Well I need a 3.5 cm wide 15cm(approx) long port for my application, so I bought this with the Intention of cutting it to length:JANTZEN AUDIO Event pour enceinte bass-reflex L 165mm O35mm - Audiophonics
When it arrived I realized that it has a conical shape like a horn. The diameter at the opening is 3.5cm exactly what I need but in the inside opening the diameter is only 2.6mm. Will this work? Why is it like this? Do I have to model my port as a 2.6cm meaning to decrease its size (that would increase the diameter though). Should I order a new port all together? I am confused.
When it arrived I realized that it has a conical shape like a horn. The diameter at the opening is 3.5cm exactly what I need but in the inside opening the diameter is only 2.6mm. Will this work? Why is it like this? Do I have to model my port as a 2.6cm meaning to decrease its size (that would increase the diameter though). Should I order a new port all together? I am confused.
It works. It’s conical because it had to come off the mold. Calculatie the port as if it were 3cm, you will be allright. I would avoid these ports with PA or critical designs, otherwise they are fine.
But if I where to do that, then my port length would be less than the original. Say 10cm for example. If I were to cut in the 10 cm mark, due to the shape of the conical port the diameter at at incision would be something in between 3.5cm and 2. 5 cm let's say aprx 2.8cm that would mean than the mean diameter of the cut piece wouldn't be 3cm anymore but 3.15 cm that would result in a different tuning frequency that the one calculated for the given length. Am I right or I am over thinking things?
Ime, any ports other than simple round tubes, will need measurements to dial in.
Even then....measurements totally rule over calculators .....
Any kind of port structure can work....if you're willing to measure and alter, re-measure and re-alter, etc, etc, ....
Some near crazy funky ports can work quite well....working on such right now 🙂
Even then....measurements totally rule over calculators .....
Any kind of port structure can work....if you're willing to measure and alter, re-measure and re-alter, etc, etc, ....
Some near crazy funky ports can work quite well....working on such right now 🙂
To bad i dont have a DATS to measure impedance and tuning frequency. Is there anyother way to do it? Like sticking a mic right next to the port or maybe the complete formula of port tuning would help?
Hi,
In my experience the calculation is most accurate when the true minimum diameter of the port is entered. In your case that's 26 to 35 mm, depending on length. Assume 35 mm for a port length of 20 mm, 26 mm for full length and interpolate the values in between.
In my experience the calculation is most accurate when the true minimum diameter of the port is entered. In your case that's 26 to 35 mm, depending on length. Assume 35 mm for a port length of 20 mm, 26 mm for full length and interpolate the values in between.
If you have Room Eq wizard and a sound card connected to your audio system, you can play single frequency sine waves starting below expected tuning moving up 1/2 hz at a time. ( start at low amplitudes, slowly increasing the volume watching cone motion to maintain safe excursions )
Tuning will be at the cone excursion minima, with excursion on either side of tuning higher.
You could also use REW to make an impedance measurement if you have a precision resistor.
Tuning will be at the cone excursion minima, with excursion on either side of tuning higher.
You could also use REW to make an impedance measurement if you have a precision resistor.
Generator is located above the red arrow, and the pop up window shows you frequency and level. The green 'play' button in the generator pop up window turns the generator on and off. Be careful how long you play sine waves at tuning, this is where power demands are greatest and the coil motion is low, and you don't want to damage a driver in the process.
Ooof. And i allready was at the limit for port air velocity, I guess it will chuff now.
Right both impedance and cone excursion is at the lowest at tuning frequency i will try to find the true tunning frequency that way, i suppose i wont be too accurate but still. Hm can I even hear distortion is simple sine waves? I mean that the only way to know i am not damaging the drivers
You can be accurate within 1/2 hz with the generator function in REW simply watching cone excursion.
Right. Let's say I want it to be 63hz what do I do if I find it to be higher or lower than that. I mean since the diameter is not constant and for a specific frequency the two dimensions are inversely proportional how should I tweak it?
Connect a larger resistor in series with the driver. Use either REW, Holm, ARTA or similar to simply sweep the range, and measure the Voltage at the terminals. You'll see the relevant shape of the impedance.
This is what Allen is saying: AudioBlog: A simple loudspeaker measurement jig for ARTA
Good impedance measure depends mainly on the quality of the sound card. However, if you simply need to find the tuning frequency of a ported box (e.g. the minimum between the two spikes), any sound card, even the integrated one, is sufficient.
I use those ports. I do my calculation on the expected length, cut oversized some 2 cm and measure, then cut again. To be on the safe side, use the max diameter as a starting point, as this will lead to a longer length, you can always cut something, OTOH if you cut too much you can't add something...
Ralf
Good impedance measure depends mainly on the quality of the sound card. However, if you simply need to find the tuning frequency of a ported box (e.g. the minimum between the two spikes), any sound card, even the integrated one, is sufficient.
I use those ports. I do my calculation on the expected length, cut oversized some 2 cm and measure, then cut again. To be on the safe side, use the max diameter as a starting point, as this will lead to a longer length, you can always cut something, OTOH if you cut too much you can't add something...
Ralf
Time to ditch those things and get a better alternative, both sides flared. Be it from the shelf or DIY. Btw port tuning doesn’t have to be exact science imho. Room acoustics dominate this frequency range and placement of the speakers is of far greater importance than port tuning.