Quote:
Originally Posted by Sam Kapasi Hi!
I am responding to your PM. Here, this should sort out any questions you may have. |
Thank you Sam.
Grizzly, you will notice the woofer Sam has used in his example has a Xmax of 12.5mm (simple Xmax is calucalted as Air gap height-Voice coil height but since useable Xmax is only one way the result of the above is divided by 2 hence in this example it is 33-8/2).
Now to describe the effects of the 3 boxes Sam has outlined (believe me these boxes are only the simpler examples).
In all 3 cases the Transducer excursion (I believe) is a calulated excursion (not actually measured) as in the curves shown in all 3 cases he transducer is being pushed to their linear XMax limits
and beyond and if one were to measure a Tranducer's behaviour in such cases the curves wold look very rough and inconsistent (take 3 different measurements and get 3 different results). LEAP is Loudspeaker Enclousure Analysis Program which is accurrate but therotical in it's results. It is excellent for understanding a tranducer's behaviour in various boxes. LEAP's sister LMS however is used to provide actual measured results. This small paper (
The Art of Speaker Design) is a good read for first timers and mor help can be found here (
Acoustics Forum • Index page).
Now back to the measurements (the above was just a preface to understand what the measurements stand for).
For each box type Sam has provided Freq vs SPL and Freq vs mm curves. Please note that the Freq vs SPL curves are at 2W while the Freq vs mm curves are at 300W. At 300W, thanks to the deviations in the power response and compression, the freq response curve will not be exactly that of the curve at 2W but for most purposes the 2W curve is adequate and which is why most manufactures only provide curves at 2.83V or 2V.
A car's cabin provides gain due to the various boundaries (chassis and body of the car) the car has. Hence the in car bass response is more extended.
You will notice that the sealed box's excursion response is more linear than that of the ported box. This is becuase below Fb the woofer in the ported box decouples from the box and hence can be easily over drive (see how fast the excursion respnse rises after about 32Hz in the ported box). A proted box is great for music that has no information below Fb but provides little protection to the woofer if this is not true.
The bandpass box (4th order bandpass in this case) can be considered as a narrowly tuned ported box where the bass output is huge in a small band but falls off rapidly outside this band. As with ported boxes, bandpass boxes also provide little protection below Fb but you will notice that within the band the bandpass box cna deliver about 6db more SPL than a sealed box.
Each box has it's merits and demerits. For general music I would recommend a sealed box but for modern music (hip hop, trance, house, etc..) ported boxes work fine. Band pass boxes are best suited for Disco where midbass energy is high.
I hope this helps (my posts have been known more to confuse than help).