measuring speaker respone

[gjeff80]

Hi everyone, I was wondering if anyone has any tips on measuring as speaker cabinet's response? The cabinet's a Folded Horn W-Bin, and I wanted to see what kind of response it gets. I have a RTA, but I would like to see if I could get one of the line Graphs, I've found some RTA software on the computer, but the only concern I have is I think I would need to use a microphone that truely has a flat response, how is it possible to just plug a microphone into your PC and use a program to measure the response when every mic has a difference response curve?

Thanks
Glenn

[OMNIFEX]

If your cabinet (Total Size) is 48 x 24 x 24, you're looking
at around 70 Hz. (- 3dB 1 watt, 1 meter)

Now, if you port the box, the lowest note will be determined
on f3 (- 3 dB) (1 watt, 1 meter measured) And, ofcourse the lowest usable frequency will be f10 (- 10dB)

Don't try to tune the box too low (Under 50 Hertz) If you're
trying to tune it under 50Hz, you might as well keep it as
a sealed enclosure.

W Bins internal chambers are small already.

[gjeff80]

Omniflex, the 15 inch cabinets i have are somewhere around 40x22x22 or something, the inside chamber volume is about 2.6 cubic feet, but they are loaded with JBL 2226H speakers, which I was told work better in a ported box, so I figured I would port the W-Bin to 40Hz. I'm sure they will breathe a little better now, but I was just wondering how to measure a graph that shows the cabinets response like you see on the tech sheets that come with the woofers.

Thanks
Glenn

[OMNIFEX]

That's easy.

Just scale a 2.6 cubic foot box, insert the JBL 2226, and
tune it to 40 Hertz.

Just keep in mind that's a very small chamber for a 15
inch driver to produce bass. Don't expect miracles!!!

Compare the tuned enclosure to the sealed enclosure.
The one that gives you the flattest line, with the lowest
f3, is the logical choice.

[gjeff80]

Yeah, I know the 2.6CF is pretty small for the 2226H woofer, these W-Bin cabs are pretty old, (18 years or so), I think they were originally loaded with Altec 421-8LF, then when I got these 2226H's It wasn't very feasible to make the inside volume larger.

Glenn

[OMNIFEX]

I do have plans that use the same concept.

They will be very loud, but, will never play very low.

Focus on the larger horns for now. They will do
better job overall.

[gjeff80]

Yeah, my idea is to use 6 of the w-bin's on the Low-End 100Hz, and below, and then using another set of the 15's on the low mid, 100Hz-500Hz.

So I'd be using 2 JBL 2240H's, 2 CV 189E's and 2 JBL 2226H on the low end, and then 2 2226H on the low-mid. The 2226H's seem like they could out perform the 2240's if I could get more volume in the chamber for them. Jbl's recommend box is 4.0 cf. tuned to 40Hz. I think I'm all set porting those cabinets, they sound nice, they a nice tight bass, of course they won't go as low as the 18's in the larger horns, but the combination of the 2226Horn w/ the other 2 18 Horns should make for some solid bass.

[RHosch]

On the original question,

The typical approach is to use a microphone that has a calibrated frequency response that if fairly flat. These mics are commonly referred to as "calibration mics", and the Behringer ECM8000 is one example of a fairly cheap version. There are other alternatives, ranging from fairly flat response microphone capsules from digikey (lower cost alternative) to really flat response calibration mics (or sometimes just called omnidirectional mics) from B&K or Earthworks.

These microphones typically need an outboard preamplifier to provide their working voltage (40V usually) and amplify the signal before being sent to your computer's soundcard. The internal mic preamps in most soundcards are (1) noisy and (2) don't supply the 40V most of these mics require (there are some microphones that don't require the external power, but they are as a general rule not as flat in frequency response, though that isn't a universal rule).

Most decent consumer grade gaming cards are good enough to make measurements of amplitude and frequency response of a speaker. Programs like TrueRTA and ETF need full duplex soundcards, and have a method of adjusting for the card's inherent non-flat frequency response. These programs, paired with a decent microphone, can make relatively accurate measurements of your speaker, room, ect.

Hope that helps.

[ziosal]

Hello ! i have mic ecm8000 pre and truerta ... i have one problem ...

i have calibrated the mic and the calibration routine soundcard ... but the line not is flat !!!!


WHY ????

sal

[catapult]

but the line not is flat !!!!

It could be a setup problem or, if you have done everything right, it is most likely a problem with your soundcard.

TrueRTA Tutorial