How much is the loss of SPL in a PR due to the losses in PR surround?
This may be a strange question for cardioid bass thread, but here is why I am asking. One way to achieve cardioid bass is by stuffing a U baffle, the U baffle delays the rear wave and the stuffing attenuates the rear wave, however the stuffing is very ineffective at lows.
So, here is an idea, instead of opening at the rear, why not use a very light cone at the rear (similar to a bass reflex box with a PR), the PR surround would attenuate the rear hopefully across a wider bandwidth, reaching lows. Of course the PR tuning should be kept very high so that its outside the pass band.
What do you guys think?
This may be a strange question for cardioid bass thread, but here is why I am asking. One way to achieve cardioid bass is by stuffing a U baffle, the U baffle delays the rear wave and the stuffing attenuates the rear wave, however the stuffing is very ineffective at lows.
So, here is an idea, instead of opening at the rear, why not use a very light cone at the rear (similar to a bass reflex box with a PR), the PR surround would attenuate the rear hopefully across a wider bandwidth, reaching lows. Of course the PR tuning should be kept very high so that its outside the pass band.
What do you guys think?
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It's the stuffing/damping that delays the rear wave, it doesn't want to be attenuated as this would reduce the cancellation. This type of cardioid is one of the least effective. I can't see how a PR to the rear would result in a delay?
I thought it was the asymmetric driver placement which contributed most of the delay, isnt it? The intention of PR is not to add any extra delay, the U baffle already provides the delay. The PR is to just attenuate, more than what can be done by stuffing
Though provoking idea, I like it 🙂
Another way to look at the cardioid is to consider it to be a superposition of a monopole source and a dipole source. Without damping, an open enclose behaves as a dipole. Add a passive radiator and the air inside the enclosure will be compressed, which implies that there (also) is a monopole source. This does not guarantee good performance yet, because their mutual phase and amplitude (as a function of frequency) must be correct.
One practical point, how would you add sufficient damping to the passive radiator? They usually are designed to have as little losses as possible.
A resonator can add delay, because it acts as a low pass filter.
Another way to look at the cardioid is to consider it to be a superposition of a monopole source and a dipole source. Without damping, an open enclose behaves as a dipole. Add a passive radiator and the air inside the enclosure will be compressed, which implies that there (also) is a monopole source. This does not guarantee good performance yet, because their mutual phase and amplitude (as a function of frequency) must be correct.
One practical point, how would you add sufficient damping to the passive radiator? They usually are designed to have as little losses as possible.
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The resonator can add delay but it is not used since its tuned much higher above the passband. The objective is just to attenuate. Delay is already a given in a U frame.
The U frame is a dipole as TBTL says, it increases the path length between the front and the back of the driver which is equivalent to a larger baffle so lowers the frequency of the cancellation.
We both are saying the same thing. When driver is asymmetrically placed, the front delay is reduced and rear delay is increased when H baffle is used as a reference.
The asymmetrical layout does change the polar response into something more cardioid like compared to an H frame or flat baffle, but to get a null at the rear from a U frame acoustic (or electrical, although it will no long be a U frame) delay is required to cause cancellation.
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