Port placement in correlation to the floor

[Mario Pankov]

Hello,

I was reading Lynn Olson`s website and I noticed some observations on the effect of the port placement on a vented box and how it changes the low freq. sound of a loudspeaker when mounted close to the floor ( ground ). He suggests that it should be mounted from 0 to 3" close to the floor and this results in much better bass performance and the speaker has better harmonics. He says that when you move the port away of the floor, the sound becomes thin like a minimonitor sound.
I didn`t find any information about this anywhere but got me interested as I am building a vented 2-way now. As the box in this design will be 36" tall and the port will be longer, this could allow me to mount it like in the Avalon Eidolon, firing down to the floor.
Does anyone have any thoughts or experience with this behaviour? I know Mr. Olson is on this forum, so I would appreciate If he could share his experience.

[Cal Weldon]

I have nowhere near the knowledge of Mr Olson but my experience is the same. I think the floor is helping to load the port similar to a horn. It gets really noticeable when you fire it rearward into a corner and make use of 90 degree walls. Some like it, some don't. I guess it depends on the drivers, the room and your tastes.

[John Sheerin]

If you put the port by the floor, it would be better placed to more powerfully excite room modes. The same if you put it closer to the wall or corner of the room (like on the back of the speaker). This would likely lead to it sounding like there was more bass.

[Mario Pankov]

Do you have any measured response with a close-to-floor port? I just received my Wm61 capsules today and once I build the meas. mic. I will do this experiment. What I will use is Speaker Workshop.

[Lynn Olson]

I am not sure of the mechanism, but it appears to be an analog of the PZM microphone - just in the other direction. The bass lift is real enough; the vent output (of the transmission line) was increased by 2 to 3 dB compared to other locations, like midway up the back of the enclosure.

It should be mentioned in passing that reflex ports and TL vents have very different spectra: the vent of a bass-reflex (vented-box enclosure) is less than an octave wide and is a narrowly-tuned, high-Q output, while by contrast the vent of a TL is similar to the output of a subwoofer. In the Ariel, the vent output was flat from 20 Hz to 100 Hz, very different than an the equivalent vent of a bass-reflex.

You have to be aware of the spectra of what's being emitted when playing these tricks with vent and/or woofer locations. I would NOT put the vent of a bass-reflex on the floor, for example - the location would magnify the vent output in an unpredictable way, and vented loudspeakers are already quite critically tuned to deliver a 4th-order response shape. Any variation away from the design center is almost certain to be a degradation.

[gedlee]

Originally Posted by John Sheerin

If you put the port by the floor, it would be better placed to more powerfully excite room modes. The same if you put it closer to the wall or corner of the room (like on the back of the speaker). This would likely lead to it sounding like there was more bass.

Yes, of course, more bass, but boomy bass because of the discrete modal excitation. You need both more bas and smoother bass.

[tinitus]

Wouldnt it all depend a lot on driver Qts and individual box/port tuning