Everest enclosure volums vs professional enclosure guide volume
Hi all,
According to this post, the original (DD55000) Everest had a bass enclosure volume of 180 litres + 27 litres = 207 litres, and an "effective volume" of 227 litres (8 cubic feet) when taking into account the ports.
Yet the JBL Professional enclosure guide states that the enclosure volume for the E145 (and several other JBL drivers, including the 2225) should be 4 cubic feet; i.e., half the actual volume used in the Everest.
Can someone please explain the discrepancy?
Apart from curiosity, the main reason I ask is that I am having a ported enclosure built (initially for a single 2225H, but I may upgrade to a different driver at a later time) and I am trying to determine the optimum enclosure volume to use...
Thanks in advance!
Richard
There is more than one "right" cabinet size
Quote:
Originally Posted by
rab
Hi all,
According to
this post, the original (DD55000) Everest had a bass enclosure volume of 180 litres + 27 litres = 207 litres, and an "effective volume" of 227 litres (8 cubic feet) when taking into account the ports.
Yet the JBL
Professional enclosure guide states that the enclosure volume for the E145 (and several other JBL drivers, including the 2225) should be 4 cubic feet; i.e., half the actual volume used in the Everest.
Can someone please explain the discrepancy?
Apart from curiosity, the main reason I ask is that I am having a ported enclosure built (initially for a single 2225H, but I may upgrade to a different driver at a later time) and I am trying to determine the optimum enclosure volume to use...
Thanks in advance!
Richard
See http://www.ht-audio.com/pages/SpeakerBasics.html. Look for "Shaping the Low-Frequency Response".
4 cu feet is "portable" (size is an object), 8 cu feet is "stationary" (size does not matter).
If you want to upgrade at a later time, the TS (Thiele Small) Parameters fs, Qt (read: Qa, Qe, Re) , Vas, should be similar. The 2226 is similar to the 2225 in this respect.
Ruediger
Additional Considerations
Quote:
Originally Posted by
fpitas
<snip>
1.) Your summary is reasonable.
<snip>
2.) Finally, if you decide you want less volume in the future, partially filling the box with an inert material (wood, bricks etc) will easily accomplish that.
<snip>
3.) Increasing the box volume is not so easy ;)
<snip>
1.) You may want to study the Thiele paper. Forum: General Audio Discussion, Thread: Technical References, Entry: Thiele Paper.
2.) You can use hard styrofoam.
3.) If the box is only for low bass and not for mid bass, you can turn the driver so that the magnet is on the outside. Saves you the "volume displaced by the driver" and adds a bit volume in the cone. Helps the driver to dissipate heat. Minimizes the shift of TS parameters due to a heated voice coil. Requires swapped cables (+ <-> -).
4.) Study the Thiele Paper for the effect of Rg on Qt (Equation 70 in 2nd part of paper). The DC resistance of the bass coil in the Xover and the cables all contribute to Rg.
Ruediger