This is for a floor standing studio monitor.
In this example, the 'sweet spot' (between mid and tweeter) is @ 46.5" above floor level... this would be ear level for someone around 6' tall, sitting on a regular computer workstation chair.
The port is a little more than 4' away from the woofer (it can easily be 18" closer to the woofer). Is there any problem with this? Should I move the port closer to the woofer?
In this example, the 'sweet spot' (between mid and tweeter) is @ 46.5" above floor level... this would be ear level for someone around 6' tall, sitting on a regular computer workstation chair.
The port is a little more than 4' away from the woofer (it can easily be 18" closer to the woofer). Is there any problem with this? Should I move the port closer to the woofer?
No, it's not a BR, but a vented TL [MLTL], so normally want the vent near/at the bottom to take advantage of its 1/4 WL harmonics to damp the vent; otherwise as you move it up you create a secondary set of harmonics that will add a dip in its mid-bass response.
I am aware of those, having built numerous TLs, but is that what this is? If the scaling is accurate, the port looks far too small.
We need to hear from the OP, as the answers to his question will be very different.
We need to hear from the OP, as the answers to his question will be very different.
I'm looking at a floor standing version of something like this:
In my drawing, the port was ~6" dia - similar to the image above.
Whether TL or BR, the port produces very low frequency where wavelengths are very long. It does not matter where you place it.
it sure do, if you have a test box then try different vent locations and run some impedance measurements and you will see that measurements will differs and some a lot
JBL in all of their Legacy series and studio monitors is puting the ports as close to the woofer as possible and on the front. JBL M2 is an exception but it uses quite new port tech, port actualy being a constant roundover without straight piece of pipe.
At the low frequencies involved ,"everything is nearby" 🙂
You need to approach 1/4 or 1/2 wavelength distances to make a significant influence, so just do the Math.
You need to approach 1/4 or 1/2 wavelength distances to make a significant influence, so just do the Math.
Any chance someone could briefly explain how this works?
It looks like the internal top to bottom length is 73.5". That's a wave length that corresponds to 182Hz. The top to bottom internal primary standing wave therefore would be 91Hz. How do 1/4 or 1/2 wavelength for the port location come into it? What would the port tuning in those cases be and how is that different than a normal port calculation?
It looks like the internal top to bottom length is 73.5". That's a wave length that corresponds to 182Hz. The top to bottom internal primary standing wave therefore would be 91Hz. How do 1/4 or 1/2 wavelength for the port location come into it? What would the port tuning in those cases be and how is that different than a normal port calculation?
Think of it this way.
Port is a source of sound and it overlaps with woofer. How would two sources of sound behave(regardless of how low is the overlap frequency) if they are mounted on the same baffle and what would happen if you would mount one on the opposite baffle.
For BR, it was stated-with a good reason, by a well respected designer, that the port should be as close to the woofer as possible, just like the speaker in post 6.
Likely because you have seen many manufacturers sell tower speakers that they call BR that ar e in fact all ML-TL variations. often non-optimized.
As a box with a vent in it transforms from something “near” square, with one dimension lengthening ehile the others shrink transitions from bass reflex to a (mass loaded) quarter-wave TL. That is the physics.
The behaviour of a straight or tapered ML-TL will be similar.
dave
When we consider the case of wjat is radiating towards us from the loudspeaker as long as the 2 sources are less than a quarter wavelength apart it is as if they are coincident.
But in an ML-TL the placement of the vent, Zv, is a factor in the shape, intensity, and placement of the harmonics, which has a direct impact on the bass response and ripple.
My Wonder, and Mr Fahey are talking about the former, celef the latter.
So it does matter.
But in an ML-TL the placement of the vent, Zv, is a factor in the shape, intensity, and placement of the harmonics, which has a direct impact on the bass response and ripple.
My Wonder, and Mr Fahey are talking about the former, celef the latter.
So it does matter.
When one mass-loads a transmission line one can shorten the line.
At some point one can design a hybrid BR/ML-TL. It isn’t one or the other but a continuum between the 2.
dave
Simulations assume the port inner end is in free space. Putting the port near an internal surface will increase the mechanical loading on the port's in-cabinet exit end, making the port appear longer and lowering the tuning frequency. An old rule of thumb was to ensure that the port was at least one diameter clear of any surface, and preferably more.