How to Modify soundbar to use non-powered

Thread Starter

izon

Joined Mar 17, 2013
196
HI, been a long time since I was here but had great help.
I'm looking for help with modifying a soundbar to just use the internal speakers directly as two separated channels. As you know a "TV" soundbar has a right and left channel (stereo) which makes it ideal for my purpose. Also with the dual channel input, I can have what I need in a long narrow compact case and much less conspicuous as two separate wall mount speakers. The application is unique. I need some sound reinforcement for seating under a small church balcony. I have no AC power available. Cost to have an electrician put in outlets would get too expensive and even if the soundbar ran on AC adapter with low voltage, I am afraid of having the soundbar active. Someone would ultimately tamper with it and mess it up so I want to use the soundbar speakers hooked directly to the source of the audio to simplify everything.

If I get a soundbar for this, can I open it up and disconnect the two speakers from the circuitry and then connect lead wires off of the speakers to drop outside the soundbar... probably would put in a 3.5mm jack to make it neat and tidy. Don't know if they are typically 8 ohm but hope you guys know how to modify /adapt things to work with a higher impedance speaker. If the impedance is not printed on the magnet, is there a way I could get a close guess with an ohmmeter?

One more thought at this time... since some of these soundbars have designed in a center channel speaker which uses the circuitry, is there any way I can make use of / tie in, this speaker as some sort of blend of the other two speakers passively? Thanks very much... if this is the wrong place for this subject matter, forgive me and direct or move it please to where it should be.
 

KeithWalker

Joined Jul 10, 2017
652
If the impedance is not printed on the magnet, is there a way I could get a close guess with an ohmmeter?

One more thought at this time... since some of these soundbars have designed in a center channel speaker which uses the circuitry, is there any way I can make use of / tie in, this speaker as some sort of blend of the other two speakers passively?
The impedance of the speakers in the sound bar is probably 8 Ohms but could be 4 Ohms. You can tell by measuring the DC resistance of the speaker coil. It will be close to the speaker's impedance so an 8 Ohm speaker will measure close to 8 Ohms.

The center speaker is a different problem. You really can't mix the two channels without a using powered electronic circuit.
Regards,
Keith
 

Alec_t

Joined Sep 17, 2013
10,901
Considering the small size of speakers in a sound bar, I would guess the circuitry applies a lot of bass boost. Without that circuitry the sound may be rather disappointing. However, lack of bass would not be too important if only speech is being broadcast.
 

KeithWalker

Joined Jul 10, 2017
652
Considering the small size of speakers in a sound bar, I would guess the circuitry applies a lot of bass boost. Without that circuitry the sound may be rather disappointing. However, lack of bass would not be too important if only speech is being broadcast.
The frequency response of the speaker depends mostly on the type of amplifier being used. Most modern semiconductor amplifiers have such low output impedance that they damp speaker resonances and flatten frequency response.
 

BobTPH

Joined Jun 5, 2013
2,254
In
The frequency response of the speaker depends mostly on the type of amplifier being used.
No. Modern amplifiers are essentially flat across audio range. The response of the speaker is far from flat and depends far more on it’s size, it’s mechanical characteristics, the crossover network, the enclosure and room acoustics.

Bob
 

KeithWalker

Joined Jul 10, 2017
652
In

No. Modern amplifiers are essentially flat across audio range. The response of the speaker is far from flat and depends far more on it’s size, it’s mechanical characteristics, the crossover network, the enclosure and room acoustics.

Bob
Modern amplifiers do have a flat frequency response. They also have a very much lower output impedance than the speakers they are driving. The damping effect of this cancels out non linearities in the speaker machanical construction and enclosure resonances. In this case the speakers are used as full range speakers so no crossover is used. The room acoustics are a secondary effect and are not affected by the amplifier or speaker.. As far as low frequency response is concerned, I will quote an exert from Wikipedia, the free encyclopedia on Damping factor:

"Large amounts of damping of the loudspeaker is not necessarily better, for example a mere 0.35 dB difference in real-life results between a high (100) and medium (20) damping factor helps to enhance the bass response of the loudspeaker by several decibels (where the impedance of the speaker would be at its maximum), which is useful if only a single speaker is used for the entire audio range"
 

BobTPH

Joined Jun 5, 2013
2,254
So you contend that a 3inch speaker and a 15 inch sp
They also have a very much lower output impedance than the speakers they are driving. The damping effect of this cancels out non linearities in the speaker machanical construction and enclosure resonances.
So you seem to be saying that a 3 inch speaker in a 0.5 liter enclosure will produce the same bass response as a 12 inch speaker in a 10 l enclosure if driven by a low impedance amplifier.

You know that is nonsense. So what are you really saying?

I am saying the characteristics of the speaker ( Thiel parameters) and the volume and design of the enclosure (sealed, ported, horn etc.) are far more important than the amplifier in determining the frequency response. This is not a controversial question. Any text on speaker design will confirm this.

Even the placement of the speaker in the room has a very noticeable effect. Compare a speaker placed in a corner on the floor to the same speaker placed 4 ft off the floor in the center of the room if you don’t believe me.

Bob
 

Audioguru again

Joined Oct 21, 2019
856
If there are more than 2 speakers already in the church then adding these ones will overload the existing amplifier.
The sound system is probably mono, not stereo and there are probably speakers at the front and at the sides. Then the system has a 70V PA amplifier that has an output transformer and each speaker has its own transformer.

If the existing amplifier has enough unused power available then the added speakers also each need a 70V transformer. The center speaker can also be used with its own 70V transformer.

The transformers on each speaker have taps marked with power (for loudness). 4W, 2W, 1W, 0.5W and 0.25W.
 

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KeithWalker

Joined Jul 10, 2017
652
So you contend that a 3inch speaker and a 15 inch sp

So you seem to be saying that a 3 inch speaker in a 0.5 liter enclosure will produce the same bass response as a 12 inch speaker in a 10 l enclosure if driven by a low impedance amplifier.

You know that is nonsense. So what are you really saying?

I am saying the characteristics of the speaker ( Thiel parameters) and the volume and design of the enclosure (sealed, ported, horn etc.) are far more important than the amplifier in determining the frequency response. This is not a controversial question. Any text on speaker design will confirm this.

Even the placement of the speaker in the room has a very noticeable effect. Compare a speaker placed in a corner on the floor to the same speaker placed 4 ft off the floor in the center of the room if you don’t believe me.

Bob
I was discussing the performance of speakers in a sound bar. I was not comparing their performance to any other type of speaker or enclosure. The placement of a speaker in a room and the acoustics of the room will greatly affect what you hear, but that is not an option here.
 

crutschow

Joined Mar 14, 2008
24,317
Here's a technique suggested by Dynaco many years back to power a center channel speaker from the left and right speakers using a stereo tube amp.
It does require that the left and right channel amplifiers have a common ground, so cannot be used with bridge amplifiers, which are often used for solid-state amps.
The presence or absence of a common connection can be determined with an ohmmeter when the amps are off.

With solid-state amps, the speaker impedances are likely not critical.

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MisterBill2

Joined Jan 23, 2018
5,177
I just installed a church sound system with four speaker boxes at 4 corners and 4 speakers on the side walls. It is strictly for speech, so it only needed to have low distortion. Impedance matching was not a big deal because a lot of loss could easily be tolerated. The amplifier has two 300 watt channels is the reason. Not very efficient but it was already owned by the church. The longer wires are about #12 from front to back, the shorter runs are #18 wire. Everybody can hear when the preacher talks.
So while a sound bar may be a very convenient way to add speakers you will need to use wire no thinner that #20, #18 is better. I would connect the ires directly to the speakers because thos 3.5mm jacks are very flimsy and subject to poor performance, and also they tend to develop short circuits in the plug unless the soldering is VERY good. Also, those plugs are made for #24 or #28 size wire. But the quality and quantity of sound from theose little speakers is not that great. How can a 2 inch speaker move much air??
 
Hello MisterBill2,
Did you connect the fours speakers on each amplifier channel in parallel? Are they each 8 ohms? Then their load is 2 ohms per channel. Few amplifiers can safely drive 2 ohms.

The little speakers in a sound bar sound fine when they are at a distance of 3m but in a church they might be 10m or more so they might need to be overpowered.

We still do not know if the church in this thread topic has a 70V PA system or if it has only 1 or 2 speakers.
Will adding parallel speakers overload the amplifier?

Another problem with adding speakers to the back of the church is echoes. The new speakers will produce sounds before the acoustical sounds go back there and will cause echoes unless the feed to the new speakers is delayed the same amount as the acoustical delay.
 

MisterBill2

Joined Jan 23, 2018
5,177
Hello MisterBill2,
Did you connect the fours speakers on each amplifier channel in parallel? Are they each 8 ohms? Then their load is 2 ohms per channel. Few amplifiers can safely drive 2 ohms.

The little speakers in a sound bar sound fine when they are at a distance of 3m but in a church they might be 10m or more so they might need to be overpowered.

We still do not know if the church in this thread topic has a 70V PA system or if it has only 1 or 2 speakers.
Will adding parallel speakers overload the amplifier?

Another problem with adding speakers to the back of the church is echoes. The new speakers will produce sounds before the acoustical sounds go back there and will cause echoes unless the feed to the new speakers is delayed the same amount as the acoustical delay.
Each amplifier output has two of the big speaker boxes connected to it, which equates to 4 ohms, the value at which the 300 watt output is specified. And one side has a bunch of very old and very long wires connected and no clue about the actual impedance at the amplifier end. So far no amplifier problems, but we are not driving anywhere near high power, probably a lot more like 15 or 20 watts . So we can live with poor efficiency.
 

Thread Starter

izon

Joined Mar 17, 2013
196
Thanks guys for all your input and knowledge. I'm very familiar with 70 volt systems and have installed many. I also know a bit about matching impedances and since this organ has two 100 watt amps in it, I don't think I will "overload" the system. I'm sure we won't be using even one half of it's power. There is no 70 volt output on these amps so can't really use that method here.

Guess in rethinking, I'm going to temporarily dismiss the soundbar idea. I'd rather use one good central, to the area, speaker aiming just to those people involved. However I would like to be able to provide as much as I can of the full spectrum of organ sound by combining the two output channels (main and flute) in an isolated manner to the single speaker I would be using. I'm hoping this can be done in a passive manner but since an active device could be located near AC power, that would be workable.

Thinking of a very small amplifier (mostly for it's isolation) but with inputs that can handle "speaker" level signal and then output at speaker level to the new speaker. Anyone familiar what would work for this need?
Thanks for your help and sorry if I've confused anyone with my straying ideas.
 
Two resistors in series make a voltage divider that reduce the speaker level down to the input level of any amplifier.
Two resistors joined together, one from the full spectrum output and the other from the flute output of the organ make a simple audio mixer to feed a new amplifier (not passive).

Both of the above can be done with 3 resistors mixing (two resistors) and attenuating (one resistor to ground) the high level signals.
 

MisterBill2

Joined Jan 23, 2018
5,177
I suggest that you not tie two amplifier outputs together because they may not have a common point, such as if they are bridge outputs. Two speakers in one enclosure, or a one to one ratio transformer to have separated the two signals, and then put that in series with the other output. The goal is to have no DC connection between the two outputs unless you know for certain that they share a common point.
 
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