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Is there a formula or an online calculator that will allow me to make a reasonable estimate of the increase in SPL that could be achieved with 2 pairs of identical speakers vs. one pair? This assumes that each pair would have identical amplification.
 

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Is there a formula or an online calculator that will allow me to make a reasonable estimate of the increase in SPL that could be achieved with 2 pairs of identical speakers vs. one pair? This assumes that each pair would have identical amplification.
It's pretty easy; you don't need an online calculator. 3dB

[This assumes the speakers are equidistant to the listener and all have the exact same type of room boundary reinforcement, for example, if the first pair are in the corners then the two new ones you add need to be in the remaining two corners.]

Placing the two new additional speakers adjacent to the first pair can eek out a tad more boost, at least for some frequencies, through a principal called "acoustic coupling". The best case scenario boost will be 6 dB instead of 3dB but you can't count on it, for all frequencies, as a 100% guarantee. It depends.
 

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Is there a formula or an online calculator that will allow me to make a reasonable estimate of the increase in SPL that could be achieved with 2 pairs of identical speakers vs. one pair? This assumes that each pair would have identical amplification.
Sure!

Double the amount of the same drivers nets you +3dB of efficiency. Since you have twice the speakers, you can have twice the power to drive them and gain another +3dB. This gives you a gain of +6dB when the speakers are co-located with each other. If you move them around the room, then that will change and likely be lower.

Using 2/4/8/16 subs this is fine, running full range speakers with the same signal (say 4 speakers with a 2 channel signal) this is not advised due to combing and many other issues. For that information, it is more a public address system type design and those have many rules to get them to work properly.
 

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"3 dB boost" is actually the answer to all of these questions:

Double the amp power? 3 dB
Double the number of equally powered speakers? 3dB
Double the number of equally powered pairs of speakers emanating sound into the same space? [your question] 3dB
 

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Is there a formula or an online calculator that will allow me to make a reasonable estimate of the increase in SPL that could be achieved with 2 pairs of identical speakers vs. one pair? This assumes that each pair would have identical amplification.
As others noted you will be gaining additional SPL but its a small increase. The truth is if you want more spl you need more power, but in the same vein it takes a considerable amount of additional power to get real gains. You could try more sensitive speakers, I think ( I will be corrected if I am wrong LOL)
 

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0dB boost is the answer to the following questions, despite the mythology found in many owner's manuals and forum posts:

Switch to bi-wiring when the original mono-wiring was an adequate gauge in the first place? 0dB.
Switch to passive bi-amping using two extra equally powered amps using one for the tweeter and one for the woofer in a two-way design? 0dB under 1974 FTC 5-rule guidelines.

Switch to active bi-amplifying [requiring not just double the amps but also an external active x-over plus calibration gear] and truly removing/bypassing the speaker's internal passive crossover [not accomplished simply by removing the jumper straps, as many people foolishly think]: Best case scenario, theoretically, "3dB". Actual measurements by active bi-amping experts? 1-2dB at most and sometimes less than 1dB, although there are some other minor benefits to active bi-amping besides slightly greater output.
 

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Did I misread previous posts?
No one metntioned bi-amp/bi-wire.
 

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By my read the OP had an interest it increasing SPL :
estimate of the increase in SPL that could be achieved . . .? .
And is considering either getting or already has access to extra, identical amps (and speakers):
This assumes that each pair would have identical amplification
I don't consider my post off topic; I'm merely suggesting what might help, by how much, and what won't.

Perhaps you are unaware of the fact that many people are under the false impression that bi-wiring and passive bi-amping can increase output, so it's not unreasonable for me to consider he may have been exposed to this pervasive mythology and I was merely trying to help.
 

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two 2-channel amps
4 speakers
4 speaker wire pairs
 

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Is there a formula or an online calculator that will allow me to make a reasonable estimate of the increase in SPL that could be achieved with 2 pairs of identical speakers vs. one pair?
I also assume your realize that reproducing one channel of a sound system from more than one location in a room causes comb filtering which objectionably alters the frequency response. Also the sound stage is poorly defined if the left and right channels are defined by two locations, not one. In some adverse environments the cons of these problems is trumped by the adverse conditions, for instance in a 4 passenger car where you want to entertain both the front and rear passengers at roughly equal levels, but I wouldn't generally recommend four stereo speakers to listeners who want a focused, well defined sound stage in a home.

Other scenarios where four or more speakers might be a good idea is a restaurant, bar, or for equally distributed sound in any venue, even a living room, where the concern is for evenly distributed sound for many listeners scattered throughout room, say at a party.
 
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Discussion Starter #11
Thanks for the responses. I take it the answer is probably 3 dB, but it might help if I explain the reason for my question. I'm currently building a dedicated listening room that is rectangular, with approximate dimensions of 23' L x 14' W x 8' H. So, a medium sized room of about 2600 cubic feet.

This room is strictly for multichannel music using 4 identical speakers in a layout resembling the quad format of the '70's. 90% of the music channels will be discrete (i.e. 3,4,5 or 5.1 channels) , though I will also listen to some 2 channel music reproduced using Dolby Pro Logic II or DTS Neo 6 to derive 4 channels from 2. There will be no center speaker, but there will be 2 subs implemented with an 80 Hz crossover.

My question about SPL has to do with speaker selection. The speakers I would like the most have a sensitivity rating of 86 dB, but my short list also includes speakers of 88, 90 and 91 dB. Will my preferred 86 dB speakers play loud enough to satisfy me? That's the big question. A couple of days ago I played some music at a volume that I would rarely exceed, while holding in my hand a Rat Shack SPL meter set to C-weighting and fast response. During loud passages, the meter stayed in the range of the mid-80's, with occasional peaks up to 92 dB. I never saw it go higher than that.

For amplification in the new room, I'm planning on a 4-channel ATI Signature class A/B amp rated at 200 wpc into 8 ohms, 300 wpc into 4. My preferred speakers are 8 ohms nominal. The 91 dB speakers are 6 ohms. None of the speakers dip below 3 ohms at any frequency.

So, although 86 dB isn't very efficient, I was hoping that 2 pairs of them would be enough to provide sufficient SPL without audible distortion. I was hoping for more than 3 dB, but maybe that will do it.

If you're wondering, all of the speakers I'm considering are Revels.
 

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Thanks for the responses. I take it the answer is probably 3 dB, but it might help if I explain the reason for my question. I'm currently building a dedicated listening room that is rectangular, with approximate dimensions of 23' L x 14' W x 8' H. So, a medium sized room of about 2600 cubic feet.

This room is strictly for multichannel music using 4 identical speakers in a layout resembling the quad format of the '70's. 90% of the music channels will be discrete (i.e. 3,4,5 or 5.1 channels) , though I will also listen to some 2 channel music reproduced using Dolby Pro Logic II or DTS Neo 6 to derive 4 channels from 2. There will be no center speaker, but there will be 2 subs implemented with an 80 Hz crossover.

My question about SPL has to do with speaker selection. The speakers I would like the most have a sensitivity rating of 86 dB, but my short list also includes speakers of 88, 90 and 91 dB. Will my preferred 86 dB speakers play loud enough to satisfy me? That's the big question. A couple of days ago I played some music at a volume that I would rarely exceed, while holding in my hand a Rat Shack SPL meter set to C-weighting and fast response. During loud passages, the meter stayed in the range of the mid-80's, with occasional peaks up to 92 dB. I never saw it go higher than that.

For amplification in the new room, I'm planning on a 4-channel ATI Signature class A/B amp rated at 200 wpc into 8 ohms, 300 wpc into 4. My preferred speakers are 8 ohms nominal. The 91 dB speakers are 6 ohms. None of the speakers dip below 3 ohms at any frequency.

So, although 86 dB isn't very efficient, I was hoping that 2 pairs of them would be enough to provide sufficient SPL without audible distortion. I was hoping for more than 3 dB, but maybe that will do it.

If you're wondering, all of the speakers I'm considering are Revels.
" A couple of days ago I played some music at a volume that I would rarely exceed, " < This. What speakers were you using, and what is their sensitivity? If their sensitivity is the same as the ones you are looking at then you will be fine. If the new speakers have a higher sensitivity, you will be fine.
 

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A couple of days ago I played some music at a volume that I would rarely exceed, while holding in my hand a Rat Shack SPL meter set to C-weighting and fast response. During loud passages, the meter stayed in the range of the mid-80's, with occasional peaks up to 92 dB. I never saw it go higher than that.
.

So, although 86 dB isn't very efficient, I was hoping that 2 pairs of them would be enough to provide sufficient SPL without audible distortion. I was hoping for more than 3 dB, but maybe that will do it.
At your normal listening levels, you will only need about 1 watt to drive them. To increase 3 dB you need to double the power to 2 watts, then double it again for each additional 3 dB increase. Even at your peaks, you should have more than enough power. Granted, that is at 1 meter and as you move away from the speaker, you need more power but you should still be more than fine.
 

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Thanks for the responses. I take it the answer is probably 3 dB, but it might help if I explain the reason for my question. I'm currently building a dedicated listening room that is rectangular, with approximate dimensions of 23' L x 14' W x 8' H. So, a medium sized room of about 2600 cubic feet.

This room is strictly for multichannel music using 4 identical speakers in a layout resembling the quad format of the '70's. 90% of the music channels will be discrete (i.e. 3,4,5 or 5.1 channels) , though I will also listen to some 2 channel music reproduced using Dolby Pro Logic II or DTS Neo 6 to derive 4 channels from 2. There will be no center speaker, but there will be 2 subs implemented with an 80 Hz crossover.

My question about SPL has to do with speaker selection. The speakers I would like the most have a sensitivity rating of 86 dB, but my short list also includes speakers of 88, 90 and 91 dB. Will my preferred 86 dB speakers play loud enough to satisfy me? That's the big question. A couple of days ago I played some music at a volume that I would rarely exceed, while holding in my hand a Rat Shack SPL meter set to C-weighting and fast response. During loud passages, the meter stayed in the range of the mid-80's, with occasional peaks up to 92 dB. I never saw it go higher than that.

For amplification in the new room, I'm planning on a 4-channel ATI Signature class A/B amp rated at 200 wpc into 8 ohms, 300 wpc into 4. My preferred speakers are 8 ohms nominal. The 91 dB speakers are 6 ohms. None of the speakers dip below 3 ohms at any frequency.

So, although 86 dB isn't very efficient, I was hoping that 2 pairs of them would be enough to provide sufficient SPL without audible distortion. I was hoping for more than 3 dB, but maybe that will do it.

If you're wondering, all of the speakers I'm considering are Revels.
I got Salon 2's in room slightly bigger then yours. Although I listen from 9 feet distance only I can crank them up above my comfort zone. Ofc I don't know how crazy loud you wanna go.
 

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Discussion Starter #15
" A couple of days ago I played some music at a volume that I would rarely exceed, " < This. What speakers were you using, and what is their sensitivity? If their sensitivity is the same as the ones you are looking at then you will be fine. If the new speakers have a higher sensitivity, you will be fine.
Monitor Audio Silver S8, and a pair of MA Silver surrounds, all 14 years old. I can't find specs on them, but they were playing in a tiny bedroom, 11' x 12', with all the speakers within 1' of the room corners. As I mentioned, the new, much larger room is currently under construction. Amplification will be different too, and the new speakers will be at least 3' from any wall. So, not even a close comparison.
 

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Discussion Starter #16
At your normal listening levels, you will only need about 1 watt to drive them. To increase 3 dB you need to double the power to 2 watts, then double it again for each additional 3 dB increase. Even at your peaks, you should have more than enough power. Granted, that is at 1 meter and as you move away from the speaker, you need more power but you should still be more than fine.
Right. Power isn't a problem, but every speaker is limited in how loudly it can play, regardless of how much power is available. Plus, as speakers approach their limit, distortion increases very rapidly. My first choice in speakers is the Revel M105, which is a 14" tall bookshelf speaker with a 5.25" mid/woofer. They weren't meant to play very loud.
 

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Monitor Audio Silver S8, and a pair of MA Silver surrounds, all 14 years old. I can't find specs on them, but they were playing in a tiny bedroom, 11' x 12', with all the speakers within 1' of the room corners. As I mentioned, the new, much larger room is currently under construction. Amplification will be different too, and the new speakers will be at least 3' from any wall. So, not even a close comparison.
WELl the spl output at a given level of amplification would be roughly the same, the sound signature might change due to room acoustics and what have you but the volume level, assuming you sit the same distance from them, should be very close. I did a little looking and I think those are a 4 ohm 90 db/w/m sensitivity speaker, or close. I couldn't find a 14 year old model, but I poked around on a few forums. So I would think that as long as you stay in the roughly 90db sensitivity range any of the speakers should output roughly the same spl, assuming they are also 4 ohm nominal.
 

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Thanks for the responses. I take it the answer is probably 3 dB, but it might help if I explain the reason for my question.. . .
This room is strictly for multichannel music using 4 identical speakers in a layout resembling the quad format of the '70's. 90% of the music channels will be discrete (i.e. 3,4,5 or 5.1 channels) , though I will also listen to some 2 channel music reproduced using Dolby Pro Logic II or DTS Neo 6 to derive 4 channels from 2. There will be no center speaker, but there will be 2 subs implemented with an 80 Hz crossover..
Hold up. Our answer of "3 dB" was based on the assumption that the added pair was reproducing the same signal and at the same level. In the vast majority of Dolby Digital, DTS, and quad material the front speakers get full level however the rears only get a fraction of the power sent to them , by design, because the desire is to still get a focus to the front sound stage. Other than an oddball event in only some movies the rears are almost never getting the full level signal. It is more "fill" than anything else.

If the question had been "I have stereo now but plan to add two more identical speakers powered by the same amplification. How much more loudly will this play for typical Dolby Digital, DTS, and properly recorded quad?" The answer is "Not much, maybe 1dB or perhaps 2dB tops and that's only for very specific scenes in the movie. In a nutshell the added speakers should be considered 'icing on the cake' which happens to make maximum output level just a tad higher in some instances"

Although we send an equal level signal to the rear surround speakers during the calibration sequence to adjust their level [and nobody does this at full, maximum output level], during normal prerecorded music/movies the signal sent to the surrounds is much lower.

In the early years of surround, which I sold, it was quite common for AVRS to have smaller amps for the rears. Say 80w/ch for the fronts and only 25w/ch for the surrounds. I never heard nor had a customer ever complain "Sounds OK but as I increase the level I notice the rears start to distort prematurely, i.e their amp is clipping yet the fronts are still doing fine." As time went on some brands realized they weren't saving all that much in using less powerful amps for the rear and they'd do better just buying one amp stage in bulk and using it for all the channels' output so that's what they did. [Plus pretty much no customer would complain, "Why am I needlessly paying for all this needless extra power for my rears when I don't actually use it" :)]

Revels are generally good to great speakers for their sound quality (but not for home dance clubs looking more for "quantity") when accompanied with a good sub(s) to lessen their burden in reproducing the hardest part of the signal, the low bass.

P.S. My link above may have trouble but Sound Stage HiFi or Sound Stage Network has detailed analysis and measurements from the NRC for the (I assume similar) Revel Performa3 M106 accessible from here.
 

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Discussion Starter #20
Hold up. Our answer of "3 dB" was based on the assumption that the added pair was reproducing the same signal and at the same level. In the vast majority of Dolby Digital, DTS, and quad material the front speakers get full level however the rears only get a fraction of the power sent to them , by design, because the desire is to still get a focus to the front sound stage. Other than an oddball event in only some movies the rears are almost never getting the full level signal. It is more "fill" than anything else.
Yes, I agree regarding movie soundtracks, but my application is 100% multichannel music, most of which is recorded and mixed with the intention of putting the listener in the middle of the soundstage. So in that respect the rears will be as active as the fronts much of the time. Still, your point is taken that I may not get a full 3 dB of benefit from the extra pair.
 
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