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View Full Version : Theory ?, box size, power handling and output.



husker77
08-12-2012, 07:14 AM
So it is my understanding that if your box is to big you lose power handling capabilities, and if it is to small you can throw more power to it, in simple terms. I know there are lots of factors involved, but in general do you lose output one way or the other.

I guess what I'm asking is if you are getting you woofer to move the same amount with less power wouldn't you get the same db's and performance? Does a larger box compensate for a smaller amp basically?

I guess I'm just curious.

pro-rabbit
08-12-2012, 09:23 AM
That is far to general honestly. The enclosure size does not alter the power handling much unless the enclosure allows the sub to reach the mechanical limits quickly, then obviously you are limited in power but even that statement is a bit general.

husker77
08-12-2012, 09:15 PM
ok, I wondered if there was kind of a rule of thumb on it, but I suppose with all the variables it isn't just a right size always involved.

pro-rabbit
08-12-2012, 09:17 PM
Yea, most "rule of thumbs" and enclosures are incorrect anyway. There is a good bit of "fudge room" in basic enclosure designs if you are just trying to "make something work".

However, the right course of action would be to design the enclosure around the product, application, and goals. That will always net the best overall result.

Moble Enclosurs
08-12-2012, 09:24 PM
Generally, in car audio, the box cannot be too big. Normally the bigger the box, the higher the inner efficiency of the design. The problem that occurs with larger enclosures is the port characteristics, and how they relate to cutoff points and tuning effects that control excursion capabilities. If a subwoofer is designed to operate at say 1000WRMS, then it should be able to do that at its in-band point of free-air lowest resistance. If not, then I would not operate it at 1000WRMS even with a higher compression and resistance from an enclosure. The problem that people run into with enclosures being too big, is trying to operate the subs out of the usable band of the subs frequency response WHEN LOADED. For this, it is wiser to figure for the free-air capabilities of a driver before any box configurations are done so it can ensure no limits thermal and possibly mechanical are tested. This is not a bad thing to do when the power difference is less than half that of the full rms power tested or stated in the specifications.
So, take the 1000RMS sub, and run its performance free-air and test its lower resistance point voltage and measure that in watts. Say, it becomes 470W free-air@ 27Hz. Then being that 470 is less than half the 1000 listed, the best best would be to maintain higher compression of the driver to push the voltage higher than 470W@its specific wiring configuration not to exceed its given listed 1000W. ZBut if say, it measures 600W free-air@say 27Hz still at lowest resistance, then a larger box will not be as much of an issue with unloading if you never exceed 600Wrms, and you can maintain similar output within 3dB average of the original output in correlation with the double power=+3dB rule, which has been proven effective. I would take a loss of 2dB to not overload a sub all day long and keep a higher efficiency from the box to keep my power requirements down and possibly get a less expensive amplifier, for musical enjoyment purposes of course. For SPL configurations, you may have a different outlook on the subject as efficiency vs power is not as sensitive in car audio for SPL as vehicle vs box ratios are.

husker77
08-12-2012, 09:29 PM
Thanks a lot Moble Enclosurs;, that was the answer I was looking for. Of course I will have to read your response 15 times and google half the words in it to fully understand. I am on here to learn so I like the in depth answers.


Yea, most "rule of thumbs" and enclosures are incorrect anyway. There is a good bit of "fudge room" in basic enclosure designs if you are just trying to "make something work".

However, the right course of action would be to design the enclosure around the product, application, and goals. That will always net the best overall result.

Like I said I am mostly just trying to learn, I really have no idea what I'm doing when it comes to designing boxes. I kind of did the one for my kid, but it really didn't turn out all that great.

pro-rabbit
08-12-2012, 09:37 PM
Thanks a lot Moble Enclosurs;, that was the answer I was looking for. Of course I will have to read your response 15 times and google half the words in it to fully understand. I am on here to learn so I like the in depth answers.



Like I said I am mostly just trying to learn, I really have no idea what I'm doing when it comes to designing boxes. I kind of did the one for my kid, but it really didn't turn out all that great.

Understandable and this can be a good place to learn over all. While I won't post paragraph long responses I will give you the more straight typical answer and if you need more clarification and mobile has not posted a lengthy answer then feel free to PM/email me and I can get you as detailed as you like.

The biggest issue with mobile audio is really that half of what we know and teach does not always work in the "real world". The stuff that does works mostly in SQ. SPL..well over my many many years of doing it I have found that nothing ever beats testing and many times the results and what works defies what math/physics would suggest. SPL is like the devil..you don't always understand why....and you just can't run away once you have fallen to that side of the light lol...

husker77
08-12-2012, 09:40 PM
The biggest issue with mobile audio is really that half of what we know and teach does not always work in the "real world".

Completely understand that.

Moble Enclosurs
08-12-2012, 09:53 PM
Understandable and this can be a good place to learn over all. While I won't post paragraph long responses I will give you the more straight typical answer and if you need more clarification and mobile has not posted a lengthy answer then feel free to PM/email me and I can get you as detailed as you like.

The biggest issue with mobile audio is really that half of what we know and teach does not always work in the "real world". The stuff that does works mostly in SQ. SPL..well over my many many years of doing it I have found that nothing ever beats testing and many times the results and what works defies what math/physics would suggest. SPL is like the devil..you don't always understand why....and you just can't run away once you have fallen to that side of the light lol...

Very true! Testing will defy anything acoustical for calculation. The reasoning is, the actual results can be given and changes made in the real world are present. The tough part is, we are not in your neighborhood to do actual testing, therefore calculation is a viable second and if you know what you are doing, can be quite accurate. Sound propagation has many constants. The things that are not constant are the environmental factors, but even those do have their own values of damping, physical reflection paths, absorption, etc. The problem there is not every vehicle is made with the same materials, nor is that a major concern in sub frequency usage being that a vehicle, regardless of size, is small compared to ELF, VLF, LF waves, therefore differences in placement and even physical constraints of a design can become less important in some factors, such as, and mainly in, SPL measurements, not SQ.

Moble Enclosurs
08-12-2012, 09:58 PM
Thanks a lot Moble Enclosurs;, that was the answer I was looking for. Of course I will have to read your response 15 times and google half the words in it to fully understand. I am on here to learn so I like the in depth answers.

Well, if you need in depth answers, I will be one of the few willing to give them :D You are welcome man.