# Can't get the BFD input levels up high enough



## monomer (Dec 3, 2006)

I downloaded REW last week and used it to measure FR of my system (speaker by speaker and over-all) and then using my receiver's eq to 'flatten' the FR... I was very pleased with the results... I got my system sounding fantastic. I was so 'pumped' after this little exercise that I decided to try and boost a shallow but wide dip (~4dB) from 47Hz to 74Hz using a DSP 1124p. So I bought one off of eBay ($65 total) and hooked it up to my Onkyo 603 via the sub-pre-amp out. When I tried to set my input levels, I saw nothing. Eventually I found that if I maxed out my sub-level in the Onkyo to +12dB and dropped all my other speakers by -12dBs AND pushed my volume to +75dB to compensate (my normal listening is usually between 45dB and 60dB) I could just get barely get the fifth green bar on the BFD to flicker (-10dB bar) while playing single sine waves from 30Hz to 70Hz. This is ridiculous and canNOT possibly be right! can it?
I found another thread started by someone with a Denon that had the same problem... unfortunately the responses he got didn't really address that aspect of his problems. However to me this is significant. It doesn't make sense to me to turn all my speaker levels to their minimum levels and meanwhile have the sub dialed up to the maximum and then have to crank my volume almost to the max to try and make up for the difference. This really sucks! :hissyfit: Has anyone else had this problem? What am I doing wrong? And, yes, my operating level button is set to -10dBV.


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## JohnM (Apr 11, 2006)

When you play your receiver's sub level calibration signal what sort of levels do you see on the BFD meter?

What signal level was set in the REW sig gen when you were playing the sine waves?


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## Wayne A. Pflughaupt (Apr 13, 2006)

Are you using a splitter between the receiver and BFD? If so that will cut the signal level. Split after the BFD if you must split.

If that doesn’t get it, you’ll need some kind of signal booster.

Regards,
Wayne


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## monomer (Dec 3, 2006)

JohnM said:


> When you play your receiver's sub level calibration signal what sort of levels do you see on the BFD meter?
> 
> What signal level was set in the REW sig gen when you were playing the sine waves?


John, Thanks... I'm glad someone has finally responded...

Please bear with me, I'm really new to all this so I'm struggling just to understand what you're asking... 
It did not occur to me to try the receiver's sub cal signal (I'll give it a try tomorrow), however what I was using was a sig gen program output from my computer (my HTPC). I figured it was the natural choice since all my music, HDTV, movies, etc. are sourced from my sound card (HTPC). When I last used REW to set-up my speakers everything was targeted to 75 dBs (sub too). But I didn't have REW running last night 'cause I was just trying to get the input level adjusted properly. However, first thing tomorrow morning, I will again try to set the BFD input level and this time I will run REW and I will also see what my receiver's sub cal does.

Wayne... nope, no splitters at all. What would you suggest by way of a signal booster? Any info is greatly appreciated. Thanks.


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## brucek (Apr 11, 2006)

> What am I doing wrong?


I looked up the specs of your receiver (Onkyo 603) and it claims 1.0 volt output from the pre-amp.
This is a bit low, but not really out of line and should still be OK to drive the BFD (but not likely full scale). The max input level to the BFD before clipping is +2dBV (about 1.25 volts). The -10dBV LED should come on at ~315 mvolts.

When you push and hold the IN/OUT button on the BFD (so it's flashing) it switches its LED's to monitor the input level. 
If you play a sub cal pink noise signal at -12db with REW (with both its Wave and Output at 1.000) and have the volume on your receiver at a level where it might be at its highest when playing a movie, what does the BFD show in its LEDs in bypass when the receivers subwoofer output trim is at 0db?

With my inexpensive preamp on my second system (that also has a max output of 1.0 volt) shows about -10dB on the LEDs with that test. It is what it is. I certainly won't put any line amp on that signal because it would just add noise.
My expensive processor on my main system has a max output of 8 volts, and it obviously can peg the LED's on the BFD if I choose.

Output levels of preamps aren't a standard. You can amplify the level, but you will also amplify the noise. You may not come out ahead, it's a **** shoot.

Do you feel the sound is degraded or not as good when you don't have the BFD in the circuit? If it sounds fine, then have the receiver output sub trim as high as you think is reasonable and carry on using the BFD. If you feel the level still needs a boost, then you can try a line amp as Wayne suggested.

brucek


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## maxcooper (Aug 21, 2006)

Was the sub working okay before the BFD was added? Or, if you remove the BFD, does the sub play at a normal level now? Actually, before you make any changes, see below...



brucek said:


> The -10dBV LED should come on at ~315mvolts.


Ah, that reminds me of something that may be causing the issue. On the back of the BFD, there are little push-button switches to choose between -10 and +4 input sensitivity (or something like that). I suspect yours are set to -10, when they should be set to +4.

-Max


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## brucek (Apr 11, 2006)

> I suspect yours are set to -10, when they should be set to +4.


You may be confused somewhat on the use of those switches.

They adjust for two operating ranges.

The -10dBV setting is for standard consumer equipment. It sets a range with a max input of +2dBV ~=+1.25vRMS.

The +4dBu setting is for pro equipment. It sets a max input of +16dBu ~=+4.9vRMS

If the input appears low you definitely want to use the standard -10dBV setting.

brucek


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## Wayne A. Pflughaupt (Apr 13, 2006)

monomer,

Did you try what brucek said?


> When you push and hold the IN/OUT button on the BFD (so it's flashing) it switches its LED's to monitor the input level.
> If you play a sub cal pink noise signal at -12db with REW (with both its Wave and Output at 1.000) and have the volume on your receiver at a level where it might be at its highest when playing a movie, what does the BFD show in its LEDs in bypass when the receivers subwoofer output trim is at 0db?


The meter normally reads the BFD’s _output_ level, which includes any filters that have been applied. Pushing and holding the IN/OUT button bypasses the filters and will allow you to see the true input level from the receiver.

You didn’t indicate if you had done any EQing with the BFD yet. It occurs to me that since your BFD is used, it probably already has a lot of filters programmed in. If it was used by the previous owner for feedback control, then it probably has a lot of cutting filters programmed in. Naturally, a lot of cutting filters will reduce the BFD’s output level, and that will be what shows up on the meter if you don’t have it in bypass mode.

If you find a huge discrepancy between the readings with the EQ in bypass mode vs. engaged, then you’ll probably want to reset the equalizer and erase all programmed filters. The manual tells you how to do this.

Regards,
Wayne


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## maxcooper (Aug 21, 2006)

brucek said:


> You may be confused somewhat on the use of those switches.
> 
> They adjust for two operating ranges.
> 
> ...


Oops! Sorry for the bad advice.

I have mine on +4 right now and it seems to work properly, but I suppose I should switch it to -10 and recalibrate.

-Max


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## monomer (Dec 3, 2006)

A really BIG THANKS to all those who've replied... I really appreciated it!

Brucek... you gave the best answer from my perspective and for my knowledge base... it made a lot of sense and I decided to purchase a CleanBox because it has a gain with a S/N better than 90 dB (I figured good enough given the frequencies I'm dealing with) and I figure using balanced signals would help with the hum problem caused by adding the BFD in. So 37 bucks and 4 days later I installed the CleanBox this way... RCA from receiver's sub's pre-out into RCA channel 1 of the CleanBox > XLR out CleanBox (channel 1) into BFD's XLR in > XLR out of BFD into XLR CleanBox (channel 2) > RCA out of CleanBox (channel 2) to the powered-sub. The gain from the CleanBox did the trick... puts me in the perfect range with adjustment in either direction. However, I did discover that the sig gen I was using was not providing as strong a signal as what actual DVDs and CDs could sometimes produce... still I think the CleanBox was necessary in my situation.

To answer the other questions posed... the receiver's pink noise was no better in output levels produced than the sig gen I used... yes, I was in by-pass mode when observing the meter levels... and yes, I had turned all 12 filters from PA to OFF.

As far as the hum is concerned... inserting the CleanBox did quiet it down a lot but still not quite as totally silent as it is without the BFD in the system. And I did discover a rather unusual response to an option in my Onkyo. It has a feature called DOUBLE BASS... when this option is selected it sends low bass signals (low pass) to both front speakers as well as the sub... of course, the signal sent to the fronts is amplified. With this feature turned ON mid-range bass is noticeably louder and somehow does sound smoother. Well, the 'short story' is with Double-Bass ON there is a sharp roll-off to my sub below about 37Hz... I found that if I turn Double-Bass OFF, I get a relatively smooth and level response out of my sub right down to just below 23Hz. Very odd behavior.

Anyway, I think I can handle everything from here... so again, to all those who responded to this thread... a really BIG THANKS!!!!!


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