[SteveRB]

Hello,

I am considering a modification to my existing set up with passive radiators. I have read a few times that they should never be facing down, due to gravity pulling on the cone. Is this a serious concern? How is this any different than an active woofer facing down?  There are several examples of commercial subs and bass amps with down facing PRs. There seems to be very little actual evidence on this...

Any insight is appreciated. Thanks.

[UpperCut]

Well, this is steep!

You can’t just come along and question audio facts - which are well proven science (so I’m told for many years over & over now) yet which are also full of contradiction and even more personal opinions as everybody, seem to make things up to suit along the way.

Mate, such a very good question I just love it, and YES of course this is of serious concern – BUT only if you let it be this way as otherwise as you already stated commercial enterprise uses it anyhow because it looks good & is selling regardless of science.

I use PR’s in all my projects builds and I (to my personal opinion) would not use it facing downwards if you do have to play around with a lot of weight and deep-deep bass because as more weight used on them as more it increases the throw downwards (over extending itself) and hampers the pull upwards drastically. So you could have problems with a many things in the reproduction of sounds.

On the other hand I would not think twice about it myself if the woofer is say 8” with 9 mm X/max, and you use two 8” Pr’s with say 10 mm ea. or a 10” PR with 10 mm, but that really has to be calculated first to see how close that all will come etc. & etc…..

If you do want low bass and a lot of that you will have to use a real PR I mean a real one which could hack punishment but also has plenty of safety zone, and that would be an EQ PR maybe a little more expensive but very suited for good heavy ongoing use. If you can play around to get the best OK, and well if not and you have to have it ‘Down firing’ give it enough space between PR & floor watch the weight and all in all do what you feel you like is suited to enjoy your sounds – as when it comes to it once you open your box things changes slidly anyway
……………. But for sure not necessarily to the bad as audio science would like to make it out to be by looking at measurements and tables!

rgs UpperCut

[JLM]

Bull!

Gravity would have a lower affect on a passive radiator than on a similar driver with the added weight of the voice coil/spider. 

What about upwards firing drivers?

What about vertically mounted drivers that gravity can in time pull it out of alignment?


Sounds like something pushed by the planer/ribbon/plasma crowd.

[SteveRB]

a good start to the discussion. Thank you both.

Here's my application: currently using a small sealed enclosure in a two-way design with a 15" woofer (Sd: 856cm^3 and Xmax: 2.4mm). I would like to add a passive radiator instead of porting for additional bass. I am not looking for super low-end. This is music only hifi. I am looking at a 12" PR (Sd: 480 cm^3 and Xmas: 10mm and Fs: 17 Hz). I do not think I would be adding any mass as the Fs is already low enough for my application.

My initial calculations show that the PR can handle well over double the air volume of the active driver. Given the low volume of air movement, the fact I'm not using this is a subwoofer configuration, and that the PR is relatively stiff to begin with... it seems reasonable that if would work fine in a mounting configuration facing down.

Just looking for some more experienced opinions here...

[UpperCut]

To get some more experienced opinions could be difficult as it looks to me already ill in the set up!

15” woofer – 2.4 mm X/max can that be right, and then using a 12” PR is just about like bridling a horse the wrong way around.

The up most basics of PR design is say 10” woofer + 12” PR, 12” woofer + 15” PR or 10” woofer with high Xmax PR or two 10” PRs etc. It would be easier to use a woofer with some better specs which also moves some air, but 2.4 mm is just a joke that would not even pull the skin of a rice pudding!

rgs UpperCut

[SteveRB]

To get some more experienced opinions could be difficult as it looks to me already ill in the set up!

15” woofer – 2.4 mm X/max can that be right, and then using a 12” PR is just about like bridling a horse the wrong way around.

The up most basics of PR design is say 10” woofer + 12” PR, 12” woofer + 15” PR or 10” woofer with high Xmax PR or two 10” PRs etc. It would be easier to use a woofer with some better specs which also moves some air, but 2.4 mm is just a joke that would not even pull the skin of a rice pudding!

rgs UpperCut

http://www.parts-express.com/eminence-kappa-15c-15-driver-4-ohm--290-459

It'll tare your head off when it's loaded in a horn and be linear up to 500Hz.


Point is. I am not changing the woofer or the horn. I can change the cabinet volume and the PR to best suit. Some folks in my circle end up adding additional cabinet volume and ports. I am designing a more elegant solution.

[UpperCut]

Well, a total different ball game now is it not? Information like that should come in the beginning when asking a question would save a lot of time!

So with that said your approach could be just fine!

rgs UpperCut

[SteveRB]

Well, a total different ball game now is it not? Information like that should come in the beginning when asking a question would save a lot of time!

So with that said your approach could be just fine!

rgs UpperCut

sorry man, didn't want to get to far off from the get-go.

so, the numbers seem fine, non?
should give a tuning around 30Hz for a relatively small enclosure?

[JohnR]

Bull!

Gravity would have a lower affect on a passive radiator than on a similar driver with the added weight of the voice coil/spider. 

Not bull, generally speaking. Passive radiators (often) have added mass, sometimes several hundred grams.

That's not always the case (hundreds of grams of mass) but it depends on the parameters of the PR and the woofer.

Steve, would make most sense to use a box modeling program with your woofer, and planned PR. I don't know how many will tell you how much the PR will sag  if pointed down but it's a start. My hunch is that it won't be useful anyway, because your box will be too small and the PR (if it has a 17Hz Fs) has too low resonant frequency.

[FullRangeMan]

Hello,

I am considering a modification to my existing set up with passive radiators. I have read a few times that they should never be facing down, due to gravity pulling on the cone. Is this a serious concern? How is this any different than an active woofer facing down?  There are several examples of commercial subs and bass amps with down facing PRs. There seems to be very little actual evidence on this...

Any insight is appreciated. Thanks.

I have read a few times that they should never be facing down, due to gravity pulling on the cone. Is this a serious concern?
If no one try it yet, dont be the first.
How is this any different than an active woofer facing down?
A sub have a motor(magnet) and a amp to up the cone, a PR have nothing, the suspension will loose soon.
Pro audio speakers are famous for bad sound unless you listen only Eletronica.

[JLM]

FRM:

Agree on the downward mounted subwoofer drivers, should be the best possible mounting if you think about the tight tolerances that need to be maintained between magnet and voice coil.  I see no practical issue here relating to sag.

But disagree on your comment regarding "bad sound" from pro audio speakers.  PA/sound reinforcement speakers - generally yes, but not studio/mastering speakers.  They are designed to be extremely accurate (imaging, frequency/phase response, intended to reveal all the warts) to the point of being dry/fatiguing versus home audio speakers that are designed to develop an emotional connection by making everything pleasing/entertaining.

[Guy 13]

If speaker manufacturers are trying to avoid having sound from the back of a driver's cone to bounce in the enclosure,
then, why have a driver or passive radiator facing the floor and bouncing the sound back into his face?

Guy 13

[JohnR]

At bass frequencies, sound is omnidirectional. It makes no difference to audible results which way the driver is facing. It's more a practical concern, the obvious factor being that the moving weight will sag (by an amount depending on weight and suspension compliance) which will reduce excursion and possibly have long-term effects. The other aspect is that down-facing drivers are generally "slot loaded" which affects the acoustic loading and reduces the effective Fs.

[FullRangeMan]

FRM:

Agree on the downward mounted subwoofer drivers, should be the best possible mounting if you think about the tight tolerances that need to be maintained between magnet and voice coil.  I see no practical issue here relating to sag.

But disagree on your comment regarding "bad sound" from pro audio speakers.  PA/sound reinforcement speakers - generally yes, but not studio/mastering speakers.  They are designed to be extremely accurate (imaging, frequency/phase response, intended to reveal all the warts) to the point of being dry/fatiguing versus home audio speakers that are designed to develop an emotional connection by making everything pleasing/entertaining.

Are the PA and automotive themselves, some woofers come to have over a thousand watts.

[bentconvert]

http://www.parts-express.com/resources-woofer-mount-up-down
Subwoofer Qualification Formulae For Downfiring Configurations

We are often asked if a particular driver is suitable for using in a down-firing configuration. Below is a formula that takes into consideration the effects gravity will have on the "sag" of the cone structure of any woofer. You will need the Fs, Vas, Sd (surface area of the cone), and the Xmax to determine the relative long term usefulness of up or down-firing any woofer.

You can calculate the sag of a driver from:

Percentage of Sag = 24,849 / ( Xmax * Fs²)

where

- 24,849 is a constant value based on the relationship of acceleration due to gravity and Pi.
- Xmax is the maximum linear excursion of a loudspeaker voice coil while remaining within the magnetic flux field (mm).
- Fs is the free-air resonant frequency of the woofer (Hz).

The following is the same formula, including the relationship of acceleration and Pi in this case:

Percentage of Sag = 981,000 / (Xmax * (2 * Pi * Fs)²)

where

- 981,000 is acceleration due to gravity (mm/S²) * 100 (for the percentage).
- Xmax is the maximum linear excursion of a loudspeaker voice coil while remaining within the magnetic flux field (mm). - Fs is the free-air resonant frequency of the woofer (Hz)
- Pi is the ratio of a circle's circumference and diameter, usually rounded to 3.14.

As a general rule of thumb, any time the sag exceeds 5% of the driver's Xmax, it's not recommended for a down-firing subwoofer application.


From my understanding, the more compliant the surround the less suitable it is for up or down firing applications

[FullRangeMan]

From my understanding, the more compliant the surround the less suitable it is for up or down firing applications

Correct. The Radiator MMS is critical to fit to the main driver.
Before purchase one must calc it or ask to the main driver manufacturer if the Radiator is suited.