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First 12v sound system plans

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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 11:11am
Yes you will need the L-Pad. It is just 2 resistors, so don't be scared ;)

107-95 = 12dB. So you need to lose 12dB of signal at the tweeter, in order for it to be the same loudness as the woofer, rather than overpowering it completely (this will sound far too harsh and terrible)

At 8 ohms, a -12dB L-Pad can be made of: one 6 ohm resistor in series with the driver, followed by one 2.6 ohm resistor in parallel with the driver.


Use 20 or 50 watt wirewound resistors. They will probably not need heatsinks but it is good practice.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 11:52am
Originally posted by studio45 studio45 wrote:

Yes you will need the L-Pad. It is just 2 resistors, so don't be scared ;)

107-95 = 12dB. So you need to lose 12dB of signal at the tweeter, in order for it to be the same loudness as the woofer, rather than overpowering it completely (this will sound far too harsh and terrible)

At 8 ohms, a -12dB L-Pad can be made of: one 6 ohm resistor in series with the driver, followed by one 2.6 ohm resistor in parallel with the driver.

Here is a calculator:  https://www.diyaudioand.com/Calculator/DriverAttenuationLPadCircuit/ - https://www.diyaudioandvideo.com/Calculator/DriverAttenuationLPadCircuit/

Use 20 or 50 watt wirewound resistors. They will probably not need heatsinks but it is good practice.

Cool perfect thanks! Ive never done anything like this before so i am out my depth, but really want to give it a go. 

So the resistors litterally just solder into the speaker cable? I saw the diagramf where they go but are they just soldered in place to the speaker cable?

Also how do you heatsink them?!
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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 1:52pm
If you look up some pictures of 50 watt metal clad resistors, you will see what I mean. You will need to mount them on something, they can't just be free-living in your box! But yes they solder inline with the speaker cables, or you can use a screw terminal block to make the connections. This would be good for testing, as you can get a few different values of resistor and swap them in and out to get exactly the right level of attenuation. 12dB might be just a bit too much, or too little. Your ears will tell you.
A heat sink is just a chunky piece of metal with fins mouled into it. Usually aluminium. It helps disperse heat generated in the resistor. You bolt or rivet the resistors to it, by their mounting holes. Or, if you end up with the ceramic type without mounting holes, you can use some heat-transfer adhesive - same stuff as used to glue heatsinks onto computer CPU's. 
But in fairness, I don't think you will be putting so much power through your tweeter, that the resistors will ever get more than warm. So probably don't worry about heatsinks for this project, unless during testing, you find you have a problem with heat. Just mount the resistors to a piece of wood using wire ties.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 2:07pm
Originally posted by studio45 studio45 wrote:

If you look up some pictures of 50 watt metal clad resistors, you will see what I mean. You will need to mount them on something, they can't just be free-living in your box! But yes they solder inline with the speaker cables, or you can use a screw terminal block to make the connections. This would be good for testing, as you can get a few different values of resistor and swap them in and out to get exactly the right level of attenuation. 12dB might be just a bit too much, or too little. Your ears will tell you.
A heat sink is just a chunky piece of metal with fins mouled into it. Usually aluminium. It helps disperse heat generated in the resistor. You bolt or rivet the resistors to it, by their mounting holes. Or, if you end up with the ceramic type without mounting holes, you can use some heat-transfer adhesive - same stuff as used to glue heatsinks onto computer CPU's. 
But in fairness, I don't think you will be putting so much power through your tweeter, that the resistors will ever get more than warm. So probably don't worry about heatsinks for this project, unless during testing, you find you have a problem with heat. Just mount the resistors to a piece of wood using wire ties.

Perfect thank you! Im glad you said about them not being "free living" in the box as thats what i wanted to know.

So i can just solder the resistors in the correct positions, cable tie to a piece of wood and then screw the wood to the inside of the speaker box.

So once ive got the mid speaker and tweeter connected to the crossover and the resistors connected to the tweeter that will then be it for the 2 way speaker. No more surprises lol? 

Do you have any reccomended sites for buying the resistors? 


Edited by Jack1991 - 10 February 2020 at 2:09pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote concept-10 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 2:15pm
Jack, we have our own 12" tapped horns, similar to the Tham 12, the Beyma 12lx60 v2s have been taken out and Thomann 12Ws are in as we speak, you will love it Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 2:24pm
Originally posted by concept-10 concept-10 wrote:

Jack, we have our own 12" tapped horns, similar to the Tham 12, the Beyma 12lx60 v2s have been taken out and Thomann 12Ws are in as we speak, you will love it Smile

Oh thats great! Im glad its working well. I cant wait to build it but want to make sure i know 100% what im doing before i even begin any of it. As i feel  like im learning another language trying to learn the ins and outs of speaker building haha
What amp are you using to power it are you running 12v too?


Edited by Jack1991 - 10 February 2020 at 2:41pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote concept-10 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 3:05pm
No, Crest buddy, another thought, you will need to high pass the Tham, there is a 12v car amp with high and low pass filters, class d and quite cheap, made by BASSFACE, I will have a look later for you. I will also have a play with high and low pass filters and give you some settings.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 7:19pm
Oh okay cool. 

Ah yeh the pioneer amp i have been looking at is class d with low/pass filters https://www.google.com/search?q=Pioneer+GM-DX874&client=ms-android-ee-uk-revc&prmd=svin&sxsrf=ACYBGNSY0DUQYHxVtfKahvNuanb7P5T5qA:1581362231740&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjb3dWw2cfnAhWhwOYKHToeCFsQ_AUoA3oECA8QAw&biw=360&bih=660&dpr=3#imgrc=utAleN-8q6LqtM

Dont you mean low pass filter the sub not high pass?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote concept-10 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 7:46pm
No, high pass around 40hz and low pass about 100-120hz.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote concept-10 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 7:52pm
This would do for your bass, bridged, with a subsonic high pass filter and a low pass to your mid tops, not a bad price.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2020 at 8:57pm
Originally posted by concept-10 concept-10 wrote:

No, high pass around 40hz and low pass about 100-120hz.


Thanks for the info and the amp recomendation 😀

The filtering though is different to what i have read everywhere else. Im not saying your wrong obviously just im real confused.

I always thought for example 1 channel with sub i would lpf the sub around 80-100hz 

And then 2nd channel with mid/top speaker i would hpf around 100-150hz
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Post Options Post Options   Thanks (0) Thanks(0)   Quote concept-10 Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2020 at 9:20pm
You still have to high pass the tham At 40ish then low pass it at 1-120 then high pas the mid top.
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