Xmax in relation of surface area?

[yepimonfire]

Not diy, but more likely to see responses here.

Can xmax be calculated from the surface area or diameter of a driver reliably? It seems when plugging the numbers into an excursion calculator , a 5.25” driver would need 16 mm of xmax to reach 50hz at 100dB @1m, yet I have no issue reaching 100dB @3m from 50hz on up with rp-150m’s 5.25” driver with <3% THD. I am positive the drivers do not have 16mm of xmax, more likely it’s about 6mm. The port tuning is 66hz. The 250c has dual 5.25” drivers and a tuning around 70hz, and can achieve 103dB @3.3m from 50hz on up. This translates to about 106 and 109dB @1m.

Assuming the port is reducing excursion across a ~20hz range, would a speaker using the same drivers in a tower with a 35hz tuning perform worse at 60-80hz when compared to the smaller box tuned to 66hz? For example, if the 250c using 2 5.25” drivers tunes to 70hz can output 109dB at 50-80hz, would a 250f, using 2 of the same drivers tuned to 35 hz require greater excursion from 60hz on up to achieve similar output?

Out of curiosity, how can excursion based on spl an frequency be calculated in a ported box without t/s parameters?


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[TLS Guy]

Not diy, but more likely to see responses here.

Can xmax be calculated from the surface area or diameter of a driver reliably? It seems when plugging the numbers into an excursion calculator , a 5.25” driver would need 16 mm of xmax to reach 50hz at 100dB @1m, yet I have no issue reaching 100dB @3m from 50hz on up with rp-150m’s 5.25” driver with <3% THD. I am positive the drivers do not have 16mm of xmax, more likely it’s about 6mm. The port tuning is 66hz. The 250c has dual 5.25” drivers and a tuning around 70hz, and can achieve 103dB @3.3m from 50hz on up. This translates to about 106 and 109dB @1m.

Assuming the port is reducing excursion across a ~20hz range, would a speaker using the same drivers in a tower with a 35hz tuning perform worse at 60-80hz when compared to the smaller box tuned to 66hz? For example, if the 250c using 2 5.25” drivers tunes to 70hz can output 109dB at 50-80hz, would a 250f, using 2 of the same drivers tuned to 35 hz require greater excursion from 60hz on up to achieve similar output?

Out of curiosity, how can excursion based on spl an frequency be calculated in a ported box without t/s parameters?


Sent from my iPhone using Tapatalk

The answer is no and no.

You do not seem to understand the physics of drivers and box tuning at all.

 

[highfigh]

Can xmax be calculated from the surface area or diameter of a driver reliably?


Assuming the port is reducing excursion across a ~20hz range, would a speaker using the same drivers in a tower with a 35hz tuning perform worse at 60-80hz when compared to the smaller box tuned to 66hz? For example, if the 250c using 2 5.25” drivers tunes to 70hz can output 109dB at 50-80hz, would a 250f, using 2 of the same drivers tuned to 35 hz require greater excursion from 60hz on up to achieve similar output?

Out of curiosity, how can excursion based on spl an frequency be calculated in a ported box without t/s parameters?

Xmax of a driver can't be calculated. It refers to the physical ability of a driver to move a specific distance in a linear manner (or not).

The port acts like a bottle when you blow across the top- it resonates well at one frequency, assuming nothing else has changed (diameter or adding/subtracting some material to the bottle. The 'tuning' is in selecting the diameter & length and mating its frequency to the response of the speaker in that particular enclosure. How much the response improves depends on the tuning frequency, box size and whether that diameter/length of port is suitable for the box. If the box is small, the Qts will be high and if it's larger, the Qts will be lower.

As TLS posted, it can't be calculated without finding the parameters. The only way to do it without those would be to guess and use trial & error testing.

 

[OscarJr]

To possibly answer you question about how you're getting so much output compared to a mathematical model, is that the mathematical model is not taking into account your specific room in your house where you have your speakers in. Room gain, standing waves, etc, can greatly change the response of a loudspeaker compared to what the speaker would do if it was suspended 2 miles up in the air and firing out in all directions.