Need WinISD help for my first cab design - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 11 Old 06-13-2019, 11:32 AM - Thread Starter
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Need WinISD help for my first cab design

I've been looking around for a single 12" cab for PA use with the following perks:
- less than 50lbs
- high power density (125db @1m half space with two cabs)
- F3 of 35Hz or lower
- passive cab
- Less than 500€/600$ total cost for DIY
- Parts available in Germany

I even had a hard time trying to find a commercial solution like this, but was planning to DIY anyways.

I decided to go with the B&C 12BG100 because of its high power handling, Xmax of 10.5mm and good performance in a small cab (and because I'm very happy with my two 21DS115's). If you know of a better driver for that application let me know!

I simulated a vented 50l cab with 35Hz tune, which gave me an F3 of just below 33Hz after dsp. Output is excursion limited, but the cab reaches 117db (1m full space in WinISD, I guess?), which would equal to 129db half space with two cabs stacked. Excellent!
There is also an efficiency (?) maximum around 60Hz, which is great since that's usually the best punchy frequency for a kick drum.

Here are the graphs and the filters applied:



Looking good to me, but as I said, this is the first time I've ever used WinISD so please point out the mistakes if I made any!


So now to my question: I have no clue about air velocity and port design, except that a flared port can reduce port noise, too much displacement can cause chuffing and that there is port compression.

Here is the air velocity graph; the port dimensions are chosen this way because I want the cab to have a slot port at the side (front firing), utilizing the full height of the cab (easier to build). 40m/s seems pretty high to me, but it's at the very bottom of what the cap will be capable of. It'll be used for some EDM DJ stuff (at weddings) occasionally, which is why I'm going for quite a 'low' tuning for music (for a 12" for PA application at least).

Also, the port seems pretty long to me with 43cm. Running the port that long would either require running it along the rear wall as well or a ~50cm deep cab, which wouldn't be that bad.
I might also increase the port dimensions and run it a little longer, as a 3cm wide port seems pretty small to me. What impact does folding the port have? Is my data correct? Does this make sense



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Last edited by peniku8; 06-13-2019 at 11:38 AM.
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post #2 of 11 Old 06-13-2019, 12:07 PM
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You should have posted this in the DIY section. Anyways, the 117 dB is at 1 meter, if compared to a sub at data-bass you would subtract 6 dB. Basically two would net you 117 dB at DB. Inside it would be louder depending on gain. Port velocity varies IMHO, higher velocity can give you chuffing but only at the extremes of the subs. If you push these to max then you would hear the chuffing sounds. It all depends on the room and how loud you plan to run them.

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post #3 of 11 Old 06-13-2019, 03:26 PM - Thread Starter
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Quote:
Originally Posted by MKtheater View Post
You should have posted this in the DIY section. Anyways, the 117 dB is at 1 meter, if compared to a sub at data-bass you would subtract 6 dB. Basically two would net you 117 dB at DB. Inside it would be louder depending on gain. Port velocity varies IMHO, higher velocity can give you chuffing but only at the extremes of the subs. If you push these to max then you would hear the chuffing sounds. It all depends on the room and how loud you plan to run them.
So you're saying WinISD shows 1m half space, rather than full space, thanks!

I'll try to reach a mod to move this to the other topic.

The goal of this cab is to get the most bass from a cab that a single person can handle easily, with stated extension.
I guess I'll have to test the cab for issues with air velocity. If theres a problem I can raise the HPF a little.

How accurate is this model in WinISD? Should I build a prototype or is it pretty reliable?

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post #4 of 11 Old 06-15-2019, 08:36 AM - Thread Starter
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Alright, got it moved over to the DIY section.
How are you guys approaching a new cab design? Build a prototype from MDF and tweak until you can build your final cab with BB ply? Or just trust the simulation?
I fooled around a little with different designs plus signal shaping, but they're all excursion limited at around 49Hz with 117db. The current cab would be perfect if the driver had an xmax of 19mm.
Another question: I'm planning to mount two handles to the sides, of which one will block parts of the port (not by much thou). Could that cause any issues?
Also, I want to cover the entire front (including the port) with a grille. How much space should I leave from the port opening to the grille? I was planning to do about 1" of clearance also for the driver.

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post #5 of 11 Old 06-15-2019, 09:19 PM
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You probably need to go with a horn design or larger than 12" drivers to meet your goal.
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post #6 of 11 Old 06-16-2019, 07:40 AM - Thread Starter
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Quote:
Originally Posted by K9woofer View Post
You probably need to go with a horn design or larger than 12" drivers to meet your goal.

Quote:
Originally Posted by peniku8 View Post
The goal of this cab is to get the most bass from a cab that a single person can handle easily, with stated extension.


I don't know how you're built, but I can't easily handle a 15" horn

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post #7 of 11 Old 06-16-2019, 09:11 AM - Thread Starter
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Here is what the cab would look like:




The braces at the front are for a grille. The holes for handles and connectors.
I solved the problem with the handle in the port with this redesign. The port area with the handle is now unused and a waste of space. Making it part of the back chamber would not improve the overall response and this way I don't have to seal the handle so tightly.


Q1: Should I break the port corner into two 45° corners, without squeezing the port, or is that lost effort?
Q2: I'm building this with 15mm BB ply, would I even need much bracing in the cab? It's not big, the largest section would be around 35cm unbraced.

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post #8 of 11 Old 06-17-2019, 09:02 AM - Thread Starter
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Added some minimalistic bracing and port corners:



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post #9 of 11 Old 06-17-2019, 11:43 AM
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I'd brace the port top panel to the panel with the circular hole in the right hand image. That will do more than the corner braces and wouldn't weigh any more.
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Last edited by scottvalentin; 06-17-2019 at 11:50 AM.
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post #10 of 11 Old 06-17-2019, 11:55 AM - Thread Starter
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Quote:
Originally Posted by scottvalentin View Post
I'd brace the port top panel to the panel with the circular hole in the right hand image. That will do more than the corner braces and wouldn't weigh any more.

At first I thought that it's not possible, because there is a small wooden base plate (for the M20 mount plate) in the center of the top (see the transparent parts in the left image), but it would be easy making the plate go across the entire top, thus acting as brace. Seems like a good idea to me!


Edit: I think you were talking about having the braces away from the top and bottom, more like on the 1/3 positions. Don't really think that's needed along with the other bracing. The cab is just a 12" cab after all.

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Last edited by peniku8; 06-17-2019 at 12:28 PM.
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post #11 of 11 Old 06-17-2019, 12:25 PM - Thread Starter
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