Sealed vs Ported Subwoofers

Yeah, what Drew said! Please don't throw a wet blanket on me unless I'm on fire.

>The sealed sub absorbs the backwave of the open baffle driver. Not really a new idea.

Not exactly.

When you add a monopole and a dipole together you get a cardioid with 4.8dB directivity (versus 0dB for a monopole) which interacts better with room modes than the monopole.

If the engineers have done their job right, their sub-woofer should become monopolar at low frequencies (you're not gaining anything below the room's fundamental resonance, and a dipole's excursion has an additional doubling for each lower octave you play) so you're not loosing low end output as you would with a dipole (that also has 4.8dB of directivity)

The sealed sub absorbs the backwave of the open baffle driver. Not really a new idea.

Tekton has a neat looking design that is quite novel. Its a sealed sub with a second driver on an open baffle on pillars a few inches directly in front of the other driver. They move in tandem, but not isobaric because there is no sealed airspace between them. Looks very interesting.

Sealed or ported both have benefits and - aspects to performance.There are ported designs that outperform sealed as there are sealed designs that outperform ported. The total design of the average subwoofer system is all about compromise. Cabinets overly small,as are most transducers drivers need massive excursions power and reinforcement from room boundaries due to the undersized nature of such compromised designs. A big reason why most do not work so well in music systems..

Duke, Nice accurate explanation. Still unless you have the ability to build your own subwoofer that you can factor your own in room response.... Normally if you built a Sealed sub with a finished Q of .5, most people would say that it had no low end output. It would be extremely tight and in the right room would be superb. Manufactures have no choice but to build subs as accurate as possible, then we are forced to deal with room interactions, which are all different from each other. Ideally a sub would come with some sort of built in rta, mic and eq circuit. We do see many subs with a low end boost, but as you alluded to, normally a filter network would be just as valuble if not more. Tim

In my opinion the central problem of low bass reproduction is room interaction. Low-frequency gain from boundary reinforcement has a significant impact on subwoofer in-room performance, so let's look at that.

But first a bit of background: The ear has relativly poor resolution in the time domain at low frequencies, but has good resolution in the frequency domain. What this means is, the in-room frequency response is the most significant factor. Subjective impressions of bass reproduction (slow, fast, tight, flabby, boomy, whatever) correlate well with the in-room frequency response.

Twelve dB per octave boost from room gain at low frequencies is theoretically possible in a perfectly rigid room, but in practice that never happens. Three or 4 dB per octave is more likely. But if we start out with a sub that is -3 dB at 25 Hz anechoic, by the time room gain is factored in, it may well be +3 to + 5 dB at 25 Hz, and thus will sound slow and sluggish (we are ignoring room modal effects here for the sake of simplicity).

A sealed box with at Qtc = .50 rolls off at 6 dB per octave, which comes pretty close to being the inverse of room gain. Therefore, subwoofers with low-Q sealed boxes often sound pretty darn good in-room, and are subjectively characterized as "tight" and "fast".

In order to generate a rolloff that even more closely approximates the inverse of typical room gain, i.e. about 3 dB per octave, we have to go to a specialized vented box. Now I realize this is counter-intuitive because vented boxes tend to be "boomy", but what we do is choose a woofer, box size, and tuning frequency that give us a 3 dB per octave rolloff from about 100 Hz on down. Such a system can be scaled to give very good in-room response to 20 Hz or below.

So I believe that both sealed and vented enclosures offer excellent opportunities for high quality in-room bass, provided the basic design takes the anticipated environment into account. Just for the record, there is much more to subwoofer design and room interaction than what I've described here.

Now if we are looking at subwoofers in general, and if we are merely speaking in generalities, sealed subs tend to give more natural-sounding in-room response. But that is because most vented subs are designed for loudest-deepest-possible-bass, because most subwoofer buyers buy based on specs. The types of subs I described above do not have impressive specs, as the -3 dB point may well be in the 50 to 60 Hz range... before room gain.

Duke
dealer/manufacturer (of both sealed and vented subs)

Unsound summed it up nicely.

IMHO, ported designs off better value, but ultimately sealed designs off better performance. I also question whether ported designs can ever be time and phase coherent.

Bob, You are correct, sealed woofers do roll off @ 12db per octave. My fingers are faster than my head. Everything else is accurate. I have built several woofers in my time. The best we did back in my old SpeakerCraft/Marcof days was a woofer facing up in a encloser that had 4 ports also facing up, it had an identical section with a woofer firing down. The four ports on both sections were joined by PVC, so the top & bottom chambers were ported into each other. There was about a one inch gap between them. We made these to look like an end table, they had the benefits of a ported system, kinda like a passive radiator, yet still rolled @ 12db per octave. I haven't seen this done anywhere else. Ed Martin designed this and it was very good indeed.
If a driver has enough LINEAR excursion, I still prefer a sealed system, but I have zero issue sitting down to a good ported design anyday.

Thanks everyone for taking the time to reply to my post. I still have to get my head around some of the information. I'll wait until my basement is finished and I have time to enjoy my system before I make any decisions.

Cheers

Jim

Bob, You are correct, sealed woofers do roll off @ 12db per octave. My fingers are faster than my head. Everything else is accurate. I have built several woofers in my time. The best we did back in my old SpeakerCraft/Marcof days was a woofer facing up in a encloser that had 4 ports also facing up, it had an identical section with a woofer firing down. The four ports on both sections were joined by PVC, so the top & bottom chambers were ported into each other. There was about a one inch gap between them. We made these to look like an end table, they had the benefits of a ported system, kinda like a passive radiator, yet still rolled @ 12db per octave. I haven't seen this done anywhere else. Ed Martin designed this and it was very good indeed.
If a driver has enough LINEAR excursion, I still prefer a sealed system, but I have zero issue sitting down to a good ported design anyday.

Drew,

Your comments remind me of the experience I had with a pair of Tannoy 15 inch Dual Concentrics I bought in 1956. They were $159 each new, whew! I put them in Hartley Boffle enclosures I built, who remembers what they were?

I drove them with Marantz model 2 amps and the voice coils bottomed out on the back plate continually. I sold them to a friend in 1962 after I built a pair of Electro Voice Patricians that rattled all the windows in my parents home. He kept them until a few years ago when he sold them; I wish I could've bought them back!

A great loudspeaker is like a great woman; If you find one, don't let her go as you may never find another.

Ken

A ported enclosure can be 3dB more efficient at the same size or play a quarter octave lower at the same efficiency.

The same driver excursion will net you perhaps an extra 1/3 octave of extension with a ported speaker.

You'll have higher excursion limited output in the bottom of a ported design's pass-band so you can use smaller + less expensive drivers.

Distortion will also be lower in the bottom of the speaker's pass-band with the port because of the reduced excursion.

Ported enclosure+driver combinations have four poles in their high-pass function for an eventual 24dB/octave roll-off function while sealed ones have just two for 12dB/octave. With sufficiently shallow roll-off room gain (12dB/octave in an infinitely rigid room below its fundamental resonance at 1130 / 2 / the longest dimension) can keep the speaker flat below its roll-off.

Ported enclosures do not load the driver once you get below the port tune, with excursion increasing to what it would be in free air. Where too much low frequency energy is present below the speaker's pass-band you'll have distortion (including midrange IM distortion on 2-way speakers) and may even run the drivers into their mechanical limits resulting in damage (some very nice drivers will bottom the voice coils on the back plate). For a given input level sealed speaker excursion remains constant with decreasing frequency.

Timlub,

Very well said. Your reply zeroes in to the fact that cost is a major factor in loudspeaker design. While Wilson uses a ported design in it's flagship speaker it delivers sound that would take a much larger design, requiring a much larger room. If you have no constraints on the size of you room or budget you can always improve on commercially designed speakers.

Ported designs are a natural compromise that is utilized in many designs because of efficiency, both in size and cost.

Designing and building a loudspeaker that prevents the front wave and back wave of a driver from meeting is easy. Choosing drivers that crave that alignment is expensive. Doing it so that it sounds better than anything else is priceless! I couldn't resist saying that!!!

Ken

There is no better..... but You can certainly prefer one over the other and there are implications of one being better over an extended period of time.
If a ported driver is ported correctly, it will be acoustically flat. If a sealed driver is in the correct encloser and you achieve a final QTS @ .707, you have an acoustically flat sealed driver. The big difference is that it is typically easier to find a driver that will achieve a very low frequency from a ported design and when the driver is at its minimum frequency a ported sub will then roll off @ 24 db per octave, so below its rolloff there is very little output. In a sealed design, once a driver hits its low frequency rolloff, it rolls @ 6db per octave, so you will still have very useable low end frequency below the point where it begins to roll. Because of this, the two do sound a little different from one to the other. Also, I had said that over time the implications are that one is better. That is because as a driver wears, its specs change, especially its qms... as the specs change a ported design has a tougher time maintaining its accuracy, where a sealed woofer will stay fairly true... Of course, that does take a fair amount of wear. As alluded to above by another... Any woofer in its perfect sealed box, will always need a larger encloser for its perfect ported box, But there are very few woofers (very few, not zero) that truly are versitile enough to use ported or sealed. I hope this helps, Tim

Subwoofers are very commonly used with electronic equalization. The inherently-smooth slow rolloff of a sealed system is best suited to equalization, and the equalization can take care of the fact that the rolloff begins at a higher frequency.

I agree, in general, with Shadorne -and- Gmuffley. Box size is another factor to consider. Using the same size box, you will get deeper extension and higher output with a ported design. The sealed box will give you a flatter and more gradual roll off. Recent sealed subwoofer designs use smaller boxes with very powerful amplifiers with compensation to achieve better output and extension. Some have been very popular. My old ported 12" Mirage(Energy) would shake the walls in a way my sealed 10" Parts Express Titanic subs will not. Ultimately, the sealed subs work better in my room.

What Shadorne said. Ported subs are usually (though not always) less damped than sealed subs. That helps for high output capability at very low frequencies (read "HT"), but might cause some issues when optimizing for a music system. However, as the other posts note, individual subwoofer designs vary, as do main speaker designs. The trick re: damping is to find a sub and mains that are similarly damped at the crossover point. I'd guess that, more often than not, a sealed sub will be a better choice, but "more often than not" is not the same thing as always.

Good Luck

Marty

Sealed generally means less resonance and group delay - so more refined bass.

Ported means higher output which can be important for HT and will give you more bass for much less money(much more efficient).

My current subwoofer is sealed and is used in my music system. I've used ported in a home theater system. What I believe to be more useful in integrating a subwoofer is getting a digital sound processing sub that allows room equalization. And just as important is being able to adjust the volume of the subwoofer independently and easily from your left/right speakers. Once I set the volume for the source signal I generally adjust the subwoofer volume to get the sound right. Useing the same static volume settings for the sub in relation to the left/right speakers in all situations is what causes so many complaints about subwoofer integration IMO.

I have 3 pairs of ported ones and one pair of sealed ones and they all work fine. As previous poster said it is the individual design that matters.

You should definitely not sell a speaker because it is or is not ported. Neither design approach is inherently better; it depends entirely on the implementation. Wilson speakers are ported and Magico prefers sealed enclosures--both produce excellent results.