First bass measurement question...

**RyanJNielson** · **12-19-06, 01:15 PM**

Hello!

My new dedicated HT is so close to being finished I can hardly stand it. Four months in the making!

I have started calibration and have taken some initial measurements using REW and I am pretty pleased with the results. The bass traps must be working!

(Here is where I would input the graph, but there is no button for Manage Attachments!)

Here's the only issue:
In my HT I currently have two subs in the front corners of the room (JBL 12" and JBL 10"). The frequency response is extremely flat at approx 75dB from 25Hz to 60Hz, then makes a 5dB minor spike at about 68dB, then suddenly plumets about 30dB at 73Hz returning to normal at 93Hz. My crossover is set at 80Hz- does this sound like a phase problem to anyone?

I will certainly experiment tonight with phase settings, moving the subs, and trying one without the other- but it's such an odd drop RIGHT at the crossover- I thought maybe you all would have some ideas.

Also- not sure if it matters, but the front speaker are relatively new and haven't been completely broken in. The subs are definitely broken in.

Thank you!

Ryan

**Wayne A. Pflughaupt** · **12-19-06, 01:31 PM**

Hi Ryan,

Quote:

(Here is where I would input the graph, but there is no button for Manage Attachments!)

We’ve been having trouble with spammers, so we had to institute a 10-post minimum before attachments for new members, to discourage them (the spammers, not the members!). There is a way for administrators to lift the minimum requirement, and hopefully I was able to do that for you (you’re the first one I’ve tried it for). See if you have the Manage Attachments button now.

Regards,
Wayne

**RyanJNielson** · **12-19-06, 01:35 PM**

Thanks, Wayne! It looks like it worked:

(Replaced Below)

What do you think? I feel like it could be a phase issue...

**brucek** · **12-19-06, 02:00 PM**

Quote:

What do you think?

Can you change your vertical scale to 45DB-105dB.. (that's the standard that we use)

brucek

**RyanJNielson** · **12-19-06, 02:23 PM**

There we go. Doesn't look as flat at this range, does it?

bass response 1.jpg

Any suggestions on taking better measurements, by the way?

**maxcooper** · **12-19-06, 09:29 PM**

Can you change the phase on the sub (switch/knob on sub, does BFD have this feature?, wire main speakers with reverse polarity just to test

, etc. -- there are many ways to change the phase) and do another measurement? My sub has continuously-variable phase. I just did measurements at 0, 90, and 180 and picked the flattest one. Comparing similar plots for your system would help to identify if the drop is a phase issue or not.

Or maybe your receiver has a delay or distance setting for the sub that may help eliminate the void?

-Max

**brucek** · **12-20-06, 07:49 AM**

Quote:

Any suggestions on taking better measurements, by the way?

Two subs is usually tricky, especially when the two aren't exactly matched in their responses. The overall response ends up reverting to the poorer, more challenged of the two. On the other hand, headroom is a positive result when using two subs. Often, when someone decides to get a new more powerful sub, they decide it would be a good idea to still use the old one, and it ends up a worse situation.

Either way, your response is quite good and I agree it would appear that you have a crossover cancellation problem. It's always best to begin measurements with a single sub, with the mains off, and the receiver in stereo mode (a non surround mode). This then allows you to see how the sub itself is acting in the room and enables you to set filters in a BFD (if that's your intent), or move the sub around the room to get the best location (front corner usually being the best).

Then in your case, you would add the second lesser sub and do a response to ensure there are the least cancellations and response changes (especially in the very bottom extension where mismatched subs are a problem).

Then once that conundrum is solved, add the mains and work on any integration problems around the crossover frequency.

REW makes all this fairly easy.

brucek

**RyanJNielson** · **12-20-06, 10:26 AM**

Thanks for the two-sub tutorial, brucek.

I did several experiments last night with the two subs, including starting with the big one as you suggested. There was and still is a peak at about 70Hz that would be nice to eliminate, but I'd need the Behringer to do so. That may be an option in the future. There was a drop just after 80Hz, but adding the lesser-powered sub defeated the null and really flattened the frequency response across the board, but maintaining the peak at 70Hz.

Integration with the fronts went very well. Slightly moving the subs helped quite a bit. Frequency response is quite good now.

Experimenting with the levels on the subs had more impact than I would have expected- very interesting.

I left my other computer at home so I can't post graphs, but perhaps tomorrow.

Ryan

**DrWho** · **12-20-06, 03:37 PM**

You might find this article helpful:
klipschcorner.com/Articles.aspx?guid=feb5d669-1513-426d-a8fc-29f8aa90869f

It makes a lot more sense when you can see the frequency response change too.

It would also be informative to provide a plot of your subwoofer's response without the mains (just unplug the speaker wires from the mains). This will tell if you the dip is the result of acoustical interference with the mains, or if it's room related. Try measuring each sub independantly too.

You can show these all at once if you use the tabs built into REW. Ignore that they say Left, Center, Right, etc.... and manually set the "speaker type" (the dropdown box that says "Fullrange, Bass Limited, etc...). Then you can click on "Measured Responses" in the drop down menu at the top right of the screen and view everything at once.

If each of your subs has a dip with the mains off, then your issue is going to be room related. EQ will only work if it's a minimum phase situation, but most acoustical issues aren't. You will want to look for boundaries (walls) that are about 4 feet away from the speakers. Reflections off these boundaries will cause cancellations at the listening position because they are 180 degrees out of phase. Peavey has a good article that describes 1/4 Wavelength Boundary Cancellaton:
peavey.com/support/technotes/soundsystems/boundarycancellation.cfm

hmmm, seems I haven't hit 10 posts yet either (so can't post clickable links)

**RyanJNielson** · **12-20-06, 03:54 PM**

Thanks for the link, I'll check it out!

**brucek** · **12-20-06, 04:21 PM**

Quote:

hmmm, seems I haven't hit 10 posts yet either (so can't post clickable links)

Just promoted your status DrWho. You should have full member status now...

brucek

**DrWho** · **12-20-06, 11:12 PM**

hmmm...seems upgrading my status didn't work. Maybe I should just run up 10 posts

(just thought I'd mention it since you seem to be testing it).

**Sonnie** · **12-21-06, 12:17 AM**

I think it's working okay... I was able to update a link in another post you made. If the restriction had been in place it would have given me the error. Either way though... you do only have two posts to go.

**DrWho** · **12-21-06, 12:39 AM**

Hmm, when I went to edit my post it wouldn't let me - and then I tried again in a few replies. This should be my 10th post

**DrWho** · **12-21-06, 12:40 AM**

so here's those links in clickable form:
Dial in a Sub By Ear
Boundary Cancellation

**RyanJNielson** · **12-21-06, 09:37 AM**

Here we go. This is about as good as I can get it in the room without the Behringer:

bass response 2.jpg

I can still re-run YPAO on my Yamaha 5790. It has 5 settings I can choose from: FRONT, FLAT, LOW, MID, and HIGH. Normally people recommend using FRONT or FLAT, I may try LOW just to see what happens. Anyone have thoughts on this?

Also, I could not eliminate the nulls around 150Hz, but I know that that is where my sub starts blending with the mains. Do you guys think that once the mains are better broken in their frequency response will improve?

**brucek** · **12-21-06, 10:35 AM**

Quote:

This is about as good as I can get it in the room without the Behringer:

Hopefully, a BFD is something you'll be getting?

Quote:

Also, I could not eliminate the nulls around 150Hz

Can you tell us what we are looking at? Is this two subs and mains together?

What is the receivers crossover frequency for the sub(s).

Quote:

but I know that that is where my sub starts blending with the mains

Can you explain this statement?

Quote:

Do you guys think that once the mains are better broken in their frequency response will improve?

They would likely sound less harsh.

brucek

**RyanJNielson** · **12-21-06, 10:43 AM**

Yes, I will probably get a Behringer. It would certainly help things out!

The graph represents the Mains and Subs together, crossover set at 80Hz. I used the sweep running through the two mains in stereo mode- I think that's how to do it correctly.

I always thought that with the crossover at 80Hz, the fronts and mains start blending at about 150Hz- I may be incorrect.

What are your thoughts on the current readings?

**brucek** · **12-21-06, 10:59 AM**

Quote:

What are your thoughts on the current readings?

I don't like the response as much as the one you posted below: This one has lots of potential.

You have much better low end extension here.

I would have liked to see the above graph with the subs only and a 80Hz sub target line on the graph as well. Then when the mains are added in, only the crossover area should be in question. This should be easily corrected with phase and a BFD.

brucek

**DrWho** · **12-21-06, 11:35 AM**

Ditto what Bruce said.

Btw, an 80Hz crossover defines the -3dB point of each speaker as being at 80Hz. In other words, this is the center around which summing is taking place. At 160Hz, your sub will be 24dB down and your mains will be 0dB down (no change on the mains). At 40Hz, your mains should be 24dB down and your sub 0dB down (no change on the sub). The entire bandwidth between 40 and 160Hz is defined as the crossover overlap region, with 80Hz being the region that the most interaction takes place (because the output levels of both speakers are the same level).

**brucek** · **12-21-06, 11:58 AM**

Yeah, ditto on what Mike said.
Ryan, this is why I was asking about your statement, "I could not eliminate the nulls around 150Hz, but I know that that is where my sub starts blending with the mains.". It just ain't so. I would assign exclusive blame to the mains for those dips. I think if you graphed out to 1000Hz, you would see all sorts of that nonsense going on. It doesn't hurt to apply some (1/6th-1/3rd octave) smoothing to the graph to get a more realisitic feel to how it may appear to your ears..... We like to see unsmoothed data posted, but for your own viewing, smoothing is a good idea.

brucek

**RyanJNielson** · **12-21-06, 12:14 PM**

Wow, LOTS of info- Thanks, guys!

I will continue to experiment and I will post the graph you suggested as well.

This process has quite a learning curve!

**Wayne A. Pflughaupt** · **12-21-06, 05:33 PM**

Quote:

The graph represents the Mains and Subs together, crossover set at 80Hz. I used the sweep running through the two mains in stereo mode- I think that's how to do it correctly.

Can you take a reading with just the 12” sub? I’m guessing it will look much better.

Regards,
Wayne

**RyanJNielson** · **12-22-06, 09:38 AM**

Wayne, I think you're right- I don't know what I was trying to do with those new measurements. I will have many posts once the holidays are over!

Thanks for the help- much appreciated!

Ryan

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