Reducing 6 ohms to 4 ohms

[blaze45]

Here is what I am trying to do. I have a few decent quality car speakers laying around and would like to finish off my home theater system. I would like to build some decent speaker boxes and have nice surround sound system. I am a college kid, so $ isnt exactly flowing like rain. However, yesterday after doing some research I found that my receiver has to have a min. of 6 ohms per channel. All the of the car speakers that I have are 4 ohms.

What I would like to do is just put in a 2 ohm resistor and call it a day. The guy at radio shack gave me the dear in the headlights look when I told him this and said there was a lot more to it then just throwing on a resistor, but this is where I am at a loss because he didnt really know himself. What else do I need to look into? What kind of resistor do I need to make this work? I dont really want to run a 2 speakers in a series as I dont have 3 extra laying around! I would be building LR RR and a center speaker to finish off my system.

thanks-

Blaze

 

[blaze45]

Here are the output ratings for my home theater amp.

70.0 Watt - 8.0 Ohm - THD 0.1 % - 1.0 channel(s) ( Front ) , 70.0 Watt - 6.0 Ohm - THD 0.1 % - 2.0 channel(s) ( Center ) , 50.0 Watt - 6.0 Ohm - THD 0.08 % - 2.0 channel(s) ( Rear ) , 30.0 Watt - 8.0 Ohm - THD 0.08 % - 1.0 channel(s) ( Front ) , 50.0 Watt - 8.0 Ohm - THD 0.08 % - 2.0 channel(s) ( Rear ) , 20.0 Watt - 6.0 Ohm - THD 0.1 % - 2.0 channel(s) ( Center )

Are they really going to sound that bad? Like you said, since they will be the RR LR, I dont think that they will see that much use, only for certain parts of the movie of course. However, the center speaker will be used a lot. At the current power output that I am looking per speaker you dont think that it will be halfway decent? My expectations are considerably low since this is kind of a ghetto way of setting up a sound system.

Thank you so much for your help thus far!

Am I going to need a resistor (the one you posted up earlier) for pos. and neg wires? Also, I dont have a subwoofer, will having one connected really make that big of a difference? As for a fan for the resistors, could I just put them in line and and let them sit static without a fan like on the carpet on the way to the spearker? What does it mean to derate at higher tempatures? Sorry if these are newb questions. I just dont want to toast my amp or pop any speakers. I am quick learner and am willing to listen.


Thanks again.

 

[blaze45]

This is great! Thank you so much for your help! I will hook them up and just see what happens. My receiver is an onkyo tx sv373. I know it has some sort of fuse in it but I am worried I will toast something. If it cant take the speaker, will it pop the fuse (I can see one inside) or will I toast something on the electronics board?

Once again, thank you so much for your help!

 

[blaze45]

Well I hooked up the RR and LR as well as the two fronts with a sub that my parents have. It put off some heat, but not anymore then normal. I only watched the first 10min of James Bond Quantum of Solace when he is racing around. I didn't hook up the center channel though. I want to run two in front in a series. I am slightly surprised that the amp survived test, although I didnt watch the movie for an extended period of time.

Everything seemed fine. Now I am off to build the boxes... I am using 2 6x9 coaxial speakers. What kind of outer dimensions should I use for the boxes? I understand that you need the proper cubic size inside the box for best quality sound. For my center I will be using 2 coaxial 6x3's. Should I just double the measurements that I would use for one??

I REALLY appreciate your help, thanks!

-Blaze

 

[blaze45]

As you can tell, my expectations are low for this setup. Is there any websites that you would recommend for placing the baffle? I cannot for the life of me seem to find where I would work out #s to figure out what size speaker box that I need. I also cannot seem to find the specs for my speaker. It only says 200 watts max operating and 98 db sensitivity w/ a 30oz magnet. Its a sentrek sr6931. The box that you mentioned above, this is what I would use for a 6x9 correct? What size box would you suggest for the two 6x3s (kenwood peak 160watts 4 ohms magnet size 8.1oz kfc1679ie) that I want to run for the center channel?

Thank you so much for help!

Blaze

 

[blaze45]

What size sheet MDF do you think that I should pick up? Alright, for the front channel- I plan on making a 7in (height)x22(width)x4in(deep) box. How would you suggest placing the baffles in the front speaker? I also herd that some people place some sort of material inside for better sound. For the RR and LR I was thinking of 8in(H)x2in(width)x 4in(deep) per your recommendations if I were to put the two 6x3s in together in a center channel ( you mentioned 16 x 4 ) so I just halfed that to come up with those #s. I plan on running the 6x3s for the RR and the LR. If I can find out how much wood I need to buy, I want to get started today. I have a round blade saw and a jig saw, but no router. How would you recomend running the wire out of the speaker box? I plan on using glue (I have some silicone here, would that work just as well?) and screws with the MDF. I dont really plan on porting these boxes, unless you really think that it is a necessity.

I really appreciate your time and help with this project!

 

[blaze45]

I am really excited to get started with this, as I go I will take a few photos. I am going out of town later this week but I think that I should have at least one done before then!!!

 

[blaze45]

Soooo I started the construction of the speakers and the kenwoods that I want to use for the RR and LR are actually 6in 1/4 from edge to edge. The actually speaker is about 5in across. This really throws off what I should do for the side speakers box size wise. Would the fact that these speakers are actually bigger then a 6x3 change your opinion that I should use them and use them for the center channel instead? I am anxiously awaiting your response as I am trying to do this as we speak lol.

I love doing DIY stuff!

 

[blaze45]

Alright then I will stick with the 6x9s in the front. However, my size estimate of the kenwoods was wrong so I am still wondering what dimensions I should go with for the RR and the LR since they are not 6x3s, they are the 6x6s... I am heading out of town to go fishing for a day or two but thursday there should be some real progress... Time difference... lol it alright. I am mountain standard time which your in Calcutta so I dont know how many hours difference that is... At any rate, I have really enjoyed our correspondence thus far and how knowledgeable about this stuff you are.

Thanks!

 

[blaze45]

Well, I really am grateful for the help! I worked on cars for quite a while and since then, everything I do has become DIY lol, sometimes it doesnt look the best but function usually turns out alright and if done properly it lasts! Ill be all over the pictures, no worries.

Thanks again!

 

[blaze45]

OK! So the first box the (7x9) has been built! I still have to put on 2 sides but for the most part, the speaker hole is cut and its mostly in one piece. However, before I seal it up, do I need a baffle in these rear speakers or just the center? Before I mount the speaker, do I need to put some sort of rubber padding around the speaker so that it seals tight or does it not matter right around the speaker?

I think thats it so I will post up some pics when I finish with the other one. Its a bit more time consuming then I first thought and I kinda hurried so I am off an 1/16th here or there and its kinda annoying. This is my first project so... The outside will be covered with some carpet that we have laying around so nobody will ever know... I am making sure that it is air tight by doing 2 layers of wood glue over the seems (we surprisingly have a lot of glue!!!). :licklips:

One last question, I would also like to put some sort of material in there because I have read that it helps with something (slipping my mind). I have some carpet padding laying around or stuff like that sort. I herd there was something cheap that you can buy that makes a really big difference? What are your recommendations?

 

[blaze45]

I did not get accomplished everything that I wanted today because I had to work but I did get a decent ways along... Here are some photos...



The glue bottle can be seen in the background. I sqeezed it and the bottle poped and then it was all over the place. Here I just piloted the holes and then put in some screws.






You can tell my measuring isnt soo hot. Its my first time really working with wood. Each time I cut it gets better and better but I am still off a lot and it makes for awkward sized boards. Shoot. lol. I have been making sure its air tight on the seems with some wood glue... The screw situation is just what I have laying around. The wood screw that is med. length works well and so I only use it when I really need to tie something down tight because I dont have very many of them left.



I would have to say the hardest part today was being off on my measurements ( I measured 3x and then cut... ) and not being able to find a compass to make sure that the speaker hole was cut right and centerd. I am about 1/2 in off on one side. I did my best to center it, but it didnt work.... I love this kinda stuff and I am really enjoying it. More progress tomorrow! My brother-in-law gave me about 150ft of copper wire today. Its a pretty thick gauge and saved me some $$$ so I didnt have to go really ghetto and tear apart a wiring harness from a car that I have laying around...

 

[blaze45]

Today went well, although it did have its set backs here an there. Building the center box was a lot easier and the box was far easier then the other two. For some people its measure twice cut once. I measured like 10 times and was still off but finally figured out what you meant by measuring on a plane. I had a hard time being level with my lines cause my square only went to 22in. Not that that is an excuse but it added to the fun. The two smaller boxes, I am ashamed of but I have learned a lot from them.

Here we go with the photos.

Wait before I forget, how much of this polyfill do I put in the boxes? There was some laying around the house. I read if you put in too much that it can decrease the sound quality while not enough will not bring the best desired results. Also, for the center channel, I cut out a center peice to sick into the box so that each speaker will have its own box or "section" if you will. This is what I needed to do correct?

How do I know which post is pos. and neg? I have always assumed that the skinny one is the ground and the fatter of the two is the pos. Am I wrong? I would like to make sure that the speaker is sealed. I have some spare bike intertube laying around. Should I find something different in the garage or will this stuff be sufficient?

I started at 10 this morning. Its now 8:30. I have no life, well while school is out anyways. :indifferent14:


Here is one of the smaller boxes..




And the terminal question-



And a test fit...


Letting the glue dry....



I tried to take a picture using the 10 sec timer on my camera. I didnt aim it very well. Enjoy.



Starting the center channel box... I didnt have anything to use as a template to cut out the holes for the speakers so I kinda eyeballed it and traced out the speakers and then used the jig saw to cut the holes. The first one I was a bit too liberal and ended up gluing back a small piece in the upper LH corner but the other hole went fine.



On this corner I put a little too much pressure on the screw and it was towards the outside to begin with and now we have this... :sad: The carpet covering will take care of it... But still..



I used some cuaulk we had laying around to make sure that it was air tight. I have read mixed results about it harming the speaker. I am letting it dry, so I dont think the fumes will be that big of a deal. Also, in the middle of the box is the ( I dont know what to call it lol ) baffle to separate the speakers. I am supposed to have this here correct?



Thats all for today. Maybe in the morning if I am feeling ambitious I will cut some of the carpet to size and cover them....

 

[blaze45]

Well, here are some more pictures. I still have yet to cover the RR or the LR with carpet.

Enjoy.
Poly fill that was laying around the house.




Finished product. I think that I still might cover the bottom, but I am not sure.



I hooked up this speaker to the FR to test it and it sounded great. Especially the mid- to high range sounds. Not soo much bass, but as a center channel, it will do its job well...


I have been thinking about making my own sub box for a home system, what kind of things could I do to put something together cheap and make the box myself? I really enjoyed this project thus far and have learned a lot. Maybe I should just buy a sub already built and ready to go? Nah... thats too much $$$ lol. Anyhow let me know what my options would be... thank you so much for your help!!!

Blaze

 

[blaze45]

Yeah they are kinda a bit ghetto one would say, but I just used what was around the house and spent a grand total of $25 for everything. It will work well for being at college. Thanks for all the help!