bob4 wrote: Elliot Thompson wrote: The flared port just reduce port shuffle noise. If you believe so, you should carefully read the aes paper that i linked

I am sorry I cannot take a paper seriously with tubes longer than the actual box it is residing in. It tells me automatically that the cabinet is so small that the tubes need to be longer than the actual enclosure in order to achieve low frequencies.

Ask yourself a question. How many times have you seen a Bass Reflex enclosure with ports sticking out of a box aimed for Sound Reinforcement?

This paper reaps Home Audio Setup as I mentioned in my previous post why such a method would be beneficial under low SPL conditions. Under High SPL Conditions in the Sound Reinforcement World which we all do, such methods are not going offer tremendous results for the majority of the sound stems from the loudspeaker, not the port. 

Not everything posted in AES is aimed for Sound Reinforcement.

Best Regards,

Elliot Thompson wrote: I am sorry I cannot take a paper seriously with tubes longer than the actual box it is residing in. It tells me automatically that the cabinet is so small that the tubes need to be longer than the actual enclosure in order to achieve low frequencies.

it's a small prototype for research….

Elliot Thompson wrote: Not everything posted in AES is aimed for Sound Reinforcement.

Agreed (well, duh… )

Elliot Thompson wrote: Ask yourself a question. How many times have you seen a Bass Reflex enclosure with ports sticking out of a box aimed for Sound Reinforcement?

  

Pellerin, Pollack, Mokerken wrote:  we proved, with the help of the phase space representations, that well tuned nozzles ensure a better global dynamical stability even for very high feeding power in the case of a dipole configu- ration and the dipole moment is then an interesting physical property which allows to build complex di- rectivity patterns in the low frequencies.

  

Pellerin, Pollack, Mokerken wrote:  We demonstrated first that it effectively exists a second cutoff frequency under the well known Helmholtz frequency which could be exploited to design sources radiating in the very low frequency domain with dipole directivity patterns and that, in theory, this frequency could be decreased near zero Hertz.

  

I don't see why any of these principles couldn't be applied to PA systems at some point.

Best Regards,

Bob

Teunos wrote:   A previous fellow of my university actually researched the flared ports in depth using Schlieren imaging. His papers can be found in public domain (or at least part II) at: http://www.academia.edu/19837501/Vortex_sound_in_bass-reflex_ports_of_loudspeakers._Part_II._A_method_to_estimate_the_point_of_separation" rel="nofollow - http://www.academia.edu/19837501/Vortex_sound_in_bass-reflex_ports_of_loudspeakers._Part_II._A_method_to_estimate_the_point_of_separation If desired i am sure the author would not mind me sharing Part I as well (being a student at his Uni).

So the conclusion is basically such a method is more beneficial for small enclosures due to the limitation of the enclosure. The ratio between the sound being 0 dB of the amplified signal and distortion without using such a method is -20 dB which is inaudible compared to a room full of punters screaming their lungs out to their favourite song.

In order to hear an equal amount of distortion as the amplified frequency, the distortion would need to be residing on a 10,000 watt amplifier to match the output of a frequency residing on a 100 watt amplifier. That would be a 20 dB ratio.

All loudspeakers offer additional harmonics in which will be looked upon as distortion however, only a few are willing to post such graphs. Unfortunately, this is what many do not realise. The source material offers more distortion today than it did 20 years ago due to many recording engineers inserting distortion/saturation plug-ins and hardware equipment designed to deliver distortion in the mix to achieve that “Analogue Sound” on Digital Audio.

The idea seems like a useful method for the Home Audiophile-Classical Music type of crowd where they get very temperamental on any type of residue sound in their household.  

Best Regards,

snowflake wrote: straight ports suffer distortion at a much lower port velocity than flared ones. if you want to make ports short it is vital that you flare them so that you don't have to make their cross section and length huge. so these methods are especially useful for PA use. "In order to hear an equal amount of distortion as the amplified frequency, the distortion would need to be residing on a 10,000 watt amplifier to match the output of a frequency residing on a 100 watt amplifier. That would be a 20 dB ratio." No. above the distortion threshold the port noise increases more than linearly with input signal - so at high volumes the distortion can completely mask the signal.

The distortion you are mentioning that is so prominent comes from the loudspeaker not the port. The port responds like a band pass filter. The port is tuned to a frequency. The tuning frequency determines the length and the radius of the port based on enclosure size and of course, the TS Parameters of the loudspeaker at a given dB level.

Unless you are tuning the cabinet extremely high (So it will ring) in which, will require a very large radius for a port, the port is not large enough to deliver equal amount of SPL as the loudspeaker at high sound pressure levels. And if you are tuning the cabinet so high that requires such a large port radius you are better off making a bass horn.

A port does not need to be the focal point in a reflex box. So the most common method to reduce any audible shuffling noise is to put the ports in the rear of the box.

It is very old method that has been around since the1950s.

I am going to expand on very large ports in small boxes that a lot of home audio guys pay no attention to for a moment. Large ports in small cabinets reduce in the internal chamber in the eyes of the loudspeaker. That of course, alters the low frequency extension. It is the next biggest culprit compared to bracing a small box to the point you lose 50% (I’ve seen some designs with higher percentages) of the internal chamber due to excessive wood bracing posing their presence inside the cabinet.

Many of you may not know Rog purposely made the G-Sub’s dimensions larger to compensate the bracing in the box to avoid losing the low frequency extension.

Best Regards,

bee wrote:   Totally agree with you, but what if some one has a box, with a port twice the length of the box, designed for pa use... its defo possible, and the gains can be massive, not only keeping the box footprint small, and keeping the port in side the box... its 100% possible...

Anything is possible. However having ports protrude in such a manner for sound reinforcement will more than likely look like a place to kotch  your foot from a punters perspective or stand on top of for whatever reasons. They will also look like a nice handle to move the box about.