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B&C 8BG51

CH Design

CH Design

Supporting Member
Apr 25, 2007
2,975
2,443
Ottawa, ON
#1
I just found this the other day. I was wondering if a pair of these in a 2500 cubic inch box tuned around 45 Hz would be suitable for use as woofers in a 3-way cabinet design for a 5-string. Would they even require a mid range driver? I don't have the experience to tell from the graphs provided to tell how far up these will remain relatively flat and smooth.

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#2
... from the B&C website
SPL.gif

FrequencyResponse.gif
 
#5
fretless_guy said:
I just found this the other day. I was wondering if a pair of these in a 2500 cubic inch box tuned around 45 Hz would be suitable for use as woofers in a 3-way cabinet design for a 5-string. Would they even require a mid range driver? I don't have the experience to tell from the graphs provided to tell how far up these will remain relatively flat and smooth.

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Click to expand...
You'd need four of them to equal the displacement of one 3015, six to equal one 3015LF. That takes them totally out of the running where price/performance is concerned.
 
#6
billfitzmaurice said:
You'd need four of them to equal the displacement of one 3015, six to equal one 3015LF. That takes them totally out of the running where price/performance is concerned.
Click to expand...

True. I wasn't necessarily thinking of price. I am more concerned with keeping the cabinet small and still having good performance than with making it "low" cost. Obviously it's not going to keep up with a 3010LF in terms of volume, but it would be nice if it could have a similar low end output relative to the overall SPL.

If I use the same FR plot and throw my model for a 3015LF in there and lower the input signal ( ~ 180 W) so that everything has the same SPL at 200 Hz, they seem to be comparable.
BC8BG51SPL_1.gif
 
#9
billfitzmaurice said:
Try it again, this time viewing the maximum SPL chart.
Click to expand...

Either I'm missing the point you are trying to make, or you are missing mine. I'm not sure.

I'm not trying to say that a pair of 8BG51's are equal to a 3015LF on a maximum SPL or similarly powered level. I'm looking at the delta between max SPL at 200 Hz and the values at 30 Hz, 40 Hz, 50 Hz, and so on. I'm assuming that if you can get two FR curves to have a similar shape (regardless of what their maximum SPL's are), if compared at similar volumes (SPL), they should sound roughly similar (as far as FR goes). If you drove a pair of 8BG51's with 500W @ 4 ohms, would it not have a similar FR to a 3015LF being driven with 180W @ 8 ohms? Maybe it's my assumption that's bad.

I think you are thinking more in terms of it wouldn't make sense as a product to gig with. In that sense you're probably right. What I have in mind is people who wouldn't mind having a REALLY small cabinet at home for practice or that they can use for low volume gigs that sacrifices efficiency for low end FR.
 
#11
I have seen a few posts where people have thought that Don used to use Dayton Series II ST210-8 speakers as his "long throw" 8's. Here is what they look like in WINISD in a box that is roughly the size as some of his 2x8 cabs compared to the B&C 8BG51's.
1.gif

... and the cone excursions
2.gif

Their doesn't seem to be a big difference between the two.
B&C 8BG51's Pro's:
  1. similar FR but in a 27% smaller cabinet
  2. similar cone excursion at 1/3 max. power
  3. each 8BG51 is 1/2 the weight (4 lbs vs. 8 lbs) of the ST210-8

The big difference that I can see is the efficiency. While the ST210-8 can only take 360W (for a pair), compared to 500W for a pair of 8BG51's, they both have similar max SPL. In other words, it takes 28% more power to get the same volume out of the B&C speakers. The other down side is that the B&C's are a lot more expensive ( $200-300 compared to $130 for a pair of Dayton 8's).
 
#12
It looks like a very nice driver, but very pricey. It's nice that it can get similar response in a tiny box. Not sure there's much more to say about it. It's rare to see an 8" woofer with such a low Fs and low Vas, definitely a specialized beast. It's pretty amazing how flat it is to 1khz also. You'd probably want to cross it over pretty low but one alphalite should keep up with two of them.

Sounds like, if its specs are accurate, it does something unique though. Staying that smooth down low in such a tiny box is very hard to do.

It might be worth ordering a reference sample and measuring some of its parameters, or asking Duke LeJeune if he's done so. I know with one of the Ciare 10s that look so nice on paper, Duke had measured a few and found the Fs to be much higher than listed.
 
#13
oh, fyi: That driver would absolutely need a midrange driver. There's a huge dip in the mids and a huge burp, for smooth response you'd definitely want a mid. I bet it sounds atrocious up top.

If you wanted smooth response, the Peavey ECX crossover's 500hz point would be ideal. Alphalite 6 and a horn above that.
 
#14
rpsands said:
If you wanted smooth response, the Peavey ECX crossover's 500hz point would be ideal. Alphalite 6 and a horn above that.
Click to expand...

500Hz? I thought it looked good up to around 800Hz.
I was actually thinking of a Beyma 5G40Nd for the mids. It's nice and small. It also goes up to 17kHz so I could save a little internal volume by not needing a horn. I'm just not sure if one could keep up to two 8BG51 woofers.
 
#15
The 8bg51 has a peak at 1khz of about 4db, according to the chart. Chances are good that would make a crossover design challenging (e.g. you might be left with a peak there). If you wanted to use a generic crossover, I would go lower. If you want to make your own, 800hz might be fine, but I'd aim for a 3rd order based on what I know anyway. Crossover design is not my strong suit so I'm just parroting here.

The 5g40nd is probably not enough to keep up with those woofers if they are pushed hard. 100w thermal handling and no padding seems like a bad idea. Especially if you were to use a generic 500hz crossover. It could be enough if you like polite mids I guess.

The nice thing about the 5g40 is that it appears to go to almost 10khz off-axis which is more than sufficient. If you're ok with off-axis falling off above 5khz, the Faital m5n12-80 might work. It's got enough sensitivity you could pad it back a few db and still keep up.

I'd use the Peavey ECX 3-way crossover, the fEarful Dayton waveguide + horn, and an Alpha 6, myself, however.
 
#16
What about four Faital 3FE20 speakers instead of a mid + a waveguide and a horn? They have a pretty low power rating (20W), but four of them should be able to keep up with two woofers, right? They are very flat through the mids and go up to 20kHz and are good off axis to around 3kHz. They aren't that expensive either. It would probably cost less to use four of those and one crossover as opposed to a mid, a waveguide, a horn, and another crossover. The small diameter would free up a lot of room on the baffle too. That would help me keep the box tall and skinny.
 
#17
Seems likely to be very expensive, but but four of them should be ~97db @ 8 ohms.

The issue I see is that you will want to line array them, and by the time you line array them instead of partially insetting a single 6" driver in between the curve of the two 8's you'll be looking at a similar cabinet width. You could also just put the six straight on top of the two 8's and make a 10" wide cabinet that's like 24" tall or so.

You don't need a waveguide + horn btw to keep up with two of those woofers. A nice soft dome tweeter or something would probably sound great and be enough.
 
#19
fretless_guy said:
US Speaker has 3FE20's for $30 a piece.
Click to expand...

That's not too shabby. Go for it -- 3" drivers still have an off-axis limitation of 10khz or so if not a little lower -- realistically starting to fall off by 5khz and gone by 10khz. So you might want to stick a done tweeter on the top there crossed over at 5-6khz. But might be worthwhile to try it without first :)
 
#20
So I've been thinking more about a 1x8 lately. I thought it might be better to start with a 1x8 just to make sure it actually sounds like I want before doubling any investment in parts. The speakers are one B&C 8B51 (or a Faital Pro 8PR200), two Faital Pro 3FE20 (800 Hz - 5 kHz), and one Morel MDT-40 (5kHz - 20 kHz). I picked the mid and tweeter based on size, off axis response and a nice flat FR in the ranges they are going to be used. I'm pretty sure that the mids and tweeter will keep up with the woofer, but are there any rules of thumb to use to make sure? Other than being expensive for this type of cabinet, are their any reasons why this combination may not be a good choice?
Here is what it would look like.
1x82x3Tweeter.gif

I know that the placement of the mids wouldn't be ideal if the cab were stood up on it's end (the mids would be horizontal, not vertical). Would the ill effect be less noticeable because they are small drivers (i.e. the centers are closer together)?
 

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