Cheap Sub for College - AVS Forum
View Poll Results: What would you choose?
DIY cheap Dayton 5 71.43%
Craigslist cheapo <$100 Sub (definitive tech. procinema pro-sub 100) from an old HTiB 0 0%
Other 2 28.57%
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post #1 of 25 Old 07-26-2012, 01:18 PM - Thread Starter
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I recently purchased a Denon AVR-1612, 2 BIC HT-6T towers and 1 BIC FH6-LCR Center for a 3.1 setup in my college apartment. I still need the sub, and it was suggested that I build one if I'm looking for some low end extension on a budget.

Some people threw together some WinISD plots with a cheap 10" Dayton SD270A-88 and a 25 W Dayton plate amp from P.E. Roughly a 3ft^3 box (after bracing) tuned to 25 Hz looked surprisingly good in all regards. The only issue I had with it was the amp did not have an auto on feature. The 70 W Dayton plate amp does have the feature, but WinISD shows that my cone excursion is going to go to 8.5mm (xmax is 6mm) and I'm worried about destroying the driver (yeah it's only $40 but I'm on a budget here)!

Could I still purchase the 70 W plate amp and turn the gain down about half way? It's not that simple is it? Does anyone have any other suggestions that might help? For your convenience I've included the Driver info just in case you'd like to do some modeling: Dayton SD270A-88
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post #2 of 25 Old 07-26-2012, 03:09 PM
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You can use the 70w, and yes, the correct gain will be fine, but gain does not work like that. The gain knob controls the amplification relative to the input signal level, not the "maximum power" that it can put out. So you'd need to figure out where the gain would need to be. That Def Tech sub should be very good for <$100.

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post #3 of 25 Old 07-26-2012, 06:27 PM - Thread Starter
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Originally Posted by DonoMan View Post

You can use the 70w, and yes, the correct gain will be fine, but gain does not work like that. The gain knob controls the amplification relative to the input signal level, not the "maximum power" that it can put out. So you'd need to figure out where the gain would need to be. That Def Tech sub should be very good for <$100.

I would assume that the gain would be logarithmic, but I can't be sure. I guess I could just play around with it and try to hear where the distortion starts to begin and then back off a bit. OR I could just get the 25 W amp and deal with turning it off. rolleyes.gif

I thought the Def Tech looked awesome until I realized it was from a HTiB, not at all like the ones they currently sell independently. I'm pretty sure it won't get down anywhere near 25 Hz with decent spl. I'm going to contact the seller and maybe go test it out with some test tones.

WinISD is putting the DIY pretty flat at 102, and 97 at 25 Hz. I fell like that's pretty awesome considering it would cost about $100 including the enclosure, driver, port, and 25 W plate amp. The only thing I would worry about then is the cone excursion below 20 Hz. Obviously this driver/sub isn't going to dig that low, but I'm worried about a low frequency signal damaging the driver.



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post #4 of 25 Old 07-26-2012, 06:38 PM
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Exceeding xmax by 2.5mm will not damage the driver, you will just have excessive distortion. You're not going to get extension to 25hz from any commercial $100 sub, even used.
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post #5 of 25 Old 07-26-2012, 06:44 PM - Thread Starter
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Originally Posted by Jay1 View Post

Exceeding xmax by 2.5mm will not damage the driver, you will just have excessive distortion. You're not going to get extension to 25hz from any commercial $100 sub, even used.

Exactly what I was thinking, so I would probably be better off building this one modeled above. What are your thoughts on the excessive cone excursion under 20 Hz? I know that it won't play that low, but will signals still get passed to it? If so, will it cause some damage/distortion?

Keeping air velocity under 15m/s should be fine right? I'm using a 3 inch x 8inch flared port.
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post #6 of 25 Old 07-26-2012, 06:58 PM
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Add a 20hz 2nd order (butterworth) high pass filter to your model, that's what the amp will have on it
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post #7 of 25 Old 07-26-2012, 07:40 PM - Thread Starter
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Thanks for the help! I'm going to order everything tonight and hopefully start building the box over the weekend! Should be able to mooch my neighbors router for a few minutes to make the cutouts biggrin.gif
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post #8 of 25 Old 07-26-2012, 09:09 PM - Thread Starter
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Oh, I didn't know that they have that on there. It should really be in the info on P.E.. In that case I don't have to worry about the low frequency issues, just the wattage problem. Most likely I'll just get the 25 W and be done with it. P.E. is down until the morning so I can't buy anything until then mad.gif
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post #9 of 25 Old 07-26-2012, 09:22 PM
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The 70 watter will be capable of about 4.5db more output, so it's a better buy if you can swing the price difference.
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post #10 of 25 Old 07-26-2012, 09:38 PM - Thread Starter
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That's a good point. I saw that, I but my only concern was that I didn't want a lot of distortion and I didn't want to damage the driver. If I get the 70 W amp and turn it down.. I won't be getting that 4 dB will I? More like 1 which wouldn't be audible..At this point, the money is really not the issue.
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post #11 of 25 Old 07-26-2012, 09:46 PM
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You can always look at a stronger driver too if the budget isn't locked. An infinity 1260 can be had for $60 from amazon. It has over twice the xmax
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post #12 of 25 Old 07-26-2012, 09:50 PM - Thread Starter
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Ok great I'll look at a fee on Amazon tomorrow and compare. Really I'd like to stay under $100 but if I can't then I'll expand the budget. Thanks for your help! I'll post again after doing some more research
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post #14 of 25 Old 07-27-2012, 12:53 PM
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Quote:
Originally Posted by anuj1450 View Post

...my only concern was that I didn't want a lot of distortion and I didn't want to damage the driver...
Actually, those two go together - driver damage sounds very bad! If you're sensitive enough to distortion, you'll never get close to damage, as HD goes way up at extreme excursionis, and HD from a sub is highly audible (20Hz 3rd harmonic is 80Hz, 5th is 320Hz).

That said, be careful who gets to twist the knobs as college students are not known for their good judgement!

HAve fun,
Frank
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post #15 of 25 Old 07-27-2012, 02:09 PM - Thread Starter
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Any thoughts on the Infinity Reference 1262w instead? It is dual voice coil and I can get a damaged box (good driver condition) for $27 shipped. My concern would be powering it because it's either 2 ohm or 8ohm. Would the dayton 70 w amp be sufficient?
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Actually, those two go together - driver damage sounds very bad! If you're sensitive enough to distortion, you'll never get close to damage...That said, be careful who gets to twist the knobs as college students are not known for their good judgement!

Is it going to be extremely obvious when there is some distortion? I'll make SURE my roommates don't turn it up any more than it should be tongue.gif
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post #16 of 25 Old 07-27-2012, 03:43 PM
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When you're dealing with really low power, a small change actually makes a big difference. Sure you could run it 8 ohm and get 45 watts from the sa70. Run the models and see what the difference is, and if it's worth a $30 difference.
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post #17 of 25 Old 07-27-2012, 10:12 PM - Thread Starter
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DANG! mad.gif I just ran the models after watching the opening ceremony.. I was dead set on that infinity reference 1262w used because it was just damaged box and a steal at $27 shipped. It's not there anymore just 2 hours later! Oh well, I'll have to keep looking for an alternative driver to the Dayton. I'm just not comfortable with it's high excursion even with such low wattage. Such a shame considering the infinity 1260w and 1262w modeled beautifully in a small 2.619cuft ported box. It would have been the perfect find in this range! mad.gif
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Originally Posted by Jay1 View Post

You can always look at a stronger driver too if the budget isn't locked. An infinity 1260 can be had for $60 from amazon. It has over twice the xmax

Do you have any other suggestions of drivers in that price range? You hit the infinity right on the money. If I can find one refurbished or open box I'll get it (right away this time). I'm really trying to have some self control and keep this on budget though! biggrin.gif ~$100 for the driver and amp is optimal.
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post #18 of 25 Old 07-28-2012, 10:01 AM
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I had the very similar Dayton SD270-88 (older shielded version) in a 3 cuft box tuned to around 28hz. I had it running off a 100 watt amp and you can tell when the driver starts to run out of excursion and reach its limits, but I doubt you could cause any real damage to it with just the 70 watt amp. At most it starts to distort when it runs out of linear travel.

Right now mine sits in a 1.4 cuft enclosure tuned to 32hz with the dayton 70 watt plate amp behind my TV, that setup I never worry about.
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post #19 of 25 Old 07-29-2012, 10:17 AM
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Quote:
Originally Posted by Jay1 View Post

Add a 20hz 2nd order (butterworth) high pass filter to your model, that's what the amp will have on it

The problem with doing that is it will attenuate the signal well above the filter point. I modeled using a filter like this on my ported subs, at 30hz; it changed my entire output curve above the cutoff. I decided that without an eq it would be worth it to risk it.
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post #20 of 25 Old 07-29-2012, 10:22 PM
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Originally Posted by JohnnyWash1 View Post

The problem with doing that is it will attenuate the signal well above the filter point. I modeled using a filter like this on my ported subs, at 30hz; it changed my entire output curve above the cutoff. I decided that without an eq it would be worth it to risk it.

Those plate amps come with a filter. Unless you open the amp up and remove the circuit, it's going to have that effect whether you model it or not.
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post #21 of 25 Old 07-29-2012, 11:15 PM
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I'm not using a plate amp, so I don't have that problem.
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post #22 of 25 Old 07-29-2012, 11:18 PM - Thread Starter
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Quote:
Originally Posted by JohnnyWash1 View Post

The problem with doing that is it will attenuate the signal well above the filter point. I modeled using a filter like this on my ported subs, at 30hz; it changed my entire output curve above the cutoff. I decided that without an eq it would be worth it to risk it.

I'm not modeling the sub to make the graph look pretty, but to see what it might actually do. (ok fine it has to look nice and curvy too tongue.gif)
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Originally Posted by Jay1 View Post

Those plate amps come with a filter. Unless you open the amp up and remove the circuit, it's going to have that effect whether you model it or not.

It's a good thing that they do too!

I think I'll "splurge" and get the 70 W and the infinity reference 1260w driver. Do you know what the actual usable length of this port would be? It's kind of odd shaped (non uniform diameter throughout and it also has massive flares) http://www.parts-express.com/pe/showdetl.cfm?Partnumber=269-165

Also, do you have any opinions on "car" amps. I saw some good deals on some 300w rms ones but I'm reluctant to even look at those.
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post #23 of 25 Old 07-30-2012, 10:28 AM
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Quote:
Originally Posted by JohnnyWash1 View Post

I'm not using a plate amp, so I don't have that problem.

We're talking about plate amps here wink.gif
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Originally Posted by anuj1450 View Post

I'm not modeling the sub to make the graph look pretty, but to see what it might actually do. (ok fine it has to look nice and curvy too tongue.gif)
It's a good thing that they do too!
I think I'll "splurge" and get the 70 W and the infinity reference 1260w driver. Do you know what the actual usable length of this port would be? It's kind of odd shaped (non uniform diameter throughout and it also has massive flares) http://www.parts-express.com/pe/showdetl.cfm?Partnumber=269-165
Also, do you have any opinions on "car" amps. I saw some good deals on some 300w rms ones but I'm reluctant to even look at those.

Measure the length of the port from the half way point on the radius of both flares to get your approximate length. The overall length of that port is 11.25", so try modeling with a much shorter length, like 9" to see if you would still be okay as a guestimate. I dont know anything about using a car amp at home.
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post #24 of 25 Old 07-30-2012, 11:24 AM
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You would need a power inverter to run a car amp at home.
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post #25 of 25 Old 08-07-2012, 07:18 PM - Thread Starter
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Quote:
Originally Posted by Jay1 View Post

We're talking about plate amps here wink.gif
Measure the length of the port from the half way point on the radius of both flares to get your approximate length. The overall length of that port is 11.25", so try modeling with a much shorter length, like 9" to see if you would still be okay as a guestimate. I dont know anything about using a car amp at home.

My main concern was actually the non uniform diameter. When it comes down to it, it's not going to make a huge difference so I'll just get it and it will have to do.
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Originally Posted by JohnnyWash1 View Post

You would need a power inverter to run a car amp at home.

Yeah I abandoned that idea as soon as it came into my head. It would be a headache with the inverter and the large amp that I'd have to find a spot for.


I got the infinity 1260w and all the MDF cut to make an 18.75" (external) cube but I need to route the holes for the driver, port, and amp. After the bracing, port, etc.. I'll be around 2.5ft^3, maybe a little more. I'm just waiting on the SA70 and I'll be all set.

Again, thanks for all the help and I'll let you guys know how it turns out!
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