Planning Another twin floor standing Subwoofer build - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 25 Old 08-24-16, 04:44 AM Thread Starter
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Re: Planning Another twin floor standing Subwoofer build

Well thanks all the same. I guess I'll have to continue with my simulated ported plan. It seems to be the best that can be done with these drivers in the circumstance. If there is no improvement to be suggested to the build plan in my first post then I'm good to go. By the way I mistyped the room volume in that post, it was meant to read 4500cuft.

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post #12 of 25 Old 08-24-16, 11:05 PM
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Re: Planning Another twin floor standing Subwoofer build

What are you simulating with, winisd? Can you post your driver and project files? I could take a look, but it sounds like you have the original design already pretty well set.


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post #13 of 25 Old 08-25-16, 12:57 AM Thread Starter
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Re: Planning Another twin floor standing Subwoofer build

Yes please. WinISD, the files are attached in my starting post.

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post #14 of 25 Old 08-25-16, 11:50 PM
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Re: Planning Another twin floor standing Subwoofer build

Sorry, I missed your files in the first post!

Excursion and air velocity look good.

I suggest you use "simulate voice coil inductance" and "use transmission line model for port design" in the advanced options, but either make a negligible impact to your design so I think you're good to go. You'll see the port resonance is fairly significant, but your 4th order 80 Hz LPF is what's keeping it nice. With the oblong design you might be able to dampen some of the t-line resonance effects with a pillow or some other dense fill at either the top or bottom of the tower.


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post #15 of 25 Old 08-26-16, 06:08 AM Thread Starter
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Re: Planning Another twin floor standing Subwoofer build

Thanks for the input. I'm happy to finally be having a discussion on the substance of this project. I had tried those advanced settings but found like you did that they didn't make a profound difference to the FR. However I still need to understand the principle and practical implications of the simulate voice coil inductance and transmission line settings if you could kindly explain. I know I'm treading a fine line with first port resonance but If you noticed in my first post the port length is considerably shorter than WinISD simulated. Much reading made me realise that WinISD tends to give a longer port length than required for a narrow boundary slot port so I rather used http://www.mobileinformationlabs.com...0lenth%201.htm for port simulation. Hopefully this together with polyfill Stuffing should get me to the envisaged tuning. This should now bring first port resonance to about 132+ hz. About the pillow, is it to combat tall cabinet air resonance or are you thinking of long panel resonance? Will the pillow still go in together with the polyfill?

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post #16 of 25 Old 08-26-16, 07:34 PM
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Re: Planning Another twin floor standing Subwoofer build

As far as I understand it, very tall or oblong cabinets start to behave less colorless and more like t-lines. The extra fill would dampen the resonant effect inside the cabinet and help it to not taint the real-world FR. It would probably also impact your final port tuning, as will the fill you've mentioned.

I've also found that smaller ports than winISD predicts provide the intended tuning, or the winISD prediction turns out being tuned lower once constructed.

The t-line model for the port adds the port resonances to the FR plots so you can see them too. I find that a very helpful reminder. I also tell myself that it's doing a more advanced calculation based on the port geometry, in some designs I have noticed a change to the shape of the FR (port's contribution) by enabling this option.


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post #17 of 25 Old 08-27-16, 11:43 AM Thread Starter
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Re: Planning Another twin floor standing Subwoofer build

Ok so for panel resonance in a long cabinet it will be okay to use horizontal bracings in the acoustic space like in this attached image?
For enclosure standing waves what about a dense layer of foam 1 inch thick glued to both top and bottom of the acoustic space in addition to polyfill?

What I worry most about is the long back panel forming the rear wall of the slot port which in most designs has no bracing. This is 38" long bringing the panel resonance within Subwoofer frequencies. I'm thinking this can be attenuated by asymmetrically placed short dowels in the height of the port all through the length of port.

Also this simulate voice coil inductance, does it represent the practical FR differences in drivers with significantly high vs low Le.?
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Planning Another twin floor standing Subwoofer build-rps20160119_211432.jpg  


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post #18 of 25 Old 08-27-16, 12:13 PM
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Re: Planning Another twin floor standing Subwoofer build

I assume it factors in Le, yeah... beyond that I'm not sure how it's implemented. Basic t/s params don't include Le so to have it included makes more sense for accuracy.

Yeah, just use some dowels. Very easy to glue in.


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post #19 of 25 Old 08-27-16, 03:50 PM Thread Starter
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Re: Planning Another twin floor standing Subwoofer build

Thanks a lot. About the amp I find that clip lights come on during loud low LFE passages. This I suppose is because of eq and signal chain gain which though it gives me what I want but is a bit too much for the amp in stereo mode. I see that I could connect both of my existing subs in a 2 ohms bridged configuration which I hear is not advisable? It does look like the subs demand more power than anticipated. Keep in mind the amp is rated at 600 watts stereo @ 4 ohms and the drivers 650 watts rms (though 300-350 in box as per simulated apparent amplifier load power). With these two new subs I'm planning, I could perhaps connect the quad subs bridged @ 4 ohms (1800 watts total) or look for another amp for the two new ones...... your thoughts?

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post #20 of 25 Old 08-27-16, 07:45 PM
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Re: Planning Another twin floor standing Subwoofer build

The driver rms watts means very little, since the excursion can vastly exceed xmax with a fraction of the rated rms power.

Using EQ above 0dB costs a LOT of amp power. Using EQ of negative gain, say -3dB at 77Hz, is free since it doesn't take extra amp power. This is more in regards to the in-room response once you get once the sub is finished, however. REW has prediction capability but in-room measurements are gold.


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