Enclosure volume affects frequency response (frequency vs output).

 

One 18" SP4

2500watts

32hz tuning

 

port area - port velocity

50in^2 28m/s

60in^2 24m/s

70in^2 20m/s

80in^2 18m/s

100in^2 14m/s

120in^2 12m/s

 

Another thing to take into consideration is the average of your impedance is going to be substantially higher than what you're "wiring to," so it makes more sense to calculate port velocity with less power than 2500watts as your amp is rated to.

 

Note the units above are meters per second, not "f/s."

 

An enclosure that takes cabin gain into account may perform better than factory spec enclosure, but it may not either. It entirely depends on how well designed it is. Your question is similar to: "If I build a custom race car in my garage, will it be better than a mustang?"

Not sure we understand your question.  As for the enclosure volume, what about the WinISD plots is confusing?  Beware if anyone answers on SMD as the last I looked no one who understands jack ever posts there.

 

You are confusing to help.  You cite frequencies that are not near reality, built a box that has a rather reasonable frequency response in car but claim otherwise, and ask loaded questions with essay like answers instead of defining what about what you have isn't working for you.  It makes it very hard to help you.  It is obvious to me you've been reading on lots of forums and are rightfully confused as you haven't understood that much of the info you have read is wrong.  Then when you don't paint the full picture but instead fill in details that this info has taught you to share makes us all wonder what you are asking.

my primary goal in all this is to learn the ins and outs of car audio. secondary goal is to build a good system. 

 

does anyone know where i can find a copy of the loud speaker cook book?

 

you mention i should factor in less power, the nominal impedance according to winisd would be about 7ohm so should i assume the sub will be getting 800 ish watts for the computation of air flow?

my primary goal in all this is to learn the ins and outs of car audio. secondary goal is to build a good system. 

 

does anyone know where i can find a copy of the loud speaker cook book?

 

you mention i should factor in less power, the nominal impedance according to winisd would be about 7ohm so should i assume the sub will be getting 800 ish watts for the computation of air flow?

Buy the book. Should be on Amazon.

 

If you read it than you should have a solid understanding. As to your secondary goal you're going to need to define what exactly you're trying to accomplish.

I've seen quite a few threads from you lately, and like Sean mentioned you seem to be all over the place as to what exactly you're trying to do, so it makes giving advice hard. ie: going from ported to 4th order bp ported for all the wrong goals.

 

Perhaps a new thread listing all the details of your previous enclosures, what you liked, what you didn't like, and listing what you want to improve on / detailed goals is the best route for help--because your collective threads are hard to keep track of.

 

As to the last question. That value isn't helpful since it's only constant near one frequency. I will let you choose how conservative you want to be when selecting a value for the power, but I would be comfortable to say that modeling with 2/3rds power would be very conservative in this situation. So if your amp is rated for 2500watts at the point you're "wiring" to than calculating port velocity with 1875watts would be "safe" in my opinion. The above "2/3rds" is no rule, I literally made it up so don't take it as gospel, but when I had my xcons, BL, icons, dcons, etc and had them wired to 1ohm with sufficient electrical supply, I occasionally measured the impedance at different frequency points across different enclosures (no way is this scientific, just anecdotal) and the impedance was well over 2ohms, so that would be equivalent to half power.

Edited September 17, 201312 yr by ssh

The best place to get a copy is on Amazon.

 

The nominal impedance is what is listed by the manufacturer. 1, 2, 4, ect.  The actual impedance will vary greatly depending on frequency, excursion, and heat.  

 

Modeling a subwoofer with a program like WinISD is a horrible way to figure frequency response as it can not predict parameter shifts that occur with power.  Give me a moment and I'll post some parameters of the same sub with small and large signals applied to it. 

see, and i thought winisd was the program to use for modeling how a speaker will behave. i think one of the reasons im flying all over the place is i do not seem to be able to find any concrete rules for speaker design and enclosure building that everyone agrees on. 

 

i will buy the book on amazon if they have an ebook

The below was is a 12 sample that was klippel tested.  The green is large signal (high voltage to make the cone move to xmax) Thiele/Small parameters.  The blue is small signal(only one volt) parameters.  The same parameters most all manufactures list for their product.  You can see by the shift in parameters (listed by each driver) that small signal parameters are not going to work well in the real world due to parameter shifts when the cone starts moving in a normal fashion.  And most computer programs can not account for these shifts

 

 

WinISD still gives you a pretty good idea on how one enclosure alignment performs against another. Would you disagree?

WinISD does a great job comparing apples to apples. But when modeling subwoofers with small signal real world measurements will be different when modeling the vehicle at listening levels due to parameter shifts.

WinIDS also does not a. Oh t for transfer function nor does it a count for inductance which when I did testing on the effects of large coils output was actually reduced upwards of 6db at some points above 40 hertz.