Sealed vs Ported Loudspeakers: Which is Better?

gene

gene

Audioholics Master Chief
Administrator
Making a speaker that can be sealed or ported, may be good marketing, but it is lousy engineering.

For any woofer optimal box sizes for a sealed and ported alignment are going to be very different. There are significant differences in driver selection and design for the two alignments.
Or a more balanced viewpoint is offering multiple tuning modes including the option to seal a ported design opens wider placement options and is in fact excellent engineering in doing so. The PB13-Ultra is this example one of engineered excellence as any owner or person that's actually heard one could vouch for.
 
E

Ed Mullen

Manufacturer
Making a speaker that can be sealed or ported, may be good marketing, but it is lousy engineering.

For any woofer optimal box sizes for a sealed and ported alignment are going to be very different. There are significant differences in driver selection and design for the two alignments.
I'll beg to differ on the 'lousy engineering' part :) - but you're certainly correct on the second half of your statement.

That is why we use a completely different variant of the Ultra 13.5" driver in our smaller SB13-Ultra subwoofer. That driver is optimized for operation in a sealed cabinet of that volume.

  • We revised motor geometry (overhung) with a very high force factor (BL^2/Re). Extensive modeling and acoustic testing indicated that this is the preferred motor alignment for a sealed application in this size cabinet.
  • We use a unique voice coil (bifilar wound, 3" diameter, aluminum, and with a longer winding height) optimized for a sealed application, resulting in higher power handling and excellent thermal management and heat dissipation.
  • We also added a unique gap extension plate (nested in the top plate) for a more symmetrical force/displacement profile, resulting in lower distortion and increased linear stroke.

In the case of the PB13-Ultra, that variant of the 13.5" driver (which is completely different that the SB13-Ultra driver) is optimized for a large cabinet volume. As such, the performance remains very good, even in sealed mode. The PB13-Ultra driver is not terribly happy in a small sealed cabinet - but as you noted it performs very well in sealed mode in a large cabinet - and that's why we confidently offer this operating mode for the PB13-Ultra.

You'll note the very low Q knee and shallow roll-off profile. This minimizes phase change with respect to frequency, and the associated GD curve is very favorable. The PB13-Ultra sounds fantastic in sealed mode, and has plenty of output for mid-size rooms.

The sealed performance is respectable, but F3 is probably too high for HT enthusiasts who want to feel the explosions.
With respect to deep extension, the PB13U in sealed mode is only down about 7 dB @ 20 Hz, relative to the 40-80 Hz reference drive level. Due to the very shallow roll-off slope (something you won't often encounter in commercial sealed offerings), when used a mid-size enclosed room which exhibits a modicum of 'room gain' (i.e., the acoustic transfer function below the modal/pressure transition frequency of the listening space) the PB13U in sealed mode can/will exhibit remarkably deep in-room extension.

My personal reference HT room has rigidly constructed boundaries and is fairly tightly enclosed, and exhibits about 18 dB of room gain at 10-12 Hz. The PB13U in sealed mode in this particular room is flat to almost 10 Hz.

Further evidence of this can been seen in PBC's review of the SB13-Ultra (which has a very similar system Q and roll-off slope as the PB13U in sealed mode). Even in his mid-size and rather open/lossy listening space, the SB13-Ultra measured flat to 15 Hz in-room.

http://forums.audioholics.com/forums/subwoofers/81423-pbcs-svsound-sb13-ultra-user-review.html
 
Steve81

Steve81

Audioholics Five-0
Revisiting the thread before things went off track, I did set things up again for sealed mode on my PB13U for some listening last night with a mixture of country and classic rock (that's right, I'm a little bit country, AND a little bit rock and roll :D ). I still can't say I had any OMG moments versus what I'm already used to with 16Hz tune. Of course, it's pretty cool to have the option, and I'm glad SVS offers it.

As a side story, in terms of sealed versus ported speakers, I first got into this hobby with acoustic suspension speakers. The first speakers I ever purchased were a pair of Cambridge Soundworks Model Six speakers. For those that are unaware, Edgar Villchur had a partner at AR when he released the AR-1, former student Henry Kloss. Kloss would go on to found KLH (he was the K), Advent, and Cambridge Soundworks. The CSW Model Six was/is (theoretically) loosely based on the old KLH Model Six. I couldn't qualify them as being great speakers by any stretch, but they were quite easy to listen to. On the other side of the coin though, I didn't find anything magical about acoustic suspension there either, and I've never caught myself pining for my old Model Sixes in spite of the fact that every speaker I own now is ported.
 
K

kaiser_soze

Audioholic Intern
But if you want to know the real reason that virtuall all modern speakers are ported

This article covers some of the issues. But Mr. Feinstein started by asserting that the AR-1, now nearly fifty years old, was inherently superior to any modern speaker in terms of quantity and quality of deep bass. (I used to also believe this, passionately.) He then proceeds to explain why ported designs are so much better than they used to be, but hardly manages to identify any advantage of ported designs. You have to look hard for it. In the second page, he wrote, “My own feeling is that the lower 3dB down point of a small ported system and its higher efficiency are thought by many companies to be worthy advantages in today’s less critical, less hobbyist-driven audio environment.” He proceeds from there to talk about group delay, and even though he prefaced that by saying that he was about to contradict himself, he did not contradict himself at all. The group delay issue points very clearly to the superiority of acoustic-suspension speakers.

Unless you believe that the world’s finest, modern speaker companies are concerned primarily with speaker efficiency and the -3dB point, to the detriment of bass quality, the article does not really explain the reason that most of the world’s finest, modern speaker companies prefer ported designs.

It all comes down to one fact: cone excursion is vastly lower with ported designs than with sealed, acoustic suspension enclosures. This translates in a rather immediate way to reduced non-linear distortion in the deep bass. With the acoustic suspension approach, the strategy is to make the suspension very floppy, using the pressure differential across the cone to provide the force that opposes the motor force. The assumption is that the restoring force will be a linear function of cone displacement. But the obvious questions are with the linearity of the motor, and also the spider, which is part of the mechanical suspension. The voice coils are very long indeed, which leads to greater self-inductance, and also greater DC resistance and thus reduced sensitivity.

The alternative approach is to avoid the large cone excursion. This fundamental advantage gets lost in all the talk about -3B points and group delay. Group delay is accompanied by a time shift for output in the deep bass, relative to the rest of the spectrum, and becomes audible when, but only when, attenuation is severe. As long as the enclosure and port are tuned to adequately low frequency, such that you do not get the steep drop-off below the -3 dB point, it is not a problem at all. But there are other drawbacks. If the diameter of the port is not great enough, compression will occur, leading to reduced low-frequency output at higher volume levels. I.e., turn up the volume loud enough, and the bass disappears, and as it does so, the cone excursion increases. And this occurs regardless at frequencies below the -3 dB point, i.e., you still have high cone excursion and high distortion. There are other potential disadvantages that may or may not be significant, depending on who you ask: organ pipe effect and midrange leakage.

For medium-sized satellite speakers that rely on a subwoofer for deep bass, there is probably no significant difference between the two types, but it depends on the size of the satellite speakers, and also on whether equalization is used. With “home theater” speaker systems that use little tiny satellite speakers, the ported approach can be advantageous if used in conjunction with equalization, the reason being that you can use equalization to correct anomalies in the frequency response and extend the bass, while the port has the net, appreciable effect of reducing cone excursion, thereby reducing distortion. This same advantage, by the same reasoning, can apply to any speaker where porting is combined with equalization, whether the equalization is built in to the speaker as in the case of a powered monitor, or is accomplished by means of (ostensible) room-correction speaker setup in a modern home theater receiver.

Ported designs also make sense with very large speakers with very large woofers, since with these speakers, the benefit of reduced cone excursion still applies, as it invariably does. Most powered monitors are ported, because the driver itself does not displace sufficient volume to be capable of strong output in the deep bass. The required amount of excursion would be so great that high distortion would occur. With this type of speaker, you tune the enclosure and the port to a frequency well below the frequency that the alignment rules says that you should use, and then use equalization to correct the anomalies in the frequency response. This type of speaker is very smart from the additional perspective of the crossover, since by using separate amplifiers for each driver, the crossover is rendered immune from interaction with the complex impedance of the driver.
 
K

kaiser_soze

Audioholic Intern
Something else that bugs me is that a lot of people are talking about Q as if a resonance is fully described by its Q. I find this very odd. Manifestly, a resonance is described by a particular frequency and by its Q. Merely by virtue of the fact that the driver itself is intrinsically an oscillator complete with a resonance, any bass reproduction is going to have a Q, but by no means does it make sense to suggest that the Q by itself determines the quality of the sound (even if distortion is not relevant or considered). For example, if you have two sealed enclosures and the system resonance for one occurs at 15 Hz while the system resonance for the other occurs at 70 Hz, they are not going to sound similar even Q is .5 for both, or .707 for both, or whatever. Given only that, it is apparent that it does not make sense to assess the difference in the sound of ported speakers vs. sealed speakers on the basis purely of Q. If a ported speaker is tuned to 10 Hz and and a sealed speaker has its system resonance at 75 Hz, you certainly are not going to be able to say anything definitive about the difference in the quality of sound between the two, from just the Q.
 
U

User5910

Enthusiast
...I think total system Q has a large and almost overwhelming influence on the character of the bass in a system.
My Rythmik F15 (sealed, servo-controlled) has a switch to select Q with options for "high (Q=0.5), med (Q=0.7), and low (Q=1.1)." I think I left it on high when I set it up but now I'll listen to some music at the different settings.
 
gene

gene

Audioholics Master Chief
Administrator
A continuation on this topic but focus on Acoustic Suspension loudspeakers:
 
TLS Guy

TLS Guy

Audioholic Slumlord
A continuation on this topic but focus on Acoustic Suspension loudspeakers:
Again I think we have an article from someone who has never built a speaker.

It was a nice review of the audio of days gone by.

However he has glossed over the issue of the fact there is no free lunch.

That SB driver that would make a good acoustic suspension driver has a sensitivity of 84 db.

The Wavecor driver has a sensitivity of 90 db.

So you come out about a wash power wise of boost for the high Q lower Fs driver versus the power required to make up the efficiency loss of that SB driver.

Now I also remember those years of the ARs. I don't want to say they were lousy speakers, but to me the bass never sounded that tight. I do clearly remember that those speakers struggled to really impress with the power available from amps at the time including solid state ones. The other thing I remember is how unreliable solid state amps were back then, especially if driving insensitive speakers.

It was the great audio pioneer Peter Walker who produced the first reliable solid state design in 1969. It was the Quad 303 with its tripled output transistor design and a power of 45 watts per channel. That was considered a lot of power back then. Many of those 303s are still going strong and come up on eBay often. My 303 from 1970 is still a runner.

But returning to SQ, I never felt that those AR designs had a particularly tight bass, in fact I always found them on the "flabby" side. However most of the competition was abysmal. So that is why I reckoned I could do better and built a Voight quarter wave pipe in 1955. I have used my own builds exclusively since.
 
gene

gene

Audioholics Master Chief
Administrator
TLS,

There are problems witg his conclusions about SVS and I'm either going to ask him to change, or omit them before publishing. Thanks for your feedback.
 
MR.MAGOO

MR.MAGOO

Audioholic General
IMO the question is not which is 'better' than the other, it's a question about how one plans to use it. Just my 02 cents...
 
colofan

colofan

Audiophyte
Stereo Integrity also makes a very capable 12 inch driver Fs 22Hz. SQL-12
 

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