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Discussion Starter #1
I'm looking at assembling a sub for the Grandkids. All HT. It doesn't have to be perfect. I have a 1.8 ft box in hand along with a 300W Bash amp. I have a plan to use a Dayton 12" HO with Fb and F3 around 28Hz.

So, now I am wondering how the Dayton 12" HF or HO will work in that box if I seal it. I can see that low frequency performance will depend on where and how much boost is applied from the amp. There will be no other equalization available.

The problem is I don't know how to model the boost in UniBox and have no experience with sealed subs. Can you recommend a boost setting and tell if this has the possibility of remaining flat into the low 20's?
 

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I doubt a sealed 12 is going to stay flat down into the 20hz range at any significant volume level unless you have a REALLY nice house curve. Down to the high 20s probably is do-able when accounting for room gain.

What size room are you putting it in and what volume levels are you looking for?
 

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Discussion Starter #3
Large, open room. Unsophisticated listeners. Low to moderate volumes employed. Flat to 30Hz @ 100dB @ 15' will be more than they have ever experienced. If they ever get wise, their daddy can buy them a real HT sub!

I think the ported HO @ 28Hz will be OK. It will probably do a little better with room effects. I'd just like to get lower if I can. What about boosting the ported box?
 

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Discussion Starter #5
Thanks Mike. It's nice to see all of them in one chart. I guess I'll stick with the ported.
 

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Thanks. I did some remeasuring. The box actually has 1.75 ft of free internal space. I'm looking at 2 x 2 1/2" ports 16-1/4" long. Would you mind looking at what happens with that and where to put the filter? Lemme know if you see something better.

Forgot to add that this is using a 115W amp I also have.
 

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Discussion Starter #9
Sorry for the confusion. I had another look at the box and discovered that it was slightly smaller than I first calculated. The volume I stated does have deductions for sub, ports and amp.

I just tossed in the 115 amp because It may have enough power and I wanted your advice on the filter in case I use it. I didn't think it through very well.

It may be better to just skip the 115W amp because the boost is separate from the filter in this amp (Foster WF-100) and it doesn't seem to model like a typical amp. I'll try to explain so as not to leave ya hanging.

There is a separate boost section in the amp. A variable resistor controls the slope of the boost curve. You can adjust the slope between 1.2 and 7 dB per octave. It peaks between 30 and 40 Hz depending on the amount of boost. It can be totally disabled, too.

The filter is a 3rd order Sallen-Key (18dB/octave) set flat to 30Hz. It is easily converted to a 2nd order filter (12dB/octave) and there is a calculator to determine adjustments by changing 2 resistors. Sorta like the more common amps.

You can enter whatever you want for freq and gain (even minus values) instead of being limited to choosing a few settings from a table. Seems pretty flexible.

I'll send you detailed info if you want to play with it.
 

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Orange, green and pink are all 1.75 cu.ft with two 2.5" ports 16.25" long. Tuning is 28.6 hz.

Pink is the Foster WF-100 with a HPF at 30 hz.

Green is the Dayton SA-100 amp with a HPF at 18 hz.

Orange is the Bash 300 amp with the factory HPF. Power input is limited to 140 watts, above that port noise is an issue with the two 2.5" ports.

White is 2 cu.ft. tuned to 25 hz with two 3" diameter ports and the Bash 300 with the factory HPF. Xmax is reached with 300 watts.

Amps Comparison.JPG
 

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Discussion Starter #11
Mike, I'm overwhelmed by the assistance you provide. Can't thank you enough.

I like the 2 ft box, but I have a store bought 1.75 box in hand. It was supposed to have close to 2.5 ft internal, but must have shrunk during shipping. This is a salvage effort and not something I would have planned from the beginning.

I guess the foster amp will look similar to the SA-100 if I move the HPF to 18Hz.

Do you think the SPL attained with 115W will be OK for HT at moderate listening levels? I'd like to save the bash amp for a more worthy project.
 

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George, here's a real world measurement to give you more food for thought. Sub is a 315HO in 1.2 ft^3 gross sealed, although it does have a piece of R19 covering one wall...Q should be in the mid .6 range. Amp is an unmodified BASH-300. Mic is about 14' from the sub in a 22'x20'x9' family room that also has an 18' high foyer+stairwell+cat walk where one wall should be. Acoustic space also opens onto other rooms...you get the idea, likely not getting a lot of help from the room. The mic is also at least 5' from the nearest wall, roughly ear height from the floor. I tagged the 18Hz point to show where the rumble filter clearly started doing it's job. As you can see, it's still quite capable down to 20Hz despite the large space.

I ran this sweep to 500hz. The xover is supposed to be at 150Hz (small satellites), despite what it looks like here. Even though I had the left main completely disconnected, I discovered the crosstalk on this particular receiver (a $100 Black Friday special Pioneer) is so poor that the sweep tone was still clearly audible at a reduced level in the RIGHT main. I'm guessing there was some phase cancellation going on that produced the drastically reduce average SPL above 40hz or so. In normal listening, it doesn't sound anything like this sweep would suggest it does.

Comparing models, the 315HF in 2 ft^3 sealed (add a bit of stuffing to your 1.75 box) should have similar extension and a bit more output across the board using the BASH-300. With the BASH300, the 315HO is amp limited in 1 ft^3 while the 315HF could theoretically be pushed past Xmax (not Xsus) at full power around 22Hz.

-Brent
 

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I found another measurement that I took at 3' from the 315HO. Mic was probably 2' from the floor...however low my tripod will go. You can clearly see the 150Hz xover now; looks like the phase cancellation from the channel crosstalk doesn't show up at this distance. Level would have been reduced from the 14' measurement to keep from overloading the mic.

-Brent
 

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Discussion Starter #15
Thanks Brent. That helps. I don't have enough experience to visualize actual performance from sealed sub charts. My main focus is trying to get as much extension as I can from a box that is ill suited for the task. SPL level is not so important as long as it supports moderate listening levels.

So far, the HO is the champ without considering room gains. I read that sealed alignments drop off at a slower rate, so maybe things are closer than they look in this situation.

I had a rare flash of brilliance this AM. I'll put the driver in the (currently) sealed box with the 115W amp. Then I'll test it and play with the filter and boost settings. If it doesn't work, I'll add a port and/or enlarge the opening for the 300W amp.

I probably won't order the driver for awhile, so I'm still hoping to find something better than the HO for a similar cost.
 

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Thanks Brent. That helps. I don't have enough experience to visualize actual performance from sealed sub charts. My main focus is trying to get as much extension as I can from a box that is ill suited for the task. SPL level is not so important as long as it supports moderate listening levels.

So far, the HO is the champ without considering room gains. I read that sealed alignments drop off at a slower rate, so maybe things are closer than they look in this situation.

I had a rare flash of brilliance this AM. I'll put the driver in the (currently) sealed box with the 115W amp. Then I'll test it and play with the filter and boost settings. If it doesn't work, I'll add a port and/or enlarge the opening for the 300W amp.

I probably won't order the driver for awhile, so I'm still hoping to find something better than the HO for a similar cost.
The point of my measurements were to show you what even a little room gain would do for a sealed box. A smaller room yields more room gain; well, technically, it just starts rolling in at a higher frequency. In my case, the WinISD model says a 1 ft^3 sealed 315HO with BASH300 should be -13.5dB at 20Hz...from the in-room measurements, it appears to only be a few dB down at most, depending on measurement position peaks/nulls. While it's not a match for the 15" ported cabinet in my dedicated theater room, the little sealed 315HO acquits itself quite nicely, especially given its size and price. It's yet another example of the 80/20 rule. :)

The 315HF would appear to be a better match for your current box, if you go sealed. It's also currently on sale this month for $119 delivered, but for some reason, the HO is not. I think you'll be hard pressed to find a better driver for the money.

If you want to get the most out of a 315HO in that box, consider ordering one of AESpeakers' PR15-1050s. You'll save some of the volume consumed by dual ports and not have to worry about port noise from undersized ports. In 2 ft^3 with a stock PR15-1050 and BASH300, the 315HO models with an f3 of 21Hz. Room gain is in effect regardless of alignment so you'd probably be looking at a mild "house curve" with that tuning. At some point, I actually plan to do this with my 315HO. Already have the PR15 on hand, but have other projects in the queue ahead of it.

-Brent
 

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Discussion Starter #17 (Edited)
Thanks Brent. I went back and had another look. I see what you mean about the HF being better if I seal the box. I like the price, too. I feel more comfortable going sealed based on your comments. I guess I just had no basis to make any assumptions about the amount of room gain I could expect.

It looks different if I go ported. Seems like the HO might model better. The chart is prettier, anyway. I can get Similar F3's (around 28 Hz) if I model the HO at 28 Fb and the HF at 22. The HF has an uglier way of getting there. I don't know how much difference it will make in the listening experience.

It appears that any choice will do better than I hoped when room gain is considered. I guess I ought to just do something and not worry too much about it.

That PR is a swell ideal. It's not in the budget or the construction plans for this deal. I'd like to do one in the future.
 

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Discussion Starter #18
I ordered the HF driver and have a question about the correct RMS power to use when modeling HP filters with boost.

Don't ya lose some power when ya add boost in a HP filter? If I add 3dB boost in a 2nd order Butterworth, do I need to reduce power in the model by 1/2?
 

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I ordered the HF driver and have a question about the correct RMS power to use when modeling HP filters with boost.

Don't ya lose some power when ya add boost in a HP filter? If I add 3dB boost in a 2nd order Butterworth, do I need to reduce power in the model by 1/2?
Apologies for taking so long to get back...

To model a rumble filter with WinISD, you want to use a Highpass/SOS user specified. It's been a while since I've read up on filters, but by definition, I *think* a Butterworh has to be Q=.7071, which will result in no peaking...at least, that's how WinISD treats them. You can compare the two by selecting the "Transfer function magnitude (EQ/Filter)" graph, which will let you see just the response of the selected EQ curve. If you enter a HP/Butterworth, no matter what you do to Q, you won't get a peak or change in the slope.

You don't lose power with EQ. The amp is capable of what it's capable of. In theory, you could limit potential output when the source signal contains content within the EQ curve and outside simultaneously. If the driver can reach its excursion limits in the EQ'd range, the out of band excursion will be limited to less than Xmax, reducing max potential output at those frequencies. But, that's a highly theoretical condition.

In the most simple of explanations, if the source signal calls for 100 watts at 25hz and you have 3dB of boost, the amp will deliver 200 watts for that 25Hz note, assuming it's capable. However, you are correct that WinISD isn't sophisticated enough to normalize the output model based on EQ and user specified input power. If you set input power at 100 watts with 3dB of boost somewhere, WinISD will show you output and excursion models that assume the amp will deliver 200 watts when needed. You can do something of a visual normalization by overlaying otherwise identical models with and without the boost. I like to adjust the input power of the EQ'd model down to compensate for the boost...say 35 watts with 3dB of boost for a 100 watt amp. Obviously, this won't be 100% accurate since boost slopes down from a peak, resulting in the model boosting that 35watts by less the further from the peak, but it kind of shows you the worst case scenario for excursion limited output at your center frequency.

-Brent
 

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Discussion Starter #20
Thanks. Simple is what I needed. What about the ability of an amp to produce a momentary surge above rated power? Is this something that could/should be considered in the design?
 
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