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Cornscala Split Bass Bin Design


No.4
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@Edgar First of all thank you. I was able to get winISD running on my beater PC and do some modeling. I played around with different volumes and tuning frequencies until I was able to get a flat output up to around 70hz. The port cross section has remained the same but winISD calls for a shorter depth for the 120 liter cab. Different sized cabs especially larger ones model a little higher output down into the 50-60hz range but this is the difference between one or two db at most. Adjusting the tuning frequency based on port cross section and cab volume makes the most difference in output. I am reading up on tuning frequency and its real effect on how low the cab will go. So far my limited understanding is that the tuning frequency is basically where the driver and the port interact. frequencies where the port is moving more air and the cone is traveling less, versus frequencies where the cone is moving further to make up for the ports inability to move enough air. (I could have this totally upside down, so if anyone has a better explanation please share it). winISD is pretty easy to use too, although it took me a second to realize I could change the units of measurement from metric to standard etc by clicking on them. I did quite a bit of converting on phone before I realized it. oops.

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20 minutes ago, No.4 said:

 So far my limited understanding is that the tuning frequency is basically where the driver and the port interact. frequencies where the port is moving more air and the cone is traveling less, versus frequencies where the cone is moving further to make up for the ports inability to move enough air.

 

Above the tuning frequency, the cone motion dominates. At the tuning frequency, the cone motion is at a minimum and the port dominates. Below the tuning frequency, the cone and the port start to move out-of-phase, so they are fighting each other. This is the reason that it's a waste of effort to try to EQ a vented enclosure below its tuning frequency. All it does is waste power and increase distortion because of high cone excursion.

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image.thumb.png.598aad4e0c291ffe6e6b3056d3aafd53.png

 

I modeled several different options for tuning frequency. All at 4 cubic feet with a port cross section of 1.5" x 5"

light blue 36hz

red 38hz

green 40hz

dark blue 45hz

purple 48hz

More research is needed to decide if the goal is to tune the box as low as possible at the expense of a few db output, or to tune higher to attain a flatter response. My hunch is that tuning lower is where I want to be because we are talking about a few db of output lost.l 

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On 1/14/2022 at 3:38 PM, No.4 said:

Another member provided the rough measurements of the port. the center tube part is probably the most critical. 

1 1/2" x 5" x & 7 1/2" = 56.25 in.

This was measured from outside edge of each flare. the total length of the ports I am making are 7 1/2". Each end of the port will be 3/4" cut at 45 degrees to create the flare.

 

I searched all over for ports similar to those.  All i could find was round ports.   Too bad those port tubes couldn't be 3D printed.   Round ports just don't look as good as the rectangular klipsch port and they would be 4"x9" in a round port. 

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14 minutes ago, mopardave said:

I searched all over for ports similar to those.  All i could find was round ports.   Too bad those port tubes couldn't be 3D printed. 

https://www.subwoofer-builder.com/flares-rectangular.htm

https://www.stevemeadedesigns.com/board/topic/164631-how-to-big-flare-a-slot-port/

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29 minutes ago, mopardave said:

I searched all over for ports similar to those.  All i could find was round ports.   Too bad those port tubes couldn't be 3D printed.   Round ports just don't look as good as the rectangular klipsch port and they would be 4"x9" in a round port. 

Actually, i think i did the math wrong. Should be 4" port with radius squared= 2x2x3.15x4.5=56.7" volume.  

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20 hours ago, Edgar said:

Too bad these aren't a bit deeper.  They would work perfect.

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7 hours ago, Rolox said:

May I ask why you chose Kappa 15C woofers? They are fantastic in a folded horn but have very limited Xmax for a reflex box IMHO...

These have been sitting in the closet for two or more years now. If I recall when I purchased these they were considered a good fit for Cornscalas (I could be wrong, again this was a couple of years ago). I know there has been some discussion lately about these not being ideal as a replacement a Cornwall bin, but I am not really building a Cornwall bin anymore. Any loss in low frequency output will be supplemented with a sub or two.

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On ‎1‎/‎16‎/‎2022 at 7:45 AM, Edgar said:

@Edgar I have definitely gone down the rabbit hole in a quest to find more info in this subject. Unfortunately most of the information I have found is geared towards building subs, but I think it is still useful in this application. I am focusing more on a flat response down to the winISD recommended tuning frequency, than trying to force lower output out of this box and driver. I modeled using both the BB4/SBB4 and QB3 configurations. I arrived at the same results with both configurations. I achieved good results with a tuning frequency of 50hz and a box volume of 3.441 ft. This volume of 3.441 ftwas derived using internal dimensions of 26"H x 22.5"W x 12.5"D, then subtracting the rough volumes of the bracing, driver, networks and area consumed by the port. Port length was calculated to be 4.76"

image.thumb.png.acd5d29c4f95687b8013bdd4038740d3.png

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1 hour ago, No.4 said:

I achieved good results with a tuning frequency of 50hz and a box volume of 3.441 ft

 

Looks like a reasonable tune for that enclosure size. As they used to say, "It's not nice to fool Mother Nature." Tuning for extended LF response generally results in poorer transient response.

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17 hours ago, No.4 said:

These have been sitting in the closet for two or more years now. If I recall when I purchased these they were considered a good fit for Cornscalas (I could be wrong, again this was a couple of years ago). I know there has been some discussion lately about these not being ideal as a replacement a Cornwall bin, but I am not really building a Cornwall bin anymore. Any loss in low frequency output will be supplemented with a sub or two.

Well if you use subs, make sure to high-pass your Cornscalas - especially if you listen loud 😉 but otherwise it will probably sound very good!

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