DrWho Posted July 5, 2005 Share Posted July 5, 2005 Ok, this has been bugging me for a while so I figured I'd go ahead and ask about it and see what all the gurus have to say about it... Let's say I have four 8 ohm speakers. I connect one of them to an amplifier at let's say 1 watt and I get 100dB of acoustical output. If I connect two of them in parallel, they present a 4 ohm load to the amplifier and I get 2 watts of current flow. However, the doubled up current splits in half (2 speakers in parallel) so each speaker still has 1 watt of current flowing through it, BUT I get a 3dB increase because I have 2 drivers playing the same material (so now I'm up to 103dB). Now let's say I hook up a total of four speakers presenting an 8ohm load (2 sets of 2 speakers in parallel wired in series with each pair). Because it's an 8ohm load, the overall system is seeing 1 watt of power and thus each driver is seeing 1/2 watt? (each 'pair' of speakers is seeing one watt, then divided by two for the parallel sections)? If that's true, then I should still be getting an overall output of 103dB, but I've doubled my power-handling and if 1 watt was my previous max, then I can support 2 watts and get 106dB? But if my amp can't put out more than 1 watt, then all I've achieved is a lower distortion design (same SPL for less cone movement)??? The reason I ask is because I won 4 promedia subwoofers off ebay for dirt cheap (like $20 total + shipping) and I was thinking of improving the bass on my current pc setup (which right now is a Sony HTIB, which has a pretty sucky one-note-wonder subwoofer). I was thinking of combing the 4 drivers into a single enclosure and power them with just one of the original plate amps that comes with the sub (which means my power handling is limited). Quote Link to comment Share on other sites More sharing options...
scriven Posted July 6, 2005 Share Posted July 6, 2005 ---------------- On 7/5/2005 11:48:09 PM DrWho wrote: Because it's an 8ohm load, the overall system is seeing 1 watt of power and thus each driver is seeing 1/2 watt? ---------------- Hi Doc, The problem is that each pair that is seeing 1/2 watt is 16 ohms not 8. The speakers in series act as a voltage divider so each driver sees 1/2 of your 1/2 watt or 1/4 watt. By all means, keep working on your perpetual motion machine! If you ever do create it I will be able to say "I knew him back when" Quote Link to comment Share on other sites More sharing options...
DrWho Posted July 6, 2005 Author Share Posted July 6, 2005 ONE set of speakers wired in parallel is a 4 ohm load (each driver is 8 ohms) Connecting TWO sets of these 4 ohms PAIRS in series present an 8 ohm load...so in series, each PAIR is seeing 1 watt. But when the parallel happens, the wattage splits and each driver sees 1/2 watt. If you connected two speakers in series you get a 16 ohm load...connecting two sets of 16 ohm pairs in parallel brings you back to 8 ohms total. So each set of 16 ohm pairs is seeing 1/2 watt, but each speaker in the 16ohm pair is also seeing 1/2 watt because they're in series. (watts split with a parallel, but stay the same when in series. Voltage stays the same across a parallel, but drops when in series). Either way, the end result is 4 woofers connected for a net total of 8ohms is each recieving 1/2 watt from the amplifier...I think. I do this all the time with stage monitors and side-fills, but I've always got more amp available. I just don't understand how 2 drivers and 4 drivers play at the same SPL for the same wattage...or how 4 drivers is only 3dB louder than just one single driver... Quote Link to comment Share on other sites More sharing options...
scriven Posted July 6, 2005 Share Posted July 6, 2005 Sorry, I misunderstood the configuration you are proposing. Your 2 parallel pairs still act as a voltage divider so each 4 ohm pair sees 1/2 watt. Quote Link to comment Share on other sites More sharing options...
DrWho Posted July 6, 2005 Author Share Posted July 6, 2005 so our net total is still only 103dB right? (when the amp is running at 1 watt) Quote Link to comment Share on other sites More sharing options...
scriven Posted July 6, 2005 Share Posted July 6, 2005 I think you are still at 100dB. Each driver is running 1/4 watt. If 1 watt produced 100dB then 1/4 watt would be down 6dB. Since you have 4 of them that brings you back to 100dB. (And probably some issues with comb filtering!) Quote Link to comment Share on other sites More sharing options...
DrWho Posted July 6, 2005 Author Share Posted July 6, 2005 Wait, how do you get 1/4 watt? lol "Your 2 parallel pairs still act as a voltage divider so each 4 ohm pair sees 1/2 watt." As far as comb-filtering...I highly doubt that will be an issue even in the 400Hz region if all the drivers are mounted next to each other. Quote Link to comment Share on other sites More sharing options...
michael hurd Posted July 6, 2005 Share Posted July 6, 2005 As you double the amount of transducers, add 6 db, so going to 4 would net you + 12 db of a single. You could run them off of a single amp, or you could invest in a little higher quality plate amp, if you could determine the amount of eq in the stocker. Quote Link to comment Share on other sites More sharing options...
scriven Posted July 6, 2005 Share Posted July 6, 2005 ---------------- On 7/6/2005 2:06:31 AM DrWho wrote: Wait, how do you get 1/4 watt? lol "Your 2 parallel pairs still act as a voltage divider so each 4 ohm pair sees 1/2 watt." ... Half the signal will go through each parallel driver, hence; 1/4 watt per driver. Quote Link to comment Share on other sites More sharing options...
DrWho Posted July 6, 2005 Author Share Posted July 6, 2005 Ok, I'm still not sold on the 1/4 watt thing so I made a picture and then all you gotta do is show where the model is wrong. The problem I have with 1/4 watt per driver is that means the overall SPL is exactly the same as for a single driver (for the same amplifier power). I even think it should come to a total of 106dB total output instead of the 103dB that I calculate because the surface area of drivers has doubled twice. Perhaps my math is wrong with the first 4 ohm pair...I know doubling up on drivers and doubling up on current gives a total 6db boost (which hurd was mentioning). If you double up twice, that's a 12dB boost, but that has to be divided by 4 due to the amplifier not being able to put out more, but that brings you back to 103dB... Quote Link to comment Share on other sites More sharing options...
michael hurd Posted July 6, 2005 Share Posted July 6, 2005 1 watt divided by 4 is still 1/4 watt in my books. You would still have at least a 6 db gain from quadrupling the number of transducers and lower distortion. The other 6 db comes if they are all receiving 1 watt, like a single driver. Quote Link to comment Share on other sites More sharing options...
michael hurd Posted July 6, 2005 Share Posted July 6, 2005 Edit: 1/4 watt is 6 db down from the proposed 100 db/w/m. So you should have 94+12=106 db Quote Link to comment Share on other sites More sharing options...
scriven Posted July 6, 2005 Share Posted July 6, 2005 Doc, The two symmetrical halves of your speaker network will act as a voltage divider so the voltage at the center point will be about 1.4 not 2.8 volts. You will be getting 1/2 watt out of each half of the network. Between the parallel drivers each will handle 1/2 of the signal resulting in 1/4 watt per driver. BTY: I like your drawing. Good work. Quote Link to comment Share on other sites More sharing options...
scriven Posted July 6, 2005 Share Posted July 6, 2005 Mike, I don't understand how you get a 6dB SPL bump from two identical drivers running at the same power. I have heard that stated before but don't understand why it works. I would expect 3dB since you are using twice the power to drive them. Are 2 drivers more efficient than a single driver? Quote Link to comment Share on other sites More sharing options...
DrWho Posted July 6, 2005 Author Share Posted July 6, 2005 ---------------- On 7/6/2005 12:21:36 PM scriven wrote: Mike, I don't understand how you get a 6dB SPL bump from two identical drivers running at the same power. I have heard that stated before but don't understand why it works. I would expect 3dB since you are using twice the power to drive them. Are 2 drivers more efficient than a single driver? ---------------- Mike's method is how I calculated the 106dB too, but I couldn't figure it out electrically. I do know that moving to 4 drivers increases the power handling by a factor of 4, but that doesn't help if you're using the same amp to drive them. Maybe it has to do with the drivers "coupling" (like it's the same electrical properties, but with 4x the cone area and 4x the power handling). The problem I have with the 1/4 watt per driver is that if you add all the watts up, you don't get 1 watt out at the end (which you have to get because watts in = watts out)...you end up with 1/2 watt flowing through the system. Quote Link to comment Share on other sites More sharing options...
scriven Posted July 6, 2005 Share Posted July 6, 2005 I am not following you. When I add up 4 drivers running at 1/4 watt each I get 1 watt. Quote Link to comment Share on other sites More sharing options...
DrWho Posted July 6, 2005 Author Share Posted July 6, 2005 Using your 1/4 watt per speaker, you add the watts across each parallel set of speakers. So the top set adds to 1/2 watt and the bottom set adds to 1/2 watt. But because the top and bottom sets are in SERIES the watts don't add or subtract...it's just 1/2 watt through the whole system (watts in = watts out). But 1/2 doesn't = 1. If you put 2.83V into a single 8 ohm speaker, you get 1 watt of current flowing into the speaker and 1 watt flowing out. 2.83V into 4 ohms yields 2 watts of current...so the first pair of speakers is seeing 2 watts (ignoring the effects of the second pair). If you take the second pair into account, the resistance doubles across the whole system and you're back to 1 watt of current flowing into the first pair when the amp is putting out 2.83V. In other words, the first pair of speakers is seeing ~1.4V which corresponds to 1/2 watt through each driver. Quote Link to comment Share on other sites More sharing options...
scriven Posted July 6, 2005 Share Posted July 6, 2005 "But because the top and bottom sets are in SERIES the watts don't add or subtract." The current doesn't add or subtract - that is not the same as the wattage. "2.83V into 4 ohms yields 2 watts of current...so the first pair of speakers is seeing 2 watts (ignoring the effects of the second pair)." You can't ignore the second pair in that calculation! You will only have 1.4V across the first pair because the second pair is in the circuit. The 1.4V across 4 ohms gives you 1/2 watt, 1/4 watt coming from each 8 ohm driver. "In other words, the first pair of speakers is seeing ~1.4V which corresponds to 1/2 watt through each driver." No it doesn't. Each driver is seeing 1.4V into an 8 ohm driver - or 1/4 watt. The 4 ohm pair will be at 1/2 watt. Quote Link to comment Share on other sites More sharing options...
Spkrdctr Posted July 6, 2005 Share Posted July 6, 2005 ---------------- On 7/6/2005 3:01:18 PM scriven wrote: The current doesn't add or subtract - that is not the same as the wattage. You can't ignore the second pair in that calculation! You will only have 1.4V across the first pair because the second pair is in the circuit. ---------------- Holy Smokes! My head was swimming reading these posts. Scriven finally gets to the problem, but it took a while. Doc, you are using the word "watt" interchangeably with current. The two do not interchange. That is what is messing up your diagram. I was thinking of the old Costello joke about whos on first when I read this.... I hope you understand scrivens answer. I wish I could draw into my posts like you did Doc. Looks cool. Good Luck on your speaker set up! Quote Link to comment Share on other sites More sharing options...
DrWho Posted July 6, 2005 Author Share Posted July 6, 2005 What's a watt then? and what's current measured in? (yikes, I feel embarassed to ask lol). I must confess, I've had absolutely no education regarding ac circuits...only DC so that's prob where my problem is. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.