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ISO 100 Build - 20hz for under $100

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123Toid
(@123toid)
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Parts Needed

Box Dimensions and Cut List

External Box Dimensions - Using 3/4" Material

  • Height: 24"
  • Width: 30"
  • Depth: 18"

This box uses 3/4" material.

Sample Cut List:

  • Front and Rear Baffle: 30" x 24"
  • Top and Bottom: 30" x 16 1/2"
  • Ends: 16 1/2" x 22 1/2"

Ports

Ports. You will need 2 of the Precision ports. If using the precision ports like I uses, you will cut the straight piece to 7" and then glue the flares on. With flared ends, it'll be about 13" in total length. These are designed to be glued on with ABS plumbers glue. However, you can use superglue or any other type of glue. Just make sure their are no air leaks in the port. If you decide to use something else, like PVC pipe a good guesstimate would be about 10" long, However, since I didn't do that, I can't say for sure. I would recommend flaring the ports if you decide to make your own.

Speaker Cutouts and Attachment

I did recess the woofer from on the outside of the box so that it would sit flush. This will be important to do if you decide to turn it into an end table. This allows you to put on around 6" legs. Without this you will want to raise the legs up higher. Each woofer is placed 12" from the bottom and 7 1/2" from the side. The ports will be 5" from the top or bottom and 15" from the sides. You will need to line up the holes correctly so you can bolt the subwoofers together. You can use a centering punch, or what I will do is put the driver in the recess and drill one hole out. Attach a bolt then drill a second hole on the other side. Attach another bolt. The woofer should no longer be able to move, then you can drill all the other holes without worrying about it moving. Just make sure to drill them directly down and not at an angle.

The easiest way to attach the woofers to the front baffle is to use bolts and nuts. I would recommend either locking nuts or double nuts to make sure they do not come loose. You can pick up bolts pretty cheap at your local hardware store. Places like Ace Hardware will sell them by the bolt, which is often times cheaper than buying them in bulk. I used 10-24 bolts that were 1 and 1/2" long. I would not use anything shorter, and it might make it easier for some if they bought 2" long screws. It would help, especially when starting the first nuts. You will need 16 of these bolts and nuts (32 nuts if you decide to double nut it).

Bracing

For the bracing I just use scarp from what I have cut that is the same size as the internal dimensions of the box. These strips I cut around 1.5" wide using that 3/4" scrap. I try to use 12 of these and make sure to glue them together. But you need to make sure you keep plenty of room to remove and install the subwoofers. Make sure they do not go over the ports or where the ports will be. I would wait to glue these in, until after the port were installed. For bracing you will want the following 1.5" strips cut.

  • 4 - 28.5" long
  • 4 - 22.5" long
  • 4 - 16.5" long

 

Wiring

Each pair of woofers will be wired parallel out of phase. This allows each woofer to move with each other. AKA when one is going in, the other is going out. On the inside of the box you will now have 4 wires that need to go to the amplifier. These will be wired in series to get to a 4 ohm load. The diagram below shows you how to do it, if you are unfamiliar with this terminology.

I used a terminal cup to pass the wires from the inside of the box to the outside of the box. You can use anything you want including binding posts. One thing to think about though, is making sure your wires will be close to your terminal cup. So when placing the woofers and screwing them down, pay attention to where you'll be attaching those wires on the woofers.

Basic Assembly Directions

There really is no right or wrong way to do this, but here is what I find the easiest. I glue all the sides on accept the baffle opposite of the woofers (I'll refer to this as the rear baffle). I'll then paint the front baffle where the woofers will be going. Once that is dry I will attach the ports. I'll also mark the height of the subwoofer on the inside of the box. I want to move on to bracing. With bracing there are a few things to keep in mind. You want to leave room for you to be able to remove the subwoofers if you ever need to. So you do not want your bracing in a way that will impede that. You'll want it outside too woofers or at least give you enough room you can remove it if you need to.

I typically glue in around 12 braces. Two going to each side. Glue these to each panel of the box and to each other. This will help the sides flexing and resonating. Keep in mind, you will not glue 4 of the braces to the rear baffle, since it still is not installed. Do not install these over the ports or in the way of your amplifier or subwoofers.

Once that is finished, I would install the drivers, make sure these are tight and secure. you can now wire these and install the terminal cups. Once that is complete you can glue on the rear baffle. I would glue this facing down, that way no glue will drip on to your woofers, ports or terminal cups. Once that is dry do your finish work and hook it up to the amplifier.

https://www.youtube.com/123toid


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Blehaa
(@blehaa)
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Nice build. I think I want to build these. This will be my first speaker build, and seems pretty straight forward. Just wanted to confirm, (excuse my lack of knowledge) I will go from the positive side amp to positive speaker 1 to negative speaker 2 to positive speaker 2 to negative speaker 1 to positive speaker 3 to negative speaker 4 to positive speaker 4 to negative speaker 3 to negative side of amp. That’s how I’m understanding the diagram you posted, just never done a speaker, nor any knowledge about parallel out of phase. 

thanks for the help. 


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TVOR-Ceasar
(@tvor-ceasar)
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@blehaa

Yes, that is exactly correct. If it makes it any easier to visualize, twist speakers 2 & 4 so they face speakers 1 & 3 respectively, and notice the wires will "X" over to the correct terminals and you can see why they need to be out of phase. 

-Charlie
https://www.youtube.com/user/TheTrueVoiceOfReason


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123Toid
(@123toid)
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@blehaa

I'm having a hard time visualizing what it is that you're saying. But I trust true voice of reason. If you do decide to go forward with it, just know that we're here to help you along the way. So when it gets to the wiring phase, you can easily just take some pictures and we'll double check and make sure that it is hooked up properly.

https://www.youtube.com/123toid


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TVOR-Ceasar
(@tvor-ceasar)
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I've got a long work day ahead, but I should have time in the afternoon to hopefully throw together a graphic that better illustrates exactly what should be done.

The diagram 123Toid supplied is 100% correct. I see where your possible confusion could be, since the drivers are in the same orientation, not facing each other and the connection plates are inverted on #'s 2 & 4. That was done for ease of diagramming.

I'll see what I can do in a few hours from now.

-Charlie
https://www.youtube.com/user/TheTrueVoiceOfReason


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Blehaa
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@tvor-ceasar

 

THANK YOU A TON. I was also wondering about the Phase on the AMP itself, do I put the switch to REV or Nor (I'm assuming Reversed or Normal). I Just submitting my order for everything, $285.85 pre tax. 


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TVOR-Ceasar
(@tvor-ceasar)
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You are quite welcome. Always willing to help if I can.

The Rev/Nor switch does sound like a phase switch. These are normally used if, when sitting at your listening position, it seems that the bass just isn't working. Most times that means the bass waves from the sub are out of phase with the main speakers, creating some sort of null at that point. If you change the switch it puts the sub up to 180 degrees out of phase, and you should notice a difference, one way or another.

-Charlie
https://www.youtube.com/user/TheTrueVoiceOfReason


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ttan98
(@ttan98)
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Thanks for your DIY a few questions, please.

I just want to clarify your wiring and installation of the drivers of your subwoofer by showing a diagram attached.

isobaric spkrs

 this image shows only 2 drivers, they other 2 drivers are identically mounted behind these 2 speakers.
Questions please refer to image:

1. these 2 drivers are wired out of phase in parallel.

2. the other 2 drivers also wired out of phase in parallel.

3. (1) and (2) are then wired in series.

if your installation is different, pls supply an actual wiring diagram/image of your DIY


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123Toid
(@123toid)
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@ttan98

 

That is correct both pairs are out of phase in parallel. The wiring from the amplifier to the two pairs is in series. I'll try to update it with a better picture sometime.

https://www.youtube.com/123toid


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123Toid
(@123toid)
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@blehaa

Sweet!  I can't wait to see it!  It is going to be killer!  Just don't start complaining when you neighbors call you up 🤣 

As far as the switch, that is up to the room.  But typically that is left in normal.

https://www.youtube.com/123toid


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ttan98
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Posted by: @123toid

@ttan98

 

That is correct both pairs are out of phase in parallel. The wiring from the amplifier to the two pairs is in series. I'll try to update it with a better picture sometime.

Thanks. Like your DIY on Tangband W5-1138SMF, for a ported single you think the optimum size is 6l or 7litre? Somewhere in between is OK?


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123Toid
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@ttan98

Thanks. That all depends on what you mean by optimum. But I usually like it closer to 10l for optimal low end. 

https://www.youtube.com/123toid


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ttan98
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Posted by: @123toid

@ttan98

Thanks. That all depends on what you mean by optimum. But I usually like it closer to 10l for optimal low end. 

The subwoofer(vented) built by Paul is closer to 6l, you think is too small? Parts express recommends 0.26cu ft(equals to about 7.3 litres), you suggest closer to 10lit. to get closer to 35hz at -3dB?


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TVOR-Ceasar
(@tvor-ceasar)
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Posted by: @ttan98
 
The subwoofer(vented) built by Paul is closer to 6l, you think is too small? Parts express recommends 0.26cu ft(equals to about 7.3 litres), you suggest closer to 10lit. to get closer to 35hz at -3dB?

Well, running the standard calcs as provided for by Thiele-Small, you get a box of 9.34 L (0.33 Cu.Ft.) with a Fb and Fp of 36.7 Hz and a F3 of 32.4 Hz. (Optimum)

Pump that to 10 L (0.355 Cu.Ft.) and you get a Fb and Fp of 35.6 Hz and a F3 of 31.1 Hz, albeit with a very minimal loss of 0.14 dB at Fb, basically unnoticeable.

And that's just pure box, not taking into account what the driver takes up, or even the port. So even if it is a 10 L box, it is probably closer to 9 L or so once the driver is installed and even less with the port.

I can only surmise what Paul is thinking in his design choice, seeing as it's a smaller driver and normally that size would be suited to a slightly higher Fb. (6 L = Fb 42, F3 40.5)
Parts express uses BassBox6, of which I am not acquainted in any way, but it seems they have a "High Quality" option that tends to shy away from absolute bottom end. (0.26 Cu.Ft. = Fb 39.3, F3 36.4) And did you ever notice they don't specify anything for the port even though it is listed as "Ported"?

-Charlie
https://www.youtube.com/user/TheTrueVoiceOfReason


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TVOR-Ceasar
(@tvor-ceasar)
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To help visualize what is going on with the wiring.
This is how most programs would draw it out, but it's not that helpful.

Standard iso wiring diagram   confusing

This is what it would look like in real life and how the wires would connect.

Correct Iso wiring diagram

Now take note, even though you are reversing the wiring on one of the drivers so that as one moves forward, the complementary one moves backward, and vice-versa, they are still in Parallel. That make the two 4 ohm drivers equal to 2 ohms. Then you do the same with the second set and have another 2 ohm pair. Now these pairs get wired together in Series making the total circuit go back to 4 ohms. 

Hope this clears things up.

-Charlie
https://www.youtube.com/user/TheTrueVoiceOfReason


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