BillFitzmaurice.info

Ok, so I did some testing between the TT and the AT. Same position firing at the corner and roughly the same voltage between the two throughout testing. My results are below...

Table Tuba...

50 hz / 4.85 V = 117 db
55 hz / 4.50 V = 119 db
60 hz / 4.33 V = 120 db
65 hz / 3.98 V = 121 db
70 hz / 3.17 V = 120 db
75 hz / 3.16 V = 118 db
80 hz / 2.99 V = 116 db

Auto Tuba...

50 hz / 4.86 V = 113 db
55 hz / 4.74 V = 114 db
60 hz / 4.50 V = 113 db
65 hz / 3.70 V = 112 db
70 hz / 3.12 V = 108 db
75 hz / 3.25 V = 110 db
80 hz / 3.04 V = 112 db

I know the voltage is different between the two, but when I did the AT, I couldn't get the same voltage numbers as with the TT for some reason. It wanted to jump .5 volts with every volume notch on the receiver so I tried to pick the closest I could.

Also, as I went up in frequencies, I would have had to keep turning up the volume just to achieve the same voltage as the lower frequencies. How come?

If this test is bogus because I didn't remain at the same voltage throughout the frequency range, I can do it again, I was just afraid to keep cranking on the volume but I also didn't want to mess with the gain on the amp.

If you're running the foster amp and did not open it up to play with the potentiometer, the curve is sloped downward the higher you go. And if you're running some other sub plate amp, alot of them have their own curves. However, if you're running the tests with a pro amplifier or basically just a flat amp, then i have no idea other than maybe the source may be the problem.

If you have checked the cab thoroughly and no leaks are apparent, then it might be that there is a leak (and a major one by looking at the number) near the inner coil which is right next to the throat.

digital_chris wrote:
Also, as I went up in frequencies, I would have had to keep turning up the volume just to achieve the same voltage as the lower frequencies. How come?

Your amp and/or your source don't have flat response. If they did voltage would remain constant. I wouldn't complain about either result. The TT seems a bit higher compared to the AT than I'd expect.

SeisTres wrote:If you're running the foster amp and did not open it up to play with the potentiometer, the curve is sloped downward the higher you go. And if you're running some other sub plate amp, alot of them have their own curves. However, if you're running the tests with a pro amplifier or basically just a flat amp, then i have no idea other than maybe the source may be the problem.

If you have checked the cab thoroughly and no leaks are apparent, then it might be that there is a leak (and a major one by looking at the number) near the inner coil which is right next to the throat.

I do have the foster and didn't play with the potentiometer yet, but I will do that soon. I do also have a couple of small leaks, 2 in the side of the cab, but even if I plug them with my finger, there is no audible difference. If I stick my head near the mouth of the AT, I can definitely hear air that sound like leaks because I don't hear anything at the mouth of my TT. I guess I just don't understand how a few tiny leaks can make such an audible difference. I might just this cab and build a better one

digital_chris wrote:I guess I just don't understand how a few tiny leaks can make such an audible difference.

They can and do. When I prototyped the first T24 I got a good result, then went inside and did something. I remeasured and it was horrid. I found that in my diddling I'd shifted the driver 1/8 inch and had a sliver sized leak around the driver gasket. I moved the driver, sealed it up and the good result came back again.
Try the stethoscope method to find the leaks, and don't forget to check around the driver gasket.

I'll give it a shot. I'm just afraid that I might have some leaks inside the cab where I can't reach. I'll see if I have any inside the chamber and around the driver, in the mouth and then the access panel. Now what about my hurricane nuts, do I need to worry about leaks coming by the threads? Even if I do, I don't really have a way to seal them anyway. The most I can do is put silicone where the allen screws thread into the hurrican nut.

I'll report back in a day or two

I ran a bead of caulking around the outside of the driver gasket and also put some in the holes where it indents and where the bolts pass through to the wood. Maybe give that a shot to seal things up 100%.

Alright, I popped off the cover and found 2 small leaks around the driver, both where the allen bolts are. Not sure if it's coming through the threads (probably not since the rest are ok). So, I decided to spread some DAP around the whole perimeter of the sub. As far as the basic DAP sealant goes, is is strong enough to keep small leaks from "breaking the seal"? I know it's latex and will peel off fairly easy so I'm just not sure about it's bonding strength.

I will test it out tomorrow and search for more leaks.

YESSS!! I found another leak!! I know it's odd to be happy about it but in this case I am because if I plug it, I can HEAR a difference in the cleanliness of the bass!! Kind of amazing to me. It's a screw hole in the chamber, it was from a screw I used to hold two panels together. I just filled that with PL tonight so it should be all set tomorrow.

Also, after I sealed up the driver with DAP, the bass coming out of the mouth already sounded cleaner, I'm excited! I will keep this updated, tomorrow I can do a final check for leaks.

I can't wait to do an SPL check again after all of this

SeisTres wrote:If you have checked the cab thoroughly and no leaks are apparent, then it might be that there is a leak (and a major one by looking at the number) near the inner coil which is right next to the throat.

How does one go about finding & remedying that situation?

Just finished up Autotuba #1 & cant play at home.... But am preparing for the worst (always the pessimist!)

Thanks!

EW wrote:

SeisTres wrote:If you have checked the cab thoroughly and no leaks are apparent, then it might be that there is a leak (and a major one by looking at the number) near the inner coil which is right next to the throat.

How does one go about finding & remedying that situation?

Just finished up Autotuba #1 & cant play at home.... But am preparing for the worst (always the pessimist!)

Thanks!

Get a toddler that can fit inside the horn mouth to pl as far back as he/she can

But really, if there is major leak in a very critical place and can no longer be reached, I think the only solution is to saw off part of the cab and reapply a new side.

Wow, a PL covered toddler.... And you thought Bills cabs were loud! Wonder what the db level of furious mommy is at 1 meter..... I'm bettin' on peaks around 140-145...

Alright, another update. Some good news and some bad news. Well, maybe not bad news but I was expecting better results. Anyway, for the good news, I fixed all the leaks and the sound coming out of the mouth was MUCH cleaner during sine wave testing in the home. I ran the freq tests at just about the same voltage and to my surprise, the db numbers really didn't change at all, not even 1db, just that the bass was so much cleaner.

Then I proceded to throw the sub back in the car, with all of my head unit settings neutralized and my amp gain at neutral as well. Aaaand, not much of a difference from before

I had to turn up the Non-Fader (subwoofer) level on the HU just like I did before I fixed the leaks to get similiar sq/spl. Somethign still seems off, must be the rest of my gear and tunig ability... : /

What SPL meter are you using? A-weighted? Calibrated?

Could it be you are not used to the sound and feel of clean, undistorted bass? Are you pointing the mouth of the AT 3-4" from the rear side panel? Check the input of the amp, see what voltage your are getting at what frequencies. This will help you figure out the correct gain structure settings on the head.

DJPhatman wrote:What SPL meter are you using? A-weighted? Calibrated?

Could it be you are not used to the sound and feel of clean, undistorted bass? Are you pointing the mouth of the AT 3-4" from the rear side panel? Check the input of the amp, see what voltage your are getting at what frequencies. This will help you figure out the correct gain structure settings on the head.

I'm using an R-Shack SPL meter and have it set to c-weighted I believe. The mouth is about 4-6 inches away from the rear side panel. What you're saying is that I should check the RCA's on the amp for voltage coming from the head unit at different frequencies? I can do that today, as well as see what kind of voltage the AT is getting at my listening volume. Last time I was hitting peaks of 20 volts and it really wan't that impressive, hmm...