran out of anymore possible items to balance the sub on.

I’ll run a frequency sweep of the sub in that location later on in the day. One sweep standing on the floor the other standing on the stool/table.

[DrWho]

There is fundamentally no difference between cutting and boosting.

Any speaker is capable of a maxSPL at any given frequency and that number does not change with either boosting or cutting.

Suggesting that cutting is ok, but boosting is not ok leads to some misunderstandings that don't necessarily prevent overdriving the equipment...

[Ge0]

Andysu wrote:

How many locations have you tried in the room including standing off the floor by any means possible will make a slight difference and even rotating it around also will be beneficial.

IMHO

WINNER

Try and solve your problem acousically first then toy around with electronic manipulation. Slight variations in placement may improve your chances of needing less EQ.

If alternate placement is not an option (i.e. wife acceptance factor) then apply the band aid and be prepared to make tradeoffs.

Ge0