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Old 11th December 2002, 04:10 PM   #1
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Default More drivers mean freq extension?

I was just wondering about this. If you use mulitiple woofers, for example 3 6.5" drivers. Even though collectivly they have a surface area (hopefully) equal to or more than one 10" driver, individually they still have less. So my question is do they operate as a whole and can go lower in freq, or do they operate as an individual, just spreading the work load out, thus allowing more volume.

I was wondering this as I was looking at the Def Tech Power 400 towers which have 2 6.5" subs and a 125 watt amp in them. They have a claimed <20 Hz extension. Individually I know it would be very hard for a 6.5" to go down to ~20 Hz especially with only 125 watts and would probably need a helluva lot of Xmax to make up for the lack of physical surface area.
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Old 11th December 2002, 04:17 PM   #2
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Drivers are based on physic so if one woofer can not reproduce a 20Hz signal, 100 woofers will not.

If the woofer can reproduce a 20Hz signal at a very very very low dB, if you put 100 woofer, the signal will be stronger but completely lost in the sea because the other signals are also stronger. It is like the signal/noise ratio.
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Old 11th December 2002, 04:24 PM   #3
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Francois is right, although multiple small drivers do lend themselves to bass boost circuits. They certainly can produce plenty of deep bass if equalisation is applied.

Nice one,
David.
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Old 11th December 2002, 04:37 PM   #4
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So like a tapered high end to make it all equal. Thus powerfull lows and subdued but equal midrange?
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Old 11th December 2002, 04:47 PM   #5
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Yep, that's it - although it's more usual to boost the bass where the drivers starts to roll-off and use high-efficiency mids & tweets that can keep up with multiple woofers.

Obviously your idea works too: the bass sets your maximum volume (determined by the drivers' diameter and Xmax) then you filter the mids & highs to get a flat frequency response.

Nice one,
David.
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Old 11th December 2002, 06:09 PM   #6
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Hallo Westrock2000,

1. A 6,5 inch bass could not make 20Hz with
useable efficiency.

2. When you have multiple drivers you will
see the efficiency rising.
say:
1 Driver 2.0% efficiency
2 Drivers 4.0% efficiency
4 Drivers 8.0% efficiency
until 16 Drivers 25.0% efficiency

More driver dosn`t bring any efficiency more.
This is called "Strahlungskopplung". But your
f max will go down. Not a problem with a sub but
a big problem when making a 2 way system with
fx 1500Hz.

3. You will notice that with more drivers(Box Volume is equal for each)
you will have a lower f res because more air is moved
(Strahlungskopplung)and increased the moved
mass.

Hope this helps, Andreas
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Old 11th December 2002, 07:30 PM   #7
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Hi Westrock2000

Regarding Your initial question I think You may find useful information and links in this thread:

Multiple Drivers to Increase Efficiency
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Old 11th December 2002, 08:00 PM   #8
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Good call, Mr Cocolino!

This link maybe relevant too:
doubling driver numbers/spl gains?
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Old 11th December 2002, 08:09 PM   #9
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Westrock,

In the bass region, a 10” driver will have the same capabilities as approximately 3 - 6.5” drivers, all else being equal. That’s where the rub is, all else is rarely going to be equal. Typically, a 10” woofer will have a lower fs then a 6.5” woofer. If you put the 3 – 6.5” woofers together, the fs will still be the same. This the Vas, and the driver Qts will be the dominate factors in how low the woofer will go in the box.

Maximum SPL is a little different story, but again, in the bass region, the 3 – 6.5” woofers will generally fall short of the capability of a single 10” woofer. A 10” woofer will usually have a higher Xmax then a 6.5” woofer and/or a 6.5” woofer with a high Xmax will have a large surround making the cone area smaller. In either case the maximum Vd (Volume Displacement) will be smaller for the 3 – 6.5” woofer making them less capable of high SPL in the bass region.

Here’s a link to a chart that will give some idea of how to compare.

Volume Displacement For SPL Chart

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