Down firing Subs? Pro's & Con's?

K

Kaspian

Enthusiast
Hello everyone,

What are the pros and cons of down firing subs? I will be in the market for a pair of subs in a few weeks. I was just wondering if I should rule them out or consider them. I do have a sub ritgh now, an JBL 10" with an 100w amp front firing. It sounds fine but its over 12 years old and its time for an upgrade.

*By the way, I dont know if it matters but the flooring where the subs will be placed is carpeted.


Thanks in advance for any input!

Kas
 
F

FirstReflection

AV Rant Co-Host
The advantage of a down-firing sub is that you are using the force of gravity to your advantage. By having the driver oriented downward, gravity is acting evenly on the driver surface. With a forward or side-firing sub, you have to be sure that the driver is very stiff and very well braced so that the force of gravity does not cause any distorted movement or alter the position of the driver relative to the cabinet over a long period of time (ie. the driver "squishing" the lower portion of the rubber surround and "stretching" the upper portion as gravity draws the driver downward.

The down-firing driver also works with gravity as it is pushed out, rather than pushing out perpendicular to the force of gravity. Having the driver on the bottom also places the weight of the driver and its magnet on the bottom of the cabinet, which typically makes the cabinet more stable and less prone to shaking.

In simplest terms, a good down-firing sub can perform equally well to a good front-firing sub. There is no reason to avoid one design or the other. One is not inherently better than the other.

Regardless of what subwoofer you choose, just be sure to decouple it from the floor. By "decouple" I simply mean that you should place some sort of "shock absorber" between the "feet" of the subwoofer and the floor.

Sound does not just travel through the air. Sound also travels through solid object. The subwoofer's cabinet will shake. When it does, that shaking gets transmitted into the floor. The floor shakes as a result and the floor is attached to the walls, which are attached to the ceiling. So with the subwoofer in contact with the floor, your entire room actually shakes in sympathy! This is not a good thing. This is distortion. A decoupling device does not completely eliminate this "room shaking" - sound travelling through the air will still cause some amount of shaking of the room. But decoupling the subwoofer GREATLY reduces the structure-borne transmission of the sound. The result is better, clearer, "tighter" bass to your ears and a GREAT reduction of being able to hear the bass in other rooms of the building! This is a huge help if you are in an apartment, but also a great help if you do not want to bother other people in your house.

I wholeheartedly recommend the Auralex GRAMMA and SubDude decoupling platforms. They cost $50 and are superb decoupling devices. They are also very well suited for down-firing subwoofers as they provide a solid, flat platform base on which the subwoofer's feet can sit and they are covered in industrial fabric that tends to work very well with the sound characteristics of down-firing subwoofers. For example, most of HSU's subs are down-firing and Dr. HSU recommends having carpet beneath those subwoofers.

Best of luck!
 
Pyrrho

Pyrrho

Audioholic Ninja
Hello everyone,

What are the pros and cons of down firing subs? I will be in the market for a pair of subs in a few weeks. I was just wondering if I should rule them out or consider them. I do have a sub ritgh now, an JBL 10" with an 100w amp front firing. It sounds fine but its over 12 years old and its time for an upgrade.

*By the way, I dont know if it matters but the flooring where the subs will be placed is carpeted.


Thanks in advance for any input!

Kas
In practical terms, it makes no difference whether it is front firing or down firing. You should simply concern yourself with the quality of the subwoofer, and not worry at all whether it is front or down firing. Basically, if one were simply "better" than the other, then there would be no reason to ever make the lessor type.
 
cwall99

cwall99

Full Audioholic
I will say this about front firing subs: it's totally cool taking off their grilles and watching those puppies jump when the LFEs are cranking.

Other than that, I don't think there's really a performance difference.

But... I do have a question regarding the de-coupling issue that was raised: my sub is sitting on the one part of the floor in my house that's on a slab (rather than over the basement). Is it as critical to de-couple a sub from the floor when it's on a slab compared to being over a basement or crawl space?

There's carpeting under the sub, if that helps.

Thanks.

BTW, Elemental Designs has a great discount going on right now.
 
walter duque

walter duque

Audioholic Samurai
IMO you get more out of a downfiring sub. I was told 3-4db. For HT I would have to say downfiring. For music I prefere my frontfiring subs. Maybe my place has just too many subs. Picture below is from new driver I just installed. Go to photobucket and you'll see frontfiring with passive radiator. Both are good. They are 12" with 1000 Watt amps and they can do some damage. Now this is only my opinion: downfiring subs are none directional, so placement is very easy the sound is just there and you don't know what direction it's coming from, it just fills up the whole room.

View attachment 7575

View attachment 7576

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F

FirstReflection

AV Rant Co-Host
If the slab is touching any other part of your house, then yes, you still need to decouple the subwoofer.

All we're talking about are physical vibrations. If one thing is shaking and it is physically in contact with another thing, then the vibrations will transmit from one thing to the other.

A decoupler is just a shock absorber. It takes those vibrations and absorbs them so that they do not pass (for the most part) from one surface to another.

Concrete shakes. It is dense - so it takes more energy to get it shaking than a less dense material - but it not a very good dampening material. So if it shakes at all, it actually transmits the vibrations very well.

Simple advice? Decouple your subwoofer no matter what. It doesn't cost much at all and the advantages can be very large indeed.
 
Pyrrho

Pyrrho

Audioholic Ninja
If the slab is touching any other part of your house, then yes, you still need to decouple the subwoofer.

All we're talking about are physical vibrations. If one thing is shaking and it is physically in contact with another thing, then the vibrations will transmit from one thing to the other.

A decoupler is just a shock absorber. It takes those vibrations and absorbs them so that they do not pass (for the most part) from one surface to another.

Concrete shakes. It is dense - so it takes more energy to get it shaking than a less dense material - but it not a very good dampening material. So if it shakes at all, it actually transmits the vibrations very well.

Simple advice? Decouple your subwoofer no matter what. It doesn't cost much at all and the advantages can be very large indeed.
So, do you think that the spikes that people put on their speakers are a bad thing, and snake oil nonsense that actually hurt the sound?
 
walter duque

walter duque

Audioholic Samurai
[
QUOTE=Pyrrho;606785]So, do you think that the spikes that people put on their speakers are a bad thing, and snake oil nonsense that actually hurt the sound?
[/QUOTE]
I have capet in my apartment, but I set my downfiring sub on a piece of marble tile with spikes and it works fine. In my house I had it directly to the floor and it will take the paint of the walls and pull the screws out of the sheet rock. As far as I am concerned I believe in spikes. If I set my towers directly on the carpet they do sound like crap. Sold a pair of Vandersteens a few years back to my buddy. Set them up in his place (with same amp) turned them on, he looked at me and I looked at him, I said I don't know what happened, well we figured it out, we did not have the spikes on the speakers. Sale went trough and everybody was happy. That's MO on spikes.
 
F

FirstReflection

AV Rant Co-Host
My experience is that decoupling is the best approach for both speakers and subwoofers. Stop the physical vibrations of the speaker or subwoofer cabinet from ever reaching the surface upon which they sit. That way, you are only hearing the sound produced by the speaker; not the sound of the speaker plus the sounds caused by the vibrations of the stand/floor/shelf/what-have-you.

So in the case of subwoofers, I advise putting a decoupling device inbetween the "feet" of the subwoofer and the floor. A really thick carpet pad can act as a decoupling device. But one issue are the "feet" on the bottom of most subwoofers. When you have all of the weight of the subwoofer supported only by 4 points, those 4 points have a great deal of downward force and can easily "sink" into most carpet pads far enough that they actually couple the subwoofer to the floor.

A similar thing happens with "spikes" for tower speakers or speaker stands. The speakers are actually directly coupled to the subfloor beneath the carpet.

There are a few things at play here. If the spikes do their job perfectly, they essentially make the speaker and the floor into one large, very massive structure. That works to make the combination more inert, simply by virtue of creating a very massive structure. With such high mass, it takes a great deal of energy to shake that structure, so in that sense, a perfect spike makes the speaker more inert.

But it is VERY easy to have a less than perfect spike. If the spike fails to completely join the speaker to the floor structure, you just end up with 4 sources of very strong vibrations. ANY shaking of the speaker at all gets focused into just those 4 points and if they manage to vibrate at all, those vibrations get transmitted into the floor and you get distortion as a result.

I say to avoid that can of worms. Decouple the speaker and you avoid this possibility entirely. If you are putting bookshelf speakers onto a stand, I suggest decoupling the speaker from the stand using Auralex MoPads or a similar decoupling device. If you are using tower speakers, I suggest putting SubDudes underneath the towers so that their spikes are NOT in contact with the floor at all!

What you will often find - if you are used to the sound of a subwoofer or speaker when it was coupled to the floor - hearing it after it has been decoupled, the bass will sound quieter and less forceful. After a bit of time though, you will realize that all that is "missing" is the vibrations of the room itself! While having the entire room shake along with the bass can be exciting and tactile, it is actually just distortion. All of that room shaking was never part of the original recording. It is a byproduct of physical shaking and that is distortion.

With speakers and subwoofers properly decoupled, you hear only the output of the speaker. So bass will seem quieter and there will be less tactile sensation of the room shaking, but you will gain an enormous amount of clarity, detail and accuracy.
 
Tomorrow

Tomorrow

Audioholic Ninja
After a bit of time though, you will realize that all that is "missing" is the vibrations of the room itself! While having the entire room shake along with the bass can be exciting and tactile, it is actually just distortion. All of that room shaking was never part of the original recording. It is a byproduct of physical shaking and that is distortion.

With speakers and subwoofers properly decoupled, you hear only the output of the speaker. So bass will seem quieter and there will be less tactile sensation of the room shaking, but you will gain an enormous amount of clarity, detail and accuracy.
I understand and agree with what you suggest...particularly for music. However, I wonder about general tactile nature of low frequencies being missed in your setup. A train rumbles by, a bomb explodes, a car or airplane crashes...all those experiences witnessed in person include tactile, felt movement when the earth you stand on or the house you stand in...moves. If you remove that feature from your playback system in an HT environment, don't you lose part of the "experience"? Distortion at 25 Hz is pretty tough to hear.
 
walter duque

walter duque

Audioholic Samurai
I understand and agree with what you suggest...particularly for music. However, I wonder about general tactile nature of low frequencies being missed in your setup. A train rumbles by, a bomb explodes, a car or airplane crashes...all those experiences witnessed in person include tactile, felt movement when the earth you stand on or the house you stand in...moves. If you remove that feature from your playback system in an HT environment, don't you lose part of the "experience"? Distortion at 25 Hz is pretty tough to hear.
Very good point. I enjoy when I get the felling when the whole structure of the buiding actually fells like it is moving, especially for HT.
 
mtrycrafts

mtrycrafts

Audioholic Slumlord
....But... I do have a question regarding the de-coupling issue that was raised: my sub is sitting on the one part of the floor in my house that's on a slab (rather than over the basement). Is it as critical to de-couple a sub from the floor when it's on a slab compared to being over a basement or crawl space?

There's carpeting under the sub, if that helps.

Thanks...
No, don't worry about it. You just don't have enough energy into that slab for it to transfer it to anything that would matter. Concrete is a 150Lb mass per cuft and bet you have a pretty good mass there to move and agitate;):D
 
I

iso9001

Audioholic Intern
My down facing PSW2500 was never a problem. Pretty nice actually,
 
A

abboudc

Audioholic Chief
The advantage of a down firing sub is that the woofer is generally protected (kids, pets, etc).

The disadvantage is you can't see the driver, if that sort of thing is important to you.
 

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