Subwoofer efficiency

[noodle_snacks]

Do programs such as winisd calculate efficiency including baffle step loss?, what happens in terms of effiency below 80hz? Should i be taking off 6db from efficency?

[454Casull]

The wavelengths of sub frequencies are much longer than typical baffles, so the baffle step doesn't exist for most subs.

[noodle_snacks]

I know that, but a normal spekaer would roll off from a 2pi to 4pi radiating space, loosing 6db in the process, does a subwoofer loose 6db at all frequencies as it is radiating into a 4pi space, as opposed to a 2pi space as it may be measured on an infinate baffle?

[Volenti]

They calculate in 4pi space and assume the efficiency is measured in 4pi space also (they have options for room loading/cabin loading ect which would be pointless if they didn't start from 4pi space).

[noodle_snacks]

could manufactuors cheat by qouting 2pi efficiency? How could you tell which was qouted?

[paulspencer]

Actually, you should look at the individual program as they are not all simulating into 4pi space. Subwoofer simulator simulates 2pi space:

http://www.geocities.com/f4ier/newsubsim.htm

You need to subtract 6db to get 4pi in this case.

No simulation program is really going to tell you the actual SPL you will get out of a subwoofer. Room gain and modes are too unpredictable for a start and they will have a big impact.

Also power compression is not normally allowed for.

Also what you simulate at 1m takes no account of the size of the room.

If anyone can come up with a comprehensive simulation/calculation of the actual max SPL achieved and then verify it with measurements, and be accurate within 3db, I'm impressed (or they are lucky).

Regarding driver efficiency, as far as I'm aware they are normally measured quasi-infinite baffle, which would be 2pi space ...

[rabbitz]

Most subs work in 2PI or PI so not an issue and BS doesn't exist in subs. Room loading and the gain control is your friend.

Have a look at the manufacturer's data sheets and will sometimes mention the testing method.

Do you have a particular application worry or just a general question?

[elambert]

Noodle, think about this for a second.... Yes manufacturers could show efficiency in 2pi however that would be a heck of a baffle... Consider the actual size of wavelengths: at 20hz you would need a baffle over 56.5 ft to keep the driver in 2pi.

Even at 150 hz the baffle size would need to be over 7.5 ft wide.

Hmmm, makes me think anyway. Is this why low freq drivers are always quite a bit lower in effeciency than mid and high freq drivers?

Then it also comes down to the integrity of the manufacturer. Car amplifiers are a prime example of this. Manufacturers of cheap car amps will subject their units to 18+v in sub-zero temp conditions for fractions of a second to be able to put overexaggerated power ratings on the amplifier so the un-wise will buy.

Ethan

[Volenti]

Originally posted by paulspencer


No simulation program is really going to tell you the actual SPL you will get out of a subwoofer. Room gain and modes are too unpredictable for a start and they will have a big impact.

Also power compression is not normally allowed for.

Also what you simulate at 1m takes no account of the size of the room.

If anyone can come up with a comprehensive simulation/calculation of the actual max SPL achieved and then verify it with measurements, and be accurate within 3db, I'm impressed (or they are lucky).

If you can get a baseline performance of a "reference" subwoofer in the intended location it's pretty straight forward to get a model of the response of whatever design you intend to use in that environment.

For example, I've measured the cabin gain of various vehicles with different sub locations and configurations of sub enclosures, I can then model a design and super impose the cabin gain on it to see how it would perform in the car (see attachment, note my measurements only cover 20-100hz hence the abrupt jump)

It's simply a matter of getting sufficient data.

[noodle_snacks]

I am just curious, i would doubt that i can get over much more than about 110db at my listening position (2-3 meters from the sub) with my adire tempest EBS. This is fine for home use but i would like more output capability for parties etc, i think i will go with a horn subwoofer of some type.