Help with slot port

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Hi, Everyone.

Can someone help with me a slot port design for this driver? Dayton Audio RSS390HO-4 15" Reference HO Subwoofer 4 Ohm

I'm going to be putting it in a vented cabinet that has inside dimensions of 17*21*15 which renders just above 3.0cf. Would like to know how much volume the slot port needs to be, I'm thinking 2 or 3" tall. I just don't know how wide or deep to make it? Is there a port volume calculator I should be looking at?
 
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Just doing some basic calculations. That 15" in 90 liters is not the best choice, at least not for BR. If you got power to waste, make it a sealed box instead.

If this volume is your restriction and you want a proper BR box, better choose the RSS315HF-4 12".
If you have your heart set on the RSS390HO-4 15", and want to make a more optimal BR box for it, it's going to need some space.

Would it work for you if you made it your stereo bench? I went that route at a point in time, the mrs. complained when I had to change it out for my next step, she liked the dark brown silk matte wood finish, and all the wires and clutter was hidden behind it.
 
I think I'm Ok with the outside dimensions of 19" x 23" x 17" deep if you want to work something up based on that. Would be 1" cherry braced with plywood on the inside. Slot port I was doing was 1" high by 13" deep, and like a trangle 17" wide on the outside 9" wide on the inside all rounded edges to reduce port turbulance.
 
The materials and what you are planning to do in terms of work sounds very good.

But the simulated result should dictate the actual plan, how you put the box together.
Have you tried running any simulations in software at all?

I really suggest that you seriously consider using two subs utilizing a single 12"/each.

It is a bit difficult to make a proper box for this 15", if you decide to push it hard and run 700watts of power through it, you get to reach xmax on a slightly larger box (29" x 17" x 19") than what you suggested, but to make it work properly in that small-ish box, you have to use a smaller than optimal port to get the tuning frequency lower, to get a proper frequency response, which again results in a rather high air speed in the port (54,7 m/sec). You do have the possibility to reduce this to 25,5 m/sec by adding a 27hz 4th order high pass filter (still a little bit higher than optimal, but I am counting on the actual slot port adding resistance to the flow so actual air speed will be a little bit lower), but then you are wasting the potential of this driver, and would be better off choosing something different. In addition to wasting potential you will add group delay with a filter, but most of it will be below 30hz, so it's not a huge problem.

Without a HP filter, you can push maybe 150 (real) watts into it before chuffing/air speed becomes an issue, you will then reach a maximal excursion of 7,6mm on 30hz (pure sine). It is a serious waste of potential if you want to avoid using a filter.

If you want a small box for that 15", make it sealed, and use some power to make up for it with eq. Again, not a perfect solution, but you can not have everything at the same time.

It may be that my personal preferences are too strict, but I would choose something else for my project, either a different driver, or a different box type (IE NOT a BR), given your size constraints.
 
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Thanks for the tips. I already have these drivers so that’s why I chose them. Question, why does the wattage need to be so high? I’ve run simulations and they don’t seem to be as bad as you’ve come up with. I get over 100db with a lower wattage and don’t drive the driver near xmax or have too high velocity through the port. I’m using term lab. I didn’t plan on pushing 700w through this as all.

What kind of DB would you expect out of your box simulation? Let me know so I can run some based on the DB you would want and we can compare notes. 150db result isn’t realistic to me that’s too loud IMO.

Again thanks for all of the tip. Also it’s worth noting I’ll be using two of these, in separate boxes, so that gives me some more SPL to work with as well. I believe it’s +6db with each additional driver. I need this driver to handle 180hz and below to work well with my open baffle setup which I’m using two 12” facial pro woofers handling 180hz - to about 2k and two ESS AMTs doing 800 and up. The overlap sounds unbelievable fyi
 
Allright, if you allready have them it's another story. I still do not understand why you chose these but that's not relevant.
And from what you are saying you are not really interested in pushing them at all.

You'll get 110db unfiltered at 150watts in a 151 liter BR, I would probably use a simple 12db/oct LP filter up top. Behaves well to ca 300hz, cross below this. (Only because of the cone construction and material)

Have a look at this sim and see if it's interesting.
FYI I think there will be no bump below 30hz because of the resistive behaviour of the slot port, it will probably just be flat-ish and roll off slow from 22hz down in-room.
 

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If you want you can post desired dimensions here, and I can run the numbers in hornresp, and check how it will work out.
Do you want a finished calculation, or do you want to figure it all out yourself?

For 150L Im getting a slot port of 2" tall by 17" wide by 18" deep. Think that's ok?

Also, when I kick the box down to 3L I get the following curve response. The 90L vs the 150L I can't seem to see much benefit of making the box bigger. I feel to receive a real benefit I have to make the box MUCH bigger than 150L which I just don't have space for.

Do me a favor, take look at these and tell me what you think. It's what I get in Term-Lab at 30w vs. what I get with 30w with 150L.

Do you think my software is off or I'm doing something wrong? Are you just looking to keep that 30hz up? Would I be able to baffle step correct my smaller box to work? I don't think I'll run more than 100w through this. I just need it to sound big enough to fill a room that's 25ft x 25ft.

Thanks for all of your help.

Note, I am looking for a flat response! So I'm not necessarily in search of a bass bump however, don't mind one.

Pics attached.
 

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Yes, the 90 liter sealed box with some eq is better for this particular driver. It can take quite a beating, get some TPA3255 maybe in PBTL if you're up for it.

I think your 3 liter box with 27hz tuning is quite amusing.

Edit:
A 15" is a bit much for a 90 liter box, a 12" would have flatter response.
 
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