Dual JBL GTO804 TT Build

[Sheddingskin]

I finished this a while ago but had some trouble building pictures. I built a 24" dual 8" TT loaded with JBL GTO804's. I built a case for a Dayton SPA250 plate amp during my down time waiting for PL to cure. Its built all with wood leftover from projects or that I found in someones trash. The brass hardware was all found in one of those plastic mini drawer things that used to be my grandpa's.

For the finish on the TT, I put fluorescent green inside the horn mouth and access chamber; the rest I painted flat black. The Deadmau5 head was planned to be painted on but due to time constraints its just a cutout that I made from a sheet of duct tape.

When I finished the sub I tested for leaks, but don't think I did it right. I didn't hear anything unusual. When it was finally placed in room in its final resting place I got to put it to its first real test with it corner/wall loaded (my room is a semi-hexagonal shape). It sounds extremely musical and can play notes that I've never heard before, let alone so clearly. But it doesn't have the oomph that I've read so much about, and this exact build combination in particular. It is very strong, but I think I can still get higher spl with my DIY ported 12" that I built. Placement probably has a lot to do with it, and that I can't really change much. I might have to re check for air tightness though. http://i722.photobucket.com/albums/ww22 ... G_0827.jpg
http://i722.photobucket.com/albums/ww22 ... G_0830.jpg
http://i722.photobucket.com/albums/ww22 ... G_0832.jpg

[SirNickity]

You also might be used to the harmonics. When you play <100Hz on a sub, you get a lot of >100Hz to go with it. Sit with it for a while, get accustomed to it, and see how you feel.

[subharmonic]

I would expement with placement.....then check to make sure you have the drivers in phase....use a 9v battery to make sure that the polarity on the jacks is pushing both subs forward when going batt+ to jack+ and - to -

Was the scrap wood you repurposed correct for the build? Seems to be less than likely chance it was. That could be an issue too.

[Gregory East]

I would think miswired dual drivers performance should be about as effective as a zombie trying to play cricket.

[Sheddingskin]

I'll definitely try the 9V test to check polarity. I just connect it the same way that I have them wired now, correct?

Sorry I wasn't clear about the wood, I used new sheets of half inch auraco for the TT, the scrap wood was just used on the little box that I built for the subwoofer.

[Bill Fitzmaurice]

but I think I can still get higher spl with my DIY ported 12" that I built.

Only above the subwoofer passband, in the form of harmonics that direct radiators produce gobs of. Folded horns don't.

[subharmonic]

I just connect it the same way that I have them wired now, correct?

Yup. Just check that they are both going the same way at the same time.

As for the airleak test, easy....just take a piece of vinyl tube and run it around all the joints and driver mounting areas you can reach while a 30hz test tone is playing at 10 VAC. That may be quite loud in the room too...just a heads up. I think forum member Bassmonster had some issues with the speaker gaskets for the JBL subs on his dually TT.

That sub should give you quite a visceral impact on most Deadmau5 tracks once setup right. Also put the sub where you want the best bass, then crawl around floor near the walls of the room until it sounds best...that is where you want to put it.

Edit:
Also looking at your pic, that couch to the left might be sucking up some energy.... not a ton. Your easiest troubleshooting now is placement, but do the airleak tests regardless of the placement tests.

[DJPhatman]

1- Are you using a crossover to send the <100Hz to the TT, and the >100Hz to the mid-high cabs? This will cause you to lose all the "punch" if the 40-100Hz is in the tops and the subs.

2- Get your tops off the floor. Place the tweeter height half way between your ear height when you are sitting and standing.

3- Try pointing the mouth of the TT more at the wall, i.e. slide the ass of the cab away from the wall more, like this:



BTW, I LOVE the neon green!

[bassmonster]

Nice build! Good to see another forum member with a 24" dual TT.

I'm also kind of confused as to why you aren't getting some serious boom. My room has awful room modes that eliminated bass in the middle of the room almost completely, but at the sitting position, bass is adequate enough, and in the corners of the room, brutal. Room modes could be a major cause, as well as leaks as already stated.

I, too, was used to "boom" of the harmonics from direct radiating subs. At first, it felt that my old 40w 8" ported sub had more "boom" at the listening position than the dual TT, but once I got used to the "natural" and "correct" sound of the TT, the ported sub never came close.

The GTO804 gasket isn't the best IMO, the rubber gasket is pretty hard rubber. I used latex caulk to seal it, as mentioned in my build thread.


Anyways nice build, and I love the color and Deadmau5 head!
BTW unless the plans have changed, there's supposed to be two sets of braces for 24" wide version, and your pictures only show one set of braces.

[Sheddingskin]

Subharmonic, I'll have to pick a 9V up but I will try that. As far as checking with tubing goes, what you described sounds exactly like what I already did except that I used a length of an old garden hose. I'll have to double check though.

DJ Phatman, I have the crossover set so the TT runs the info below about 80 Hz or a little higher. I've been playing around with the exact setting a little. The plate amp has an internal high pass at 90 Hz, but its only 6 dB/octave. I took your advice on the tops, they are now raised up on some cinder block that I had laying around. I definitely noticed some difference in imaging when I did that, and it just looks plain cooler now. The TT is toed into the corner a little more now as well as moving the couch a little further away from it. Thanks on the neon green! I saw a rattle can of it cheap and just had to do it. I have a black light set up in front of the mouth so you can see a green glow coming from the corner. Another color changing light that we have makes the Deadmau5 head and orange surrounds on the CV alternate in their glowing, which is pretty dang cool to see.

Bassmonster, thanks! It wouldn't have been done without your inspiration. I think being used to the direct radiating subs has a lot to do with it also. After these adjustments I'm getting much more solid bass. It is definitely different bass than I'm used to, its so much cleaner and more accurate sounding. If I still problems or just get bored on a rainy day I'll try the caulk or possibly this pipe sealant that I used on my other sub builds. You caught me on the bracing, I read the plans over and over again but somehow missed that when they said that one brace between the dual drivers was sufficient it didn't mean all through the build. Its too late now, but thankfully the sub feels extremely solid and I can feel almost no vibration on the cab itself when playing.

I also think a lot of my problem is coming from my amp, as there will be periods where the bass will be sounding amazing and then it will cut out a little or drop in level. This happens much more often at regular listening levels and only seldomly when I have it at party levels. I think I'm going to contact Parts Express or Dayton about the amp, and if that doesn't work I guess I'll be forced to go for the setup I wanted in the first place: a pro amp and BBE crossover with the sonic maximizer built in.

[Bill Fitzmaurice]

BBE..sonic maximizer

Put the money into a good EQ.

[subharmonic]

Its probably just the bass blending into the rest of the music as it should. Also at lower levels your ears are less sensitive to lower frequencies. Thats what the "Loudness" button used to do with stereos.

I'm with Bill on sound exciters. IMO they ruin the sound balance rather than help. Before you buy a pro amp you may want to check your voltage swing on your current one.

[Radian]

I have the crossover set so the TT runs the info below about 80 Hz or a little higher.

Go a little lower...try somewhere between 60-70 Hz. The TT has a rising response. You're not hearing the lows as loud as they could be.

The plate amp has an internal high pass at 90 Hz, but its only 6 dB/octave.

That has nothing to do with the subwoofer signal. That's the high pass for the line-level output (the RCA outs, AKA "pass-through" signal).

[subharmonic]

BBE..sonic maximizer

Put the money into a good EQ.

Inquiring minds want to know. What do you consider good EQs for home?

[shawn_g]

Inquiring minds want to know. What do you consider good EQs for home?

I've been eyeing the MiniDSP. It's a small 2x4 system processor that's programmed via computer. It has crossovers, delay, and a 31 band graphic EQ or 6 band parametric. The cheapest one is $100 without an enclosure.