Bigger than needed pa enclosures.

[holger honda]

Hello all audiowizards.
Looking at conventional PA systems one often sees fairly big enclosures for the "top" part wich usually contains one or two 12 or 15s and then a compression driver.
Now theese speakers usually dont play the bottom 120 hz or so since they usually are actively crossed to match one or more subwoofer.In thereory they could be pretty small...
I wonder are they so big so they CAN play deeper if such a signal is fed to them, or is there some kind of headroom space in there to increase spl?
Or why are they made bigger than they play?
If a speaker is playing only the Midbass and up why not make it smaller?

 

[OMNIFEX]

Dude, your question is kinda broad.

Here are some reasons why PA Tops are generally large.

1. Horn-Loading. The Horn's Mouth will be the deciding factor, on how loud it will play, at the given frequencies.

2. Weight. When your box is too light, it will start dancing on top
of the sub, when you are driving the bass.

3. Matching. Some people want all there boxes to match according to size.

4. Stand Alone. Many of those Dual 12/15 cabs, can play lower, and, are used to play lower notes when you don't need to carry
subs.

You mentioned mid bass. Midbass has a different meaning to each builder. Midbass for me is all the way down to 70Hz.

Some would say 150 Hz. So, each box is built to whatever the sound dude considers midbass.


<--------- ROCK ON !

 

[mike.e]

All those things +
Large drivers
Large drivers requiring large boxes
Large efficient drivers requiring even larger boxes for some bass extension

a 1cubic ft box with 90db/1watt drivers arent going to do the job
Hoffmans iron law!

Small,low F3,efficient, - chose 2

 

[paulspencer]

Bigger than needed .... for what???

The necessary size relates to the relationship between:

* output
* bass extension
* efficiency
* power handling

So it really depends on what output level you are trying to achieve as well. They may in fact need to be big to achieve the output required, depending on the power handling and efficiency for the given bandwidth.

Is there a specific target requirement here? Application? Output? Home use? PA?

 

[holger honda]

clarification

Well here is is.
IF you have a dedicated top to go with a dedicated sub is there any reason to make the top able to play frequencys that it will not have to handle.
fex this 12inch woofer wich really require a 130l vented box to play some bass,but a 40l sealed box would do in theory because it wont play anything below 110hz anyway.
Sure if I want a big,heavy "big speakers need big enclosure" type thing I woul not settle with anything less than a 130l box.
But I dont.

 

[paulspencer]

See how it models and that should tell you. I can't see any need for a large vented box in this case, just as long as the sealed box isn't too small, in which case you get a peak in the response before rolloff.

 

[OMNIFEX]

Re: clarification

Well here is is.
IF you have a dedicated top to go with a dedicated sub is there any reason to make the top able to play frequencys that it will not have to handle.

Here's your answer dude...............

Originally posted by OMNIFEX
4. Stand Alone. Many of those Dual 12/15 cabs, can play lower, and, are used to play lower notes when you don't need to carry
subs

 

[pinkmouse]

Something to bear in mind sizewise, is that a main consideration for pro boxes is how neatly they pack in the truck, and stack/fly by the side of the stage. This often leads to bigger boxes than you would initially expect...

 

[turk 182]

let him make a smaller box so that when he's pushing the spl level and the drivers cones are pressure modulating the higher frequencies he'll start understanding the reason for the size.
if the lower end of the bandwidth is suffering from too small a box it's going to require some real help from x-over and equalization as well as phase alignment to get it to keep up /match the subs

 

[weltersys]

Well here is is.
IF you have a dedicated top to go with a dedicated sub is there any reason to make the top able to play frequencys that it will not have to handle.
fex this 12inch woofer wich really require a 130l vented box to play some bass,but a 40l sealed box would do in theory because it wont play anything below 110hz anyway.
Sure if I want a big,heavy "big speakers need big enclosure" type thing I woul not settle with anything less than a 130l box.
But I dont.

Then use an appropriately sized box, no reason to lug around bigger, heavier boxes than are needed. That said, most speakers used for PA will be rolling off below around 200 Hz in a 40L sealed box, you still may want to port at a higher frequency with a smaller box.

Most of the PA top boxes are made for "full range" use, designing for the intended frequency range can give better results than that compromise.

I built a pair of horn loaded 2x6" with tweeter that are only 26.5" x 15" x 11.25" that perform great with a crossover around 100 Hz, they can hit around 125 dB in their range.
Plenty loud for around 200 people (with subs) but the pair can easily be carried one in each hand.