HI everyone
I'm carrying a question on JBL subs equipped with the 2242H driver since many years.
The JBL 4645B or C is an example. On 4645B/C pdf is clearly shown (more clear on 4645B!) two frequency response: "with" o "without" EQ. They say that without equalization the f3 of the system is limited to about 35Hz (the fs of the 2242) while with "equalization" the system can go down to about 22Hz.
Now, on a cinema forum, a very competent tech told me that this kind of subwoofer, like other brands as EV, are intended to be used with B6 filter that adds a 6dB boost at about 30Hz and apply a high pass filter under the same frequency.
I had the chance to make a quick test between triple chamber 4688 (rated 28Hz without equalization) and 4645B and I realize that without equalization (was a quick test!) the 4688 outperform greatly the 4645B. And this explain to me why most of the technician says that the 4688 is the top even if it can handle only 600W in 150Kg!
Ok, so where is the problem? I'd like to know more of this "EQ" 'cause it's not so easy to put 6dB at 30Hz on a subwoofer is the system is not designed for that signal, isn't it?
My search of knowledge is not only for home use where I can identify immediately any kind of problem if the driver is overdriven. I'd like to know what consideration should be done installing an array of subs with this filter in a theater for example (I'm not an installer but sometimes I make something... it's an hobby! ). If 4x4645B are enough, just an example, for a theater 20 meters long, what parameters I have to take in consideration if I put a B6 filter on the line?
A friend of mine simulated the 4645B driver and box and told me that the system is NOT B6 aligned. So I asked JBL (just to have confirmation of the type of equalization needed!) but they told me that they can't help me and that I should ask an installer... I was just asking for system specs! EV and QSC write them on pdf!
On the Market I can find two filters (made by RDL and QSC) made specifically for subwoofers that needs equalization "like 4645B"
http://www.fullcompass.com/Products/...pid=SKU--28502
RDL apply the boost at 32Hz, QSC at 25Hz... I'm a bit confused!!
Can someone help me better understanding this argument?
Thanks and bye!
Antonio