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front porting vs rear porting

Aenema

Aenema

Apr 18, 2001
573
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Michigan
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#1
i found an old post that was a very interesting read. it was originally about sealed cabs vs ported cabs but got into great detail on the ported cabs. i have a few questions about porting.

1. many bass playas have found rear ported cabs to have a tighter sound then front ported cabs. i know this is not "always" true but most of the time it seems to be the case. why is this?

2. ive heard that a front port results in more mid range. is this true?
 
#3
Aenema said:
i found an old post that was a very interesting read. it was originally about sealed cabs vs ported cabs but got into great detail on the ported cabs. i have a few questions about porting.

...
Click to expand...

Would you mind posting the link to that thread? I am in
the middle of redoing a cab, and I would love to read it over.
Thanks!

I leave the rest to the experts.
 
#6
wurmhole said:
Andy has a nice discussion on this topic over on the acme site. acme
Click to expand...

directly from acme's website
"Tell your friends that the reason your B-1 system sounds so good is that the tremendous innovation of a side-mounted port results in some type of magical quantum-leap in performance. In fact, the truth is much less exciting: a high-quality woofer in a solid and correctly-tuned enclosure. Feel free to let other people lose sleep over where their ports are located. Now you know the truth."

interesting yet humorous at the same time. :p
 
#10
Aenema said:
since port placement has nothing to do with a "tighter' sound... what is the main factor in tight bass response? i know sealed cabs have tighter response but what gives a ported cab tighter response?
Click to expand...

There are a wide variety of factors that will effect how "tight" your sound will be. Its a combination of amp and cab designs.
 
#11
Aenema said:
since port placement has nothing to do with a "tighter' sound... what is the main factor in tight bass response? i know sealed cabs have tighter response but what gives a ported cab tighter response?
Click to expand...

Lots of things! Everything from cone material to magnet strengeth to suspension stiffness, all of which are reflected in the speakers Thiele Small paramaters. That's why these specs became the basis of cab design.

Generally speaking the better the group delay, the tighter and faster a cab will sound. That's partly why sealed cabs are so fast. By their nature they have a better group delay than ported cabs.

You can vary your group delay by changing the cab's porting and cabinet size but there's a problem - doing this also affects the cab's frequency response, yet another factor which contributes to a speakers tightness or tubbiness. Speaker that go lower are more likely to exhibit tubbiness because the soundwaves of the lower frequencies are larger the therefore take longer to form. The trouble with bass cabs is that they have to go pretty low. You don't hear guitarists talking about "fast response cabs" because it's simply not a concern given their frequency range.

Good cab design can get around this to a point but everything in cab design is a balance of tradeoffs, including freq response, group delay, speaker excursion, size, weight, the list goes on.
 
#12
Aenema said:
i found an old post that was a very interesting read. it was originally about sealed cabs vs ported cabs but got into great detail on the ported cabs. i have a few questions about porting.

1. many bass playas have found rear ported cabs to have a tighter sound then front ported cabs. i know this is not "always" true but most of the time it seems to be the case. why is this?

2. ive heard that a front port results in more mid range. is this true?
Click to expand...

I think the answer to your second question answers it all. A front ported box with no stuffing will have more midrange and upper bass coming out of the port than the exact same box with a port on the back. This would cause the rear ported box to sound "tighter" (I would call it cleaner). The proper use of stuffing or lining should make the difference negligible.

Ralf
 
#13
Petebass said:
Generally speaking the better the group delay, the tighter and faster a cab will sound. That's partly why sealed cabs are so fast. By their nature they have a better group delay than ported cabs.
Click to expand...


what the heck is "group delay"?? definition please if your going to use technical nomenclature..
 
#14
tonenazi said:
what the heck is "group delay"?? definition please if your going to use technical nomenclature..
Click to expand...

Ok imagine you have a long line of people and each one of them represents a certain frequency. They've all been asked wait till the starting gun fires, then run towards a wall which if 100 yards away. Which they do, and they all reach it at the same time. That's Zero group delay.

Now lets get a bit more realistic. Some people are in better shape than others, some are more naturally athletic etc..... so they all reach the wall at a different time. That's Group delay.

When you look at a group delay chart, it tells you which frequencies hit the wall latest, and exactly how late they'll be. 20ms is considered pretty large group delay and will usually result in audible mud.

I can post a typical group delay chart if you like, but it's pretty boring stuff if you're not into cab designing.
 
#16
Aenema said:
so what are some cabs with good group delay? acme? EA? epifani? do PA's generally have really good group delay? is that why my bass sounds so "tight" thru a PA?
Click to expand...

It's not that simple. Manufacturers don't publish group delay stats. And even if they did, group delay isn't the be all and end all. Some designs, for example folded horns, will exhibit group delay but it's not a problem. Remember what I said about the speaker's component characteristics and T/S data. It's a series of things combining so it's probably not a good idea to try and localise it too much.

As for PA's sounding tight - I can't say I agree. More often than not bass through the PA to me sounds like the proverbial hand over the mouth - Muffled! But how much of that is the sound guy's fault? Probably a lot, but that's another thread.........

My advice is to let your ears decide which sound tighter to you.
 
#17
ive ran my bass (since it has an onboard preamp) direct thru a mackie mixer to a PA with 15' EV's and my bass never sounded so detailed and tight. it had my swr bass 750/goliath III setup beat in clarity by a long shot. i never heard my bass sound so growly and tight. i play a peavey cirrus tiger eye.

so it could be the head that muffles or warms up the sound, could be the cab, could be a combination. interesting... i like to understand why my gear sounds the way it sounds. thanx petebass.
 
#18
Perhaps your PA speakers don't have quite the bass response of your bass cab, eliminating some low frequencies that really don't contribute to nice audible bass tone. To me this is the source of most mud. Perhaps cutting the bass on your head or putting a 50Hz filter in before the power amp will yield a quality result for you. There is a very detailed thread on high pass filters that could be of help.
 
#19
wurmhole said:
Perhaps your PA speakers don't have quite the bass response of your bass cab, eliminating some low frequencies that really don't contribute to nice audible bass tone. To me this is the source of most mud.
Click to expand...

What he said.....
 
#20
Based on what I've heard comparing various rigs to my Acme one, and based on the theory behind sixth order alignment, Acmes have extremely low group delay for ported cabs. This tightness to the response is further assisted by the ports being well shaped and sized (no chuffing) and the cabs being suitably acoustically treated with internal wadding.

Also, if you use a high pass filter to remove some of the extreme low end (fundamentals of very lowest notes plus pointless percussive sub-harmonics) the sound gets even tighter.

Alex
 

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