BFD Questions

**gacole2000** · **05-30-06, 11:00 PM**

Hello. I have a BFD 1124P on the way and have been reading through the guide. Excuse me if I missed these and for asking dumb questions, but I find myself very confused. I added a bass trap and acoustic treatments recently and I really want to get my system "dialed in" with my 12.3 coming soon. Thanks for any help!

Questions:

1. I realize that a calibrated mic will be better, but can I continue to use my trusty RS SPL w/ corrections or must I buy even more equipment to start using the BDF?

2. Do I connect it using my LFE output? Amp LFE-BDF-Sub

3. Must I have a laptop (no computer in basement) w/ a good soundcard and mic to use the REW or can I take my readings and bring them to my desktop for assistance?

Curve attached and thanks for bearing with me!

**Otto** · **05-30-06, 11:17 PM**

Hi there,

I just went through this, so I might be able to help.

Quote:

1. I realize that a calibrated mic will be better, but can I continue to use my trusty RS SPL w/ corrections or must I buy even more equipment to start using the BDF?

They talk about it in the manual, so it seems to be sanctioned. That's how I did my measurements. I agree that a better mic will give better results, but for me this was a good starting point. Not necessary to buy any other stuff.

Quote:

2. Do I connect it using my LFE output? Amp LFE-BDF-Sub

Yeah, that's how I did it. I also considered using my left and right preamp outputs, to maintain stereo, but I ended up using just the sub output of my preamp. One thing that I was never clear on was -- can I process two different sets of filters (i.e., left and right) at the same time?

Quote:

3. Must I have a laptop (no computer in basement) w/ a good soundcard and mic to use the REW or can I take my readings and bring them to my desktop for assistance?

Well, I don't know how important the quality of the sound card will be. The program measures the frequency response of the soundcard, and adjusts for it. I used an old SoundBlaster card that had a MIDI port on it, and it seemed to work fine. Like the mic, I suppose a better sound card could yield better results. Still, the things we're trying to measure aren't terribly detailed.

One thing, though -- I think the manual said NOT to use the soundcard mic input, but rather to use the line-in input. So I think you'll need to use some kind of preamp between the mic and the soundcard line-in input. I used a Fostex digital 8 track recorder as a preamp. I suppose Radio Shack has something you could use as a preamp, if not something dsigned specifically for that. Also, my laptop doesn't have a line-in at all, so I couldn't use that PC. I could be wrong about the don't-use-a-mic-input thing, and I'm sure someone will correct me if I'm wrong.

Good luck with your setup. Like I said, I just did it this weekend, and couldn't be happier, especially for the price.

-- Otto

**gacole2000** · **05-30-06, 11:22 PM**

Thanks Otto! What kind of cable did you run from the RS SPL and did you "Y" you LFE into the BDF or just use L or R inputs? I have an old (P1 75Hz) IBM Thinkpad I may try and give a try.

Regards- Greg

**Sonnie** · **05-30-06, 11:43 PM**

Otto has served you well on #1 and #2... the RS meter is fine when used with the proper correction file available from the Downloads page. You sub pre-out or LFE out is the proper output to use to the BFD.

I'll address #3 a little further. In order to use REW, you will a computer. You don't have to have a laptop, but it nice if you do so that you don't have to lug a desktop computer into the room. Short of having some sort of computer will make it difficult to use REW. If you do have a laptop then you will need an outboard sound card (USB is preferred) since most laptops do not come standard with the proper input and output you need to use REW.

If you don't want to lug your desktop down to your basement then you can use the old manual method of measuring outlined in the BFD Guide. It's painful in comparison to lugging your computer down to your basement though. Having that computer there and being able to see real time sweep measurement responses is priceless.

The attached Excel file you have provided is not a good example for us all here to compare. It's not a standard we use. Try downloading the proper Excel Workbook from the Downloads page and use it if you don't plan on using REW. Make sure you download the proper Excel Workbook for your particular RS SPL Meter model. The corrections values are specific depending on model.

Quote:

Otto wrote:

One thing that I was never clear on was -- can I process two different sets of filters (i.e., left and right) at the same time?

If you mean to generate 24 filters for one sub using both left and right channels... then I believe the answer is yes. I have not tried this but supposedly it can be done. Sub Pre-Out >>> BFD Input 1 >>> BFD Output 1 >>> BFD Input 2 >>> BFD Output 2 >>> Sub Input. Then simply engage both channels, but do not engage them simultaneously as then they will be in couple mode and carry the save filters for each channel.

If you mean having two subs and using the left channel for one sub and the right channel for another sub... yes. Simply feed both inputs on the BFD with your sub pre-out (you may have to use a splitter if you don't have dual sub pre-outs). Feed each output of the BFD to a sub and engage both channels as described above.

Now... if you simply want two sets of filters for the same sub you will use two different presets. The 1124 has 10 presets per channel. For instance, I have a house curve set of filters on preset 4 and a flat response set of filters on preset 5. I can switch between the two. If you only have one sub then setting up different filters in the left channel and right channel would require changing your cables between the two sets of inputs/outputs... not a feasible option.

**Otto** · **05-31-06, 12:27 AM**

Quote:

If you do have a laptop then you will need an outboard sound card (USB is preferred)

Of course, the USB sound card; didn't even think of it. I had this convoluted thing going using an 8-track as a preamp. So, in that case (I have a desktop machine handy and it has a line-in input), but suppose I don't have an 8-track recorder -- what do I use as a preamp between the output of the RS meter and the line-in of the soundcard?

Quote:

If you mean having two subs and using the left channel for one sub and the right channel for another sub... yes. Simply feed both inputs on the BFD with your sub pre-out (you may have to use a splitter if you don't have dual sub pre-outs). Feed each output of the BFD to a sub and engage both channels as described above.

Yeah, I think that's what I was wanting. But I wanted to use preamp L and R outputs to maintain stereo in the subs of my mains. However, using it with the dual sub outs gives me the bass management signal from my processor. I think ultimately that's better, but I may consider EQing my sub separately from my mains (i.e., mains on the Right channel, with one set of filters, and sub on the Left channel, with its own set of filters.

I spent a fair amount of time on this last weekend, though, so I may just use it for a while. After getting accustomed to it, I may like it, or I may tweak it...

I was just never able to engage both channels. I could couple them, but I could never get them to both light up without doing the couple thing.

Thanks,

-- Otto

**Otto** · **05-31-06, 12:38 AM**

Quote:

Thanks Otto! What kind of cable did you run from the RS SPL and did you "Y" you LFE into the BDF or just use L or R inputs?

Hi Greg,

I used a long RCA cable that I made a while ago to go from the RS SPL to my "preamp" (Fostex 8-track). I used an RCA to 1/4" mono plug adapter that went into The Fostex. The Fostex then fed the PC's line-in input, in stereo, using a 1/8" headphone jack. If you use a USB external soundcard, I'm not sure what the inputs are (I would guess 1/8" headphone style and/or RCA). I'm pretty sure you can get whatever cable at RS.

For inputs from my preamp to the BFD I used the dual sub outputs on my preamp into either channel on the BFD. I initially wanted to use L and R, but I'll get the benefits of the preamp's bass management if I use the sub out instead. I think this is the way to go, unless you really want to maintain stereo separation in using stereo subs. I have built in subs in my mains (so I could try to maintain stereo subs), and I can run my M&K sub in stereo, so I thought I'd give it a try, but I bagged it. I now run my mains off of a "Y" on channel 1 on the BFD, and the M&K sub, in mono, straight out of the BFD right channel.

Best luck!

-- Otto

**Sonnie** · **05-31-06, 01:49 AM**

Quote:

Otto wrote:

what do I use as a preamp between the output of the RS meter and the line-in of the soundcard?

All you need is a stereo mini plug y-adapter. The stereo mini plug will plug into the input of your sound card and the other end will have a female left and right (red and white) RCA connector. Connect the RCA output of the RS meter to either the left or right RCA input. You'll select left or right channel in REW and REW will act as your preamp control center.

Quote:

Otto wrote:

but I may consider EQing my sub separately from my mains (i.e., mains on the Right channel, with one set of filters, and sub on the Left channel, with its own set of filters.

If you put your mains on one channel of the BFD then you will have to combine the left and right channel, thus creating a mono signal. Not recommended. Plus the BFD is not recommended for anything other than sub eq'ing anyway... it just ain't got the goods.

Quote:

Otto wrote:

I was just never able to engage both channels. I could couple them, but I could never get them to both light up without doing the couple thing.

You should be able to press the Left Engine button and then press the Right Engine button. Both will be on and individually filtering. You would enter couple mode by pressing and holding both Left and Right engine buttons at the same time.

**gacole2000** · **05-31-06, 07:12 AM**

Thanks guys!

At this point, I will not be using the REW until I can get a better laptop. Therefore, can I plug my RS SPL directly into the BFD using an RCA cable (w/ adapter)? I am hoping to dive right in when the BFD gets here and I need to pick up any small items I may need to make this happen.

**brucek** · **05-31-06, 08:11 AM**

Quote:

Therefore, can I plug my RS SPL directly into the BFD

No, the RS SPL meter is used to take sound level measurements that feed to a computer, so that you can see and adjust your subwoofers frequency response using the BFD as an equalizer.

brucek

**Sonnie** · **05-31-06, 11:15 AM**

Quote:

brucek wrote:

No, the RS SPL meter is used to take sound level measurements that feed to a computer, so that you can see and adjust your subwoofers frequency response using the BFD as an equalizer.

OR... as stated previously, you can use it via the old fashioned way and take manual measurements, in which case you wouldn't connect the RS SPL meter to anything.

Ahh... there's the diagram that you have been hiding from me.

**Otto** · **05-31-06, 11:33 AM**

Greg,

If you have a desktop machine that would suffice, I'd suggest going so far as to lug it into the room in which your system is located. I didn't try the manual method of measuring and tweaking, but I cannot imagine that it would be as accurate and efficient as the REW. Really, that thing is just measure, tweak a bit, click and save! I'm just so impressed with its capability.

-- Otto

**Sonnie** · **05-31-06, 01:28 PM**

Coming from someone who used the manual method for years.... Otto is absolutely 100% correct!

Do yourself a favor... lug the computer downstairs.

**gacole2000** · **05-31-06, 10:59 PM**

Thanks guys. I forgot I still have my old computer out in the garage (98 SE will work I hope). I'm going to get it set up for downstairs! The old 21" CRT monitor is a beast... So I only need a few cables/adapters and I'm good to go right?

**gacole2000** · **06-02-06, 12:01 AM**

Please offer feedback on my curve w/ mains & SVS. The BFD will be here tomorrow, I'm hoping it will take care of these issues. I tried to take the reading w/ my sub only and to get to 80 db at 100Hz I had to turn it up to an uncomfortable level. So I took my readings with my mains/sub. Is this common?

**Sonnie** · **06-02-06, 01:05 AM**

That doesn't look so bad at all. The BFD should be able to handle it fine. BUT, REW will most likely reveal more problem areas to deal with.

Measure your sub only because we can't do anything with your mains via the BFD. Let's see exactly what the BFD will deal with. Don't worry about getting to 80db at 100hz... that's probably above your x-over point anyway, which should most likely be 80hz or less. Just use the same level you just used and measure... where ever 100hz comes in.. it comes in... this is what you want to know.

**Otto** · **06-02-06, 01:10 AM**

Hi Greg,

Is your sub crossed over at a frequency lower than 100 Hz? That would lend to decreased sub output at 100Hz. Your curve seems to take a dive at about 80 Hz, but I doubt that's all due to the crossover (if it's at 80 Hz). That appears too steep to be a crossover.

What's it look like without the mains engaged?

It looks like, from the graph you have here, that your mains are going to carry on their signal at about 80 dB (roughly). You should be able to crank up your sub enough to get about 80 dB at the valleys, and then apply attenuation using the BFD. That's what I did, and I think it worked out great.

Good luck with your BFD this weekend; I know I spent too much time with mine last weekend.

-- Otto

**brucek** · **06-02-06, 07:00 AM**

Quote:

get to 80 db at 100Hz

80dB at about 50Hz would be fine. I admit with single tones it gets real loud and the place shakes quite a bit. With that sub you were producing 98db at 18hz.....that's ground shaking.

You'd find with REW that the frequency sweep used for measuring is quite short and painless and a lot quicker than the single tones. You should use it.

The BFD will easily flatten that response, which is already pretty good.

brucek

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