| xstephanx |
Hello,
Recently someone has brought it to my attention that drivers can sag when in a downfiring configuration. After doing the calculation for downfiring suitability at partsexpress, I came out with 5.6% it says that the maximum sag should be 5%. is it ok? what are the mal effects of too much sag? I dont really want to side fire casue I've got all these plans to make one REALLLLY nice table out of it.
:bawling: |
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| m4dm4n |
| The only thing i can remember is that spl will lower because of shorter xmax. |
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| johninCR |
With down firing you always give up some Xmax and therefore lose some max SPL at low frequencies. It affects some drivers more than other and yours seems to be just over what they say is the recommended limit. Over time it has a negative affect on the surround of any driver because it is constantly pulled by gravity, so your surrounds will wear out sooner.
Supposedly they is no affect on sonic performance, but that doesn't make sense intuitively to me, but I'll take their word for it. For tables, I always prefer to use 2 drivers and a manifold if it needs to be a stealthy sub. That way the mechanical vibrations cancel out and give you a vibration free table. It also enables a push/pull alignment which reduces distortion, maybe not audibly but theoretically. I have noticed less room rattles with push/pull. I was told once that distortion make your room rattle more than non-distorted sound and that's why a cheapie, boomy, sub can make the room rattle without providing any real low bass. |
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| simon5 |
It's on the limit, you'll have lower Xmax. I think it will still be ok.
Can you consider another driver for your table?
A Shiva for example. |
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| Ron E |
The 5% rule is just a rule of thumb. Whether you want to go more than 5% is up to you. THe risk is permanent deformation of the spider, meaning the coil becomes offset from its natural center, reducing Xmax by the amount of sag. THere were some woofers by Audio Concepts (DV12) that were very notorious for cone sag - they sagged progressively more and more until they didn't work properly, but it took a number of years for the effect to take place. The effect would be progressively increasing even order distortion.
I guess the safest thing is not to downfire, but it is up to you. I think you could still make a pretty nice looking table with the woofers firing sideways. If you had two woofers firing opposite directions you could cancel vibrations as well. |
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| xstephanx |
| Well its one dayton 15" QUATRO woofer(rubber surround so surround deterioration should not be as much as a problem) from partsexpress getting 240 watts in a sonotube enclosure. in a 14x10 room(if im feeling generous, probably closer to 12x9) I should have NO trouble with SPL. I say table cause I have plans to cover in in a veneer and then 3 4" tall brass legs out the top with some 1/4" glass on top. the sonotube is 24" diameter. I also got an idea to put it sideways, cover it in fur fabric, and put my caribou horns onnit( i think theyre from a caribou) if I feel like making something wild, but I'd much rather something elegant and nice looking(an unusual trait for a 14 year old boy) |
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| johninCR |
Be careful with glass on top of a sono tube sub. They have a tendency to start jumping around at high output.
And if you do the caribou antler thing be sure to post a pick. I want to see that. |
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| xstephanx |
| damn now im tempted to do the caribou antler thing too. and about the glass 1/4 inch thick glass 24" diameter will weigh alot, i could prob also move up to 1/2. btw last time i calculated the dayton has about .4L more linear displacement than a shiva. |
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| simon5 |
| Yes, more displacement but Shiva is designed for downfiring operation. You could still use a Tempest if you want a 15 incher which is designed for downfiring operation also. |
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| xstephanx |
| oh my god i would LOVE a tempest, but im 14, and xmas is JUST around the corner. and my rents are already buying me the amp. so that doesnt really work out, unless someone has a tempest theyd be willing to sell me? plus Ive already got a 7 cu ft box, changing drivers now would be a pain, and the dayton should still have more displacement even after the 5% excursion limitation I think. |
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| simon5 |
| Hehe the Dayton will be great, don't worry! Good luck with your design! |
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| xstephanx |
| sorry im just...worrysome, thank you so much for the quick replys to all people who repled and ill definately have pictures up when its done, and i might just put on some of them horns too... |
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| johninCR |
| Rents? A land baron at 14. Keep building your empire and retire at 21. In the meantime, put something heavy at the bottom, not the top on that sono tube. Making it very top heavy with plans for max excursion could hurt if it tips. |
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| xstephanx |
| 20 lb driver isnt good enough? its obviously going to have legs at the bottom, maybe pull off an SVS and put a hard reflecting surface at the bottom? I just got some of this 1" wood made from soy bean, VERY dead, VERY hard, VERY heavy. kinda like particle board but heavier stiffer. and johninCR, rents is youngin lingo for PARENTS. although i really like your plan about retiring at 21. Dont all of you wish you had a son who was obsessed with HT and DIY audio?:devilr: |
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| johninCR |
| You have to talk them into getting you a projector, if you're into HT. Nothing like lifesize video to go with the lifesize audio. |
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| xstephanx |
| oh believe me i want one, but how much does a bottom of the line projector cost? yeah thats what a thought, i still need a 5.1 reciever(just something that will get me 5.1 surround and a subwoofer out, nothing special) and my surrounds could definately use an upgrade. I also need a new video card so i can get a decent sized tv hooked up to this. |
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| Jack Keck |
| Thinking about using one of those Quatro drivers from PE? That 5.6% figure looked sorta famiiliar.:D |
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| johninCR |
| quote: | Originally posted by xstephanx
oh believe me i want one, but how much does a bottom of the line projector cost? yeah thats what a thought, i still need a 5.1 reciever(just something that will get me 5.1 surround and a subwoofer out, nothing special) and my surrounds could definately use an upgrade. I also need a new video card so i can get a decent sized tv hooked up to this. |
You can DIY one for about $100 or so. There's a whole forum about it here at DIYaudio. Have your computer do everything. Use an a/b switch to send the monitor signal to your projector. Get a 5.1 audio card and if you build high efficiency speakers you can get some of those $30 Tamps from Target at have plenty of power. They're so efficient you can run them off of batteries. $300 or so and finish your speakers and you'd have everything including a projector. Build the "rents" a projector to and I'm sure getting the 3 bills out of them will be a piece of cake. |
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| xstephanx |
| Holy, dude, I didn't think you could build a prejoector for 100! and I have a 5.1 surround sound card already, audigy LS(It works pretty well). And im in CANADA we dont have target here. I am thinking of getting those quest floorstanders down from 200 to 80 a pair at futureshop though, hell worst comes to worst I use em as rears. |
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| simon5 |
| You can get Infinity at Futureshop, I would take that over Quest... |
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| xstephanx |
| can you get free money at futureshop too? infinities are like 300 someodd. Im starting to consider the DIY route, if it wasnt for the complex crossovers, a TMM or an MTM floorstander would be very nice. I guess its time to start checking pawn shops ETC, for a 5.1 compatable reciever. Back on topic, the sag on the dayton sub is .5mm, how can that make any difference in output? or more prone to bottoming? its quite rare to run the sub .5mm away from bottoming. |
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| BassAwdyO |
| .5mm isnt going to be anything huge on your excursion, and it will further prevent driver bottoming if anything(unless your sub is mounted magnet down). Something I have learned about cone sag is, you can actually use it to your advantage. If you find a driver that has a good amount of sag, then get a pair, mount them clamshell isobaric, and voila. One sub sags out, the other sags in, and your one way linear excursion is INCREASED by the amount of sag. Typically linear excursion is increased anyhow due to the fact that the BL curve is rarely symmetrical to the line Xmax= 0. I.E. on dumaxt tests the adire brahma shows 25mm one way excursion inward, and 30mm one way excursion outward before BL drops below 71%. If you mounted two brahmas clamshell isobaric you would get ~30mm one way excursion. |
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| bwbass |
| But one driver would be out of it's motor's flux for the last 5mm of travel on each stroke, and would only be driven by coupling of the other driver. Seems like the net system motor strength would drop by half past 25mm. |
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| BassAwdyO |
| The average BL of the two drivers doesnt drop below 50% until ~33mm one way excursion. At 30mm the BL would be right around 8 N/A. 71% BL is reached at 29.5mm. The average BL curve is EXTREMELY flat between -18mm and +18mm with less than .2N/A of change from 14.5N/A. At least thats the way it would look if dumax is 100% accurate. Here's what I did, I took the dumax graph, then I overlayed a mirrored image of the measured curve, then averaged the two curves to get the red curve. Image is below |
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