Rear ported cabs....WHY...?

[bob atherton]

A small rant, if I may…?

I use a Markbass LMIII with two TC RS2x10 cabs. This is a great little set up and it is serving me well, most of the time.
My beef is that the RS cabs have rear ports for the very low bass. WHY? My previous Ashdowns also had rear ports and maybe I should have learnt my lesson from those. The thing is that I’m now playing a lot more gigs again and at most venues the rig sound great; in fact I’ve never had so many complimentary comments about the sound.

The problem is at some venues and at outdoor gigs there are issues. At some clubs the cabs boom a bit, less than the Ashdowns but it’s still a problem. I often have to quite dramatically change my EQ on the amp to get over this; this in turn gives me a rather odd sound on stage even though it’s sounds not too bad out front.

With outdoor gigs all the deep bass is just blowin’ in the wind, and I’m not getting the depth on stage. When I had my Ashdowns I didn’t play the outdoor gigs and I may not have bought the TC’s if I had done.

So why oh why do cabinet manufactures put ports on the back of their cabs? This makes the sound so location dependant that it can become a PITA.

If I ever change my cabs again, and to be honest I probably will not, I’m not one to switch amps and cabs very often, I will definitely get cabs with no ports or front ones but never again rear ports.

Rant over.

[4-string]

Why not? I'm not so sure it really makes much difference soundwise. Front ported cabs need bigger baffles, which is probably why some cabs are rear ported. Simply to keep the size down.

Mostly guessing here though, as (almost) always.

[bassteban]

So you don't see the gnomes going in & out...

[JimmyM]

Originally Posted by 4-string

Why not? I'm not so sure it really makes much difference soundwise. Front ported cabs need bigger baffles, which is probably why some cabs are rear ported. Simply to keep the size down.

Mostly guessing here though, as (almost) always.

Accurate guessing. Port location makes absolutely no difference at all. If the port was in the front, the OP would hear no difference.

[bassteban]

Originally Posted by caaraa

Have a look.

@ what?

[T-Bird]

Hi.

Originally Posted by bob atherton

With outdoor gigs all the deep bass is just blowin’ in the wind, and I’m not getting the depth on stage. When I had my Ashdowns I didn’t play the outdoor gigs and I may not have bought the TC’s if I had done.

LOL

Originally Posted by bob atherton

So why oh why do cabinet manufactures put ports on the back of their cabs? This makes the sound so location dependant that it can become a PITA.

Because for every player that knows that the ports HAVE TO be on the front, there's a person who knows that the ports HAVE TO be on the rear. Then there's the minority who have paid attention in school and know that for the Helmholz resonator to work, the opening location is moot.

It's also easier to put the ports on the rear wall rather than on the front for manufacturing reasons.

Unless one positions a rear ported cab, regardless of the designation, closer than the effective port diameter from the wall or another obstacle, there's no difference between the port locations on the bass frequencies.

Regards
Sam

[arai]

Originally Posted by JimmyM

Accurate guessing. Port location makes absolutely no difference at all. If the port was in the front, the OP would hear no difference.

I thought it did if the port is close to a wall?
most of us end up having the rear of our cabs close to a wall at some stage

[rodl2005]

I simply make sure the rear ported cab is at least the ports diameter distance away from the wall behind it.
Seems pretty easy to me.

[KJung]

Originally Posted by arai

I thought it did if the port is close to a wall?
most of us end up having the rear of our cabs close to a wall at some stage

Only if the port is so close (under 5 inches or so) that it is literally blocked. Zero issue otherwise.

[Zooberwerx]

Originally Posted by bassteban

So you don't see the gnomes going in & out...

A-ha! I thought so! Andy Lewis (Acme) says that port placement is of no consequence...I bet he's in on it, too.

Riis
Bassist and paranoid conspiracy buff

[steve_rolfeca]

IME/IMO, room dependencies like the ones the OP is struggling with, tend to be more about cab voicing than anything else.

Ashdown and TC cabs both have pretty prominent bumps in the low mids. Over the years, I've found that to be the kiss of death when you get into a bad room.

[billfitzmaurice]

Originally Posted by bob atherton

So why oh why do cabinet manufactures put ports on the back of their cabs?

Because port location makes absolutely no difference to low end output. The radiation angle of the low frequencies is 360 degrees. The main reason for rear placement is when the cab is too small to fit them on the front.

At some clubs the cabs boom a bit, less than the Ashdowns but it’s still a problem. I often have to quite dramatically change my EQ on the amp to get over this;

Boom is caused by too small a cab and/or room acoustics. The reason your amp has EQ is so that you can compensate.

With outdoor gigs all the deep bass is just blowin’ in the wind, and I’m not getting the depth on stage

Outdoors there's no room boundary reinforcement, so you need twice the cab count for the same output.

Rant over.

And unjustified.

[bob atherton]

Originally Posted by billfitzmaurice

And unjustified.

Well..... I'm no so sure that I don't have some small grounds for the smallest rantet..

I have a pretty decent hi-fi system and have tried many speakers in our quite dificult (sound wise) sitting room. All the speakers that we tried with rear ports got very bass heavy and set the room off the closer they go to a boundry wall. We are taliking much further than the port size here. Some of these speakers only lost their boom in the room at about two feet away from the wall. As the speakers got closer to the wall the boom increased.

I know that very low frequencies are omnidirectional compared to the higher ones but there is still a lot of air (you can feel it) pumping out of those ports. Once hitting the wall I'm guessing , if my school physics is correct, that the phase would be reversed adding more problems.

Also I use the same TC cabs in our rehearsal room and positioning of these has been very critical not to get that room going as well.

I think that an infinite baffle design has got to make more sense, to me anyway.

Got to say though that when the planets align with the venue acoustics the rig sound just great.

Maybe they put them at the back so one really cant see the gnomes going in and out...

[Mr. Foxen]

Originally Posted by bob atherton

Once hitting the wall I'm guessing , if my school physics is correct, that the phase would be reversed adding more problems.

Doesn't work like that, its to do with the wavelength, so lows bouncing of the walls will be a very tony bit out of phase (like a few degrees)with the counterpart going forwards, but mostly be in the same direction, thus reinforcing.

[KJung]

Originally Posted by bob atherton

Well..... I'm no so sure that I don't have some small grounds for the smallest rantet..

I have a pretty decent hi-fi system and have tried many speakers in our quite dificult (sound wise) sitting room. All the speakers that we tried with rear ports got very bass heavy and set the room off the closer they go to a boundry wall. We are taliking much further than the port size here. Some of these speakers only lost their boom in the room at about two feet away from the wall. As the speakers got closer to the wall the boom increased.

I know that very low frequencies are omnidirectional compared to the higher ones but there is still a lot of air (you can feel it) pumping out of those ports. Once hitting the wall I'm guessing , if my school physics is correct, that the phase would be reversed adding more problems.

Also I use the same TC cabs in our rehearsal room and positioning of these has been very critical not to get that room going as well.

I think that an infinite baffle design has got to make more sense, to me anyway.

Got to say though that when the planets align with the venue acoustics the rig sound just great.

Maybe they put them at the back so one really cant see the gnomes going in and out...

Probably not. That's like saying 'all the speakers are covered in black tolex, and they all sound boomy as you get them closer to the wall'. You are misattributing causality. For the most part, a front ported speaker will sound similarly 'more bassy' as you get it closer to the wall.

[Jerrold Tiers]

A speaker on the ground outside away from walls has "half space" to radiate into...... All the "top half of the sphere" if you imagine a sphere around the speaker.

back it up against a wall, and you cut half of that "half sphere"...... now it is 1/4 space.

back it into a corner, and you cut it in half again, to 1/8 space.

Why is this important?

because the highs are directional out the front, and don't change, BUT the lows are omnidirectional, and spread out in all directions.

Now, if you measure a speaker outdoors on the ground, in "half space", the lows have to "fill" half space. And they will, since they are omnidirectional.

Next measure against a wall..... now all the power that was going to the volume of "apace" behind the speaker is coming forward along with what was there before. So twice the power is directed to the front as before. That alters the balance vs the unchanged highs.

Put it in a corner, and all the power that was going off to one side is now directed out to the front, doubling the "out front" bass power.

OF COURSE that will change the "balance" of the sound.

Then, there is a matter of phase reversal against the wall. it IS TRUE. But only because of travel distance.....

If you put the speaker 5 feet from the wall, the travel distance is 10 feet.... 100Hz (10 foot wavelength approx) will be reinforced, but 50 hz will travel a half wave and the returning reflected wave will be 180 deg out of phase, canceling at least some of the sound energy.

If you go to 2.5 feet, 200 Hz is reinforced, 100 is canceled.

These are approximate numbers, but the effect is real.

And it depends how solid the wall is. Brick, pretty solid. Drywall, not so much.

[staindbass]

does the group delay change with the port on the back? (meaning the sound from the port arrives at your ear later because its farther away ?)

[seamonkey]

Ports should be covered with a grill so varmints don't crawl inside.

[Russell L]

Originally Posted by seamonkey

Ports should be covered with a grill so varmints don't crawl inside.

The gnomes could have a key, huh?LOL.

In comparing my Markbass 151P rear-ported cab to my old Trace Elliot 115 front-ported cab, the Trace sounds as if the sound is right there in front of the cab, whereas the 151P sounds as if the sound is more all around me, and deeper (although that could be the cab/speaker tuning at work). Maybe the porting has nothing to do with it, but it SEEMS to affect where the note feels like it is. It's as if the front port puts the sound right in front. Is that possible, or an illusion? I dunno.

[Bassflute]

Originally Posted by JimmyM

Accurate guessing. Port location makes absolutely no difference at all. If the port was in the front, the OP would hear no difference.

Originally Posted by bob atherton

A small rant, if I may…?

I use a Markbass LMIII with two TC RS2x10 cabs. This is a great little set up and it is serving me well, most of the time.
My beef is that the RS cabs have rear ports for the very low bass. WHY? My previous Ashdowns also had rear ports and maybe I should have learnt my lesson from those. The thing is that I’m now playing a lot more gigs again and at most venues the rig sound great; in fact I’ve never had so many complimentary comments about the sound.

The problem is at some venues and at outdoor gigs there are issues. At some clubs the cabs boom a bit, less than the Ashdowns but it’s still a problem. I often have to quite dramatically change my EQ on the amp to get over this; this in turn gives me a rather odd sound on stage even though it’s sounds not too bad out front.

With outdoor gigs all the deep bass is just blowin’ in the wind, and I’m not getting the depth on stage. When I had my Ashdowns I didn’t play the outdoor gigs and I may not have bought the TC’s if I had done.

So why oh why do cabinet manufactures put ports on the back of their cabs? This makes the sound so location dependant that it can become a PITA.

If I ever change my cabs again, and to be honest I probably will not, I’m not one to switch amps and cabs very often, I will definitely get cabs with no ports or front ones but never again rear ports.

Rant over.

Port location makes a BIG difference if you have to set up near a wall or a corner - it projects all the boom and subsonic stuff RIGHT where you DON'T want it. With forward facing ports, you are NEVER going to have them directed right into a corner, and sometimes you have no choice as to where your cabs get set up.

Originally Posted by KJung

Probably not. That's like saying 'all the speakers are covered in black tolex, and they all sound boomy as you get them closer to the wall'. You are misattributing causality. For the most part, a front ported speaker will sound similarly 'more bassy' as you get it closer to the wall.

All the chuff and boom going straight into a corner can make for significant problems...

I'm with the OP on this...don't like rear ports at all on bass cabs. Put them on the front, where we can control it, and even enjoy it.

Cheers,
Cameron