Down-Firing Port Clearance

[Gov]

I have a new sub on order that has down-firing ports. It comes with 1" inch rubber feet on the bottom, but I have medium thick carpet (freise) and an 8 lb pad. I am concerned that the ports will not have the much clearance underneath. The Auralex isolation risers are not an option for me as this sub is as high as I can go in the space I am putting it in.
How much clearance is really needed for the ports? Will I be OK?

Thanks

 

[bpape]

The 1" seems pretty tight as is. If its sinking into the carpet, I suspect you're going to be choking off the port output. I'd probably paint a board or something to stick under it to prevent the feet from going down into the carpet by spreading the weight out.

Bryan

 

[MatthewB.]

Gov, I had the same exact issue when I tossed out the cheapie driver in an extra DCM sub that had two 12" drivers and one was down firing. When I installed my two extra SVS ISD Drivers (after I upgraded to NSD) Anyway the ISD driver was much thicker than the DCM driver, so it laid directly on the floor. So i went to Home Depot looking for a way to raise the sub without hindering the driver and came up with Table Leg End caps. The table leg peg in the middle fit in the dowel of the sub leg and was a perfect fit. This does two things, it raised my sub 2" off the floor (they also sell 1-3" lifts) and stabalized the sub more than the tiny legs on the sub. Here's a picture giving you an idea. The Table end caps BTW retail for about 1.00/ea and cn be stained or painted. I never got around to doing either, but you have that option.

 

[walter duque]

I have a downfiring sub which I have metal spikes on it and I placed it on large marbel tile. I glued the spike disk to the tile (to keep it from slipping off) and it works fine since I have a thick carpet.

http://www.sourcespeaker.com/SW12ULT-DFSub.html

 

[annunaki]

If a port is downfiring, it is a poor design choice to not have at least the clearance of the port's diameter before coming into contact with a surface. A woofer is a bit different situation and can have less clearance.

Example:

A 3" port should have at least 3" of clearance before a solid object or any large surface.

Slot vents should have the round vent equivalent for clearance. So with a 25 in^2 vent one would want a bare minimum 5.5" of clearance as it is close to a 5.5" vent.

I hope this makes sense.

Now a woofer does not require as much clearance for the simple fact that the velocity of air moving from the cone is not pressurized/loaded nearly as much as in a vent. The airspeed is so low that a conventional 12" woofer could have as little as 2" of clearance assuming the sides are all open & exposed. So long as the surround has physical clearance, it should be fine.

 

[Gov]

I am specifically referring to the new Epik Phoenix http://www.epiksubwoofers.com/portedphoenix.html. The owner Chad tells me it should not be a problem, however, it has me thinking because even with the 1" legs, its going to sink into the carpeting. The ports would probably be touching the top of the carpet. What is the down side to this? I know my old Mirage S12 had this design as well.

 

[Tomorrow]

I'll give a nod to the accuracy of Annunaki's post. You'll need roughly the distance from a boundary equal to the diameter of the port(s). Backflow issues can result if it's closer, even at the slow speed of the air exiting the port.

This looks like a really nice sub, Gov. Congrats. But it kind of bugs me that they use this sales pitch...when the design seems a bit questionable. I've never had, nor can imagine side-firing ports distracting from my listening experience.

The Phoenix uses two high-flow flared ports to effortlessly sweep the air in the subsonic realm without a hint of extraneous noise. To further enhance their silent-running onslaught, the ports are down-firing, and don't distract from your movie or music listening experience.

Features
Boundary loaded ported high output design

I think it will perform okay for you. But I guess I'd worry about the longevity of the unit. It's difficult to tell if it will be an issue with this particular design. Dunno.

 

[Gov]

Well...I am now having second thoughts about this particular sub I initally was interested in the Dragon a sealed sub, but noticed the Phoenix was louder lower and both the same mid-upper bass.

 

[Tomorrow]

Well...I am now having second thoughts about this particular sub I initally was interested in the Dragon a sealed sub, but noticed the Phoenix was louder lower and both the same mid-upper bass.

How high will your architectural limitations allow you to raise the Phoenix? (No pun intended.)

 

[Gov]

Maybe one inch. I don't think that will be enough to get the maximum performance from the subwoofer then.

 

[Exit]

I am sitting here looking at my downward firing SVS PB12+2 and it looks like the gap from the woofers to the baseplate is about 3" if that is any use to you.

 

[annunaki]

Exit SVS was smart and rear fired the ports to help alleviate these issues.

Having the ports choked off can induce unwanted compression & noise. Every inch will help in maximizing performance. I just find it odd that a somewhat credible manufacturer would make such an error in design. It is not as though this is new information. Chances are the ports are under compression anyway (most commercial designs are) and it will not make a big difference.

 

[croseiv]

You need just enough clearance so the water doesn't splash back and hit your derriere..

 

[mike c]

i remember someone mentioned that the Epik conquest had a port that was close to an inner wall to lower the tuning?

could a wall/floor outside the port have the same effect?

 

[annunaki]

i remember someone mentioned that the Epik conquest had a port that was close to an inner wall to lower the tuning?

could a wall/floor outside the port have the same effect?

To a degree, yes, it is called correction factor. The problem is that it increases vent mach, and potentially compression, at the same time. There is no free lunch.

 

[Gov]

Well, I decided to hold off on this sub for now until I read a few reviews on it. It seems like this port design is a bit suspect. Thanks to all your input, I greatly appreciate it

 

[Gov]

Does anyone think it would be acceptable to turn this subwoofer on its side and have the ports either on the left or right side of the cabinet? I have fired off an e-mail to Epik asking. Just wondering what you guys think.

Thanks

 

[mike c]

i think it's no problem

 

[Gov]

Via e-mail I corresponded with Epik today and was advised that it is a "no no" to turn a boundary loaded ported subwoofer (like the Phoenix) on its side.

Epik wrote:

"We designed the sub with these things in mind. The Phoenix can be set on hardwood floors or carpets without a problem.

Down firing subs are not new. Many other companies have used similar designs and engineering in regards to feet, etc. We have designed ours with all these in mind. Again, we do measure, test and engineer our subs so they work for our customers.

I can't imagine any carpeting that would alter the output of the sub. If however, there is such a carpet, then you'd simply raise the sub up with a little shim under its feet, so it sits above the carpet just a bit more.

On another note, I talked with the owner here for just a moment to see what would actually happen if you placed a boundary loaded sub sideways. Turns out it's a very bad idea.

If you were to place the Phoenix on its side, it would drastically affect the tuning of the sub and most likely, you would find the whole sub incurs damage from it."

 

[popotoys]

can you not just make 4 larger diameter but same thickness feet for the sub to sit on? this would reduce the lbs\sq\inch on the floor this reducing the amout the sub sinks in the carpet.