JBL GTO sub bass project

[JBL 4645]

Sealed is the best option here.
Any shape will be ok, as long as it is 40L, or around 55L exterior with 18mm walls.

Are you going to build the boxes yourself?
With that many subs calculating the dimensions to maximize your MDF sheets is a good idea indeed!

pos

Sigh I guess I’ll have too! The timber yard might charge twice the amount the build. I think even for hole cut they charge not sure if its £5.00 or 20.00 pounds with the (router drill bit), so I have to phone before going down to the yard and find out what the hole size cuts cost.

I’ll make the box myself with timber battens placed around the inside and countersink the holes on the outside, glue and screw it up tight and run some extra sealant around the inside to make sure it’s (air-tight).


Also the GTO is fitted with (Parallel or Series connections)

Which is the best option to get two GTO to run at 4 ohm load because I don’t think the Alesis RA500 which I plan to get might not like what it sees as its rated down at 4 ohms, I don’t want to start causing (popping sounds) because its been ran in the wrong order of wiring.

I would like to run a single amp on each sub but the cost of the amps will be skyrocketing in cost! Plus I have to get another DCX2496 to add the crossover slopes and few LP filter added.

[Ruediger]

In Thiele's paper there is alignment #10, a B5 alignment: f3/fs = 1.0, Vas/Vab = 1.0, Qt = 0.447.

That means: f3 = fs = 23.5 Hz, Vab = Vas = 98 liter.

You need a passive filter as well. See the Thiele paper. It is in the "General Audio Discussions" forum here at Lansing Heritage in the "Technical References" thread.

Ruediger

[pos]

Try not to go much smaller than 40L. On the other hand you can go larger without problem.

[pos]

In Thiele's paper there is alignment #10, a B5 alignment: f3/fs = 1.0, Vas/Vab = 1.0, Qt = 0.447.

That means: f3 = fs = 23.5 Hz, Vab = Vas = 98 liter.

You need a passive filter as well. See the Thiele paper. It is in the "General Audio Discussions" forum here at Lansing Heritage in the "Technical References" thread.

Ruediger

That means a box more than twice the size of the sealed one, plus dealing with the vent...
The sealed box is the easy option, very forgiving with errors in box size, and predicatable in load to the amplifier, and in excursion. With 8 or 16 subs to build, mainly with the goal of smoothing the response across the room (and not max SPL), the sealed option looks like the way to go IMHO.

[JBL 4645]

Cheers pos / Ruediger

Okay I’ll keep to those the perimeters.

Just been chatting to my dad about how many cuts I can get out of 4x8 sheet.

I need to get the MDF sheet cut in half and then get the rest of the cuts out of it as the saw is most likely 4mm thick and most the cut sized MDF won’t be at the same size. I guess this why it took my friend so long to do the other sub bass box it was mostly sanding it down to shape the box.

Roughly where do you see the (excursion) occurring at, what frequency? Not that it worries me I doubt I’d be running it at Earthquake levels! LOL It would take a lot of subs to do that to make the town rumble!

I have the Crown power calculator that shows me how much is required for given distance at 85db.

Every time I run the other JBL sub and due to room nulls dips and peaks from its location to sofa, at times its running far too high which sends the neighbours barking mad! LOL Well it can’t worse than listening to dog barking for some 12 hours none-stop in the day!

It’s when I’m playing a certain part of the low end frequency under or around +100dbc I get an polite knock on the door.

So I’ve got more frequency SPL db at the front corner of the room and less of it is reaching the sofa at given distance away! Therefore I have to push it many db higher for the frequency loss! So more subs around the room will require less power yet they might producer purer stronger tones at less power!

[pos]

with sealed boxes you do not have to worry about excursion that much. The driver are never unloaded like in a reflex box under the tuning frequency. You will simply have an increasing excursion as you go lower in frequency (4 times the excursion when going 1 octave lower, if you eq to get a constant SPL at all frequencies).
You will most probably be limited by your amplifier.

You better buy a multimeter to test your wiring (Re), because with 16 dual coil woofers you better knwo what you are doing when plugin something into your amplifier (don't knwo if the alesis has good protections).
Also a battery to test polarity (one woofer out of phase will be difficult to notice)

[JBL 4645]

pos cheers for the resonances.

That’s more or less what I read somewhere a few days ago about (air compression) or the box being tighter seal the cone when pressing on it is stiffer rather than having bit of flex.

Okay so sealed it is. I’ll call up tomorrow and get an estimate on the size cuts and the hole cut out.

Oh, I’m not replacing the other JBL sub that still stays!

Oh yes good point tip I’ll check with 1.5v battery to make sure.

I have an analogue volt meter.

The Alesis are rated 4 to 8 ohms.

The JBL GTO 1202D are rated 1 to 4 ohm

I read that is a way of wiring the 4 ohms speakers to give an 8 ohm resistance?

I’ve hardly used the volt meter it has X1K and X10 which setting should I select?

I see the green scale on the volt meter that runs from 0 ohm to 200 ohm it’s not a good picture I’m afraid. Its a KINZO 18D265

I’m afraid I agree about the EQ and limiting the amps power but I hope it needs less if I can get smoothness as even as possible with less demand from the PEQ (parametric) that will be good, but I’ll have to see how each one progresses I might run into a few snags or difficulties.

[Ruediger]

I wasn't aware of the low impedance of these speakers. Wiring them in series has a bad influence on the resulting Qt. Forget about the Thiele alignment. Or get an amp which can handle 1 Ohm loads.

Ruediger

[JBL 4645]

I wasn't aware of the low impedance of these speakers. Wiring them in series has a bad influence on the resulting Qt. Forget about the Thiele alignment. Or get an amp which can handle 1 Ohm loads.

Ruediger

When I stuffed into the Eltax sub and warped a towel around the edges to make it tight as possible it played without any issues (that is without any issues that I couldn’t see).

A 1 ohm amp, I wonder how much that will cost?

[JBL 4645]

I almost I almost forgot about the terminal plate for the back of the loudspeaker!

I’ll get these

http://www.maplin.co.uk/module.aspx?...C=SO&U=Strat15

Loudspeaker Lever Terminals
only £1.49

Then again these for tighter grip!!

http://www.maplin.co.uk/Module.aspx?ModuleNo=1077

Twin Terminal Post
only £3.39

I’m not really fused about which ones, but on budget the spring load terminal plate will be bit flatter and I get it near to the wall.

I’ve got to make a few trips now!!

[Hoerninger]

A 1 ohm amp, I wonder how much that will cost?

It might be a choice to buy 16 pieces of 50 Watt amp kits with one sufficient power supply.
>What is the intension of your project
___________
Peter

[JBL 4645]

Morning Peter

I’ve got to make a few trips!

I was just doing the size up and about to pop out. The intention is nuclear meltdown! just kidding. Car amps will do it! But need transform to run them and the cost I can see it being enormous!

There has to be cheaper means around this, there has to be?

See you in jiffy

[hjames]

Of course, if you need a a bunch of 50 watt amps, you could look for an Adcom GFA-2535.
Its got 4 channels at 60w/ch. Plus, one pair can be bridged to roughly 150w ... so its versatile.
I've got one of those for my 2 surrounds and center - its a good amp with a good sound.
Get a pair of those and you have 8 channels at 60w/ch - if you wanted 50w/ch, 60 will certainly do!


I know Rotel made some 5 channel amps of about the same wattage for home theatre use ...

There are others, but those are good quality, yet old enough to be reasonable priced on the used market.

But if brand and quality isn't important, there are a lot more possibilities.

[Hoerninger]

The intention is nuclear meltdown!

See you in jiffy

War with some neighbours?
Und tschüß
____________
Peter

[Ruediger]

I checked the description on the net (www.jbl.com). The 1202D is a Dual-2-Ohm-Voice-Coil Subwoofer with an impedance of either 4 Ohm or 1 Ohm, depending on the wiring. So no problems.

Ruediger