Speaker crossover help

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,899
OK, I know I said "Crossover" but what I'm looking for is just a simple cap to separate the low from the high frequencies. I have these speakers from an old Mac computer. It died. But I kept the speakers and want to use them. I have a bluetooth amp that can drive them but I don't want to be sending base notes to the tweeters. A simple capacitor to block out the lower frequencies is what I've seen so many times before. I don't want, need or have space for crossovers, just enough room to throw a couple caps in the case. YouTube isn't much help. Besides there's no telling what fool I'm going to encounter, who's going to tell me to go with some stupid setup that doesn't work for my need.

These are the speakers I have.

1708725044726.png

Each speaker has its own wire so where it wires into the amp I can put a blocking cap in there. I'd just like to know what's the best value for the situation I have. This is going to be a gift for my wife. She's forever playing music from her phone speakers and it's just not very loud nor does it sound very good.
 

eetech00

Joined Jun 8, 2013
3,946
OK, I know I said "Crossover" but what I'm looking for is just a simple cap to separate the low from the high frequencies. I have these speakers from an old Mac computer. It died. But I kept the speakers and want to use them. I have a bluetooth amp that can drive them but I don't want to be sending base notes to the tweeters. A simple capacitor to block out the lower frequencies is what I've seen so many times before. I don't want, need or have space for crossovers, just enough room to throw a couple caps in the case. YouTube isn't much help. Besides there's no telling what fool I'm going to encounter, who's going to tell me to go with some stupid setup that doesn't work for my need.

These are the speakers I have.

View attachment 316019

Each speaker has its own wire so where it wires into the amp I can put a blocking cap in there. I'd just like to know what's the best value for the situation I have. This is going to be a gift for my wife. She's forever playing music from her phone speakers and it's just not very loud nor does it sound very good.
If the speakers have separate wires, you might check the amplifer first. It might already have the necessary filtering.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,899
I graduated high school with remedial math skills. Two Pi, that I understand. "f" is that Frequency? "R", what's R?
 

crutschow

Joined Mar 14, 2008
34,420
Measure the DC resistance of the tweeters with a multimeter.
The rated AC impedance is typically a little above that (e.g. an 8 ohm nominal rated speaker will likely measure 5-7 ohms for example).
You then need to guess at where you want the high frequency rolloff is best, and use C = 1 / (2πfR) to determine the capacitor value for the nominal speaker impedance (R) and the rolloff frequency (f).
A frequency of around 2kHz for that would likely be a good starting point.
You can play with the cap value higher or lower depending upon how it sounds.

The capacitor, of course, needs to be a non-polarized type (Parts Express is one place for those).
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,899
If the speakers have separate wires, you might check the amplifer first. It might already have the necessary filtering.
Nope. Amplifier has individual outputs for Right and Left speakers. Nothing more.

Measure the DC resistance of the tweeters with a multimeter.
The rated AC impedance is typically a little above that (e.g. an 8 ohm nominal rated speaker will likely measure 5-7 ohms for example).
You then need to guess at where you want the high frequency rolloff is best, and use C = 1 / (2πfR) to determine the capacitor value for the nominal speaker impedance (R) and the rolloff frequency (f).
A frequency of around 2kHz for that would likely be a good starting point.
You can play with the cap value higher or lower depending upon how it sounds.

The capacitor, of course, needs to be a non-polarized type (Parts Express is one place for those).
OK, I don't know what frequency is best for a two speaker system. I'm totally open to suggestions.
 

Ian0

Joined Aug 7, 2020
9,807
I graduated high school with remedial math skills. Two Pi, that I understand. "f" is that Frequency? "R", what's R?
The resistance or nominal impedance of the speaker. For tweeters the two values will be quite similar. Usually 8Ω for hi-fi. 4Ω for automotive, 16Ω (or 15 Ω) for anything with valves, but who knows for computers.
Crossover frequency depends on the size of the dome tweeter. 4kHz-5kHz would be good for a 25mm dome. Higher for smaller domes.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,899
Well, I'm in the wood shop this afternoon. I'll have to take some measurements later tonight.

Since normal hearing range is from 25Hz to 20KHz, I'd imagine I probably want to roll the tweeter on at around 10KHz. Again, your opinion matters. You're far more experienced than I am at this. At best I throw stuff together. If it works - I'm a genius. If it fails - it was never going to work. Even if it has a chance.
 

LowQCab

Joined Nov 6, 2012
4,067
Have You looked inside those Plastic-Speaker-Boxes to see if they contain Capacitors inside ?

You may want to restrict the ""Bass"" Frequencies too, with another Capacitor,
because those teeny-weensy ""Woofers"" can be destroyed by Frequencies below ~200hz.

A pair of "Book-shelf" style Speakers would be much more satisfactory.
.
.
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300-7140 HR .jpg.
 

MrChips

Joined Oct 2, 2009
30,802
10kHz is way too high. Think frequency on a logarithmic scale.
2kHz is typical for a 2-way speaker system. 4.5kHz for high frequency tweeter in a 3-way system.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,899
Going to have to take this computer in for servicing. I find myself having to restart it numerous times each day. Enough is enough!

OK, forgot what I was saying before the lockup. But I managed to bang out this drawing.
1708728520876.png
Will the mis-matched impedances be an issue for the small amp?
This is the amp:
https://www.amazon.com/dp/B07X65P6H1
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,899
Have You looked inside those Plastic-Speaker-Boxes to see if they contain Capacitors inside ?

You may want to restrict the ""Bass"" Frequencies too, with another Capacitor,
because those teeny-weensy ""Woofers"" can be destroyed by Frequencies below ~200hz.

A pair of "Book-shelf" style Speakers would be much more satisfactory.
.
.
.
View attachment 316026.
Thanks for the warning about the low frequencies.

Size is paramount in this instance. My wife likes to throw her cell phone on the kitchen counter and play music while she does whatever she's doing in there. Sometimes cooking, sometimes baking, sometimes she's remodeling. I don't stop her; it's not worth the arguments. Anyway, her birthday is coming up in a few weeks and I'm building this very small cabinet with these very small speakers. The amp plays sufficiently for its size and the size of the speakers. The base frequencies might not be an issue but I'll still take that under advisement. On that note - what would you recommend to protect the base speakers?
 

crutschow

Joined Mar 14, 2008
34,420
Will the mis-matched impedances be an issue for the small amp?
Amps don't really see the mismatch, all they see is one composite impedance.
The only concern is if it gets too low, and the amp you posted is rated for 4Ω speakers, so I don't see a problem.
 
Last edited:

BobTPH

Joined Jun 5, 2013
8,952
I would not bother. What you have there is essentially two tweeters. And it is not like you are going to be powering them with 50W. I would be very surprised if there was an audible difference with or without a capacitor.
 

crutschow

Joined Mar 14, 2008
34,420
I would not bother. What you have there is essentially two tweeters. And it is not like you are going to be powering them with 50W. I would be very surprised if there was an audible difference with or without a capacitor.
There not be any audible difference until, perhaps, the tweeters blow.
Those are likely cheap tweeters with a low power handling capability, which loud, low frequency sounds may blow without the capacitor.
The capacitor is cheap insurance.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,899
I would be very surprised if there was an audible difference with or without a capacitor.
During testing I saw the tweeters trying to move quite a bit. I figure it's worth protecting them.
I sure wish I could talk You out of using these "Speakers".
This isn't a high fidelity system, just something for the wife to enjoy her music without pumping her cell phone speaker(s) at max volume.

The bigger picture of this is going to be the wood working aspect of it. A cheap gift made by hand can be more appreciated than when someone spends a lot on a gift. It's the thought, the sentiment that counts.

If I wanted bookshelf speakers I'd have bought an amplifier to suit. But then I'm just giving her something I bought.

Anyone who's visited QualityWoodcraftOfSunset.com may have noticed a cell phone charger made out of Juniper wood from a tree that was in my front yard. There's even a small box for her sewing stuff made from that tree. But maybe we should start a new website: AAW (All About Wood). But maybe then someone might come there looking for adult pictures.
 
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