Sealed vs. Ported Subwoofer Enclosures in Pro Audio

Lee Douglas

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Jan 15, 2011
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

Thankful no one mentioned passive radiator designs. Doh!
Used to have pair of Klipsch KP-4000 subs with a 18" and a 15" passive radiator with matching tops. :) Wasn't over fond of them, but they worked. I also have a few Bag End Infra subs around, which are a sealed design. But the ported subs are the ones that go out most often.
 
Jan 19, 2011
898
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Oslo, Norway, Norway
drbentsen.no
Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

Using the scientific method of MNAUTMS* I came up with these plots. I used WinISDs suggested box size/alignment, put in a signal at rated max long term power and played around with a BW HP filter to keep cone excursion in check.

For comparison, a 18SW115 is simulated in a vented box using the same methods. To me, it looks like it will behave very well in both a sealed and a vented box. Obviously it has more output in a vented box, but as far as I can tell, it would sound pretty good in a sealed box.

If I were to build any of these, I would probably select a 18SW115 based on these simulations. The question is, can we actually trust them? Is it this easy?



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* Moving Numbers Around Until They Make Sense
 

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Jul 30, 2012
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Tampere Finland
Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

Using the scientific method of MNAUTMS* I came up with these plots. I used WinISDs suggested box size/alignment, put in a signal at rated max long term power and played around with a BW HP filter to keep cone excursion in check.

For comparison, a 18SW115 is simulated in a vented box using the same methods. To me, it looks like it will behave very well in both a sealed and a vented box. Obviously it has more output in a vented box, but as far as I can tell, it would sound pretty good in a sealed box.

If I were to build any of these, I would probably select a 18SW115 based on these simulations. The question is, can we actually trust them? Is it this easy?



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* Moving Numbers Around Until They Make Sense
Hello

Since the box volumes are so close - if I read your graphs right - pick one size and build it with ports, measure what you get, then block the ports with plywood and measure again. Then share results with us and finish building more boxes of your choice.


While on subject - I just ordered Harris BassBox Pro with X-over Pro. Anything that I should be awre of particularly with this program. Strenghts / weak points .
 
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Peter Morris

Senior
May 8, 2011
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Australia
Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

Using the scientific method of MNAUTMS* I came up with these plots. I used WinISDs suggested box size/alignment, put in a signal at rated max long term power and played around with a BW HP filter to keep cone excursion in check.

For comparison, a 18SW115 is simulated in a vented box using the same methods. To me, it looks like it will behave very well in both a sealed and a vented box. Obviously it has more output in a vented box, but as far as I can tell, it would sound pretty good in a sealed box.

If I were to build any of these, I would probably select a 18SW115 based on these simulations. The question is, can we actually trust them? Is it this easy?



----
* Moving Numbers Around Until They Make Sense
The enclosure size the WinISD selected for the ported box was too small for this application –B&C recommend 150L for the 18SW115, 18sound recommend 100 – 350L for the 18TWL3000 – I used around 160L for the alignments I posted. A good general purpose Sub should go solid down to 40Hz and be usable to about 30Hz. What WinISD suggested didn't go low enough.
 
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Peter Morris

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May 8, 2011
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

Here is an example of a driver designed for sealed enclosure compared to a ported box – basically you get the same frequency response in the same size box and with a 1000 watts they both Xmax at about 30Hz.
The difference is the B&C makes about 8dB more in a ported box! If you use the B&C in a seal box you will not get the LF extension.

https://www.parts-express.com/dayton-audio-um18-22-18-ultimax-dvc-subwoofer-2-ohms-per-coil--295-518
 

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Jan 19, 2011
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drbentsen.no
Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

I did the same sim with a BMS driver just for fun, it's a huge difference.
Both drivers are in enclosures recommended by the manufacturer.

Would have been fun though to build one and listen to it, but that driver is a lot of $$$.
 

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Peter Morris

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May 8, 2011
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

I may not have been clear with my post - the seal boxes uses a driver with a low Fs and a high Qes (19.5Hz / 0.62) and a huge Xmax of 22mm.

This driver gave the same frequency response as the B&C in the same size, but ported box. The idea was to show how efficiency is compromised when you compare the sealed enclosure with a ported enclosure with the same response.
 

Art Welter

Senior
Jan 11, 2011
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

I did the same sim with a BMS driver just for fun, it's a huge difference.
Both drivers are in enclosures recommended by the manufacturer.

Would have been fun though to build one and listen to it, but that driver is a lot of $$$.
And worth every dollar/euro/whatever.
As you have already noted, BR (bass reflex) has a 5 dB or so advantage over sealed, so you need twice the amplification and drivers to make up for that difference. Going from BR to a TH (tapped horn) design gains another 6 dB. The TH has to be slightly larger than the BR, so one still can achieve slightly higher output density (SPL per truck volume) with BR over TH, at the expense of twice the drivers and amplifiers.

This horn has standard truck integers and is as easy to build as a BR using the same two drivers and the complex porting needed to eliminate port compression at the displacement levels the BC18SW115-4 can effortlessly provide.

http://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers.html

The Lab 12 was a real achievement a dozen years ago (or was it 14?) but in terms of linear response and power compression, the BC18SW115-4 is hands down the clear winner for output density. That said, a pair of Lab 12s are more sensitive (more output per given voltage) than one BC18SW115-4, so if you don't need the increased SPL the BC18SW115-4 can provide due to far better thermal management (and greater Xmax/Xvar), it still is a cost effective option. However, cost effective comes at a weight disadvantage...

In the picture below, taken on my last gig before "retirement", there are 32 eight inch speakers (28 horn loaded, 4 BR center fill) and ten 3" diaphragm HF drivers above 2 single 18" Keystones. In spite of suffering from food poisoning, Jason Raboin had a really nice mix going on just the second day of the LSD tour, and the rig had 6-10 dB headroom available, just loafing along.
Very nice memories from that show, great to hear a group of young (relative to me;^) musicians and sound engineers "doing it right".

Art
 

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Jim McKeveny

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Dec 11, 2012
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

Was Jason on a DiGiCo SD9 by then? LSD are SD Series converts now..

Pardon the comparison, but Keystones remind me (visually) of Karlson's. (Showing my age, aren't I)?
 
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

The port in a box acts as a second radiator, and a radiator with an amount of gain. They are a straightforward way of reducing the excursion of a driver, while providing additional acoustic output, at the bottom end of the passband where drivers need the most help. For a long time the performance of Helmholtz resonators (i.e. ports) was linear enough that they supplemented the output of drivers without too much fuss. The case for ports is pretty easy to make with five minutes fiddling around with Theile Small parameters.

Now the drivers are displacing enough air that ports are starting to be the long pole in the tent, performance wise. The need to be bigger, and more aerodynamic, to continue to keep pace. The challenge to this is that the mechanics of a fluid exiting and opening and entering the same opening are totally different. So ports need to be a compromise between helping air enter the port and exit the port.

The alternative is to make folded horns. In a horn the pressures are high near the throat, but the volume velocity is low, so this tends to help minimize the effects of turbulence in the air around the folds, at least near the throat. As one nears the mouth the pressure becomes lower and the volume velocity grows higher. Folded horns, too, eventually end up with problems of air turbulence in the vicinity of their bends.

One could argue that a sealed box is immune to these effects, but then you've got the nonlinearities of a loudspeaker that needs to move through more displacement for the same output. Also, air itself starts to experience nonlinear compliance behavior at high volumes, so even the air "spring" behind the driver in a sealed box is not as linear as we would hope. Sealed boxes also lack a way to dissipate the substantial heat generated by the driver's motor structure, at least in the conventional "cone out" mounting configuration.

There are always compromises in play, success lies in the skill of navigating them.

This was my first thought. In the land of home stereo and car boom the speakers are often put into sealed boxes but those speakers are typically giant slugs that take bazzillions of watts to move them. As a side note about those hi-wattage slug type speakers - my speaker friend has always said that even if you have the extra power to push those crazy new thumper type speakers they don't sound as good as a more efficient traditional pro audio type with fewer watts at the same perceived volume level. The subtleties of the music are never as pleasing and often missing so Mr. Bozak was correct with his classical music observations.
 

Jim McKeveny

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Dec 11, 2012
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

There is a "Chicken v. Egg" thing at work here also: Who really drives fresh design?

Box marketers will not design a cabinet around a cone that doesn't exist in easy supply. The (now) lowly Eminence Omega Pro 18 had an Fs of 24hz. True sub range. Anything new in the same size class with less than 30hz? Not that I have seen.

Horsepower, xmax, and DSP management rule the day.
 
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Fred Campbell

Freshman
Dec 1, 2013
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

I hope that this is not going off at too much of a tangent, but one of the forum members at Speakerplans seems to advocate designing bass cabinets based on the maximum output response rather than the frequency response.

Here is a link to an example.

http://forum.speakerplans.com/cab-sizes-in-winisd_topic62574_post623574.html

What are your opinions about this design approach? It looks plausible, but I have not seen this method used by others. Most other designers go for the traditional maximum extension, naturally flat, response.

Thanks. FC
 

John Roberts

Graduate Student
Jan 12, 2011
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

There is a "Chicken v. Egg" thing at work here also: Who really drives fresh design?

Box marketers will not design a cabinet around a cone that doesn't exist in easy supply. The (now) lowly Eminence Omega Pro 18 had an Fs of 24hz. True sub range. Anything new in the same size class with less than 30hz? Not that I have seen.
Commercial loudspeaker manufacturers will sometimes use standard drivers for low cost boxes to keep the price down, but a semi-custom driver is one of the variables that a speaker engineer can tweak. The driver design is still limited to using available subcomponents, unless there is a price no object budget. Occasionally a manufacturer will invest in a wholly new driver, if nothing exists that is close..
Horsepower, xmax, and DSP management rule the day.
More horsepower has allowed speaker designers to trade off efficiency for other benefits. DSP is changing the rules but still early days.

JR
 

David Morison

Freshman
Aug 21, 2012
138
6
18
Aberdeen, Scotland
Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

I hope that this is not going off at too much of a tangent, but one of the forum members at Speakerplans seems to advocate designing bass cabinets based on the maximum output response rather than the frequency response.

Here is a link to an example.

http://forum.speakerplans.com/cab-sizes-in-winisd_topic62574_post623574.html

What are your opinions about this design approach? It looks plausible, but I have not seen this method used by others. Most other designers go for the traditional maximum extension, naturally flat, response.

Thanks. FC
Hi Fred, hope you don’t mind a comment from JV….

I don’t quite see it the same way (unless I’m misreading you, in which case my apologies…). You seem to be presenting it as an “either/or” situation, whereas the reality in most cases is probably a bit of both.

I can’t think of any responsible designer who wouldn’t check whether or not a modelled response becomes excursion limited before reaching full power and then adjusting accordingly, which seems to be what happened in the linked thread.

Specifically in the case of more basic, affordable drivers as in that thread, it’s almost inevitable that the max flat/smooth response results in at least one of A: an unfeasibly big box and/or B: running out of excursion at relatively low power*. So, what would be the benefit of going ahead and building that box? None really, IMO.

So, the next step is to either change the driver for a more capable unit (almost certainly requiring throwing more money at the project) or adjusting the box size, tuning & processing to get a more practical outcome, as in that thread.

HTH,
David.

*From the assumptions: Lower budget>smaller/weaker magnet>lower BL>higher Qes.
 

Fred Campbell

Freshman
Dec 1, 2013
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

All comments welcome (within reason :)~:)~:smile: ).

I didn't intend to say it was an either or situation. In fact I wasn't suggesting anything more asking. It just seems that most info I read that people recommend the largest cabinet possible to extend the low end response, assuming it is suitable for the drive unit parameters of course. The method linked suggests ignoring that and concentrate on maximum output and then eq flat. I’m just curious why this method is not more widely recommended or discussed if it is any good.

Obviously a drive unit that can go low, flat and not run out of excursion is good, but they seem to have the down side of being expensive, not very efficient or both.

There are a number of threads on the topic over at Speakerplans, but some get acrimonious so I am reluctant to link to them. It also confirms that at least some people think there is no merit to this design method.
 

Per Søvik

Graduate Student
Jan 31, 2012
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Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

I’m just curious why this method is not more widely recommended or discussed if it is any good.
I believe a lot of manufacturers of higher end systems take this approach. If a speaker is going to be used with, and corrected by, a DSP anyway, why compromise something that can't be corrected for something that is easily corrected?
Peaks are obviously the easiest thing to correct, and moderate dips higher up in the frequency range aren't too hard either. Many manufacturers make a very good job of correcting phase anomalies in their DSPs, and excursion control is very much wrapped up as well. That leaves the job of producing maximum output (and minimum distortion if applicable) in the targeted bottom octave for a given excursion limit.
 

David Morison

Freshman
Aug 21, 2012
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Aberdeen, Scotland
Re: Sealed vs. Ported Subwoofer Enclosures in Pro Audio

<snip>
The method linked suggests ignoring that and concentrate on maximum output and then eq flat. I’m just curious why this method is not more widely recommended or discussed if it is any good.
I think it comes down to a couple of things (one of which at least was missed in the linked thread).

First is to identify the intended purpose of the project. Steve B in that thread clearly made some assumptions about what level of output would be "useful", however if the project was just to add a bit more bass to a home stereo for example, then maybe the lower, excursion limited SPL of the flatter design would have been acceptable.

Secondly, as a sweeping generalisation, the more compromised one's starting point (eg by budget restricting driver options), then the more one would have to deviate from the ideal and use the various compromises to yield a practical end result.

(Having said that, as Per mentions, there are clear examples of much higher end projects also starting with nothing like a flat response - lots of EAW's subs for example, as attached. Just goes to show that it's not easy to make a completely representative generalisation.)
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