I have a pair of small speaker units I want to repurpose, from the 90s. They were part of a mid range midfi unit. They have a tweeter and a 4" mid speaker each. They are well presented and work well with the original unit. They have 4 wires out of the back of each cab. The label on the back of the speaker cabs says "mid range 6 ohm, hi range 6 ohm". There has not been any damage to them as far as I know. Measuring the ohms on a meter gives ? 5 ohms over one pair of wires. The other pair has no needle movement in any combination with the 4 wires. This is the same on both cabs. (In mean only one pair of the 4 wires in any combination gives an ohmmeter measurement. Red and Black, if you are curious, from a choice of Red, Black, Blue and White.).

I want to replace the main amp unit due to obsolescence - no line in. I am looking to connect these speakers to an amp set up with simply L and R. I think I have determined the mid and high speakers work - sounds ok and no history of damage. I have not cut the back of the speakers open to see how they are connected, though I could.

I can see this article somewhat informs me, but not completely how one might consider wiring them. I had a look through ohmmeter design chapter, and circuit theory design chapters, but until I see how they are wired, I am just don't know. I think I need to cut the back open - so can do over the weekend. For wiring speakers up like this, is there a page I should be looking at about impedance? I can see some forums talking about making a crossover... ...seems those that know might say this is a little complex, and perhaps I should just buy some reasonable quality mid sized speakers.

Any links from your bookmarks I could look at?

 

Hi clexp,
In the High pair, is there a cross-over unit, that would give an open reading.
Look here for some info.
E
https://soundcertified.com/what-are-tweeters-what-do-tweeters-do/

 

Welcome to AAC.

Hi clexp,
In the High pair, is there a cross-over unit, that would give an open reading.
Look here for some info.
E
https://soundcertified.com/what-are-tweeters-what-do-tweeters-do/

That's definitely possible. Another possibility is the tweeters are piezo speakers. I don't know if they have a readable ohmage. It wouldn't make sense to wire each speaker independently and have a crossover network inside. With a network you'd only have the two wires input. With four wires I'm guessing each set is for an independent speaker. Really haven't seen that arrangement before - but heck! Anything's possible. These speakers may have been driven by a graphic equalizer with individual "Range" outputs.

Just wondering; what are you doing for base? Sounds like these speakers are good for mid-range and high-range.

I HAVE seen speakers with a capacitor to block lower frequencies and allow the high frequencies through, but those often are just wired with two wires powering the box. Two wires go to the main (mid) speaker with the tweeter in parallel to the main speaker, only there's a blocking cap preventing lower frequencies from attempting to drive the tweeter. That's what I've seen most commonly.

 

Thanks for the quick replies.

I will take a bit of time to digest the tweeter article. SoundCertified is new to me, their articles are thorough.

The original amp unit has 4 crimp ports on the back for each speaker cabinet. I can't tell if the crossover is in the original amp or if instead it has separate amp for high range (I don't know what typical manufacturing practices for this were in the 90s). The whole thing belongs to the wife, she got it from her parents for passing exams. These days she resorts to music from Youtube from her phone. I am sure I can do something to make part of this gift useful again.

For bass, honestly.. ..I had not considered bass, I was going to assume that is sufficiently covered by the mid unit given my audience expectations. Seriously, anything is going to be better than phone speakers.

 

hi clex,
Just follow this diagram, mid and high in parallel.
E

 

Are the terminals on the amplifier labeled?

 

If there is no conduction between the two HF terminals, they probably have a built-in crossover, and are intended for “bi wiring” a fad where the two filters are joined to a single amplifier by two cables.
Either do just that, or connect the HF+ and MF+ together, and connect the HF- and MF- together, then connect the + and - to the amplifier output terminals.
Before you do, take out the midrange unit, and beck that there really is a crossover inside. (Otherwise, you’ll have a dead tweeter)
It’s unlikely that there is a piezo, as they were not used on quality hi-if.

 

Radio Shack Minimus-7 speakers had a 4" woofer and 1" tweeter. They had a rated response from 50Hz to 22kHz and produced fairly good bass. They were rated at 40W but each woofer was marked 5W.

Some audio systems had the crossover circuit in the amplifiers. Then each speaker (bass, midrange and tweeter) had its own amplifier.

 

It's usually only used in high end systems, but it could be a bi-amp connection where each speaker had its own amp.
The advantage of that is the speaker always sees the desirable low impedance of the amp output at all frequencies, and the crossover is accurately (and more cheaply) done at the low level amp input signal, so any change in speaker impedance with frequency has no affect on the crossover points.
But that doesn't explain the lack of a resistance measurement for the one speaker.

 

Are the terminals on the amplifier labeled?

They are, the terminals are colour coded to match the wires.

 

It's usually only used in high end systems, but it could be a bi-amp connection where each speaker had its own amp.
The advantage of that is the speaker always sees the desirable low impedance of the amp output at all frequencies, and the crossover is accurately (and more cheaply) done at the low level amp input signal, so any change in speaker impedance with frequency has no affect on the crossover points.
But that doesn't explain the lack of a resistance measurement for the one speaker.

The truth is on the horizon, it's not a *very* high end unit. Panasonic SB-PM21 and manual. Purchased by non audiophiles for a non audiophile. More coming when I open them up. That link is somebody else's. Thanks so far.

 

The "low" frequency amplifiers produce 15 Whats at a horrible 10% of clipping distortion which is 10 Watts to 12 Watts at low distortion.
50Hz is rated at -16dB then 0dB might be at the same level as 800Hz and higher frequencies. No deep bass.
Edit: Corrected the numbers.

 

So it's a low end system.
It may have been cheaper to use two lower power amplifiers with crossovers in the amplifier, than one larger amplifier with larger (and more expensive) components for a speaker level crossover.

Or maybe it was done just for being able to advertise a "Bi-Amp" system.

 

The "low" frequency amplifiers produce 15 Whats at a horrible 10% of clipping distortion which is 10 Watts to 12 Watts at low distortion.
50Hz is rated at -10dB then 80Hz or 150Hz might be at the same level as higher frequencies. No deep bass.

Ah, you've called by bluff there, not fully sure of meaning. Let me try: no significant production of volume below 50hz?
So that would be the amp. The replacement amp has not been sourced. If the problem is only the amp as you point out, do you consider the speakers a no go for full range sound? You are quoting page 15, and providing interpretation. I can't see an immediately obvious section in the book for reading around the same, any pointers?

Should I use these speakers at all? I sort of think so. My target audience is really not fussy here, and we are stepping up from a low bar, we don't have to go far. I am in with 'reduce, reuse, recycle' if possible.

 

So it's a low end system.

Absolutely. Well in 'consumer' territory.

Or maybe it was done just for being able to advertise a "Bi-Amp" system.

Indeed, I have thought the very same on a few occasions thus far. I am intrigued to find out. I have a window of time to look inside the unit late Sunday. Will share findings. Thank you again.

 

Should I use these speakers at all?

Using the speakers should be fine, but you probably will have to add a crossover circuit for the two speakers in each cabinet as they likely don't have one.
Parts Express has a good selection of crossover components.
The two amps have a 3500Hz crossover, so that frequency for a two-way crossover would be appropriate.

 

The cheap 4" speakers cannot produce low frequencies, any amplifier can if its designer wants it to produce them.
Another amplifier might feed bass frequencies to the 4" speakers that might blow them up.

The manual says on P15: 50Hz at -16dB. Then 800Hz produces the full output loudness (12W). 400Hz will produce the loudness of 6W. 200Hz will produce the loudness of 3W, 100Hz will produce the loudness of 1.5W, and 50Hz will produce the output loudness of only a little less than 0.75W.

The speakers produce a faint sound level of only 82dB at 1W and 1m which is less than half the loudness of normal speakers.

 

My cheap clock radio played no bass sounds and it shrieked its high frequencies. The speaker in it was only 3".
I replaced three audio coupling capacitors with higher values so that its electronics could produce bass.
I disconnected the 3" speaker and connected a speaker I made with a 6.5" woofer, a high quality dome tweeter and a crossover network that I designed.
I installed them in a ported enclosure that I designed to match the woofer specs.
Now it sounds great when playing FM radio music.

 

But that doesn't explain the lack of a resistance measurement for the one speaker.

A piezo would explain lack of resistance.

 

I susoect that when you open it you will find the tweeter connected via a capacitor, which is enough of a “crossover” to avoid damage. I further suspect that if you check the 4 outputs, you will find that there are really only two, they are connected inside to one amp.

Bob