Direct Radiating vs. Down firing subs

sprintz · March 2004

... for home theatre use in 15'x15' room.

It seams that only the vintage Polk subwoofers used the down-firing design, while many current models of other manufacturers use down firing designs. What are the pro's / con's of the two designs?
S.

PolkWannabie · March 2004

Most SVS subs are down firing as well ...

Tour2ma · March 2004

Don't believe that's true of SVS's boxes, PW. The cylinders fire down and port up, yes? But most the boxes look to have drivers in the sides.

sprintz,
There's a fairly lengthy thread around here on this very topic. Do you know how to use the site's search engine?

If not, holler and I'll be happy to lend a hand...

And Welcome to the Club...

PolkWannabie · March 2004

Actually I believe all the SVS boxes with the possible exception of the B4 fire down and port to the rear ...

Contained in all SVS box descriptions is ...

Down-firing woofers with distinctive SVS integrated base-plate

which then points at another link typified by this ...

http://www.svsubwoofers.com/subs_pb2_plus_features.htm#base

dave shepard · March 2004

The SVS B4 is side mounted while the other ones like mine are on the bottom.

Dave

Tour2ma · March 2004

My apologies, PW, you're correct. I guess I had the 4 pictured in my head and transposed it to the other box sub's...

The reason I knew about the cylinders was Doc's story of a friend's firing its port plug into the air.

Damn, that makes twice this year I've been wrong about something...

PolkWannabie · March 2004

No apology necessary ...

See my followup question to you on a different issue in Off Topic and/or PM

Tour2ma · March 2004

Got it...

... and I'm sorry about apologizing unnecessarily.

dave shepard · March 2004

Tour, it's better then arguing unnecessarily to get your count up

.

Tour2ma · March 2004

*

==============
* single smilie is the lowest investment post padding.

VR3 · March 2004

I will take a shot at it...and probally will be wrong...

We have the M&K and the SVS in the same room basically..

The M&K, obviously a lesser subwoofer, is front and down firing. The SVS is down firing on a platform built onto the subwoofer.

The SVS is much harder to localize, not just because it is a better subwoofer but because the bass is going on all sides of the subwoofer instead of just leaving one side. When you have a forward firing sub, the bass is radiating in one direction it seems (atleast in my room), it basically covers the right side, and a little bit of the left. But it is definetely heavier on the right.

It is more localized than anything else in the room even at 60hz. It is very easy to tell where it is at just because with bass, although omni-directional, in a regular room, it starts at a source. The bass is radiating at a source. So if you have a forward firing subwoofer, it is radiating at a source that is flinging it all in one direction...

With a down-firing sub it seems to me the bass would spread infront, behind, side to side of the subwoofer....it has no real boundary other than the room.
But of course, the bass still starts at a source, but I would think it would be harder to find..

That is my common sense knowledge of it, granted it is probally not right! lol

- Sid Da Kid

dave shepard · March 2004

For me in my room the pounding people take is a no brainer where it is comming from, they take one look at the front stage and say "holy ****" then the beating commences

..

Tour2ma · March 2004

Sid,

The lower limit of human ability to locate sound by hearing alone is 80 to 90 Hz (your mileage may vary).

That said, you may be able to locate lower frequency by feeling the pressure waves radiating from the source. Frontfiring may lend itself more to this means, but the difference should be slight based upon the little I have read on the subject.

Don't know what spl you're localizing 60 Hz at, but try doing it at fairly low volume to limit localization by feel. If you still can it may be that the M&K is generating a harmonic. Is one driver still dead?

Now here's one for your brain pan...
Why is the lower limit of localization higher than the lower frequency limit of hearing?

Hint #1: Think about what you've learned about how you localize sound in the SDA discussions 'round here...

VR3 · March 2004

Higher frequency passes through the driver, higher frequencies has a shorter wave length than bass wave lengths.

My guess is, the more higher frequency going through the sub involves more direct reflections than everywhere sound.

If that makes sense.

I think I understand why, but I am probally wrong.

- Sid Da Kid

Yes one driver is still blew in my M&K, but you can't hear it from a distance or up close. It just moves with the air, slight noise, maybe 30-40db at most while the active is playing 90-100db. It works better with one blown to me.

Tour2ma · March 2004

Not really on track yet...

Think SDA interaural cross-talk cancelation and how you locate sound sources, first..

madmax · March 2004

Originally posted by Tour2ma
you may be able to locate lower frequency by feeling the pressure waves radiating from the source. Frontfiring may lend itself more to this means, but the difference should be slight based upon the little I have read on the subject.her than the lower frequency limit of hearing?

Not that you said anything wrong but I will argue anyway. Front firing subs can be localized easily if any noise is being made by the woofer. Not harmonics necessarily, just noise. Downward firing woofers can mask much of any noise made by the woofers.

madmax

KarlJShields · March 2004

What a great thread! No bashing, name-calling or flaming--and some education is taking place. I've learned something, anyway.

Originally posted by Tour2ma
Now here's one for your brain pan...
Why is the lower limit of localization higher than the lower frequency limit of hearing?

Hint #1: Think about what you've learned about how you localize sound in the SDA discussions 'round here...

C'mon Tour--don't leave us hanging...

VR3 · March 2004

The main cause for localizing a sub is......

1) Distortion
2) Driver Noise
3) High Frequency crossing

When you make the driver produce more than it can handle, it plays louder, infact if you cross your sub at 60 hz (turn it half way on the sub amp if it allows), then cross it to 80hz, it will bottum out basically. The higher you cross it, the less you have to turn it up. However, in reality you are getting no more volume than you were at 60hz. The bass plays the same, works the same. It is just having to move more air to create the frequencies you desire.

The more you cross it, the more work the driver has to do. This can cause distortion, driver noise, cross talk (probally the wrong word to use).

As you cross it, the sub is producing frequencies it should not, kinda like a Bose cube.

They say you can place it under a couch, but if you did - you would have 25% of the voice coming under your butt, and the rest infront of you.

Higher cross, more it has to do. Harder it works. The more stress it puts on the driver. More distortion it puts out. The more you hear it and what it is doing.

That is the best I can do. Have a great day!

- Sid The Insomniac Kid

Tour,
I THINK I UNDERSTAND!

The SDA is to keep things seperate, where they should be and where they should not.

When you cross your subwoofer higher, it produces things it can not correctly place, therefore it puts things out of place. This makes it localized. Just like the SDA design. The SDA design is supposed to eliminate cross-talk between the right and left channel.

Tour2ma · March 2004

Patience KS, letting Sid work this one through.

Sid,
Getting somewhere with the last bit... (not sure about the "25% butt" stuff above that though)... And you're right about some of the reasons you might locate a sub, but let's assume a clean signal...

OK, let's step this off...

You're facing 12 o'clock and a car backfires at the 2 o'clock position 20 feet away from your right ear. Given that the speed of sound in air is 775 mph or ~1135 feet/ second...

How long does it take the sound to reach your right ear?

How long to your left ear?

More later...

KarlJShields · March 2004

Originally posted by Tour2ma
Patience KS, letting Sid work this one through.

Yep, that's the answer I was hoping for...something about teaching a man to fish for himself comes to mind. Keep up the good work.

Tour2ma · March 2004

Thanks... now let's just hope I know what I'm talking about...

Pauly · March 2004

nano second?

Airplay355 · March 2004

.01762114537444933... seconds?

gregit · March 2004

Don't forget to account for the Doppler Effect produced by Earth's spinning motion (coriolas factorization constants vary by latitude)

Oh yeah..don't forget the effects of temperature.."At freezing (0º Celcius), sound travels through air at 331 meters per second (about 740 mph). But, at 20ºC, room temperature, sound travels at 343 meters per second (767 mph)."

Tour2ma · March 2004

Originally posted by Airplay355
.01762114537444933... seconds?

And the left ear?

Pauly · March 2004

if you are hard of hearing how does that factor in?

Direct Radiating vs. Down firing subs

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