What to Do With a Lot of Salvaged Speakers?

[Sarah Szabo]

I have taken apart a few old TV's and other devices and have acquired a decent quantity (About 6-8) of (8 & 16) ohm speakers. The wattage differs for each set, the larger centre ones are 10W, the left and right speakers are both 5W. I know that speakers need a cabinet to work properly (They're not in a cabinet), but I have a carpentry hobby, so I might be able to make them using calculators online for the dimensions.

What should I do with the speakers? Could they be made into some kind of surround sound system for a small room? Are there any drivers that can drive such a variable array of speakers?

Some of the speakers:

 

[kellys_eye]

The internet (via China) is full of small audio amplifier modules that could be used with these speakers.

You could wire a number of them in series/parallel combinations to get a 'decent' impedance (8Ω would be a good place to be) and make a pair of cabinets for a stereo solution; you can replace speakers from a 5.1 or 7.1 surround sound system.....

I fitted 4 in my workshop connected to a 'surround sound' stereo radio (ex car) for some soothing tunes!

 

[WHONOES]

You can have a lot of fun and learn a lot playing with small speakers. That's how I started out in the early 70's.
If you want to use some online calculators, you will need to know the Thiele - Small characteristics of the units. For the cheap units you have recovered no such data will exist. You can however, carry out measurements to ascertain these but, it is not easy and will require some particular test equipment such as, a signal generator, a small power amplifier and a DMM plus a small test enclosure.
If you are keen to learn about speaker design and construction, the best way forward would be to buy Vance Dickason's book, "The Loudspeaker Design Cookbook" it will tell you everything you need to know. Alternatively, you could just build a box and see what happens.

 

[Audioguru]

A good speaker sounds good. Those cheap little speakers will sound awful. If they produce any bass then it will be boomy and sound like a bongo drum. They will have a shrieking peak in the upper midrange. Boom, shriek, boom, shriek. Awful sounds.

In the '70ies there was a speaker project in a magazine called The Sweet Sixteen. It had 16 completely different speakers so that their responses could average out. I think it sounded awful because most of its speakers had a boom and a shriek.

 

[hevans1944]

Playing with inexpensive or salvaged speakers is an interesting side hobby to electronics. Most of us have succumbed to that particular bug early in our careers. I can recall articles in Popular Electronics around 1961 on "Sweet Sixteen" loudspeaker arrays (4x4 arrays of cheap 5" speakers) that were supposed to have the extended bass response of a single large twelve or fifteen inch loudspeaker. I didn't bite on that, but a lot of hobbyists did. From what I read later, it was a total fail at reproducing low frequency bass notes, but I never had the opportunity to actually listen to one of them. When we could afford it, wife and I purchased a pair of used Jensen loudspeakers. Those held up through raising two girls and two boys before the loudspeakers finally died... probably from being over-driven during one (or all) of our kids teen-aged years.

What I did eventually do was build two small unvented enclosures for a pair of small, new, replacement loudspeakers intended for mounting in automobile doors. Mounting the speakers in car doors is apparently effective in isolating the rear pressure wave from the front pressure wave of the speaker, thereby avoiding interference effects. But we got rid of the car before installing the speakers, which I discovered a few years later in their original packing boxes.

Mounting a speaker in a sealed box filled with sound-absorbing material is supposed to also be effective. About as effective as mounting a speaker on an "infinite wall" or on a car door to isolate the front and back sides. What I ended up with was two very heavy, bookshelf-sized, speakers with mediocre sound reproduction quality. Useful, but not high-fidelity by any stretch of the imagination. I still haul them out from time-to-time and drive them with a small Radio Shack stereo amplifier pumping out maybe five watts per channel on a good day. Good enough for listening to YouTube music videos on my desktop PC or laptop or streaming audio clips ripped from CDs.

So, yeah, go ahead and build some cabinets... play around with bass-reflex designs and ported tube designs. Go for measuring the Thiele-Small characteristics and use those to guide your enclosure design. By the time you are thirty and are making some big bux in your chosen career, you will probably gladly pay some of those big bux for an off-the-shelf solution, so you can spend more time actually listening to music while pursuing an electronics hobby on the workbench. Well, that works for me but your mileage (or kilometers) may differ.

 

[WHONOES]

Mounting a speaker in a closed box is a good place to start. Some form of panel damping such as carpet felt should be glued to the cabinet walls then the remaining volume loosely filled with kapok or polyester wadding. High end speakers would most likely use lambs wool for various reasons. A speaker with what could be called a single note bass response is generally an indicator of a cabinet that is to small.
Bass - reflex and ported designs are the same thing by different names. There are other methods of bass loading to get best performance but none is perfect.
I bought my first pair of quality speakers in 1976 a pair of Wharfdale's if I remember correctly but they didn't stop me experimenting with my own designs using the Wharfdale's as my yardstick.
I still play at building speakers and the current one's achieve a -3dB response of 33Hz using a 6 1/2" bass driver.
I also design and build my own power amps having done so again, from the early 70's.
So get stuck in, you never know where it will take you.

 

[BobK]

If the "large" center speakers in that picture can handle 10W, I've got a bridge in Brooklyn I can sell you. More likely 1 W at max.

Bob

 

[Audioguru]

Bob, you are correct. The little Chinese speakers have a very tiny decimal point that cannot be seen so the 10W speakers are actually 1.0W and the 5W speakers are 0.5W.

 

[WHONOES]

A good speaker sounds good. Those cheap little speakers will sound awful. If they produce any bass then it will be boomy and sound like a bongo drum. They will have a shrieking peak in the upper midrange. Boom, shriek, boom, shriek. Awful sounds.

In the '70ies there was a speaker project in a magazine called The Sweet Sixteen. It had 16 completely different speakers so that their responses could average out. I think it sounded awful because most of its speakers had a boom and a shriek.

You can make smallish indifferent speakers sound reasonable by using contouring filters. Bose did it for many years (and may still do so).

 

[Audioguru]

Many years ago I bought a pair of Radio Shack Minimus 7 speakers. They used a long throw 4" woofer and a dome tweeter and sounded very good. Bose probably copied them.

The cheap little speakers used in a TV are too small and are not long throw for good bass and there are no tweeters for good highs. They are shriekers, not speakers.

 

[BobK]

They are shriekers, not speakers.

Depends on whether you are nostalgic for the days that you listened to the Washington Senators games on your little transistor radio hidden under the pillow when you were supposed to be sleeping.

Bob

 

[darren adcock]

Gluing springs to the cones to make bodge-it spring reverb with a piezo out is fun and surprisingly effective, especially if you find a way to vary the springs tension.

 

[WHONOES]

Depends on whether you are nostalgic for the days that you listened to the Washington Senators games on your little transistor radio hidden under the pillow when you were supposed to be sleeping.

Bob

Used to do the same here in the UK except we listened to Radio Luxemburg with all that glorious music of the sixties.

 

[hevans1944]

Back in the day, I sometimes salvaged the magnets from small loudspeakers. However, better, stronger, magnets can be salvaged today from the internal works of hard-disk drives with a lot less trouble.

Depends on whether you are nostalgic for the days ...

Nostalgia is okay. But my remembrance was hiding a low-wattage night-light on an extension cord under a blanket so I could stay up and read Tom Swift or Hardy Boys Mysteries when I was supposed to be sleeping. In retrospect, I don't think I fooled anyone but myself, because I'm pretty sure my parents could still see the light faintly shining under the blanket... I know I could when my own kids tried it. But like my parents, I ignored it. Better to read a book than watch television. Radio, especially short-wave radio, was another story. As a young teenager I used to listen to Dad's Hallicrafter S-38 SW radio with a set of earphones late into the morning hours, especially on weekends:

 

[Mike F]

One of the most important part of getting interconnected speakers to sound good is their phase relationship, one to another.
A simple way to determine the Polarity of a speaker is to use a AA battery and suitable Red and Black (or different colors) wires to connect the battery to the speaker briefly.
As you connect the battery make note of which way the speaker cone moves. If the cone moves toward you that's positive. Away from you that's negative. Find a way to mark each speaker positive (+)
For best response and sound speakers should be connected
As follows:
in Series + - + - +


In Parallel
+ -
+-
+ -

Most speakers in small radios or TVs will be 4 ohms inpedence.

Four 4 ohm speakers in series will equal 16 ohms.
Two such combination in parallel will equal 8 ohms.

I 'm probably leaving out something but have fun. If at first you don't succeed don't give up. Solve the problem and you will learn. Stay curious.

 

[Audioguru]

A speaker has a mechanical resonance frequency that increases when in an enclosure. The sound level increases at resonance. The extremely low output impedance of a solid state amplifier (0.04 ohms or less) damps the resonance creating no peak in the response. Connecting speakers in series prevents the amplifier from damping the resonance so the sound level will increase at resonance and will be boomy like a bongo drum. One note bass.

 

[Joe Williams]

I have taken apart a few old TV's and other devices and have acquired a decent quantity (About 6-8) of (8 & 16) ohm speakers. The wattage differs for each set, the larger centre ones are 10W, the left and right speakers are both 5W. I know that speakers need a cabinet to work properly (They're not in a cabinet), but I have a carpentry hobby, so I might be able to make them using calculators online for the dimensions.

What should I do with the speakers? Could they be made into some kind of surround sound system for a small room? Are there any drivers that can drive such a variable array of speakers?

Some of the speakers:

Send them to me. I make mini amps for cigar box guitars with them.

 

[WHONOES]

A speaker has a mechanical resonance frequency that increases when in an enclosure. The sound level increases at resonance. The extremely low output impedance of a solid state amplifier (0.04 ohms or less) damps the resonance creating no peak in the response. Connecting speakers in series prevents the amplifier from damping the resonance so the sound level will increase at resonance and will be boomy like a bongo drum. One note bass.

You are partly right and partly wrong.
Yes a speaker does have a mechanical resonance plus an electrical resonance as well as several other factors that determine how it will perform in a particular enclosure. One of these is its Qts (which is a sum of mechanical and electrical Q's) which can vary from below 0.2 to well over 1. The lower Q versions are generally well controlled and have a lower resonance with higher Q types not being so.
The enclosure does indeed have an effect of the resonant frequency of the driver and is determined by the enclosure Q. Lower Q values of 0.5 or so will give a very gentle roll off and exhibit well controlled bass and good transient response whereas Q values of over 1 will start to cause a peak in the bass response and exhibit a muddier bass sound along with an inferior transient response. Much higher Q's will cause substantially more magnification of a resonance. A Q of 2 will cause a 6dB hump and a Q of 10 will cause a hump of over 20dB. The Q is determined by the size of the enclosure. The size of the enclosure is determined by the driver characteristics including its Vas (volume equivalent compliance). The higher Q types gives the so called boom box which is essentially a one note bass response.
Connecting 2 speakers in series will not cause a one note effect. The damping effect of the amplifier is actually slightly enhanced because of the increase in impedance. Damping is the ratio of amp output impedance versus the speakers impedance. A low amplifier output impedance is generally wrecked by the inclusion of the speaker leads (necessary) in the DC resistance of the crossover which is one reason why active speakers sound better (but that's another story).

 

[Audioguru]

It is simple to hear a "bongo drum" resonance of a speaker or with two speakers in series:
1) Tap the cone of a speaker that is disconnected. It makes a "bong" resonant sound. Then short it or connect it to an idling modern amp (not an old amp that has vacuum tubes) and tap its cone. It makes a "thud" sound with no resonance.
2) Connect two speakers (especially the same kind) in series and tap the cone of one. The resonance will be damped only a little. A speaker has a higher impedance at resonance that could be 40 ohms for an 8 ohm speaker. then an identical speaker in series poorly damps its resonance. Speaker leads or the resistance of a crossover network are nowhere near 40 ohms.

Since many old amplifiers with vacuum tubes (valves?) had no negative feedback from the output then their output impedance was as high as the speaker impedance which allowed a speaker to resonate. So most old speakers were made with a low Q. Modern solid state amplifiers have an extremely low output impedance (rated as the damping factor) so many modern speakers are made more efficient with a fairly high Q which is damped by the amplifier.

 

[WHONOES]

It is simple to hear a "bongo drum" resonance of a speaker or with two speakers in series:
1) Tap the cone of a speaker that is disconnected. It makes a "bong" resonant sound. Then short it or connect it to an idling modern amp (not an old amp that has vacuum tubes) and tap its cone. It makes a "thud" sound with no resonance.
2) Connect two speakers (especially the same kind) in series and tap the cone of one. The resonance will be damped only a little. A speaker has a higher impedance at resonance that could be 40 ohms for an 8 ohm speaker. then an identical speaker in series poorly damps its resonance. Speaker leads or the resistance of a crossover network are nowhere near 40 ohms.

Since many old amplifiers with vacuum tubes (valves?) had no negative feedback from the output then their output impedance was as high as the speaker impedance which allowed a speaker to resonate. So most old speakers were made with a low Q. Modern solid state amplifiers have an extremely low output impedance (rated as the damping factor) so many modern speakers are made more efficient with a fairly high Q which is damped by the amplifier.

Yes tapping a disconnected speaker in series with another will cause the non-tapped speaker to make a noise. Assuming that they are both in a box then it is the pressure pulse from the first speaker that causes the second unit to respond with the physics of the enclosure having an influence. If they are not in a box then there will be no effect. There will be no electrical damping because they do not have a closed circuit. If they have then they must be in parallel.
Yes they will bong a bit when tapped even a single unit, if not connected to an amp but how often do you run speakers without an amplifier?????
A valve amp will also show a small amount of "bong" but not enough to turn to into a one note bass system. That as I have said before requires a deliberately undersized or poorly designed enclosure.
You misunderstand the bit about speaker leads and crossovers. The damping impedance that the speaker chassis sees at its terminals is the combination of the amplifier output impedance plus the series dc resistance of the leads and crossover. This is why large diameter , low resistance cables are recommended Also, the inductance and to a lesser extent, capacitance of the leads will also have an effect. Damping factor is generally nominal speaker impedance / source impedance.