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Old 6th May 2011, 11:02 AM   #1
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Default Effects of series resistor on driver.

This discussion is with reference to some information available on net and things experienced by me.

1) Based on the information provided by ESP site, Can we say that baffle diffraction correction using series RL, with driver changes characteristic (Qts) of driver along with shaping input signals for correcting baffle diffraction. Is it true? How to handle this?

2) In the thread “Sonic Quality of L-pad attenuator for tweeter” I was trying to discuss this issue.
I felt that the sonic quality (clarity) of tweeters were getting blur (it didn’t sound clean or detailed high frequencies). Now while I added RL based baffle correction. To my satellite speakers I found that the graph look quite flat. But the cleanliness in the sound disappeared.
The dialogs were not very clear. And I had to put efforts to understand them.
I carried this experiment on some other small speakers too and got same result. So does it mean that addition of series resistor changes Qts of driver and same holds true even when apply baffle step diffraction correction.

Has anybody experienced same or can help me understanding how to handle this?
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Old 6th May 2011, 11:59 AM   #2
sreten is offline sreten  United Kingdom
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Hi,

The RL method of BSC is the crudest method, generally you don't need R.
What you should do usually is oversize the low pass inductor, see links.
But FWIW Qts is not affected much as the L "bypasses" the R.
R will still interact with the drivers inductance in the midrange.

Also FWIW L-pads on tweeters do affect Qts, the source impedance
driving the tweeter is the two L-pad values in parallel. Conversely
L-padded tweeters are less sensitive to high impedance amplifiers.

rgds, sreten.

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Old 6th May 2011, 01:47 PM   #3
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Quote:
Originally Posted by Aucosticraft View Post
This discussion is with reference to some information available on net and things experienced by me.

1) Based on the information provided by ESP site, Can we say that baffle diffraction correction using series RL, with driver changes characteristic (Qts) of driver along with shaping input signals for correcting baffle diffraction. Is it true? How to handle this?

2) In the thread “Sonic Quality of L-pad attenuator for tweeter” I was trying to discuss this issue.
I felt that the sonic quality (clarity) of tweeters were getting blur (it didn’t sound clean or detailed high frequencies). Now while I added RL based baffle correction. To my satellite speakers I found that the graph look quite flat. But the cleanliness in the sound disappeared.
The dialogs were not very clear. And I had to put efforts to understand them.
I carried this experiment on some other small speakers too and got same result. So does it mean that addition of series resistor changes Qts of driver and same holds true even when apply baffle step diffraction correction.

Has anybody experienced same or can help me understanding how to handle this?
The (valid) answeres come from classical filter network theory. There is little to dispute.

1. inserting a resistor in series with a woofer not only increases the Q of the woofer circuit it reduces the damping factor of the amplifier. This will exaggerate any tendency to supurious output at the driver/enclosure's resonant frequency. So called tight bass occurs when F3 of the system is low and system low frequency Q is 0.7 or less. 0.7 gives the lowest F3 without an FR peak.

Some experimenters feel putting a small resistor, say 1 ohm in series with a speaker system or woofer will deliberately obtain the effect of increasing Q making a solid state amplifier sound more like a tube amplifier. This works best on high inertial mass woofers such as 12" acoustic suspension designs.

2. In theory using an L pad for a tweeter does not change the crossover frequency. An L Pad consists of two potentiometers, one in series and one in parallel. As one increases in value when you turn the shaft, the other decreases proportionally causing the filter circuit ahead of it to see the same impendance regardless of the L-pad's setting. If the tweeter were a pure resistor whose value was perfectly matched to the L pad, turning it would only affect the ouptut level of the tweeter (by reducing output you may affect what you perceive as clarity.) However, tweeters have inductance as well so the L-pad is not perfect. It is the best cheap solution to changing the output level and usually works fairly well. The use of a potentiometer instead of an L pad is not recommended because it changes the F3 of the filter network.

By far the best arrangement is an active crossover network, multi amping, and active multiband equalizers for each driver. A series high pass filter cap for the midrange and tweeter is advisable to prevent damage to them from turn on thumps and other low frequency amplifier disturbances (after the active crossover.) This system design arrangement gives the designer the greatest flexibility in tailoring the response of each driver to the overall system goals. It's also not a bad way to design a speaker system. Once optimal response is found, you can often design a much cheaper if not quite as perfect passive crossover network to match its performance. By comparison the passive network is crude, flawed, and far less flexible but it is much cheaper. It also conforms to audiophile notions of what a speaker system should be.
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Old 9th May 2011, 05:08 AM   #4
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Sorry, My net was down for quite a long time. So I could not be here. And Thanks for the response I will read the link provided here.
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Old 9th May 2011, 08:21 AM   #5
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"The RL method of BSC is the crudest method, generally you don't need R.
What you should do usually is oversize the low pass inductor, see links.
But FWIW Qts is not affected much as the L "bypasses" the R.
R will still interact with the drivers inductance in the midrange.

Also FWIW L-pads on tweeters do affect Qts, the source impedance
driving the tweeter is the two L-pad values in parallel. Conversely
L-padded tweeters are less sensitive to high impedance amplifiers.
"




Whats FWIW ?
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Old 9th May 2011, 10:52 AM   #6
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FWIW: For What It's Worth
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