Might be in over my head..........

[Vidmaven]

OK so I just got my dual AV123 MFW-15 subs to replace my Velodyne F-1500R. I decided it was time to get dedicated and EQ my subs to get some nice, tight clean LFE in my HT. A couple of months ago I purchased four 6" thick 5' high bass traps and put them in each corner to go with the acoustic treatments I already had. This improved the lows and reduced the boominess. But now I have the MFWs I felt the urge to take it a step further. Yesterday I received my BFD1124P and happily went to Radio Shack to pick up four 1/4" to RCA converters. I hooked up the Behringer and ran the split signal from my Yamaha's subwoofer out to the BFD's inputs and then ran the BFD's outputs to the subs. As soon as I turned everything on I immediately noticed a hum in the subs and all of my speakers. I have read that the Behringer can introduce hum into your system but I'm not sure what to do about it. I didn't even get as far as graphing the system (yes I'm doing it the manual way as my laptop is too old to handle REW ) because I was bothered by the hum. Prior to hooking up the BFD the only hum I had was in one of the MFWs. Any advice would be appreciated. I am hoping to get the hum addressed so I can start the laborious process (from what I've read) of EQ'ing my system. I'm sure once I start that I will have a few more questions for the local experts here, hence the starting of this thread.

[tonyvdb]

First of all welcome to the Shack,

Do you have your BFD hooked up to the same power as the rest of the system? if so then sometimes building a cheater plug that lifts the ground on the BFD will remove the hum.

[Vidmaven]

tonyvdb wrote:

First of all welcome to the Shack,

Do you have your BFD hooked up to the same power as the rest of the system? if so then sometimes building a cheater plug that lifts the ground on the BFD will remove the hum.

Thanks for the welcome.

Yes I do have the BFD hooked up to the same power. Unfortunately the nearest outlet that is not on the same circuit as the rest of the system is 20 feet away. I thought about the cheater plug thing but I am hesitant as I always read that it is dangerous to do. In fact I was considering putting a cheater plug on the BFD and hooking it up to the switched outlet on my Yamaha so it would turn on with the rest of the system (amps on delay of course), right now I have to turn it on manually as my powercenter has no open outlets. I read that you can leave it on all the time if you want but I figure why waste the electricity and wear and tear on the unit if I don't need to.

[Wayne A. Pflughaupt]

You might want to review the BFD hum sticky thread. Lots of good info on dealing with the hum there.

Regards,
Wayne

[Vidmaven]

Wayne A. Pflughaupt wrote:

You might want to review the BFD hum sticky thread. Lots of good info on dealing with the hum there.

Regards,
Wayne

Thanks Wayne. I read that thread and I'm going to try to troublehoot the hum tonight if I get a chance. I really want to get it cleared up so I can get on with EQ'ing the system.

[Vidmaven]

So I ran some measurements last night and plotted a graph (see attached). Looks like I have a serious null at 45Hz and a few peaks at 20, 25-31.5, 56 and 80, if I'm reading it right. I'm not sure why the dB level drops so much after the null, maybe someone can give me an idea what's going on there. I ran the test from my listening position with the xover set at 200Hz. I'm trying to get my head around what to do with the BFD to treat the problem areas so I'm reading all of the info on this site over and over.

[brucek]

The first thing you need to do is set your crossover to the value you would normally use and then take another measure. It will give you a better picture of what you will need to do with the BFD.

You should also lower the entire measurement level and bring it down to a more reasonable ~75dB.

You'll have to deal with that null by either repositioning the sub or the listening position. The BFD can't be used for that.

Hopefully, you're not too tired of listening to those tones, and you can post another plot with the suggestions.

brucek

[Vidmaven]

brucek wrote:

The first thing you need to do is set your crossover to the value you would normally use and then take another measure. It will give you a better picture of what you will need to do with the BFD.

You should also lower the entire measurement level and bring it down to a more reasonable ~75dB.

You'll have to deal with that null by either repositioning the sub or the listening position. The BFD can't be used for that.

Hopefully, you're not too tired of listening to those tones, and you can post another plot with the suggestions.

brucek

Thanks Bruce. I usually run the crossover at 80Hz so I will set it there.

As far as the measurement level I was following the BFD guide instructions and using the 16Hz tone to set the level at +3dB to +5dB at 70 on the RS meter prior to conducting the FR measurements. Is there another way I should be setting the level? I can't use the reference level on my Yamaha (0dB) as that is extremely loud.

I am going to try and move the subs slightly to see if I can reduce that null somewhat. I am limited in my positioning choices however unless I move furniture around to accommodate.

My son is helping me plot the FR so it's not too bad. Now if you ask him he might tell you he's tired of listening to them.

[brucek]

As far as the measurement level I was following the BFD guide instructions and using the 16Hz tone to set the level at +3dB to +5dB at 70 on the RS meter prior to conducting the FR measurements. Is there another way I should be setting the level?

Yeah, you have to get a bit creative about that setting. First, you have to correct the level on the needle in your head, so if it reads 75dB on the dial, it will become ~10dB more by adding the rough correction factor of the meter. In addition, if you have a peak at that frequency, again it will be a bit high. Simply take a reading around 16Hz and enter it into the Excel graph and see where it sits. If its around 75-80dB, you're good.

Now if you ask him he might tell you he's tired of listening to them

No doubt. I'll tell you who really loves listening to those tones - woman. They can't get enough of that......... yikes.
My suggestion (strong one too) is to find a way to set up a PC and use REW. One little whoop and the test is done and the graph drawn. It's particularly satisfying after spending days with the manual system.

brucek

[Vidmaven]

OK so I set the xover at 80Hz and put the meter in my exact listening position. Still think the initial measurement level is too high. But the graph looks better.....I think. I'm going to reduce the initial volume by 10dB and run the test tones again.

[Vidmaven]

I think I got it this time.

[Wayne A. Pflughaupt]

Looks nice. A 1/3-octave filter @ ~31.5 Hz and cut a few dB should smooth it right out. If it takes more than about - 6 dB you might have to make the filter a bit narrower.

Regards,
Wayne

[Vidmaven]

brucek wrote:

My suggestion (strong one too) is to find a way to set up a PC and use REW. One little whoop and the test is done and the graph drawn. It's particularly satisfying after spending days with the manual system.

brucek

I wish I had that option but unfortunately I don't have access to a laptop with a duplex soundcard and moving a PC into my HT is more work than doing this manually. That plus I guess I'm a glutton for punishment. I'm still holding out hope that I may be able to get my hands on a laptop so I can do this the right way but for now this is as good as it gets.

[brucek]

I think I got it this time.

Yeah, that's good.

Normally we extend the horizontal out to ~160Hz on the Excel graph.

You can see the target for an 80Hz crossover (in a perfect world) that I show below (using the same axis as you did).

So you have a small peak at 31Hz (not worth bothering with) and still a bit of a dip at ~50Hz. You might find that when you add the mains that the dip fills in somewhat depending on the phase of the sub. Either way, your response is still quite good and extends very low.

Perfect 80Hz crossover





brucek

[Vidmaven]

brucek wrote:

Yeah, that's good.

Normally we extend the horizontal out to ~160Hz on the Excel graph.

You can see the target for an 80Hz crossover (in a perfect world) that I show below (using the same axis as you did).

So you have a small peak at 31Hz (not worth bothering with) and still a bit of a dip at ~50Hz. You might find that when you add the mains that the dip fills in somewhat depending on the phase of the sub. Either way, your response is still quite good and extends very low.

Perfect 80Hz crossover
Attachment 8139


Attachment 8140

brucek

Thanks Bruce.
So I don't need to use the BFD at all?
How about adding in a house curve? Is it necessary?

[brucek]

So I don't need to use the BFD at all?

Well, they are kinda fun, and they are a miracle for people that have large resonant peaks, but, you are digitizing your signal, and you have to mess with, and be concerned about, the dynamic range of the signal coming to and leaving that digitizer. Depends on whether you want to do that or not.

You could, for example, raise the entire sub signal until the ~50Hz area was at a level of the red line in my diagram, and then cut down everything at 31Hz until the response tracked a perfect target.

Again, you would get a better, and more accurate picture with REW.

I might do another test with the mains added in (and still do the measure the same as with the sub only). It would give you another perspective of the situation.

As far as a house curve is concerned, again you need to add the mains and get a feel for the perceived (not measured) level of the bass. If you play a signal at 100Hz and at 30Hz, do they sound about the same. If not you need to raise the bass somewhat. If the measured curve looks perfect, then it would demand that you shelve up the bottom end with a house curve. To do that without REW would be a challenge.

brucek

[Vidmaven]

I think for now I'll consider myself lucky that I have a pretty even FR curve and bypass the BFD. If I manage to get my hands on a laptop I'll run REW and see what it can do.

Should I consider pulling the BFD out of the system since it's not being used? Or does it not degrade the signal enough when passed through to make a difference?

I will conduct a test of the full system this evening to see what it looks like.

Thanks for the help and advice.

[brucek]

Or does it not degrade the signal enough when passed through to make a difference?

The BFD in bypass still digitizes the signal. It's not a true bypass. You would have to remove it for a true bypass.

brucek