audio-talk

I bought a pair of diy'd speakers a few years ago consisting of vintage goodmans 15" and their ARU vents, must say I was impressed at the time
The sound of a big box, better transients, and lack of the reflex sound, what's not to like ?

I think I've got a similar type of sound with my red semi OBs... which is sort of a similar type of path for the rear sound wave.?

Thats the nice bit steve, that they dont seem to sound like a reflex box at all
The intrinsic characteristics are the same, but the sound is more 'complete' for want of a better word.

steve s wrote: ↑Thu Sep 16, 2021 8:16 pm I think I've got a similar type of sound with my red semi OBs... which is sort of a similar type of path for the rear sound wave.?

Yes,
I was telling Ant while I was at his place, that the up-firing APR vent he’d made was producing a similar effect to that from the ones on your speakers. The improvement in air and space, was immediately apparent as soon as I walked in.
Because he had made the tops as decorative end caps, like the Gale 401, it was easy to quickly A/B the speakers, with and without the vent in operation.
Emma said it was like putting the performers back in their boxes when the tops were on and blocking the vents, which I thought was a perfect description.
On my 12in speakers, I put the APR vent in the bottom, so as to get a bit more extension at the bass end, so I don’t get the height and space effect, but the tonal balance and freedom of Ant’s speakers is strikingly similar to mine, now he has done the aperiodic conversion.

That's nice to hear, my view is that the big vent gets the speaker closer to the open baffle sound, but without the open baffle compromised bass.
It's all compromises, but that's the best one in my view..

What does the APR vent actually consist of ?

A 3mm layer of highly compressed wool felt and a 25mm layer of not very compressed wool felt

came across my ecm8000 mic and interface this morning so i decided to do some measuring with it and rew

downloaded a generic calibration file for it and used pink noise to see what the speakers look like
no idea if i did things right, but it correlates to what i think im hearing
for some reason i couldnt get much volume out of the mic so the actual spl figures are likely to be wrong.....

here is the on axis at 1m for the left

and right

and the left in green, right in orange, seated in purple and the averaged trace in pink. interesting peaks at about 1k and 3.3k on all of them which i presume is to do with the two wizzers on the driver and an 11k dropout where i sit

interesting to look at, what does it tell me...

Maybe chris our resident measurement meister can tell me what ive done wrong to get what look like fairly benign looking plots

I would think those peaks at 1 and 3.3k will be artifacts of the phone/app rather that actually in the room.

It wasnt the phone app this time, its using an ecm8000 mic, um2 interface and a macbook with rew, the calibration file is a generic one for the mic so there is room for error there

I bought the mic this time last year and hadnt used it until today, ive not used rew before either so ive probably not set it up correctly. Those plots look too reasonable to me

Ok, but either way, tight large peaks like that are likely to be a measurement artifact. The display would probably help with some filtering on it, and or a sweep rather than pink noise. The y axis scale is such that it will hide most response details.

There are plenty of options to delve into, i did have a play with the scaling so i should be able to isolate a frequency band with it
Ill have a play with it now i have the files to faff with

Ant wrote: ↑Fri May 06, 2022 12:45 pm and the left in green, right in orange, seated in purple and the averaged trace in pink. interesting peaks at about 1k and 3.3k on all of them which i presume is to do with the two wizzers on the driver and an 11k dropout where i sit

interesting to look at, what does it tell me...

Maybe chris our resident measurement meister can tell me what ive done wrong to get what look like fairly benign looking plots

They do look rather benign, and also very quiet - around 0dB implies to me that you might've just measured the input noise of the interface. Some things to try/check/do:

- Is +48V switched on? Condenser mics like the ECM8000 need phantom power. The corresponding red LED on the front should be lit.
- Is the mic gain control set so the "sig" LED on the front lights up during testing? You can also try making noise yourself - talk, clap, whatever - the sig/clip LEDs should flash accordingly. On REW, when I click "check levels" in the measurement window, I usually aim for between -20dBFS and -40dBFS, depending on what I'm trying to achieve.
- As with all the Behringer interfaces, make sure the "direct monitor" button is off. Out, in this case. On one of my units, I opened it up and removed the plastic cover so that a screwdriver had to be poked in to activate it.

I'd also recommend 1/12th-octave smoothing to make things a bit clearer. 1/24 if you're trying to chase down something in a narrow frequency range.

Chris