Hi,
you can reach any frequency limit with a small enclosure ...
The compromise is between
- efficiency
- maximum sound pressure level (at given tolerated distortion level)
- lower frequency limit
- impulse response
- cabinet size
Extreme alignments in favour of one of these parameters cause
the others to be compromised. A very small speaker with small
membrane area will have excessive excursion above the tuning
frequency, when tuned low.
Use of a passive radiator does not change the limits of alignment,
but helps to avoid a very long port which is neccessary for low
tuning of small enclosures.
Long channels may cause resonance problems and might refuse
to work properly at the tuning frequency. As a rule of thumb, a port
should not be longer than 1/12 wavelength of the tuning frequency,
otherwise the port cannot be seen as a pure mass reactance anymore.
When port has too small cross section you get noise from turbulent
flow. Many simple BR calculators do not show the cone excursion of
the driver dependent on frequency, which rises hope a cabinet
could be tuned as you like without reaching mechanical limits.
Cheers
you can reach any frequency limit with a small enclosure ...
The compromise is between
- efficiency
- maximum sound pressure level (at given tolerated distortion level)
- lower frequency limit
- impulse response
- cabinet size
Extreme alignments in favour of one of these parameters cause
the others to be compromised. A very small speaker with small
membrane area will have excessive excursion above the tuning
frequency, when tuned low.
Use of a passive radiator does not change the limits of alignment,
but helps to avoid a very long port which is neccessary for low
tuning of small enclosures.
Long channels may cause resonance problems and might refuse
to work properly at the tuning frequency. As a rule of thumb, a port
should not be longer than 1/12 wavelength of the tuning frequency,
otherwise the port cannot be seen as a pure mass reactance anymore.
When port has too small cross section you get noise from turbulent
flow. Many simple BR calculators do not show the cone excursion of
the driver dependent on frequency, which rises hope a cabinet
could be tuned as you like without reaching mechanical limits.
Cheers
I'd suggest that's a good & probably accurate guess
Erm... Without EQ? Are you serious
You'd need a 12" driver with an FS well below 20Hz with a low Qts & a Vas of less than 1.5cuft (the box size) in the case of a ported box.Again with no EQ & 2 x 12" in a sealed box each driver would need to have an Fs of about 12.5Hz with a Qts of 0.35 & a Vas of about 1.5cuft (42L) or less due to volume taken up by the drivers in the enclosure.
I know of no such animals
LineArray has hit the nail on the head, you can't have it all - but you can have one thing. To go that low with no EQ you'd need a seriously inefficient driver which will result in a low output.
The idea that you can have any -3db point you want per volume is certainly valid. It's just that as cabinet volume decreases it eventually becomes impossible to maintain flat response without having driver displacement decrease, which means smaller diameter drivers, and lower efficiency.
There is no rule that says you can't have an 8" driver in 1.5 cu.ft. that goes flat to 25Hz. Easily achieveable with the right driver. The number of off the shelf driver candidates rises quickly if you're willing to add a bit of moving mass.
There is no rule that says you can't have an 8" driver in 1.5 cu.ft. that goes flat to 25Hz. Easily achieveable with the right driver. The number of off the shelf driver candidates rises quickly if you're willing to add a bit of moving mass.
Another "trick" you can pull with a suitably low Fs speaker is raising Qe by adding series resistance. Look at the poted response of the Tang Band W8-740P with a Qe raised to around .45. You'd have to calculate what this will do to Qts and precisely how much series resistance it would require. I didn't bother. Transient response will be adversely affected, overall efficiency will decrease futher, and Vb will inflate considerably. But, it would be essentially flat to 25Hz.
I have seen at least one driver (for car use) that had to be mounted with the magnet assembly outside the box, because the recommended enclosure volume was too small to accomodate the driver. In other words, the enclosure was smaller than the cardboard box the driver came in. As I recall, it was very inefficient - needed something like a 1000 watt amp. (No, I can't remember the driver model.)
Erm... Without EQ? Are you serious
The OP only asked if it was possible to get a F3 of 25Hz without EQ in a 3 ft^3 enclosure
It is achievable in that size enclosure but not without some compromises.
For instance:
- what was not provided was what his budget for drivers and amp would be
- what his output SPL expectations would be
- etc
Please look again
I think that says 1.5cuft not 3ft^3 with no EQ
The answer is unless you have some extraordinary driver - NO
The biggest problem you will find in trying to go down that far in such a small volume is that the motors on otherwise compatible drivers are actually too strong. So, "extraordinary" far as a requirement in the driver compartment is not real good terminology. The reason you don't find a lot of small drivers designed to run flat that far down is efficiency and power handling is so bad that it's hardly practical (read: nobody would buy it).
Please look again
I think that says 1.5cuft not 3ft^3 with no EQ
The answer is unless you have some extraordinary driver - NO
You are correct, lol,I like the idea of mounting a driver with the magnet structure hanging outside the box to allow for a little more volume.
Using a clam shell isobarik for a mid bass now.
Here is a possible tho not perfect candidate.
FS is a little high.
AE Speakers Online Store
TD12H - 8ohm
Fs: 26.7Hz
Qms: 3.72
Vas: 160L
Cms: .4mm/N
Mms: 88.6g
Rms: 4kg/s
Xmax: 14mm
Sd: 530sqcm
Qes: .25
Re: 6.5ohm
Le: .3mH
Z: 8ohm
Bl: 19.7Tm
Pe: 500W
Qts: .23
1W SPL: 92.9dB
$289 ea.
Using a clam shell isobarik for a mid bass now.
Here is a possible tho not perfect candidate.
FS is a little high.
AE Speakers Online Store
TD12H - 8ohm
Fs: 26.7Hz
Qms: 3.72
Vas: 160L
Cms: .4mm/N
Mms: 88.6g
Rms: 4kg/s
Xmax: 14mm
Sd: 530sqcm
Qes: .25
Re: 6.5ohm
Le: .3mH
Z: 8ohm
Bl: 19.7Tm
Pe: 500W
Qts: .23
1W SPL: 92.9dB
$289 ea.
That is a very low Q driver. It will yield good efficiency but is a very poor choice for low bass extension. It will take lots of EQ to run to 25 Hz. A little time with a free box calculator software and some review of Thiel and Small equations will show you where you need to go. Look at the T/S parameters of the 10" driver recommended by Steve Dunlap for comparison. For extension to 25Hz in 1.5 cu.Ft you will need a much higher Qts and less VAS.
adding mass
I agree this is a way to go. Add mass, bring Qts up and fs down,
thereby having a driver with low Vas.
A driver has to be found with considerable excursion.
Instead of glueing mass to the cone directly i once added a port
directly behind the driver,which results in a (as) small (as possible)
BR Box in the BR Box.
This is not a totally unknown design ...
Problem is smooth transition to the midrange, since the inner port
attached to the driver will be out of phase with the cone above some frequency.
The added mass reactance will be decoupled and the efficiency
of the driver rises towards midrange, which can be compensated with a filter.
The inner helmholtz resonator (compartment and especially port) can be
made lossy for smooth transition to midrange ...
Interesting but complex, i tuned the inner chamber/port compartment
before mounting it in the BR Box.
Of cause glueing some bits to the cone is easier ...
Cheers
I agree this is a way to go. Add mass, bring Qts up and fs down,
thereby having a driver with low Vas.
A driver has to be found with considerable excursion.
Instead of glueing mass to the cone directly i once added a port
directly behind the driver,which results in a (as) small (as possible)
BR Box in the BR Box.
This is not a totally unknown design ...
Problem is smooth transition to the midrange, since the inner port
attached to the driver will be out of phase with the cone above some frequency.
The added mass reactance will be decoupled and the efficiency
of the driver rises towards midrange, which can be compensated with a filter.
The inner helmholtz resonator (compartment and especially port) can be
made lossy for smooth transition to midrange ...
Interesting but complex, i tuned the inner chamber/port compartment
before mounting it in the BR Box.
Of cause glueing some bits to the cone is easier ...
Cheers
Bassically you're looking for a driver with a low Fs (around 25 Hz or lower), a highish Qts (between 0,39 and 0,55 should do fine) and a low Vas (ultimately 60 L (2 ft^2) or lower (for a ported/passive radiator enclosure).
If you're going for a small driver (smaller then 12") it's easier to find a driver with low Vas but a low Fs will be more difficult.
For instance if you look a the Lab12: Fs 22 Hz, Qts 0,38, Vas 125 L (4,6 ft^2). Everything is perfect except that the Vas is way to high. If you load 2 of these drivers in an isobaric configuration you will halve Vas, which makes 2,3 ft^2 (62,5 L). In isobaric configuration this should get you an f3 around 25 Hz. Using a low pass at 80-105 Hz will aslo make it pretty flat in it's range.
It's a bit and perhaps expensive though, so you might just look for a driver with T/S-parameters that equal the isobaric parameters of the Lab12. Isobaric loading lowers the efficiency/ overall output in exchange for a smaller box volume.
Regards Johan
If you're going for a small driver (smaller then 12") it's easier to find a driver with low Vas but a low Fs will be more difficult.
For instance if you look a the Lab12: Fs 22 Hz, Qts 0,38, Vas 125 L (4,6 ft^2). Everything is perfect except that the Vas is way to high. If you load 2 of these drivers in an isobaric configuration you will halve Vas, which makes 2,3 ft^2 (62,5 L). In isobaric configuration this should get you an f3 around 25 Hz. Using a low pass at 80-105 Hz will aslo make it pretty flat in it's range.
It's a bit and perhaps expensive though, so you might just look for a driver with T/S-parameters that equal the isobaric parameters of the Lab12. Isobaric loading lowers the efficiency/ overall output in exchange for a smaller box volume.
Regards Johan
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except, such a driver does not exist.
and... the isobaric while it does halve the VAS will suck up a high % of that little 1.5cuft...
Bottom line, not a good project. Use the existing cabinet to house a smaller driver, as suggested earlier, which means building a flat bit of wood (or mdf) with a circle cut out for a smaller driver to screw on the front and cover the 12" "hole".
_-_-bear
and... the isobaric while it does halve the VAS will suck up a high % of that little 1.5cuft...
Bottom line, not a good project. Use the existing cabinet to house a smaller driver, as suggested earlier, which means building a flat bit of wood (or mdf) with a circle cut out for a smaller driver to screw on the front and cover the 12" "hole".
_-_-bear
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