Cone sag...not a myth...a reality.
You guys might want to take a look at a couple of fuzzy pictures I made.
http://www.scottaudio.com/sag.html
That woofer has a permanent suspension take set. Over the last 5 months since I first posted that, and linked to it on the Madisound board I haven't had one person give me any reason other than "if it only moves a little it won't do that" for why their woofer won't look like the Rockford after a long period of time. Mechanical spring devices under load suffer from fatigue. Make it so that the fatigue won't be noticable over a useful lifespan, and my guess is that you couldn't get the woofer to move without several kilowatts of amplifier.
Scott Hinson
You guys might want to take a look at a couple of fuzzy pictures I made.
http://www.scottaudio.com/sag.html
That woofer has a permanent suspension take set. Over the last 5 months since I first posted that, and linked to it on the Madisound board I haven't had one person give me any reason other than "if it only moves a little it won't do that" for why their woofer won't look like the Rockford after a long period of time. Mechanical spring devices under load suffer from fatigue. Make it so that the fatigue won't be noticable over a useful lifespan, and my guess is that you couldn't get the woofer to move without several kilowatts of amplifier.
Scott Hinson
A couple of quick points.
First, the magnet has NO effect on the cone unless there is current throught the voice coil. It does not serve as a stabilizing element to help prevent sagging when the woofer is idle.
Second, as I mentioned some time ago in a previous thread?, sagging is very much a reality in some cases. I've seen woofers sag so much in just a few years that they were acting as diodes. On the other hand, I just recently opened up an RH Labs downfiring woofer box that is least 20 years old and no sagging. It all depends on the suspension and mass.
First, the magnet has NO effect on the cone unless there is current throught the voice coil. It does not serve as a stabilizing element to help prevent sagging when the woofer is idle.
Second, as I mentioned some time ago in a previous thread?, sagging is very much a reality in some cases. I've seen woofers sag so much in just a few years that they were acting as diodes. On the other hand, I just recently opened up an RH Labs downfiring woofer box that is least 20 years old and no sagging. It all depends on the suspension and mass.
IMHO, it’s the quality of the subwoofer has everything to do with the quality of the sound, not which way it’s facing. Considering the well-made subwoofer operating at higher outputs near the fb of the box will easily produce distortions levels of 3 or 4%. A poorly made will produce much higher distortions. At this distortion level, it really doesn’t matter what way the driver is facing, or what little tweaks you may try to catch bass magic in a bottle. I've heard great sounding subs and terrible sounding subs in both configurations.
The preference of the general buying public for one configuration over the other has more to do esthetics and price then anything else. “Where will the wife allow me to put this thing?” “Will it match the furniture?” “Is it too big for the living room?” “Should I buy a stereo pair?”
For me, once I made the subwoofers, the question would be how best to blend their (stereo) outputs with the mid-bass speakers. To me that means a forward facing woofer in proximity to the mid-bass.
The preference of the general buying public for one configuration over the other has more to do esthetics and price then anything else. “Where will the wife allow me to put this thing?” “Will it match the furniture?” “Is it too big for the living room?” “Should I buy a stereo pair?”
For me, once I made the subwoofers, the question would be how best to blend their (stereo) outputs with the mid-bass speakers. To me that means a forward facing woofer in proximity to the mid-bass.
Someone, somewhere, sometime, posted a set of equations that will figure for you whether a woofer will down-mount well or not, and I wish I had written them down!
It stands to reason that a driver with higher Qms, lower Xmax, and lower moving mass will suffer less sag; obviously, a car woofer has low Qms, high Xmax, and very large moving mass, therefore, it will OVBIOUSLY sag and destroy itself over a relatively short period of time!
The ideal drivers for this would have paper cones (or very light poly cones) cloth or paper accordion surrounds, and be 12" or bigger so they could have low Xmax and still produce low notes well.
I suspect that the various 24"+ woofers out there would work well. Since drivers that large have little use for high Xmax or heavy cones, and the suspension already has to be pretty heavy-duty in order to keep the 24"+ of shearing force from making rubbing sounds, they'd probably last a good long time before sagging detrimentally.
All drivers, mounted like this, will sag eventually. All drivers mounted horizontally will sag and rub. The catch is that with one design, you can just turn the driver over and it will, over time, correct itself. Down-firing requires a new box, and reversing it might not help, depending on the level of damage.
It stands to reason that a driver with higher Qms, lower Xmax, and lower moving mass will suffer less sag; obviously, a car woofer has low Qms, high Xmax, and very large moving mass, therefore, it will OVBIOUSLY sag and destroy itself over a relatively short period of time!
The ideal drivers for this would have paper cones (or very light poly cones) cloth or paper accordion surrounds, and be 12" or bigger so they could have low Xmax and still produce low notes well.
I suspect that the various 24"+ woofers out there would work well. Since drivers that large have little use for high Xmax or heavy cones, and the suspension already has to be pretty heavy-duty in order to keep the 24"+ of shearing force from making rubbing sounds, they'd probably last a good long time before sagging detrimentally.
All drivers, mounted like this, will sag eventually. All drivers mounted horizontally will sag and rub. The catch is that with one design, you can just turn the driver over and it will, over time, correct itself. Down-firing requires a new box, and reversing it might not help, depending on the level of damage.
"80% of manufacturers...."
the most obvioys reason for the side firing subs is footprint. Tall, narrow towers have a much higher WAF than 16" wide cabinets.
the most obvioys reason for the side firing subs is footprint. Tall, narrow towers have a much higher WAF than 16" wide cabinets.
oops, posted too soon...
Something to consider when designing a box for a downfiring sub is that the driver will be slot loaded against the floor.
Something to consider when designing a box for a downfiring sub is that the driver will be slot loaded against the floor.
Cone sag approximation formula (courtesy the Adire site):
All figures are metric (Vas = litres, Sd = cm^2)
Driver suspension compliance (Cms) = Vas / (1180 * c^2 * (Sd/10000)^2)
Driver mass (Mms) = 1 / ((2*pi*Fs)^2 * Cms)
Sag = Cms * Mms * g (where g = 9.81 m/s^2)
http://www.adireaudio.com/tech_papers/driver_orientation.htm
In summary:
"If the sag is more than 5% If the sag is more than 5% of the Xmax of the driver, then it's not meant for horizontal mounting."
Dave.
All figures are metric (Vas = litres, Sd = cm^2)
Driver suspension compliance (Cms) = Vas / (1180 * c^2 * (Sd/10000)^2)
Driver mass (Mms) = 1 / ((2*pi*Fs)^2 * Cms)
Sag = Cms * Mms * g (where g = 9.81 m/s^2)
http://www.adireaudio.com/tech_papers/driver_orientation.htm
In summary:
"If the sag is more than 5% If the sag is more than 5% of the Xmax of the driver, then it's not meant for horizontal mounting."
Dave.
I'm glad someone noted that sagging is not only a problem with down (and up) firing drivers. It happens with some drivers in the normal side firing orientation also, though if caught early enough, the driver can be turned to even out the sag. I have read that this happens with some tweeters with very light suspensions, but the worst case scenario I have come across was a pair of Leak Sandwichs (with the 13 inch styrofoam/aluminum foil woofer). The surround had compleatly slid off the upper part of the cone. Granted this was probably a matter of incompatible glue and damping compound on the cloth half roll surround, but it shows it can happen.
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"80% of manufacturers...."
Not only does a slim tower have higher WAF, it will also result in a lighter overall box. A downfiring woofer in a cabinet of the same hight as another cabinet with a side firing woofer will weigh considerably more...
UPS and FedEx have 70 pound per package weight limits, so most speaker manufacturers try to keep size small enough to ship to customers.
Dave, you beat me to posting Adire's set of calcualtions...
Not only does a slim tower have higher WAF, it will also result in a lighter overall box. A downfiring woofer in a cabinet of the same hight as another cabinet with a side firing woofer will weigh considerably more...
UPS and FedEx have 70 pound per package weight limits, so most speaker manufacturers try to keep size small enough to ship to customers.
Dave, you beat me to posting Adire's set of calcualtions...
Re: "80% of manufacturers...."
Steve
I don't get it. Please expand or clarify.Eric said:
Steve
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"I don't get it. Please expand or clarify."
Be happy to!
A tower speaker with a down firing sub will necessitate a box with four wide panels (front, back, 2 sides). A tower speaker with a side firing sub will necessitate a box with two wide panels (sides) and two narrow panels (front and back). The two additional wide panels needed to enclose the down firing driver will also need internal braces that are larger than the braces necessary to brace a thin tower. All of this extra material adds up to more weight. Even if the squarish box for the down firing driver does not extend all of the way to the top of the tower enclosure, it will require more physical material than will a thin tower design with the same drivers.
Hope this clarifies a bit...
Be happy to!
A tower speaker with a down firing sub will necessitate a box with four wide panels (front, back, 2 sides). A tower speaker with a side firing sub will necessitate a box with two wide panels (sides) and two narrow panels (front and back). The two additional wide panels needed to enclose the down firing driver will also need internal braces that are larger than the braces necessary to brace a thin tower. All of this extra material adds up to more weight. Even if the squarish box for the down firing driver does not extend all of the way to the top of the tower enclosure, it will require more physical material than will a thin tower design with the same drivers.
Hope this clarifies a bit...
Hmmm ...
If you take a cube of 1 cu ft (external) volume and compare it with a box which is half the thickness and double the height ie. 2ft x 1 ft x 1/2ft (to give the same external volume) ...
Then, the 6 walls of the cube are each 1 sq ft. Total wall area is 6 sq ft.
However, the walls of the rectangular cabinet are:
2 walls @ 2ft x 1/2ft = 2 sq ft
2 walls @ 1ft x 1/2ft = 1 sq ft
2 walls @ 2ft x 1 ft = 4 sq ft
Add it up and you get a total of 7 sq ft of wall area.
If you were to go further and make a box of 4ft x 1ft x 1/4ft (same volume again), the total wall area would come to 10.5 sq ft.
More wall = more mass and, possibly, more bracing.
Of course, we're dealing with internal volume rather than external volume and I can't be bothered to make the calculation for this but I think that the same general principle applies.
I'm sorry to be pedantic but I think you're mistaken.
Steve
If you take a cube of 1 cu ft (external) volume and compare it with a box which is half the thickness and double the height ie. 2ft x 1 ft x 1/2ft (to give the same external volume) ...
Then, the 6 walls of the cube are each 1 sq ft. Total wall area is 6 sq ft.
However, the walls of the rectangular cabinet are:
2 walls @ 2ft x 1/2ft = 2 sq ft
2 walls @ 1ft x 1/2ft = 1 sq ft
2 walls @ 2ft x 1 ft = 4 sq ft
Add it up and you get a total of 7 sq ft of wall area.
If you were to go further and make a box of 4ft x 1ft x 1/4ft (same volume again), the total wall area would come to 10.5 sq ft.
More wall = more mass and, possibly, more bracing.
Of course, we're dealing with internal volume rather than external volume and I can't be bothered to make the calculation for this but I think that the same general principle applies.
I'm sorry to be pedantic but I think you're mistaken.
Steve
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Hmmm... Apples don't always compare well to Oranges. I appreciate your calculations, Steve, but think we are diverging a bit...
In re-reading the last several posts here, it appears we may be talking about two different things. My interpretation of the discussion question, following up with Illusus, is "why don't floor standing, full range, tower speakers have down firing subs?" It occurs to me that you may be answering the question "why don't stand alone dedicated subwoofers have down firing subs?"
Are we now back on the same page? 😉
In re-reading the last several posts here, it appears we may be talking about two different things. My interpretation of the discussion question, following up with Illusus, is "why don't floor standing, full range, tower speakers have down firing subs?" It occurs to me that you may be answering the question "why don't stand alone dedicated subwoofers have down firing subs?"
Are we now back on the same page? 😉
Eric said:
The reason being that tower speakers have side-firing subs and not down-firing subs is......
Unlike the old, original floor standing speakers like Klipsch Cornwalls for example, the 15" driver faced forward, resulting in a 20" wide front baffle, (same as if it were facing the floor), which is not the best thing to have. (Not so hot imaging and or staging, plus lots of reflections on the baffle.)
Tower speakers were originally designed to act like small bookshelf speakers, (which have superior imaging and staging), meaning they have smaller, narrow front baffles with less reflections. In turn, this results in better imaging and staging like bookshelf speakers, but with the added benefit of having a built-in sub for better bass response, and no speaker stands, or stand alone subs. Generally, woofer cones are wider than their baskets are deep, so side mounting them was the most logical thing to do in order to keep the front baffles of the towers as narrow as possible.
Plus, having a subwoofer enclosure with two different sized walls (shoe box shaped), such as in tower speakers, is going to result in better quality bass than an enclosure with equal sized walls (perfect square), due to higher frequency standing waves well above the crossover frequency, or something like that. I'm not sure exactly, but I do know that the "shoe box" enclosure is a better choice than the "cube" enclosure.
Also, if down-firing subs are supposed to be better because of some kind of reflections off the floor cancelling out certain frequncies coming from the cone, then what the heck good are all the other reflections that are down there that's not cancelling anything out? Is it to purposely smear what remaining bass is left to smithereens?!
The reason there isn't more down firing is rather simple, front firing sells better and always has. Front firing is much more difficult to place, so the charge seems like ignorance. The only reason a down firing design sounds muddy is a cheap amp or the crossover is too high and the same sound is being received from two sources. If you do buy one from a reputable company or build one yourself, ensure you adjust the crossover point until you only hear your main speakers, and the bass seems to be coming from them.🙂
17% of US population lives in Apartments, Condos or Townhomes, where down-firing subs need not apply.
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I believe cone sag can be an issue over a long period. I have a duel 12 downfire that was made in 74' I believe. I thought miller and kreisel came out with the first home subwoofers. But thats another story. Anyhow these downfiring phase linears have sag. They still work ok for 40 year old speakers. But I always found it hard to control boom unless its in a large room.
Downfiring and upfiring sag is indeed an issue. In some drivers (Lowthers) you even must rotate the driver because it'll sag when mounted "normally"- firing towards the listener. It's not a quality issue.
I use downfiring- but I do so with manifolds. Best of both worlds- built in high-pass filter from downfiring, I get force cancellation by mounting them Push-Pull, and no worries about cone sag because they're still mounted "normally". Also, I get some free LF Eq this way- a lower Fc and higher Qtc due to the airload.
That said, I used an adire 15" for a while upfiring and didn't have any issues for the year or so that I used that configuration.
I use downfiring- but I do so with manifolds. Best of both worlds- built in high-pass filter from downfiring, I get force cancellation by mounting them Push-Pull, and no worries about cone sag because they're still mounted "normally". Also, I get some free LF Eq this way- a lower Fc and higher Qtc due to the airload.
That said, I used an adire 15" for a while upfiring and didn't have any issues for the year or so that I used that configuration.
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