Here's the spec on the driver:
Specifications: *Power Handling: 80 watts RMS/120 watts max *VCdia: 1.5" *Le: 1.2 mH *Impedance: 8 ohms per coil *Re: 3.10 ohms *Frequency range: 30-1,500 Hz *Fs: 25 Hz *SPL: 92.7 dB 2.83V/1m *Vas: 3.90 cu. ft. *Qms: 3.20 *Qes: .43 *Qts: .38 *Xmax: 6 mm *Dimensions: Overall Diameter: 10-5/8", Cutout Diameter: 9", Mounting Depth: 4-3/4"
I used the program offered for free by. www.ajdesigner.com
The port I used was for a 4" diameter and converted the dimensions to use a rectangular port.
Specifications: *Power Handling: 80 watts RMS/120 watts max *VCdia: 1.5" *Le: 1.2 mH *Impedance: 8 ohms per coil *Re: 3.10 ohms *Frequency range: 30-1,500 Hz *Fs: 25 Hz *SPL: 92.7 dB 2.83V/1m *Vas: 3.90 cu. ft. *Qms: 3.20 *Qes: .43 *Qts: .38 *Xmax: 6 mm *Dimensions: Overall Diameter: 10-5/8", Cutout Diameter: 9", Mounting Depth: 4-3/4"
I used the program offered for free by. www.ajdesigner.com
The port I used was for a 4" diameter and converted the dimensions to use a rectangular port.
This is a home subwoofer. I do not know the issues involved with pasive filters. The sealed chamber volume is: 43.5 liters and 31.256 liters for the ported chamber. The port size is 10 mm with a volume of 2.25 liters. I used a 15mH inductor and 100Uf capacitor for the filter. I am new to this so any assiatance is appreciated. Thanks
Well something seems wrong with your filter if you ask me..... Since the sub is 8ohm DVC I would assume you wired in parallel for 4 ohm operation. For a 2nd order low pass filter at 60hz into 4ohms one needs a 1000uf capacitor wired in parallel with the driver, and a 15mH inductor wired in series with the driver and capacitor. You said you used a 100uF..... I think that would be first order up to somewhere around 500hz and then it would begin 2nd order filtering. If this is the only crossover you are using to filter out high frequencys then this is likely why it sounds so bad!
In a bandpass enclosure, above the bandpass the system acts as two sealed boxes(the ports cease to exist functionally) and all the sound created by the driver is absorbed/transmitted through the cabinet walls. Once you get down to the tuning of the front chamber the port loads the driver for additional efficency. Below the tuning of the front chamber, the front chamber doesnt exist(functionally) and the system acts as if it were plainly a sealed box(for 4th order bandpass).
Because your filter is probably inadequate it is letting high levels of out of bandwidth signal go to the sub. The sub is playing those high frequencys, the box is trying to damp them, and probably most of what you're hearing is this
In a bandpass enclosure, above the bandpass the system acts as two sealed boxes(the ports cease to exist functionally) and all the sound created by the driver is absorbed/transmitted through the cabinet walls. Once you get down to the tuning of the front chamber the port loads the driver for additional efficency. Below the tuning of the front chamber, the front chamber doesnt exist(functionally) and the system acts as if it were plainly a sealed box(for 4th order bandpass).
Because your filter is probably inadequate it is letting high levels of out of bandwidth signal go to the sub. The sub is playing those high frequencys, the box is trying to damp them, and probably most of what you're hearing is this
The filter may not necessariliy be wrong in the way you describe there. There are many ways to build a 2nd-order filter because you can change the Q.
There are two issues with the filter. The first is that passive filters need a stable, constant impedance to work into. The impedance of pretty much any driver/box combination in the bass range varies wildly. Secondly the filter is not even required because the box itself performs the filtering function on the mid and high (in principle).
I think you may also be misleading with your comments on the operation of the box, particularly the bit about all the sound being absorbed or transmitted through the cabinet walls. A bandpass box cuts off the sound above the tuning frequency because the vent appears to be a very low acoustic impedance. Through the tuning frequency sound is let out OK and the cone is supported by the vent giving an efficiency gain, then as you say below the tuning frequency the vent is totally open but the characteristics of the sealed box become prevalent.
There are two issues with the filter. The first is that passive filters need a stable, constant impedance to work into. The impedance of pretty much any driver/box combination in the bass range varies wildly. Secondly the filter is not even required because the box itself performs the filtering function on the mid and high (in principle).
I think you may also be misleading with your comments on the operation of the box, particularly the bit about all the sound being absorbed or transmitted through the cabinet walls. A bandpass box cuts off the sound above the tuning frequency because the vent appears to be a very low acoustic impedance. Through the tuning frequency sound is let out OK and the cone is supported by the vent giving an efficiency gain, then as you say below the tuning frequency the vent is totally open but the characteristics of the sealed box become prevalent.
I presume you have tuned the box to 47Hz or so? Your port dimensions make no sense, you need to supply height and width of the port slot and the length of the port.
Assuming you have it tuned correctly, you should have a fine response from ~30 to ~80Hz. Try running it without the filter and see if it gets a lot louder - if so, you may have wired the filter incorrectly.
Note that the DCR of a 15mH inductor may have a substantial effect on Qts of thr driver, increasing Qts and requiring a larger box. Do you know what teh DC resistance of the inductor is?
Assuming you have it tuned correctly, you should have a fine response from ~30 to ~80Hz. Try running it without the filter and see if it gets a lot louder - if so, you may have wired the filter incorrectly.
Note that the DCR of a 15mH inductor may have a substantial effect on Qts of thr driver, increasing Qts and requiring a larger box. Do you know what teh DC resistance of the inductor is?
I am feeding the voice coils separately and each has its low pass filter. I do not hear the mid and high frequency when running the sub. I hear the real low bases when I am near the box, but once I step away from the sub about 5 feet, I can no longer hear the lows. Should I remove the filters and add damping materials in the sealed chamber?
You could simply have the coils wired out of phase and that would make it so that very little sound comes out - switching the leads on one of teh VC's red for black would tell you if that is the case..... If that fails, I would at least try and remove the filters and see if that changes anything... But first, what is the associated equipment and how have you got it hooked up?
One thing many people are not aware of is that there is not that much stuff <60Hz in a lot of popular music.
Adding damping in either the sealed or vented chamber will not do anything useful.
Try putting the sub in a different location in the room as well, you could be sitting in a standing wave null.
One thing many people are not aware of is that there is not that much stuff <60Hz in a lot of popular music.
Adding damping in either the sealed or vented chamber will not do anything useful.
Try putting the sub in a different location in the room as well, you could be sitting in a standing wave null.
richie, think about how a ported box works. near tuning(slightly above and below) the port loads the driver decreasing excursion and raising efficiency. Below the tuning of the port the driver unloads and the enclosure doesn't help out at all(24db/octave rolloff). above the frequenys where the port provides loading the response is the same as a sealed enclosure and group delay is also the same. This is because the port blocks higher frequencys so basically the box acts as if t doesnt have a port.
Well with a bandpass enclosure you start with a sealed enclosure and stick a vented one on the other side. The entire backwave is absorbed in the sealed enclosure while the frontwave is filtered by the ported enclsoure. When you get to the point of -10db attenuation on the high side of the FR only 1/10th of the sound that the speaker is creating escapes the port. The remaining 9/10ths is trapped inside the enclosure. Where does that sound go? Well if the enclosure walls can flex or vibrate at all thats where it will mostly end up.
If you ask me, bandpass enclosures need at least 18db/octave filtering, if not 24!
Well with a bandpass enclosure you start with a sealed enclosure and stick a vented one on the other side. The entire backwave is absorbed in the sealed enclosure while the frontwave is filtered by the ported enclsoure. When you get to the point of -10db attenuation on the high side of the FR only 1/10th of the sound that the speaker is creating escapes the port. The remaining 9/10ths is trapped inside the enclosure. Where does that sound go? Well if the enclosure walls can flex or vibrate at all thats where it will mostly end up.
If you ask me, bandpass enclosures need at least 18db/octave filtering, if not 24!
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