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Discussion Starter #1 (Edited)
Hi everyone. I've been reading through many of the threads and have really enjoyed getting very confused and overwhelmed with the information. That said, I obviously have no past knowledge of the technical area of home audio. I figure that the best way to learn is dive in and actually do it.

Since my basement 5.1 system is missing the .1, the plan is to build one of these LLT's. I am leaning towards the IXL 18.2.2 powered by the ep2500. Seems like a popular choice. With these components in mind, I have downloaded WinISD to try and model the driver. Asaserfi's tutorial was a great resource to start with. So I loaded on the information in WinISD and wanted to make sure I have not missed anything or made any errors. I cannot post pics yet so I'll just give the information I inputted on each tab.

DRIVER: downloaded parameters from this site.

BOX: Volume: 400 liters, Tuning Freq: 15 Hz

VENTS: Number 1, shape: circle, diameter 8.00 in - The following were calc'd by the program- Vent length: 35.64 in, 1st port resonance: 189.83 Hz

PLOT: kept default settings

SIGNAL: Input Power: 500W, Series resistance 2.00 ohm (not really sure if I should have changed this from the default of 0.1 ohm)

EQ/Filter - none

Are these inputs correct? What do I need to change? Should I be increasing the power input since the ep2500 puts out more power? Anything else come to mind that I need to change?


On to the graphs. With these inputs the graphs show these results:

Transfer Function Magnitude: Graph arcs up to +1 dB around 30 Hz and starts to roll off around 25 Hz and passing 0 round 18 Hz.

SPL - around 113 dB at 20 Hz.

Cone Excursion: Peaks up around 22 Hz and exceeds Xmax around 13 Hz

Port Velocity: Peaks around 12 Hz at 20.446 m/s.

Is there anything wrong with these graphs? Please let me know if you have any suggestions on how to improve this setup.

Thanks for helping me learn WinISD!!!!!!
John
 

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Leave the Series resistance at default and increase the input power to 750 watts.

You can downsize a bit if you want. 350 liters tuned to 15 hz. Input power of 800 watts. One 8 inch vent 42 inches long. Airspeed will be 24 m/s. Spl 115 db at 20 hz.

WinISD states the net volume required for the cabinet volume. You have to add the displacement of the sub, port and bracing to the net volume to get the internal volume of the cabinet.
 

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Discussion Starter #3
Thanks Mike!

I'll make these changes and then try modeling it with specs you provided to see how the graphs differ.

Am I understanding you correctly, the volume that is inputted in WinISD is net volume after the reduction of the bracing, driver, port. So if the volume of the empty box is 400L and the total of the bracing, driver and port is say 50L when I should input 350L in WinISD. Correct or do I have this backwards? My apologies for my ignorance in this.

We could always pass on these formalities and you could just send my one of the IXL's that you built (hahahaha). I really enjoy the diy aspect of the build and prefer to learn as I go.

Thanks
John
 

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You have it right. If you are modeling 400 liters, you can add the displacement of the port , sub and bracing (say 50 liters) to that to get the internal volume of the cabinet you need to build. (450 liters) Or as you said, subtract the 50 liters and remodel at 350 liters. The port length will change with the smaller cabinet volume.
 

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Discussion Starter #6
Thanks Mike / Fred.

Do you know of any builds I could follow using the 350L tuned to 15Hz? I was looking at the IXL 18 Easy Button by NeoDan and was wondering if it would be OK to change the port to 8 in x 37.30 in. I believe it would change the net box volume to approx 385L at 15Hz and appears to model very similar to the 350L at 15Hz. The only noticeable change I see is that the port resonance goes from 158.63Hz at 350L to 181.83Hz at 385L. Is this good or bad and why? Any downside in this setup?

Thanks
John
 

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Discussion Starter #8 (Edited)
Thanks for the links. I really like the idea of a down firing sub with two young kids and there friends always playing in the house.

I'm assuming all subs will need to be crossed over at 80hz to keep it from playing the higher frequencies. Since I'm planning to use the ep2500, does this mean that I will also need to run the signal through an external crossover? or can this be achieved with the receiver? My receiver is the Yamaha RX-V661. If I need an external crossover can you please recommend one.

One more question. What is the acceptable range (max m/s) for port air velocity?
 

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Discussion Starter #10
Great. Just ordered the ep2500 and will order the IXL 18 in a few weeks.

Once I get everything build and hooked up (more questions to come), I'll worry about how to get the Yamaha to crossover the signal to the sub at 80hz. Hopefully it does it automatically.

Mike - Thanks for all your help. I know my questions are pretty basic knowledge to most but I have to start somewhere.

John
 

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Discussion Starter #12
No external crossover needed, the Yamaha will do it. For port air velocity 26 m/s is the onset of port compression, but with program material it can go as high as 30 m/s without "chuffing". (port noise)

I'm a little confused on how to relate this to the port air velocity graph in WinISD. In the attached graph the air velocity exceeds the 26 m/s - 30 m/s range around 15hz at 800W. Would this indicate that around 15hz chuffing would occur? Is the goal to ensure that the graph does not exceed the 26 to 30 m/s range?

Edit: OK, it appears that I do not know how to post pics. I'll try posting it again after I read up on the how too.
 

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Discussion Starter #15 (Edited)
It arrived already. I ordered the ep2500 yesterday afternoon and it arrived today already. This amp is a lot bigger and heavier than I thought it would be. Now the excitement of the build is kicking in. Cannot wait to get the IXL 18 and build the box. Unfortunately it will have to wait until next month. Need to finish the L shaped computer desk that I am building for my wife.

 

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Discussion Starter #17
I was attempting to model myn's build that you provide the link to above. Figures from his thread.

Vb 13.34 cu ft - (I calculated to 377L, hopefully this is correct)
Total (excluding items displaced) 15 cu ft
Fb 14.48 hz (tuning freq)
F3 25.33 hz - (I'm not sure what this is)
3 4" x 34 Ports
No damping

Using input power of 800w. No filters/eq.

Are these the results that you are getting?
 

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Discussion Starter #19 (Edited)
Started playing around with with Google SketchUp and the enclosure volume calculator. Target design for the box is for a net volume of 350L tuned to 15hz. Let me know what you think. Is the bracing adequate? Any suggestions would be appreciated.

Specifics:
Overall dimensions: 49"L X 24"H X 25"D
Gross volume: 411.57 L (14.534 cu ft)
Net volume: approx 349 L (12.325 cu ft)
Port displacement: 1.303 cu ft
Drive displacement: .365 cu ft
Bracing displacement: .538 cu ft





 
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