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Old 18th February 2004, 05:27 PM   #1
alex_g is offline alex_g  United States
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Question Front firing vs down firing sub?

Hey guys,

I'm in the process to design my sub. I got the driver from partsexpress and I got an idea how to build the cabinet but...
I was planning to build down firing sub but I noticed that all modern subs are front firing.
What the difference does it makes and if in driver manual they didn't say anything about it is it safe to build down firing?

Thanks
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Old 18th February 2004, 06:06 PM   #2
BAM is offline BAM
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Part of it is that a lot of modern subs have long excursion drivers with soft suspensions and heavy diaphragms for a low Fs. SVS and HSU, some of the most highly-regarded sub manufacturers out there (for home theater gear, for price/performance ratio) use downfiring designs.
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Old 18th February 2004, 06:15 PM   #3
alex_g is offline alex_g  United States
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Here is the driver that I'm gonna use.
http://www.partsexpress.com/pe/showd...D=120478&DID=7

Of course I will put sub on legs - I can even make them litle bit higher so I can avoide suging.

Can you tell me am I safe with this driver to use down firing?
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Old 18th February 2004, 06:26 PM   #4
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Right. The soft suspension and/or weak motor assembly of some drivers causes the driver to sag in a downfiring configuration, effectively reducing full-wave x-max.

Because of so many front firing designs, I think that's become a popular asthetic option with many builders, myself included.

Personally, I think a down firing design is a more sound design. The cone will emit upper frequency harmonics, and while inaudible, could cause localization of the bass unit in a typical listening room. Facing the sub down will help mask the higher frequency emissions of the driver. That being said, when I build my sub, it'll face forward, because I like to see the driver.
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Old 18th February 2004, 07:11 PM   #5
Svante is offline Svante  Sweden
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Quote:
Originally posted by alex_g
Here is the driver that I'm gonna use.
http://www.partsexpress.com/pe/showd...D=120478&DID=7

Of course I will put sub on legs - I can even make them litle bit higher so I can avoide suging.

Can you tell me am I safe with this driver to use down firing?
Well, the cone mass is 0.104 kg, which would mean a downforce of 9.81*0.104=1.02 newtons. The compliance is 0.33 mm/N which would leave you with a drop of 1.02*0.33=0.34 mm. Xmax is 10 mm, and this will now be reduced to 9.66 mm. This means that max output level drops by 20*log(10/9.66) = 0.3 dB. No big deal.

Isn't math wonderful?

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Old 18th February 2004, 07:47 PM   #6
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What about 2 years later. How much will have the cone sagged from the center position?
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Old 18th February 2004, 08:04 PM   #7
AGGEMAM is offline AGGEMAM  Denmark
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If you mount it backside out in a downfiring application that is suplied by a single-ended amplifier output, you actually improve max output level by the same amount.
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Old 18th February 2004, 08:28 PM   #8
Svante is offline Svante  Sweden
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Quote:
Originally posted by Bill Fitzpatrick
What about 2 years later. How much will have the cone sagged from the center position?
That would depend on the long term Cms, which I have never seen stated in data sheets.
Seriously, this would depend on the material in the suspension. But even if the sag is 2mm, the max level drop would be only 20*log(10/8) = 1.9 dB. But this is theory, practical experience might say something else. Anyone?
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Old 18th February 2004, 08:30 PM   #9
Svante is offline Svante  Sweden
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Quote:
Originally posted by AGGEMAM
If you mount it backside out in a downfiring application that is suplied by a single-ended amplifier output, you actually improve max output level by the same amount.
No, the sag will reduce the "overhang" of the voice coil on the upper side. This overhang is symmetrical, so it does not matter which side that is reduced.
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Old 18th February 2004, 08:31 PM   #10
AGGEMAM is offline AGGEMAM  Denmark
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Quote:
Originally posted by Svante
No, the sag will reduce the "overhang" of the voice coil on the upper side. This overhang is symmetrical, so it does not matter which side that is reduced.
It will? Even if you have the same polarity as before?
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