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Discussion Starter #1 (Edited)
Okay so after much hopefully useful cerebral activity, I have decided am going to do another pair of floor standing subs almost identical to the ones I did and posted on this thread in another forum. http://forums.audioholics.com/forums/threads/twin-tall-floor-standing-12-inch-subwoofer-build.97538/. My goals are moderate sub20hz extension at a moderate spl in a moderately small enclosure. My subs are same as I used in the previous build (and still have are a pair of)12 inch Epik sentinel drivers. Typically they achieve good sub20hz extension in small enclosures. I have attached the driver data and WinISD Sim files. Essentially this is a 3(net)cuft ported enclosure tuned to 18hz. Previously I used twin flared round ports and tuned to 19hz but I plan to get a longer, wider port by doing a slot port and this will increase the enclosure depth, hence the difference from the Previn ious twins. It will be 39.5 inches tall(minus feet), 14.5"W and 17"D. The slot will be bottom of baffle beneath the driver, and 13"W, 1.75"H and 51.625" deep, folding off of the bottom, up to the upper end of the back. It will have top, bottom and horizontal bracings in the net space, supporting the front and lower port walls, as well as small port bracings to combat back and bottom panel resonance. The port ends will be flared as extensively as is feasible, as well as curving the port edges at the port folding. Now I realize from previous critiques that this driver gets the best power handling in a significantly smaller box but from experience with the subs I have been using and from WinISD simulations, it forgoes 50%of its power handling in exchange for increased sub20hz spl/extension in this enclosure design. This appears to be because of its high Xmax and in spite of its very low Qts. In this design the allowable excursion limit is reached at 800 watts/12.5Hz with a 2nd order 14hz HPF. The apparent amplifier power load at that point however is 400 watts. So although the driver is designed for boxes less than 2cuft, it still appears safe in this design volume because of its large Xmax. The box baffle will be doubled (1.5")and the inner port wall will be of 0 . 5 " thickness to conserve internal volume. The feet will four rubber discs and it will be finished in matte black.
I intend to run the four subs with qsc rmx1850hd, two per channel stereo in a 2ohm connection. I hope to get 350-400watts per sub in view of the apparent amp power load simulated. I expect to use them in a 400 cuft sitting room open to an adjoining dining room. So this is what I have come up with, what do you guys think about this before I start building?
 

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Looks great! Glad to see you designed for HPF, power, and excursion.
 

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I can't effectively model subwoofer designs, so I'm not able to help you in that area, but I did have a few questions...

Are those pictures of the current subwoofers? And if so, what are they not giving you? It sounds like you want to essentially duplicate them, so I'm curious as to why go through all that work to end up back at what seems like the starting point.
 

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Discussion Starter #4 (Edited)
Thanks for the encouragement. I hope to have the pleasure of getting up to 110 db of 16hz from the quad subs with this minimalist footprint approach. Relatively unobtrusive physical sub presence. This driver is truly incredible, I wish I had more. Check out what appears to be an IB build with this driver
 

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Discussion Starter #5
Jim this is a very salient question. Truth to tell,I love the two I have dearly, SQwise I have no complaints. Where I am its really difficult to lay hands on good sub drivers so when I feel the upgrade itch, I naturally turn to drivers I already have. In doing this build I hope to achieve (1) scratching the upgrade itch. (2) get a potential 6db up on the entire FR especially in the sub20s without a difficult-to-blend bulky sitting room presence as well as better room coverage. (3) bury the chuffing I hear sometimes from my subs during intense LFE with fresh additional similar subs having larger ports/lower port airspeed as well as slightly more low extension. With the new subs the 3db FR range should be about 17.5 - 80hz anechoic.
 

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Discussion Starter #6
What I am not very sure of is whether the qsc rmx1850hd has enough power to run the quad subs. Am I correct in assuming that the apparent amplifier load power is in practice the power handling limit of each of these subs inside the proposed enclosure. In other words is the apparent amplifier load power the excursion limit while the Rms power the thermal limit?
 

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Excursion shows you what the sub must be able to take, xmax and xmech, also with the power reference below its RMS thermal rating.

Apparent amp load in VA shows you what your amplifier must sup ply, generally if it's higher than bench tested power then you can expect clipping and should plan for a bigger amp.

In all cases build and try it out if it's close or so. If everything's all in the clear then it will be monster setup....
 

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Discussion Starter #9
Sorry for the late reply. Please Russ if you are good with tapped horns and Hornresp I would appreciate it if you can simulate with this driver a tapped horn that has good output down to 10 hz, (I have no clue how to do this) I'm willing to abandon this design in favor of that. Thanks for the offer. That should be a real upgrade.
 

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Figures! I don't have any experience with horns and have only played with Hornresp...
 

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Discussion Starter #11
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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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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Discussion Starter #13
Yes please. WinISD, the files are attached in my starting post.
 

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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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Discussion Starter #15
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/HowTo-1Woofer-Box-CAL Port lenth 1.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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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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Discussion Starter #17
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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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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Discussion Starter #19
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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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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