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Old 31st July 2001, 12:31 AM   #1
Ignite is offline Ignite  Canada
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I am wondering about what happens when one uses multiple drivers of the same type in terms of wattage, impedance and SPL. Using a home theatre reciever, assume i get 150W per channel with five channels. I wish to use two or three of the same woofer for each speaker, and that woofer just happens to be rated at 150W RMS @ 8 ohms. This reciever is rated for 8-16 ohms per channel. If I connect two or more of the woofers in parallel, I will surely destroy the reciever's amp. However, if I connect them in series, the reciever will produce much less wattage. Is it possible to design some wiring such that the load is 8 ohms (or 6 ohms I suppose, I sincerely doubt any reputable reciever manufacturer would make it so your amp blows up with a 6 ohm load.. that would be asking for trouble) without using 4 or more speakers or something with a bunch of resistors that waste power?
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Old 31st July 2001, 02:27 AM   #2
Super is offline Super  United States
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I dont think that hooking up multiple drivers in series will decrease the output of your amp, but it will decrease the output of the individual drivers. Also, why do you want to use more than two bass drivers? Few HT receivers go up to 150 wpc, so there would most likely be a lack of power for each of the drivers, thereby decreasing performance.
Bi or tri amping could compensate for the power loss, but you will more than likely have to include resistors/other components in the crossover to compensate for the load, unless your receiver were rated down to about 2 ohms. (The least you'd probably get away with on some modern receivers is 4 ohms)
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Old 31st July 2001, 02:46 AM   #3
Ignite is offline Ignite  Canada
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Obviously it will increase it. If I hook up two 8 ohm speakers in series it will create 4 ohms of impedance, dramatically increasing the wattage generated by the amp into the speakers.
And since when does underpowering a speaker decrease performance? And yes, I know it can destroy it if you are stupid. But I never have heard that using, say, a 100W speaker with an 80W amp is a terrible-sounding thing.


[Edited by Ignite on 07-30-2001 at 09:58 PM]
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Old 31st July 2001, 03:07 AM   #4
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Ignite,
There are several factors at play here.
One is that HT receivers tend to have a lot of circuitry (5 separate amplifiers, in addition to tuners, preamps, Dolby chips, etc.) jammed into one chassis. To make matters worse, they're generally running off the same power supply. If you start running low Z speakers, the amplifiers are going to have to deliver more current, which means more heat will be developed inside the receiver. The power supply will also have to deal with the problem times 5. More heat. So, as a result, it's not uncommon to see the 8 ohm and up restriction. To put it in plain English, they had to cut corners in order to get all that stuff crammed into one box.
How tight is the restriction? Good question. It will vary from manufacturer to manufacturer. Honestly, I wouldn't care to push the envelope too far. 6 ohms is probably okay, but bear in mind that these are nominal ratings, and that the end result is frequently lower, particularly in certain frequency ranges.
There isn't a good way to do three drivers, other than all in series (24 ohms) or all in parallel (2.7 ohms). Yes, putting two in parallel, then adding one in series will give you 12 ohms, but it will not work the drivers evenly.
How about using two 4 ohm drivers in series?

Grey
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Old 31st July 2001, 03:44 AM   #5
Super is offline Super  United States
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Quote:
Originally posted by Ignite
Obviously it will increase it. If I hook up two 8 ohm speakers in series it will create 4 ohms of impedance, dramatically increasing the wattage generated by the amp into the speakers.
And since when does underpowering a speaker decrease performance? And yes, I know it can destroy it if you are stupid. But I never have heard that using, say, a 100W speaker with an 80W amp is a terrible-sounding thing.


[Edited by Ignite on 07-30-2001 at 09:58 PM]
I never intended it to mean that it will decrease the performance of the driver, merely the bass and decibal output caused by the wider dispersion of power. Sorry for the misunderstanding.

(For example, an 80 watt receiver isn't going to pump out suitable sound/volume for a speaker using large numbers of drivers, like a line array speaker featuring 4+ driver arrangmenets)
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Old 31st July 2001, 06:25 AM   #6
jteef is offline jteef  United States
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yeah, two or more 4 ohm drivers will be your best bet. Most manufacterers do have a 4 ohm and 8 ohm model for of their speakers. Remember, your tweeters need power also! And unless you are using very high efficiency tweeters, I really dont see a point to more than one woofer per speaker in a HT setup. Unless you just love bass... have you thought about porting? I know it isn't very common in HT setups, but it will allow for a lower 3dB frequency and should have about the same or more sensitivity than two drivers with half the power.

jt
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Old 31st July 2001, 10:46 PM   #7
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Ignite, you mean 2 each 8 Ohm units in paralell to create 4 Ohm?

Petter
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