Multiple HT Speakers

[Zene]

Hi .. I have 30 - 6 1/2" 4 ohm FR (misnomer) speakers for 5.1 HT.
I am going to try to use as many as impedances will allow.
I've asked this before but forgot answers and maybe newer thinking will help.
All three fronts will be equal amounts, but would like to know
proportions of rear surround quantities to aim for. The less I need, say 2 each in rears vs. 4 for fronts the more can go up front.
Anyone care to comment? If not I can live with my 1980's RS speakers.
Zene

[Wayne A. Pflughaupt]

Anyone care to comment?

Love to Zene, but I didn’t understand any of that. Are you asking if you can use say, ten speakers for surround sound instead of the usual five or so?

Regards,
Wayne

[jackfish]

If you wire speakers in parallel you end up with half the impedence value, wire them in series and you double the impedence. The math is pretty simple even with multiples of speakers. Most HT amps should be run at 6 or 8 ohms, most do not like a load 4 ohms or lower. I'd shoot for 8 ohms for any given channel. Also, I think 4 for the rears, 6 for the center and 8 for the fronts would work.

So if you wire two 4 ohm speakers in series it will yield 8 ohms. If you take two speakers so wired and run them in series with another two so wired it will yield 16 ohms, in parallel it would be 4 ohms.

This explains it, including series/parallel wiring.
http://www.termpro.com/articles/spkrz.html

Stacking many speakers together could result in phase problems.

[Zene]

Thanks Jay ... Wiring is no problem but did see that 5 would yield 8 ohms with one in series. Never encountered that before. Is it acceptable to do that or do they have to be even quantity clusters, 2,3,4 etc.?
Also, why less for center channel, thought they should be same as fronts?
Plan to curve the arrays to help eliminate notch problems. Will that change your opinion on quantity per channel?
Zene

[jackfish]

They can be any multiple as long as the end result of parallel/series combinations is a 6 to 8 ohm load on the amplifier. The center channel should complement the front speakers, so that array could be equal to that of each front but doesn't have to.

[Zene]

Didn't come close to answering my question, but thanks for the input. Probably my inability to explain my question. Did learn though.
Zene

[jackfish]

Ok, let me try this. Most of your program material is going to come from your fronts, they should dominate. The center channel usually emphasizes voice and other material and while it can sometimes emit up to 50% of the program material it doesn't usually need to equal the size or capability of one of the front channel speakers. The surround speakers are often the closest to the listener and provide only enhancement and directional material.

Each front channel is 8 speakers with:
4 in series/parallel for 4 Ohms
wired in series with
4 in series/parallel for 4 Ohms
resulting in 8 Ohms

The center channel is 6 speakers with:
4 in parallel for 2 Ohms
wired in parallel with
2 in series for 16 Ohms
resulting in 8 Ohms

Each surround channel is 4 speakers with:
3 in series/parallel for 2.66667 Ohms (2 in series in parallel with one)
wired in series with
1 speaker for 4 Ohms
resulting in 6.66667 Ohms

If you are dead set on a dominant center channel you could go 6 for each front channel, 10 for the center channel and 4 for each surround channel. As such:

Each front channel is 6 speakers with:
4 in parallel for 2 Ohms
wired in parallel with
2 in series for 16 Ohms
resulting in 8 Ohms

The center channel is 10 speakers with:
4 in series for 32 Ohms
wired in parallel with
4 in series for 32 Ohms
resulting in 16 Ohms
wired in parallel with
2 wired in series for 16 Ohms
resulting in 8 Ohms

Each surround channel is 4 speakers with:
3 in series/parallel for 2.66667 Ohms (2 in series in parallel with one)
wired in series with
1 speaker for 4 Ohms
resulting in 6.66667 Ohms

Or even 8 for the fronts, 10 for the center, and two (in series for 8 Ohms) for the surrounds. Experiment and see which sounds best.

In some of these arrangements not all speakers will draw the same power, but this shouldn't make a big difference if one uses the receiver to balance or equalize the sound of the system.

[Zene]

Thanks Jackfish .. I did not mean you specifically in comments, sorry, but do appreciate your more detailed explanation. Glad I don't need huge amounts for the rears. That would eat into the total quantity quickly.
I will build in modules of two so I can experiment.
Would you come over for some many many days and help me build 15 panels? On my large map it's only about 16".
Zene

[Wayne A. Pflughaupt]

Just keep in mind that there’s no free lunch. You can wire a lot of speakers together so that the load is ultimately 8-ohms, or whatever your receiver needs, but you’re still driving the amplifier harder to power them all.

Regards,
Wayne

[Zene]

Wayne ... Heard that before, but never understood. If the efficiency is greater for multiples, increased by +3dB per doubling then they should take less power for the same output. 'splain, plz? Could make a big difference on my choices as I only have 50 watts per channel.
Zene

[Wayne A. Pflughaupt]

If the efficiency is greater for multiples, increased by +3dB per doubling then they should take less power for the same output.

Not likely. Think about it: Tagging on more and more speakers requires less and less power to drive the lot of them – does that really make sense? So eventually you have 15 speakers on a single amp channel, and you can drive them to 100 dB SPL with half a watt?

The “increased +3 dB per doubling” – how does that happen? Well, if you start with one speaker and add a second to a separate channel – i.e., stereo – you get +3dB not simply because you doubled the number of speakers, but because you doubled the amplifier power as well.

The same holds when you double the speakers on a single amp channel: you’re pulling twice the power from the amp to get that +3dB. Either way, it required double the power to get the increase in SPL.

This is a lot different from say, connecting multiple sub drivers to an amp (although that’s not the best idea either). Consider that it’s a given fact that passive crossovers soak up power. With a multi- 2- or 3-way-speaker-per amp set up like you’re talking about, you’re piling on a lot of passive crossovers to the amp.

Any way you cut it, it makes for a very inefficient system, not an efficient one.

Basically, you get the best performance from your amp with a single speaker per channel. It's as simple as that.

Regards,
Wayne

[Joe L.]

Each surround channel is 4 speakers with:
3 in series/parallel for 2.66667 Ohms (2 in series in parallel with one)
wired in series with
1 speaker for 4 Ohms
resulting in 6.66667 Ohms

In addition to what others have already said, it is NOT enough to simply wire speakers in series/parallel combinations to satisfy an amplifier.

In the example you gave, you have two of the speakers doing hardly any work and the fourth getting over twice the power of the third. Let me try to explain with an example

lets say the drivers are rated for 25 watts each and your amplifier is 100 watts per channel into 8 ohms. Sounds like you have a perfect match... but you are misled.

Using Ohms Law, we can determine the amplifier would be putting out 28.28 volts at full power into 8 ohms. (square root of power in watts times resistance = 28.28)

Let's assume you have a really good power supply in the amplifier and that the amplifier will produce only slightly less voltage when loaded with a 6.666 ohm load. Let's say it will output 28 volts to keep my math simple.

Now, I know you are probably used to amplifiers being rated in watts, but in reality, most output a constant voltage (at their max output) This is why they produce more power when connect to 4 ohm load than when connected to an 8 ohm load. They are then rated at how much power that voltage will result when connected to a given resistance. A perfect amplifier will produce twice as much power into a 4 ohm load as an 8 ohm load.

So, connecting your 6.6666 ohm load on an amplifier outputting a voltage of 28 volts will result in 4.2 amperes of current flowing ( again,Ohms law, voltage divided by resistance = 4.2 amperes )

Now, that 4.2 amperes of current flows through the one 4 ohm speaker entirely, but it is split between the three wired in series/parallel. To determine how it splits it is easiest for me to first calculate the voltage across that three. It is the difference between the supply voltage (28) and the voltage dropped across the single 4 ohm driver. We can calculate the voltage across the single driver using Ohms law (resistance * current = voltage) so 4 * 4.2 = 16.8 volts. That leaves 11.2 volts across the three series/parallel connected drivers.

OK... now... Lets calculate how the power is being distributed to the 4 drivers now that we know their resistance and the current through them.
First, the one driver with 4.2 amps flowing through it and 16.8 volts across it.
( voltage * voltage ) / resistance = power, so
( 16.8 * 16.8 ) / 4 = 70.56 watts

Now, each of the two in series in the three series/parallel...
We have 5.7 volts across each of the two in series... (11.2 volts total)
( voltage * voltage ) / resistance = power, so
(5.7 * 5.7 ) / 4 = 8.1 watts to each of the two drivers in series.

Now, the one driver in parallel with the two has 11.2 volts across it.
(11.2 * 11.2 ) / 4 = 31.35 watts

So... one of your drivers is being fed 70.56 watts, two others are being fed 8.1 watts each, and the last driver is being fed 31.35 watts. Seem like a slightly uneven distribution of power to you? It does to me.

When connecting series parallel combinations of drivers you usually want an even distribution of power so they all do equal work. In your proposed wiring one driver will soon burn out as it is being driven with way more power than it was rated. A second is being driven with slightly more than it is rated for, it may last longer... and two are doing hardly nothing... Probably not your original intent.

Instead of your wiring, I might suggest two in parallel, in series with another two in parallel. Then, the 28 volts from the amplifier will result in 14 volts across each driver.
(14 * 14 ) / 4 = 49 watts.
Remember, earlier I said a perfect amplifier will deliver twice the power into 4 ohms than into 8... well... the 4 in series/parallel as I described would be a 4 ohm load and your amplifier would be outputting near 200 watts, split evenly between your 4 drivers (49 watts per driver), still more than they are rated for, but at least you can turn the amplifier down and have the drivers doing equal work.

Joe L.

[jackfish]

Thanks Joe, I guess I was erroneously trying to stay away from a 4 Ohm load, but you are correct it would be better all around to have a 4 Ohm load and equal power distribution than to have such a power disparity. In any event this sounds like a project that is frought with potential problems.

[Joe L.]

There are several enclosure designs where multiple identical drivers are used.

One is in a "line array" where instead of a "point source" you put a series of drivers in a line, each as close to the ones above and below it as possible. Usually, you will see a line of tweeters adjacent to a line of midrange drivers. The center-to-center distances of the drivers is critical for them to couple together to act as a line source.

An example of a line array is here http://home.earthlink.net/~jmiyake/_...s/setUp3op.jpg

The other time you see multiple identical drivers is where a single woofer does not have enough surface area and displacement to produce the same sound pressure level as the midrange and tweeter in a given enclosure. You must move a lot more air to make loud low frequency sounds than to make loud high frequency sounds. In fact, most tweeters must be padded to make them less efficient when used in combination with midrange and woofer drivers.

Many good designs for home theater use will have two woofers surrounding a single tweeter. It takes the combined surface area of the two woofers to make low frequency sounds at theater reference levels equal to that produced by the one tweeter.

In fact, that is exactly the arrangement of drivers in my Left and Right front channels in my theater. I built the Audax Signature Series a little over 4 years ago. Left and right were MTM, center is WMTW, and surround channels are MT.

You can see my DIY Theater speakers here. (I had not yet finished their stands and the surround speakers are sitting on the stage to the left of my center channel, the surround channel enclosures had just been completed)


There is a lot involved in loudspeaker design... more drivers is not necessarily better. I followed a highly regarded design and built my own enclosures. That was enough of a challenge for me.

Below are my surround channels under construction, after veneer was applied, but before I applied the black finish... oh yes, they are more than loud enough with one woofer and one tweeter.

Joe L.

[Zene]

Wayne A. Pflughaupt wrote:

Not likely. Think about it: Tagging on more and more speakers requires less and less power to drive the lot of them – does that really make sense? So eventually you have 15 speakers on a single amp channel, and you can drive them to 100 dB SPL with half a watt?

The “increased +3 dB per doubling” – how does that happen? Well, if you start with one speaker and add a second to a separate channel – i.e., stereo – you get +3dB not simply because you doubled the number of speakers, but because you doubled the amplifier power as well.

The same holds when you double the speakers on a single amp channel: you’re pulling twice the power from the amp to get that +3dB. Either way, it required double the power to get the increase in SPL.

Wayne ... Sending copy of response from man that knows, builds and websites his OB array project.
"Zene, the effect can be both measured and computed mathematically.

doubling of speakers, same power = +3db
doubling of power, same speakers = +3db
doubling of both = +3db

that's according to the law of nature regards conversion of electric power to waves of sound pressure; Why it happens? Because
the power is distributed to bigger surface moving in phase, and that is doubling of the surface. When a wave starts traveling off and alone the baffle, less energy (by 3db) is required if it find it is supported by another cone moving in unison.

A related effect is 6db swings in baffle responce, due to in- and out- of phase between the cone and the baffle edge.

Anyone can setup a little experiment using radioshack SPL meter to experience the effect, or even using a laptop+mic+ any control with dB meter such as Nero Wave Editor, etc, etc. Note: a baffle or box with 1 speaker needs be comapred to the same rig with N speakers clustered closely. A rig with N speakers among which only 1 is working is bad and should not be used in measurments. Dmitry Nizh

Zene

[Zene]

Did want to say thanks to all in separate post.
Sure will help get this mess on better track.
Zene

[Wayne A. Pflughaupt]

Zene wrote:

Wayne ... Sending copy of response from man that knows, builds and websites his OB array project.
"Zene, the effect can be both measured and computed mathematically.

doubling of speakers, same power = +3db
doubling of power, same speakers = +3db
doubling of both = +3db

that's according to the law of nature regards conversion of electric power to waves of sound pressure; Why it happens? Because
the power is distributed to bigger surface moving in phase, and that is doubling of the surface. When a wave starts traveling off and alone the baffle, less energy (by 3db) is required if it find it is supported by another cone moving in unison.

A related effect is 6db swings in baffle responce, due to in- and out- of phase between the cone and the baffle edge.

Anyone can setup a little experiment using radioshack SPL meter to experience the effect, or even using a laptop+mic+ any control with dB meter such as Nero Wave Editor, etc, etc. Note: a baffle or box with 1 speaker needs be comapred to the same rig with N speakers clustered closely. A rig with N speakers among which only 1 is working is bad and should not be used in measurments. Dmitry Nizh

Zene

You do know he’s basically telling you the same thing I did, right?

Regards,
Wayne

[salvasol]

Zene wrote:

Hi .. I have 30 - 6 1/2" 4 ohm FR (misnomer) speakers for 5.1 HT.
I am going to try to use as many as impedances will allow.

Just wondering ... Did you ever connected the speakers in parallel/series??? ...

[Zene]

Salvasol ... No haven't got around to it yet, still procrastinating.
Looks like a winter project.
Zene

[salvasol]

Zene wrote:

Salvasol ... No haven't got around to it yet, still procrastinating.
Looks like a winter project. Zene

I did a connection last week but only using four speakers each L + R channel ... I'm opening a new thread to get opinions if you want to follow up ...