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The 18" PA sub project that failed..... |
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Arrowsmith 
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Joined: 25 July 2018 Location: Sweden Status: Offline Points: 5 |
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 Topic: The 18" PA sub project that failed.....Posted: 25 July 2018 at 4:11pm |
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Hi all, I have a question from Sweden!
Some days ago I built a ported box for my 18" sub wich I intend to use in a larger room and I used Win ISD to do the thinking for me. (WinISD Pro Alpha 0.50a7) I used a P.audio EM18-LB600 for this project. WinISD calculated a 263L box tuned to 40Hz with a rectangular port 400x70mm (280cm2) with a length 60,9mm, and that was what i built..... Put some dampening on the walls of the enclosure and tested it..... Well that didn't work too well... Sounded Sh*t..... Sitting just in front of it within 1m, well OK then everything would sound atleast something. Take a few steps back - totally dead - Something is really wrong here..... The area of the port is almost equal to a round port of 190mm diameter so I did the same calculation in another, almost 20 year old Swedish program called Probox and did get totally different portlength. Instead of WinISD 60.9mm Probox suggested 230mm with the same portarea. And if I force Probox to take the 60.9mm port it plots a curve that is rather sad looking. Is WinISD doing this calculation wrong for me because of user error or anything else? I 've never heard anything bad about WinISD before. Anyone else got similar problems? Is there anyone that could do a calculation in another "known to work" program to compare the result for me I would be glad. I dont get this..... 263 liters ported box tuned to 40Hz Link to the needed P.Audio driver info: http://emnordic-prod-cdn.azureedge.net/storage/ma/345b3ac56b6f4fe1820892f22920a405/35b4860133bd424b817d697743c067ce/pdf/B246F33B1CD1175458BE07F99A1A95DCE9ACB666/583624.pdf - https://emnordic-prod-cdn.azureedge.net/storage/ma/345b3ac56b6f4fe1820892f22920a405/35b4860133bd424b817d697743c067ce/pdf/B246F33B1CD1175458BE07F99A1A95DCE9ACB666/583624.pdf Small pictures from the build... hard to read, sorry for that. Well... Please look for errors  Best regards! //Arrowsmith http://forumbilder.se/H7GR6/img-20180724-115711-5-medium -  ------------- http://forumbilder.se/H7GR6/img-20180724-204512-6-medium -  Finished and ready for testing. From here it was all downhill.... http://forumbilder.se/H7GR6/dump1 -  Win ISD 263L 40Hz http://forumbilder.se/H7GR6/dump3 -  Win ISD tells me 60.9mm port is the right way to go. http://forumbilder.se/H7GR6/1 -  Probox plots the curve with 70mm short portlength diameter 190mm (283,4 cm2) . Could not go shorter without Probox changing the box volume. http://forumbilder.se/H7GR6/2 -  Probox recommends 230mm port instead for 40Hz with a better result. |
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nickyburnell
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Joined: 06 February 2005 Status: Offline Points: 4410 |
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Posted: 25 July 2018 at 4:33pm |
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I came up with a similar problem years ago with a Wembley B Line driver in a tall (yours long) and not deep cab. Build this and try your driver in it but leave port shelf to be adjustable length so you can run some test tones and see For the record, Winisd has different results to Bass Box pro on a regular basis. Also putting manufacturers suggested designs in Winisd can give some mighty weird results. Edit. I have also had low output from a 2x18 500l cab recently, seriously low notes but no spl. Probably why the GSub on here is a little small in capacity, the man knew the compromises needed to get some attack.  Your cab is mighty big for that single driver IMHOEdited by nickyburnell - 25 July 2018 at 4:35pm |
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It's everything, not everythink!
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DMorison
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Joined: 14 March 2007 Location: Aberdeen Status: Offline Points: 1649 |
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Posted: 25 July 2018 at 4:52pm |
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Your images are very small so I can't see much detail on them, so won't comment directly on what they show.
However, there is one thing to be aware of. WinISD calculates vent length assuming that the inside end of the vent is well away from any of the other walls of the cabinet. When you build it in against the side or end of the cabinet as you have done, three out of the 4 walls of the port are much longer than the remaining wall, and this leads to the sir in the port behaving as if it's a longer port. I've only ever seen one attempt to account for this in predicting port lengths and it involved doing a manual calculation instead of trusting a modelling program's value:  Using that formula your 60.9mm port length might result in a port tuning just below 26Hz, probably a lot lower than that driver wants, which may account for the poor sound. Another thing to be aware of - if you're in a smaller room, then where you and the speaker are in the room can significantly change the way it sounds - this is because the wavelengths of the frequencies a sub is producing are long enough that there can be cancellations due to reflections between the room walls. Try putting the sub in a corner and walking around the room to see if the sound is different in different places. Hope this helps, David.
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Arrowsmith
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Joined: 25 July 2018 Location: Sweden Status: Offline Points: 5 |
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Posted: 25 July 2018 at 7:05pm |
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Hi there and thanks for your replies!
@Nickyburnell I will give this cabinet a couple of tries with different alterations before building a brand new one, but we sure might end up there..... Yes the box might be big for the driver, I just took the values from WinISD and swallowed the bait (as we say here in Sweden) that might be my problem now. As the design is as it is, it's quite easy to block off the upper part of the box and end up with 190L instead to test the difference. I might do that in a day or two to compare the difference. I'm verry curious because the total lack of SPL. @Dmorison Well it sure makes sense that making a port "on the bottom" of the cabinet might alter the values now when you mention it. I sure didn't think about that. As quite a noob it might be best to redesign it and go for a more conventional round pipe and atleast eliminate one of the potential flaws in this design. And 26Hz is way to low for this driver, 35Hz would be the limit according to the documentation. the room where I am testing it is 10X10M and with 3.5m high ceiling. Edited by Arrowsmith - 25 July 2018 at 7:06pm |
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odc04r
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Joined: 12 July 2006 Location: Sarfampton Status: Offline Points: 5482 |
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Posted: 25 July 2018 at 7:20pm |
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If you have only tested it indoors, in one position, move it around a bit or even better take it outside. You could well be experiencing standing room waves nulling out a lot of the signal.
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Peter Jan
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Joined: 16 December 2008 Location: Belgium Status: Offline Points: 1019 |
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Posted: 25 July 2018 at 7:31pm |
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It all starts with the speaker's T/S parameters.
With such high Qes/Qts values, you either put it in a smallish cab and tune higher up to get some SPL/power capacity, but very meager low extention. Or make the cab really BIG, tune lower than Fs, so you get a pretty flat response, solid low extention, but little SPL/power capacity. In short : this is not the right speaker to use in anger as a mobile/rental PA/DJ sub. For use in a "home" rig, it could work nicely, but.... BIG cab, solid lows, moderate SPL capability. You could keep the cab you just build, but modify it to put a second speaker in it in an isobaric configuration. But there's not free lunch with that... you have to double the speakers, need four times the power (double for each speaker, ~600 Watts total) to get the same SPL/response as one cab that is double the size (450-500 liter), but uses only one speaker and a lot less power (~150 Watts). Edited by Peter Jan - 25 July 2018 at 8:03pm |
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Arrowsmith
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Joined: 25 July 2018 Location: Sweden Status: Offline Points: 5 |
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Posted: 27 July 2018 at 12:36pm |
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Thanks for all your inputs regarding my problem.
@odc04r Yes, I have tried to move it around a bit, to be honest -not a whole lot because I was quite sad and disappointed and gave up a bit. But I couldn't see any big differences when I tested. @Peter jan I have tried to put different cab volumes in my Probox program and I'm thinking about cutting away 100 L from my box and make it 160L with two round ports instead 103mm diameter and 160mm long. In Probox that would lift the SPL at least +2dB between 55-75Hz and it might still be able to put out some lows. What do you (or anyone else) think about that idea? Im posting the calculated result below. http://forumbilder.se/H7H49/plot -  Edited by Arrowsmith - 27 July 2018 at 12:37pm |
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mobiele eenheid
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Joined: 15 August 2004 Location: Netherlands Status: Offline Points: 1568 |
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Posted: 27 July 2018 at 1:46pm |
Johan |
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Arrowsmith
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Posted: 27 July 2018 at 8:17pm |
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@mobiele eenheid I guess that is to lower the airspeed in the port and less likely make blowing noises? instead of 2 ports 103mm x 160mm according to Probox. 3x103mm in area is 249,8 cm2 Drivers Sd 1225/5 = 245 cm2 So that would do then if i understand you right?
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make it 160L with two round ports instead 103mm diameter and160mm long