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Tuning an enclosure below the driver's Fs???

 

Anonymous
 
will this have any inverse effects on the sound the driver will produce???
 

Silver Member
Username: Insearchofbass

Post Number: 807
Registered: Jun-04
heres a write up i found for you


EBS - 4th Order Large Vented Enclosure with Low Tuning

Basic Theory



EBS- Extended Bass Shelf. This is only one of the various different types of vented alignments which are possible and follows many of the same characteristics of vented enclosures. The idea is to intentionally design the enclosure to be 125-175% larger than the optimal calculated volume and then tune the enclosure much lower than optimal as well. The result is a significant amount of extended low frequency response. When the response curve is simulated, a visible "shelf" can be seen in the curve just above the tuning frequency before it sharply rolls off. The LEAP manual explains EBS theory like this: "The name [EBS] was derived simply from the visible appearance of the response curve. The bass response is extended to a lower frequency than would be possible from the QB3 alignment, but at a lower level or shelf relative to the mid band level. Although the EBS alignment is not a nice neat flat alignment such as the QB3, it is very often a much better choice than the QB3. The EBS alignment has some interesting features. Consider a loudspeaker with a Qts of 0.30, the QB3 alignment would have about 2dB more output at a frequency of twice the Fs, while the EBS alignment would have over 2db more output at Fs In most cases the EBS alignments will have far more subjective [low] bass than the QB3 alignments. Also, if you were to equalize the responses flat to Fs, 10db more boost would be required for the QB3 versus the EBS. This can dramatically consume large amounts of headroom in the power amplifier, and may also far exceed the linear excursion limits of the speaker. The EBS alignment will maintain much lower cone excursion at frequencies near Fb than is possible with the QB3 alignment. This can be very important for high power systems."
Advantages

Extended low frequency response down into the teens. Subsonic earth shattering bass response. Increased efficiency at the lower frequencies (below 25 Hz) but decreased efficiency at higher frequencies (above 30 Hz). This is a rough figure since many different combinations can be designed to yield specific results. In general, low frequency is extended and efficiency increased at the expense of reduced efficiency at higher frequencies.
Disadvantages

Cut-off rate can be as high 36 dB/octave below fB. Transient response is degraded as a result of this. However it may be argued that because the tuning frequency is so low, that is it far enough out of normal operating range that it may be considered a negligible downside. The enclosure size is huge. Anywhere from 5-15 cubic feet depending on the size of the driver being used. Power handling capability of driver is reduced anywhere from 25-50%. Driver may reach Xmax sooner above fB even if it never reaches Xmax right at or below fB. Lack of real presence. Lack of kick or punch. The overall impact of the bass is much softer. Signals between 40 and 60 Hz are significantly reduced. Harder to "sell" because most people are more receiving to a pronounced upper bass response rather than an incredibly low and deep bass response . It takes 8 times as much power (as well as moving air) to make 20 Hz sound as loud as 40 Hz.
Best Applications

Where the truly deepest of all heavenly deep bass is desired. For drivers with a large Xmax and the ability to consume large amounts of power. For drivers whose T/S parameters dictate an optimal enclosure size that's smaller than what the designer wants to build. Large Home Theaters and varying kinds of music with heavy bass tracks would take the best advantage of this enclosure alignment.
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