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I’m modeling them in winisd and not sure if I’m doing something wrong but in a small 4ft cabinet, the optimal sealed size the ported cabinet 4ft also still performs better?
why would you put this drive in a sealed would it sound better ?I’ve read that the ported boxes need to be huge but winisd seems to be telling me ported is better at any size?
 

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I’m modeling them in winisd and not sure if I’m doing something wrong but in a small 4ft cabinet, the optimal sealed size the ported cabinet 4ft also still performs better?
why would you put this drive in a sealed would it sound better ?I’ve read that the ported boxes need to be huge but winisd seems to be telling me ported is better at any size?
Sure, until you actually build the thing. 4 cubic feet is without considering bracing, the actual displacement of the driver, or the volume that the port takes up inside the box. When you consider how large a port will need to be to keep the velocity down below 11 m/ second at full power input, it's going to require a larger box just to fit the port.

I'd recommend at least an 8" diameter round port for a 15" driver, and you will find with a low tune in a small box that this is a non-starter, due to it's length.

Either you must accept higher port air speed, tune lower, use a larger box, or move to a pair of passive radiators that are the same size as the cone or larger in diameter.


Forget what the 'default' box looks like that pops up in WinISD, or sticking to various old school alignments. I look at cone excursion, port velocity and impedance when designing a ported enclosure, along with a realistic voice coil temperature rise, and the maximum amount of power you plan on dumping into the enclosure.

Quick tip, if you place your cursor in a box in WinISD, you can use your up and down buttons to watch what happens in real time.
 

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I’m modeling them in winisd and not sure if I’m doing something wrong but in a small 4ft cabinet, the optimal sealed size the ported cabinet 4ft also still performs better?
why would you put this drive in a sealed would it sound better ?I’ve read that the ported boxes need to be huge but winisd seems to be telling me ported is better at any size?
No idea what your actual questions are as you didn't post your models, but I have a UM-15 in a ~4.3 cuft net sealed and it works well. Dual UM-12 opposed sealed in same size cab in opposite corner of room, smooth results across all listening postions.
 

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I’m modeling them in winisd and not sure if I’m doing something wrong but in a small 4ft cabinet, the optimal sealed size the ported cabinet 4ft also still performs better?
why would you put this drive in a sealed would it sound better ?I’ve read that the ported boxes need to be huge but winisd seems to be telling me ported is better at any size?
Define "performs better".

A ported box compare to a sealed box can:

1: Be the same size as a sealed box and have a lower F3 (but have a quicker rolloff below F3)
2: Be smaller than the sealed box with the same F3 (but quicker rolloff below F3)
3: Be larger than the sealed box and have a MUCH lower F3 (again, and quicker rolloff below F3).
4: Ports are usually inexpensive to implement and materials to make your own are readily available, slot ports are even easier.

Why not go ported all the time, every time?

1: Sharper knees in change of frequency response increases group delay.
2: Vent resonances are nasty, can be audible if not carefully designed around, and become more of a problem with long ports (read that: low tuned subs).
3: Ports get longer the lower you tune, the larger the port diameter, or the smaller the box. It can become impractical to fit a large enough diameter port to keep vent velocity (and chuffing/compression) down to reasonable levels without having a huge amount of port folded into the box or external.
4: If you're pushing things hard, you'll need DSP in the form of a high pass filter (HPF) to protect the driver from unloading below vent tuning. This isn't a big deal as nearly everyone has access to some form of DSP, or could for a couple hundred bucks, but it's another step that has to be taken.

Sealed is small, cheap, the rolloff often works nicely with room gain, doesn't need a HPF, and most importantly is pretty hard to screw up unless you really just make the thing way too small. Pretty much slap any box together with reasonable material that's within +/- 20% of your target box size and it'll likely sound reasonable. Try that cavalier attitude with a ported box and you're not going to be a happy Rhett 151.
 

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Why not go ported all the time, every time?
...
Sealed is small, cheap, the rolloff often works nicely with room gain, doesn't need a HPF, and most importantly is pretty hard to screw up unless you really just make the thing way too small. Pretty much slap any box together with reasonable material that's within +/- 20% of your target box size and it'll likely sound reasonable. Try that cavalier attitude with a ported box and you're not going to be a happy Rhett 151.
Couldn't have stated it better. All of my earlier boxes were ported because I wanted the highest output at the F3, but that comes at a cost. All except my VBSS variant are now sealed after many iterations with ported, and I am very pleased with them (you do need more power to get the lower output where you might want it though). They dig low, don't have the distortion my ported cabs had, etc.

Not saying ported don't have their place, but in my situation (non-dedicated spaces, suspended floor) sealed work much better for me.

In a no-holds-barred space I would be looking at Devastators though.
 

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Discussion Starter #6
Thanks for you help I am now Leaning to the sealed box the few dbs at f3 I don’t think is worth the effort especially if it will introduce more distortion.
More power to get down low ? I have a nx3000 amp this should be enough to push two um 15s low in sealed boxes, also you’re saying in the sealed box’s the mini dsp HD no longer necessary with the standard amp ?
 

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Common rule is that it will take 2-3 sealed subs to reach the same spl of a single, well designed, large vented sub. I had a pair of Dayton classic 15in subs down-firing in 4.5 cubic foot end tables on each end of my couch and they sounded pretty good but I never turned them up to their limits and the tactile response would have been largely the same if they had been sealed. I probably could have just made them sealed and saved a lot of time. It depends on what you actually "need". You will need more power around 20hz after you eq them though if you go sealed. As stated above, you have to keep an eye on other parameters, like xmax if you are pushing them at low frequencies. You get the most out of vented enclosures when you make them really big because you are increasing the efficiency at low frequencies. As they get smaller, they begin to model closer to sealed after you add in eq.

3097492
 

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I have a nx3000 amp this should be enough to push two um 15s low in sealed boxes, also you’re saying in the sealed box’s the mini dsp HD no longer necessary with the standard amp ?
You'll still want the minidsp for EQ if your NX3000 isn't the dsp version.

If your limitation is 4 cu. ft., I'd just do sealed. The big differences will be if you double that size for ported(8 cubes tuned to ~19 Hz, for example). You probably don't need a HP filter for ported in the 4 cubes with that amount of power, but if you did use one, that would further lessen the difference between those alignments.
 

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What kind of distortion?

Properly implemented (sufficient port size and HPF), ported has lower distortion from much lower excursion at the bottom end.
Yep. You don't have to prefer ported but you have to acknowledge they have some advantages. Lower distortion around tuning is one of them. Distortion and excursion are in bed with one another.
 

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What kind of distortion?

Properly implemented (sufficient port size and HPF), ported has lower distortion from much lower excursion at the bottom end.

Yep. You don't have to prefer ported but you have to acknowledge they have some advantages. Lower distortion around tuning is one of them. Distortion and excursion are in bed with one another.
Yeah, bad design trying to stuff the UM15 into a box too small, going for too low a tune. Probably a bad choice of words, the chuffing was considerable at higher levels.

The UMs just want bigger boxes, and I didn't have the space to do them properly. Sealed at that size, similar to OP's noted size, works well for this application (family room, not the main HT space).
 

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As others have said, a UM15 just needs a MUCH bigger box to get the most out of it when ported. My UM15 is in ~11cuft net and tuned to ~18hz. I'm getting ~14hz in-room response with 16hz LPF, ~16hz in-room with 18hz LPF (after making it bottom a couple of times with the lower LPF), and hit reference levels with a single sub. With ~4cuft, sealed, a lot of power, and DSP is absolutely the way to go.
 
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