When making a response curve...

[Howard]

Where should the SPL meter be placed?
In listening position or next to the sub close to the port or what?

Thanks

[BillFitzmaurice]

It depends mostly on where you're doing the measuring. Indoors room response overshadows the response of the speaker, so close field micing (1 cm from the cone and the port with the average summed) is required. Outdoors away from reflective surfaces you can go with a 1 meter reading. In either case you get a result that will bear no resemblance to in-room response, but it's the most accurate way to see what the box is actually doing.

[Howard]

Thank you sir.
Assuming my SPL meter arrives tomorrow, I'll give it a go both close to the sub, and in the listening position

[paulspencer]

Depends on what you want to know. If you want quasi anechoic response then do what Bill said. If its vented then you have to combine the driver and port response.

If you want to see what the room is doing to the response then you should put the sub where you will place it and measure exactly in your listening position. This will tell you what you are really hearing, and helps with room mode eq.

[russbryant]

If you only have an SPL meter then your only choice is to measure from the listening position. I don't think you will get a valid measurement at a close mic position with just an SPL meter. Same goes for the outdoor 1 meter measurement, you still have to contend with ground bounce.
An SPL meter basically just gives you a manual way to do RTA analysis.

Russ

[paulspencer]

Russ, how is an SPL meter different to any other mic?

[Centauri]

Originally posted by russbryant
Same goes for the outdoor 1 meter measurement, you still have to contend with ground bounce.

When measuring a sub with any type of measuring equipment it is usual to place the mic AT ground level to avoid this reflection.

One problem I see with using an SPL meter for manual RTA is that the meter does not know what frequency it is listening to. You may plot a relatively high level for a low frequency when in fact that signal could easily contain high harmonics of the fundamental tone. I think an fft analyser would give better results.

Cheers

[russbryant]

Paul,

SPL meters in general are too slow to respond and have no way to gate the signal so you end up measuring the driver response plus the room.

Some SPL meters such as the ones from Radio Shack do have an analog output that can be used as a mic but the response of the RS SPL meters is pretty bad. There are calibration curves and aslo hardware mods available but it's much easier and cheaper to buy a panasonic mic capsule and a small brass tube from Ace Hardware and build your own. Less than $5.


Centauri,

Bill didn't make it clear that he was talking about a ground plane measurement so most newbies wouldn't know the difference. I still wouldn't measure a sub at 1 meter, outside, ground plane or not. You need a lot of room for a 20 HZ signal.

Much easier to do a close mic measurement.


Russ

[Grandma´s_SUB]

-About measuring SPL-
Its cool and cheap but you need this:
-microphone panasonic capsule (like russbryant said)
-need full duplex soun card
-freeware speaker work shop
-diy hi-qualitiy microphone preamp
-diy JIG(resistors....read about it)

BUT the best part is,that you have all documentation and GUIDE at
http://www.audiodiycentral.com/ntutorials.shtml

Enyoy!

Dean