[4891ttt]

Hi, I have a question about ported speakers. What is the highest frequency that can be coming up from the port of a bass-reflex design? Let's take a 2-way speaker that has a crossover frequency of 2khz and a frequency response of 75hz to 20khz since the low frequency driver (which is supported by the port) has response from 75hz to 2khz does that mean some mid-range energy is also coming up from the port? Thank you for helping..

 

[4891ttt]

I thought this because I want to know if ports have any effect on mid-range frequencies, since the low frequency driver in 2-way systems has a wide range they also reproduce a 400Hz (for example) signal and since it's not directional as a 10kHz signal the driver cone is sending some of it inside the box and than it's directed to the port, which I think can lead to midrange coloration or even the lower midrange characteristics of a bipolar design.. (if it's rear ported)

 

[Iamjcl]

I'm no speaker designer, but I think you've answered your own question. I agree that some of that sound comes out of the port.


The problem with this, as I understand it, is that it is out of phase (maybe not 180 out, but out) with the direct sound.


I've used port plugs before (B&W 602s3 - came with the plugs) when using a subwoofer, as I liked the sound better. Don't know if its because of what you mention.


I'd like to add a question to yours - what downside (besides reducing LF extenstion) is there to using port plugs in a ported speaker?

 

[mayhem13]

To answer the question correctly, you'd need to know the tuning frequency of the enclosure. Yes some midrange frequencies escape through the port. Are they capable of coloring the sound. That's questionable and depends on the design of the enclosure. A good design doesn't line up the port with the rear wave of the woofers rather it should be offset a bit. In the case of the front firing port, the rear of the enclosure is usually sufficiently damped to absorb and diffract the rear wave as to eliminate any direct midrange that may reflect and escape from the port. The rear wave as in a dipole is 180 out of phase as well. As for port plugs, the 'improvement' in the sound comes from the change in 'Q' of the box, not the reduction of escaped midrange frequencies. Some the most acclaimed 2 Way and Fullrange speaker systems utilize ports very effectively to increase bass response. If it's still a major concern for you, look for a three way system where the woofers are in their own chamber in the enclosure where the the playback is limited by the crossover. IMO there are plenty of more important things working against a speaker system than port midrange leakage.

 

[4891ttt]

Thanks for the reply.. it includes almost all the answers I needed.. But I wonder something about that 2-way speakers with absorbing rear enclosure, what is the approximate response curve of the port above the tuning frequency? Also... which 2-way speakers have that design?

 

[J_Palmer_Cass]



Quote:
Originally Posted by mayhem13 /forum/post/15531778



Some the most acclaimed 2 Way and Fullrange speaker systems utilize ports very effectively to increase bass response.

That does not mean that they will ever blend well with a dedicated subwoofer. 180 degrees out of phase at the port frequency makes blending any ported speaker with a subwoofer a difficult thing to do properly. You can have a similar problem blending a sealed "full range" speaker with a ported subwoofer!

 

[J_Palmer_Cass]



Quote:
Originally Posted by Iamjcl /forum/post/15531482


I'm no speaker designer, but I think you've answered your own question. I agree that some of that sound comes out of the port.


The problem with this, as I understand it, is that it is out of phase (maybe not 180 out, but out) with the direct sound.


I've used port plugs before (B&W 602s3 - came with the plugs) when using a subwoofer, as I liked the sound better. Don't know if its because of what you mention.


I'd like to add a question to yours - what downside (besides reducing LF extenstion) is there to using port plugs in a ported speaker?

No downside. When used with a subwoofer, plug the ports of the main speakers. If no subwoofer is used, leave well enough alone.

 

[mayhem13]



Quote:
Originally Posted by J_Palmer_Cass /forum/post/15532926


That does not mean that they will ever blend well with a dedicated subwoofer. 180 degrees out of phase at the port frequency makes blending any ported speaker with a subwoofer a difficult thing to do properly. You can have a similar problem blending a sealed "full range" speaker with a ported subwoofer!

The Original post didn't indicate sub integration, so i left well enough alone.

 

[mayhem13]



Quote:
Originally Posted by 4891ttt /forum/post/15532649


Thanks for the reply.. it includes almost all the answers I needed.. But I wonder something about that 2-way speakers with absorbing rear enclosure, what is the approximate response curve of the port above the tuning frequency? Also... which 2-way speakers have that design?

That would be by design on an individual basis.


Any speaker worth buying should have some damping material added to the inside of the enclosure. How much and what type is debatable and outside the scope of this thread. Look inside the port to see if the cabinet has damping material or just bare interior walls. A flashlight should do the trick. For rear ported speaker, if you see the woofers while looking inside, it may be an issue.

 

[4891ttt]

Yes all speakers have that material inside, I just wasn't sure what it was for until now, thanks..

 

[sivadselim]

Are you asking about the port's actual output, as designed, or the sound from the backside of the drivers that escapes through the port. They are two different things.


The port's output, as designed, should be near the low-end response of the speakers. Mid-range frequncies should not be physically produced by the port.

 

[Iamjcl]

Interesting info...


Again, I'm no speaker engineer, but I think the tuning freq. of the enclosure attempts to route frequencies below that figure to the port, while above that the woofer itself directly (from the front of the cone) produces the (most) sound.


But, as the OP was concerned, I don't think ONLY information below that frequency comes out of the port. Ideally, yes, but practically (sound insulation in the box, shape of the box, location/size of the port, resonances inside the enclosure) probably not.


On using the plugs, what was mentioned above is exactly why I used them. I didn't have a need for the lower extension, as subs were being used, but always wondered if there were other factors that could be worsened.


Thanks for the replies.

 

[sivadselim]



Quote:
Originally Posted by Iamjcl /forum/post/15536861


On using the plugs, what was mentioned above is exactly why I used them. I didn't have a need for the lower extension, as subs were being used, but always wondered if there were other factors that could be worsened.

Just an FYI. Generally, plugging a speaker's port(s) actually increases the extension at the expense of some output higher in the FR curve. Granted, this lower extension is not usually audible so the apparent audible difference between a ported and plugged configuration is that there is more low-end output from the ported configuration in the range that IS audible.


Just as an example, here is an FR graph of the SVS MTS-01 showing both the plugged and ported configurations and the difference in the roll-off characteristics. The ported configuration has a lower -3dB point. The -3dB point of the ported configuration is 60Hz. But you can see that at 60Hz, the plugged configuration's output at 60Hz is lower. Eyeballing it, relative to the point that the ported configuration's curve crosses the 60Hz line, it appears that the plugged configuration is probably -3dB ~75Hz or so.

Many contend that because of the shape of the curve, a plugged configuration can help to yield better integration with the subwoofer, but this is probably a broad statement.

 

[Iamjcl]

Thanks - interesting FR graph. Less of a difference than I would have expected!

 

[sivadselim]



Quote:
Originally Posted by Iamjcl /forum/post/15537681


Thanks - interesting FR graph. Less of a difference than I would have expected!

Still, it IS significant. The difference at 40Hz is ~5dB. And because of the different shapes and slopes of the curves' roll-offs, the speaker WILL definitely sound relatively different in the 2 configurations.


Interestingly, too, note that the plugged configuration appears to have slightly more output in the range from 100Hz to 200Hz or even higher. And, note the differences in the range from 200Hz and 500Hz.

 

[4891ttt]

I was just wondering the damping level of the material inside the box for any frequencies above the tuning frequency.

 

[J_Palmer_Cass]



Quote:
Originally Posted by sivadselim /forum/post/15537663




Many contend that because of the shape of the curve, a plugged configuration can help to yield better integration with the subwoofer, but this is probably a broad statement.

Regardless of what "many" contend the issue is phase at the port frequency, and not FR. Plug the port, and you do not get an 180 degree phase inversion at the port frequency. Kind of hard to blend the mains with a sub when phase of the mains goes 180 degrees out of phase at the port frequency. That is the reason that THX requires sealed main speakers in order to get a THX speaker rating.

 

[craig john]



Quote:
Originally Posted by J_Palmer_Cass /forum/post/15541038


That is the reason that THX requires sealed main speakers in order to get a THX speaker rating.

http://www.klipsch.com/products/details/kl-650-thx.aspx


Craig

 

[J_Palmer_Cass]



Quote:
Originally Posted by craig john /forum/post/15544637

http://www.klipsch.com/products/details/kl-650-thx.aspx


Craig

That is a THX Ultra2 speaker. That is a different speaker specification than the standard THX specification. If those speakers were used in a small room, I am sure that you would have issues with phase interference at the port frequency.


http://www.hometheatermag.com/bootcamp/116/index4.html



QUOTE:


"Before he broke the system down into its complementary parts, Laurie explained that some of Ultra 2's additional goals were "to perform at its best with both movies and music with one speaker layout and be less room-dependent." THX Ultra front loudspeakers, for example, were originally optimized for movie soundtracks and were required to have focused vertical directivity. This radiation pattern prevents sound from spraying up toward the ceiling or down toward the floor, which might cause audible colorations, thus providing clean dialogue and clear sound effects. Unfortunately, the vertical D'Appolito driver array that most manufacturers employ to meet this specification tends to create a less-than-smooth vertical off-axis frequency response. In the last decade or two, considerable research and listening experiments have shown that a smooth off- and on-axis frequency response is important to a system's sound quality. The Ultra specification works great for movie soundtracks and can sound good with music played in an acoustically treated high-end home theater where the uneven off-axis response can be absorbed, but it is often criticized with music playback in the more-lively living rooms that the speakers were intended for. While THX's ideal goal is still to limit undesirable early reflections, they have laid the responsibility for achieving it in the hands of the consumer. THX Ultra 2's front-speaker specification places a greater premium on having a "well-defined, smoothly varying frequency response both on- and off-axis," which guarantees that both music and movies will sound good in both dedicated theater rooms and general-purpose living areas."

 

[cschang]



Quote:
Originally Posted by J_Palmer_Cass /forum/post/15541038


Regardless of what "many" contend the issue is phase at the port frequency, and not FR. Plug the port, and you do not get an 180 degree phase inversion at the port frequency. Kind of hard to blend the mains with a sub when phase of the mains goes 180 degrees out of phase at the port frequency. That is the reason that THX requires sealed main speakers in order to get a THX speaker rating.

But you do not crossover to the sub at the port tuning of the speaker, you should do so above it.