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Bill 3

I'm not an expert on this but looking at the graphs you have posted, the RP-L18 and the IXL18 look to have better transfer functions and max SLP curves than the FiCar - that is, if flatter is better. :dunno: Can someone please explain the impact/relevance of the transfer magnitiude function?

Higher output at tuning just means it's louder down lower (if the tuning is low). As far as I'm aware, most people seem to find a gradual rise in SLP output (in room, not anechoic) as the frequency lowers, to be more pleasing than either flat or dropping SLP - hence the desired house curves many people shoot for with equalisation - check out the BFD forums. Given room gain, the gradual drop-off from the driver/box is compensated by the gradual increase in room gain as the frequency lowers. So less role-off at lower tuning (flatter SLP curves) is usually considered better and so more desirable. By the way, lowering the receiver volume makes the bass drop at lower frequencies more pronounced so if you like to listen at lower listening levels, the higher output at lower frequencies is even more desirable. Hence the loudness buttons fitted on amplifiers years ago, which gave treble/bass boost for when listening at lower volumes.
 

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Discussion Starter #22
BlueeyedFrog, I like the thought of the higher output at lower frequencies. I like to be able to feel the bass at lower levels. When just hanging out and talking while listening to music and be able to notice the impressive bass without it sounding overbearing would be great.

Ricci, I double checked the numbers I had input for my Fi driver and it appears that I had entered the Fs in the Qms spot (23.8 is a lot different than 5.73) plus I listed the Re as 1.4 where it should have been 2.8 (2 coils).

All of the sudden, I am all over the Fi. It nearly resembles the SS, only better in some areas. Boy does it like volume though. ****, I was hoping to find a driver close to the SS only in a smaller volume so I could use the 24" dia tube.
 

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I have heard that output at sub-20hz has little relevance for music listening, unless of course you are listening to pipe organ music or similar. It's probably more relevant for movies. Modern music kick drums are around 30hz I think (or 40-60hz?) but don't quote me...

If you have the space then it sounds like the FiCar is the winner however, if not, the Mach5s will fit in 24" sonotubes of a managable size.
 

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Discussion Starter #24
Good point on the music. But I guess the same applies to "casually" watching something with others, I think it wold be great to have a little rumble in there without having volume, of course what I am refering to here is probably in the higher frequencies also.

Anyway, I think the 24" tubes would be a better fit, the 30"ers will fit. I will also try and post new graphs with the re-done Fi's tomorrow so you can see what I am refering to.
 

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550 litres is just too big for the Mach5s and yes, the lower peak "swish" is not desirable. Rather, you want a gentle slope which will be boosted to flat, or better, a nice house curve, with the aid of room gain. Steve Callas helped me with the design of my next subs using the Mach5s:
Not sure about 30"+ ports. This puts the first port resonance pretty low right? I have heard a good rule of thumb is to put the resonance >300Hz, this limits you to ~21".
 

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Here's the nieghborhood I'd be looking at for each driver:

Mach5 = 365 liters with three 4" ports 32" long each, yielding ~15hz tune

FiCar (dual 2ohm coils) = 625 liters with one 8" diameter port 26" long, yielding ~13.6hz tune

SS (dual 2ohm coils) = 600 liters with one 8" port 29" long, yieldng ~13.5hz tune


Tranfer function magnitude is just a static FR - use it in the beginning of a design to help narrow down volume and tuning. Once you like the FR, add some power in the signal section, and then tab over to spl, excursion, and port velocity to make sure everything looks ok. It doesn't matter if your excursion goes over claimed xmax with high power, I was wrong in my early LLT explanation about amp limiting. Just as long as you aren't already grossly crossing xmax limits before reaching acceptable output levels, you will be fine. All three options should be able to get you to 115db peaks indoors using a dedicated EP2500 without much trouble as long as you aren't sitting extremely far away from the sub.
 

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Discussion Starter #28
Ok guys, here are the graphs with the correct numbers for all drivers (I hope), Using the volumes and frequencies that Steve suggested and using 750W (due to a single Behringer EP2500).

Thanks for all the help and suggestions and corrections.

Bill
 

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Discussion Starter #29
Here we go :spend:

I will not add up the constants like amp, MDF for endcaps, and the rest of the building supplies. Btw, only 24" and 30" are the only sizes available locally (no 26" or 28").

SS: 30" x 12' Sonotube ($140) + 2 of RL-p18 D2 ($780 plus ship or $860) = $1000

FiCar: 30" x 12' Sonotube ($140) + 2 of Q18 D2 ($618 inc ship)= $758

Mach5Audio: 24" x 12' Sonotube ($95) + 2 of IXL-18.4 ($250 inc ship)= $595

So, if you ignore the $ difference and not worried about size, would you prefer the SS with the SPL advantage below 20Hz or the Fi with the SPL advantage above 20Hz.

Looking at $, to me the Fi offers more bang for the buck over the SS, the question now becomes - does the lower tuning and higher overall SPL gives the edge to the Fi over the Mach:scratch: The size advantage is nice, but not really that big of deal and the $ difference isn't a deal breaker either. Sure wish I could audition.
 

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I think the Fi Q hits the sweet spot - you're getting more displacement than the Mach5, are able to dig a bit deeper, use more port area, and have a more damped driver. Keep in mind that the rolloff that shows up with your Fi model is a bit exagerrated due to the way WinISD models inductance and because your vertical scale is quite small. When built and measured in real life, all 3 options will have a relatively flat FR across the spectrum.
 

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I think the Fi Q hits the sweet spot - you're getting more displacement than the Mach5, are able to dig a bit deeper, use more port area, and have a more damped driver. Keep in mind that the rolloff that shows up with your Fi model is a bit exagerrated due to the way WinISD models inductance and because your vertical scale is quite small. When built and measured in real life, all 3 options will have a relatively flat FR across the spectrum.
For what it's worth...I built my sonosub with the Q18 and have been extremely happy... Here's my build thread:

http://www.avsforum.com/avs-vb/showthread.php?t=938083

Here's my measurements thread
http://www.hometheatershack.com/forums/rew-forum/8294-2nd-time-around-measurements.html



Matt
 

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Discussion Starter #32
Thanks for the input guys. I have more or less decided on the Fi and your input confirmed it. Kind of waiting on Scott (Fi) to get back with me - hopefully soon since it looks like I will be sending $ his way.

Looks like other than a few building materials I will get locally, I need to get an amp bought. Probably going to be Guitar Center online for a refurb EP2500.

Looks like I am copying Mattlock. :T

Thanks again,
Bill
 

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Thanks for the input guys. I have more or less decided on the Fi and your input confirmed it. Kind of waiting on Scott (Fi) to get back with me - hopefully soon since it looks like I will be sending $ his way.

Looks like other than a few building materials I will get locally, I need to get an amp bought. Probably going to be Guitar Center online for a refurb EP2500.

Looks like I am copying Mattlock. :T

Thanks again,
Bill

You won't be dissapointed....look forward to seeing your progress...you may even convince me to build a second twin to sit beside my first one.. :bigsmile:
 

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Discussion Starter #34
Q18's and EP2500 have been ordered. Sonotube and MDF have been aquired. No turning back now. :spend:
 
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