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Multi-Way Conventional loudspeakers with crossovers

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Old 10th December 2012, 07:35 PM   #21
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Hi greyhnd, from the pictures you supplied it looks like there is only one component in the crossover, a capacitor. If this is the case then it will be on the tweeter, and the woofers will be running full range.

Since you have two woofers and the speakers are rated at 8 ohms nominal impedance, there are two possibilities.
1. the existing woofers are 4 ohms impedance each and wired in series to give 8 ohms total.
2. the existing woofers are 16 ohms impedance each and wired in parallel to give 8 ohms total.
I guess there is another possibility and that is that the impedance rating on the back of the box is an arbitrary figure marketing chose

If the drivers are wired in series when you swap in one (or both) of the new woofers the impedance will rise to 12 ohms or 16 ohms which will mean higher resistance and therefore lower sound output. for a given drive voltage. (depending on efficiency differences between the woofers).

If the original drivers were 16 ohms and wired in parallel, then when you add a single 8 ohm driver you will get uneven sharing of the current between the drivers, with more of the current going to the lower impedance driver.

If there was a coil on the woofers (in the crossover) then yes changes in impedance would change the frequency at which the crossover cuts in.

Tony,.
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Old 10th December 2012, 10:43 PM   #22
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Hi Tony and thanks for your reply.

After reading your post, I'm not exactly sure the easiest and/or best way to solve the problem. One of my concerns is that the Lepai T-amp I'm powering the speakers with is rated from 4 - 8 Ohms, and it puts out 13W @ 8ohms and 20W @ 4ohms. If I'm not mistaken, the amp will see an 8ohm load regardless on the box that currently has both factory speakers? So if the MCM speakers are both 8 ohms, where does that put me? If I'd known then what I know now I would've ordered 4 ohm replacements.

I hate like the devil to invest a bunch of money in this project, but I'm also not willing to accept defeat. Stubborn perhaps or foolhardy. The speakar with both the MCM drivers installed actually sounds "fuller" then the stock speaker. Do I need to wire the speakers to the crossover differently, or replace/modify the crossover that's in place? I have no problem experimenting, but I'm not smart enough to figure out what direction to go.

My goal is to use the speakers with the new TV I have ordered. I intend to power them with the t-amp if that makes a difference.
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Old 10th December 2012, 11:29 PM   #23
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Quote:
Originally Posted by greyhnd View Post
Lepai T-amp I'm powering the speakers with is rated from 4 - 8 Ohms, and it puts out 13W @ 8ohms and 20W @ 4ohms.
T2020?

dave
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Old 11th December 2012, 01:34 AM   #24
greyhnd is offline greyhnd  United States
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Dave - Yes sir, that's the little Lepai t-amp I'm using. It's not too bad if the tone controls are put on defeat. I bought a 5 amp power supply and it never misses a beat, or at least so far it's been reliable.
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Old 11th December 2012, 01:40 AM   #25
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Hi greyhnd as a start so we know what we are dealing with, if you have a multimeter, put it in ohms mode and measure the resistance of one of the MCM woofers (disconnected) and also measure the resistance of one of the kenwoods.

The next step is to trace out exactly where the wires connect from your panel/crossover to the speakers. It looks from the pictures like the woofers don't have any crossover components, but I'm not certain about that.

If the speakers turn out to be wired in series currently, you should be able to wire them in parallel instead though the resulting impedance will be nominally 4 ohms. The dc resistance of the new MCM's should give a pretty good indication as to what the minimum impedance would be.

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Old 11th December 2012, 01:53 AM   #26
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Quote:
Originally Posted by greyhnd View Post
Dave - Yes sir, that's the little Lepai t-amp I'm using.
6 watts into 8, 10 into 4.

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Old 11th December 2012, 03:12 AM   #27
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Tony - Yes I do in fact have a multimeter. I'll get the measurements on both the Kenwood and the MCM speakers. I'll also see if I can diagram the way the wiring is. My freehand drawing skills on the computer are poor and that's being generous, but I'll see if I can make something that will be helpful.

Dave - When you indicate 6W @ 8 ohms and 10W @ 4ohms, I assume you mean per speaker? The little sucker gets loud, but several years ago I had a tube amp that put out about 6 watts and I used it to power some Dahlquist DCM-9c studio monitors. It never lacked in performance.
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Old 11th December 2012, 03:25 AM   #28
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That is the rated power per channel at reasonable distortion levels.

So in normal parlence, unless specified outherwisem the Lapai would be refered to as a 6W amp.

Everyone should own one.

dave
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Old 11th December 2012, 06:15 AM   #29
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Do what I do. Draw with a pencil on paper and take a digital photo Much quicker and usually a better result (for me) than trying to use a paint program!

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Old 11th December 2012, 08:35 PM   #30
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Okay guys, I checked the ohms and made a diagram of the crossover, such as it is.

The Kenwood woofers measured between 14 - 15 ohms. The MCM woofers (both) measured dead on at 7 ohms.

As far as the crossover is concerned it's about as simple as I've ever looked at. As you can see in my diagram, the negative wires from both woofers and the tweeter go directly to the negative terminal connector. The woofers positive wires go directly to the positive terminal connector. The tweeter positive passes through the cap then on to the positive terminal connector. I still haven't been able to determine the values for that little cap. I can't see it well enough to get the numbers.

Xover.jpg
Hopefully this will suffice. If still unclear I'll do as Tony suggested and hand draw one and take a digital pic.
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