I recently purchased a 12" subwoofer driver on eBay. It's from a Monitor Audio RS W12 sub (http://www.monitoraudio.co.uk/product.php?application=8&range=2&product=17&area=2).
It seems to be a very stiff driver. Having done some brief tests, it would seem that the drivers Fs is at about 50Hz! I want to run some more definitive tests, but in the mean time it would seem that Qts is about 0.52 and Vas about 10.1 L (I'm less sure of that one though, need to get my hands on some scales).
How could a 12" woofer with specs like this be made to give good low end? My thoughts are that maybe Monitor Audio use a Linkwitz transform circuit in their sub. On the other hand maybe I have a dodgy driver.
What are your thoughts and comments?
Cheers,
Steve.
It seems to be a very stiff driver. Having done some brief tests, it would seem that the drivers Fs is at about 50Hz! I want to run some more definitive tests, but in the mean time it would seem that Qts is about 0.52 and Vas about 10.1 L (I'm less sure of that one though, need to get my hands on some scales).
How could a 12" woofer with specs like this be made to give good low end? My thoughts are that maybe Monitor Audio use a Linkwitz transform circuit in their sub. On the other hand maybe I have a dodgy driver.
What are your thoughts and comments?
Cheers,
Steve.
Right, this driver definitely has and Fs in the region of 50Hz. I'm wondering if it is possible to lower Fs by making the suspension less stiff (it's REALLY stiff at the moment). Could this be done with solvents? How would it be done? I think there are two spiders, one could be taken off, not so keen on that though.
If it is possible to make the suspension less stiff, would there be any other changes other than Fs and Vas? Would the Qms or Qes change at all?
If you think this is a crazy idea, please let me know. I don't want a ruined driver on my hands that I could have sold and gotten my money back for.
If it is possible to make the suspension less stiff, would there be any other changes other than Fs and Vas? Would the Qms or Qes change at all?
If you think this is a crazy idea, please let me know. I don't want a ruined driver on my hands that I could have sold and gotten my money back for.
Hi.
This woofer has good potential for Linkwitz transform. The high Fs is a good thing, as you want to drive it below Fs and the high Qts is also good for the sealed box.
How did you measure it? Speaker workshop? Your mention of a scale says that you have no reliable weights. A double A (AA) cell is around 24 grams, that's pretty much what I use (one or two).
You will want to make a temporary sealed box around 30 litres to test it for suitability. Build the box, install the driver and drive it with 100 watts at 20 Hz. If it makes no racket, it should be ok.
This woofer has good potential for Linkwitz transform. The high Fs is a good thing, as you want to drive it below Fs and the high Qts is also good for the sealed box.
How did you measure it? Speaker workshop? Your mention of a scale says that you have no reliable weights. A double A (AA) cell is around 24 grams, that's pretty much what I use (one or two).
You will want to make a temporary sealed box around 30 litres to test it for suitability. Build the box, install the driver and drive it with 100 watts at 20 Hz. If it makes no racket, it should be ok.
Thanks for the reply!
Guys, thank you so much for responding!
I added 16 x 2 pence coins plus Bluetac and measured using a Wallin jig and Speaker Workshop. Apparently that's about 128g, but I'll have to borrow some scales to get a proper Vas reading. Assuming that it is 128g, Vas=11.85 Litres or 0.418 cu ft. Qts is 0.5 and Fs is 49.4 Hz.
As the driver is at the moment (without out a Linkwitz Transform) it models as having an F3 of 70Hz and a Qts of 0.6 in a 30 Litre box (in WinISD).
Having seen Zaph's Dayton RSS315HF woofer project (http://www.zaphaudio.com/archives.html), I was quite tempted to sell the Monitor Audio driver and see if I could get hold of one of those RSS315HF drivers. Don't know where I would get one in the UK though.
Is the driver I have worth hanging on to and worth the extra money of a powerful amp and Linkwitz Transform circuit? Is the power/size ratio a good trade off? Won't thermal compression be an issue?
Cheers.
Guys, thank you so much for responding!
I added 16 x 2 pence coins plus Bluetac and measured using a Wallin jig and Speaker Workshop. Apparently that's about 128g, but I'll have to borrow some scales to get a proper Vas reading. Assuming that it is 128g, Vas=11.85 Litres or 0.418 cu ft. Qts is 0.5 and Fs is 49.4 Hz.
As the driver is at the moment (without out a Linkwitz Transform) it models as having an F3 of 70Hz and a Qts of 0.6 in a 30 Litre box (in WinISD).
Having seen Zaph's Dayton RSS315HF woofer project (http://www.zaphaudio.com/archives.html), I was quite tempted to sell the Monitor Audio driver and see if I could get hold of one of those RSS315HF drivers. Don't know where I would get one in the UK though.
Is the driver I have worth hanging on to and worth the extra money of a powerful amp and Linkwitz Transform circuit? Is the power/size ratio a good trade off? Won't thermal compression be an issue?
Cheers.
Here we go: -
The magnet is 18cm in diameter and 4cm tall. The vent in the pole piece is 3.5cm in diameter. The voice coil former would appear to be about 7.5/8cm (or about 3") in diameter.
The top of the coil (which I can see through those holes in the side of the basket) would appear to overhang the top of the top plate by about 9mm. The top plate is 5mm. Assuming that the coil overhangs the bottom of the top plate by the same amount, this would give an xmax of 9mm in each direction would it not?
When I had it hooked up to my Nad C320BEE for testing/running in, as I increased the power it seemed to get to a point where the excursion stopped increasing. Increasing the power much further than the point at which this happened just caused my amp to cut out, but the cone seemed to be moving by about that amount (9mm), though I can't say for certain.
What sort of amp would you recommend to power something like this (assuming the use of a Linkwitz Transform)? Are there any power amp kits or modules out there that aren't hugely expensive?
I'm sure it's not entirely impossible that I could build an amp myself, would this be any cheaper?
Cheers.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The magnet is 18cm in diameter and 4cm tall. The vent in the pole piece is 3.5cm in diameter. The voice coil former would appear to be about 7.5/8cm (or about 3") in diameter.
The top of the coil (which I can see through those holes in the side of the basket) would appear to overhang the top of the top plate by about 9mm. The top plate is 5mm. Assuming that the coil overhangs the bottom of the top plate by the same amount, this would give an xmax of 9mm in each direction would it not?
When I had it hooked up to my Nad C320BEE for testing/running in, as I increased the power it seemed to get to a point where the excursion stopped increasing. Increasing the power much further than the point at which this happened just caused my amp to cut out, but the cone seemed to be moving by about that amount (9mm), though I can't say for certain.
What sort of amp would you recommend to power something like this (assuming the use of a Linkwitz Transform)? Are there any power amp kits or modules out there that aren't hugely expensive?
I'm sure it's not entirely impossible that I could build an amp myself, would this be any cheaper?
Cheers.
Depending on options available I would recomend a 300-500 watt amp. I mean in reality the linkwitz transform is going to require in the multi thousand watt below say 30-35hz, but thats based on matching peak output above that level, which isn't necassary. If you assume a listening level of 100 decibles or less, then you could get away with less power. It will always be limited, and always wont handle the power it needs at 20hz with that much equalization, so I would still stay within the power limits of the driver, which is probably less than 500 watts. Obviously 500 watts was used originally and they probably used either a LT cuircit or some type of equalization, and output was probably limited to between 85-100 decibles. In room will be better of course. It's hard to say without knowing the xmax and speaker power handeling to know how far you can stretch that though. If you are going to build yourself, 500 watts might be a bit more difficult. However you can buy 300 watt amps so cheap anymore it seems like a worthwhile investment over rolling your own.
I wonder if this little baby could be used to create that LT?
http://www.reckhorn.com/index.php?ln=en&prod=b1
http://www.reckhorn.com/index.php?ln=en&prod=b1
Think I may have found a suitable amp:
http://www.bmm-electronics.com/Product.asp?Product_ID=4710
What do you think?
I reckon the electronics will probably come to something in the order of £150 to £200. I'll have to start saving the pennies!
http://www.bmm-electronics.com/Product.asp?Product_ID=4710
What do you think?
I reckon the electronics will probably come to something in the order of £150 to £200. I'll have to start saving the pennies!
The driver has a decent looking basket and nice size magnet, go for it! 
The amp looks good too, although with a LT you can never have enough power. The 700w version might be more suitable depending on how loud you want to listen, although once you get to those power levels with a single 12 you'll start to bottom out/fry the driver before you run out of amp.
I'd start by measuring the un-EQ'd driver in it's enclosure in room before you start building your LT, that way you'll have a better idea how much extension you need to add.
The amp looks good too, although with a LT you can never have enough power. The 700w version might be more suitable depending on how loud you want to listen, although once you get to those power levels with a single 12 you'll start to bottom out/fry the driver before you run out of amp.
I'd start by measuring the un-EQ'd driver in it's enclosure in room before you start building your LT, that way you'll have a better idea how much extension you need to add.
I would even argue that you don't use a classic LT cuircit, if you have the ability, and instead develop your own curve based on in room needs. A lot of time you can get better use of the driver without exceeding its limited if you don't apply the same level of extension that Linkwitz specifies. I mean you will notice that even applying 3 decibles of boost at 20hz and comparing to a reference at 100hz and 100 watts, you will need over 1000 watts at 20hz and be exceeding the limits of the driver. Even lowering that to 10 watts will require around 500 watts at 20hz and often are just at the limits of drivers.
I made a version of this woofer in WinISD based on some best guesses. This isn't accurate for sure without better numbers, but I took a TC Sounds TC-9 and revised its perameters to look like a woofer with a stiffer suspension and a higher fs, along with a lower xmax, as I would expect the xmax of that speaker to be more like 15mm rather than the 28mm of the TC-9. In a .35 cubic foot box this theoretical woofer would take 5 watts to hit 100 decibles at 80hz, which is the crossover point I set. It is about the same down to about 60hz where it begins to rise. At 50hz it rises to around 60 watts, at 30hz its around 600 watts, and at 20hz it would require 1800 watts to produce that 100 decibles. Mind you by 30hz it is also exceeding xmax. Now the argument that most give, and a valid one it is, would be that real life music or movies would never see that, as that can only be replicated with test tones. However, my experience with eqing a subwoofer has shown that you reach the limits far more often than these proponents would suggest, especially with more modern electornic music and movies with artificially loud low frequency effects and sounds. I have listened to Techno that has nothing more than warble tones and pink noise going in the background which would easily exercise these limits. Of course, even 100 decibles is a bit loud for normal listening, so again, the reality of this is a little different. I feel this is probably a decent enough replication of the results achieved by monitor audio because the response and output does work with the numbers they give. This sub would peak within its limits at around 98 decibles anechoic using a 700 watt amp. That is very reasonable for a factory built subwoofer in a sealed box.
Increases the box size to 30L (1 cubit foot), does improve the response some but hurts the power handeling from a mechanical stand point. You will exceed xmax more easily. It becomes a trade off on where you want the response to be best, and probably using the larger box would be smart, as it would improve the output to more like 103 decibles at 50hz and 99db's at 20hz, not really bad at all.
Increases the box size to 30L (1 cubit foot), does improve the response some but hurts the power handeling from a mechanical stand point. You will exceed xmax more easily. It becomes a trade off on where you want the response to be best, and probably using the larger box would be smart, as it would improve the output to more like 103 decibles at 50hz and 99db's at 20hz, not really bad at all.
Ah scratch those numbers, they are a little off, I just noticed the vas was only 11 liters, that really reduced the efficiency a lot. Brought output down to in the mid 90's, made it less efficient, but did improve the mechanical limits a bit. I think it really will need quite an amp to work its best. None the less, in room, real life, it will work pretty well, but I still recomend avoiding the amount of boost that the LT applies and doing so based on the needs in room.
Modeled response in UniBox in a 30 Litre box gives and F3 of 68 Hz and a Qtc of 0.613:
Excursion at 350 Watts:
What I want is a sub with a F3 somewhere between 30 and 40 Hz (perhaps 35Hz or so) and a Qtc between 0.5 and 0.7. This would seem to give a maximum output of about 103dB on the flat part of the graph, although I'm not likely going to have any sub play quite that loud without upsetting the neighbors.
I'll have to do some more home work, but I'm still leaning towards a Linkwitz Transform solution.
What do you think of my plots?
An externally hosted image should be here but it was not working when we last tested it.
Excursion at 350 Watts:
An externally hosted image should be here but it was not working when we last tested it.
What I want is a sub with a F3 somewhere between 30 and 40 Hz (perhaps 35Hz or so) and a Qtc between 0.5 and 0.7. This would seem to give a maximum output of about 103dB on the flat part of the graph, although I'm not likely going to have any sub play quite that loud without upsetting the neighbors.
I'll have to do some more home work, but I'm still leaning towards a Linkwitz Transform solution.
What do you think of my plots?
Selling
If anyone is interested, the subwoofer driver mentioned in this thread is for sale on eBay. I don't really have the finances to make optimal use of this driver and could really do with the money. If there is someone out there (in the UK) who has the time and money to make good use of this driver, the auction is on www.ebay.co.uk and the auction number is 180124445232.
Thanks again to all of those who contributed to this thread.
If anyone is interested, the subwoofer driver mentioned in this thread is for sale on eBay. I don't really have the finances to make optimal use of this driver and could really do with the money. If there is someone out there (in the UK) who has the time and money to make good use of this driver, the auction is on www.ebay.co.uk and the auction number is 180124445232.
Thanks again to all of those who contributed to this thread.
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