Why are most speakers rear ported instead of front ported ?
- Thread starter Nitin K
- Start date
Point well noted, thanks.
keith_correa
Well-Known Member
To what?
Let me put it this way:
In 2 speakers, all other things being the same EXCEPT the port location [front & rear]:
1. if the speakers suffer from the issue that @Vineethkumar01 mentioned in Post # 7, the front ported speaker will sound worse than the rear ported.
2. if there is inadequate space between the port outlet and the wall, the rear ported speaker will sound worse than the front ported one.
ajuvignesh
Well-Known Member
"The downward-firing, angled reflex port helps to reduce room boundary effects and facilitates easy loudspeaker placement."
- says Tannoy for xt6f
"Ideal for small to medium-sized rooms, the F501 is supplied with a dedicated plinth incorporating our BassTraxTM Tractrix diffuser system, which integrates bass energy uniformly into the room"
-says Fyne audio for its F501.
- says Tannoy for xt6f
"Ideal for small to medium-sized rooms, the F501 is supplied with a dedicated plinth incorporating our BassTraxTM Tractrix diffuser system, which integrates bass energy uniformly into the room"
-says Fyne audio for its F501.
IndianEars
Well-Known Member
WOW! This is an active thread ! 2 Pages and it began at noon today....
My core expertise is not in Loudspeaker design, but my understanding is:
1. A port moves air into the room.... Just like a speaker driver does.
2. The Port is "Tuned" to move the most at typically in the LF (Low Freq) when the the driver output rolls off.
The Output from the port is meant to AUGMENT the (rolling off) LF from the Woofer.
Hence it is essential that port Port's Output is IN PHASE with the LF driver, if the port is located on the same face as the LF diver (usually on the Front Face)
If the Port's output is Out of phase with the LF Driver, then the Port MUST be located at the rear of the speaker, if the Woofer is on the Front Face of the speaker.
Its Only if the Port Output is in phase with the speaker, that the port can be located on the Front face of the speaker.
The Output Phase Of the port, I believe is the PRIME Criteria for deciding the location of the port... Front or Rear of the speaker.
keith_correa
Well-Known Member
At frequencies where the port most comes into play, when the cone moves in, the air moves out of the port. What does that tell us about the phase of the port? 
IndianEars
Well-Known Member
If only things were so simple.....
The Length the wave travels, determines if the Port output is a Node or anti-node.... Just like in a room, where the speaker creates Nodes and antinodes at multiple points in a room....
The Length the wave travels, determines if the Port output is a Node or anti-node.... Just like in a room, where the speaker creates Nodes and antinodes at multiple points in a room....
keith_correa
Well-Known Member
That affects the location of the port on a given plane. Does not affect rear/front placement of the port.
Vineethkumar01
Well-Known Member
Hi @IndianEars,
I think the argument of port output cancelling the woofer output due to phase mismatch is not valid for typical bass reflex designs (transmission line type designs need a bit more deeper thinking I guess due to the long lengths of the tunnel). The port is a helmholtz resonator, whose output peaks at the tuning frequency. At the tuning frequency, the driver works minimum. Port works maximum in producing sound output at that frequency. You can see this in my measurements here: https://www.hifivision.com/threads/audibility-of-port-resonances.85679/ around 38 Hz, where there is a notch in driver output and a peak in port output.
Above and below the tuning frequency, the port output reduces, (ideally) to the point that it acts like a port is not there (leaving aside pipe resonance frequencies). Below the box tuning frequency, the port essentially acts like a hole in the box. this will cause leakage of frequencies out of phase with the drivers sound (comes from backside of the driver) and cause cancellation (hence the 24 dB/octave fall off in low frequency output in bass reflex boxes unlike a 12 dB per octave sealed box fall off).
Also, think about the wavelengths at the low frequencies, at a 40 Hz tuning, we have a full wavelength of 17m. Hence the path length difference between port output and driver output is of the order of less than half a meter (typically). We need about 8.5 metre (180 degrees out of phase) of path length to create destructive interference between driver output and port output at this frequency.
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Thanks to everyone here in the thread for trying to clear my doubts especially & for taking the time & efforts to explain. From the discussions of audio guru's like Vineethkumar01, IndianEars & Keith_Correa , I could only grasp few aspects but the other technical explanations frankly went over my head. But nevertheless got the basic idea.
surfatwork
Well-Known Member
Great discussion. Wonderful points @Vineethkumar01
Need more high quality threads like this on our forum instead of the car crash TV we are sometimes regaled with.
Need more high quality threads like this on our forum instead of the car crash TV we are sometimes regaled with.
As mentioned in my views over #16 Front port would be suited for those who have space challenges for placing rear ported speakers. It would differ from person to person depending on available space and also the type & design of speakers, cabinets, etc etc being used.
As a former DJ, the professional equipment used including bass bins are all Front ported. None of them are rear ported as the intend is to provide the best bass effects to the listening area / dance floor. I am sure even all our theatres / cinemas use also front firing bass speakers with front ports. The speakers which we call TOPs contain mid bass drivers and horn /Bullet tweeters. These speakers too are Front Ported.
Isn't this the intent of all speakers, bass or not?
Trying to understand this (in relation to port placement) Wavelength can be found by dividing the speed of sound in feet which is 1,130 feet / second by the frequency we need to find the length of. Dividing 1,130 by 40 produces a quotient of around 28 feet. Therefore, a 40 Hz. wave is 28 feet long….
Vineethkumar01
Well-Known Member
just noticed the mistake. All wavelengths are valid for 20Hz. For 40Hz, everything should be divided by 2.
Decadent_Spectre
Well-Known Member
Most professional speakers are front ported. Home audio speakers do have examples of a rear port but I honestly wonder if sometimes it is an aesthetic choice. In other times perhaps people expect end users to use them near boundaries to reinforce the bass, perhaps they assume that their customers want this? Others might design it so that the rear port placed near a wall does not boom but augments the speakers weak native bass response, as such they intend for the wall to support the bass from their small speakers which would otherwise be anemic sounding. As someone pointed out sometimes there isn't a whole lot of space on the front baffle if one is trying to minimize the speaker size. One needs to remember that when it comes to home audio speaker output capacity, reliability and perhaps measured response is not of as high importance as making sure the speaker is compact,aesthetically pleasing and meets the price point the manufacturer wishes to target. These three things (size,aesthetics,cost) along with brand name drive the consumer speaker segment in my view.
As a side note I honestly believe that 90%+ of consumers would be better served with a cheap Behringer professional speakers with a 10-15" woofer and CD along with a DSP/Pro amp. The problem with this approach is that it is larger and more complex. Consumers often will perceive it to have low "fidelity" compared to equally priced home audio speakers and perhaps above all consumers are not comfortable with this notion of using professional speakers at home.
Never really thought about rear ports to be honest but since the topic came up here are my random thoughts on it after pondering for a moment.
As a side note I honestly believe that 90%+ of consumers would be better served with a cheap Behringer professional speakers with a 10-15" woofer and CD along with a DSP/Pro amp. The problem with this approach is that it is larger and more complex. Consumers often will perceive it to have low "fidelity" compared to equally priced home audio speakers and perhaps above all consumers are not comfortable with this notion of using professional speakers at home.
Never really thought about rear ports to be honest but since the topic came up here are my random thoughts on it after pondering for a moment.
Home audio speakers come in all sizes, so no question of size restriction. Price point, again, home audio speakers cost much more than their pro counterparts, so, not restricted by price either. Aesthetics is probably the only aspect that is given equal or more importance than sound quality.
My observation has been that pro speakers are all about delivering maximum wattage. Their horn tweeters are designed to project and emphasise higher frequencies over a larger area, and have a tendency to sound harsh, and are also directional. Horns do an excellent job in an open area setting.
Soft dome tweeters, popular in home audio, have better dispersion, and they sound smoother, ideal for close-proximity listening conditions of a typical home audio set up. Again, exceptions to use of horn loaded tweeters in home audio exist, e.g Klipsch. They deliver higher dynamics, but can get fatiguing in a close-proximity environment.
But, there are pro speakers with horn tweeters that sound sweet, as well, exceptions exist, but they do come at a higher price point. I do agree that a well made pro speaker can sound fantastic, and at a much lower price than its home audio counterpart. It's just that their ABS enclosures that make them less than ideal, from a home decor point of view.
Decadent_Spectre
Well-Known Member
I disagree. Most home speakers sold are small and relatively cheap. Yes there are the larger ones and more expensive ones but very few of the systems that are large and cost upwards of 100,000 US$ are sold. I use this as a random price point but I have observed that in home audio most large speakers are very expensive compared to what they offer. Pro systems are not cheap by any means, if you compare it to a million $ stereo home set then yes it is cheap but by and large both home and pro speakers have a wide price range.
Maximum wattage is a very limited way to describe it, they are mostly about offering high output for long duration with good reliability as well as a frequency response that does not degrade too much as you push the limits. This is of course for a decent or good pro system, the cheaper units are not as good at the limits but then they are still far superior to home systems. The CD in "horn tweeters" as you call them are not designed to "project" nor emphasize higher frequencies, they are designed to do what I said before, produce high output, for long duration, with reliability and keep the response the same as it was at low volume. Again it varies by price point, the one particular point about the CDs in horns is that they are designed to provide directivity, directivity makes it seem like they are projecting it while sensitivity makes it seem like they are emphasizing it. Far superior to any dome. CDs can indeed sound harsh above 5-6K~, thats where the dome has an advantage but a dome can't even hope to produce the same level of output. I don't know why you claim they have better dispersion, they have wider uncontrolled dispersion, if this is better in your view good, it isn't for most. CDs require DSP for home usage to sound good.
Good sounding pro speakers rarely come in plastic enclosures, I am glad you agree that pro speakers sound good, better than anything in home audio if you know how to use a DSP. Matching to taste is key for user preference and DSP enables this, home speakers lack the output, thermal and mechanical capabilities to be DSPed as liberally as a pro speaker. Pro speakers are too large for homes and people don't like their looks but otherwise no home speaker can compare. The home speakers primary advantage is the out of the box tuning/voicing by the manufacturer. If you don't know how to use a DSP you will be lost with a pro speaker as out of the box with its relatively flattish response and horn mounted CD it will take your ear off. If you have no DSP or don't know how to tune it you will curse yourself for buying a pro speaker. Most home users don't know the response they are hearing and like (they would be in for a surprise if they measure it, especially with no smoothing and a window no more than 20db), and that's fine because a flat response (and Harman's marketing) sound like rubbish.
This is in fact, a great query. This piqued my curiosity and i've been mugging up a lot on this. And, it appears that this has been a common topic on all popular audio forums. There have been various reasons, from technical to aesthetics. But, there has been no ONE definite answer. It'll be interesting to know more about this directly from a speaker designer.
Here's an excerpt from a speaker manufacturer.
"Ok, here's a test, as a manufacturer I'm not a big fan of rear ports either but visually they are generally easier to place on the back. Larger bore ports also leak a fair amount of midrange which can have quite a negative impact on the overall sound when placed on the front unless internal baffling is used which is not always an option in smaller models.
On our recent Compact 1 we wanted to make the design as small as possible so the port was put on the rear. I've just done a redesign to see how it would work on the front - it makes the speaker 3cm taller (handily gives around 1 litre of extra volume which it may well benefit from in terms of bass output)
What do you think? Does it ruin the look, make the speaker too big for it's bookshelf/desktop usage (25cm tall now), limits placement of logo so I may have to go angled top corner which would mean left/right pairs for symmetry - do you even prefer it?"
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