4th order isobaric box/es, and TL box designs
- Thread starter smgreen20
- Start date
smgreen20
Active Member
Here's an update to my question. I just cut/paste from another post I made on another forum.
I'm looking into changing my box from a ported box to a 4th order isobaric compound box. I input the data into WinISD and it came up with a solution of .46 cf for the rear sealed chamber and .825 for the front/ported chamber. On another forum site I was told that I need to halve both of those sizes given. If that's true, then that's pushing it for me to even try to fit the motor assembly in the box. But I know you tune the box and halving that would change the port dimensions, correct?
So I ask, What do I do?
If I knew how to copy/paste the screen, I would post the WinISD results. I love the looks of the freq curve for this setup, it's exactly what I'm after. Higher low end output w/the SQ of a sealed box.
The subs I am using are two TREO SSi12.22's.
Need you help guys. I still can't get the java ware to load on the link given above.
HELP!!!!!!
I'm looking into changing my box from a ported box to a 4th order isobaric compound box. I input the data into WinISD and it came up with a solution of .46 cf for the rear sealed chamber and .825 for the front/ported chamber. On another forum site I was told that I need to halve both of those sizes given. If that's true, then that's pushing it for me to even try to fit the motor assembly in the box. But I know you tune the box and halving that would change the port dimensions, correct?
So I ask, What do I do?
If I knew how to copy/paste the screen, I would post the WinISD results. I love the looks of the freq curve for this setup, it's exactly what I'm after. Higher low end output w/the SQ of a sealed box.
The subs I am using are two TREO SSi12.22's.
Need you help guys. I still can't get the java ware to load on the link given above.
HELP!!!!!!
I don't have time to actually model your ideas and confirm or deny your recommended specs, but I wanted to comment on a couple of things...
Room for the Motor Assemblies:
The box volume in which you place the woofers needs to take into account the amount of displacement the entire woofer takes up in the enclosure. So, if you have a target effective volume of 0.46 ft^3, then you need to know how much volume the woofer will take up. If the woofer takes 0.3 ft^3, then you need to design the enclosure to have an internal volume of 0.76 ft^3 and install the woofer so it takes 0.3 ft^3 and leaves an effective open volume of 0.46 ft^3. So, there is always room for the woofer motor assembly.
Designing for target response:
You really need to ensure the resulting response curve for your modelled system is as flat as possible. If it has a high peak of more than 1.5dB on either end of the bandpass range, or a dip of more than 1.5dB in the middle of the operating range, the resulting sound will be resonant and ring immensely. Where the response has a significantly peak the reproduced would will ring and be extremely pronounced at that frequency. So, if you tune the system so there is a peak of more than 3dB at, say, 30Hz, when you play music you will find it difficult to make out the music and sound in the 35 - 50Hz range and instead everything will have a very pronounced "BOOOOOOONNNNNG" sound at exactly 30Hz. So bass drums will always go "BOOOOOOOOOOOOOOONG" at 30Hz regardless of how they were recorded. Bass guitars will go "BOOOOOOOOOOOONG" at 30Hz regardless of the notes the bass player is playing. And so on.
Note, though, that this effect happens at both ends of the response. So if there is a peak at 30Hz, a dip in the middle, and another peak at 80Hz, then the bass sound of your woofer will ring out at both 30Hz and at 80Hz. So, if there is a sound in the recording centered at 50Hz the sound you hear will be ringing out at 30Hz and 80Hz. if the sound is centered above 60Hz, the sound you hear will be ringing out at 80Hz no matter what. Sounds below 40Hz will always ring out at 30Hz.
Again, all the descriptions above are based on a theoretical system with a resonance at 30Hz and another at 80Hz.
The only way to remedy the ringing problem which results in a sub that sounds like a one note mess is to design your solution so the edges of the response curve are actually a bit lower in level than the center. Doing that narrows the effective output range, but it cleans up the sound and makes the sub more musical and natural sounding.
Room for the Motor Assemblies:
The box volume in which you place the woofers needs to take into account the amount of displacement the entire woofer takes up in the enclosure. So, if you have a target effective volume of 0.46 ft^3, then you need to know how much volume the woofer will take up. If the woofer takes 0.3 ft^3, then you need to design the enclosure to have an internal volume of 0.76 ft^3 and install the woofer so it takes 0.3 ft^3 and leaves an effective open volume of 0.46 ft^3. So, there is always room for the woofer motor assembly.
Designing for target response:
You really need to ensure the resulting response curve for your modelled system is as flat as possible. If it has a high peak of more than 1.5dB on either end of the bandpass range, or a dip of more than 1.5dB in the middle of the operating range, the resulting sound will be resonant and ring immensely. Where the response has a significantly peak the reproduced would will ring and be extremely pronounced at that frequency. So, if you tune the system so there is a peak of more than 3dB at, say, 30Hz, when you play music you will find it difficult to make out the music and sound in the 35 - 50Hz range and instead everything will have a very pronounced "BOOOOOOONNNNNG" sound at exactly 30Hz. So bass drums will always go "BOOOOOOOOOOOOOOONG" at 30Hz regardless of how they were recorded. Bass guitars will go "BOOOOOOOOOOOONG" at 30Hz regardless of the notes the bass player is playing. And so on.
Note, though, that this effect happens at both ends of the response. So if there is a peak at 30Hz, a dip in the middle, and another peak at 80Hz, then the bass sound of your woofer will ring out at both 30Hz and at 80Hz. So, if there is a sound in the recording centered at 50Hz the sound you hear will be ringing out at 30Hz and 80Hz. if the sound is centered above 60Hz, the sound you hear will be ringing out at 80Hz no matter what. Sounds below 40Hz will always ring out at 30Hz.
Again, all the descriptions above are based on a theoretical system with a resonance at 30Hz and another at 80Hz.
The only way to remedy the ringing problem which results in a sub that sounds like a one note mess is to design your solution so the edges of the response curve are actually a bit lower in level than the center. Doing that narrows the effective output range, but it cleans up the sound and makes the sub more musical and natural sounding.
smgreen20
Active Member
Also wanted to add that, .....
A sealed box for the two 12"s has a freq response that starts to roll off at 60Hz/-1 dB, 47Hz/-2 dB, 40Hz/-3 dB, and 30Hz/-8 dB. It's that -8 dB at 30Hz that is killing me. Some of the music I listen to has some serious output in that area, Korn, Chimaira and want the added output in that region w/o adding EQ.
I have a SSF at 25Hz @ 18dB/oct and I lowpass it at 63Hz @ 24dB/oct. So the above response is perfect for my settings/wants.
A sealed box for the two 12"s has a freq response that starts to roll off at 60Hz/-1 dB, 47Hz/-2 dB, 40Hz/-3 dB, and 30Hz/-8 dB. It's that -8 dB at 30Hz that is killing me. Some of the music I listen to has some serious output in that area, Korn, Chimaira and want the added output in that region w/o adding EQ.
I have a SSF at 25Hz @ 18dB/oct and I lowpass it at 63Hz @ 24dB/oct. So the above response is perfect for my settings/wants.
No, the port cannot be the same.
Once you cut the effective volume in half, you need to model the port dimensions. What is the tuning frequency of the ported side of the modelled enclosure? That that frequency and go to ISD online and put in the new target volume (1.5 ft^3), put in the target tuning frequency, and enter the port diameter you want to use. It will tell you want length the port needs to be.
Once you cut the effective volume in half, you need to model the port dimensions. What is the tuning frequency of the ported side of the modelled enclosure? That that frequency and go to ISD online and put in the new target volume (1.5 ft^3), put in the target tuning frequency, and enter the port diameter you want to use. It will tell you want length the port needs to be.