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Aberslam74's picture
Last seen: 8 years 1 month ago
Joined: Oct 14 2015 - 7:11pm
Speaker Port/s, Phase, and Crossover

My question is:

Should the output of driver/s and port/s be considered when selecting an active crossover frequency (AVR, etc.) if the goal is bext phase/time coherence and subwoofer integration?

Are these phase in/differences audible?

Everything I read indicates that a speakers port/s are 360 degrees out of phase (1 cycle of delay) from the driver/s that affect the port/s.

"Since the backwave is already in opposite polarity with the front wave, this inversion brings the two emissions in phase (although the vent emission is lagging by one wave period) and therefore they reinforce each other. This has the useful purpose of producing higher output (for any given driver excursion compared to a closed box) or, conversely, a similar output with a smaller excursion (which means less driver distortion). The penalty incurred for this reinforcement is time smearing: in essence the vent resonance augments main driver output by imposing a "resonant tail" on it."

This leads to the understand that if you are using speakers with ports and a subwoofer/s, you have three sources of output in certain frequency ranges: the driver/s, the port/s, and the subwoofer/s.

This can lead to phase mis-alignment, cancellation, and time-smearing.

Most people seem to agree that fully bung-ing speaker ports alters their behavior in ways that are detrimental, since the driver/s were designed for a ported enclosure.

I have yet to find a speaker review that includes frequency response graphs for ported (un-bunged), partially bunged, and bunged.

Instead of bunging the port/s, it seems that selecting an active crossover frequency (in an AVR, etc.) based on the driver and port output would be another work around.

If we compare the frequency response graphs for speakers, that include the port output, it would lead to me to believe that if we want maximum phase coherence, we should pick the crossover point based on the driver and port output, not the sum of the two.

For example, if we look at the KEF R700 frequency response:

The drivers have 10 db more output at 80 Hz than the ports. This would lead me to believe that 80 Hz would be a fine active crossover setting (AVR, etc.).

For another example, if we look at the KEF LS50 frequency response:

The diver has almost 10 db more output at 100 Hz than the port. This would lead me to believe that 100 Hz would be a better active crossover setting (AVR, etc.).

I understand that room acoustics/gain will alter the frequency response. However, the will not alter the ratio of output from driver and port (in my understanding).

Should the output of driver/s and port/s be considered when selecting an active crossover frequency (AVR, etc.) if the goal is bext phase/time coherence and subwoofer integration?

Are these phase in/differences audible?



commsysman's picture
Last seen: 1 year 12 months ago
Joined: Apr 4 2006 - 11:33am

The simple fact is that AVRs that use room correction software and adjust the crossover frequencies do so independently of the speaker design, and this can introduce all sorts of problems, as you suggest.

If you read reviewer's comments when testing speakers, you will find that many find that the software actually makes the system sound worse in many cases due to various effects on phase and distortion, and they end up disabling it to get the best sound quality.

Speaker systems can be designed to have correct time, space and phase alignment; all Vandersteen designs are done this way and this results in a fundamentally superior sound quality to my ears. It is more expensive to do properly, but the oats are always better before they go through the horse.

I happen to be one of those dinosaurs who maintain that a good 2.1 system is better-sounding than a 5.1 system in any case, so there is probably no hope for me.

michael green
michael green's picture
Last seen: 5 years 6 months ago
Joined: Jan 10 2011 - 6:11pm
count me in too

I have never been crazy about the 5.1, and in every case ended up going phantom 4.2. Ok, I'm 56 got that over with :)

2.1, 2.2, 2 and 4.1 or 4.2 have always seemed to fit within a more balanced spread from what I have experienced even though many go for that center boost. For myself those odd numbers in setups always stick out as such. I would also agree that the 2.1 is a special setup that can produce some serious magic as you learn your room and speaker blends.

I only use caps & resistors on my mains BTW. Inductors on mains is a no no in my designing these days. The sub is a little different, and for that I've always enjoyed the Paradigm X-30 to do my dirty work.

I might also add, for my higher end models of speakers the decision to go port or portless is decided in the listening room itself.

michael green

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