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
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
Here is the driver that I'm gonna use.
http://www.partsexpress.com/pe/show...&St3=71648730&DS_ID=3&Product_ID=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?
http://www.partsexpress.com/pe/show...&St3=71648730&DS_ID=3&Product_ID=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?
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.
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.
alex_g said:Here is the driver that I'm gonna use.
http://www.partsexpress.com/pe/show...&St3=71648730&DS_ID=3&Product_ID=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?
Bill Fitzpatrick said:
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?
alex_g said:Here is the driver that I'm gonna use.
http://www.partsexpress.com/pe/show...&St3=71648730&DS_ID=3&Product_ID=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?
...and it might actually be possible to compensate for the sag by putting a DC current in the right direction through the coil. The force from gravity is g * Mms= 9.81*0.104 = 1.02 N. To get this force with a BL of 12.92, a current of 1.02/12.92=79 mA is required. This can be arranged if the amplifier has a voltage offset of Re*0.079=3.50*0.079=0.28 volts.
But probably that is overkill to get the 0.3 dB extra output.
AGGEMAM said:
Regardless of what way the driver is facing, and regardless of the polarity, you have a driver oscillating in BOTH directions in order to produce the sound wave. Reducing maximum x-max in either direction will reduce the overall amplitude unless you want it to bottom out at the crest of each wave in one of the two directions.
AGGEMAM said:
Yes. As you may know, a music signal is generally symmetrical, The cone moves inwards just as much as it moves outwards. To cope with this, the overhang is also symmetrical, in order to always keep current conducting copper in the magnetic gap. This overhang determines the Xmax value of the driver. Permanently pulling the cone in *either* direction reduces this overhang on one side, reducing the maximum excursion on that side. Since there is symmetry, it does not matter which side that is affected, no matter how the signal is polarised (unless you use some special test signal).
AGGEMAM said:
Oh yes it does. First, what do you mean with a single ended amplifier? Would that be the same as a non-bridged amplifier? In that case you still have two output transistors which draw current in the two different directions. So, unless the amplifier is broken, there will be symmetry in the electric signal.
I *think* I understand what you mean, and I *think* that you have not understood how the loudspeaker cone essentially moves symmetrically? Anyway, the deviance from symmetry in the signal, the driver and the air is really small, so no the driver orientation does not matter (up- or downfiring)
I was just under the impression that it took more force to compress air than expand it. Damn my physics teacher. (Although he couldn't really be blamed since it's well over 10 years since I left school, I might just remember incorrectly).
EDIT: And in any case we would be talking flyspecks here, but then again a 0.38 db loss is that too.
EDIT: And in any case we would be talking flyspecks here, but then again a 0.38 db loss is that too.
AGGEMAM said:
Well, your physics teacher was probably right when it comes to compressors and stuff. In the case of the loudspeaker the effect is hardly noticeable, though.
Math warning
: The approximation that the loudspeaker builder uses is 1/(1+x) is approx = 1-x. x being the relative compression of the volume. If x<<1 the approximation is good. For example if x=0.01, we get: 1/(1+0.01)=0.990099 which is appox 1-0.01=0.990000. For x=0.9 the approximation is poor, 1/1.9=0.53, 1-0.9=0.1, but we never get there with loudspeakers.Hey gurus,
Another question.
On web site where I got this sub I got manual and this manual says for closed box best internal valume is 1 cu ft.
According my calculation best valume should be 1.4 cu ft.
Today I got magazine from them and I found this driver and they are telling that best valume is 1.3 cu ft.
What volume should I use?
Another question.
On web site where I got this sub I got manual and this manual says for closed box best internal valume is 1 cu ft.
According my calculation best valume should be 1.4 cu ft.
Today I got magazine from them and I found this driver and they are telling that best valume is 1.3 cu ft.
What volume should I use?
Bill Fitzpatrick said:
Possibly a lot.
http://www.scottaudio.com/sag.html
As I say in the site text, I've never bought into the whole "If it only moves 5% or less it's okay." I've posted this link numerous times to the Madisound board, the DIY Speaker (Bass List) List, the Parts Express forum and now here.
I've never had a driver designer or a mechanical engineer explain to me how this wouldn't eventually happen to other drivers in other up/down firing situations. The car environment probably accelerated this drivers decline, but I think it is safe to say it will happen other places as well. I've heard stories of pro-sound drivers taking a set on the shelf.
I still have that cone/spider assembly. It still looks exactly like the picture.
All of my drivers are stored vertically.
Scott Hinson
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