Questions for my Project (sound deadening, subwoofer enclosure design)

[blacknteal831]

Well, I'm about ready to start putting together my sound system in my truck, just gotta order my wire and waiting for some stuff to get in stock with Resonix and Parts Express. I do have a couple loose ends I'm trying to solve as I wait on the last of my purchases.

Mainly, I'm trying to decide how much sound deadening I should be doing in my truck, and have some questions about my subwoofer enclosure.

So I've been messing around with WinISD some more and gotten the hang of it mostly (had problems at first with putting in too many T/S specs and getting bad driver data at first).

I'm building a ported enclosure of some sort for my Alpine S-W10D4, and per previous recommendations was looking at putting it in a 1.2 net enclosure and tuning it low, around 32 Hz. The only thing that has hung me up some is the design of the enclosure.

Using a few calculators online, with my 550W amp and the size enclosure I'm using, I need at least 14in² of port area minimum, with an optimal around 21 sq in, so larger than a 4" port. Even a 4" port needs about 25" of port length, plus space on the open end. I could build a long but shallow box to fit the 4" aero port, but using a proper sized port (4.25 ID for the 14 sq inches) starts making the box too long without at least one bend in the pipe (and the larger diameters with ports would also require a deeper box as well, throwing off the space provided). A 4" port would definitely be too small for this enclosure, correct?

Going with the idea the 4" port will be too small, this kind of has me thinking a round port would be out, which I thought eliminated me building the box myself. I haven't done a real woodworking project in years, so don't have a lot of confidence in building a slot ported box properly (or if I did, I'm not sure about my time invested vs cost to buy).

However, looking around I came across passive radiators (again, kinda new to the whole audio world) and started messing around with plotting those in WinISD. The biggest benefit would be that I could build the box myself no problem. Unfortunately, it seems like a large number of PR's are designed for enclosure/sub combos that don't match up with mine very well. I had some ok plots with two 10" passives, but there was a significant drop off compared to the sub in a ported box. The one I found that would work best is a PSI 15" Passive with ~400g of mass added to the cone, though I did have to adjust the box size to accommodate the PR and sub (15.5x15.5x13" interior measurements to fit the drivers on opposite sides of the box). Here's the plots I came up with:

Passive Radiator Enclosure (Red) vs Ported Enclosure (Green)


Given I am quite new at all of this, I can tell that the plots of course are mostly similar, with a bigger bump in the 30's with the PR. But I have very little experience determining what this actually means, and if it would be bad for my desired setup (mostly SQ). If it was a problem, would a DSP be able to adjust the signal enough to fix that?

Also, I haven't been able to figure out how to plot much beyond that graph and port velocity. Anything I should be concerned with like sub xmax with either box? Also, the Dayton DSP is out of stock until late July, and depending on my order from Resonix, I would have everything I need to install the project minus the DSP by the middle of next month. How essential would a subsonic filter be for either enclosure? (my mono amp doesn't have a HPF/subsonic crossover on it, didn't worry about it given the plan for a DSP) I'd plan to install it once I got it, but I'm excited to start getting my sound system installed already by just running high level signals to both amps, but don't want to mess something up by not having the subsonic filter.

And finally, speaking of sound deadening, I do have a question concerning my doors. I don't plan to leave the rear speakers in my 2017 F150 Supercab hooked up, but should I still plan on sound deadening the rear doors? They are quite small, so I wouldn't have too much to do, but is it worth is still? I'm thinking at least some dampening material on the outer and inner skins and CCF to decouple the door card, but not as extensive as my front doors. I am planning on some dampening material along the back wall as well, but don't really plan to get under the seats or on the roof at this time.

Sorry for the scattershot of ideas and questions, and thanks for all the help!

[lithium]

4" port with a 90* elbow will be fine (just measure the elbow length along the center line of the bend). Heck, you could have some part of the port external to the enclosure if you like, just correctly calc your net volume. Remember the port can terminate on any side of the enclosure as long as it isn't blocked.

The extra cost for the PR is only worth it if you really need to decrease the gross volume of the enclosure.

The door w/o a speaker installed would benefit somewhat with some deadening. a barrier product to reduce road noise (assuming you're doing the other doors) might be worth it. Personally, I would just do some CLD and CCF and see how it sounds.

If you do not have a hpf or subsonic on a ported box because with playing below tuning. Plot cone excursion to see why.

[mikeyt]

You can use two round ports if you need to. I used www.mobileinformationlabs.com to figure mine out. You load in all the specs and it'll give you what you need. I wanted a "small" big box. I made a 2.5ft3 box that wanted to go along the back seat angle of my daughters' 2001 4runner. It has cargo space but I didn't want to take up all the room so I made a modified wedge to make that happen which moved it towards the front using the back seat angle to do that. So then I had tat shallow box problem for porting purposes. After going on that website I was able to play around with using two ports trying different sizes to give me the length I needed. And I did what lithium said. I used PVC with elbows and turned them to fit.

[Grinder]

Op, if the peak vent velocity result for the 4" port (12.56 in^2) at 550W is as high as ~40 m/s, that will probably be fine in terms of audible port noise/chuffing through an adequately flared port (such as this: https://www.parts-express.com/precis...e-kit--268-352 ), particularly to the extent you're not using every last bit of the available 550W. While the rule of thumb is 22 m/s or less in terms of minimizing vent compression for maximum output, vent compression won't matter to the extent you're not using every last bit of the available 550W.

While I'm no expert (but reasonably well versed in WinISD), both response plots look fine to me, and are equally well within the range of correction with DSP. However, modeling can tell you only so much; and then everything changes when you put the box in the car.

I wouldn't worry too much about running without SSF/HPF while you await your DSP. Just be conservative with the volume control. For additional peace of mind, you might for example run low volume sweeps while observing excursion, and then gradually turn up the volume to give you an idea how far you can safely push it before excursion begins to get crazy.

[blacknteal831]

Alright, so I'd been using Triticum's Improved Port Area Calculator to get the numbers I was using, hence the minimum of 4.25 inches (he has a maximum of 32 m/s for flared ports), I think it stayed under 40 m/s with a 4" according to WinISD so that brings a port back as an option to consider then. I'll have to mess around with the designers to see what I can mock up to fit both the flared port and fit where I'm thinking. I figured one 90 wouldn't be a problem, it's just even longer lengths would need more than a single bend in the port to fit. And I know the plots are only so useful, but it at least gives some comparisons. Plus I think it was pretty useful to compare different PR's, some of them clearly are designed for subs that are vastly different than mine/this application.

And it's not that space is at an extreme premium, but the less room the box would take up, the better. The truck is used to get all my stuff and tools to and from work, so a smaller size of course leaves me more room for the trucks primary purpose. Besides, I gotta imagine it'd be a wash in cost of building my own box using a PR vs paying someone to build a slot ported box for me, so cost wasn't as much of a consideration there. A flared port box I build myself would be the cheapest option for sure, so I'm going to play around and model some boxes up with that in mind.

As far as deadening and sound proofing goes, I probably don't plan to go all out with MLV or anything like that at this time. I plan to really deaden my front doors on both the inner and outer skins, get some CLD on the back wall and rear doors, and to feed a length of 3/8" surgical tubing through the weather stripping around my door seal. They let in a lot of wind noise, to the point it sounds like my window is barely cracked open at times. Unfortunately it seems to be a well known problem with the F150's, but that's a pretty easy fix at least. I don't have the desire to take out my headliner on my own at all to install MLV, or pulling apart the rest of the interior to do the floor pan. So I figure it isn't worth doing the doors either if I'm not doing the rest of the car.

And I had read about ported boxes having a problem with playing below tuning, hence the need for a SSF. But that's what I was thinking, if I don't push the volume, I'd hope it would be ok. The reality is I'm excited and *might* be able to get it all installed before I'd get the DSP, but that is not set in stone with my work schedule always being in flux. Good to know I can get it going if I have the time as long as I'm cautious though.

Thanks everyone!

[Grinder]

Yeah, Triticum's Improved Port Area Calculator is a great tool, but as I assume you know, is not intended to be more than a better rough guide than some earlier methods and/or rules of thumb. If if you're below 40 m/s in WinISD, I think you'll be fine in terms of vent noise through one of those Precision Ports.

Apologies for stating the obvious, that modeling can only tell you so much. All I meant was that the in-cabin response would likely require greater correction than the modeled anechoic response, so don't worry too much about correcting one or the other of those two quite reasonable response curves.

I'd be even further out of my depth commenting on deadening, so I'll leave that to others.

Good luck with the build. Let us know how it goes.