Taking sweeps with both mains/sub or just one main/sub?

**bigbwb** · **02-11-09, 06:16 PM**

Hello,

I have been busy trying different settings & etc with my BFD & RS SPL meter with REW. One thing I noticed is that when I do sweeps with just the sound card output going into one channel of the receiver is that the results are way off compared to using a Y splitter running the one output into the splitter then into the receiver? This then allows both main speakers and the sub to playback the sweep versus just one speaker and the sub playing. I assume using both front speakers and the sub is most accurate, is that correct?

Thanks,

Brandon

**brucek** · **02-11-09, 06:26 PM**

Quote:

One thing I noticed is that when I do sweeps with just the sound card output going into one channel of the receiver is that the results are way off compared to using a Y splitter running the one output into the splitter then into the receiver?

Well, the level and response will certainly be different because you've added another amplified speaker in another location when you drive both channels.

You can't really say one way is more accurate than the other. You have to decide what you want to measure. Sub, sub + left speaker, sub + right speaker, sub + right + left speakers, left speaker, right speaker, right + left speaker................

brucek

**bigbwb** · **02-11-09, 07:40 PM**

well my goal was to really get the most accurate picture of my system when playing in 2.1(meaning the front speakers & sub on only). After taking measurments in this fashion, my room response is very flat from 15hz-100hz, but if I only use the sweep with one speaker and the sub, theres a huge null around 80hz.

So I did all my EQing on the BFD with both speakers & the sub playing the sweep.

Does this seem logical to you?

Thanks Bruce!

Brandon

**brucek** · **02-11-09, 08:01 PM**

Quote:

So I did all my EQing on the BFD with both speakers & the sub playing the sweep.

Does this seem logical to you?

Well, the accepted method to use is to play the sub with the mains shut off. Simply disconnect them if you have a receiver or shut off the mains amplifier if you have separates.

Once the sub is equalized, then add both the mains and adjust the subs phase control to remove and dip or peak at the crossover.

brucek

**bigbwb** · **02-11-09, 08:12 PM**

Bruce,
i did take a measurement after all my EQ work with just the sub playing the sweep and it was very very close to the other plots I had taken except of course the gradual drop starting around 60hz as it approaches the crossover

I assume its normal for the sub alone to start dropping off around 60hz even though I use a 80hz crossover?

I did manipulate the phase control and found my 180* setting had the best integration between the mains & sub with a very minimal dip.

I appreciate the help!

Brandon

**bigbwb** · **02-11-09, 08:16 PM**

I will try and upload some plots too.

The green one is my yamaha reciever(80hz crossover)

The blue one is my parasound 2100 preamp with a sub out and its own 80hz crossover. It has HT bypass.

Both plots are with both my main L&R speakers & sub playing.

**brucek** · **02-11-09, 08:38 PM**

Quote:

I assume its normal for the sub alone to start dropping off around 60hz even though I use a 80hz crossover?

You should have the target line turned on in REW with the crossover target set and you'll know exactly what the line should look like.

Quote:

some plots

They look good.

brucek

**bigbwb** · **02-12-09, 06:30 PM**

Bruce,
are there any negative side effects by starting the EQing process with all 3(L&R mains & sub) playing the sweep? I have always done it this way and the results are very good as seen above. But in an above post of yours you had me thinking this was not quite right?

Just trying to get a handle on whats right/wrong.

Thanks,

Brandon

**brucek** · **02-13-09, 01:22 AM**

Quote:

are there any negative side effects by starting the EQing process with all 3(L&R mains & sub) playing the sweep?

The trouble is that you can't really get a picture of the sub(s) when the mains are active. You need to do the sub(s) first and then add the mains.

brucek

**bigbwb** · **02-13-09, 10:15 AM**

Quote:

brucek wrote:

The trouble is that you can't really get a picture of the sub(s) when the mains are active. You need to do the sub(s) first and then add the mains.

brucek

True, but what gets me is that I could EQ just the sub, but then as soon as I add the mains, I have to go back and reEQ any dips/peaks that were just introduced. So this seems counterintuitive considering no one ever just listens to the sub & no mains

Sure I could EQ just the sub to be extremelely flat, but is that giving me a true picture considering once the mains are playing the rooms repsonse will be very different anyway?

I am not trying to argue your point, just trying to understand the logic behind it thats all

**brucek** · **02-13-09, 12:55 PM**

Quote:

So this seems counterintuitive

Yeah, the reasoning is that you get a better picture of the situation if you measure and EQ separately. In fact you should really do each main speaker separately also, until the final tweak. You have no idea what's happening when you EQ with (sub + two mains), especially over the crossover area.

If you start with the sub and get it tracking the target, and then do each main, and position them for the best response, the only work you'll have to do when you play them in concert is usually the phase. Suppose one of the mains has a dip in it because of its positioning in relation to a wall. If you saw that dip when you only measured the sub+ mains, how would you know that a small movement of that main would have cleared the problem. Instead, you propose to add EQ to the sub. Perhaps one of your seating positions would now notice the dip in the main.

But in some cases you will indeed have to add some more EQ once you add the mains to the sub.

But, whatever works for you is the best.

brucek

**bigbwb** · **02-13-09, 01:28 PM**

Bruce,

Ok. that makes sense. So basically just EQ the sub alone first. Then do a sweep with each individual main speaker playing without the sub to find the best placement(I assume the flattest you can find in your given area). After this you will have the sub EQed alone and the best placement for the mains choosen then its time to play them all together for the final phase tweaks & etc?
Just want to be clear as I can try it this weekend.

Thanks,
Brandon

**brucek** · **02-13-09, 01:50 PM**

Yep, that's the general drill....

**jmalto** · **02-14-09, 09:43 AM**

Curious, I always thought the BFD was not recommended to EQ the mains?

**bigbwb** · **02-14-09, 09:49 AM**

Quote:

jmalto wrote:

Curious, I always thought the BFD was not recommended to EQ the mains?

Thats not whats happening here. I am simply measuring with & without the mains playing when doing the sweeps. My question for Bruce was whether or not to include the mains with the sub or not when starting to EQ the sub. In the end, the BFD is just flattening out my subs repsonse.

Take care,
Brandon

**jmalto** · **02-14-09, 09:51 AM**

Quote:

bigbwb wrote:

Thats not whats happening here. I am simply measuring with & without the mains playing when doing the sweeps. My question for Bruce was whether or not to include the mains with the sub or not when starting to EQ the sub. In the end, the BFD is just flattening out my subs repsonse.

Take care,
Brandon

Brandon - Ah, I assumed you were going to use the BFD again from a response earlier in the thread where you said that is what you EQ'd with the BFD.

Bruce is helping me accomplish the same goal you are after, except I have 3 subwoofers which makes it worse

**bigbwb** · **02-14-09, 09:58 AM**

Quote:

jmalto wrote:

Brandon - Ah, I assumed you were going to use the BFD again from a response earlier in the thread where you said that is what you EQ'd with the BFD.

Bruce is helping me accomplish the same goal you are after, except I have 3 subwoofers which makes it worse

gotcha!

Good luck with that

**stealthgear** · **02-16-09, 01:37 PM**

Seeing as how much the sub response dramatically changes depending where you are in the room, I dont see why you'd want to EQ the sub, unless it really wasn't performing well overall. The phase changes dramatically. I know I never listen in the same exact spot. You might decide against EQ if its not making it better in all the main listening zones overall. Do lots of measurements and compare them.

**bigbwb** · **02-16-09, 01:53 PM**

Stealth,

The purpose of EQing my sub allows me to have a much flatter room response than before in my listening position. You are correct, other locations may produce a different response, but who cares, at least my spot sounds the best it can and thats what matters when you are listening critically. I never truly bothered taking measurments elsewhere considering i only sit in one spot(as does the wife next to me) and i only move around if i am walking through the room.

I guess your post seems like you dont agree with EQing a sub for ones listening position?

**brucek** · **02-16-09, 02:54 PM**

Quote:

Do lots of measurements and compare them.

Yeah, most people do this. They take a series of measures from the various listening positions and use the average feature in REW to create a profile for the best overall equalization.
Then they also take a single sweet spot measure to create a sweet spot profile for critical listening.
There's really no reason to avoid equalizing a sub simply because it performs different at the different listening positions.

brucek

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