ScottRHinson said:
Interesting picture! This would mean that there are long term effects that might matter. I wonder if this applies to all suspension materials, and I don't have the answer. The followup to this would be: Is there any effect when the loudspeaker is monted vertically? The sag would be smaller, but given the small tolerances in the magnetic gap, little displacement would be needed to make the coil touch the iron.
It reminds me of another thing. At times I have got fed up with all of my cables to headphones and whatever that gets stuck under my chair. So I suspended them in a rubberband from the ceiling. It was not hard tensed or anything, but *none* of the rubberbands I could find would last more than a few weeks.
I am constantly rolling over my cables with my chair again...
Taken from PartsExpress http://www.partsexpress.com/resources/downfire.html
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.
Parts Express 2003 All Rights Reserved
Scott - Seems like that issue would be less likely if the vert-mounted woofer was down-firing reverse-phase. Thoughts?
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.
Parts Express 2003 All Rights Reserved
Scott - Seems like that issue would be less likely if the vert-mounted woofer was down-firing reverse-phase. Thoughts?
This formula says exactly the same as I did in a previous post, but in another way. I used Mms and Cms, they use Fs instead. The result is the same.
This resoning does however completely ignore long term effect of having the constant gravitational force pullung the cone downwards.
Scott, you say that this was a car mounted speaker. Have you seen the effect on home speakers as well, or is it this single speaker? I'm just thinking that the temperatures in a car can be very high in the summertime, and that this could *almost* melt the rubber/spider, at least soften it.
This resoning does however completely ignore long term effect of having the constant gravitational force pullung the cone downwards.
Scott, you say that this was a car mounted speaker. Have you seen the effect on home speakers as well, or is it this single speaker? I'm just thinking that the temperatures in a car can be very high in the summertime, and that this could *almost* melt the rubber/spider, at least soften it.
I have seen the permanent sag effects in the home environment.
It was in the 70's. The drivers were CTS 12W19; 12" woofers. There were 4 mounted down-firing in a coffee table. After a few years the cones had sagged about 1 inch. I vowed never to build down-firing systems again.
If that can't happen today, I'll believe it when I see it.
It was in the 70's. The drivers were CTS 12W19; 12" woofers. There were 4 mounted down-firing in a coffee table. After a few years the cones had sagged about 1 inch. I vowed never to build down-firing systems again.
If that can't happen today, I'll believe it when I see it.
Svante said:
Speaking of that particular case - where it seems the spider had been pulled away from the cone, an in-phase down-firing alignment would be "pulling" on the spider, while a rev-phase up-firing alignment would be pushing on it. The latter would seem to be more healthy...for the spyder at least.
Lusso5 said:
Correct me if I am wrong, but isn't the problem with the driver at the photo is that the spider is not "flat". Over time the gravity and heat has made the spider become permanently deformed.This would mean that the coil is no longer centered in the magnetic gap, which in turn would limit the xmax in the upward direction of the picture. It would not take much signal until the white ring would enter the magnetic gap instead of the coil. This would lead to severe distorsion.
There seems to be a misconception here that the cone mainly moves in one direction (outwards?) when a music signal is played. This is not the case. In general, music signals are just as symmetrical as a sine wave, and the cone moves both in- and outwards. This means that the polarity of the electrical connection (=the phase) does not matter at all, when it comes to the mounting. The phase of the electrical connection cannot compensate the "sag", unless there is DC coming out of the amplifier.
In an isobaric configuration, swapping the drivers once a year, would balance the sag.
Lusso5 said:
No, this is not correct. The idea is that the weight of the cone/voice coil moves the surround/spider into a new position. The weight of the cone does not change if it's pointed up or down, and therefore the effect would be no different.
I have no doubt that the temperature of the car hastened the process. I also have no doubt that most home woofers stay in service much longer than car woofers. (Unless you are...say...me!)
I've heard of pro-sound drivers doing this on the shelf at the repair shop or dealer, in doors, climate controlled conditions. This from fairly reputable friends in town....
Scott Hinson
Svante said:
I may be a little "affected" but I also rotate them every few months. So, I don't know...I've heard in the 70's with very large woofers and soft suspensions that over time this may happen. I've never personally experienced this...and as long as my Outlook alerts keep popping up, and I dutifully go through all my stock drivers and my home systems (possibly more than 50 drivers on hand ) I won't ever experiance it. I haven't done it with drivers smaller than 6.5", and I've never had a problem. Again though, I have a fairly high turnover rate at my house...nothing has stayed in one place longer than a year.
Scott
ScottRHinson said:
I may have totally lied! Walking around the house I realized I may have a set of bookshelfs that have been around for almost two years. I'll have to give them some sweeps for T/S parameters and compare them to the measurements I took a few years ago to see if there is any drift. (That's if I can find the old measurements, possibly a BIG if.) At any rate I can make some distortion plots to see if there are any significant differences between the "old" driver and some new ones I have that haven't been used and have been subject to rotation. I doubt it will show anythign it's a 6.5" CSX driver, but it's worth a shot! I only wish I had a real rub&buzz test system!!! ($$)
Scott
My thoughts are I personally would prefer forward firing bass. However I think downward firing are far better when it comes to looks especially if it is a bit of a lifestyle system and is meant to be as discrete as possible. They also have a much better WAF.
It is probably quite difficult to tell the difference in practice and this will also depend on the room floors etc which would be a big factor, but when it comes to sound it must be better having that driver point directly towards or into a room rather than at the floor. I have listened to a few subs and some good speakers which have bass drivers orientated or directed at the floor and yes there is lots of slam but its not quite the same as having it directed into the room. Isolation is another factor if the speakers going up and down unless there is dead weight on top of it, it is not going to have the same affect as some spikes or rubber feet underneath it griping and holding it from movement especially if its powerful amp and a lot of movement on the driver.
I would always go for the forward firing if its an option.
It is probably quite difficult to tell the difference in practice and this will also depend on the room floors etc which would be a big factor, but when it comes to sound it must be better having that driver point directly towards or into a room rather than at the floor. I have listened to a few subs and some good speakers which have bass drivers orientated or directed at the floor and yes there is lots of slam but its not quite the same as having it directed into the room. Isolation is another factor if the speakers going up and down unless there is dead weight on top of it, it is not going to have the same affect as some spikes or rubber feet underneath it griping and holding it from movement especially if its powerful amp and a lot of movement on the driver.
I would always go for the forward firing if its an option.
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