I've got a '99 Ford F-250 extended cab that could really use some help in the low end. I don't need anything crazy at all, but my currently speakers have a hard time with anything below ~80Hz, so it definitely needs some help down there. I've already purchased a Dayton Audio SD215A-88 8" driver mostly to bump my purchase over $100 for free shipping. 
It looks like it should do nicely in a ~.75 - 1 ft^3 ported box tuned to roughly 38Hz (haven't plotted anything out just yet). Currently, I'm thinking my best bet is to make a center console (with cup holders for disguise) for the back seat and stuff the sub in there. I'm trying to figure out if I should have the sub face downward, or point forward into the front bench seat.
I know facing downward is generally preferred, but I would lose a good 2" of box space doing it that way. Plus, I'm a little concerned that firing into the carpet would absorb some of the punch. My other option is to point it forward right into the front center seat, which is usually folded down for a console/arm rest. My biggest concern with this route is that I will hear the bass lop-sided and coming from under my right arm rather than enveloping the cabin. I've heard of the theory that your ear can't pinpoint the source of a wavelength longer than the longest length of the listening space, which should negate the issue. However, my computer room is about a 20' x 20' square, so the wavelength for that is about 57Hz. I just spun around in my chair, played a 45 and 35 Hz sine wave, and could pinpoint where the sub was both times, so that's bogus.
Does anyone have experience with a near-field off-listening-axis sub firing down vs forward to share?
It looks like it should do nicely in a ~.75 - 1 ft^3 ported box tuned to roughly 38Hz (haven't plotted anything out just yet). Currently, I'm thinking my best bet is to make a center console (with cup holders for disguise) for the back seat and stuff the sub in there. I'm trying to figure out if I should have the sub face downward, or point forward into the front bench seat.I know facing downward is generally preferred, but I would lose a good 2" of box space doing it that way. Plus, I'm a little concerned that firing into the carpet would absorb some of the punch. My other option is to point it forward right into the front center seat, which is usually folded down for a console/arm rest. My biggest concern with this route is that I will hear the bass lop-sided and coming from under my right arm rather than enveloping the cabin. I've heard of the theory that your ear can't pinpoint the source of a wavelength longer than the longest length of the listening space, which should negate the issue. However, my computer room is about a 20' x 20' square, so the wavelength for that is about 57Hz. I just spun around in my chair, played a 45 and 35 Hz sine wave, and could pinpoint where the sub was both times, so that's bogus.
Does anyone have experience with a near-field off-listening-axis sub firing down vs forward to share?
Inside 1 m, the WLs are so long that the sub would have to be XO'd > ~172 Hz, which is below where carpeting will have little, if any, affect and too high for good summation with the mains.
Regardless, even if rated for downfiring, not a good plan for such a 'buckboard' riding truck if my buddy's 2000 F350 is any indication, especially since based on published specs its initial sag is 4.3% out of a 5% max offset, so over time may be too much for sure.
GM
Regardless, even if rated for downfiring, not a good plan for such a 'buckboard' riding truck if my buddy's 2000 F350 is any indication, especially since based on published specs its initial sag is 4.3% out of a 5% max offset, so over time may be too much for sure.
GM
Don't forget that, apart from suspension sag, you will increase THD due to the non-linearity caused by mounting the speaker facing upwards or downwards - you have gravity assisting the cone movement one way and resisting it the other. In other words, the cone's mass appears different to the motive force on each half-cycle. Further, the cone will move more readily towards Xmax in the 'downward' direction as the voice coil has already been displaced away from its usual rest position, ie. centred in the magnetic gap.
Cheers, Carl.
Cheers, Carl.
Nope. Mass can't "appear different". It's always the same.
The weight of the cone may cause some slight displacement if it is oriented facing up or down, but usually this is very small compared to the driver's Xmax, so the impact on THD should be pretty low. If it was significant, they'd be a lot less commercial subwoofers out there with drivers oriented that way
.Nope. Mass can't "appear different". It's always the same.
The weight of the cone may cause some slight displacement if it is oriented facing up or down, but usually this is very small compared to the driver's Xmax, so the impact on THD should be pretty low. If it was significant, they'd be a lot less commercial subwoofers out there with drivers oriented that way
Hi Brian,
Thanks for picking up this confusion. You are absolutely right that mass can never change, it's only that we usually talk about mass in relation to 'moving mass' in loudspeaker terms and perhaps I was trying to over-simplify my point. Perhaps I should have talked about force rather than mass. In the context about which I am speaking, the real-world effect is that the mass does indeed 'appear different' to the driving force, since it is assisted in one direction by gravity, and impeded by it in the other. The force required to displace the cone from its rest position is lower in the downward direction.
Put as simply as possible, the cone will move further downwards than upwards when fed a sine wave signal. This would show up as increased THD in a similar fashion to a non-symmetrical suspension stiffness regardless of any sag. (Hold a heavy weight in one hand and try to move it vertically up and down rapidly; non-linearity of velocity and acceleration will be quite evident!). Similarly, a mass hanging on a spring will not exhibit pure simple harmonic motion about its rest position, as would a pendulum, where the restoring force is equal either side of it.). As we all know, Force = Mass x Acceleration, so Acceleration = Force/Mass. In the downward direction, the force generated by the voice coil has 'g' added to it and subtracted from it in the upwards direction; acceleration and displacement are affected.
The effect, as you say, is small on a loudspeaker but it is definitely measurable and real, and mounting a subwoofer like this is simply and obviously non-optimal. Life is a compromise, audio doubly so! Vertical mounting of subwoofers should be avoided if at all possible unless sound quality comes second to looks or convenience. Note that there are few, if any, PA subwoofers which are mounted this way, even though they possess very stiff suspensions compared to 'floppy' hifi drive units. I would only ever choose the least favourable design as a last resort, otherwise fundamental principles and engineering correctness prevail.
Cheers, Carl.
Oh good grief. No need to get all "smarter than thou". The mass is constant, gravity is constant (barring elevation changes to avoid smarty-pants comments) and non-related to cone movement, the cone moves the same amount in each direction compared with its resting point at that orientation, and the difference in THD is effectively negligible unless playing darn near full excursion, in which case, a larger driver should've been used in the first place. Yet none of these even answer any of the questions I've asked in the first place.
Because:
I'm all for receiving feedback and GM's response was quite helpful. What I'm not interested in is starting a theory and technicality war that is hardly even relevant in my application. Is Borg 'technically' right about sag? Of course. Does it matter in the slightest in my application? No. (unless the washboarding effect GM mentioned is significant) All it does is pull the thread off-topic.
BB, why do you recommend a down-firing over front-firing?
Yeah, I skipped over those due to lack of time/enthusiasm since so much has already been posted on the net and all my nearfield experience has been in the home with only a mobile audio app's up-firing 12" 'HIFI' woofer in a '70 Camaro trunk.
BTW, basic rooms are 1/2 WL resonators, so ~1130 ft_sec/2/20 ft = ~28.25 Hz corner frequency, though your ears will probably still 'locate' the sub due to the room's higher order modes, which is made much worse due to being square, so even in your truck with its much higher corner frequency, reduced amplitude modes and being much better damped, I imagine it's still going to be easy to locate with it ~next to you due to needing a fairly high XO point.
Anyway, out of curiosity I googled down firing in a Ford, so based on this you may be fine doing it, though I believe that at least long term it won't be with the intended driver: How do the down-firing enclosures sound??? - F150online Forums
Anyway, good luck with it and please let us know what did/didn't work.
GM
Yeah, my main vehicles have always been roadsters, motorcycles, so just concentrate on the ~250-2500 Hz phone BW. The pickups, I added underdash horns and a pair of 'FR' drivers in a common box behind the seats for 'spaciousness' and some I've upgraded the dash speakers, though the current Toyota is bone stock since all I normally listen to is talk radio while driving in Hotlanta's literally 'killer' traffic.
GM
GM
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