Effect of a change in gain to subs?

L

Loren Jones

Sophomore
Jun 25, 2011
155
0
16
Hampton Roads VA
Hi,

Quick theoretical question. In a system with a traditional left and right sub, each driven off of a separate output of the DSP and therefore each with its own amp, what will be the effect in terms of acoustic output of decreasing the DSP output to each of the subs by 3 db? Will it be a 3 db reduction in the LF output in the room, 6 db reduction, somewhere in between, more than 6 db or less than 3 db? The subs are about 40 ft apart and LPF is at 80hz.

I suspect the answer is that it depends on where you are in the room and what frequency you are measuring but I don't know enough acoustics to be sure. Obviously this question is more for theoretical understanding as the level of the subs will be adjusted by measuring and or listening, but I am just trying to understand. I recently decreased the outputs from the DSP 3 db as described above and it seemed like the LF output in the room went down more than 3db. I don't have very accurate measurement tools or skills so....

Thanks,
Loren Jones
 
Re: Effect of a change in gain to subs?

Ignoring the vector summation lets insert some (round) numbers.

Say woofer L is originally getting 200W, and gets reduced -3dB to 100W, and woofer R changes the same 200W to 100W.

The simple perfect sum 400W drops to 200W or -3dB. Since changing the power level does not change "how" they sum, -3dB is -3dB is -3 dB.


JR
 
Re: Effect of a change in gain to subs?

Loren said:
I recently decreased the outputs from the DSP 3 db as described above and it seemed like the LF output in the room went down more than 3db.
Click to expand...

Hi Loren:

Three things come to mind as probable contributions to your subjective observation:

1. The lower the SPL, the higher the LF haystack required to achieve a given perceived tonal distribution.

2. Reduction in limiter engagement. The harder you drive the subs into the limiters, the more compressed that portion of the spectrum is, thus the higher the RMS and perceived volume.

3. Higher levels of distortion at identical SPL's sound louder. Some studies have shown that a 10% increase in distortion (very easy to achieve with loudspeakers) can result in apparent SPL increases of 10dB. Distortion ramps up very quickly when approaching the maximum output of either an amplifier or loudspeaker. Backing off 3dB can clean up the distortion markedly.

JR is right. A dB is a dB. Living in that world removes many opportunities for confusion.
 
Re: Effect of a change in gain to subs?

John Roberts said:
Ignoring the vector summation lets insert some (round) numbers.

Say woofer L is originally getting 200W, and gets reduced -3dB to 100W, and woofer R changes the same 200W to 100W.

The simple perfect sum 400W drops to 200W or -3dB. Since changing the power level does not change "how" they sum, -3dB is -3dB is -3 dB.


JR
Click to expand...

Thanks John,

That makes sense. I was making it too difficult I guess.

Loren
 
Re: Effect of a change in gain to subs?

Langston Holland said:
Hi Loren:

Three things come to mind as probable contributions to your subjective observation:

1. The lower the SPL, the higher the LF haystack required to achieve a given perceived tonal distribution.

2. Reduction in limiter engagement. The harder you drive the subs into the limiters, the more compressed that portion of the spectrum is, thus the higher the RMS and perceived volume.

3. Higher levels of distortion at identical SPL's sound louder. Some studies have shown that a 10% increase in distortion (very easy to achieve with loudspeakers) can result in apparent SPL increases of 10dB. Distortion ramps up very quickly when approaching the maximum output of either an amplifier or loudspeaker. Backing off 3dB can clean up the distortion markedly.

JR is right. A dB is a dB. Living in that world removes many opportunities for confusion.
Click to expand...

Thanks Langston,

The amps output rating doesn't even equal the continuous power rating of the subs so I don't think we are dealing with loudspeaker distortion to a significant extent. The subs are also not going to be getting out of their linear range with regards to displacement at the power in question. There is no system limiter in place and I NEVER even see a clip light on any of the amps in our system. Anyway, certainly what John stated and you affirmed makes perfect sense. Whether the subs were center stacked and coupling perfectly or LR stacked and creating lobes and nulls, the power is still 3db less thus it follows the output will also be 3 db less regardless of the acoustics (and assuming everything is operating in a linear range).

Loren
 
Re: Effect of a change in gain to subs?

Well then, with #'s 2 and 3 eliminated, that leaves #1. :)

Restated: A 3dB reduction in the sub spectrum will sound like a 6dB (or more) reduction in the mid frequencies.

---

Art Welter brought this now obvious concept to my attention.
 
Last edited:
Re: Effect of a change in gain to subs?

While you didn't mention which cabinets you are using, I wouldn't underestimate the amount of distortion in typical bass loudspeakers, nor how much that influences how they sound.

I even suspect one well respected brand that doesn't make as much distortion as everybody else occasionally gets accused of low output because of it's linearity...

Our brain often uses distortion as a marker for loudness while with low bass, distortion often just sounds like mo bass because it lands on frequencies we hear louder....

of course YMMV

JR
 
Re: Effect of a change in gain to subs?

John Roberts said:
While you didn't mention which cabinets you are using, I wouldn't underestimate the amount of distortion in typical bass loudspeakers, nor how much that influences how they sound.

I even suspect one well respected brand that doesn't make as much distortion as everybody else occasionally gets accused of low output because of it's linearity...

Our brain often uses distortion as a marker for loudness while with low bass, distortion often just sounds like mo bass because it lands on frequencies we hear louder....

of course YMMV

JR
Click to expand...

JR,

I have heard that about the Danley subs but have never heard one myself. I assume that is the brand you were mentioning.

These subs are built by me. The design was done by Phil Graham and my statements regarding the fact that the subs are in their linear operating range at the given power levels are based on Phil's model. They are 21" RCF drivers in a vented cabinet. So I trust Phil's modelling of the system, but they certainly have never been measured to see what the distortion or other performance parameters are.

I understand about the distortion in the subs ending up in frequencies that our ears are more sensitive to thus distorted bass will sound louder than "clean" bass at the same level.

Thanks,
Loren
 
Re: Effect of a change in gain to subs?

Langston Holland said:
Well then, with #'s 2 and 3 eliminated, that leaves #1. :)

Restated: A 3dB reduction in the sub spectrum will sound like a 6dB (or more) reduction in the mid frequencies.

---

lter brought this now obvious concept to my attention.
Click to expand...

Langston,

I need to try to get your link to work. It wouldn't open on my mac. That is interesting about the perception of changes in bass output though. I guess I knew that if I would have thought through it.

Loren
 
Top Bottom