Is there a reason to have separate chambers ? I can imagine there is some kind (?) of interference but don't have much reference for why one would or would not separate the drivers from one another.
Dual 18" Separate Chambers ??
- Thread starter Brandon G Romanowski
- Start date
Re: Dual 18" Separate Chambers ??
The biggest argument I have heard is that should one driver in the box fail, it will not affect the acoustic loading of the other driver, and vice versa.
If the 2 drivers are in the same chamber and one dies, the failed one becomes a passive radiator and the loading on the working one would change quite a bit.
If they are in separate chambers and one died, the working one wouldn't "see" much of a difference and would continue to sound "normal"
The biggest argument I have heard is that should one driver in the box fail, it will not affect the acoustic loading of the other driver, and vice versa.
If the 2 drivers are in the same chamber and one dies, the failed one becomes a passive radiator and the loading on the working one would change quite a bit.
If they are in separate chambers and one died, the working one wouldn't "see" much of a difference and would continue to sound "normal"
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Tim Weaver
Senior
Re: Dual 18" Separate Chambers ??
To carry that one step further, if one driver fails the other one usually kills itself because it finds itself in twice the box volume it should be. Over-excursion is not your friend.
To carry that one step further, if one driver fails the other one usually kills itself because it finds itself in twice the box volume it should be. Over-excursion is not your friend.
Re: Dual 18" Separate Chambers ??
Are there any audio related issues with using two drivers in the same chamber ? Do they negatively impact each other when they are both working ?
Edit: if you have two drivers in a single chamber could you separate them into two separate chambers and still be driving the same chamber volume per driver ?
Are there any audio related issues with using two drivers in the same chamber ? Do they negatively impact each other when they are both working ?
Edit: if you have two drivers in a single chamber could you separate them into two separate chambers and still be driving the same chamber volume per driver ?
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Re: Dual 18" Separate Chambers ??
No
Not sure if I follow. If you split the box in half, you'll have basically the same volume per driver, minus the wood, and the change in port volume required to maintain tuning frequency.
No
Not sure if I follow. If you split the box in half, you'll have basically the same volume per driver, minus the wood, and the change in port volume required to maintain tuning frequency.
Re: Dual 18" Separate Chambers ??
Yes that is what I was asking, and thanks for the reply. Let me see if I have this right... You are saying the box volume would be the same (minus the wood) but the port volume would change and so would the tuning freq. of the port and therefore the box? Is that true even if you divide the ports equally ?
Yes that is what I was asking, and thanks for the reply. Let me see if I have this right... You are saying the box volume would be the same (minus the wood) but the port volume would change and so would the tuning freq. of the port and therefore the box? Is that true even if you divide the ports equally ?
Tim Weaver
Senior
Re: Dual 18" Separate Chambers ??
If you have 2 drivers in a box where both drivers share the same volume of air you calculate the port using both woofers' parameters (Volume of displacement or Vd). If you divide the box volume in half, you not only would need 2 ports (one for each side), which changes the size of each port (smaller diameter ports can be used because each is only carrying half the load as before) but you are also using only one woofer to drive that port which changes the size again (half the driver Vd). Therefor the math is different, even though the end result needs to be the same.
The ports themselves don't care what size the box is (within reason anyway, the woofer will dictate box size way more than the port will). They are simply a tuned pipe that resonates at a frequency. The biggest challenge is getting a port that is big enough to not "whistle" when a lot of air is moving through it, yet is still small enough to actually fit inside the cabinet. A 1" diameter port can be tuned pretty low and be very short but it will not pass enough air to be useful. For subs you need large diameter ports and the larger the port diameter, the longer it needs to be for a given frequency.
If you have 2 drivers in a box where both drivers share the same volume of air you calculate the port using both woofers' parameters (Volume of displacement or Vd). If you divide the box volume in half, you not only would need 2 ports (one for each side), which changes the size of each port (smaller diameter ports can be used because each is only carrying half the load as before) but you are also using only one woofer to drive that port which changes the size again (half the driver Vd). Therefor the math is different, even though the end result needs to be the same.
The ports themselves don't care what size the box is (within reason anyway, the woofer will dictate box size way more than the port will). They are simply a tuned pipe that resonates at a frequency. The biggest challenge is getting a port that is big enough to not "whistle" when a lot of air is moving through it, yet is still small enough to actually fit inside the cabinet. A 1" diameter port can be tuned pretty low and be very short but it will not pass enough air to be useful. For subs you need large diameter ports and the larger the port diameter, the longer it needs to be for a given frequency.
Re: Dual 18" Separate Chambers ??
So if I had a perfectly semetrical subwoofer with two 18" drivers and two ports and I sawed it in half and capped the ends to make two co pletely separate subwoofers, you are saying they would not work the same as if they were left as one because the port tuning would change. Is that right ?
So if I had a perfectly semetrical subwoofer with two 18" drivers and two ports and I sawed it in half and capped the ends to make two co pletely separate subwoofers, you are saying they would not work the same as if they were left as one because the port tuning would change. Is that right ?
Tim Weaver
Senior
Re: Dual 18" Separate Chambers ??
If that is the case, then no the tuning would not change. If, for example, You had a box that was ported on each end and tuned to say, 35 hz, then when you cut it in half each port is still tuned to 35 hz but is still dealing with same amount of "work" as it did in the full size box. Where before it was doing half the work being driven by 2 drivers, now it is doing all the work but only driven by one driver.
This only works in the case you are describing though.
If that is the case, then no the tuning would not change. If, for example, You had a box that was ported on each end and tuned to say, 35 hz, then when you cut it in half each port is still tuned to 35 hz but is still dealing with same amount of "work" as it did in the full size box. Where before it was doing half the work being driven by 2 drivers, now it is doing all the work but only driven by one driver.
This only works in the case you are describing though.
Tim Weaver
Senior
Re: Dual 18" Separate Chambers ??
I would recommend downloading WinIsd and playing around with it.
http://www.linearteam.dk/default.aspx?pageid=winisd
It will help you visualize whats going on a little better. It's not the best design software out there, but it is easy to learn and I've built a couple of subs using it and they tend to perform like the models.
I would recommend downloading WinIsd and playing around with it.
http://www.linearteam.dk/default.aspx?pageid=winisd
It will help you visualize whats going on a little better. It's not the best design software out there, but it is easy to learn and I've built a couple of subs using it and they tend to perform like the models.
Re: Dual 18" Separate Chambers ??
Brandon,
Half the volume and half the port area will give you nearly the same tuning frequency, but in practice the port tuning function is slightly nonlinear, so a large box with two ports will be tuned slightly lower than the half box with one port.
What are you trying to do exactly? The articles I wrote for October's and November's issues of FOH cover a broad swath of the issues related to vented boxes. I suggest you look at them.
Brandon,
Half the volume and half the port area will give you nearly the same tuning frequency, but in practice the port tuning function is slightly nonlinear, so a large box with two ports will be tuned slightly lower than the half box with one port.
What are you trying to do exactly? The articles I wrote for October's and November's issues of FOH cover a broad swath of the issues related to vented boxes. I suggest you look at them.
Re: Dual 18" Separate Chambers ??
I did read them, very good articles by the way. I'm not intending on cutting any boxes in half
I am putting the current subs under the microscope. These subs have two 18"s in a single chamber and a problem with port choking. The rectangle ports that run along the two longest sides of the cabinet have 8 handles taking up some amount of their volume. The ports are also not flared on either end and the dense foam that lines the back wall of the chamber seems to almost plug the port entrances.... those are some observations so far, I am working on what tests and measurements to make so I really have a full picture of how these boxes work.
I did read them, very good articles by the way. I'm not intending on cutting any boxes in half
I am putting the current subs under the microscope. These subs have two 18"s in a single chamber and a problem with port choking. The rectangle ports that run along the two longest sides of the cabinet have 8 handles taking up some amount of their volume. The ports are also not flared on either end and the dense foam that lines the back wall of the chamber seems to almost plug the port entrances.... those are some observations so far, I am working on what tests and measurements to make so I really have a full picture of how these boxes work.Re: Dual 18" Separate Chambers ??
One of the best, but not easiest, ways to see port behavior with increasing output is to measure the driver impedance at different input voltages.
I did read them, very good articles by the way. I'm not intending on cutting any boxes in half
One of the best, but not easiest, ways to see port behavior with increasing output is to measure the driver impedance at different input voltages.
Re: Dual 18" Separate Chambers ??
How would I measure impedance at different voltages? with a VOM and a sine wave generator .. and patience? There's no way to do it with a WT3 is there ?
I did do an RTA where I turned up pink noise in 3dB intervals with infinite averaging for 30 seconds at a time. the first few captures looked the same, after a certain level (I didn't keep track of voltage) the out of band noise and distortion would increase by 6dB or more in some spots, after that it got to the point where the pass band information would not increase by the 3dB but again the slop would.
How would I measure impedance at different voltages? with a VOM and a sine wave generator .. and patience? There's no way to do it with a WT3 is there ?
I did do an RTA where I turned up pink noise in 3dB intervals with infinite averaging for 30 seconds at a time. the first few captures looked the same, after a certain level (I didn't keep track of voltage) the out of band noise and distortion would increase by 6dB or more in some spots, after that it got to the point where the pass band information would not increase by the 3dB but again the slop would.
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Re: Dual 18" Separate Chambers ??
I recommend a LinearX VI Box:
http://www.linearx.com/products/accessories/Vibox/VIBOX_1.htm
And mind the details here:
http://www.soundforums.net/live/threads/2486-Loudspeaker-to-Line-Level-Pad
This is a totally fine way to test what is going on, too. You can use the amplifier gain and known crest factor of your signal to calculate the input voltages close enough for this kind of characterization. You can also use Don Keele's 30-80Hz "thump" tone to pretty easily figure out when things fall apart for a given vented box. Steadily increase the level and all sorts of "noises" will appear. I'll usually stick earplugs in and listen right on the enclosure for gak with his stimuli once the levels get high enough. Or just hire me to design you something that will work proper from the outset~:-D~:grin:
I recommend a LinearX VI Box:
http://www.linearx.com/products/accessories/Vibox/VIBOX_1.htm
And mind the details here:
http://www.soundforums.net/live/threads/2486-Loudspeaker-to-Line-Level-Pad
This is a totally fine way to test what is going on, too. You can use the amplifier gain and known crest factor of your signal to calculate the input voltages close enough for this kind of characterization. You can also use Don Keele's 30-80Hz "thump" tone to pretty easily figure out when things fall apart for a given vented box. Steadily increase the level and all sorts of "noises" will appear. I'll usually stick earplugs in and listen right on the enclosure for gak with his stimuli once the levels get high enough. Or just hire me to design you something that will work proper from the outset
~:-D~:grin:
Re: Dual 18" Separate Chambers ??
Another advantage to each driver having its own seperate cabinet, is that with a "divider" the wood spans are now smaller. This makes for less vibration-ie a stiffer cabinet.
A solid divider that goes from side to side and front to back adds a lot of strength to the overall cabinet.
Another advantage to each driver having its own seperate cabinet, is that with a "divider" the wood spans are now smaller. This makes for less vibration-ie a stiffer cabinet.
A solid divider that goes from side to side and front to back adds a lot of strength to the overall cabinet.
Re: Dual 18" Separate Chambers ??
Other than the increase of weight the divider adds, there are no downsides to individual box per driver, and many reasons in favor.
The individual cabinets also reduce intermodulation distortion slightly too, compared to two drivers sharing a single enclosure.
Other than the increase of weight the divider adds, there are no downsides to individual box per driver, and many reasons in favor.