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Acoustic Elegance SBP15-4 review
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Green Bay, WI
Re: Acoustic Elegance SBP15-4 review
Originally Posted by
The sub can handle anything you throw at it, from Brad Paisley’s I Wish You’d Stay, to the extreme lows of an organ, to fast-paced, hard-hitting dubstep and everything in between. The kick drum in Alice in Chains’ No Excuses will hit you so hard it is painful. The sub always moves with authority. In Metallica’s One, the double-bass towards the final half of the song are clear and extremely distinguishable – you can hear and feel each full, individual strike of the drum in perfect time. Limit to Your Love by James Blake begins abruptly with absurdly quick pulsating bass, which the SBP keeps up with perfectly. When the pulsating stops on a dime, so does the sub. This song is a magnificent test for any subwoofer, and the sub passes it with flying colors.
As is with any rear subwoofer, without time alignment, lower notes will of course reveal the location. With proper time alignment, this only occurs with drawn-out low frequencies and the great majority of the time you will forget the sub is even back there.
Thanks for the great review Ally. I did want to note that IB woofers are back in production now. The IB(xx)AU series will be up on the online store soon. Otherwise people can always email about them. I currently have about 20 motors built and ready to go as orders come in.
One of the biggest things I hear all the time is how quickly transients can be played with the woofers. Most any woofer can loudly play a long drawn out tone at high levels. It is when a woofer is asked to stop and start quickly that most have trouble. This is a function of the motor and the control that it has over the VC.
The main issue is flux modulation. As the VC is energized it becomes and electromagnet. As this electromagnet moves through the permanent magnetic field, it pushes it around, or "modulates" it. A good way to envision the effects is with a magnet near an old tv or computer monitor. As you move the magnet you can see the images move, change colors, etc. The VC has similar effect on the magnetic field in the motor of the woofer every time it moves back and forth. The more
input, the more significant effect which is why efficiency is important.
The VC is trying to push against the permanent magnetic field, but that field is moving. Imagine trying to push off of a solid wall vs pushing off of a wall with a sponge on it. The solid wall lets you push with full force instantly. The sponge first has to compress until you reach the solid wall, then when you push off the sponge will expand and change the rate at which you push off. The modulated flux field is very similar. It is very apparent when the flux field first has to settle before the VC itself completely stops moving. There is just no real control over the VC by the motor.
Klippel has a chart stating the various types of distortions and their causes. You can see that flux modulation has effects in both the sound pressure and current. It creates harmonic distortion not only in the audible sound, but even distorts the impedance curve and amount of current being applied to the woofer. What you end up with is a VC that isn't getting the right amount of current in a magnetic field that is unable to push the VC properly. The flux modulation is the most significant factor in distortion and "provides unique symptoms which are sufficient for the identification of the nonlinearity" meaning they are measurable and audible results. This is the primary factor in odd order harmonic distortions. The odd order are much more audible than even order.
To get rid of this issue we need to short all the eddy currents coming from the VC that move the magnetic field around. This will keep the flux field from moving and as a result get rid of the distortions. We do the same thing that is done in transformers to lower inductance. The full copper sleeve on the pole shorts any currents before they are able to move the flux field around. It results in a huge difference in harmonic distortion across the board. It also is very significant in how quickly transients can be handled. Listening to bass guitar solos where notes are quickly plucked and start/stop very fast is very telling. There is a short passage at the beginning of Duende by Black Light Syndrome I use to show this often. As the notes are played quickly with most woofers you will only hear a change of tone. With woofers with proper shorting rings, you can clearly hear each note start and stop. If you want to read a little more on what is done in the Lambda motors you can see the following page:
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