Bl important?

pkgum

Member
2001-10-27 4:56 pm
sydney
I found the Bl rating of the Blueprint 1503 to be relatively low at 20 compared to other similar drivers. Does this matter in a high excursion driver like a Blueprint?
Why is the Bl of the Blueprint 1503 so low anyway?

For those who say that a BP can shake the whole house up, I'm not disagreeing with u, it's just the question of whether it can do that with smooth power and finesse.

In emailing Pat of Blueprintdrivers he replied :

" Okay. So I will concede that Bl is important. But Bl is a product of "B" (the motors strength) and "l" (the length of the wire in the gap). But If I measure a dual 8 ohm coil in series (16 ohms) then the Bl will be double of what the 4 ohm (both coils in parallel, which is internally what the 03 coil is). So should I measure it this way to have a significantly higher Bl to make the numbers look "better". This will not change the actual drivers specs or how it works at all, just the Bl product (due to the change in length of wire not the actual motors strength). The motor has plenty of strength, even with the large gaps that we run. It would be possible to tighten up the tolerences some, but we like the specs where they are and do not want them to change (which would happen with a tighter gap). "


What if the other companies of the similar drivers I've compared with the Blueprint, didn't measure a dual 8ohm coil in series, but still got a much higher Bl than the Blueprint...



Note: Still...I think the Blueprint is a fantastic driver
 
pkgum said:
What if the other companies of the similar drivers I've compared with the Blueprint, didn't measure a dual 8ohm coil in series, but still got a much higher Bl than the Blueprint...

You've certainly got a point there ... most the big excursion drivers with DVC's that i've seen have their specs measured with the coils in parallel.

Try comparing B for various drivers.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Gum:

To be honest, I don't really bother with that stuff. If you can get independent verification from users that the driver lives up to it's publiched specs when put into an enclosure, that's fine with me.

I assume a competent designer can take a large magnet and not waste it by bad design. So I don't sweat that stuff. Some manufacturers seem to get more out of smaller magnets than other manufacturers as well. Why? I don't know.

If the unit puts out what the Thiele-Small parameters indicate it will, I am happy.

Here is a web page by the well regarded Lambda Acoustics-makers of Stryke speakers-to the effect that small differences in Bl product is of less than critical importance:
http://www.lambdacoustics.com/library/whitepapers/bl_mms.htm

There is some question I have about Blueprints, having never used one. That is the matter of a shorting ring, or Faraday ring, in the magnet system. This prevents the voice coil, as it approaches Fb in a ported box, to actually travel all the way back to the end of it's excursion, so that it can move forward only. This actually clips off half the wave form.

You would think that the condition would sound terrible, but in fact it takes the form of "second harmonic distortion", which musically is called the "first overtone", and actually sounds very musical. The only trouble is, the phenomenon takes away your lowest fundamental and replaces it with the first overtone. It could sound worse, true, but you are missing your lowest fundamentals!

I do not know if the phenomenon occurs in the sealed box.

There are other ways of preventing this "suck-in" phenomenon besides. I would be interested if Blueprint uses those, instead of a shorting ring.