Underpowered receiver

[bnairb]

Don't know much about audio equipment, except that I want LOUDER music from my speakers. Currently, I've been told they are clipping(therefore blowing the fuses in the RE-38's). I think I need an external amp, but I'm unclear on what to get and how to set it up.

I would like to amp up at least the front speakers when listening to music, but still be able to use them for watching tv/surround sound etc. Here's what I have:

Fronts Cerwin-Vega RE-38's. These are older but I believe the specs are:
Power Handling (RMS): 5 to 400 Watts RMS
Frequency Response: 27Hz-20kHz
Sensitivity (dB): 102 dB dB
Impedance (Ohms): 4 Ohms

Center & sub are also Cerwin-vega, don't have the specs handy, but not sure if they matter or not. Don't currently have surround speakers but hope to add some in the future.

Receiver is Yamaha RX-V2700 specs:
Minimum RMS output power
(20 Hz to 20 kHz, 0.04% THD, 8 Ω)
Front: 140 W + 140 W
Center: 140 W
Surround: 140 W + 140 W
Surround back: 140 W + 140 W

Yamaha pre outs jacks are:
1 center
1 sub woofer
Front L/R
Surround L/R
Surround Back/Presence L/R

So what are my options for listening to music LOUD but also watching tv w/surround?

 

[rnatalli]

I'm surprised you're clipping as the 2700 has a good amp section and those CV's are very sensitive. Are you sure there isn't a short at the speaker terminals?

In any case, if you're looking for gobs of power, I would look at the Behringer and Yamaha pro amps. A couple other options are a 2-channel, class AB amp from Emotiva or 2-channel, class D amp from D-Sonic.

 

[Adam]

I know that around here it's not recommended to change the speaker impedance switch on a receiver, but perhaps you could give that a try and see if it makes any difference. The manual for the 2700 specifically mentions that 4-Ohm speakers can be used for the front speakers, but it does recommend setting the speaker impedance option to "6ΩMIN" in that case.

 

[njedpx3]

McIntosh

Get A McIntosh MC2KW

With 102 dB sensitivity ( very,very efficient speaker) and 140 watts ( 8 ohms) approximately 280 watts into 4 ohms ( unless your receiver is current limited) I can't image you are clipping uless you are running 110 dB or louder; hurts my ears just to think of something that loud!

Good Luck!

Forest Man

 

[TLS Guy]

Don't know much about audio equipment, except that I want LOUDER music from my speakers. Currently, I've been told they are clipping(therefore blowing the fuses in the RE-38's). I think I need an external amp, but I'm unclear on what to get and how to set it up.

I would like to amp up at least the front speakers when listening to music, but still be able to use them for watching tv/surround sound etc. Here's what I have:

Fronts Cerwin-Vega RE-38's. These are older but I believe the specs are:
Power Handling (RMS): 5 to 400 Watts RMS
Frequency Response: 27Hz-20kHz
Sensitivity (dB): 102 dB dB
Impedance (Ohms): 4 Ohms

Center & sub are also Cerwin-vega, don't have the specs handy, but not sure if they matter or not. Don't currently have surround speakers but hope to add some in the future.

Receiver is Yamaha RX-V2700 specs:
Minimum RMS output power
(20 Hz to 20 kHz, 0.04% THD, 8 Ω)
Front: 140 W + 140 W
Center: 140 W
Surround: 140 W + 140 W
Surround back: 140 W + 140 W

Yamaha pre outs jacks are:
1 center
1 sub woofer
Front L/R
Surround L/R
Surround Back/Presence L/R

So what are my options for listening to music LOUD but also watching tv w/surround?

Your problem is not lack of power but fuses. You can't protect a speaker with a line fuse, without getting the problem you are having.

A fuse in a speaker is a thoroughly bad idea, and has nothing to recommend it. If the fuse is large enough it will not protect the speaker, and if it protects the speaker it will blow all the time when it should not. Also fuses greatly increase thermal compression. The reason that fuses can not protect a speaker without your problem is because speakers are reactive loads, and voltage and and current are not in phase. So there is true power and apparent power. The apparent power is usually about 30 % or more greater than the true power. However the current for the apparent power has to be supplied. However the current for the apparent power is what blows the fuse, and the true power blows the speaker..

This is one instant where the correct answer is to short out the fuse.

 

[PENG]

Don't know much about audio equipment, except that I want LOUDER music from my speakers. Currently, I've been told they are clipping(therefore blowing the fuses in the RE-38's). I think I need an external amp, but I'm unclear on what to get and how to set it up.

Sound like you do need an external amp but please give us the specs of the speaker line fuses. With a full spec we should be able to tell you if in fact they are blowing due to clipping.

 

[PENG]

Your problem is not lack of power but fuses. You can't protect a speaker with a line fuse, without getting the problem you are having.

I am not sure if there are enough info to support this claim.

Also fuses greatly increase thermal compression. The reason that fuses can not protect a speaker without your problem is because speakers are reactive loads, and voltage and and current are not in phase.

I would think that the manufacturer should know what they are doing. If coordinated properly you may be able to use fuses that offer protection but overall you may be still be right that it may be a bad idea for other reasons.

So there is true power and apparent power. The apparent power is usually about 30 % or more greater than the true power. However the current for the apparent power has to be supplied. However the current for the apparent power is what blows the fuse, and the true power blows the speaker..

Current is current whether it is in phase with the applied voltage or not, it can still blow the load just the same. You push high enough current through a pure inductor, that is power factor almost equal 0 (Cosine 90), it will blow that inductor, true power or not.

 

[TLS Guy]

I am not sure if there are enough info to support this claim.



I would think that the manufacturer should know what they are doing. If coordinated properly you may be able to use fuses that offer protection but overall you may be still be right that it may be a bad idea for other reasons.



Current is current whether it is in phase with the applied voltage or not, it can still blow the load just the same. You push high enough current through a pure inductor, that is power factor almost equal 0 (Cosine 90), it will blow that inductor, true power or not.

Not the heating effect though. Many years back manufacturers had a vogue for putting fuses in the speaker leads. The result was what the OP is experiencing. This is why the practice dropped out of favor pretty quickly, as well as for reasons of thermal compression, as the resistance of the fuse varies widely getting very high close to the blow point. Now the fuses are fast blow and they are not the load the speaker is. The heating in the voice coil over time, is entirely due to the true power, not the apparent power, as the load gives back the apparent power. However the current still flows to and from the load via the fuse. So the heating effect in the voice coil is the power in watts, not the VA rating.

It is the same as installing a generator. The power that the generator can supply is the rating of the generator in KW. However the wiring from the generator has to be beefy enough for the KVA rating which is the bigger number. For instance my generator here is 14 KW, but the the KVA rating is 17 KVA. So on the true power delivered basis you would think that a cable of 58 watt capacity would be enough, but it actually needs to be 71 amp, and for margin 80 amp. So that is what had to be installed.

 

[bnairb]

Sound like you do need an external amp but please give us the specs of the speaker line fuses. With a full spec we should be able to tell you if in fact they are blowing due to clipping.

The fuses in the back of the RE-38's are 2.5 amp slow blow. If I remember right, they used to blow at different times, but I think that is before we realized we were not using slow blow fuses. Since then, both speaker fuses will blow at the exact same time.

 

[bnairb]

Get A McIntosh
With 102 dB sensitivity ( very,very efficient speaker) and 140 watts ( 8 ohms) approximately 280 watts into 4 ohms ( unless your receiver is current limited) I can't image you are clipping uless you are running 110 dB or louder; hurts my ears just to think of something that loud!

Good Luck!

Forest Man

The settings on the 2700 are 8 or 6 ohms. Under 6 ohms in the manual, for FRONT it says "the impedance of each speaker must be 4 ohms or higher".

Also in the specs it says:
Dynamic Power (IHF)
8/6/4/2 Ω ........................................................ 170/205/265/345 W

So I'm assuming my max watts at 4 ohms for the fronts is 265.

A couple of years ago I noted that the 2700's volume control range is-80db to +16db and I was blowing fuses around +2db. Of course this test may have been while using fast blow fuse, don't remember

And yes, we like it loud. Must be careful with "Banditos" by the Refreshments

 

[TLS Guy]

The fuses in the back of the RE-38's are 2.5 amp slow blow. If I remember right, they used to blow at different times, but I think that is before we realized we were not using slow blow fuses. Since then, both speaker fuses will blow at the exact same time.

The power consumed by the speaker is the square of the current X impedance.

So working your fuse situation, your fuses are 2.5 map the square of 2.5 is 6.25 X 4 ohm (your speaker impedance is 25 watts. So you fuses will blow when an average of 25 watts is reached. With those speakers that should be loud. However because of the reactive nature of the load the fuses are probably blowing at a somewhat lower power level, depending on the phase angle.

If your speakers can truly handle 400 watts you would need 10 amp fuses.

Fuse size would be power 400 watts/impedance 4 Ohm which is 100. The current is the square root of 100 which is 10 amps. So there you have your problem.

The issue is that the power a speaker can handle is frequency selective, for instance the speaker can handle a lot less power in the tweeter range. So manufacturers used to fuse well below total rated power as otherwise the tweeter was not protected. If your speakers are old enough that they are before the invention of ferro fluid tweeter cooling, then you may well blow your tweeter if you play them louder. It was tweeter burnout before ferro fluid that caused speaker manufacturers to do the cheap and nasty thing of inserting fuses.

If your tweeters have ferro fluid just get rid of the fuses. If they don't have ferro fuid and you want it louder, buy more up to date speakers. This fuse business in speakers pretty much died out with the introduction of ferrofluid speaker cooling.

 

[JerryLove]

Don't know much about audio equipment, except that I want LOUDER music from my speakers.
[...]
Power Handling (RMS): 5 to 400 Watts RMS
Frequency Response: 27Hz-20kHz
Sensitivity (dB): 102 dB dB
Impedance (Ohms): 4 Ohms

[...]
Front: 140 W + 140 W
Center: 140 W
Surround: 140 W + 140 W
Surround back: 140 W + 140 W

Without adjusting for 4 ohms (which would theoretically double amperage, but likely the AVR can't do that), 140W into 102db sensitivity = >122db, louder than a jet engine (http://www.howstuffworks.com/question124.htm).

 

[njedpx3]

lots of current

The settings on the 2700 are 8 or 6 ohms. Under 6 ohms in the manual, for FRONT it says "the impedance of each speaker must be 4 ohms or higher".

Also in the specs it says:
Dynamic Power (IHF)
8/6/4/2 Ω ........................................................ 170/205/265/345 W

So I'm assuming my max watts at 4 ohms for the fronts is 265.

A couple of years ago I noted that the 2700's volume control range is-80db to +16db and I was blowing fuses around +2db. Of course this test may have been while using fast blow fuse, don't remember

And yes, we like it loud. Must be careful with "Banditos" by the Refreshments

Okay lets assume 265 watts into 4 ohms and for illustration assume a pure resistive load. Power = v^2/r 265= v^2/4 so v=8.139 volts. Power is also V*I so 265=8.139* I . therefore maximum I is 32.56 Amperes. IMHO a 2.5 slow-blow fuse will never work! except at very low levels.

You can add an external amplifier by connecting input to front pre-outs and connecting the speakers to the amp. The McIntosh Amp I mentioned earlier is a 2000 watt amplifier and very costly and very high quality. A very good less expensive two channel amp is the Behringher EP2500. But with 2.5 amp fuses, you are still going to blow the fuses. As TLS stated, this maybe one case whereby the fuses should be bypassed, i.e. short across the fuse end connector terminals.

Good Luck!

Forest Man

P.S.- Glad you like loud music! Rock On!

 

[bnairb]

How would i find out if the tweeters have ferro fluid?
Also, I like the RE-38's and can't afford to replace them right now. I don't want to destroy them, so to protect them could I just use a higher amp fuse (10 amp I think you said) instead of shorting it. Not knowing the speaker business, should I blow the tweeters, can I just get new, better tweeters and install them in the RE-38's instead of having to completely new speakers $$$ ?

 

[TLS Guy]

Okay lets assume 265 watts into 4 ohms and for illustration assume a pure resistive load. Power = v^2/r 265= v^2/4 so v=8.139 volts. Power is also V*I so 265=8.139* I . therefore maximum I is 32.56 Amperes. IMHO a 2.5 slow-blow fuse will never work! except at very low levels.

You can add an external amplifier by connecting input to front pre-outs and connecting the speakers to the amp. The McIntosh Amp I mentioned earlier is a 2000 watt amplifier and very costly and very high quality. A very good less expensive two channel amp is the Behringher EP2500. But with 2.5 amp fuses, you are still going to blow the fuses. As TLS stated, this maybe one case whereby the fuses should be bypassed, i.e. short across the fuse end connector terminals.

Good Luck!

Forest Man

P.S.- Glad you like loud music! Rock On!

for 265 watts it would be 8.1 amps. Power = curreent squared X resistance. So 265 watts/4 = 66.25. The square root of 66.25 is 8.1 amps.

You really need to know if that speaker has ferro fluid cooled tweeters. Ferro fluid started to be introduced in the early eighties, and was pretty much universal by the end of that decade. Cerwin Vega are in my view a junk speaker company, so my guess is that they would have put in forro fluid cooled tweeters later rather than earlier, but you need to check.

 

[njedpx3]

Math Error

for 265 watts it would be 8.1 amps. Power = curreent squared X resistance. So 265 watts/4 = 66.25. The square root of 66.25 is 8.1 amps.

You really need to know if that speaker has ferro fluid cooled tweeters. Ferro fluid started to be introduced in the early eighties, and was pretty much universal by the end of that decade. Cerwin Vega are in my view a junk speaker company, so my guess is that they would have put in forro fluid cooled tweeters later rather than earlier, but you need to check.

Mea Culpa OP , bnairb . TLS thanks for correcting my math -Geesh! I divided by 4 instead of multiplying --it was early

Okay what I meant to say P=v^2/4 265=V^2/4 V^2 = 1060 v= 32.55

Therefore P=I*V 265=I*32.55 I= 8.1394 amperes


Peace ,

Forest Man

 

[bnairb]

For fun, I emailed CV to ask about the ferro fluid in the RE-38's.

They said: Yes they carried ferro

So I guess I'm all set to short the fuse or install a bigger & see what happens??

 

[M Code]

The 2700 will deliver more power into 4 Ohms when the switch is in the 8 Ohms position.. The basic reason is that Yamaha has that feature to keep the output stage from self-destruction due to the higher current potential into 4 Ohms so they decrease the power supply voltage accordingly..

Sounds like you are overdriving the amplifier and/or you have too much EQ boost. The only solution would be to add a separate component power amplifier..

However that system must be incredibly loud...

Just my $0.01..

 

[PENG]

The heating in the voice coil over time, is entirely due to the true power, not the apparent power, as the load gives back the apparent power. However the current still flows to and from the load via the fuse. So the heating effect in the voice coil is the power in watts, not the VA rating.

I see that there is some misconception here. Let's review some basic electrical theory again, we both know the impedance of a speaker varies with frequencies and impedance, consider the formula:

Z=R+j2πfL+1/j2πfC

where Z is the impedance, L is the inductance, C is the capacitance and R is the resistance. Note that R is not dependent on f (frequency).

Let's say the resistance of the voice coil (for clarity, ignore effect of X-over) is 2 ohms, then the heating effect is proportional to I2R so if the current I is 10A, the so call real power is 1022=200W regardless of the phase angle between the 10A current and the voltage. Now you will agree that a resistive load does produce heat so this voice coil will have to dissipate 200W Depending on how long the 10A current sustains and the speaker design, it may or may not blow the voice coil.

It is the same as installing a generator. The power that the generator can supply is the rating of the generator in KW. However the wiring from the generator has to be beefy enough for the KVA rating which is the bigger number. For instance my generator here is 14 KW, but the KVA rating is 17 KVA. So on the true power delivered basis you would think that a cable of 58 watt capacity would be enough, but it actually needs to be 71 amp, and for margin 80 amp. So that is what had to be installed.

Exactly, that is why transformers and generators all have to be rated in KVA or MVA. Rating them in KW and MW is less informative because you cannot calculate the current without knowing the power factor and that depends on the electrical characteristic (e.g. impedance) of the load.

If you load up your generator with an inductor with very low inductance, hence low inductive reactance = 2πfL, the current will be extremely high even though a wattmeter will measure very little watts (so call real power). The fact is, even though in this example the "real power" is low, if the current is high than what your generator is rated for it will still blow it unless you have adequate overload and short circuit protection. The protective circuit does not care what the power factor (phase angle) is because it knows it is the magnitude of the current that matters not whether it is doing "real" work for you or "not".

I hope this help clarify things a little.

 

[TLS Guy]

I see that there is some misconception here. Let's review some basic electrical theory again, we both know the impedance of a speaker varies with frequencies and impedance, consider the formula:

Z=R+j2πfL+1/j2πfC

where Z is the impedance, L is the inductance, C is the capacitance and R is the resistance. Note that R is not dependent on f (frequency).

Let's say the resistance of the voice coil (for clarity, ignore effect of X-over) is 2 ohms, then the heating effect is proportional to I2R so if the current I is 10A, the so call real power is 1022=200W regardless of the phase angle between the 10A current and the voltage. Now you will agree that a resistive load does produce heat so this voice coil will have to dissipate 200W Depending on how long the 10A current sustains and the speaker design, it may or may not blow the voice coil.




Exactly, that is why transformers and generators all have to be rated in KVA or MVA. Rating them in KW and MW is less informative because you cannot calculate the current without knowing the power factor and that depends on the electrical characteristic (e.g. impedance) of the load.

If you load up your generator with an inductor with very low inductance, hence low inductive reactance = 2πfL, the current will be extremely high even though a wattmeter will measure very little watts (so call real power). The fact is, even though in this example the "real power" is low, if the current is high than what your generator is rated for it will still blow it unless you have adequate overload and short circuit protection. The protective circuit does not care what the power factor (phase angle) is because it knows it is the magnitude of the current that matters not whether it is doing "real" work for you or "not".

I hope this help clarify things a little.

Yes, Peng that is absolutely correct, a generator, or UPS, what ever device you are using for supply, must be rated the KVA requirement AND the true power in watts of the anticipated load.

However the fuse is in the connecting cable, so the only factor of concern is the current between the source and the load. As far as a load is concerned, (let it be a speaker) then the only thing that will generate heat in the load is the true power.