EQ'ing sub the correct way? LFE/Redirected bass - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 5 Old 04-12-16, 03:29 AM Thread Starter
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EQ'ing sub the correct way? LFE/Redirected bass

Hello guys

I have a couple of questions when EQing my system. I use 100% parametric EQ for my whole system which consists of:

2 x passive sub woofers powered and EQ'ed by a inuke 6000DSP

Receiver is a Yamaha RX-2040 used for EQ'ing the main speakers.

When i EQ the subwoofers i set the LFP to 80hz/butterworth 24db and HPF to 20hz/butterworth 24db in the inuke

I sweep the LFE in REW (which is 10 db higher so i set the setting 10db lower) and EQ to fit the target. When done i EQ the speakers to target in the yamaha PEQ settings.

The problem is that the combined frequency response of the subs + fronts combined does not show the right target - there is allways a hole in the crossover area. I have experiemented a lot with different phase settings but never sorted it out.

But then i tried to make a sweep with Left front speaker + sub and while disconnecting the left front speaker and to my surprice the output around the crossover was lower! Here is the difference between a normal subwoofer(LFE) sweep -10db versus a sweep with combined sub+front (which i assume is the redirected bass)

Image below

Blue is redirected and black is LFE

This leaves me with 2 concerns.

1. Does this mean that i am EQ'ing it wrong when using the LFE? Should i use the response that comes from the redirected bass when EQ'ing and let the LFE "live its own life"?

2. As the Yamaha does not have a LPF on the LFE channel setting i am afraid that there will be a hole in the respons as the LFE is rolled off at 80hz on the subs but will continue on the fronts up to 120hz.

I guess that my only option is to set the LPF in the inuke to 120hz which is not ideal as i cannot eq the roll off to the 80hz crossover target between sub/fronts....

What do you guys think?
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post #2 of 5 Old 04-12-16, 04:41 AM
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Re: EQ'ing sub the correct way? LFE/Redirected bass

Not sure what you mean by the Yamaha not having a LPF on the LFE. If you engage the subwoofer output in the Yamaha, there will be a LPF in place, probably 80 Hz. If you’re applying another LP in the iNuke, then that will get you problems. You don’t need both.


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post #3 of 5 Old 04-12-16, 05:43 AM Thread Starter
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Re: EQ'ing sub the correct way? LFE/Redirected bass

In many receivers you can set your LPF on the LFE to a certain HZ.

like this

This is not possible in the yamaha. My by measurements it looks to be fixed at 120hz.

The thing is that i want a 80hz crossover and i want to EQ the crossover roll off to target. The only way to do this is by setting a 80hz LFP in the inuke (this way i get xo 80 and LFE 80)and EQ it to target. However when i afterwards measure the LFE and redirected bass the response differs as shown in the picture above.

You are right, it is getting me into problems. But what is the right approach?

Either just EQ to 120hz target on the LFE and assume that the 80 xo roll off is ok or use the trick where i measure front + sub but leave the front disconnected to see the redirected bass, then EQ to 80hz target and ignore the LFE?
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post #4 of 5 Old 04-12-16, 07:34 AM
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Re: EQ'ing sub the correct way? LFE/Redirected bass

One thing to keep in mind is the lpf you're talking about in the denon is not going to effect the crossover at all. What it's doing is telling the avr where to cut off the top of the lfe signal present in a 5/7.1 soundtrack. The lfe (.1) in a soundtrack is a separate channel that is from 1hz-120hz. This is only going to effect playback in an actual soundtrack and not REW sweeps which will sweep as low as you want to but the lfe in a soundtrack is processed independently and only if its present.(unlike REW or test tones).

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post #5 of 5 Old 04-12-16, 08:07 AM
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Re: EQ'ing sub the correct way? LFE/Redirected bass

Late, and just another way to offer the same advice:

Yes, your #1 is correct. The only way to be sure that redirected bass is operating correctly is to measure FL, SW, and FL+SW and also the FR, SW and FR+SW. Also the same series for the CC is good idea. If there is good SPL fill in the XO range then the distance/delays are set reasonably well. There can sometimes be a room mode difference for a main speaker vs the SW in one of the main speakers that makes it impossible to have all 3 fronts with good SPL fill. In that case just chose the best setting.

The LFE is a separate channel. Within the AVR, the mains XO settings has no impact on the LPF . The LPF is normally set to 120 (or 80Hz); either is fine. Audyssey recommends 120Hz. There is normally no program material in the LFE channel that is >80hz. The program material is mixed that way by design, but I've read there are a few reported exceptions going up to 120Hz.

SW EQ will effect both redirected bass and LFE signals and that is good because the room impact on the SW is the same for both cases so EQ using the redirected bass.

I don't recommend setting redirected bass XO distance/delays using the LFE channel measurements. It may in some cases be a similar result depending on the settings, but the only sure way is to measure the actual operating situation for redirected bass.

It is not a good idea to set an LPF filter in another box like a P-amp. That is very likely to cause more issues. If you a very advanced there may be some cases where it makes sense, but those are unrelated to proper setup of redirected bass.
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bass , correct , eqing , lfe or redirected

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