| Dave Jones |
I'm still obsessing over this Qtc = .5 subwoofer thing.
Most of the popular subwoofer drivers have a Qts around .4 - the Shiva is an example. A closed box for such a woofer yielding a Qtc of .5 would have to be around 8 cubic feet or a bit less with stuffing. That's larger than I would prefer.
The Peerless 12 inch XLS woofer has a Qts of .21. It would require a box of only a little over 1 cubic foot. But that low Qts means the Fs => Fb goes up by a factor of almost 2 1/2 when you put it in the box.
A Qts somewhere in between would be preferable, assuming the Vas and Fs are low enough.
Is there no such thing as a subwoofer driver with a medium lowish Q, maybe around 0.3, and reasonable Vas and Fs numbers? If there is, I can't find it.
Would it be reasonable to use the Peerless with a resistor in series to raise the Q? |
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| 454Casull |
| You won't be able to satisfy that voice in your mind unless you get that magical 0.5, eh? |
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| mikee12345 |
LOL dave! u and ur qtc=0.5
IB several shivas and be happy!
The xls wont go well in a sealed box.
Think about building Dipole or IB
You can use RDO to achieve the Qtc you want.
see 'the cult of the infinitely baffled'
CHeers! |
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| GM |
>Is there no such thing as a subwoofer driver with a medium lowish Q, maybe around 0.3, and reasonable Vas and Fs numbers? If there is, I can't find it.
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Nope, you give away too much efficiency for most folks.
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>Would it be reasonable to use the Peerless with a resistor in series to raise the Q?
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At the signal level between the preamp and sub amp. If I'm going to trade efficiency for BW in a sub, then my preference is to mass load it and 'kill two birds with one stone' by lowering Fs and raising Qts.
2x mass based on published specs:
SPLeff'
81.777
n0'
0.0009456
Qts'
0.281
Qms'
5.233
Qes'
0.297
Fs'
12.799
mass ratio
2.000
m' (g)
406.459
Mass (g)
203.2290
Qts
0.199
Fs
18.100
Qms
3.7000
Qes
0.2100
Vas (L)
139.330
diameter (cm)
25.360
added mass (g)
203.230
GM |
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| SY |
| The old Peerless TA305F would have fit your requirements. I think that Zalytron still sells their knock-off version of it. Might be worth a look. I've got a couple of the originals (they're the drivers in the ugly TLs in my garage), but they need new surrounds, which I'll get to as soon as the 436 other things on my plate get done. |
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| roddyama |
| This Dayton moves the curve up about 2Hz from the Mark II, but in a 2.5cu.ft. box. Both have a sensitivity of about 87dbWm in the closed box. |
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| phase_accurate |
There are nowadys some long-excursion P.A. drivers available, and also some models that are somehow inbetween P.A. and HiFi like this one:
http://www.monacor.de/produkte/Prod...m?aID=3244&UG=0
Put it into a closed box and use an LTF to achieve whatever response you like.
Regards
Charles
P.S.: I like a Qtc of 0.5 as well ! |
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| Dave Jones |
| quote: | Originally posted by roddyama
The Dayton 12" Titanic Mark II gives you a Qtc of .5 in a 3.9cu.ft. box, an f3 of 44.7Hz, and an f6 of ~31Hz. |
That's not what I get. How do you figure? |
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| roddyama |
| quote: | Originally posted by Dave Jones
That's not what I get. How do you figure? |
BB-Pro. I set the Qtc to .5 and let the box size change as it will, and that's what comes out. BTW, Ql was (I'm at work now so I can't check) around 8 and the box was filled with absorbent material. |
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| Dave Jones |
By Jove, I think I've got it.
SAE 1204 in a 3 cu ft box. (2.88 nominal)
That yields a Q of 0.5, and if Mr. Colloms is right about room lift (for my room), it will be dead flat to 31Hz and -3db at 23Hz with no EQ.
The driver manufacturer is well regarded.
Someone please take a look at the picture, and tell me how to mount the thing in the opening.
http://www.apexjr.com/speakerstuff.html |
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| GM |
I've used this driver, it's well constructed. I didn't suggest it since I thought it was long gone from the marketplace and its inductance is too high for the app. IMO. It wasn't a big seller.
Good luck getting it flat to 31Hz in-room though unless the room is either extremely small and/or extremely well built due to its highish inductance.
GM |
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| planet10 |
| quote: | Originally posted by Dave Jones
Anyone know anything about a "SAE 1204" from Apex Jr? |
This is a driver built by Lambda for Stryke. I have one in a box and ChrisB has one in an 18" cube with a ParaPixen. It works really well. Like most drivers aimed at being subs it doesn't go all that high. i have yet to see any pictures on the net that do this beauty justice.
dave |
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| Dave Jones |
| quote: | Originally posted by planet10
This is a driver built by Lambda for Stryke. I have one in a box and ChrisB has one in an 18" cube with a ParaPixen. It works really well. Like most drivers aimed at being subs it doesn't go all that high. i have yet to see any pictures on the net that do this beauty justice.
dave |
What's a ParaPixen?
Now a real dumb question: How do you mount that driver? Do you just cut a hole in the baffle and drop the driver in from the outside? |
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| Dave Jones |
| quote: | Originally posted by GM
I've used this driver, it's well constructed. I didn't suggest it since I thought it was long gone from the marketplace and its inductance is too high for the app. IMO. It wasn't a big seller.
Good luck getting it flat to 31Hz in-room though unless the room is either extremely small and/or extremely well built due to its highish inductance.
GM |
Please elaborate on the inductance. I've heard that low inductance is a Good Thing, but I'm ignernt as to why. |
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| planet10 |
| quote: | Originally posted by Dave Jones
What's a ParaPixen? |
Steve @ ApexJr got his foothold with the DIY community by selling some 2K surplus ParaPix (Paramount Pictures) plate amplifiers. These are 2 x LM3875 with mono support circuitry. They cost $20 each + another $20 if you wanted a suitable power transformer. An excellent deal.
| quote: | | Now a real dumb question: How do you mount that driver? Do you just cut a hole in the baffle and drop the driver in from the outside? |
The SAE 1024? Yep that will work -- the same as most drivers... if you want to be real tidy you can do a rebate too.
dave |
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| GM |
>Please elaborate on the inductance. I've heard that low inductance is a Good Thing, but I'm ignernt as to why.
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"Inductance is that property of an electrical circuit which tends to prevent a change in current", or so says the textbook. Anyway, it causes the impedance to rise and the FR to rise to a point where the mass of the driver combined with the rising impedance causes a roll off of its HF response.
If you look at Rodd's FR plot, you'll see that it looks nothing like what WINISD predicts, except the box controlled 6dB/octave (0.5 Qtc) roll off below F3 of course. Since impedance is rising, the FR tracks it till it reaches its mass corner (2*(Fs/Qes)), then instead of flattening out it falls because the continued impedance rise keeps the motor from efficiently using the power available. With a much lower inductance, the FR is much flatter so the roll off is much more gradual on both sides of the mass corner, extending its effective BW and maximizing its transient response potential.
It does have the advantage of increased efficiency over a narrow BW compared to a lower inductance motor, but the tradeoff is increased harmonic distortion, so whatever transient response gains you get from a low Q alignment gets somewhat negated.
WRT getting a flat in-room response, theoretical room gain curves (which unfortunately are just 'pipe dreams' for most of the rooms I've measured) don't sum very flat with a typical medium-high inductance sub driver.
This of course doesn't mean it won't have enough output for the app. or sound obviously bad, just don't be surprised if you have to use considerable EQ to get a measured flat in-room response, and that if distortion measurements are made that they aren't what a 0.5Qtc implies.
GM |
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