First X-over

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well, this is my first attempt at a two-way. from recepe, not my own.
the all aluminum mtm from last years catalog. A 732. vifa/dayton.
maybe put into action next weekend. it is stock except for and added 2 ohm resistor pre-woofer to bring to 6 ohm. thanks phil

[rogoll]

Re: First X-over

Wow! What is the wattage rating on the lower resistor? I imagine that's the 2 Ohm one in series with the woofer?

[johnastockman]

Re: First X-over

Unfortunately, adding a resistor to get them to a more amp-friendly 6 or 8 ohms changes more than the overall impedance of the speaker. If the resistor is before the woofers and their XO, it's going to be taking a majority of the wattage and could get too hot if it's not rated high enough. When I first started hanging around here, I was told that it's never a good idea to do this...too many variables will happen, which can affect the final SQ, usually in a negative way. It could work, and you might like how it sounds, but without a final check of the impedance (and not with just a multi-meter), the result you're after with bringing them up to 6 ohms might not work out that way. Impedance is dependent on frequency, not a constant figure across the speaker's freq. range.

John A.

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Re: First X-over

pehaps i'll check it both ways and see what sounds best. how would one check to see if this is a good move or not? i have read that my onkyo, even though it claims good to 6 ohm, will do a four ohm load.. will see. this 2 ohm resistor addition was suggested to be ok by phillip arcario so maybe it just might be ok.

[Wolf]

Re: First X-over

pehaps i'll check it both ways and see what sounds best. how would one check to see if this is a good move or not? i have read that my onkyo, even though it claims good to 6 ohm, will do a four ohm load.. will see. this 2 ohm resistor addition was suggested to be ok by phillip arcario so maybe it just might be ok.

Even if you did add a 2 ohm for a net impedance increase, it should be applied before BOTH xovers. This is because if you only place this in the woofer network, the tweeter will then become too loud in reference to the woofer. The 2 ohm you used should be placed 'globally', instead of 'locally'.
Later,
Wolf

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Re: First X-over

the risistor is a dale d50 50watt.
wolf, what you say is logical. i' try that too.
i have no way to measure any of this.

[mgrabow]

Re: First X-over

You have studied I see. Nice spacing... Want a job? [just kidding... the ecomomy is killing me]

[Bob Scott]

Re: First X-over

I like the air core inductors, and the film caps.
That's the first time I've seen perforated hardboard used as a PCB!

I'm also planning a couple of Xovers. Why does everyone seem to avoid the convenience of using terminal strips? Example from Radio Shack, (shown upside down to illustrate the total absence of their technical expertise):

Not everything needs to be on PCB! I believe Mouser also handles a LARGE variety of these. Digikey and Jameco don't.

I'm also going to copy British Industries old method of mounting crossover parts and terminal strips on small pieces of high quality plywood, the thin multilayer kind you find in crafts stores. Oh, and L pads on the tweeters to compensate for frequency response changes with room acoustics.

[Edit]: You do realize that adding a 2 Ohm resistor in series with a speaker increases its Q, don't you? I believe that you can calculate the change by taking a look at the equation for Thiele Small parameters for electrical Qes in Wikipedia, that is, if you need to.

Bob

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Re: First X-over

i removed the 2ohm resistors. it made the woofers dull and the tweeter loud. i'm guessing it needed to be incorperated globaly and not locally.:D i have seen where many have claimed that their onkyo 606 can handled a 4 ohm load just fine, so, so will i. i do have a fan blowing fresh air over the unit through a rather large heatsink.
question: will these get hot? can i screw them down with a piece of foam under or will they need air flow? ie; stands?

[Wolf]

Peg-board is easier to use....

I like the air core inductors, and the film caps.
That's the first time I've seen perforated hardboard used as a PCB!

Funny- that's my typical method! Peg-board and zip-ties RULE!!

This network weighs in at 3 oz shy of 3 pounds.
What a brick!!





Terminal strips are not really intuitive. If you can solder point-to-point in a layout, and aline your parts well, you can do it very compactly without need of terminal strips. The above is a good illustration of that.

Later,
Wolf

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Re: First X-over

everything i know ive learned from reading and looking at the nice pictures here. i did have to drill four holes so things would look just right.

[johnastockman]

Re: First X-over

i removed the 2ohm resistors. it made the woofers dull and the tweeter loud. i'm guessing it needed to be incorperated globaly and not locally.:D i have seen where many have claimed that their onkyo 606 can handled a 4 ohm load just fine, so, so will i. i do have a fan blowing fresh air over the unit through a rather large heatsink.
question: will these get hot? can i screw them down with a piece of foam under or will they need air flow? ie; stands?

Onkyo are pretty rugged regarding this. A few friends have various models of Onkyo HT receivers and they all have 4 ohm MTMs for front L & R. One guy has an Onkyo stereo receiver with a pair of the large D8 MTMs. Never a complaint about over-heating. We had extremely few service issues with Onkyo when I worked at the audio store. Unless you're running it at elevated volume for long periods, there shouldn't be any problems.

John A.

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Re: First X-over

thanks john. that give me a little confidence. with the three day comming, i should be able to have these in the house.

wolf, i used hot glue too.
thanks mg.

btw, when i first priced this project, the components for the x-over were just 65 dollars! now $130.

[johnastockman]

Re: First X-over

thanks john. that give me a little confidence. with the three day comming, i should be able to have these in the house.

wolf, i used hot glue too.
thanks mg.

btw, when i first priced this project, the components for the x-over were just 65 dollars! now $130.

Sometimes all my audio store experience helps, although it has given me a fair amount of a skeptic's attitude regarding commercial stuff, whether mass-market or high-end/boutique. Most of it relates to speakers, not electronics. Speakers seem to be different animals when it comes to most consumers understanding how things work and so many blindly follow all the hype and techno BS (and the overall looks too) that OEM's put out there. Let us know how things are coming along with your set-up and your impressions of the SQ and and issues you might have. Pics, also!

John A.