1.5 cu/ft3 box--can -3db @ 25hz be reached? - diyAudio
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Old 28th January 2010, 10:54 AM   #1
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Default 1.5 cu/ft3 box--can -3db @ 25hz be reached?

Without EQing the heck out of it? (Invent new laws of physics?)

It has a 12" cut out for a driver.

Thanks
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Old 28th January 2010, 11:00 AM   #2
AndrewT is offline AndrewT  Scotland
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I don't think a 3cub ft box can reach that target without EQ, but I'm just guessing.
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Old 28th January 2010, 04:44 PM   #3
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If you went ported or with passive radiators a single 12" in that size enclosure could easily achieve a F3 of 25Hz. Sealed you will probably require 2x 12"
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Old 28th January 2010, 05:07 PM   #4
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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
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Old 28th January 2010, 06:13 PM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by LineArray View Post
you can reach any frequency limit with a small enclosure ...
where does this come from?
He asked
Quote:
Without EQing
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Old 28th January 2010, 06:14 PM   #6
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Quote:
Originally Posted by AndrewT View Post
I don't think a 3cub ft box can reach that target without EQ, but I'm just guessing.
I'd suggest that's a good & probably accurate guess
Quote:
Originally Posted by Cokewithlime View Post
If you went ported or with passive radiators a single 12" in that size enclosure could easily achieve a F3 of 25Hz. Sealed you will probably require 2x 12"
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.
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Old 28th January 2010, 06:19 PM   #7
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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.
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Old 28th January 2010, 06:54 PM   #8
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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.
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Old 28th January 2010, 07:42 PM   #9
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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.)
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Old 28th January 2010, 07:54 PM   #10
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Quote:
Originally Posted by event horizon View Post
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.
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
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