Note that's just the vent output. Not the combined output from both driver and vent.
A smooth vent output above Fb suggests good damping of harmonic resonances.
Why you look at the undamped eigenmodes so you can see when the Zd cancels the 1t unwanted harmonic, but you need damping to determiine final result.
But that wasn’t the kind of df under damped i mean.
Quite undamped box.
dave
Without context doesn’t tell me much.
I’m more used to seeing these as a set:
dave
For TL design, I tend to focus a lot on what the predicted vent output is going to look like, as that's where all the resonances are going to show up.
An important article by John S Wright, best printed out for legibility. Tried OCR to get clearer text, couldn't stop laughing at how 'off' it was.
This guy was pretty serious about recreating the TDL Reference Standard :
https://tdldiy.wordpress.com/
Three transmission Lines in one cabinet !!!
He used Tangband Bi-radials for the two bass drivers and didn't match the impedance of the original drivers.
Difficult, as the original bi-radials are a pair wired in parallel with 8Ω and 16Ω coils !
There is nothing quite like well designed and executed Transmission line speakers, nothing sounds close.
This guy was pretty serious about recreating the TDL Reference Standard :
https://tdldiy.wordpress.com/
Three transmission Lines in one cabinet !!!
He used Tangband Bi-radials for the two bass drivers and didn't match the impedance of the original drivers.
Difficult, as the original bi-radials are a pair wired in parallel with 8Ω and 16Ω coils !
There is nothing quite like well designed and executed Transmission line speakers, nothing sounds close.
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This is something I simply don't understand with Videos and forum chat about attempted measurements of acoustics in your shed or whatever. Unless you have access to a 1.5M deep wedged Anechoic Chamber mounted on rubber ( huge specialist installation) with all the Bruel & Kajer test gear to perform analysis, why bother? One will only pick up room modes and all manner of other interference's, that will then result in 'tuning' the experimental cab/ drivers combo to the space you measured it in.
Its a rough guide at best, even if performed in an acoustically treated studio environ.
According to the technique described in the following publication, access to a large anechoic chamber is not required for low-frequency measurements. It allows simple measurements to be made of frequency response, power response, distortion, and electroacoustical efficiency using nearfield sound-pressure measurements.
Admittedly, it does require some additional post processing to be done, but that is well within acceptable bounds with respect to means and time-scales available to diyAudio-ers.
Of course, another measurement method that obviates the need for an anechoic chamber predates that of Keele:
The technique described therein is based on measurement of the acoustical pressure within the loudspeaker enclosure, and it was suggested that it provides useful response measurements up to about 200 Hz.
Keele, Jr., D. B. (1974). "Low-Frequency Loudspeaker Assessment by Nearfield Sound-Pressure Measurement". Journal of the Audio Engineering Society, Vol. 22, No. 3, pages 154–162.
Admittedly, it does require some additional post processing to be done, but that is well within acceptable bounds with respect to means and time-scales available to diyAudio-ers.
Of course, another measurement method that obviates the need for an anechoic chamber predates that of Keele:
Small, R. H. (1972). "Simplified Loudspeaker Measurements at Low Frequencies". Journal of the Audio Engineering Society, Vol. 20, No. 1, pages 28–33.
The technique described therein is based on measurement of the acoustical pressure within the loudspeaker enclosure, and it was suggested that it provides useful response measurements up to about 200 Hz.
The last time looking into that, the DIY answer was free air tests in a field. Off the ground on a solid stand pinned to the ground, no rain, not too hot, not too cold! Good amp. Pink noise and Accurate mics. Way better than any building internal, except an anechoic chamber.
Who listens to a Cello inside the sound chamber? One wouldn't even place pickups or mics inside for amplifing
Apparently, there are a tiny amount of universities than now sport an anechoic chamber as part of their facilities.
Perhaps an interested generous soul may post a definitive list of locations for all to view...
Who listens to a Cello inside the sound chamber? One wouldn't even place pickups or mics inside for amplifing
Apparently, there are a tiny amount of universities than now sport an anechoic chamber as part of their facilities.
Perhaps an interested generous soul may post a definitive list of locations for all to view...
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The publications referred to above clearly indicated that, for low-frequency measurements up to 200 Hz, both near-field and internal sound pressure measurements are worth using. They can all give the required anechoic-like response results in an accurate manner, subject of course to the microphone's own frequency response characteristics. And I must admit to being confused by the reference to listening to cellos inside anechoic chambers. 🙂
So, I don't understand why there might still be a leaning towards free-air tests in a field for low-frequency measurements. Above 200–300 Hz, it's also now readily possible to use gated measurements to determine what is equivalent to an anechoic response. Of course, free-air tests can give you both the low-frequency and higher-frequency response results in one go. And there probably are better choices of excitation signal than pink noise, such as maximum-length sequences (MLS) or a variety of rapid frequency sweep signals (chirps).
Although there may be a reasonable list of universities with anechoic chambers of various sizes at their disposal, would they be willing to allow hobbyist loudspeaker constructors on site to use them?
So, I don't understand why there might still be a leaning towards free-air tests in a field for low-frequency measurements. Above 200–300 Hz, it's also now readily possible to use gated measurements to determine what is equivalent to an anechoic response. Of course, free-air tests can give you both the low-frequency and higher-frequency response results in one go. And there probably are better choices of excitation signal than pink noise, such as maximum-length sequences (MLS) or a variety of rapid frequency sweep signals (chirps).
Although there may be a reasonable list of universities with anechoic chambers of various sizes at their disposal, would they be willing to allow hobbyist loudspeaker constructors on site to use them?
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