Group Delay/phase responce |
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tb_mike
Old Croc Joined: 01 October 2004 Location: New Zealand Status: Offline Points: 2744 |
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Posted: 17 August 2006 at 10:12pm |
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Hey Paulo those are good links!
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tb_mike
Old Croc Joined: 01 October 2004 Location: New Zealand Status: Offline Points: 2744 |
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Sorry,my german only consists of 2yrs at secondary school,not quite enough I think!
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Paulo Duto
Registered User Joined: 06 January 2005 Location: Brazil Status: Offline Points: 123 |
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See also John L Murphy's collection of posts to Bass list mentioning Journal of the Acoustic Society of America Vol 63, nr 5, pp 1478-1483 (May 1978) Blauert and Laws... and
Regards,
Paulo.
Edited by Paulo Duto - 17 August 2006 at 6:27pm |
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Paulo Duto
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unknown_artist
New Member Joined: 02 June 2005 Location: Germany Status: Offline Points: 7 |
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If you're able to understand the german language, there are great publications available(including the question:what kind of improvements are "hear"able....) |
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tb_mike
Old Croc Joined: 01 October 2004 Location: New Zealand Status: Offline Points: 2744 |
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I find it easy to visualise with step response/impulse response measurements. The acoustic response is easily understood here.
Although this may be a simplification...I havent bothered with FIR study yet.
Once people realise what it is,then you have to see if your ear can even hear what looks bad on a graph. It certainly is sensitive to certain things in certain frequency ranges but not others. Edited by tb_mike - 16 August 2006 at 9:52pm |
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unknown_artist
New Member Joined: 02 June 2005 Location: Germany Status: Offline Points: 7 |
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Hm,
the best case is that you design your system as a minimum phase system(it's not possible to have "faster" system without the use of FIR filters[which quit have delay to work even at low frequencys]). It's a disputed question whether you can hear group delay. Definitely you can hear it at low frequencies and you can hear it when theres a jump in the group Delay at your crossover (for example at 1500Hz)-> then transients will be torned up(don't know if it's the right word)- for example a snare or somthing like this... So you have to try to get a flat group delay(group delay means the derivative of phase -> a spectrally delay) |
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tb_mike
Old Croc Joined: 01 October 2004 Location: New Zealand Status: Offline Points: 2744 |
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godathunder
Old Croc Joined: 19 July 2004 Location: wicklow Status: Offline Points: 1834 |
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Im not sure that Im remotely correct here but my understanding is that the cabinet produces differing resistance to cone movement at differing frequencies. This resistance to cone movement alters the reactive component and hence impedence of the coil. since the phase angle is the ratio of the coil resistance (constant) to impedence if the impedence changes then the phase changes. Corrections anyone?
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LOUDER THAN LOUD
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kevinmcdonough
Old Croc Joined: 27 June 2005 Location: Glasgow Status: Offline Points: 3751 |
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LOL
thanks for your replys guys. I already know most of the info, i understand WHAT phase is, what fourier transforms are and the graphs etc. I suppose my question wasn't phrased very well but i kind of ment more WHY Why does a speaker play different frequencies at different delays/phases. and what building meathods are to be avoided or used in order to minimise this effect. I'm refering to mostly to reflex as thats what i'm working on at the moment but just all designs in general really. kev |
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djtosco
Registered User Joined: 26 September 2004 Status: Offline Points: 58 |
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Any linear system could be represented by a transfer function, which contains all the informations about its behaviour. Even a loudspeaker+enclosure, under a certain degree of approximation, is a linear system with a transfer function (TF). A linear system with a sine wave at the input, gives you a sine wave at the output with the same frequency, but eventually different amplitude and phase. The frequency response is the plot which represents the ratio between the amplitude of the output ant the input (usually in dB) at the different frequencies. The phase response plot represents the difference in phase between the input and the output at the different freqeuncies. A phase difference is a time difference, and thus the group delay. A non-linear phase response cause the fact that the system produces a frequency-dependent delay. Any waveform (Fourier's theory) could be represented by a sum of sine waves. But because of the group delay, the waves at the different frequency are differently delayed. This cause a different shape in the input and output waveforms. So, we want an almost constant group delay (the value is not so important, and could be easily compensated with a DSP), thus an almost linear phase response (the group delay is the opposite of the derivative of the phase respect to the frequency in rad/s)
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soundsystemdan
Young Croc Joined: 04 April 2005 Location: Leeds UK Status: Offline Points: 716 |
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well what type of cabinet ae you refering to?
afaik these things affect reflex and bandpasss designs. I probably know little more than you about what causes it, i dont think phase response is much of an issue, except at crossover frequencies or if you're combining non identical cabinets. As far as making group delay better or worse, it would depend what you want out of your cab, be it depth, kick or efficiency, or maybe size is important too. volume and tuning frequencies can affect power handling too. I expect you know some of this all ready. I'm in the process of trial-and-error mdf prototyping different reflex designs. Hopefully by the end of the week I'll be able to post some findings. |
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kevinmcdonough
Old Croc Joined: 27 June 2005 Location: Glasgow Status: Offline Points: 3751 |
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LOL anyone? |
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