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Old 1st April 2004, 09:52 AM   #1
dumrum is offline dumrum  India
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Default Doubts on Phase Response and Frequency Response

Hi,
I have used WinISD for the design of my boxes. I had plans for building a 2.8 litre box, but when I analyzed my driver parameters with WinISD, I found that it suggested .8litres for a flattest Frequency response.
I tuned the port to 54 Hz.
My first question is whether the data posted below will lead to a decent sounding speaker?

Freq Gain Phase SPL
[Hz] [dB] [deg] [dB]
20.00 -32.65 273.98 57.45
25.00 -26.08 260.93 64.02
30.00 -20.68 248.57 69.42
35.00 -16.06 236.06 74.04
40.00 -12.02 222.68 78.08
45.00 -8.50 207.83 81.60
50.00 -5.55 191.25 84.55
55.00 -3.28 173.40 86.82
60.00 -1.74 155.61 88.36
65.00 -0.85 139.39 89.25
70.00 -0.40 125.55 89.70
75.00 -0.22 114.15 89.88
80.00 -0.16 104.81 89.94
85.00 -0.15 97.09 89.95
90.00 -0.17 90.62 89.93
95.00 -0.20 85.11 89.90
100.00 -0.22 80.34 89.88
105.00 -0.25 76.17 89.85
110.00 -0.26 72.47 89.84
115.00 -0.27 69.16 89.83
120.00 -0.28 66.18 89.82
125.00 -0.28 63.46 89.82
130.00 -0.28 60.99 89.82
135.00 -0.28 58.71 89.82
140.00 -0.28 56.61 89.82
145.00 -0.27 54.67 89.83
150.00 -0.27 52.86 89.83
155.00 -0.26 51.17 89.84
160.00 -0.26 49.59 89.84
165.00 -0.25 48.11 89.85
170.00 -0.24 46.71 89.86
175.00 -0.23 45.40 89.87
180.00 -0.23 44.16 89.87
185.00 -0.22 42.99 89.88
190.00 -0.21 41.88 89.89
195.00 -0.21 40.83 89.89
200.00 -0.20 39.82 89.90

Could someone tell me what the Phase plot actually signifies? I see that the frequency 90Hz is 90 degrees in Phase. So does this mean the 90Hz will get cancelled out?
Kindly tell me what to aim for a Phase plot to be like?


The next question I have is with respect to the enclosure volume. I increased the volume to 2.8 litres in WiniSD and found a huge peak in freq response at arounf 50-60 Hz.
I read elsewhere that the bass response can be greatly improved by increasing the Box size. So will this really work for me? is there anything I am not looking into?
Kindly reply.
Excuse my lack of knowledge , but I am a very interested person in DIY.
Regards,
Linoj.
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Old 1st April 2004, 12:13 PM   #2
sreten is offline sreten  United Kingdom
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Post your driver parameters,

sreten.
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Old 1st April 2004, 03:10 PM   #3
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Those phases plots-are those from WinISD? The reason I ask is that there are two types of phase-acoustic phase and impedance phase of the voice coil.

For the impedance phase of the voice coil, at your port tuning frequency of 55 Hz, the voice coild impedance phase should be near zero.

The acoustic phase of the port should be 90 out of phase with the cone at the port tuning frequency.

Your reading for phase at 55 Hz is 173.4. Which would not seem to fit either one unless you're in a situation where 180 out of phase actually equals 0, in which case you would be close to what you should be for voice coil impedance phase.
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Old 2nd April 2004, 02:12 PM   #4
dumrum is offline dumrum  India
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Quote:
Originally posted by sreten
Post your driver parameters,

sreten.
The TS parameters for my driver are as below: BTW it is just a locally manufactured Woofer .
Fres = 36 Hz
Qms= 3.57
Qes=0.29
Qts=0.27
Vas = 60litres
Sd = 240cm^2
Speaker Impedance at resonance = 101Ohm



Quote:
Originally posted by kelticwizard
Those phases plots-are those from WinISD? The reason I ask is that there are two types of phase-acoustic phase and impedance phase of the voice coil.
I am using WinISD beta.

And could you please explain a little more on what we shud aim from the Phase reponse curve to be like?

Thanks a lot,

Linoj.
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Old 2nd April 2004, 02:51 PM   #5
sreten is offline sreten  United Kingdom
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I wouldn't worry about the phase response too much.

Sealed is simply better than reflex.

Results I get from your parameters :

sreten.
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Old 2nd April 2004, 05:20 PM   #6
dumrum is offline dumrum  India
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Quote:
Originally posted by sreten
I wouldn't worry about the phase response too much.

Sealed is simply better than reflex.

Results I get from your parameters :

sreten.

Thank you srenten for the reply. But could you please tell me how the 3db frequency should be like? I had designed so that the 3db freq was around 54Hz.But for closed box, it seems to have gone much higher....
Could you please tell me the significance of the -3db cutoff frequency?
Thanks,
Linoj.
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Old 2nd April 2004, 05:38 PM   #7
sreten is offline sreten  United Kingdom
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IMO for bass the -3dB point is irrelevant.

-6dB is more commonly used and is sensible.

-10dB is regarded as the absolute bass limit.

How you juggle these is up to you, but I like
the blue/red lines, good room integration IMO.

sreten.
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Old 2nd April 2004, 06:06 PM   #8
markp is offline markp  United States
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The blue box will be the best bet. Dont worry about the phase at very low freqs (under 150hz) as the wavelength is so long it is unimportant in a normal size room.
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Old 2nd April 2004, 07:11 PM   #9
Svante is offline Svante  Sweden
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Quote:
Originally posted by sreten
IMO for bass the -3dB point is irrelevant.

-6dB is more commonly used and is sensible.

-10dB is regarded as the absolute bass limit.

How you juggle these is up to you, but I like
the blue/red lines, good room integration IMO.

sreten.

So, you're really saying that reflex is better than sealed?
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Old 2nd April 2004, 07:49 PM   #10
markp is offline markp  United States
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In many cases the sealed box has a higher F3 but rolls off at 12Db/oct while a ported box will have a lower F3 but rolls off at a much steeper rate and by the time you get down to about 1/2 of F3 the sealed box has more usable output than the ported box. It also can be EQed much more easily to get that low end to extend further. In your case that point where the sealed box output is higher than the ported box is too low to be of any use. The ported boxes have much more output without the use of any EQ in the listenable area of 40-100Hz. You are essentially getting 6Db more output from the yellow to the blue boxes in that region. That is a four time increase in power for the sealed box to catch up to the ported box!
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