Rear Ported

[philpot1001]

Can someone explain to me why most manufacturers of floor standers make their speakers rear ported? Is there a sonic advantage? because as far as i can tell all it does is make the speakers more difficult to place! My old Missions are front ported and never caused me a problem in any house ive lived in, surely a front ported speaker would be more advantageous, or am i missing something?

 

[Vladimir]

Ports are like how car exaust make the car want to move forward by propolsuion even when you are breaking the wheels (which is why cars don't stop immediately). The engine (in this case the woofer) makes bass and sends it a little bit on the front and a little bit on the back through the port. The front bass is the one you want to hear and the excess they tuck it in in the back to hide, but if it's close to a wall it reflects back and you get double the bass than you wanted. If the port is in the front, you can get all the bass set right out of the factory. If cars had the mufflers on the front, they would stop immediately when you hit the breaks.

I'm no professional hi-fi reviewer or engineer, but I think this is how it works. YMMV

 

[philpot1001]

not sure i get the car analogy, however i see the point about chucking the excess bass out of the back....however, obviously speakers "can" be designed with a front port working along with the drivers - there are a few examples of this, my speakers included. Just seems like most speaker manufacturers prefer the rear ported design which creates potential problems for the user.......i guess most floorstanders are naturally bass heavy and need a rear port to bring them back into normality.

Just need to be careful about demo rooms and the sales people moving speakers a meter or so away from the wall, if you cant replicate that at home.

 

[Al ears]

Mostly it is all down to aesthetics I feel. Manufacturers put ports where it suits the speaker design some are bottom ported and some have none at all. In general call speakers prefer a bit of space around them and some rear ported are intended to be close to walls to reinforce the bass.

You just have to do your homework and see which are most likely to work well within your own listening room.

 

[chebby]

Ports are like how car exaust make the car want to move forward by propolsuion even when you are breaking the wheels (which is why cars don't stop immediately). The engine (in this case the woofer) makes bass and sends it a little bit on the front and a little bit on the back through the port. The front bass is the one you want to hear and the excess they tuck it in in the back to hide, but if it's close to a wall it reflects back and you get double the bass than you wanted. If the port is in the front, you can get all the bass set right out of the factory. If cars had the mufflers on the front, they would stop immediately when you hit the breaks.

I'm no professional hi-fi reviewer or engineer, but I think this is how it works. YMMV

LOL! Thompsonuxb would've been proud to write that.

 

[MajorFubar]

If cars had the mufflers on the front, they would stop immediately when you hit the breaks.

No, really they would not lol, It's an exhaust not the outlet of a jet engine.

 

[plastic penguin]

Speaker manufactuers are totally f####d up. They've reduced the cabinet size to accommodate smaller living/listening space, but when the cabinets are smaller they don't have room at the front for ports. The answer? Stick them in the back! That means, however, generally speaking, speakers have to be placed further away from the back wall. Not really the answer.

That's why ATC, Spendor and others benefit from sealed units: You can make the cabinets bigger and less fussy about positioning.

On the whole floorstanders are seen as generally better: More space at the front for ports, or underneath firing - and like Rega it gives more scope for side firing speakers.

 

[philpot1001]

much to my chagrin i dont realy like the look of the Spendour or ATC units (although ive never seen them in the flesh to be fair). The Tannoy 6.4's with Auxiliary bass units look like they may offer some benefit regarding placement..............also i dont actually know i have an issue regarding placement lol, as mine are front ported never had that issue, however when i come to replace them i am keenly aware i cant really go futher out from the wall than ~30 inches so rear ported "may" cause issues....or may not. Will just have to suck it and see what i can get away with.

 

[Al ears]

Ports are like how car exaust make the car want to move forward by propolsuion even when you are breaking the wheels (which is why cars don't stop immediately). The engine (in this case the woofer) makes bass and sends it a little bit on the front and a little bit on the back through the port. The front bass is the one you want to hear and the excess they tuck it in in the back to hide, but if it's close to a wall it reflects back and you get double the bass than you wanted. If the port is in the front, you can get all the bass set right out of the factory. If cars had the mufflers on the front, they would stop immediately when you hit the breaks.

I'm no professional hi-fi reviewer or engineer, but I think this is how it works. YMMV

LOL! Thompsonuxb would've been proud to write that.

And he would have been wrong.

 

[chebby]

much to my chagrin i dont realy like the look of the Spendour or ATC units (although ive never seen them in the flesh to be fair). The Tannoy 6.4's with Auxiliary bass units look like they may offer some benefit regarding placement..............also i dont actually know i have an issue regarding placement lol, as mine are front ported never had that issue, however when i come to replace them i am keenly aware i cant really go futher out from the wall than ~30 inches so rear ported "may" cause issues....or may not. Will just have to suck it and see what i can get away with.

My rear-ported speakers thrive in corners and close up to walls. The manufacturer designed them for this kind of placement and recommend it in their instructions.

Having loudspeakers 30" away from walls is insane unless you have a [large] dedicated listening room that serves no other purpose.

 

[Vladimir]

Speaker manufactuers are totally f####d up. They've reduced the cabinet size to accommodate smaller living/listening space, but when the cabinets are smaller they don't have room at the front for ports. The answer? Stick them in the back!

Good point.

When you think about it, if they put the port on top, it might push the speakers down and couple them more, and the factory doesn't really know if you want to couple or decouple your speakers. If the port is on the bottom, propolsuion will have a lift up motion and by Sir Isaac Newsome's law of action and reaction make the speaker lighter, thus more decoupled!

Aha, you say! But what if I wanted my speakers coupled?

Perhaps they should put ports on all 6 sides and with bottle caps for each user to decide where they want the bass propolsuion to be direction. I mean come on. It's not hard.

 

[Vladimir]

Ports are like how car exaust make the car want to move forward by propolsuion even when you are breaking the wheels (which is why cars don't stop immediately). The engine (in this case the woofer) makes bass and sends it a little bit on the front and a little bit on the back through the port. The front bass is the one you want to hear and the excess they tuck it in in the back to hide, but if it's close to a wall it reflects back and you get double the bass than you wanted. If the port is in the front, you can get all the bass set right out of the factory. If cars had the mufflers on the front, they would stop immediately when you hit the breaks.

I'm no professional hi-fi reviewer or engineer, but I think this is how it works. YMMV

LOL! Thompsonuxb would've been proud to write that.

And he would have been wrong.

I'm no professional rocket science reviewer but I'm pretty sure propolsuion exists.

BTW listening to Courtney Pine's - Journey to the Urge Within. *music2* Sounds very good, even with the ports on the back.

 

[Blacksabbath25]

my dali opticons 6 floor standing speakers have 2 rear ports at the back on each speaker and they are big cabnet speakers too but i do understand why i do have 2 rear ports on each as they have to move so much air from the bass drivers but if i bunged them they would sound muffled in there sound

 

[matt49]

When you think about it, if they put the port on top, it might push the speakers down and couple them more [...]

... and dust would get in through the port.

 

[Vladimir]

When you think about it, if they put the port on top, it might push the speakers down and couple them more [...]

... and dust would get in through the port.

Not in a Naim system. You have to keep those running 24/7 to have them sound good.

 

[davedotco]

We haven't had one in a while. Nice to see the 'Thompson Technique' of posting complete rubbish being employed by so many, nice stirring Vlad.

If anyone is genuinely interested in the issue of where ports are placed on a box loudspeaker, the answers are in a concurrent thread...

http://www.whathifi.com/forum/hi-fi/q-acoustics-bt3-review

Specifically posts 10, 11, 13 and 14.

 

[plastic penguin]

Surely by the nature of BOOKSHELF or standmount speaker they are designed for limited spaces. Then surely if they are placed on a shelf or a sideboard or stand they shouldn't have rear ports, unless they have the bass depth of a portable transistor radio.

 

[Vladimir]

Nice to see the 'Thompson Technique' ...

I think I cracked the formula. Use common sense but be entirely devoid of any laws of physics applying to this Universe.

Back to regular program.

The basics I mentioned above are available to anyone with access to the internet. Take a look at any polar response measurements of box loudspeakers.



This is typical of most box loudspeakers, there is very little energy above about 1kHz radiated to the rear, but bass frequencies are near omnidirectional.

Reflections from the backwall will obviously by dominated by bass as no high frequencies are present to be reflected, Ergo, the bass at the listening position gets boosted, other frequencies are not.

The designer balances the forward response plus the reflections (bass) to give a balanced response at the listening position. The position that the speakers are in when making that evaluation is then the 'best' position for the speakers with respect to tonal balance.

The engineer can design speakers for whatever position he wants, though 'audiophiles' love 3D soundstaging which requires speakers to be well clear of the room boundaries, so most are balanced for this type of positioning.

When they get in peoples homes they often find themselves poorly placed, close to room boundaries, so sound fat and bloated. Thats just the way it is.

Of course port positioning can make a difference.

Very low frequencies may not be directional but a port with all its noise, distortion (usually greater than the drive units) and wind tunnel effect certainly can be. Look at ported speaker response graphs and you will see that on occasions port output bleeds into the lower mids which will clearly have an effect especially if the port faces the listener.

Not just that, I long have been an advocate of either IB design or, if you must have a port, downward firing for more ease of positioning and lack of audible internal reflections.

Not suggesting otherwise DM.

The point being made is that the position of the port, front or rear, makes no difference to the the positioning of the loudpeaker and the resultant bass response.

(Unless a rear ported speaker is placed so close to a boundary (a few inches) that it actually 'loads' the port changing it's behaviour)

You are quite right regarding port noise, low frequency induced 'chuffing' effects can be particularly noticeable on speakers designed to play loud and other factors, mostly midrange being reflected out of the port can be quite a problem.

There are ways to minimise these issues but they are particularly difficult to implement on smaller speakers, so rear porting is popular.

So it is better to have the port in the back to reduce 'audible port chuffing' (I think that's how professional reviewers call it) and 'bleeding into the lower mids'. Why does front firing port get recommended so much? *scratch_one-s_head*

Two reasons Vlad. Firstly the idea that rearporting makes placement near a boundary 'difficult' is widespread, even among people that should know better, and secondly, I think putting all the complicated woodwork, cutouts, rebates etc onto one panel simplifies construction, important in the budget market.

 

[emperor's new clothes]

Hi Vlad,

The car analogy isn't valid even in a very rare gas tubine engined car, where thrust is often measured by inlet:exhaust (P27) engine pressure ratio. A car exhaust generates negligible thrust and braking is mainly a factor of turning kinetic energy -1/2MVsquared - into brake energy (heat). If the car exhaust vented forward, then as speed rises the back pressure would increase through the exhaust system causing severe flow problems.

 

[davedotco]

Nice to see the 'Thompson Technique' ...

I think I cracked the formula. Use common sense but be entirely devoid of any laws of physics applying to this Universe.

Back to regular program.

The basics I mentioned above are available to anyone with access to the internet. Take a look at any polar response measurements of box loudspeakers.

This is typical of most box loudspeakers, there is very little energy above about 1kHz radiated to the rear, but bass frequencies are near omnidirectional.

Reflections from the backwall will obviously by dominated by bass as no high frequencies are present to be reflected, Ergo, the bass at the listening position gets boosted, other frequencies are not.

The designer balances the forward response plus the reflections (bass) to give a balanced response at the listening position. The position that the speakers are in when making that evaluation is then the 'best' position for the speakers with respect to tonal balance.

The engineer can design speakers for whatever position he wants, though 'audiophiles' love 3D soundstaging which requires speakers to be well clear of the room boundaries, so most are balanced for this type of positioning.

When they get in peoples homes they often find themselves poorly placed, close to room boundaries, so sound fat and bloated. Thats just the way it is.

Of course port positioning can make a difference.

Very low frequencies may not be directional but a port with all its noise, distortion (usually greater than the drive units) and wind tunnel effect certainly can be. Look at ported speaker response graphs and you will see that on occasions port output bleeds into the lower mids which will clearly have an effect especially if the port faces the listener.

Not just that, I long have been an advocate of either IB design or, if you must have a port, downward firing for more ease of positioning and lack of audible internal reflections.

Not suggesting otherwise DM.

The point being made is that the position of the port, front or rear, makes no difference to the the positioning of the loudpeaker and the resultant bass response.

(Unless a rear ported speaker is placed so close to a boundary (a few inches) that it actually 'loads' the port changing it's behaviour)

You are quite right regarding port noise, low frequency induced 'chuffing' effects can be particularly noticeable on speakers designed to play loud and other factors, mostly midrange being reflected out of the port can be quite a problem.

There are ways to minimise these issues but they are particularly difficult to implement on smaller speakers, so rear porting is popular.

So it is better to have the port in the back to reduce 'audible port chuffing' (I think that's how professional reviewers call it) and 'bleeding into the lower mids'. Why does front firing port get recommended so much? *scratch_one-s_head*

Two reasons Vlad. Firstly the idea that rearporting makes placement near a boundary 'difficult' is widespread, even among people that should know better, and secondly, I think putting all the complicated woodwork, cutouts, rebates etc onto one panel simplifies construction, important in the budget market.

Excellent work Vlad, cheared up a dull and wet monday afternoon.

Reminds me of the time when someone asked Thompson the following question.

Q) Which is more important to man, the sun or the moon?

A) (After some thought) The moon obviously, as it gives us some illumination so that we are able to see a little bit at night, the sun is not so important as it only comes out in the daytime, when it is light anyway.

 

[emperor's new clothes]

Hi Blacksabbath,

The Opticon 6 has 2 ports as the bass driver is in a separate enclosure. On the IKon 6 the bass port is forward facing, the mid rear.

 

[emperor's new clothes]

Vlad,

I guess you got me with that one

 

[Vladimir]

Hi Vlad,

The car analogy isn't valid even in a very rare gas tubine engined car, where thrust is often measured by inlet:exhaust (P27) engine pressure ratio. A car exhaust generates negligible thrust and braking is mainly a factor of turning kinetic energy -1/2MVsquared - into brake energy (heat). If the car exhaust vented forward, then as speed rises the back pressure would increase through the exhaust system causing severe flow problems.

Back pressure is what is neglegable. Do you know how much power a V8 engine has? A lot. What is a little bit of breeze gonna do to it. No, you are thinking the wrong way. Simple math wont help you with this.

One way to stop the forward momentum from the exhaust is to shut off the engine, but that would also stop the breaking. Modern cars have that connected with electronics and pumps. Notice how old cars had their mufflers pointing upwards. It helped the car sit better on the road AND didn't make s much problem with breaking. Back then people knew what they were doing.

Think about it. lol

 

[Vladimir]

Vlad,

I guess you got me with that one

It's not hard.

 

[MajorFubar]

Nice to see the 'Thompson Technique' ...

I think I cracked the formula. Use common sense but be entirely devoid of any laws of physics applying to this Universe.

Back to regular program.

That's a shame it was just getting good