Two 8" driver equivalent to one 12"?
The max size of subwoofer driver available in my god-forsaken town is 8". However I was told that 2 of these would be equivalent to a single 12" driver, since the effective cone area is almost the same. Is this true?
No specs available for these speakers except 180W, 8-ohms.
Under these circumstances the best enclosure for this would probably be a sealed one. But would a port offer any advantage even though its not tuned? This assuming the vent is made quite large to avoid port noises.
The max size of subwoofer driver available in my god-forsaken town is 8". However I was told that 2 of these would be equivalent to a single 12" driver, since the effective cone area is almost the same. Is this true?
No specs available for these speakers except 180W, 8-ohms.
Under these circumstances the best enclosure for this would probably be a sealed one. But would a port offer any advantage even though its not tuned? This assuming the vent is made quite large to avoid port noises.
Re: Two 8" driver equivalent to one 12"?
Well just using basic math, surface area of a flat circle is A=3.14(r*r)
so 8"
A=(3.14)(16) = 50.24
and 12"
A=(3.14)(36) = 113.04
So you would need at least 2 8" woofers to match a single 12".
However even though they have the same area as a 12" as a system, individually they are still 8", so I don't know if these means your still limited to the frequency response of a 8" driver.
At first I thought it said 8" is the biggest allowed in your town...I was like what kind of rule is that!
PS: If that math is wrong, I'm sorry. I'm stupid
Well just using basic math, surface area of a flat circle is A=3.14(r*r)
so 8"
A=(3.14)(16) = 50.24
and 12"
A=(3.14)(36) = 113.04
So you would need at least 2 8" woofers to match a single 12".
However even though they have the same area as a 12" as a system, individually they are still 8", so I don't know if these means your still limited to the frequency response of a 8" driver.
At first I thought it said 8" is the biggest allowed in your town...I was like what kind of rule is that!
PS: If that math is wrong, I'm sorry. I'm stupid
For a sub driver, as well as Fs being important (quite likely higher for the 8" units compared to 12"), the maximum excersion needs to be considered. It is much easier to design a 12" long excersion driver than an 8", and this will limit the output at low frequencies.
If you don't have any other specs than power (ie. no T/S specs), then you will not be able to design the appropriate cabinet, and will most likely shred the speakers.
Cheers
If you don't have any other specs than power (ie. no T/S specs), then you will not be able to design the appropriate cabinet, and will most likely shred the speakers.
Cheers
Well, looking at a few of peerless' data sheets it appears as if 8" drivers have about 1/2 of the equivalent piston area as a 12" driver. However the Xmax is also about half, typically, which would mean that you would need *four* 8" drivers for the same max acoustic output.
You may design a bass-reflex box, but then you would need the T/S parameters for the driver, and it is not sure that the driver is suited for a BR box. If the T/S parameters are not available from the vendor, you can measure them yourself.
You may design a bass-reflex box, but then you would need the T/S parameters for the driver, and it is not sure that the driver is suited for a BR box. If the T/S parameters are not available from the vendor, you can measure them yourself.
Re: Two 8" driver equivalent to one 12"?
My opinion -> make the box as big as conveniently possible and then make the port to tune it to 30-35Hz. Even if it doesn't increase the output much at these low frequencies, it will definitely reduce the cone excursion to maybe a quarter of what it would have been. Gives a lot of scope for winding up the bass...roshan101 said:Under these circumstances the best enclosure for this would probably be a sealed one. But would a port offer any advantage even though its not tuned? This assuming the vent is made quite large to avoid port noises.
A couple of hints.
When we talk of driver size, we talk about the outside of the basket. So a 12" driver really does not have a 12" cone. It has a 10.5" cone, or thereabouts.
Rule of thumb: for speakers whose baskets are 8" or higher, the cone diameter is 1.5 inches smaller than the basket diameter. So a 15" speaker has a 13.5" cone diameter.
For speakers with baskets under 8 inches, cone diameter is 1 inch less than basket diameter. So a 6.5" speaker has a 5.5" cone diameter. These are approximations, but they will work well enough in any program or calculation you need.
You might be surprised if you measure with a ruler. I just want to point out that these approximations include one half of the surround, so a ruler might decieve you a little. But this is the accepted method.
Although there is a tendency for cone excursion to get larger as the cone diameter increases, this is not always the case. There are long throw 8 inchers. However, I would say the average 8 incher has a cone excursion of ±4.5 mm, while the average 8 incher ±6mm. So it is greater, but not twice as great. And there are higher excursion woofers for both sizes.
When we talk of driver size, we talk about the outside of the basket. So a 12" driver really does not have a 12" cone. It has a 10.5" cone, or thereabouts.
Rule of thumb: for speakers whose baskets are 8" or higher, the cone diameter is 1.5 inches smaller than the basket diameter. So a 15" speaker has a 13.5" cone diameter.
For speakers with baskets under 8 inches, cone diameter is 1 inch less than basket diameter. So a 6.5" speaker has a 5.5" cone diameter. These are approximations, but they will work well enough in any program or calculation you need.
You might be surprised if you measure with a ruler. I just want to point out that these approximations include one half of the surround, so a ruler might decieve you a little. But this is the accepted method.
Although there is a tendency for cone excursion to get larger as the cone diameter increases, this is not always the case. There are long throw 8 inchers. However, I would say the average 8 incher has a cone excursion of ±4.5 mm, while the average 8 incher ±6mm. So it is greater, but not twice as great. And there are higher excursion woofers for both sizes.
kelticwizard said:
Do you mean the average 12-incher has an Xmax of +/- 6mm? This seems fairly small if the subject is 12-inch subwoofers.
You are right, that would be for the average 12 inch woofer. That would be small for a 12 inch that marketed itseld as a 12 inch sub.
For a long time, ±6mm was indeed as large as most speakers available to the DIYer. Changed about 10 years ago or so.
For a long time, ±6mm was indeed as large as most speakers available to the DIYer. Changed about 10 years ago or so.
old-timey rough rule of thumb
with all other things equal -
We used to figure that two 12" drivers equaled a 15"
Two 10" drivers equal a 12"
Two 8" drivers equal a 10"
That wasn't exact or linear. This was back 30 or more years ago before you had so many different advances in design, longer excursions, etc. Of course this was before you had programs you could plug numbers into, etc. For that matter, this was before you had personal computers _big grin_
However, it probably is still an effective rough rule of thumb, looking at Svante's post and comments.
Bottom line, instead of buying 8 inchers locally, why don't you buy a kit on-line?
Even if freight and customs are higher than you would like, it seems to me like you would be better off with 12" drivers.
Regards
Ken L
Svante said:
kelticwizard said:
with all other things equal -
We used to figure that two 12" drivers equaled a 15"
Two 10" drivers equal a 12"
Two 8" drivers equal a 10"
That wasn't exact or linear. This was back 30 or more years ago before you had so many different advances in design, longer excursions, etc. Of course this was before you had programs you could plug numbers into, etc. For that matter, this was before you had personal computers _big grin_
However, it probably is still an effective rough rule of thumb, looking at Svante's post and comments.
Bottom line, instead of buying 8 inchers locally, why don't you buy a kit on-line?
Even if freight and customs are higher than you would like, it seems to me like you would be better off with 12" drivers.
Regards
Ken L
Re: Two 8" driver equivalent to one 12"?
normally an "8 inch" woofer has a Sd of about 200-220cm2 while most 12" woofers have an Sd of 420-450cm2 so you are parlty correct. However in practice the Xmax of most 12" drivers is higher than most 8" drivers. I have still to find an equation that relates Xmax to SPL (we know more Xmax results in more SPL but is this realtion linear, square, cube, or more complex?) for now i assume it is linear just for simplicity so 440cm x 8mm (one way Linear Xmax of average 12") > 2 x 220 x 6mm (one way linear Xmax of 8").
having said that 2 x 8" also has its advantages for one they can be cut off at a higher freq., passive stereo sub etc...
not having T/S parametrs it is diffcult to guess the size of box you need. sealed boxes are more forgiving of such miscalibarations. my guess would be for you would be to try a 1.5 cu. ft. sealed box (per driver).
roshan101 said:The max size of subwoofer driver available in my god-forsaken town is 8". ...No specs available for these speakers except 180W, 8-ohms....
normally an "8 inch" woofer has a Sd of about 200-220cm2 while most 12" woofers have an Sd of 420-450cm2 so you are parlty correct. However in practice the Xmax of most 12" drivers is higher than most 8" drivers. I have still to find an equation that relates Xmax to SPL (we know more Xmax results in more SPL but is this realtion linear, square, cube, or more complex?) for now i assume it is linear just for simplicity so 440cm x 8mm (one way Linear Xmax of average 12") > 2 x 220 x 6mm (one way linear Xmax of 8").
having said that 2 x 8" also has its advantages for one they can be cut off at a higher freq., passive stereo sub etc...
not having T/S parametrs it is diffcult to guess the size of box you need. sealed boxes are more forgiving of such miscalibarations. my guess would be for you would be to try a 1.5 cu. ft. sealed box (per driver).
Bill Fitzpatrick said:
and used push-push...
not yet mentioned is that it is rare to find an 8 that has an Fs as low as a 12.
dave
hi
8 inch 180 w rms ? whats the price , the vc size ? and spl or flatness of low frequency produced in relation to input power
i mean how much output does your 8 inch give when i supply 120 w rms sine and sweep it from 45 to 100 hz
and what type of a 12 inch would you have bought if it was available in your gdfs town
as i know of a single 8 inch take on 12 inches
and 1 - 12 inches take on 4 - 8 inches
in a simple application the rule of sd can play
where as in serious sub woofer high power applications there are a lot of other driver details to be looked into
for eg
it is quite evident that the 8 inch cone will need to travel longer to produce a certain low freq than the 12 inch one
what i have said is nothing new
what i imply is - phisically for the 8 inch to achieve this the surround will need to have a larger roll profile than the 12 to travel longer
to have a larger roll it will cover a larger space of the entir cone unit (the id and od of the surround will increase along with the roll) ?
therfore reducing sd of the piston further
needing a larger travel to comenste this reduction
for navin whom i am sure will go through this and will need some mathematics , experimentally i have seen for every reduction of sd unit you get a ~ 4 db fall in spl there fore you have to build in a heavier mag assembly and a larger coil to travel longer
this ratio is about 1:3 that is for every reduction of a sd unit i have to increase the surround roll 3 times
and obviously increase spider size ets
roshan i need the following size and details to repy to your above qs along with the spl asked above
8 inch mag size , hight of top plates , bottom plate type (bumped or not)
pull the cone upwards towards you and measure the upward excursion in mm
measure the cone depth and dia , the surround od and id
the surround roll depth (rough estimation in mm)
the spider size and if the driver employs a pregressive or regressive roll
the stiffness of the spider and material (you can tell me the colour i can estimate the material)
check the spider carefully and tell me how much chemical is on it
ie
if the spider is porous and to what extenct
then i need the same above details of a 12 inch you would have gone in for provided it was available
having the 8 inch and the 12 inch figures from you we can constructivly proceed on the discussion
otherwise so many people are replying and helping the above (my qs) will help us to go further
suranjan
transducer design engineer
8 inch 180 w rms ? whats the price , the vc size ? and spl or flatness of low frequency produced in relation to input power
i mean how much output does your 8 inch give when i supply 120 w rms sine and sweep it from 45 to 100 hz
and what type of a 12 inch would you have bought if it was available in your gdfs town
as i know of a single 8 inch take on 12 inches
and 1 - 12 inches take on 4 - 8 inches
in a simple application the rule of sd can play
where as in serious sub woofer high power applications there are a lot of other driver details to be looked into
for eg
it is quite evident that the 8 inch cone will need to travel longer to produce a certain low freq than the 12 inch one
what i have said is nothing new
what i imply is - phisically for the 8 inch to achieve this the surround will need to have a larger roll profile than the 12 to travel longer
to have a larger roll it will cover a larger space of the entir cone unit (the id and od of the surround will increase along with the roll) ?
therfore reducing sd of the piston further
needing a larger travel to comenste this reduction
for navin whom i am sure will go through this and will need some mathematics , experimentally i have seen for every reduction of sd unit you get a ~ 4 db fall in spl there fore you have to build in a heavier mag assembly and a larger coil to travel longer
this ratio is about 1:3 that is for every reduction of a sd unit i have to increase the surround roll 3 times
and obviously increase spider size ets
roshan i need the following size and details to repy to your above qs along with the spl asked above
8 inch mag size , hight of top plates , bottom plate type (bumped or not)
pull the cone upwards towards you and measure the upward excursion in mm
measure the cone depth and dia , the surround od and id
the surround roll depth (rough estimation in mm)
the spider size and if the driver employs a pregressive or regressive roll
the stiffness of the spider and material (you can tell me the colour i can estimate the material)
check the spider carefully and tell me how much chemical is on it
ie
if the spider is porous and to what extenct
then i need the same above details of a 12 inch you would have gone in for provided it was available
having the 8 inch and the 12 inch figures from you we can constructivly proceed on the discussion
otherwise so many people are replying and helping the above (my qs) will help us to go further
suranjan
transducer design engineer
IMHO, I'm with Ken L in post #11. I may not be of quite his vintage _grin_ but...
With all other parameters being equal and,
When you compare area of cone and excursion, I believe:
2 X 6.5 = 8"
2 X 8 = 10"
2 X 10 = 12"
2 X 12 = 15"
This assumes an equal ohm load ie:
The two 6.5 drivers would have to be 16 ohms in parrallel or 4 ohms in series
Cheers,
Cal
With all other parameters being equal and,
When you compare area of cone and excursion, I believe:
2 X 6.5 = 8"
2 X 8 = 10"
2 X 10 = 12"
2 X 12 = 15"
This assumes an equal ohm load ie:
The two 6.5 drivers would have to be 16 ohms in parrallel or 4 ohms in series
Cheers,
Cal
Thanks guys for all the advice.
Based on your replies I've realised it doesnt make sense to get multiple 8" with no parameters available and waste time and energy constructing the subwoofer cabinet doing guess work. For all you know after taking so much trouble you could end up with a piece of junk. Of course one could always build a sealed cabinet but then these lack that punch compared to ported.
Will take a trip to Bangalore city soon and check out some good 12" driver with all specs available and construct the enclosure accordingly.
Suranjan, I really appreciate your offer to help estimate the parameters based on the physical appearance & dimensions, but it wouldn't do justice taking your time considering these cost just Rs. 550/- per piece (approx $15 USD). Its a brand called Toyotone - being in Calcutta I suppose you would've heard of it.
Based on your replies I've realised it doesnt make sense to get multiple 8" with no parameters available and waste time and energy constructing the subwoofer cabinet doing guess work. For all you know after taking so much trouble you could end up with a piece of junk. Of course one could always build a sealed cabinet but then these lack that punch compared to ported.
Will take a trip to Bangalore city soon and check out some good 12" driver with all specs available and construct the enclosure accordingly.
Suranjan, I really appreciate your offer to help estimate the parameters based on the physical appearance & dimensions, but it wouldn't do justice taking your time considering these cost just Rs. 550/- per piece (approx $15 USD). Its a brand called Toyotone - being in Calcutta I suppose you would've heard of it.
Okay.......I'm a twin speaker advocate......two sim units sound better and fuller than a large singe cone.......I commonly use 2x 10" per cab, sounds way better than single 12".
If your amp can take 4 ohms Z then for the better.
If you've lost the parameters for a particular unit, then closed box offers more flexibility and is less critical. However as others said it lacks punch but smoother resp
For no hope cases; for acoustic susp units to get something up and running....my golden rule
8"unit choose box vol 0,6-0,8cuft
10"unit choose box vol 1-1,5 cuft
12" unit choose box vol 2-3,5 cuft
15"unit choose box vol 5-9 cuft
rich
If your amp can take 4 ohms Z then for the better.
If you've lost the parameters for a particular unit, then closed box offers more flexibility and is less critical. However as others said it lacks punch but smoother resp
For no hope cases; for acoustic susp units to get something up and running....my golden rule
8"unit choose box vol 0,6-0,8cuft
10"unit choose box vol 1-1,5 cuft
12" unit choose box vol 2-3,5 cuft
15"unit choose box vol 5-9 cuft
rich
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