CHR-70 bass reflex

[Andy17]

Im planning to build a pair of these for monitors for my computer.

Would you suggest lowing the port freq from 59hz to something a little lower? say 40 to 45?...

That is more than a "little" lower!
In simulation you won't gain much bass with lower Fb in a 7l enclosure.
For 47Hz you need ~14l. But it is only a small driver with 50cm2 cone an 4mm Xmax. So you have to take care with the power!

 

[fastbike1]

As others have said, lowering the tuing that much won't work. Here's what will happen:

In the Microtowers (~21 Liters) a 54.5 Hz tuning gives F3/F10 of 47/41. Tuned to 40 Hz give F3/F10 73/31. Anything below low 50's causes the knee to droop very badly.

Im planning to build a pair of these for monitors for my computer.

Would you suggest lowing the port freq from 59hz to something a little lower? say 40 to 45?

Any idea how long the port would have to be then?

 

[planet10]

In the Microtowers (~21 Liters) a 54.5 Hz tuning gives F3/F10 of 47/41. Tuned to 40 Hz give F3/F10 73/31.

microTowers ia not a good example. It is an ML-TL not a BR.

dave

 

[Andy17]

Hi all,
a little update to my ShoeBox 70.3.
I wasn't entirely satisfied with sound when it stand "free" and was driven with the normal amplifier.
Ok, not the application I use it, but some other may use the Box "free" without any active correction.
So I build up a cheap measurement equipment. A mic with MCE-4500, a mic-preamp with NE5532 and s small amp
with TDA1516. As I have to learn a bit more about ARTA and the mic is not calibrated I will not post any measurement charts.
I think the measurement equipment is good enough to make comparison measurements

I end up with a Filter 1.5mH||6.8Ohm.
(According to the placement of the speaker try 1mH .. 1.5mH)
(If you want more highs try 1 .. 2.2uF in parallel)

 

[rongon]

Re: subsonic filters to protect little full-rangers:

Why not put the filter at the input of the power amp? A simple RC filter can be made with a -3dB point below 20 Hz. Assuming the input impedance of the following (solid state) amp is let's say 10k ohms, 1uF in series with the signal should give you a high pass filter with -3dB point at 16 Hz. That will be a slow rolloff -6dB/octave filter, but should help. You could make the capacitor smaller to change the -3dB point. 470nF would give you -3dB @ 34 Hz.

If you're using a tube or FET amp with a high input impedance, you can do this much better, using smaller value capacitors (which work better than larger value caps). 100k ohms and 100nF would get you that same -3dB point at 16 Hz.

An RC filter at line level should be much less damaging to the final sound than a large-value LC between the amp output and the speaker driver. Right?

--

 

[chrisb]

Re: subsonic filters to protect little full-rangers:

Why not put the filter at the input of the power amp? A simple RC filter can be made with a -3dB point below 20 Hz. Assuming the input impedance of the following (solid state) amp is let's say 10k ohms, 1uF in series with the signal should give you a high pass filter with -3dB point at 16 Hz. That will be a slow rolloff -6dB/octave filter, but should help. You could make the capacitor smaller to change the -3dB point. 470nF would give you -3dB @ 34 Hz.

If you're using a tube or FET amp with a high input impedance, you can do this much better, using smaller value capacitors (which work better than larger value caps). 100k ohms and 100nF would get you that same -3dB point at 16 Hz.

An RC filter at line leel should be much less damaging to the final sound than a large-value LC between the amp output and the speaker driver. Right?

--

+1 - you'd still wanna do some math to set values for the particular application