Understanding the use of inductors in bandpass subwoofers and impedance curves.
I've had two small bandpass subs (neither impressed me). One used a capacitor on the pass-through, a rudimentary high-pass filter to the main speakers. The other uses an inductor, a low-pass filter to the drivers.
I always believed bandpass subs didn't need filters, so I assume the inductor's purpose is related to impedance.
This brings me to the impedance curve of the setup. How many peaks would there be?
1 at the resonant frequency of sub driver.
1 at frequency sub's port.
1 at the resonant frequency of the satellite's woofer.
1 at the resonant frequency of the satellite's port.
Is that right?
I've had two small bandpass subs (neither impressed me). One used a capacitor on the pass-through, a rudimentary high-pass filter to the main speakers. The other uses an inductor, a low-pass filter to the drivers.
I always believed bandpass subs didn't need filters, so I assume the inductor's purpose is related to impedance.
This brings me to the impedance curve of the setup. How many peaks would there be?
1 at the resonant frequency of sub driver.
1 at frequency sub's port.
1 at the resonant frequency of the satellite's woofer.
1 at the resonant frequency of the satellite's port.
Is that right?
Not sure about the inductor, but without any passive components a 4th order bandpass will have 2 peaks, with the dip between them being at the port tuning frequency.
A 6th order will have 3 peaks, with each dip being at the tuning frequency of one of the ports.
To understand what happens when you run a satellite connected via a passive crossover, you'd need to model it in something like VituixCAD.
A 6th order will have 3 peaks, with each dip being at the tuning frequency of one of the ports.
To understand what happens when you run a satellite connected via a passive crossover, you'd need to model it in something like VituixCAD.
Most bandpass subs need additional LP filters of some sort to get rid of upper out of band response.
A free air speaker has one impedance peak at Fs (free air resonance peak).
The speaker in a sealed box also has a single impedance peak Fc, at a higher frequency than Fs.
A bass reflex speaker will have two peaks, one on either side of Fb (Frequency of Box tuning), which is the lowest impedance.
As David already mentioned, a 4th order bandpass will have 2 peaks, the dip at Fb.
There will also be minor impedance peaks at the port's pipe resonance frequency.
The upper out of band port pipe resonance may cause a large peak, and upper speaker breakup may also be emitted through the port.
This upper "garbage" can be reduced with stuffing the vented part of the box, but that also reduces the low frequency output, or an inductor (single pole 6dB/octave filter) or inductor & capacitor (two pole 12dB/octave filter) can be used.
Passive filters add expense, stuffing takes more labor, cheap subs don't want either..
In the above example, the simulated (red trace) pipe resonance in the 200-400Hz range show up in the measured (blue) response, but the "garbage" above does not, a fourth order filter (brown trace) gets rid of it.
Without the filter, the upper "garbage" sounds louder than the sub output.
Thank you. Assuming the Mission filter is 8.5mF is the filter frequency 150hz using the original 8ohm driver what is the frequency using a 6ohm load?
Would 9mF have any effect on the minimum impendance?
Would 9mF have any effect on the minimum impendance?
Also at higher powers, you do not want hundreds of watts going to the speaker at 120-250Hz. It is still a lot of power and little movement = no cooling. Many extended range bass drivers get burnt that way. They might not like anything above 90-100Hz.
A series inductor (mH, not mF) increases impedance above the crossover point, a series capacitor increases impedance below the crossover point.
Without knowing the frequency of the upper bandpass impedance peak in your cabinet, can't say what the effect of the 8.5mH coil would be, but it should not affect the impedance at Fb.
Capacitors are measured in fractions of Farads (F), inductors fractions of Henrys (mH, millihenry).
In the usual values of capacitors used for crossovers, 1 µF, uF, or mF = 1 microfarad.
In other contexts, mF is the official abbreviation for millifarads.
https://www.omnicalculator.com/physics/crossover
Assuming a fixed impedance of 8 ohms, 8.5mH does a 150Hz crossover, at 6ohms about 112 Hz.
You could measure the response with REW and see the actual results 😉 .
It's just a silly sub designed to give a little more welly to a 30 + 30w Micro system.
The mF / mH thing was a typo.
I'm trying to simulate a 6th order bandpass sub to supplement stand speakers in the living room. I had hoped for as small a box as possible. Frequency response 30-80 Hz. So far, I have the following results from Hornresp, but there is definitely something I haven't picked up on. Speaker is Faital pro 10HP1020.
If you plan to use a passive crossover you need to take the impedance response into account to determine the proper components to reduce the upper frequency response junk.
Burnt up VC ends are the death of many high Xmax drivers in horns, fullrange PA speakers that are only used as tops, that's of course true. But it is very rarely the case you have an extended time of high-power going on in 120-250 Hz without having anything going on below that, so that scenario can happen but it's not very likely. And the fact that high power coils are much more expensive than an active crossover I don't think we will see a high power passive sub/sat combination ever again.
I thought we are talking bass, and in this case bandpass designs too, which have serious impedance minimum in the top end of the used range. And that's real bad for synthetic music. The limiter will have a lot of work to do. Otherwise you are right.
At least one inductor in line with the woofer will help.
To assist this 6db filter a zobel C+R at the driver between + and - will help. Something like 6ohms and 30uF, what you have at hand will do.
Better is to measure, but there are online calculators for impedance linearization of loudspeakers. You can take for that the Re from the driver and Le from the datasheet.
To assist this 6db filter a zobel C+R at the driver between + and - will help. Something like 6ohms and 30uF, what you have at hand will do.
Better is to measure, but there are online calculators for impedance linearization of loudspeakers. You can take for that the Re from the driver and Le from the datasheet.
Well, it is a SUBwoofer. 9 out of 10 times, the sub will be low pass filtered at 80hz.
Apparently, you did not build what you modeled.
Your 60-100hz measurement (blue line) does not match your 60-100hz model.
Is the model 2pi?
Is the measurement 2pi also?
Your 60-100hz measurement (blue line) does not match your 60-100hz model.
Is the model 2pi?
Is the measurement 2pi also?
Simulating in 2,0 pi, unless you're going to hang it 5 meters into the air and free from all walls, as a start.
Correlating the port area to the air displacement. So simulate it with the power it's going to get IRL, then make sure the port velocity preferably stays below 17 m/s.
Perhaps start your own topic, unless you wanted people to react to stuff said in February, all over 😉
That's correct, I modeled what I built.
That was as close as I could get the model to what I built without spending much time on a design I'd already sold.
The upper cone breakup garbage never matches the model, Hornresp assumes a pistonic cone motion.
I used Hornresp Ang=2.0xPi, half space radiation, the speaker's radiating surface located on one (infinite) boundary, like a speaker buried on the surface of the (flat..) Earth pointing up to the sky.
The outdoor ground plane measurement was taken with the mic at two meters from the speaker's front vertical radiating surface.
Anyway, you've asked about the Bowtie sub's radiation angle before:
https://www.diyaudio.com/community/threads/12-bandpass-subwoofers.413904/page-2#post-7720757
Art
How did you model what you built when the HR model shows a rising response and your measurements shows a substantial decreasing response?
I'm not referring to the "upper cone break up garbage." The 20hz-80hz response is all that really matters when it comes to SUBwoofers.