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Old 2nd December 2005, 10:16 AM   #1
Glen1 is offline Glen1  Australia
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Default Help with WinISD and XLS 12

Hi guys,
I've got myself a Peerless XLS12 830500 driver and a 200 watt subwoofer plate amp. The amp has a highpass filter set at 17Hz but I'm not sure of the rate. I have decided to build a vented box of between 40 and 60 litres using flanged fort ends. The sub is for home theatre use in a room 14' x 20' with 9' ceilings.
I give WinISD a go and after a couple of goes found it pretty easy to use. I ended up with some nice coloured lines but then realised I don't know what sort of response I should be looking for.

Can anybody give me some ideas of what a good response curve and what I can expect fom this driver.

Thanks.
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Old 2nd December 2005, 10:43 AM   #2
damo21 is offline damo21  Australia
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I also have the identical combination, XLS 830500 and 200W with rumble filter. It seems this combo is ideal for vented box systems for movies. But I'm attempting to use it in a closed system for music/audio reproduction, in 80L sealed application. I haven't built it yet. If it sounds dodgey, I'll build the box as below, and find a better driver for my sealed box....

As for vented, I got some good advice from the XLS distributer:

Consider using 45L (air volume) box, a 90mm diameter pvc plumbing pipe as your port, as this is a common plumbing size and suited to this. You could attach 2 elbows to bend it around inside your box, and you need to flare the ends as much as possible to stop the pipe from chuffing. Basically, the longer you can make the pipe, the more bass extension you will get, but remember that the end of the pipe must be at least 75mm away from any wall inside your box for best performance, so this is a restriction. Also, make sure you brace the box inside and brace the port from moving, so you need to allow more volume internally for all of these extra items.
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Old 2nd December 2005, 11:26 AM   #3
Did it Himself
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The response curve should be smooth and it's not a big problem if it droops off gradually as the room will have a boosting function of it's own that will broadly compensate.

As for the tuning, a 90mm vent is just about acceptable. Just make sure that you tune it no higher than about 35Hz or it will chuff badly and because below the tuning frequency the cone will be unloaded.
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Old 2nd December 2005, 02:11 PM   #4
damo21 is offline damo21  Australia
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According to Collo's experiments on anti-chuffing, what really matters is the ratio of cross-sectional areas of flared end of port and port itself, and the diameter of the port. Basically, the bigger the port flare the more air velocity you can have through your port without chuffing. Also, bigger port diameter allows faster flow too. You can download his calculator to determine max velocity.

Also, you can use WinISD Pro to design vented boxes and check that the max velocity through the port doesn't exceed the value given by Collo's calculator for your particular port design.

I guess the aim for vented boxes is to design a box/vent which gives maximum bass extension for your particular driver/amp without exceeding the specs for your driver, and also staying within the safe non-chuffing air velocities for your port.

Is the only reason for not having a huge box for vented systems asthetics?

Check this:
http://www.diyaudio.com/wiki/index.p...n%27t+chuff%21
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Old 2nd December 2005, 03:01 PM   #5
Did it Himself
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No, if you go too big on the box you will lose flatness of response, depth of response, and power handling.
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Old 2nd December 2005, 05:18 PM   #6
damo21 is offline damo21  Australia
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Ok, I've come to a nice compromise with 2 designs using the Peerless XLS 830500 driven by 200Wrms plate amp with 17Hz hp:

Critical Q=0.5 sealed sub: 32.5L box

or

Vented 65L (tuned to 18.5Hz)
Port: 100mm diameter Pvc pipe x 1.0m long
Flares: 50mm each end

This vented arrangement including the highpass filter at 17Hz ensures that the cone stays within its excursion limits below 20Hz. Also, the port velocity never exceeds 20m/s so port flare of 50mm at each end is heaps to prevent chuffing (should be fine up to 30m/s, will make bigger if I can be bothered).
Group delay is a maximum at 48ms at 16Hz, which, according to the GD wiki, should be unnoticable at such a low frequency.
Here is a graph of group delay vs frequency for the 2 subs above:
Attached Images
File Type: gif untitled.gif (13.8 KB, 179 views)
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Old 2nd December 2005, 05:28 PM   #7
damo21 is offline damo21  Australia
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And graph of SPL vs Hz (without lowpass crossover):
(yellow = Critical Q sealed)
(blue = vented)

I'm going to build both of these when my driver arrives and I'll post here when I know how they sound.
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File Type: gif untitled2.gif (14.5 KB, 177 views)
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Old 2nd December 2005, 05:47 PM   #8
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I see you have included a high-pass filter in the model. This does make the initial design harder IMO. I start off by getting the low end right then doing another pass at the design with the filter added. You may have done that, I don't know.

Both of those designs are going to need EQ. I think you can shrink the vented box down a bit.

Yes a comparative test is a great idea.
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Old 2nd December 2005, 06:07 PM   #9
damo21 is offline damo21  Australia
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I was hoping that maybe there is enough room gain not to include EQ. Otherwise I'm in a spot of strife.
Btw here is an updated graph showing the theoretical fitted curve of inaudible group delay superimposed on the graph above:
(NB: Paul Spencer says these extrapolations are purely experimental, there have been no tests to verify this. Still, it's good to fall below these values i think.)
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Old 2nd December 2005, 08:25 PM   #10
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Over here (the Netherlands) most people seem to use, GD max= Frequency x Delay = <400, i.e. 10 ms at 40 Hz. The shape would matter here. Rather a smooth GD as one that is peak like.

The line as in the thumbnail above would suggest that the GD of about any 6th order bandpass would stay well below audibility while it's supposed not to be. Even more so, it would be rather difficult to create a sub with audible GD if this truly is the case.

The groupdelay as showed looks like as it is without lowpass filter? In that case you can add an aditional portion of GD to the graph. If you cross the sub lowish the overal GD will (in lots cases) be high enough to delay the top with 6-10 msec. Which would ultimately result in a relative very low GD.

Are you seriously going to compare the 2 design on difference in GD? Or am I missing out on a joke here?

Wkr Johan
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