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Troble running bass test tones. Need help equalizing. (1 Viewer)

RuslanM

Agent
Joined
Nov 4, 2002
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34


Hello forum,

I've been trying to create my first graph on the SVS 25-31 and ran into problems. I've set my receiver to the reference level (75db) and started playing the test tones. However, the receiver kept on shutting off on the 32Hz tone. I lowered the volume to -5 below reference and was able to run test tones until I hit 45Hz tone and the receiver shut down again.

So, eventually I had to put the volume to -15db below reference to be able to play the test tones. But still I could only get to 125Hz when receiver shut down again. If I lower the volume more I'll be able to play the last 3 sweeps but I wouldn't be able to see them on SPL since these sweeps show below 60Hz.

Now, my subwoofer out level is set to -5 on the receiver, all speakers are off, receiver is in stereo mode, crossover set to 100Hz. My receiver is Denon 3802 (110W) and I never had any problems with it.

The above graph was taken at -15db below reference and shows values from 20Hz to 125Hz. What do you guys think? I just got my BFD yesterday and plan on playing with it some time next weekend. But before I wanted to get your opinions and suggestions on how I should approach it with this response. So far I've been doing a lot of reading on this forum and probably have read every single thread on BFD and house curve. However, I think that each graph is pretty unique and there're many ways to approach it. So, I wanted to get some help from more experienced people especially Wayne and Brucek. Your opinions are welcome.


Thanks in advance,
Ruslan.
 

Tom Vodhanel

Senior HTF Member
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Sep 4, 1998
Messages
2,241
Hi Ruslan,

Not sure what you are using for the test tones...but running high levels for FR checks is a bad idea. This is definitely an *abuse* of the subwoofer...and you could easily damage the driver like this.

PLEASE, use a LOW spl level to set the EQ. 70dB,75dBs..something like that.

BTW, the graph wasn't showing up for me.

Tom V.
SVS
 

Doug_B

Screenwriter
Joined
Feb 11, 2001
Messages
1,081
I don't see the image, either. In any case, no need to have the volume the same for all frequencies, as long as you provide the appropriate offset for each when you graph them (a pain, yes, but doable). Are you using test tones generated by your receiver or via a different source (e.g., CD)?

Doug
 

RuslanM

Agent
Joined
Nov 4, 2002
Messages
34
Thanks for the replies. I was using Styke's basszone cd and the volume is -15 below reference (calibrated to 75db).
The image shows everytime I reload this page - strange.
 

RuslanM

Agent
Joined
Nov 4, 2002
Messages
34
For those of you that can't see the image here's the table:

206168.5
226975.5
257782.0
2881.585.5
31.58790.0
3682.585.0
4076.579.0
457678.0
5071.573.0
567778.5
636162.5
717071.5
806465.5
896566.5
1006870.0
1116768.0
1255757.5
 

Edward J M

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Sep 22, 2002
Messages
2,031
Ruslan:

How are you powering this subwoofer? Is this a passive 25-31CS, or a powered 25-31PCi? How is the subwoofer connected to the Denon?

Regards,

Ed
 

RuslanM

Agent
Joined
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Messages
34
Ed,

The subwoofer is a powered 25-31PC+. It is connected to the Denon's subwoofer preout.

P.S. Strangely the link doesn't work, but if you copy and paste the link in your browser it works. :confused:

Ruslan.
 

Edward J M

Senior HTF Member
Joined
Sep 22, 2002
Messages
2,031
Ruslan:

There is something very odd going on if you are using a powered sub and your Denon keeps shutting off while attempting to play bass test tones.

The only reason your Denon should go into self protect mode is if its amplifier is being asked to deliver a high current signal beyond its capabilities and there is a risk of overheating or damage.

When you say "all speakers are off", what does that exactly mean? Are they disconnected or electronically set to off/no in the bass management section of the receiver?

Also,I'm not familiar with Styke's "basszone" CD. Is is Dolby Digital, or stereo?

What are the bass managment settings for your Denon for Dolby Digital/DTS, and for stereo playback? What size are all your speakers set to, and what is the sub setting? If your speakers are set to large and your sub is set to LFE+Mains, perhaps you are sendind the mains a full range signal and that is why your Denon keeps shutting off.

I think you should figure out why your Denon is shutting off before you proceed with fine tuning your subwoofer's FR. That doesn't sound healthy.

Regards,

Ed
 

RuslanM

Agent
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Nov 4, 2002
Messages
34
Ed,

The speakers are disconnected. I don't know if it's possible to switch them off electronically. However, all speakers are set to small with the subwoofer on and crossover set at 100Hz. I'm not sending LFE to mains.

I'm not sure whether the tones are stereo or Dolby, but I've also tried the tones that are pointed in BFD guide. I've tried running the tones in both stereo and DD with the same results. However there's a difference in settings between two in the receiver - in case of DD the sub out is set to -5.

I'm still puzzled why it keeps shutting off. Something must be wrong here.

Thanks,
Ruslan.
 

Randall Duncan

Stunt Coordinator
Joined
Apr 24, 2003
Messages
105
P.S. Strangely the link doesn't work, but if you copy and paste the link in your browser it works.
The image won't show on HTF's site because it's hosted by
GeoCities, and GeoCities doesn't allow hotlinking. Hotlinking
is when you put an image on a page that is not hosted by the
same server as the image.

Why the link won't work... Well... That's kinda' strange. :confused:

BTW, I really have no input for the problem you're having
with your receiver, because it sounds too strange and almost
not possible.
 

RuslanM

Agent
Joined
Nov 4, 2002
Messages
34
I've rechecked all settings yesterday - everything seems in order. Also all connections are clean. I'm running out of ideas. Does anyone has any opinions? Can anyone comment on the graph?

Ruslan.
 

RuslanM

Agent
Joined
Nov 4, 2002
Messages
34
OK. Finally the problem is solved. I had a faulty cable.

Now, I can start working on the graph. Does anyone have any suggestions? How should I approach a peak at 32Hz? If I try to create a house curve (which I kind of have) how much should I lower the peak and how do I and should I flatten the response in lower FRs?

This is my first attempt to equalize a subwoofer and I apologize if the questions are dumb and have been asked before.

Thanks,
Ruslan.
 

Edward J M

Senior HTF Member
Joined
Sep 22, 2002
Messages
2,031
That is most excellent, Ruslan. The Denon is thanking you as I type this. :emoji_thumbsup:

Your in-room curve is typical of the 25-31 series - a healthy bump at 30 and back to baseline at 25. My 20-39 shows a very similar curve, except mine occurs 5 Hz lower.

First try reversing your phase and see if it brings up that dip at 80 Hz.

Then experiment with placement and pull it away from a tight corner (if that is where it is) and see if the room gain 30 Hz peak drops a bit in relation to the midrange.

After that, Wayne can take over with his house curve and BFD magic. :b

Ed
 

RuslanM

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Nov 4, 2002
Messages
34
Ed,

Thanks for the suggestions. I'll play with it this weekend.
Hopefully Wayne will join the discussion.

Ruslan.
 

Wayne A. Pflughaupt

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Then experiment with placement and pull it away from a tight corner...
I’ll have to respectfully disagree with Edward on this one: No need to experiment with placement when you’re using an equalizer. Keep it in the corner for maximum output; the EQ will adjust the response irregularities just as good (or better) from the corner as another location.

You’ve got a pretty easy situation here, only a few irregularities and nicely symmetrical. Works well with an equalizer, since the filters boost or cut symmetrically. A 1/3-octave filter centered at 30Hz will go a long way to reducing that peak. Cut it about 15dB and take new readings. With the new readings pay attention to the 22Hz and 50Hz numbers. They should stay the same as the original readings. If not, tighten up the filter a little (i.e., less than 1/3-octave).

The 55Hz peak and the 63Hz dip are pretty narrow; they might well be inaudible. If you want to take a crack at them, try 1/12-octave filters, or perhaps a little narrower.

After you flatten response you will want to dial in the proper house curve. You can find out how to do this following the directions at this link. Further info can be found at this link.

This post by brucek tells how to adjust a BFD for a house curve, if you’re starting from flat response.

If you aren’t clear on what a house curve is or why you need one, you might want to first read the information at this link.

Regards,
Wayne A. Pflughaupt
 

RuslanM

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Nov 4, 2002
Messages
34
Thanks Wayne. I was hopping you'll join this thread. I was reading a lot of posts from you and Brucek on this forum and learned a great deal about equalizing and house curve. I just don't have any practical experience with it.

There's one thing I'm still not sure about - do I need to flatten the response first and dial a house curve on the flat response or should I try to go for house curve from initial graph? Which approach is right and easier to do?

Thanks again for you reply,
Ruslan.
 

Wayne A. Pflughaupt

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Which approach is easiest depends on the initial readings. Since all rooms are different, some response curves naturally lend themselves to first being flattened. Others, the necessary equalization, once applied, ends up with something resembling a house curve.

In your situation you will need a combination of both. The 1/3-octave filter at 30Hz, properly tweaked, will give you a large, flat area more than an octave wide. The other two filters I recommended will further flatten response, but at a lower dB level (which will “play” into the house curve). Once you have smoothed your response (eliminated the “mountains and valleys”) you will end up having to overlay additional filters to achieve your curve.

Regards,
Wayne A. Pflughaupt
 

RuslanM

Agent
Joined
Nov 4, 2002
Messages
34
Hi Wayne,

I finally got my BFD connected this weekend and put in the first filter, sat down and started taking measurements. I immediately noticed that something was wrong. The frequencies were going up and down all over the graph- not what was expected. I rechecked if all but one filters were off in BFD and put it in the "bypass" mode to recreate the initial graph.

I got pretty weird results. In some places the graph was similar to the one I published here and in others it was completely different. For example instead of peak at 31.5 I now have a 5db dip. Unfortunately, I'm on another PC at work and can not post the graph, but I will do it tonight. I even rechecked the frequencies again to make sure that I didn't make a mistake.

Now, I'm kind of confused. Either I'm doing something wrong now or I didn't take the measurements correctly the first time. As far as I understand the BFD should not affect the response in the "bypass" mode, right?

Anyway, I'll try to post the graph later today and hope to talk to you soon.

Thanks again for your patience and help,
Ruslan.
 

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