Are there any cons of down firing a subwoofer?
For arguments sake, say I were to take a Full Marty from GSG with a Dayton UM18-22 and face it down with 5" legs. The floor is wood over concrete slab, ground level no basement. The driver & port would be facing the floor.
What issues, if any, could I expect from this arrangement?
For arguments sake, say I were to take a Full Marty from GSG with a Dayton UM18-22 and face it down with 5" legs. The floor is wood over concrete slab, ground level no basement. The driver & port would be facing the floor.
What issues, if any, could I expect from this arrangement?
Sag over time is a big one. The suspension loses its battle with gravity over time and the TS perams change a lot. The vc falls out of the gap a little. It does depend on hoe stiff the suspension is but it will happen over time.
That appears to give you the instantaneous sag. ie, if you turn the driver to be face down, how much does the cone move?
Over the time scale of years, the "zero" position will shift, and the problem becomes obvious.
My recommendation, if down-firing is desired, would be to include a small DC PSU that passes enough current to allow the voice coil to hold the cone's weight.
Chris
Over the time scale of years, the "zero" position will shift, and the problem becomes obvious.
My recommendation, if down-firing is desired, would be to include a small DC PSU that passes enough current to allow the voice coil to hold the cone's weight.
Chris
Well, the way I viewed it is that if I did the math right, Fs must drop to ~15 Hz, a ~43% drop in which case the driver needs either rebuilding or replacing IME.
If you had two smaller drivers mounted back to back on the sides of the box, they could be mounted lower ( almost on the floor ), this arrangement would cancel out reaction forces, solve the sag problem and mean that they could be used on a wooden floor if you wanted to use them in a different room.
My purpose is aesthetics. Having a cabinet which does not show any speakers, ports or grill cloth provides a host decorating options, even if the cabinet is largish.
I suppose I could face the driver(s) and ports towards a wall as long as I kept it at least 5" from the wall. Perhaps have the top extend 5" past the cabinet to ensure the distance. I would nee to make sure the wall it "faced" was not resonant in the low frequency band pass or its harmonics.
I suppose I could face the driver(s) and ports towards a wall as long as I kept it at least 5" from the wall. Perhaps have the top extend 5" past the cabinet to ensure the distance. I would nee to make sure the wall it "faced" was not resonant in the low frequency band pass or its harmonics.
A cabinet that does not show any speakers ? a concept than intrigues myself, here is an example of a tiny omni, after hearing what it sounds like I'm very tempted to make a much larger floor standing speaker, with a rear firing bass driver. Another idea that interests me is using two bas drivers back to back, but inside the cabinet and vented through a hole in the bottom.
Could you build a sub with two opposed woofers firing inwards into a slot that opens underneath?
Something that hasn't been mentioned, but since there can be an offset in the suspension because of gravity, down firing subwoofers also will have (a little bit) more distortion.
Using a DC supply to counter act this doesn't seem to be a very good idea, since this will create additional heat etc.
But the thought behind it isn't strange 🙂
Depending on the woofer as well, some seem to have a natural coil offset. (see; https://audioxpress.com/categories/vc-testbench )
So I guess you can counter act that this way to some point.
Although figuring out how much exactly is not gonna be easy (that also counts for the DC offset idea)
Using a DC supply to counter act this doesn't seem to be a very good idea, since this will create additional heat etc.
But the thought behind it isn't strange 🙂
Depending on the woofer as well, some seem to have a natural coil offset. (see; https://audioxpress.com/categories/vc-testbench )
So I guess you can counter act that this way to some point.
Although figuring out how much exactly is not gonna be easy (that also counts for the DC offset idea)
What about the sound?
My experience has been down firing subs do not sound as good as front firing subs. I've been given many subs by my circle of friends over the years and I tried them all on my system. Most were down firing designs and I ended up turning them on their sides for front firing because the bass had more detail, clarity, and definition than it did in the down firing position. The floor in my listening room is linoleum over concrete. Sorry, I can't back this up with any measurements or simulations, it's just my listening experience, repeated with five different subs giving very similar results. I suppose it may vary with the sub Xo frequency, which I usually set around 120Hz. I would be interested in hearing the experiences of others on the subject.
To the OP, you may want to try it both ways before you commit.
My experience has been down firing subs do not sound as good as front firing subs. I've been given many subs by my circle of friends over the years and I tried them all on my system. Most were down firing designs and I ended up turning them on their sides for front firing because the bass had more detail, clarity, and definition than it did in the down firing position. The floor in my listening room is linoleum over concrete. Sorry, I can't back this up with any measurements or simulations, it's just my listening experience, repeated with five different subs giving very similar results. I suppose it may vary with the sub Xo frequency, which I usually set around 120Hz. I would be interested in hearing the experiences of others on the subject.
To the OP, you may want to try it both ways before you commit.
I have dual OB subwoofers for everything above 30-40 hz. These are very articulate.
I am looking for sub 40 hz in a package which is aesthetically pleasing. The room is ~3,800 cu ft. The main purpose is HT special effects.
OK, I would think there are little or no acoustic problems with down firing of special effects below 40 Hz and considering your other subs.
Given that the current required will be small, the amount of heat will be tiny.
Well, it'd need some way to disconnect the DC supply when the amp's powered up. Relay activated by the amp's PSU?
For those worried about the heat, it's worth doing the maths. Example below.
Let's say we want one of these:
http://www.seas.no/images/stories/prestige/pdfdatasheet/h1252_l22rnx_p_datasheet.pdf
Mounted down-firing. I happen to be listening to four of them, so that's probably why I chose it.
Anyway, we have BL=8.15N/A, and Mmd=27g=0.027kg.
We want to apply 9.81*0.027kg of force = 0.26487N.
At 8.15N/A, we need 0.26487/8.15=32.5mA.
Power dissipated = (I^2)R=0.0325*0.0325*6=6mW
Would anyone like to argue that the driver might get excessively hot at 6mW dissipation?
Chris
I guess you have a fair point.
Although I wouldn't call that a decent subwoofer. 😀
But even for a 10 inch sub with BL=17 and Mmd=140 grams it wouldn't make much of a difference.
Amplifiers is no issue, just deliberately set an offset with the amplifier I guess 🙂
Would a light coil spring acting on the cone reduce sag ? After watching a youtube vid of valve spring surge, it might be possible that it would add some distortion.