Axiom Home Page Forums General Discussion Technical Questions Sealed vs Vented Subs...and impact

I have a couple of questions about subs, that I haven't been able to find answers to.

1. With all things being equal, what is the difference between a sealed and vented design?

This question comes to mind especially when looking at the Rythmik line of subs. They have vented and ported designs with the same 15" driver and amp. Many have claimed that sealed designs are better for music and more detailed. On the other hand, vented designs are said to have "group delay", where the bass signal has a slight delay, when it is played, which slightly muddy's things up. But, maybe a positive side effect (for say, explosions in a movie scene) is that the vented design may be perceived as louder at the same volume level, because of this slight delay. So if two subs are basically equal in frequency response, up until the subs hit their limit, will these things be apparent? Has there been any blind (double or single) testing done to show that "group delay" is actually something noticeable during different pieces of music or movie passages? Are there any other differences between sealed and vented subs, that show up in the listening experience.

2. What factor contributes to impact in a movie scene?

What I mean is that if you have two different subs level matched, playing within their limits in the room, with very similar flat frequency response curves (from say 20Hz to 80Hz), is one sub going to have more of an impact (thump you in the chest bass in action movies) than the other? Does a larger driver (or sum or areas of drivers, if there are two drivers) play a factor in this? Or, does sealed vs. vented design play a factor? Does the volume of the box, play a factor? Or does the amount of RMS wattage that of the amp play a factor? Or, is there anything else that plays a factor?

subs, and other kinds of speakers, are ALWAYS compromises in every facet you can think of.
you would learn a lot by reading reviews in some specialized sites.

From my (limited) knowledge on the subject, yes, a sealed design (if all other factors are equal) will yield tighter bass as people call it. So what about all of the ported subs? Well, sound travels through a medium (air in this case) and the more air you can move, the more "bass" you can get. A port allows for more air movement.

You will also hear people "tuning" their subs for even lower frequencies by messing with port sizes/lengths. With a sealed box, it would seem that things are a little more limited.

I am probably 200% wrong, but that is what I used when I built a sub box for my car years ago. I wanted the tight bass and not massive bass (I wanted to add to the music, not dominate the music) so I went sealed.

Home theater, to me, is a different story, and I like ported better.

One is sealed, the other vented. Really.

There is a lot of myth in the sealed vs. vented debate. How well a sub reproduces a given frequency is a direct result of the quality of parts and the quality of the design.

Where sealed subs are damped by the sealed internal air mass, a (good) vented sub relies on motor strength to start and stop the driver properly to accurately reproduce sound.

Because of the way a sealed sub rolls off gradually, it will often require some equalization (either a cut in higher frequencies, and/or a boost in lower frequencies) to give flat output across its range.

A vented sub will require a high pass filter to keep frequencies below its optimal range from destroying the driver (no natural damping as with a sealed design).

A driver designed for use in sealed enclosures will not work as well in a vented design and vice versa.

As for group delay, there are well known and respected designers on both sides of that argument and you can find some interesting discussions on avsforum.com and diyaudio.com where both sides duke it out.


Nope.


Yes and yes. In general, you will need more power with a sealed design than ported to produce the same volume and range of sound. A lot depends on driver design and efficiency as well though.

Also, ported systems need internal volume to reproduce those extended lower notes so they tend to be bigger, often bigger than your average person wants.

If you want the point made with real examples go to the diy subs and speakers sub-forum at avsforum.com and search for a thread by bossobass on his dual opposed 15" sealed sub design. It is very compact and fed by something like 4,000 watts of power to produce incredible bass from 10Hz on up.

Then search for a thread on the wolfhorn a 'ported' (well horn loaded actually) design at the other end of the spectrum. It produces the same bass with a fraction of the power, but is, um, quite large.

If you skipped all the way to the bottom to see if I had a point , you can get similarly good (sic) bass from either design, just in different ways.

Excellent post, Fred.

Quite frankly, in my experience, this design difference between the two types and what some perceive as being preferential for movies or music or visa versa, I believe is highly overblown. In my case, I have both types in my system(FOUR total) and either works for any type of sound coming through it equally well. With a multiple sub arrangement especially, as long as they are relatively close in power capabilities and frequency range along with being phased and balanced properly, it won't really matter what type of sub it might be. Room interaction will have a much greater affect on what you are hearing and getting it right than the design characteristics.

Aha. I knew I didn't have to read the whole thing.

casey, that's exactly the kind of well-reasoned, first-hand feedback that I find valuable, and that I think is a signature element of the Axiom forum. It is also the sort of thing that will get you torched at AVS.

So if you locate the best place in a small room (say 12 ft by 17 ft with 8 ft ceilings) for the EP800 and level match it with the rest of the speakers. Place an EP400 on top of the EP800 and level match it to the rest of the speakers. Have an external EQ, trim the bass of the EP800 below 20Hz, so that it has the same frequency response as the EP400. Then you will not notice the difference (in terms of the amount of tactile bass and impact of it) between the two if you A/B them on heavy bass scenes, like chapter 4 of Master and Commander, or the the bridge of khazad dum in the Fellowship of the Rings, for example?



What subs do you have that are sealed and ported? You have two of each design integrated at the same time in the same room? Are you saying that you have done an A/B comparison of both of the sealed and ported subs in your room and didn't really notice a difference?


Again, this question came to me when looking at the Rythmik line of subwoofers. They have a 15" sub in either a sealed or ported design with what seems like the same driver and amp and just about the same price. The ported design has a slightly larger cabinet. For a few hundred dollars more they have a sealed sub using two of those same drivers (at least they seem to be from as far as I can tell) the same amp and obviously a larger cabinet to fit the two drivers. So for almost the same money you can have three very different subwoofers, in terms of the design. I'm just confused as to what the difference would be between these. The only obvious difference that I can see is that the one with two drivers is probably more capable in a larger room, due to the amount of air that it can move in comparison with the other two.

Axiom has a slightly similar offering. The EP600 and EP800 are nearly the same size cabinet. The 600 has one 12" driver and is ported. The 800 has two drivers and is sealed. The frequency response curves look very similar (the 800 playing slightly lower), so do they sound identical with those same from 20Hz to 80Hz, if they are playing within their limits?

In my listening tests of subs at Axiom (not nearly as elaborate or extended as listening tests of other Axiom speakers), I'd say yes, the 800 and 600 do not differ in a qualitative sense. That is, I don't write down on the rating sheet stuff like, "Oh, it's obviously a sealed sub!" Or "something tells me this is a ported subwoofer".

"Tactile impact" from subwoofers is a product of extension and output capability. The reason Ian made the 800 a sealed design with two drivers (as opposed to the ported 600 with one driver) was to offer deeper bass extension without port noise that would otherwise intrude at very low frequencies from a vented design, and also to increase the overall output.

Remember that with a sealed design, you are "throwing away" all the back energy from the driver, so you have to have larger amplifiers or double up on drivers to achieve the same SPL that could be obtained from a ported single-driver design, other things being equal.

The comparison you mention, with the 400 on top of an 800, is kind of specious, at least in a large room. The 400 was designed for deep bass extension in a small room, so it isn't capable of the same SPL as the larger EP800. If tactile impact were the criterion, the EP800 would win, simply because of its greater output capability.

Regards,
Alan

I am trying to really understand what contributes to impact, which I why I am comparing two very different sealed subwoofers. Both are sealed, but the EP800 can obviously play lower than the EP400 and at MUCH greater SPL levels. But, I was trying to take the extra extension and capabilities for much higher SPL's out of the comparison, by say comparing them in a quite small room and having some external EQ that cuts out the extra extension of the EP800. So, under these circumstances what would be the difference between the two subs in a bass heavy movie scene? Would we be able to feel the extra impact using the EP800 in a bass heavy action movie, in explosions, gunshots, trains passing by, etc.? As long as we aren't pushing the EP400 further than it can go. Or, is the reason for going moving up the Axiom line (or other subwoofer manufacters, as well) just a matter of extension and high SPL capabilities, needed as rooms get larger.

Thank you for the complimentary response and that is why I rarely, if ever, view the AVS website. Far too many of the "contributors" and I use the term loosely, seem to want to spend much of their time doing hatchet jobs on equipment or products they "perceive" they don't like without actually ever having heard it. Rather than having meaningful, informative discourse about our hobby, much of that forum seems to prefer confrontation and very often unwarranted criticism that is useless to people who actually wish to possibly learn something.

Amen. Sometimes I farm AVS for some specific technical information, but it's a terrible, joyless place to hang out.

Forgive me for not being able to keep track, but which subs are you using in your system at present?

Is AVS the same thing as avsforum.com, or something else?

one in the same, if you've ever been there it will make sense. More arguing and conjecture than anything.

Yup. That's exactly it. You will benefit from lower extension in a small room as well. In movies, there is significant content below 20 Hz (kaboom! ).

Think about it this way. If you take a ball of string and cut three sections to exactly 3" using a razor blade, scissors and a cleaver. If you mix them up and lay them side by side, can you tell which was cut by wach instrument? No. That is because the instrument used does not change the nature of what you have created.

NickB, for me I get more IMPACT from movies/music via my M80s and now VP160 than I ever have from my SVS PB13 Ultra. That impact, chest thump is from a higher frequency than most subs are set up well to play, either due to design, setup factors or any other numerous points. This desire for impact (as well as a little better lower midrange warmth) is what led me to purchase a full range speaker for my mains and now for my center. I get much more rumble, seat of the pants feel from my sub but again this is also due to my set up, crossover points etc.

Holy Crap!

After all these years, an easily-understood explanation of the String Theory!

This is a great answer. So chasing after the biggest and baddest sub for impact is sort of a waste of time. Not to say that there isn't a justification for the SVS PB13 Ultra. If you have a large room and/or want that sub 20Hz frequency response then that is a reason for a sub like the Ultra 13.

So you are saying that the chest thump is over 80Hz? What are you crossing over your center and fronts at?

When it comes to subs in general, over the years, I have seen settings on several of them whereby if you wanted that extra thump from movies the control was targeted in the 40>50Hz range, generally not down in the 20Hz area. With that low of a frequency, room interaction tends to be more critical in determining whether or not the sub can produce it and even if it can, one generally "feels" it as opposed to hearing it.

here's a chart that might be useful:
http://renegademinds.com/Portals/0/GDT/Remove-Instruments/Interactive-Frequency-Chart.png

I disagree with that charts naming scheme my sub can hit 15hz with authority and I never feel it in my chest. I think that chest thump most people are looking for is listed being in the bottom - boom/punch area and depending on your room can be hard to reproduce.

All I know is once I moved up to the M80s I was getting more in the way of chest thump when watching movies, listening to music etc. and adding the VP180 really added some impact with multichannel listening, my VP160 slightly less so than the 180(from what I can remember) but still adds more to the effect.

I think you are correct Jay. I seem to remember that chest thump is up in the 60-150 Hz range, which explains why you feel it with your mains and center.

Here's another thing to chew on:

"The main problem with quantifying 'fast' versus 'slow' bass is that the cues that our ear/brain use to make that determination don't come from the frequencies below 80 Hz, they come from the frequencies from roughly 80 to 500Hz. So yes, transient response is very important, but not the transient response of the subs, but rather the transient response of the midbasses. Earl Geddes would have a field day over this one."

from site.

A lot of what is 'commonly known' about subs is incorrect.

If this is true, then it is pretty scary what many professional reviewers are saying. They will often discuss the how "slow" and "fast" the bass of the subwoofer is. Yet many of them probably have the crossover set at 80Hz. So what are they hearing exactly? Maybe they are continuing the "well known" myth (or fact I don't know) that sealed subs have "faster" bass and ported have "slower" bass.

I like sealed subs for music b/c you don't get port noise but they usually don't have as much depth for movies. A hybrid sub switching between sealed/ported may make us all happy. Anyone try the HSU VTF15H?

Nick. Yes, what some reviewers write is scary.

jball. Port noise is a potential downside to a ported design if it is not well executed, or the sub is pushed beyond its capabilities, but it is not an inevitable outcome of the design.

I hear absolutely no port noise in my EP350 and it is absolutely faithful in its music reproduction.

FWIW, a passive radiator design gives you some of the advantages of sealed (smaller size, absolutely no risk of port noise) and some of the advantages of ported (efficiency/extension gains from better air mass coupling). The downside here is the cost of the radiator, which is a sub driver without the motor.

i always use my sub tuned to 16 Hz (one foam plug used).
on the loudest parts of:
Hanna / Band of Brothers / WOTW / Super 8 / Master & Commander DVD and T4, i have never heard wind noise from the ports; and this with playback levels always at Reference.
i also run my sub 3 dB hot relative to Odyssey calibration.

The only time I ever heard port noise on my EP500 with even serious bass was when there was a cat toy stuck deep in it. After contacting Axiom for help, I felt pretty silly when I discovered the true cause.

I was thinking about the area of the driver in the SVS Ultra 13 vs the 4 Axiom 6.5 inch bass drivers. The area of the SVS driver is pi/4 * 13^2 = 132.7 (approximately). The area of the 4 Axiom drivers is 4*(pi/4)*6.5^2 = 132.7 (approximately) (I thought is was kind of a funny coincidence when the numbers came out exactly the same). So if the SVS is handling the bass in 60Hz to 80Hz range, or the Axioms are handling the bass in that region, there should be no difference in the amount of air that is being moved (this is a bit of an oversimplification since both the SVS and the Axioms are ported and so the size of the port and the size of the enclosure are disregarded, and we are comparing them as if they are sealed this way). So there doesn't seem to be any reason why there would be more chest thump if the Axioms are handling the 60Hz to 80Hz range, or the SVS is. This leads me to believe that it must be 80Hz to 150Hz that is giving that chest thump.

On the other hand, when jakewash moved up to the larger VP160, center channel speaker, and maybe set the crossover 60Hz or lower, then there would be more air moved by the front speakers and center channel, in comparison to just the one SVS 13" driver. If he were to go with multiple subs, then that would no longer be the case and maybe the more chest thump would come from letting the dual subs handle the 60Hz to 80Hz region, by setting the crossover for the front speakers at 80Hz.

i suppose you could hear a mouse inside..."squeak squeak"

;-)

a good say to check on this fast or slow subs (response) is to shut down the amps and leave only the sub on while music is playing.
i find it's not very "musical".
when i hear very low freq. sounds that seem to be directional, this is caused, i suspect, by harmonics of the instrument playing those sounds, higher than 80 Hz.

Cool! I'm to lazy to figure things like that out. I does show why the M80 has such good bass. Though there is more to a good driver than radiating area, it sure is a good start.

Yeah, Jacques; I've suggested a few times in the past that disconnecting the speakers while leaving all settings the same(e.g., with a crossover to the sub of 80Hz or lower)and then listening to bass-heavy music on the sub alone will cure any illusions that subs are "musical", "fast", "tight", etc. Any such qualities of bass instruments(and also being able to localize them)are due to upper harmonics played by the speakers, not the sub.