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2004-3-16
发表于 2004-3-22 18:58 | 显示全部楼层
[upload=gif]uploadImages/200432218555374000.gif[/upload]
The figure to the left is indicative of the power response of speakers with different radiation characteristics. All speakers are assumed to have the same flat, on axis frequency response. The omnidirectional speaker (black line) is presented as the 0dB reference. A true omnidirectional speaker would have uniform power response at all frequencies. The omnidirectional speaker is representative of a perfect monopole.

A practical monopole speaker (brown), assumed to be a typical 3-way design, has a power response similar to that of the omnidirectional system below the baffle step. As the frequency rises through the baffle step region, and midrange and tweeter become directional, the power response contiinually decreases with frequency. To obtain a smooth porwer response through the midrange/tweetr transition, care must be taken to choose the crossover frequency in a region where the midrange and tweeter have similar directional characteristics. This will, in part, depend on the choice of baffle size as well as the driver characteristics.

The bipolar midrange speaker (blue), assumed to be a 3-way design with rear firing midrange, has a power response similar to the practical monopole and omnidirectional speakers at low frequency. However, as the frequencies rises through the baffle step region the radiated power does not fall off as quickly as the pratical monopole due to the rear radiation. As the frequency continues to rise the power response will follow that of the pratical monopole since only a forward firing tweeter is present. Care must be taken in the transition between midrange and tweeter to prevent the possibility of an audible discontinuity in the power response.

The dipole response (red) is based on an open back 3-way design with only a forward firing tweeter. At low frequency the ratiated power is 4.8dB lower than a monopole. As the frequency rises through the baffle step region, the radiation undegoes a transition from true dipole to bipolar like radiation with the exception that the phase of the rear radiation is inverted. Above the frequency where this transition is complete, the power response is similar to that of a bipolar speaker system.

The violet cure is representitive of the addition of a rear tweeter to an open backed 3-way design. The rear tweeter improves the power response and has a clearly audible effect on the system preformance addig clarity and openness to the sound.

Note: The curvers in the figure are not intended to be an accurate representation of the power vs frequency for the systems discussed. They are only qualitative representations of the differences between the systems.

Time aligned, Phase coherent, Phase aligned, Transient accurate, What's up with(4529字节)(石牌,3-8 20:23 阅读:2)
1) Acoustic center or AC:

As I shall refer to it, the acoustic center of a driver is the position, on the driver axis, relative to which the driver exhibits a minimum phase response. This position is usually measured with reference to the mounting surface of the driver. For a tweeter this would be the face plate. For a woofer it would be the mounting flange on the basket. The minimum phase acoustic center (AC) is located approximately at the point where the dome or cone of the driver is attached to the voice coil. Thus for a tweeter the AC may be positioned just several mm from the face plate surface. For a woofer the AC may be several cm behind the mounting flange. When defined this way, the acoustic center is a fixed point in space.

2) Relative offset:

The term relative offset is used to indicate the difference between the ACs of the woofer and tweeter. For example if it is stated that the relative offset between the woofer and the tweeter is 23 mm this would typically mean that the woofer AC is located 23 mm behind the tweeter.

3) Target response:

The target response refers to the frequency response function, both amplitude and phase, that one attemps to match the acoustic output of a speaker system or a cro
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