Measuring the iBiBk + Fostex FE126E

[mrbubbs]

Hello, all...

It's been a long time since I decided to build an iBiBk and I finally am to the point that I'm experimenting with stuffing, suprabaffles, etc. I recently got a cheap SPL meter and a frequency generator and thought I'd do some testing. I was concerned that even my severely cheap, old speakers that I used to have hooked up to my TV seemed to have clearer speech than my iBiBk enclosures. It sounded as if someone was talking through a cardboard tube (best way I have to describe it).

I took several readings of two different cabinets. My old 2-way bookshelf speakers and my new iBiBk with FE126E. Attached is a graph of the bookshelf speaker vs. iBiBk vs. iBiBk that was stuffed to the 1st form as shown at Bigger Is Better 'BIB' Cabinet Dimensions - ZillaSpeak in the Stuffing options section.

I'd like to know if these graphs look somewhat accurate or if my measuring technique is way off. I would like to improve the "vocal range", as I found on wikipedia to be about 80 Hz to 1100 Hz. Should I keep stuffing the cabinet and making changes or should I be happy with what I have based on my driver and cabinet selection? A lot of subjective questions, I know... but I wanted some others' input on the situation.

[planet10]

Can you post pictures? I'd love to see a set of these.

Is the SPL ledgend on the right correct? Those are huge SPL for that driver.

dave

[mrbubbs]

I'm still in the sanding phase of the construction. They certainly aren't as nice as JohninCR's iBiBks!

I made very crude measurements. The sound meter was only about 6" from the center of the driver, whereas I think most measure 1 meter or so? I wasn't sure, and I wanted some data I could start with, so I just setup the test quickly. I turned up the volume with my test tone at 20Hz so that I could hear the frequency reasonably well. Unfortunately, all the other frequencies were just a lot louder! I did wear hearing protection, but it still shook my head when I was near the speaker, haha. What I was after was a relative difference when I modified conditions, such as adding stuffing, etc.

[planet10]

You need to get into the far-field. Probably 2-3 meters with this speaker.

dave

[mrbubbs]

Okay. Will test from there from now on. Thanks!

Originally Posted by planet10

You need to get into the far-field. Probably 2-3 meters with this speaker.

dave

[mavric]

congtrats in the IBIB, if you have to wear ear protection, can you please post some pics? Please?

[mrbubbs]

Originally Posted by mavric

congtrats in the IBIB, if you have to wear ear protection, can you please post some pics? Please?

I just wear ear protection for safety's sake.... ehh.. a bit of a redundant statement, I guess. Just testing some ordinary 4.5" drivers. Nothing too crazy going on. Unfortunately, I was testing them too close!

[markturner]

I just wanted to comment that in my limited experience speech intelligibility can be an interesting problem to solve, and I believe that some frequencies higher than 4 khz may affect distinguishing some of the consonants (t, f, s, h, sh in English for instance) whereas some of the lower frequencies are involved in other consonants and vowels are among the lowest. One site I used to try and understand this was Understanding Audiograms, Hearing Loss, and Speech Intelligibility, but there are many others when you look around.

I've run into this while trying to listen to audio books while driving across the country of all things. My car's sound may be adjusted to listen to music inoffensively, but when I stick an audio book or a podcast on I often cannot understand a thing without having it so loud that it hurt. It can depend on whether it's a female or male voice too, which is probably because the root frequency (vowel sounds) are an octave or so apart.

[PJN]

Judging from the rising response that you posted it looks like you could use a baffle step correction circuit to level out the response. a 1.5 mH inductor and a resistor in the 3 to 6 ohm range might be a good start. You can bypass the BSC filter with a small cap to increase the high frequencies, a cap from 1 to 2 uF might be a good start. There is some great excel spreadsheets on Jeff Bagby's sight that you can use to help calculate such things.

jbagby

PJN