Levels not right after EQ and boost question

[frodaddy]

I followed the instructions for REQW to calibrate the input/output/receiver before EQ'ing my subwoofers. I turned the receiver's subwoofer gain to 0 and adjusted the subwoofer amp gain to 75dB while taking measurements. Now that it's all done, I have to put my receiver at max +12dB to get to some decent SPL, but I can't go into "showoff" mode unless I turn up the gain on my amp.

So, would turning up the gain on my amp create a different baseline measurement? I hope the answer is "no" because I don't want to haul the PC in my living room again and have to take new measurements.

My boost question: Is there such thing as a "net boost"? Meaning, if I have a large boost of +15 but other cuts around it to make the difference from the baseline curve to the new one zero out in that area, does that break the rule of not doing a large boost? After playing around with REQW, I found that sometimes it's easier to make a large boost to get a section of the curve going in the direction you want, then make cuts to fit the house curve. If I posted my before and after graphs it would appear all I did was use cuts everywhere, but in fact I used the previously mentioned method to get my curve to fit.

Any help is appreciated!

[ThomasW]

Now that you've made the measurements, set the amp level so it does what you want it to.

Yes the use of EQ can result in a net boost or cut. More expensive EQ's have a output level control that allows the creation of what's called 'unity gain' to compensate for this effect.

[frodaddy]

Thanks Thomas!! I looked over the curves last night to make sure I wasn't doing too much "net" boosting, and I found at 20Hz I had a 10dB boost.
It looks like I have some minor adjusting to do, and it's great news that I won't have to take new measurements since my levels were off!!

This forum is awesome! Thanks again

[frodaddy]

I wanted to follow up on this. I've been over my friend's house EQ'ing his setup, and I came back to mine to see if I overlooked anything. I've been trying to get some good output from my system after I came home and I kept clipping the signal. It turns out that on my EQ I had the -10dB switch activated instead of using the +4dB switch. I also had to adjust levels in my Toshiba A1 player since it is known to have drastically low output on the sub channel. Now I don't clip the signal, and although the gains are lower on my amp they are still set at 3/4 volume. I'm using an EP1500 in 4ohm 2ch mode with my 4 Dayton IB 15's.

Also something about the "net gain" question. I did some listening for sound quality, and I found the bass to be very muddy in certain sequences. I bypassed the filters, and it cleared up. So, basically what I found is the "net gain" isn't a good technique to use when trying to fit your response to your house curve.

And finally, after I got over these hurdles I've learned the lesson about using too much boost. It's interesting because in my case the only indication I had was the bass sounded garbeled: The woofers weren't near excursion, the amp wasn't clipping, and the EQ's signal was fine as well. So now I'm strictly going by the +3db max rule and keeping the bandwidth narrow; and even then I can tell some slight distortion!

I hope this can help someone in the future!

[peted]

This is interesting frodaddy.

I have been using some boost, as described in my project thread to compensate for excessively low output from the BFD due to massive cuts to the mid-bass signal.

I wonder what causes this if nothing is clipping? The inability of the BFD to boost the signal, maybe over a wide bandwith?

Maybe this is the BFD's reduced S/N ratio caused by boosting showing through?

I have not noticed this yet, with a wide +16 boost at 20Hz, with cuts from 20Hz on up to keep the curve in line. I am just trying to avoid strictly using cuts to bring the curve down to the lowest point because I am left with no output and I do plan to use the minimum boost needed to have sufficient output going to my sub amp.

With my system, once I push the +4 buttom, the system noise floor jumps up significantly. Did you notice this garbled effect at -10, or +4, or both?

Another thought, maybe if your signal going into the BFD is really low (not lighting up many LEDs), your signal is getting lost in the noise of the BFD, then boost coming from the BFD will boost everything up, including the noise floor? This would be exacerbated at +4. If your sub channel from the receiver has low output, you probably want to use -10. The +4 is to allow really hot signals from the receiver without clipping, or as required by large cuts in the BFD to get sufficient signal out the back end.

Pete

[ThomasW]

frodaddy said:

So now I'm strictly going by the +3db max rule and keeping the bandwidth narrow; and even then I can tell some slight distortion!

I'm not sure what the +3dB rule is, but if the idea is that using boost higher than +3db is a bad thing, that's not my experience with one exception (see paragraph below for more on this). I've been using a BFD for more than 6yrs, and have experiments with a variety of filter settings. Not even using the higher levels of boost did the BFD create noticable distortion in the sytem. So if one has a problem using higher amounts of boost, I suspect the cause is elsewhere. (amp clipping, drivers being overdriven due to low Vd, etc)

Narrow bandwidth filters are actually the more problematic with regard to SQ, because those types of filters actually create overall changes the "Q" of the sub (IOW, if you have a Qtc of say 0.5, the Qtc can increase with the use of narrowband filters of a higher amplitude, so apply the +3dB rule in this instance). So IMO narrowband filters should be used only when there is no other alternative, since the most 'benign' filter settings are relatively broad (aka wideband) ones.

[peted]

admin said:

narrowband filters should be used only when there is no other alternative, since the most 'benign' filter settings are relatively broad (aka wideband) ones.

Can you loosely define "narrowband" in terms of fraction of octave?

[ThomasW]

peted said:

Can you loosely define "narrowband" in terms of fraction of octave?

The more narrow the filter the more problematic it becomes. Very narrow filters, so-call 'notch filters' are the worse offenders. So settings like 1/60, 2/60, etc, should be avoided.

[frodaddy]

peted said:

This is interesting frodaddy.

I have been using some boost, as described in my project thread to compensate for excessively low output from the BFD due to massive cuts to the mid-bass signal.

I wonder what causes this if nothing is clipping? The inability of the BFD to boost the signal, maybe over a wide bandwith?

Maybe this is the BFD's reduced S/N ratio caused by boosting showing through?

I have not noticed this yet, with a wide +16 boost at 20Hz, with cuts from 20Hz on up to keep the curve in line. I am just trying to avoid strictly using cuts to bring the curve down to the lowest point because I am left with no output and I do plan to use the minimum boost needed to have sufficient output going to my sub amp.

With my system, once I push the +4 button, the system noise floor jumps up significantly. Did you notice this garbled effect at -10, or +4, or both?

Another thought, maybe if your signal going into the BFD is really low (not lighting up many LEDs), your signal is getting lost in the noise of the BFD, then boost coming from the BFD will boost everything up, including the noise floor? This would be exacerbated at +4. If your sub channel from the receiver has low output, you probably want to use -10. The +4 is to allow really hot signals from the receiver without clipping, or as required by large cuts in the BFD to get sufficient signal out the back end.

Pete

I'm glad you mentioned the line level button because I didn't think about it the way you've explained how it works. The reason I used the +4 is because I was clipping the signal on the EQ, but I couldn't get any volume from my sub if I didn't. It was an odd problem because I would think that if I'm clipping the signal then I'd have TOO MUCH output, but it was just the opposite. When I EQ'd my friend's setup, we also had to use the +4 button. We are both using the Toshiba HD-A1 DVD player, however. When I was using a different DVD player I didn't have this problem.

I'm really not sure what to make of the SQ problem that I'm experiencing in relation to using alot of boost; or even a "net boost". Again, I'm not clipping the signal or the amp when it happens and my subs aren't near xmax. I'm having a pronounced garbled/muddied sound at the frequency I boosted, and with that single filter removed that effect is gone. Also after I used more moderate boost, the effect was not audible to my ears. To get a little more detailed, the original setting that was using too much boost was a +6dB boost centered around a small peak in a larger null at 49Hz with a bandwidth of 10/60. Now I'm using two boosts on either side of the small peak in the larger null: 46.5Hz, +3dB, 5/60 and 53.25Hz, +3dB, 3/60.

Thomas, the +3dB rule was something that, if I recall correctly, was read on this forum. The explanation for using as little boost as possible is that it's a multiplier in relation to watts, so a 3dB boost would need 3 times the wattage needed to play that boosted area. So if one of my subs needed 70w to play a signal centered around 50Hz and I do a 6dB boost with a bandwith that extends from 45-55Hz, then that frequency range now needs 420w. Please let me know if I have this wrong!! I believe the reason I'm having the distortion is because I'm using a lower quality subwoofer that can't handle the bigger boost (thus power) that I was giving it.

I haven't had good experiences using wider bandwidth filters and I prefer to use smaller ones now. But if the narrow bandwidth filters cause worse SQ, then can I blame the reason I'm not noticing a drop in SQ because my drivers are lower quality to begin with? I'm not sure what conclusions I can make right now since my follow up comments seem to have been partially false on both counts.

[peted]

frodaddy said:

I'm glad you mentioned the line level button because I didn't think about it the way you've explained how it works. The reason I used the +4 is because I was clipping the signal on the EQ, but I couldn't get any volume from my sub if I didn't. It was an odd problem because I would think that if I'm clipping the signal then I'd have TOO MUCH output, but it was just the opposite.

Not sure I am following here. Were you clipping the input or the output on the BFD?

Using +4 does allow to crank up your output from the receiver to the BFD, but it does not give you an increased output at the back end of the BFD (it does not boost the output signal), except for that increase gained by upping the output from the receiver to the BFD. In my experience, you do get more noise, so I used some boost in the BFD filters to allow me to operate at -10 and turn my sub amp and receiver down in the process.

BTW, the Shack forum may be the source of the +3dB guideline. I never saw it here.

Pete

[frodaddy]

peted said:

Not sure I am following here. Were you clipping the input or the output on the BFD?

The clip indicator lights were clipping, so I was clipping the output. If the +4 button is used when dealing with really hot signals on the input side, then what must have been happening was when in I was in -10 mode I was sending signals that were too hot to the EQ which in turn clipped the output. This would have created a ceiling for how loud I could run my subs, and this explains why I couldn't get any volume out of my system with the setting at -10. Here's a play-by-play on this entire problem which should also reveal my thought process on the subject:

The original problem was I wasn't getting much volume on the sub channel with my new Toshiba HD-A1 player; when I say much volume I'm talking about a -15dB difference. The DVD player was setup with defaults, my AV receiver was set at max +12dB, and my EP1500 was cranked all the way up. With my EP1500 all the way up, my Dayton 15 IB's ran in parallel, they were getting 225w each!! That's PLENTY of power to destroy these in an infinite baffle setup. I had to find out what was wrong.

Since my receiver and sub amp were cranked all the way up, the source of the problem was the DVD player. The fix for this problem is to use the onboard level settings like this: Leave the subwoofer gain at 0dB, and reduce the main speakers to -10dB. Then on your AV receiver, adjust your main speaker gain ~ +10dB to compensate. Once I did this I was able to get more volume from the system (not full volume still) and I was now clipping the EQ. Still the gain on the AV receiver had to be set to max +12dB and the EP1500 sub amp maxed out.

At this point I did alot of testing to find out what was going wrong in my signal path. I found a dip switch on my EP1500 for a clip limiter and it was turned ON. Turning it off gave me a few more dB but not what my system is capable of. My final testing was bypassing the AV Receiver AND the EQ. The DVD player's analog sub out was hooked directly to the EP1500 sub amp. In this configuration, I still couldn't get all the volume I needed and had to turn the EP1500 gain up. Finally when I was hooking the other equipment back in line, I noticed the -10 / +4 dB button and decided to try it since it was the last thing I haven't done. This turned out to solve my signal clipping problems. Then I was able to turn the AV receiver's sub gain down several notches and the gain on the EP1500 was turned down several dB also.

Hopefully this will provide more insight to why I'm confused about the +4dB button's role in fixing my signal clipping problem. In theory, I should be able to REVERSE the settings on the DVD player and select the -10dB button on the EQ but in practice it does not work this way. My best friend also has a Toshiba HD-A1, a Behringer DSP1124p EQ, and but a bigger Behringer EP2500 amp. We also had to use the +4dB button on the EQ to get normal volume from the sub system.

[peted]

Can you post your BFD filters from REW that you were using when you were having the original low output problem, even with the sub amp and receiver cranked up?

If you are clipping the output now, the EP1500 should have plenty of signal, just lower the input to the BFD from the source to prevent this clipping. But, you have garbled noise still, I think. I would verify on an offending scene at the same volume on the receiver with the sub amp turned off that neither the input or output on the BFD are clipping.

Also, I don't have HD-DVD. Do you need to hook up the DVD player line outs because the receiver can't decode the True-HD audio (from coax or optical)? Is this sub out designed to go directly to a sub, or is it supposed to go to a processor for pre-amplification?

[ryans]

frodaddy said:

In this configuration, I still couldn't get all the volume I needed and had to turn the EP1500 gain up. Finally when I was hooking the other equipment back in line, I noticed the -10 / +4 dB button and decided to try it since it was the last thing I haven't done. This turned out to solve my signal clipping problems. Then I was able to turn the AV receiver's sub gain down several notches and the gain on the EP1500 was turned down several dB also.

There seems to be a misconception about using the gain knobs on pro amplifiers. There is nothing wrong with turning these gain knobs all the way up to maximum in order to get the levels you need.

Also note that running them at less than maximum does NOT guarantee that you will not overdrive/clip the amplifier.

[frodaddy]

peted said:

Can you post your BFD filters from REW that you were using when you were having the original low output problem, even with the sub amp and receiver cranked up?

If you are clipping the output now, the EP1500 should have plenty of signal, just lower the input to the BFD from the source to prevent this clipping. But, you have garbled noise still, I think. I would verify on an offending scene at the same volume on the receiver with the sub amp turned off that neither the input or output on the BFD are clipping.

Also, I don't have HD-DVD. Do you need to hook up the DVD player line outs because the receiver can't decode the True-HD audio (from coax or optical)? Is this sub out designed to go directly to a sub, or is it supposed to go to a processor for pre-amplification?

Everything is working beautifully now. I've posted the settings below. Note that they didn't change very much because I didn't solve the problem with EQ'ing. Pete I read your post on how you fixed a very similiar problem to mine. I was going to use your method, but I can't do it with my particular setup. I don't clip the output signal at all right now, but the indicator lights on the EQ get VERY close to it. I don't have any headroom left on the signal output side.

I was getting the distortion at 50hz where I boosted. I did back to back testing using the Lion King's chapter 1 logo. Waterfall charts indicate it is centered right at 50Hz.

The fuzz EQ setting:
Filter 1: ON PA Fc 184.0Hz Gain -33.0dB BW/60 9.0
Filter 2: ON PA Fc 20.0Hz Gain 4.0dB BW/60 4.0
Filter 3: ON PA Fc 144.2Hz Gain -17.0dB BW/60 10.0
Filter 4: ON PA Fc 126.8Hz Gain -11.0dB BW/60 9.0
Filter 5: ON PA Fc 123.8Hz Gain -15.0dB BW/60 5.0
Filter 6: ON PA Fc 85.0Hz Gain 4.0dB BW/60 2.0
Filter 7: ON PA Fc 91.0Hz Gain -12.0dB BW/60 5.0
Filter 8: ON PA Fc 35.3Hz Gain -12.0dB BW/60 8.0
Filter 9: ON PA Fc 76.6Hz Gain -9.0dB BW/60 10.0
Filter 10: ON PA Fc 49.0Hz Gain 6.0dB BW/60 10.0
Filter 11: ON PA Fc 23.8Hz Gain -4.0dB BW/60 12.0
Filter 12: ON PA Fc 103.8Hz Gain -13.0dB BW/60 5.0

Here's the EQ that fixed my fuzz:
Filter 1: ON PA Fc 184.0Hz Gain -26.0dB BW/60 9.0
Filter 2: ON PA Fc 20.0Hz Gain 4.0dB BW/60 4.0
Filter 3: ON PA Fc 144.2Hz Gain -18.0dB BW/60 10.0
Filter 4: ON PA Fc 126.8Hz Gain -23.0dB BW/60 9.0
Filter 5: ON PA Fc 53.2Hz Gain 3.0dB BW/60 3.0
Filter 6: ON PA Fc 85.0Hz Gain 3.0dB BW/60 2.0
Filter 7: ON PA Fc 91.0Hz Gain -12.0dB BW/60 5.0
Filter 8: ON PA Fc 35.3Hz Gain -13.0dB BW/60 5.0
Filter 9: ON PA Fc 76.6Hz Gain -8.0dB BW/60 10.0
Filter 10: ON PA Fc 46.5Hz Gain 3.0dB BW/60 5.0
Filter 11: ON PA Fc 23.8Hz Gain -4.0dB BW/60 12.0
Filter 12: ON PA Fc 103.8Hz Gain -13.0dB BW/60 5.0

Here is the unequalized room measurement taken yesterday:


Here is the in room measurement after EQ'ing:


The Toshiba HD-A1 has an onboard decoder that decodes the soundtrack no matter what. It has an optical connection that sends Dolby Digital and DTS signals but it's NOT a pass-through; the soundtrack is decoded within the player then re-encoded for output. It also has analog 5.1 RCA outputs in which the onboard decoder will send a TrueHD, DD+, DD, and DTS signal over the analog. The fact that the player decodes everything that goes through it is important because the level setting within the player is sent through ALL of it's outputs.
There isn't a volume control, so the outputs are designed to be used in conjuntion with an AV Receiver or pre-processor. I merely used the analog out on the DVD player to bypass as much equipment as possible that was in-line with the sub. My normal connections are DVD -> AV Receiver -> EQ -> Pro Amp. I have both the optical and analog outputs connected to my AV Receiver; most movies I watch are standard DVDs so I use the optical connection. I only use the analogs when I'm watching an HD movie.

[peted]

That is strange that you have fuzz with one set of those filters and not the other. The only thing I can think of is maybe a fault in the BFD that would cause that, but who knows. At least you have managed to eliminate it.

You are already basically doing what I did to eliminate the low output: using some boost. I started with 100% cuts in the beginning.

Pete