BillFitzmaurice.info

What will happen with a T60 with no access panels on it, what will it sound like while testing? I'm curious because since the driver chamber is open It seems that it would be a little difficult to test the seal of the driver, but since that's what the plans say (and forum members) I'll trust that it will still be easy to detect if there are any driver leaks.

Use the hose method with low freq sine wave and you will still hear any leaks around the driver/baffle area and driver chamber areas even with access panels removed. They will sound like puffs of air through the hose. After you are confident there are no leaks inside, install the access panels and hose test around the access panels. If there are no leaks you're good to go.

There was a piece of wood that had previously broken out and leaked badly. Bondo'ed the menacing gap. This was during the driver mounting leak test and it was quite obvious (audible even before I grabbed my stethoscope). Wish the t39 was as obvious. Will keep this up to date as I fix this thing. I'm so wishing I didn't have work tomorrow...

After patching the leak last night and hooking it up today, I regret to say but it is significantly underperforming.

Performed outside ground plane
Frequency Voltage dB at one meter
60 2.8 +- 0.1 v 88.9
50 2.8 +-0.1 v 87
40 2.8 +-0.1 v 83
30 2.8 +-0.1 v 78.6
25 2.8 +-0.1 v 77.3
It takes 10.2 V at 50 Hz to produce 95 dB

Things I know, low frequencies will read ~3 dB too low due to C-weighting
I've tested the driver area for leaks and the access panels.
What's weird is this is roughly 13 dB down, very similar to my T39 readings... However, I will say that it is not concert loud at full blast... which (according to T60 chart) should be around 118-122 dB outside playing music referenced to 1 m...

AFAIK, no one tests at one metre.
I wondering if that's the source of your problem, for both cabs.

Honestly, if you think you have no leaks, crank the thing up, see what you reckon then.
I find it hard to believe you could have low output for whatever reason in two different cabs,
unless the only common denominator in both cabs is the same driver...

They have different lab 12's. I bought them new in box. 1 from leland 1 from amazon.

Right, so that's not the problem.

Crank it up!

played some bass heavy songs at about 20 V. and lets just say I wasn't impressed. 94-96 dB... Something sounds like it is loose inside but everything is heavily sealed with pl... don't know what that is...

MissileCrisis wrote: played some bass heavy songs at about 20 V. and lets just say I wasn't impressed. 94-96 dB... Something sounds like it is loose inside but everything is heavily sealed with pl... don't know what that is...

I'd check that meter. You should get those levels with 2v.

i will say that neither 1 t48, or 1 t30, EVER blew me away in singles outdoors, even when getting up to war volume. takes multiples for sure. Given that 1 t48 is louder across its passband, I'd say thats why you're not getting "concert volume" outdoors (you only have 1 cab).

I'd still check that meter.

Ok now i'm worried... at 45 Hz playing at 3.9 v with the one side panel off I get ~86 dBs referenced to 1 W that's 83 dB.... Mightly close to the panel on measurement... Thoughts? It's weird because I will bet my life that the access panel isn't leaking (thoroughly tested that with stethoscope).

I have the same SPL meter as another forum member who got 118 dB with his T45 at 48 V in the center of a room. My ears agree that it is not 12 dB off, at most it is 3 dB off.

unless you're driving over to said other forum members house to borrow their meter, I doubt you have the "same" one.

just because its the same model means very little. theres variation in plenty of audio equipment, and if you look at the variations in Measurment mic curves (for mics in the 40 to 400 dollar range) you will find they are all over the place.

Point is, if Bill says it can do 99 dB /watt at 50 Hz outside and the cab does 85, something is seriously wrong.

measure 10 meters, 28.3 volts.

and get a different decibel meter. or better yet buy a cheap measurmen tmic (apex 220 for 40 bucks) and download room eq wizard. you'll also need a usb audio device with phantom power on a mic in.