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Discussion Starter · #1 · (Edited)
Well hello,

I blew up my MJ 18 subwoofer. It has now been replaced with an IXL 18.2.2

I have moved on and don't have my old computer with my old calculations. I tried to input some data into WINISD pro. The modelling looks way off. I maybe did something wrong this time, or last time(3 years ago).

My box has an interior volume of 290.18 litres. I have 3 ports of 4 inch abs pipe - 22 inches long.
If I subtract the ports volumes I get 273.26 litres. Is this the figure I should use?

This is yielding a tuning frequency of 23.17 hz ?

This is much different than I had calculated before = 18 hz

What should I do now? Thanks

Also - I have the Reckhorn B1. I used to set the subsonic control at 16 or so. Where should I set it to know? I want to prevent blow up. Thanks
 

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Discussion Starter · #2 ·
If I am doing Winisd correctly - I can flatten the curve and extend the bass by blocking off one port completely. That is; run with 2 ports instead of 3 gives a tune freq of 18.92
Or should I run with 1 port for a tune of 13.38

Summary,
3 ports = 23.17
2 ports = 18.92
1 port = 13.38

Not sure if I am doing things properly?
 

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Discussion Starter · #4 · (Edited)
The subwoofer amp is a Tapco 2500. I am only using the bottom 1/3 of the volume range. I now see where my calculations went off. I used 4.5 " as the diameter rather than 4"

With 20.68 as the tune frequency - where should I set the Reckhorn low frequency filter?
 

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Discussion Starter · #6 ·
I believe the amp will put out 2500 watts in to 4 ohms.
The IXL 18 subwoofer I have is somewhat special, being a 2 ohm load. 1+1
This may make it more responsive to power. I believe the amp is oversized for either a 4 ohm or a 2 ohm example.
 

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Blocking 1 port will give you a tuning off 16.75 and as Mike says put the hpf at 16hz you should be good for 1000 watts input power and have a port velocity off 34 m/s at 16hz max. I very much doubt you will hear any noise. I am running well over 40 m/s on my low tune and don't hear an ounce of noise even at high levels.

Here are the three winisd files for you low, mid and high tunes with varied input and hpf settings to keep you within xmax.

Low tune: 650 watts input power. Max velocity 40 m/s
Mid tune: 1000 watts input power. Max velocity 34 m/s
High tune: 1200 watts input power. Max velocity 30 m/s

You could leave the high tune at 1000 watts as it won't make that much difference in spl.
 

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Discussion Starter · #10 ·
I would be tempted to use the low tune option except it says 650 watts compared to 1000 watts if tuned to 16 hz. Where do the max watts figures come from? Can the 13 hz tuned box run at 1000 watts? I think the Reckhorn is able to adjust down to 14 hz, but would have to look that up?
 

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A 13hz tune would require a different length port of around 18 inches long. To keep excursion in check the input power will vary with different tunings. I can't find a manual any where for the Tapco 2500. It says 2500 watts into 4 ohms bridged and 750 watts into 4 ohms stereo but that doesn't say whether it is RMS or Peak power.
 

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Discussion Starter · #13 ·
I just reviewed my Tapco manual. Duh! I thought I could drive 2 ohm loads with this amp, and I can, just not in bridged mono.

I have now rehooked up to one channel only which should safely drive 2 ohm loads. The volume is way down now from what I had been doing.

In bridged mono that amp may have been 5000 watts into 2 ohms?

So the power handling specs are derived from xmax and box specs. I am getting old. I knew that 3 years ago but have forgotten some of that now. Must relearn.
 

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Discussion Starter · #15 ·
Thanks Mike.
I needed a sub bad and the only one available was a bit different. They had parts available to build a 2 ohm IXL
I can only assume over the years they have manufactured many custom configurations. They specifically asked me if my amp could drive 2 ohm loads and I checked it out and said yes. I did not happen to see 2 ohm is not recommended in bridged mono mode, which was my default hookup.
 

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Discussion Starter · #17 ·
One channel specs out as 1400 watts "Continuous Sine Wave Average Output Power, per channel, both channels driven"

This is according to the Mackie FR Series 2500 manual, which I have handy now. (mine is a Tapco)
 
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