Frankensub - a cheap Edge meets a marginally less cheap GT5

[celshady]

Hi //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I've been running a cheapo active Edge EDB12A sub for about 5 years.

About 6 months ago I noticed the centre of the cone had come away and it was buzzing. Sooo, I ripped it off and used some adhesive resin to glue it back. Wasn't really thinking beyond 'fix it'. From this point onwards the bass was still there but only in volume - I'd lost all my low frequencies.

I put up with it for a bit but it was essentially pointless. This week I decided to shove a new woofer in the box rather than buy a whole new box - genius thinking right? I took the old edge woofer out, measured the depth of the box quickly and badly with a Tintin ruler I got for my 14th birthday, decided I had enough space for a JBL GT5 and bought one.

Today it arrived and I shoved the GT5 in and remounted it, using maybe 4 of the old screw holes and making 4 new holes very close to the old ones because I'm a thorough kind of chap. It was a bit of a squeeze, and for a while I thought it was resting on the port tube thingemer, but a bit of wiggling got it past whatever the obstruction was (possibly the amp mounting bit, which had been shaved off anyway). I have no idea how close the coil is to the tube, but my best guess is very.

Preparing myself for it to vibrate against the tube and make me sad I stuck it in the car and connected it up (thanking sweet baby Jesus for the quick release kit), turned the gain and boost down to half for the running-in period and tried it out.

It seems fine. No vibration suggesting I've mounted it badly or I'm hitting the tube.

I can't imagine I'm the first person to try this, so has anyone else done something similar? Anything I should know or look out for?

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[celshady]

Huh, today it doesn't seem to be working at all. I must be cursed

 

[celshady]

Nope, it's working (idiot) but it needs tuning

 

[hispls 5,000+ posts]

Not really getting the question???

If you put a woofer in a box that seals the rear wave off from the front wave it will make sound. Whatever you've done may or may not be optimum (most likely not if you're using a prefab box), but you should be able to play music on it. Apart from the moving parts, having some part of the woofer touching something won't mechanically hurt anything.

 

[celshady]

Yeah I didn't really phrase it well. I guess I'm wondering how the sound will be affected by having a different woofer in a prefab box. I would presume that a deeper woofer would need a deeper box, or is it all about the different properties? Thing is I don't know what the specs are for the Edge woofer I took out, so no idea if the JBL is close or not.

 

[bbeljefe]

No one can tell you if the sub you installed will work well without knowing the specs of the box and the sub that was in it. It could be that the JBL sub is a good match for that box and it could be the opposite but mounting depth is not an indicator.

Ultimately, if the JBL sub sounds good to you then it will work just fine. But the thing that worries me is your comment about turning the gain down to half way for break in. Unless you're running a line out converter from a factory head unit or you have an aftermarket head unit with very low preamp voltage... your gain was and still is too high.

Gain is not a volume control to be set to preference. It is a voltage matching pot that should be set when the amp is installed and not changed. Chances are that your gain setting is the cause of your original sub's death and if you don't address the problem now, you'll wind up with another dead sub.

As for the "break in" period... it's not something you have to do. A speaker's suspension will loosen up after ~8 hours of play time and that's going to happen whether you want it to or not. Going easy on the sub will make it take longer to break in but it won't help the sub live longer or sound better at all. Assuming you have a clean signal, play it the first time like you plan to play it after the "break in" period. It will either break or it will work. If it breaks, there's a defect and you want to know that sooner rather than later.

 

[celshady]

But the thing that worries me is your comment about turning the gain down to half way for break in. Unless you're running a line out converter from a factory head unit or you have an aftermarket head unit with very low preamp voltage... your gain was and still is too high.
Gain is not a volume control to be set to preference. It is a voltage matching pot that should be set when the amp is installed and not changed. Chances are that your gain setting is the cause of your original sub's death and if you don't address the problem now, you'll wind up with another dead sub.

As for the "break in" period... it's not something you have to do. A speaker's suspension will loosen up after ~8 hours of play time and that's going to happen whether you want it to or not. Going easy on the sub will make it take longer to break in but it won't help the sub live longer or sound better at all. Assuming you have a clean signal, play it the first time like you plan to play it after the "break in" period. It will either break or it will work. If it breaks, there's a defect and you want to know that sooner rather than later.

Thanks, that's really good info! As you have correctly summed up, I really don't know what I'm doing!

I have an aftermarket head unit but no notion of preamp voltage until I find the model number and look it up.

What spec should I be looking for on the new JBL sub (since I have a spec sheet for that) to match the gain dial to?

 

[bbeljefe]

Thanks, that's really good info! As you have correctly summed up, I really don't know what I'm doing!
I have an aftermarket head unit but no notion of preamp voltage until I find the model number and look it up.

What spec should I be looking for on the new JBL sub (since I have a spec sheet for that) to match the gain dial to?

There is no spec on the sub that will affect gain setting. Gain setting matches the preamp voltage (output) to your amp's input sensitivity and how many or what kind of subs you have connected to the amp doesn't matter.

Get me the model number of your head unit and I'll do my best to help you get the gain set to a safe level without you having to have any test equipment. If you have a multimeter you can get closer with the gain setting but it's not altogether necessary. Also... do you have your front speakers on an external amplifier or are they running from head unit power?

 

[celshady]

There is no spec on the sub that will affect gain setting. Gain setting matches the preamp voltage (output) to your amp's input sensitivity and how many or what kind of subs you have connected to the amp doesn't matter.
Get me the model number of your head unit and I'll do my best to help you get the gain set to a safe level without you having to have any test equipment. If you have a multimeter you can get closer with the gain setting but it's not altogether necessary. Also... do you have your front speakers on an external amplifier or are they running from head unit power?

Thanks, that's very generous of you!

The model number of the head unit is 'JVC KW-XR811'. I also have 2 front and 2 rear speakers running from head unit power.

I can likely dig a multimeter out too //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[bbeljefe]

If your front stage is on head unit power you'll want to set the head unit volume control at 50-55% of full volume for gain setting. If that head unit goes to 45 then that setting would be 23-5. That setting is about where the head unit amplifier will begin to distort. After that, set bass/treble and or all EQs to flat, turn off any loudness or bass boost circuits and find yourself a 40Hz -5dB test tone. You can get the DD-1 test tracks here at the bottom of the page, then convert the .rar file and use track #3 .

Then, on your amp, set gain & bass boost(if any) to their lowest setting and set the low pass filter to its highest setting. Set the meter to AC voltage on the 200 volt scale and with the sub disconnected, probe the speaker outputs from the amp while playing the 40Hz tone mentioned above. Then turn the gain up until your meter displays the target voltage.

Since I don't know if your amp is setup for 4Ω or 2Ω operation, there are two choices on the target voltage. If it's a 2Ω stable amp and we set the gain for 300 watts on your 4Ω sub it's likely to overdrive the amp but, if we set it to 150 watts we may be leaving some power on the table. With that in mind, set the amp to 25 volts of output first. The gain knob should end up somewhere around the 1 o'clock position. If so, it's not 2Ω stable. But if it's still at or around the 10 o'clock position, you have more power available safely. And in the latter case, go ahead and turn the gain up until the output voltage is 34 volts.