So lots of options to go with, thanks.
Remember that I do not need a subwoofer that goes above 100hz as my EV studio 500s do very well above that plus my soround are also good down to 40hz (everything is crossed over at 80hz except my Studio 500s as I run them full range also.
My real focus is on the 15-80hz range something that will play nice with my PB13u
So lots of options to go with, thanks.
Remember that I do not need a subwoofer that goes above 100hz as my EV studio 500s do very well above that plus my soround are also good down to 40hz (everything is crossed over at 80hz except my Studio 500s as I run them full range also.
My real focus is on the 15-80hz range something that will play nice with my PB13u
Sorry, I'm giving you way more information than you really need to make a decision. It creates some confusion in the point I'm trying to make. Basically, subwoofer design is a balancing act. Certain factors are immutable, and so we use that information to balance the trade-offs in reaching our design goals. Your goal is a) to get the most distortion free output between 15hz and 80hz, and b) to achieve that using an existing box not designed for sub-40hz.
One of the often overlooked parameters in modeling is power consumption, basically the efficiency of the design at all usable frequencies. The reason is an assumption that there is just limitless amounts of power available. That you will hit XMAX long before you hit the power limits. While often true, the reality is that many subs today have enough XMAX to make power demands really high, unreasonably high for a domestic outlet (even a 20 amp outlet). Often these subs are powered by amps that are lucky to achieve 60% efficiency (regardless of the manufacturer's claims) which is a further problem.
That means you need to consider what you can achieve in your home with your power. That is why I look at the overall system power usage to achieve a given output, with the different designs EQed to have the same response shape. That helps me. I also look at how this relates to the mechanical limits like XMAX (but know that you do have a small margin beyond this of usable output). Next I look at the sub 20hz roll-off without exceeding my power or mechanical limits because room gain is a big factor.
Between a ported and sealed design, like we are proposing here, you are looking on the order of 10-20dB's more output efficiency for the ported design at the port tuning frequency. Somewhere around 25hz or so in my proposed approach. That is huge. However, that difference goes away by 20hz and by 18hz the sealed design exceeds the output of the ported design. That means that in room, the ported design will have no usable output below 20hz, but the sealed design will still have usable output down to 15hz and below. However, the sealed design is inefficient over its usable bandwidth, and in fact, the Dayton Reference sub (like all typical home sub drivers) are inefficient compared to the pro driver option above the tuning frequency. The Pro driver will achieve the same output with a lot less power. How much less you ask, well look:
Green: Dayton 15" Pro drivers ported 25hz
Red: Dayton Reference HO Dual ported 25hz
Blue: Dayton Reference HF Dual Sealed
*All EQed to have the same response
This is an unrealistic example used to make a point as the blue line, the sealed design, can't handle that much power. It's limited to 1600 watts RMS, but it could handle around 2000 watts peak, not momentary but with a musical signal. To achieve the same output as the ported designs, the sealed design needs many times more power than the other two. The HF and HO Reference drivers are not so different. This is the result of judicious EQ as the natural response of the sealed designs starts to roll-off a little at 80hz and the port tuning of the ported design prevents this. The ported design I'm showing here has a broad Q to the port tuning and a shallower roll-off, it isn't as peaky at tuning.
Ok so the sealed design is inefficient, but the ported designs show difference too. The area between 42hz and 80hz shows that the Pro design uses far less power. Around 250 watts vs 800 watts at the crest of the power curve. Here is why I think that is still important. While there is more energy demand at lower frequencies, there is more content at the higher low frequencies. Meaning the sub will be tasked with producing those midbass frequencies more often than the low frequencies, while the low frequencies will demand more power due to their being louder and more power hungry (as most subs are less efficient at LF's), it won't be as often. You might say that 250 watts vs 800 watts is no big thing because you have big enough amps, but in practice, 800 watts is a lot of power.
So you have a decision to make with all of this. The Dayton Reference series subs will have the flattest response out of the box. No EQ needed. They will both be less efficient than the Pro driver. The Pro driver will, even with EQ, use less power for a given response shape, but they will require EQ to get a flat response. Both ported designs will not have output down to 15Hz. It isn't possible with this box as it would require tuning much lower. But all is not lost. You can plug one of the two ports and, if you lengthen them to 20", will reduce the tuning into the mid-teens. Port noise will go up quite a bit, but we are still talking about 108dB at 15hz before port noise becomes unreasonable. This holds true for both the Reference and Pro driver. The pro driver remains the more efficient driver, requiring a lot less power above 45hz for a given output. All of these drivers are exceedingly clean with low distortion. However, I happen to think the pro driver will be even cleaner and have less power compression. It handles twice as much power and is more robust.
So if I were in your shoes, I would first figure out if you can extend the length of the ports from their current length to above 20 inches. I would make sure the elbows you find can fit and if there is sufficient length. My port models assume a straight port, 90 degree ports have more noise, so if there is sufficient room for using 45's instead of 90's to make a more gradual 90 bend, I would do that. I worry there is no room, but you should measure and see. Assuming the ported option is viable, I would then go with the pro driver. For $400 retail for the pair, it's a really good value. I believe it will exceed the output of your SVS sub at all frequencies by a lot, simply because it has so much displacement and is so much bigger.
If you can't make the ports work at all, there is no way to extend both of them, then I would go with the Reference driver's, either of them, and I would seal the ports. The HF will have a little flatter response and a bit more output down low. It's natural response will match the room gain of your room to provide a fairly flat response, so I don't think it will need a lot of EQ, but you could add a shelf filter to boost its low end. Normally I would tell you that the sealed designs have lower group delay, but actually, once the EQ and filters are applied, the sealed designs had higher group delay, which is because the port tuning didn't impact group delay until below 20Hz, and the high pass filters had far more group delay. That means the ported design really is the better sounding and better performing model in every objective measure I can simulate.
I also simulated this driver just to see what would happen if we added a lot more XMAX to the equation: http://stereointegrity.com/product/hst18-18-subwoofer/
Some might argue this is what you should use, but my simulations show that it's a) only better below 30hz, and b) not well suited to your box. It's too big and not possible to optimally tune. It will be boomy.
Im now thinking a sealed box may give me what I need as Im not looking for massive output just something to add to my room to smooth it out. My PB13U is sufficient however sometimes I feel its maxing out before I get the full potential of what I would like. My room is 14ft wide by 24ft long with an 8ft ceiling.
Ive got alot going on this week so not much time to do much with this project but I will check out porting options this weekend if I get to a plumbing store by my place.
Im now thinking a sealed box may give me what I need as Im not looking for massive output just something to add to my room to smooth it out. My PB13U is sufficient however sometimes I feel its maxing out before I get the full potential of what I would like. My room is 14ft wide by 24ft long with an 8ft ceiling.
Ive got alot going on this week so not much time to do much with this project but I will check out porting options this weekend if I get to a plumbing store by my place.
Yeah you can always make it an either or subwoofer. If you do that, I would consider the Dayton Reference HO as the better option. Two of those is best, the box would be too big for just one. Then you extend each port to be a total of about 20 inches long. To plug them, just stuff something in there. Most manufacturers use a plug of polyurethane foam around .5" larger than the port itself and about 4" to 6" long.
Once you decide what to do, I can help with any EQ and crossover changes needed (though with this particular setup, not much is needed).
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