Why are so many speakers rear ported!?

Richy1984

Active Member
Simple question really. Why, if it then means that they are picky with positioning, are so many more expensive speakers rear ported?
 

PSM1

Distinguished Member
Some of it could be to do with the look of the speaker. Ports are not the prettiest things in the world so sticking them at the back out of sight is probably good design point. There may be other advantages as well sonically but not sure.
 

beanoir

Active Member
because front porting a speaker requires a greater surface area of the baffle, the greater the surface area of the baffle the greater the distortion of the sound wave from reflections from off of the baffle.

Thats the simple answer, i'm sure some would put it more gracefully but I'm eating lunch!
 

Wilseus

Active Member
I always thought Royd had a good solution with their Minstrel loudspeaker where the bass port was in one side of the cabinet. That way you could tweak the sound by having them both point inwards or outwards.
 

Richy1984

Active Member
because front porting a speaker requires a greater surface area of the baffle, the greater the surface area of the baffle the greater the distortion of the sound wave from reflections from off of the baffle.

Thats the simple answer, i'm sure some would put it more gracefully but I'm eating lunch!
that doesnt make much sense to me. whats the baffle? and why does it regquire greater surface area.

I often think piorts when nicely styled can look pretty good.

Its just annoying how many are rear ported as I'd love to have a pair of RX1s or similar but I havent the space where my stands are, to give anymore than about 5-8" space behind them and on one side.
 

Gixxerblade

Active Member
The baffle is the front of the speaker where the drivers go. If you think the speakers will be too close to the wall and too boomy block the port. I have my rear-ported speakers that close.
 

Richy1984

Active Member
The baffle is the front of the speaker where the drivers go. If you think the speakers will be too close to the wall and too boomy block the port. I have my rear-ported speakers that close.
I see.

If I was to upgrade, is it not wasting my money a bit though by then putting in port bungs? as surel that affects the speaker's ability to play certain notes?

I dont really understand what the ports do, and the effect that blocking them would have! Can you please explain.
 

l34052

Well-known Member
Im no expert but from my knowledge every driver has an optimal cabinet and port length and size to achieve good bass.

Blue Wizard on here can explain better but i think ive covered the very basics on why speakers are ported.
 

Richy1984

Active Member
A ported design is called a bass reflex:
Bass reflex - Wikipedia, the free encyclopedia

I suggest you try and get an home demonstration of any speakers you are interested in. Blocking the port may reduce boom - it depends.

You can buy sealed speakers.
ok. I'll have a read.
Where does home demo's?

The thing I dont get with port bungs is that by putting them in, you stop the port from doing what the speaker designers intended, and as such surely lose some sound quality or some of the speakers range? Does it just dull the bass boom or does it null the mids a bit as well?
 

BlueWizard

Distinguished Member
BUNGS -

When you place a speaker close to one or more boundary walls, you get a boost in the bass. But the bass is usually accompanied by timing errors in the midrange. In short, the excess bass reflecting off the wall muddies the midrange. You can bung/plug the port to soften the bass, and this will help clean up the midrange. Since the position boosts the bass, and plugging the port reduces the bass, it balances out.

I had the exact problem with some bass heavy JBL Stadium speakers. They did not like being 1 foot from the wall behind. Plugging the port did improve them, but these speakers really needed to be 18" minimum from the wall, and 24" would have been even better.

My new speakers, also rear ported, are quite happy to be 12" from the wall.

The port diameter and length are relative to the volume of the cabinet, much like the pipe on a pipe organ. In general, they are tuned to resonate that the resonance frequency of the bass driver. The resonance frequency of the bass driver is the point where all the resistive, capacitive, and inductive aspects of the speaker are at their peak. The effective impedance of the drive can be 10 time or more than the rated impedance of the speaker at the resonant point. This resonance typically occurs around 30hz.

A tuned ported cabinet is actually an anti-resonant chamber. Functionally, the resonance of the port/cabinet counters the resonance peak in the bass driver. Also, having a hole in the cabinet, reduces the spring tension of the air in the cabinet making it easier for the speaker to move and raising the efficiency.

The advantage is that the bass response is flatter to a lower frequency, but when it drops off, it drops off quickly. A seal cabinet, or acoustic suspension cabinet, will start dropping sooner, but will fade much slower.

In many cases, especially in bookshelf speakers, the port is in the rear simply because there isn't room on the front. In floorstanding, it is a question of appearance. Some people don't mind seeing the ports, some designers prefer to hid them.

Technically, it doesn't matter where the port is, it can be top, bottom, front, back, or side. A top port might seem a good idea, but if you throw a party and your guest set their drink on the speaker and spill them, it is going to run straight down in to the port. That and people will tend to use them for ashtrays.

Several speakers use bottom ports, few to none use side ports, none use top port, for most it is front or rear.

I personally feel most people completely underestimate how far forward they can have their speakers. In my case, I simply move my speakers forward until the front of the speaker is even with the front of the equipment cabinet, and that gives me 12" behind the speaker. Which for the floorstanding speakers I have now, works fine.

Steve/bluewizard
 
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Richy1984

Active Member
Thanks very much for the extensive post.

I understand the porting idea more now. However I am still not sure on one point, and that is...

If I upgrade my speakers (due to wanting better clarity and greater quality), I'm thinking BX2 ---> RX1, but I havent quite got the space to let them breath as much as they might need, I understyand that I can pop the supplied port bung in, but does this degrade any frequwencies in any way (other than to tame the bass)??

Or do the port bungs simply tame the bass, but still allow other frequencies to play clearly and as intended?
 

Wilseus

Active Member
I understyand that I can pop the supplied port bung in, but does this degrade any frequwencies in any way (other than to tame the bass)??

Or do the port bungs simply tame the bass, but still allow other frequencies to play clearly and as intended?

It just reduces the bass. This is because above the port frequency the cabinet behaves as a sealed box anyway. The woofers will also, in theory, take more punishment. :D This is because below the port frequency it's as though there's no cabinet there at all! Therefore there's nothing to stop the voice coil, given enough power, moving beyond its limits, wrecking the woofer. Blocking the port stops this happening.
 
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AEJim

Active Member
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?

Interesting to hear your thoughts!

Cheers,


James Luce
Brand Manager
Acoustic Energy.

NewCompact.jpg
 

bluedroog

Well-known Member
A rear ported speaker can have the effect of reinforcing the bass from the rear walls, if you've got the space to move them say 18 inches from the rear this can be useful. Given most of us in the UK have poxy sized living spaces rear ported speakers can be more of a problem in practical terms.

James - I like the look of all of the to be honest. If pushed I prefer it without the port on show and more compact but not enough to compromise sound. Front ported are more practical for me especially with compact speaker likely to be up against a wall or on a shelf. These could be interesting for my Mini-T amp....
 
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Jules

Distinguished Member
Rear ported speakers are a pain.
I think KEF nailed it with their Q700 speakers. No rear ports, no front ports... instead they use a 'fake' bass driver which moves in sympathy with the main driver... acting like a port without the drawbacks of a port.
 

Gixxerblade

Active Member
Rear ported speakers are a pain.
I think KEF nailed it with their Q700 speakers. No rear ports, no front ports... instead they use a 'fake' bass driver which moves in sympathy with the main driver... acting like a port without the drawbacks of a port.

Rear ports are generally OK - all speaker designs have issues. Passive radiators which I assume you mean by fake bass driver have their own issues.

James
I prefer the version without a front port but both look nice to me.
 

Richy1984

Active Member
Both look great. TBH I cant decide which looks better. To me it would just depend on which was least fussy about positioning.
 

Wilseus

Active Member
There must be my 'ideal' speaker that isn't the size of my Yamahas and can be close to a wall. I haven't bought new speakers for a few years but I never found anything I liked that fitted that bill. Some must exist.

I think some Linn speakers are designed to be right up against a wall, or at least that used to be the case.
 
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jason shep

Well-known Member
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?

Interesting to hear your thoughts!

Cheers,


James Luce
Brand Manager
Acoustic Energy.

image

Hi James,
i think the baffles look great with the chamfer around the drivers but for me rectangular cabinets are very ugly,with the materials & manufacturing techniques available today i'm surprised speakers are still being designed to look like boxes,only my opinion & you did ask for people's thoughts ;)
 

Replicant

Active Member
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?

Interesting to hear your thoughts!

Cheers,


James Luce
Brand Manager
Acoustic Energy.

image

I actually prefer the look of the front ported design for what its worth
 

Scotty Pro

Well-known Member
FWIW I also prefer the look of the front ported design.
I have 5 Dali's 3 Ikons for the front and 2 Lektors for the rear surrounds, all of them front ported and they do look the business :smashin:

also my Kef's are front ported and my little Missions are also front ported :D

If you leave the grills on the speaker then no-one but you will know if they are front ported or not. I personally remove the grills on mine even though the Dali's look rather cool with them on. Either way they are a nice looking speaker (see Avatar) and sound great as well :thumbsup:
 

sergiup

Distinguished Member
Interesting to hear your thoughts!

Cheers,

James Luce

FWIW I also prefer the look of the front ported design.

Personally I have to echo this - I very much prefer front ported designs as well. It's less restrictive in terms of placement and I just find it to look better for some reason. I also like Dali's approach of two smaller front ports instead of one bigger one, it just looks better (Ikon 1, Lektor 1 and 2).

James - even in light of the above, the front ported experimental design you posted actually looks quite pleasing as well. Personally I don't think an angled corner AE logo would look that good, I would say keep it horizontal. Just out of curiosity, how much extra engineering would you need to invest to do something like Dali's two-port design, and what impact would it have on sound etc? Maybe it could allow you to place them between the two active drivers and make it the same size as the original design?

On a more general note: although as Steve says a tuned cabinet is supposed to counter a bass driver's resonant frequency, wouldn't a well tuned sealed cabinet actually provide a cleaner, more honest sound (especially if combined with a subwoofer)? My reasoning is that while a port will give a relatively small cabinet a better bass response, it also unavoidably just creates an additional sound source to interfere with the active drivers; while you could design the port to reduce constructive or destructive interference, that probably won't work across the entire frequency range. I would imagine you'd also have similar trouble with a second passive driver instead of a port.

I would love to have the time (and suitably equipped workshop) to experiment with speaker designs, unfortunately that's not going to happen too soon...
 

scottthehat

Distinguished Member
My floor standers are front and rear ported, tried bunging the rear and it makes on difference, and they are right in the corners of the room , but as more and more me people have subs doesn't it make it easier to use rear ported.
 

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