Hi,
I am planning a to build for a separate woofer module, to be used as the woofer in budget a 3 way system. The plan is to cross from the midrange using passive line level XO, at about 500Hz, and then hand over to the sub at about 60-80 Hz.
Being a budget project, the midrange and tweeter will be using the Madisound RB kit, in a separate enclosure. I'm planning to use the NHT surplus woofer NPT-11-084-2 for the woofers. The T/S parameters are as follows.
Re 5.67
Fs 29.3
Qms 1.585
Qes 0.307
Qts 0.257
Vas 81.96
Cms 0.001081
Mms 27.3
diameter 172
BL 9.63
SPL 90.08
Zmax 34.9
Sd 0.02324
Xmax 6.0
Using WINISD, i simulated a closed box with 4 drivers (bought 8, since they are so cheap), and got a 50 litre box, with F3 at 80 Hz. Does that look about right? I'm just surprised that the F3 is so high, since the Fs of the drivers are 30 Hz.
Are these drivers suited for sealed alignment, or is bass reflex more suitable? I chose sealed for less time delay, and since i am using a subwoofer.
Thanks for comments and advice!
I am planning a to build for a separate woofer module, to be used as the woofer in budget a 3 way system. The plan is to cross from the midrange using passive line level XO, at about 500Hz, and then hand over to the sub at about 60-80 Hz.
Being a budget project, the midrange and tweeter will be using the Madisound RB kit, in a separate enclosure. I'm planning to use the NHT surplus woofer NPT-11-084-2 for the woofers. The T/S parameters are as follows.
Re 5.67
Fs 29.3
Qms 1.585
Qes 0.307
Qts 0.257
Vas 81.96
Cms 0.001081
Mms 27.3
diameter 172
BL 9.63
SPL 90.08
Zmax 34.9
Sd 0.02324
Xmax 6.0
Using WINISD, i simulated a closed box with 4 drivers (bought 8, since they are so cheap), and got a 50 litre box, with F3 at 80 Hz. Does that look about right? I'm just surprised that the F3 is so high, since the Fs of the drivers are 30 Hz.
Are these drivers suited for sealed alignment, or is bass reflex more suitable? I chose sealed for less time delay, and since i am using a subwoofer.
Thanks for comments and advice!
Come on guys, any advise for an aspiring newbie on a budget?
One more question:
Should i have 4 woofers on the front baffle, like a full height floorstander, or should i have 2 forward firing, and 2 rear firing in a half height enclosure, aka brute force baffle step correction?
I think brute force BSC should have better efficiency. Since i'm crossing at about the BSC corner frequency of 500 Hz, i should gain anywhere between 2-4dB ( max of 6dB in anechoic) with this setup.
What about tactile slam? I have a feeling 4 direct firing 8 inchers should give better slam. Hmm..
Cheers!
One more question:
Should i have 4 woofers on the front baffle, like a full height floorstander, or should i have 2 forward firing, and 2 rear firing in a half height enclosure, aka brute force baffle step correction?
I think brute force BSC should have better efficiency. Since i'm crossing at about the BSC corner frequency of 500 Hz, i should gain anywhere between 2-4dB ( max of 6dB in anechoic) with this setup.
What about tactile slam? I have a feeling 4 direct firing 8 inchers should give better slam. Hmm..
Cheers!
Moondog,
Would this 15 incher be able to keep up? I'm debating building this TL or a tapped horn for the greater efficiency. : ))
http://www.diyaudio.com/forums/showthread.php?t=112178
You mean 4 woofers, 2 front and 2 back firing? Is 80 Hz a good crossover between the woofers and the sub?
Thanks! Keep the comments flowing!
Would this 15 incher be able to keep up? I'm debating building this TL or a tapped horn for the greater efficiency. : ))
http://www.diyaudio.com/forums/showthread.php?t=112178
You mean 4 woofers, 2 front and 2 back firing? Is 80 Hz a good crossover between the woofers and the sub?
Thanks! Keep the comments flowing!
Johan,
I was thinking about that, but i read about brute force BSC, basically a bipole system. The front 2 woofers start diffracting around the front baffle and losing 3-6dB at about 500 Hz (depending on baffle width) at the same time as the rear 2 woofers diffract around the back baffle.
http://www.t-linespeakers.org/tech/bafflestep/intro-bds.html
However, since there is no output above 500Hz due to the low pass, maybe there is no 'step' in the frequency response due the baffle step. I was however also thinking about using the woofer module as a 'stand' for the midrange+tweeter enclosure.
You are probably right about the cleaniness of forward firing for vocals, and 'slam' which is part of the reason why i chose 4 woofers.
Bill,
I recalculated using AJ Sealed Designer ( used winisd previously) and got the same result for sealed - 50 litres, 80Hz F3. 4 drivers, multiplied VAS by 4...
The reason i chose sealed was for the better transient response, since i will be crossing from this woofer to a 15" TL sub at about 60-80 Hz.
Anyone know where i went wrong?
I recalculated using AJ Sealed Designer ( used winisd previously) and got the same result for sealed - 50 litres, 80Hz F3. 4 drivers, multiplied VAS by 4...
The reason i chose sealed was for the better transient response, since i will be crossing from this woofer to a 15" TL sub at about 60-80 Hz.
Anyone know where i went wrong?
FWIW, using WinISD Pro's slightly adjusted specs, my most accurate calculator suggests an empty (net) ~42.658 Vb/0.707 Qtc/86.75 Hz F3, Fb for four which considering the low Qts seems reasonable to me.
Adding enough series resistance to double Qts trades 6 dB of efficiency for a ~43.47 Hz F3, Fb/0.707 Qtc albeit at the further expense of a 278.101 L cab.
Bottom line, a fairly large reverse tapered TL (TQWT) is typically the best trade-off between size, F3, SQ for low Qts drivers if horn loading isn't an option.
GM
Adding enough series resistance to double Qts trades 6 dB of efficiency for a ~43.47 Hz F3, Fb/0.707 Qtc albeit at the further expense of a 278.101 L cab.
Bottom line, a fairly large reverse tapered TL (TQWT) is typically the best trade-off between size, F3, SQ for low Qts drivers if horn loading isn't an option.
GM
You're welcome!
If you look up the basic box formulas you'll see that Qts dominates which makes sense if you think about it. A strong motor (low Qts) has a naturally high F3 referenced to Fs, so with a maximally flat alignment having a Fb = F3, the cab has to be small relative to its Vas to push the driver's Fs up to its F3. Conversely, a weak motor (high Fs) will have a low F3 referenced to Fs, so needs a large cab referenced to its Vas to keep from raising the driver's Fs much.
GM
If you look up the basic box formulas you'll see that Qts dominates which makes sense if you think about it. A strong motor (low Qts) has a naturally high F3 referenced to Fs, so with a maximally flat alignment having a Fb = F3, the cab has to be small relative to its Vas to push the driver's Fs up to its F3. Conversely, a weak motor (high Fs) will have a low F3 referenced to Fs, so needs a large cab referenced to its Vas to keep from raising the driver's Fs much.
GM
Quote "4 woofers is overkill, "
well if they are so cheap and already purchased why not go for the front and rear box, brute force baffle step correction has its advantages, and to maintain the nominal impedance 4 woofers in series / parallel is the obvious way to go as 16 and 24 ohm drivers are few and far between these days.
well if they are so cheap and already purchased why not go for the front and rear box, brute force baffle step correction has its advantages, and to maintain the nominal impedance 4 woofers in series / parallel is the obvious way to go as 16 and 24 ohm drivers are few and far between these days.
Actually, my intention is for 2 woofers per enclosure. BUT, Ridley has a 80 dollar minimum order, and a 30 lbs max shipping weight per box... i can't hit 80 dollars with 4 woofers, (these things are too darned cheap
), can't fit 6 woofers in one box, so what the heck...Will probably build it with 2 first. A 4 woofer forward firing tower is pretty initimidating, size wise. Will probably save the remaining 4 woofers for my next upgrade. Perhaps a line array tweeter and midrange will be able to keep up with 4 woofs.
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Did a quick sim in Excel for the PLLXO... Only added algebraically, not sure how to calculate phase response for the LP and HP filter for vector summation. Will have to work on it some more.
Also did not take BSC into account. The woofer probably need to be 2-4 dB 'hotter'.
Also did not take BSC into account. The woofer probably need to be 2-4 dB 'hotter'.
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Another sanity check: This woofer has Qts of 0.257 and EBP about 95 iirc.
What major trade offs are there by using it in a small sealed enclosure, instead of a bass reflex like it was designed to live in?
Would efficiency be a problem? Its 90dB/W, will it have problems keeping up with the mid and tweeter, which are about 90dB/W? I lose about 5dB with the PLLXO, and i need another 2-4dB extra for BSC.
Hmm..
What major trade offs are there by using it in a small sealed enclosure, instead of a bass reflex like it was designed to live in?
Would efficiency be a problem? Its 90dB/W, will it have problems keeping up with the mid and tweeter, which are about 90dB/W? I lose about 5dB with the PLLXO, and i need another 2-4dB extra for BSC.
Hmm..
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