What's new

Ported vs Sealed speakers bass response more than meets the ear? (1 Viewer)

Chris PC

Senior HTF Member
Joined
May 12, 2001
Messages
3,975
I am curious if some ported speakers respond differently in terms of bass frequencies than sealed speakers sound. My interest is how each speaker reproduces the first sound wave of bass frequencies from a standing start. By "first", I mean, the driver is not playing any bass and then a 30 hz frequency is reproduced. How does the speaker produce bass from a standing start?
Here is my understanding and my question.
In a speaker such as the one I have, the 6.5" drivers have a small surface area. When the bass frequency is played, the drivers intitial motion is outward. This doesn't create much bass because the 6.5" driver (even though there are 3 drivers in the case of my speaker) does not have a large surface area. When the driver moves backwards, the bass frequencies emerge from the port and are much louder than the sound produced alone when the driver moved forward.
In a sealed speaker, the intitial soundwave reproduction involves the forward motion of the driver. In this case, the bass produced in the first instant of the sound waveform is the same full bass sound as it is for all the subsequent waveforms that the sealed speaker produces.
Effectively, full bass response is not achieved from a ported speaker until after, for example, 1/30 of second for 30 hz bass or 1/60 of a second for 60 hz. It takes one full cycle before that full ported bass sound exits the speaker port vs the instant bass response of a sealed speaker.
I am not saying that the result sounds like "delayed bass", since the delay even for a 30 hz bass sound is only 1/30 of a second, but then again, I don't know, so I won't rule that out either. I just wonder whether the delay doesn't result in there being a difference in the character of the bass sound itself.
Does this difference in bass sound pressure result in any unique difference in sound character between ported and sealed speakers?
In a ported subwoofer with a 10" 12" or 15" driver, the surface area is quite large. Therefore, I imagine the initial forward motion of the driver produces a larger intitial start to the soundwave than smaller speakers. In other words, ported subwoofers with large drivers don't suffer as much from this intial difference in the soundwave.
Anybody want to comment on this? I suspect a little more is happening than I explain here, but I just wonder if ported speakers sound different than sealed speakers in there bass character for a reason beyond simply their frequency response. Perhaps the way the intitial bass frequency begins plays a part in the sound character of each type of speaker.
My curiosity stems from my going from sealed speakers to ported speakers and always suspecting that "something" sounds a bit odd with the ported speakers. Could be just placement.
I appreciate any more insight into the differences between ported and sealed speakers. I posted this question on another forum in a rather long winded question and I haven't had any feedback.
Thanks for any insight :)
 

John Garcia

Senior HTF Member
Joined
Jun 24, 1999
Messages
11,571
Location
NorCal
Real Name
John
The initial motion is not out, but in. When the coil energizes, it pulls the cone IN, it does not PUSH it at first.
The difference you hear is most likely that ported speakers tend to produce more bass, particularly in their tuned frequency - a function of the size, shape, design, location and length of the port. Essentially, you are hearing both the front wave and the result of the back wave's air moving through the port (often accompanied by a bit of turbulence at the exit of the port from the accelerated airflow.) Ported speakers often sound a bit less accurate because the bass driver's cone is not as controlled by the volume of air inside the speaker as in a sealed design. The advantage of a ported speaker, however, is that they tend to be more efficient due to the fact that the driver does not have to "fight" the internal air mass and they can also be tuned to accentuate specific frequencies. As you mentioned, there is a slight delay between the front wave and the tuned back wave exiting the port. This delay is likely so short that it would be very difficult to notice. Ported speakers also allow a slightly smaller enclosure due to the fact that the air volume is not being used to control the driver's movement. The higher efficiency allows ported speakers to provide more bass with less power, at the expense of some accuracy.
Sealed speakers are often more accurate thanks to the "spring" effect the trapped air mass gives, but also require a bit more power to drive for that same reason. As the cone moves further in, the sub has to be pulled harder to compress the air inside. A sealed enclosure must be more carefully designed also, as the size and shape can have an impact on how the driver performs, with respect to the "bounce" of the back wave and to having an appropriate amount of air within the enclosure for the specific driver to move.
Personally, I prefer the sound of a properly designed sealed speaker, particularly subs. Though all my speakers are ported, including my sub. When I build my car subs, I always go sealed, and feed them with a ton of power. Feel the rumble in your chest...:D
 

Chris PC

Senior HTF Member
Joined
May 12, 2001
Messages
3,975
Thanks for the feedback guys. Sorry for the outburst cry for help!

So you are saying that the cone moves in first? Does this happen the same way with sealed speakers?

That doesn't necessarily make sense to me. a voice coil replicates the sound waveform, does it not? Do all speakers do the same thing? Doesn't it depend soley on the intitial sound waveform? If the waveform is positive to start, then the cone moves out, if the sound waveform starts with a negative motion, then the cone moves in, correct?

My curiosity about the ported sound waves aside, I understood that ported speakers are more accurate over their operating range than sealed speakers because the cones are moving less. I have witnessed this first hand. Watching my PSB's at a given frequency, the cones are moving a fraction of the distance that the cones on my old sealed Bostons are moving. Still, I take your comment about accuracy and store it in my memory as an opinion to be considered.
 

John Garcia

Senior HTF Member
Joined
Jun 24, 1999
Messages
11,571
Location
NorCal
Real Name
John
So you are saying that the cone moves in first? Does this happen the same way with sealed speakers?
I don't know. I am certainly no expert.

As far as cone movement, I believe it is more of a function of driver and enclosure design than something specific between a ported vs sealed design. This will vary with the size of the magnet and voice coil type and size, as well as enclosure size, tuning, etc... A smaller driver in a smaller, sealed enclosure may exhibit more movement than a larger driver in a ported enclosure.
 

Chris PC

Senior HTF Member
Joined
May 12, 2001
Messages
3,975
I disagree. I think the cone moves out. I still think something different is happening. It is not until the driver moves backwards that the port is activated so I wonder how this affects the sound. Anyone?
 

John Garcia

Senior HTF Member
Joined
Jun 24, 1999
Messages
11,571
Location
NorCal
Real Name
John
You may be correct, and that would mean that the driver is in constant tension from the magnetic field, and when the coil is energized, it moves out. Either way, in or out, I don't see really how this would make a difference in sound. It's the movement that creates the sound.
My Mini Monitors don't seem to move a whole lot, but there's plenty of air coming from the port on my sub. :D
 

kevin_tomb

Stunt Coordinator
Joined
Dec 19, 2001
Messages
146
actually it depends on the polarity of the speaker.....which way the plus and minus are hooked up. as to whether there is more bass one way or the other...its the same whether the cone is moving in or out...as long as the speaker is linear in its movement in both directions..
 

John Garcia

Senior HTF Member
Joined
Jun 24, 1999
Messages
11,571
Location
NorCal
Real Name
John
Those things are SWEET. I saw them at my local dealer a few months ago. Haven't had a chance to hear them yet though...
 

Chris PC

Senior HTF Member
Joined
May 12, 2001
Messages
3,975
Well the speakers are wired with the correct polarity.

Regardless, I am still wondering whether a correctly wired driver in a ported or sealed speaker will move outward first. Maybe not all waveforms start with a forward motion, but given the same waveform, each speaker driver in both a ported and sealed speaker should move in the same direction as the other. It is only when the driver moves in the opposite direction that the port produces bass. in a sealed driver, the speaker moves forward and creates the bass instantly. If you use a 30 hz bass soundwave as a reference, the ported speaker will not make bass for 1/30 of a second. That is, if the forward motion of the driver does not create enough volume, and I believe this is the case. Our brains can detect differences in sound arrival times of quite small amounts. What I'm asking, is whether the delay of bass response in the ported speaker makes it sound different. I re-visit this here because I stress that I think the initial motion of the driver will be forward. I am not positive, and I guess different sounds sometimes start differently. Regardless, with both speakers re-producing the same waveform, they act differently and I'm wondering how much of this difference accounts for any difference is the character of the sound.

Anybody else?
 

Chris PC

Senior HTF Member
Joined
May 12, 2001
Messages
3,975
I don't understand how a ported speaker, and the port itself produce a bass sound wave then. I understand they are not totally "out of phase", but could you explain how the ported speaker makes sound then? The article doesn't explain what happens but if you look at the picture (animated GIF) of the driver and port in resonance, the port and driver might not be going in opposite directions, but there is a lag between when the driver moves forward and when the port moves forward. I assume this forward motion is what creates the bass. if you ignored the port below and assumed the above driver was in a sealed speaker, you understand my point that the bass is created and radiated outward from each speaker type at different times. Is that correct? if so, that is weird. That difference in time is exactly what I am trying to figure out.

I guess I have more to learn about how ported speakers work.

So are you saying that the lag between the driver and the port are such that there is no affect in terms of the time of the bass wave when compared to a sealed speaker? I would have to argue that there would still be a difference in the time that the bass radiates away from a ported speaker vs a sealed speaker and this is what I am curious about.
 

Jack Gilvey

Senior HTF Member
Joined
Mar 13, 1999
Messages
4,948
They are not "out of phase" when they meet outside the box, because the box, port and driver are tuned to be in phase. If you designed a box improperly, then yes, the port and driver would be out of phase or otherwise not in resonance.
Not really, the article explains it pretty well actually.

The mass of air in the port and the driver itself are two loosely coupled resonators. When the driver approaches Fb, the tuned frequency, the air, or passive radiator, resonates, augmenting output. Try not to picture the driver "pushing and pulling" the air in and out of the port. The port/PR does lag slightly in a reflex, hence the greater group delay, but it can push the F3 down far enough that the GD peak is essentially out of the critical passband of the sub. In general, the driver is spending more time in its most linear area with the damping provided by a well-designed reflex system, leading to lower distortion.

That's not to say that reflex sounds the same or better than a sealed, it doesn't, just that it's tough to judge what "should" sound better based on the many misconceptions thrown around, or whether the driver goes in or out first. "Forward motion" doesn't "create the bass"...resonance involves compressing and rarifying the air...back and forth.
 

Chris PC

Senior HTF Member
Joined
May 12, 2001
Messages
3,975
Interesting. I'll have to read the article AGAIN. Its just that, to me, in order for sound to exit the port, it has to be first acted on by the motion of the speaker driver. Anyways, it sounds like that "group delay" is closer to what I am interested in finding out about.

Also, I understand this:

"Forward motion" doesn't "create the bass"...resonance involves compressing and rarifying the air...back and forth.
But now apply this principle to sealed and ported speakers. if a bass sound wave sent to a speaker contains an initial positive motion, the sealed speaker will move forward, compressing the air. The ported speaker will surely move forward also, but the air it compresses in front of it is less responsible for the ultimate compressed air in the sound wave it creates when compared to the port. When I look at ported speaker frequency response curves, the drivers taper off an the port takes over, so this is a reflection of the above. Correct me if I'm wrong, but when the speaker in a ported enclosure reaches its limit of forward motion, the air in front of it is compressed, but the port has not yet produced any compression. is this not correct? It is after this point that the port creates compression to form a sound wave. Otherwise, the port would be creating a compression of air outward when the speaker is moving outward and that makes no sense to me. when I talk in these terms, I am talking in absolutes. So if the port in fact creates the compression of the sound wave the instant the speaker stops moving forward, but not necessarily when it is moving backward, then that is different. But in both cases, you see that the port compressed wave and the compressed wave created by a sealed speaker are not identical in their timing of creation. Yes or no? is this the group delay you speak of? The "group" meaning the delay in relation to the other non-port generated soundwaves.

How about this. Lets say you take two speakers, one sealed and one ported design, both comparable to one another in frequency response, at least, for the purpose of this experiment, we'll assume that we don't square off two totally disimilar speakers (EG we use speakers with similar frequency response, taking into account the differences between ported and sealed. We just don't want to compare speakers that are extremely different). Then, if you had a microphone and placed it in an anechoic room to record the wave exiting a sealed and a ported speaker, how would the recorded sound waves compared to one another? What would be different? Is the group delay precisely what I am after here?

This is exactly what I want to know. Also, since there is a lag or 'group delay', we'd compare with a broadrange of frequencies and noise, and not just bass tones. For instance, you'd want to see if the bass frequency arrived at the microphone at a different time than the midrange and treble of, for instance, a bass drum kick.

So that is what I am after.
 

Jack Gilvey

Senior HTF Member
Joined
Mar 13, 1999
Messages
4,948
But in both cases, you see that the port compressed wave and the compressed wave created by a sealed speaker are not identical in their timing of creation. Yes or no? is this the group delay you speak of? The "group" meaning the delay in relation to the other non-port generated soundwaves.
Group delay is not just occuring because of the port...all subs have group delay. It's the delay between higher and lower sounds, not between port and non-port frequencies.
 

Chris PC

Senior HTF Member
Joined
May 12, 2001
Messages
3,975
Still need to understand more. Like I said in the last statement, regardless of how we say the speaker works, I'd like to see a frequency time graph for a sealed and ported speaker and then I'd learn something. Heck, I have a PC, a soundcard and a microphone, a pair of sealed speakers and a pair of ported speakers so maybe I should find some software and toy with spectrum analysis of speaker output. Trouble is, I don't have an anechoic room.
Thanks for the help though, you are definitely helping me understand it more. Its just that, when I look at a sealed speaker, I can easily understand how the motion of the sealed driver creates the sound wave that I hear. When I see a ported speaker, its not so easy.
It makes no sense becasue you're picturing it as two resonators rigidly coupled by the air in the box (driver goes in, air gets pushed out the port), but what you describe is close to what happens.
I realize its not rigidly coupled, but sealed and ported systems must sound different for a reason related to the port response in terms of time. It may not be as simple as the driver going in and the air gets pushed out the port, but its got to involve the driver moving the air to begin with or why would we even need a driver. My guess is that because of the enclosure and port, the driver doesn't have to move nearly as much to reproduce the wave. Perhaps this shorter distance translates to less time required to create the wave and so the time is equal to that of a sealed speaker creating the sound wave. The trouble is, it still messes my brain up because the driver motion appears to be in the opposite in direction when compared to a sealed speaker. I mean, how can forward motion create a compression wave at the port? I can't see that. I can only see the drivers reverse motion creating a wave at the port. I understand its not rigid, but you still get my point?
I need or want to know exactly what is happening in a ported speaker that causes the port bass sound waves to be produced and how that compares to a sealed speaker.
I need to see more and study more. It interests me. I saw the different designs for speakers, like the isobaric, the bandpass etc. very interesting stuff. I must see more. I wish there was a course I could take :)
What is that really cool book that everyone buys? I used to hear about here and there but I've forgotten the name now.
 

Chris PC

Senior HTF Member
Joined
May 12, 2001
Messages
3,975
Anybody else want to specifically explain the difference between ported and sealed speakers?

Here, try this on for size:

Comparing ported vs sealed speakers, using similar sized drivers or speakers with comparable frequency response, for one complete wavelength of, say, the beginning of a 30 hz sinewave. Feed both speakers a sinewave which starts with a positive compression, (motion depicted on the graph above the zero point).

Sealed speaker:

Upon receiving the input signal, the sealed speaker moves forward to its limit and then back towards its limit in the opposite direction and then returns to rest. When the sealed speaker driver moved forward, a compression was created in front of the driver, then the speaker moved backwards through its resting point to its limits in the other direction, thereby creating a rarefaction. So the result was a sound wave starting with a compression and ending with a rarefraction.

Ported speaker:

When the ported speaker driver receives the exact same 30 hz sinewave, the driver first moves forward, albeit, a much smaller distance, and this creates a much smaller soundwave compression in front of the driver, (and I think perhaps a rarefaction at the port? Either way, I understand that the are not in phase such that they cancel one another out, at least not in the ports range of reponse. Outside the ports range ?), then the speaker moves backwards to its limit in the other direction creating a compression wave at the port exit, and then finally back to its resting point. This is not a rigid system, meaning that the port wave is not occuring directly in synch with the motion of the driver. I'm not sure how this affects the system, but its important to remember.

If we compare the times of compression, they seem to occur roughly 180 degrees apart (roughly because of the non-rigid driver and port coupling mentioned above). So because this coupling of the driver and the port is not rigid, such that the 180 degrees we are talking about is not a rigid 1/60 of a second, I'm not sure if the onset of the port wave is faster or slower or what the implications of this coupling mean. (Also, because the ported speaker driver doesn't move as much, I wondered if that reduced movement translates into faster activation, but that didn't make sense since each wavelength has to occur linearly (at least for a sinewave) over the wavelength. A 30 hz wavelength has to be created over a length of time of 1/30 of a second. The driver cannot accelerate forward and then back, such that it reaches its back most position faster, because then it would have to accelerate and then decelerate. Not sure about this.)

So does anybody see what I see? Sealed speaker receives signal and creates compression with forward driver motion. Ported speaker receives signal and creates its dominant compression with the reverse motion of its driver. Look at the graph for a ported speaker and you will see that the response of the driver below a certain point drops off rapidly and the speaker port dominates, verifying that the forward motion of the driver does not create the compression wave the same way the sealed speaker does.

Do the ports in ported speakers produce bass that is 180 degrees out of phase with sealed speakers or ?? That is the impression that I get.
 

Users who are viewing this thread

Forum Sponsors

Forum statistics

Threads
346,906
Messages
4,794,392
Members
141,929
Latest member
2handband
Top