Two questions here... #1 What are the real world sonic differences between identical speakers in the same room, one being rear ported and one being front ported? I've read/come to understand that front ported work better nearer back and side walls than rear ported? Why, how, what?
#2 If you were building LCR two ways with LF drivers only in enclosures tuned to 30hz and crossed at 1600hz which way would you go?The HF drivers will not be integrated in the LF enclosure and will sit on top. I plan to place them about 12 inches from the wall with the L/R about 17 inches from the sidewalls.
School me. Thanks
#2 If you were building LCR two ways with LF drivers only in enclosures tuned to 30hz and crossed at 1600hz which way would you go?The HF drivers will not be integrated in the LF enclosure and will sit on top. I plan to place them about 12 inches from the wall with the L/R about 17 inches from the sidewalls.
School me. Thanks
Look at the comb filter effect of a port. You can see higher frequencies coming out of the port. They are attenuated more and more at higher and higher frequencies, but they are there.
If you put the port up front, those higher frequencies are facing toward you.
A rear port will have some additional attenuation, because they are not facing toward you.
As mentioned earlier, the rear facing port may be interfered with when placed too close to a surface.
Don't forget the tower designs that put the port at the bottom (and the good designs of this topology take into account the floor that affects the port tuning).
I have seen side mounted woofers, but do not remember seeing a side mounted port.
If you put the port up front, those higher frequencies are facing toward you.
A rear port will have some additional attenuation, because they are not facing toward you.
As mentioned earlier, the rear facing port may be interfered with when placed too close to a surface.
Don't forget the tower designs that put the port at the bottom (and the good designs of this topology take into account the floor that affects the port tuning).
I have seen side mounted woofers, but do not remember seeing a side mounted port.
The attached rule of thumb may help you make your decision on port placement. The site from which it originates is an amusing read!
https://sonicscoop.com/2017/12/14/the-1-speaker-placement-tip-speaker-manuals-get-completely-wrong/
Arguably, as long as the minimum distance of the rear mounted reflex port to the wall is no smaller than the diameter of the port itself, then you are good to go.
Certainly, given your 12" clearance, the typically dimensioned, rear mounted port should work just fine.
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Please elaborate...on the actual bottom?....or at the bottom of the front baffle?
I only ask because I've seen designers that "routinely" design speakers that use a slotted port at the bottom of their front baffle and haven't seen any designs using ports in the bottom of the speaker other than subs.
From the responses I gather that rear porting is perhaps used more often simply so the extraneous noise that can and does make it's way out the port is aimed away from the listeners and that makes perfect sense. BUT, I'm still curious about real/observed characteristics of how front vs rear ports speakers interact with sidewalls. Thanks for all the great input, I'm learning some good things.
Useful information on locating a port on the base of an enclosure can be found in this diyAudio link:
Real benefit of down-firing reflex port
See, in particular, posts #6 and #7.
How ports interact with walls is discussed in this link (see section 3):
Barefaced Bass - The mysteries of ports
Barefaced Bass - The mysteries of ports
To create a space no smaller than the diameter of the downward firing port, I would suggest.
Wharfedale have utilised what they call a 'slot-loaded distributed port', where a down firing port tube opens into a slot formed between the cabinet and a plinth in a way similar to which you suggest.
If you look at the image at the bottom of the link, you'll see the arrangement.
Diamond 11 – WHARFEDALE
If you look at the image at the bottom of the link, you'll see the arrangement.
Diamond 11 – WHARFEDALE
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^^ That's sort of a half **sed power port.
Having it on the bottom means no ugly hole on the front panel, which if placed badly can be a diffractive element to the MF/HF, reduces the amount of MF that will be audible at the MLP, especially with a carpeted floor; it's basically invisible. And you can use a power port.
Not having it on the rear means I can design for corner placement, and not have to listen to audiophile dribble about "now you have to place it far out into the room".
The other advantage to a bottom port is if you want to build some small standmounts, and tune them low, you can run a large diameter port, external to the enclosure and integrate it into the stand.
Having it on the bottom means no ugly hole on the front panel, which if placed badly can be a diffractive element to the MF/HF, reduces the amount of MF that will be audible at the MLP, especially with a carpeted floor; it's basically invisible. And you can use a power port.
Not having it on the rear means I can design for corner placement, and not have to listen to audiophile dribble about "now you have to place it far out into the room".
The other advantage to a bottom port is if you want to build some small standmounts, and tune them low, you can run a large diameter port, external to the enclosure and integrate it into the stand.
Canton Reference 3.2 DC loudspeaker | Stereophile.com
So, do you just calculate the port + the space between the bottom of the cabinet and the floor/plinth?
So, do you just calculate the port + the space between the bottom of the cabinet and the floor/plinth?
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Given the relatively large size of the gap between loudspeaker base and plinth in the Cantons, I would guess the port dimensions are probably calculated as standard.
On the other hand, Wharfedale vents the port tube into a narrow slot.
The addition of the extra air mass/resistance must necessitate a modification to the standard method of port tuning, which Wharfedale is unlikely to share with us!
I would be very cautious when placing a port on the bottom of the loudspeaker. Port on the back is good for a couple of reasons but two main ones are 1.avoiding midrange leakage problems 2.avoiding port resonance issues.
If we examine Wharfedale port system, few things bother me - not knowing the measurements of course.
First, the angle between tube and slot is 90 degrees. Any "knee" will disturb air flow more than a straight tube. Second, combined length of port and slot is substantial. It wouldn't surprise me to see a port resonance spike somewhere between 500-1000Hz, maybe even lower. Since it is open on all 4 sides, it radiates that resonance in all directions - unlike back port. Third, while there is a flare inside the box and in transition from tube to slot, there is no flare on the slot itself. It could be that all that surface doesn't need roundover to avoid turbulence but it raises my eyebrow.
So, without extensive testing and measurements i wouldn't be able to say it is a clear improvement over port on the back.
If we examine Wharfedale port system, few things bother me - not knowing the measurements of course.
First, the angle between tube and slot is 90 degrees. Any "knee" will disturb air flow more than a straight tube. Second, combined length of port and slot is substantial. It wouldn't surprise me to see a port resonance spike somewhere between 500-1000Hz, maybe even lower. Since it is open on all 4 sides, it radiates that resonance in all directions - unlike back port. Third, while there is a flare inside the box and in transition from tube to slot, there is no flare on the slot itself. It could be that all that surface doesn't need roundover to avoid turbulence but it raises my eyebrow.
So, without extensive testing and measurements i wouldn't be able to say it is a clear improvement over port on the back.
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