Can a 4 ohm resistor be used to increase a 4 ohm subwoofer to make it 8 ohms? I heard that it would lead to boominess. Can someone help?
Yes, it would sound looser and boomier. Also, about half the amplifier power would be wasted as heat.
Better to get a different amplifier instead. It actually has been done, but there are better ways to go.
Better to get a different amplifier instead. It actually has been done, but there are better ways to go.
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Not a good idea. The woofer is often the least sensitive driver and it is the other drivers that require attenuation. What is you intend by increasing the impedance?
Hi Cal Weldon! This subwoofers are intended as passive add ons with passive 120 Hz crossovers to existing 2 way front L/R speakers. But I'm worried adding another two 4 ohm subwoofers might cause my 6-8 ohm rated amp to overheat.
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Have you plotted the actual impedance of the woofer including the passive crossover. If you are using a sealed box the woofer impedance will be higher than the nominal value around the box tuning frequency. Depending on the type of passive crossover, the impedance may remain above the nominal value over most of the operating range.
If you can find an amplifier to make the subs active that is a much better plan. A 120hz passive crossover has some large and expensive components and you have no way to balance the level to match the 2 ways.
You don’t need a lot of power for subs in a music system IME. 50wpc goes a long way. I have 2 -15” subs in my system crossed over at about 50hz and powered by a Crown CDI1000. The amp is rated for 275wpc at 8 ohms. Even playing it very loud I almost never see the -10db indicator light come on. That would be 27.5 watts rms.
If you can find an amplifier to make the subs active that is a much better plan. A 120hz passive crossover has some large and expensive components and you have no way to balance the level to match the 2 ways.
You don’t need a lot of power for subs in a music system IME. 50wpc goes a long way. I have 2 -15” subs in my system crossed over at about 50hz and powered by a Crown CDI1000. The amp is rated for 275wpc at 8 ohms. Even playing it very loud I almost never see the -10db indicator light come on. That would be 27.5 watts rms.
You're going to have to tell us more about your set up. Sometimes the 8 ohm rating is when you are running four channels. If that's the case you can add caps to your L/R front speakers and parallel the woofers to them.
Hi Cal Weldon! The amp is a 7 channel Denon avr 4308 with a rating of 140 wpc,6-8 ohm. There are only two channels for the front L/R.
I rarely use it for watching movies. Currently only hooked up to a 2 way L/R front speakers with 6.5" 8 ohm Seas woofers and 6 ohm Seas tweeters.
I have these two 4 ohm 10" subs that I intend to add to the set up. But I'm worried abt the amp not being able to handle the additional load. What is your advise?
I rarely use it for watching movies. Currently only hooked up to a 2 way L/R front speakers with 6.5" 8 ohm Seas woofers and 6 ohm Seas tweeters.
I have these two 4 ohm 10" subs that I intend to add to the set up. But I'm worried abt the amp not being able to handle the additional load. What is your advise?
Hi! Thanks for your reply. I'm a noob and am just getting into this. I don't know much abt plotting impedance and the technical aspects involved. I just bought these 2 low pass crossovers in an attempt at connecting the passive 4 ohm subs to my front L/R. The amp is a7 channel Denon avr 4308 rated at 140 wpc.
But I've been warned by some people not to do it. A bit confused. What's your suggestion?
I’m not a video fan at all. Strictly stereo here. I do have one possible suggestion
On some AVRs you can assign 2 channels as Bi amp channels. In other words, the L and R stereo signals can be internally routed to 2 of the unused channels to allow for stereo bi amping. Our upstairs system uses a Cambridge 7 channel receiver with this feature. If your Denon can do this, you effectively have 2 channels you can dedicate to driving the subs through the crossovers using the L and R stereo signals. Check the AVR manual to see if there are ways of doing this. You may even be able to route a filtered subwoofer signal to unused channels and not need the passive crossover, even if you do it through an external rca cable from a subwoofer output to unused channel inputs.
On some AVRs you can assign 2 channels as Bi amp channels. In other words, the L and R stereo signals can be internally routed to 2 of the unused channels to allow for stereo bi amping. Our upstairs system uses a Cambridge 7 channel receiver with this feature. If your Denon can do this, you effectively have 2 channels you can dedicate to driving the subs through the crossovers using the L and R stereo signals. Check the AVR manual to see if there are ways of doing this. You may even be able to route a filtered subwoofer signal to unused channels and not need the passive crossover, even if you do it through an external rca cable from a subwoofer output to unused channel inputs.
Yes. My Denon also has an additional assignable 2 channels. But I'm not sure if the subwoofer signal can be routed to just this 2 assignable channels.
Is it possible to loop back the amp's LFE subwoofer output signal back into one of the unused amp's inputs?
Pls see the low pass filters and the back of my amp in the above pics.
I just measured the total impedance of the subwoofer connected with low pass crossover in parallel to the binding posts of the 2 way speakers and the multi meter reads abt 6 ohms. Does this mean it's ok to use the subwoofers connected this way,since my amp is rated for 6-8 ohm speakers? Is the total impedance of 6 ohms is what the amp will "see"?
Pls see the above pictures of the subwoofer low pass and the amp for your reference. Tks!
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Check your receivers operating manual to see if you can route the sub signals to a pair of unused outputs. I see that the pair on the left of the main group are labelled surround bi amp and there is another channel further to the left labelled Amp Assign 2
The fact that these channels are assignable leads me to believe that you can do that from the remote and have the low level signals sent to the assigned channel. You need to take a deep dive into the manual to see what can be done in terms of the routing. It is probably the size of a phone book, but it’s got to be done.
It would be highly preferred to go this route rather than using the passive crossover because the internal crossover likely has steeper slopes and adjustable turnover frequencies, level adjustment etc.
The fact that these channels are assignable leads me to believe that you can do that from the remote and have the low level signals sent to the assigned channel. You need to take a deep dive into the manual to see what can be done in terms of the routing. It is probably the size of a phone book, but it’s got to be done.
It would be highly preferred to go this route rather than using the passive crossover because the internal crossover likely has steeper slopes and adjustable turnover frequencies, level adjustment etc.
Ok.I'll try that. In the meantime,does the total impedance with the subwoofer connected with the low pass to the binding posts of the 2 way speakers in parallel equal to the actual load the amp will be driving? I measured abt 6 ohms at the binding posts with the subwoofers connected.
Not too sure about what you read because regular multimeters have trouble with low resistance measurements.
Set multimeter to lowest resistance scale (200 ohm?), touch black probe to red probe, what do you read?
It will NOT be zero ,but some low value, say between 0.4 and 1.2 ohm.
Then measure subwoofer resistance and substract the value you found before.
If you measured 6Ω with a DMM then you have measured DCR not impedance. Impedance will be around 8Ω nominal but it is frequency dependant.
JMF and I posted at the same time.
JMF and I posted at the same time.
Hi Cal Weldon! Yes I'm aware that impedance is frequency dependant. But,is there a way to determine the nominal impedance of the 3 drivers?
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Hi JMF, Thanks for your input. Yes I know about the dmm's lead resistance and zeroing. After subtracting that,it is abt 6 ohms. Would it then be correct to assume that the total load is ard 6 ohms that the amp will see?
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If you have an 8 ohm speaker and you are putting a 4 ohm woofer in parallel with it, you can expect to have trouble when your receiver is only rated at 6 ohms minimum. You would normally calculate the nominal parallel speaker impedance to be (1/ (1/8+1/4))=2.7 ohms. Have you looked a using the Bi amp speaker terminals to give the passive subs their own amplifier channel? This has a much better chance of working without overloading the amplifier.
Download the manual if you don’t have a printed copy and figure out what is possible for those biamp terminals.
Download the manual if you don’t have a printed copy and figure out what is possible for those biamp terminals.