question about non ported speakers

**tonyvdb** · **11-23-07, 01:29 PM**

What is the deal with some speakers not having any hole in them to allow for air to move in and out (ported) I have a set of Mission 762's and they have no hole in the cabinet. What effect does this have? Its my understanding that this tightens up the bass. How does the cabinet "breath", is this not hard on the drivers?

**Josuah** · **11-23-07, 03:14 PM**

A port isn't used to allow a cabinet/speaker to "breathe" (except in one case I'll mention afterwards). The purpose of a port is to act as a Helmholtz resonator; in simple terms, the low frequencies of the speaker are produced by the movement of air through the port, rather than from the driver pushing air back and forth (although it is the driver movement that is causing the air in the port to move).

Sealed speakers do not have a port. Generally speaking, sealed speakers will not play as low because the low frequencies that would be produced by the port are not being produced anymore. The argument for tightening up the bass comes from the fact there can be either a delay in sound being produced by a port versus a driver or at high volumes distortion from the small port. But that is not a universal truth. Rear ported speakers can also sound boomy if they are placed close to the wall.

I have seen one or two speakers that have been designed with a tiny hole, not to act as a port, but to let air in and out. Usually, a sealed speaker is supposed to be sealed and you don't want any air to leak in or out. The compression of the air actually has an effect on the driver, of course. However, in these speakers, I guess they did not want that to be a factor for whatever reason.

**tonyvdb** · **11-23-07, 04:00 PM**

Thanks Josuah,
Thats kind of what I thought. Now just for curiosity, if I was to put a hole in the cabinet could this change the speakers sound for the bad? (don't worry I wont do this I'm just interested)

**avaserfi** · **11-23-07, 06:42 PM**

Just placing a hole in any given cabinet isn't a good idea. Various drivers can work in both a sealed and/or ported cabinet and you can use programs like WinISD to model how each driver would behave in a given situation, but one thing to note is not only does the size of the cabinet change, but if you are doing a ported cabinet one must take into account port size both diameter/width-height and length as ports are very rarely just a hole.

So if you just randomly put a hole in your cabs it would likely sound like bad as you would need to model the driver and build a new cabinet accordingly.

**Josuah** · **11-23-07, 07:32 PM**

I'm assuming you mean a random hole, instead of a port. If the hole doesn't actually go all the way through the enclosure, it might not have much of an effect, especially if you end up creating the hole to stick in a mounting thing (I don't know what they're called, but the threaded thing you'd screw into) because then there's no loss of material.

However, if the hole goes all the way through then you're going to mess up the air pressure expected by the speaker designer, and at higher SPL it might make wheezy noises. A hole will also change the vibrational characteristics of the enclosure, maybe. Which is also a bad thing.

**tonyvdb** · **11-23-07, 07:42 PM**

LOL, Thanks guys, I was thinking of a real port with tube and all as the speakers that may be getting (floorstanders) for my living room system are also non ported and have a woofer located on the side of each cabinet. I just thought that was sort of strange but from what you are saying this is more common than I thought.

**ISLAND1000** · **11-23-07, 10:46 PM**

A hole in a sealed box is like a hole in a plate glass window. I say try it, "see" what happens.

**Josuah** · **11-24-07, 01:42 PM**

Ports are a common design choice because it lets the specs say something like 40Hz-20kHz +/-3dB, instead of 100Hz-20kHz +/-3dB. So it's not that surprising you think it's weird for them to be missing. For myself, I've found that I don't use the ports on any of my ported speakers; my crossovers are set high enough to bypass them, for the most part. This is partially due to my specific set up, and partially because I know how ports model in WinISD.

**warpdrive** · **12-16-07, 02:34 PM**

Quote:

tonyvdb wrote:

Thanks Josuah,
Thats kind of what I thought. Now just for curiosity, if I was to put a hole in the cabinet could this change the speakers sound for the bad? (don't worry I wont do this I'm just interested)

No, you wouldn't want to do that. If a speaker is designed with no port, putting a hole will completely change the way it sounds. If you just need to mount the speaker, you can drill holes into the cabinet but it should still be sealed tightly.

**conchyjoe7** · **12-22-07, 03:25 PM**

Most speakers with no ports are "acoustic suspension". They are excellent speakers with one drawback. In order to have great bass, because the cabinet is sealed it usually requires a much larger cabinet than ported speakers. They also tend to require more power...as the cabinet is "pressurized" so to speak... to reproduce the same SPL as a ported speaker. That said, IMO, and that of many others; the bass seems to be much tighter and deeper if done right. There are variations on this theme with excellent results being had by using "transmission line" loading which allows a smaller cabinet and employes long "tunnels" that fool the driver into thinking it is in a much larger box. Transmission line (true ones) speakers are few and far between today due mostly to the cost involved, but they're well worth seeking out and auditioning if one has the opportunity. A good example of a properly done transmission line is the old DCM Time Window 1A, which had remarkably tight and musical bass for the small woofer it employed. That speaker is still sought after by old timers like myself. You can occasionally find a good pair on eBay, but make sure the woofers have been refoamed as they were prone to foam disintegration.
Personally, I love a good acoustic suspension speaker...

Cheers,
Konky.

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