Passive Bi-amping

[RMK!]

I just upgraded my main speakers and would like to make sure that I am doing them justice from a power perspective. Everyone from the sales person who sold them to me to reviews of the speakers to other owner’s comments lead me to believe that I have purchased speakers that are “power hungry”. The specs on the speakers are:

Monitor Audio GR60
Frequency Response +/- 3dB 28Hz-30KHZ
Sensitivity (1W@1M) 90dB
Nominal Impedance (Ohms) 6
Power Handling RMS (W) 200

Is the 3805 capable of driving these speakers? If not, I am not opposed to purchasing a power amplifier to address this. I thought the Audioholics 3805 review gave me a quick and inexpensive way to address the power issue.

Several others and I have done the 3805 bi-amping and have had mixed results. In response to my questions about this, forum members have referred to this as “ghetto amping” and a “waste of wire” and recommended a separate power amp. There have been comments made about differences in the quality of the 3805 internal amps inferring that the zone 2&3 amps are inferior to the main zone amp but no data was presented to backup this assertion. Interestingly, there has been no comment from the review author on this subject nor was this addressed in the review. The only down side mentioned in the review was a reported but not verified low frequency hum generated by increasing the bass level several db’s.

I have to wonder if Clint still stands behind his “qualified” 3805 bi-amping recommendation and claim of 240 (2 X 120) watts power to the fronts (where you need it most) giving an additional 3dB headroom. It would be nice to hear a definitive statement as to the effectiveness of this procedure.

I understand that room acoustics and speaker positioning have a large effect on how the speakers sound and I am working on that but I would also like to get to the bottom of the bi-amping mystery. Is passive bi-amping pointless? Does this provide the 240 watts and 3dB additional headroom?

Sorry to keep carping on this, but before I spend $2K on 200 watts of power I’d like to know that what I already have cannot provide it.

 

[Snarl]

How do the new speakers sound on your Denon ?

I would think if you crank them and they sound great that would be all you need ?

 

[gene]

I have to wonder if Clint still stands behind his “qualified” 3805 bi-amping recommendation and claim of 240 (2 X 120) watts power to the fronts (where you need it most) giving an additional 3dB headroom. It would be nice to hear a definitive statement as to the effectiveness of this procedure.

You're not really getting 3dB of headroom since the amp isn't being bridged to double power to the entire speaker. What you are getting is two amps driving a broken up reactive speaker load which can increase system linearity since each amp is only driving a portion of the loudspeaker and the back EMF from each portion of the system is not intermodulating with the same amplifier. Try it if you aren't running 7.1 and see if it works for you. Its effectiveness is dependent on your speaker load and listening conditions.

 

[Spiffyfast]

No need to spend 2 grand on a 200 watt amp, check out Outlaw Audio

http://www.outlawaudio.com/products/200.html

200 watt mono amp, only $299 each and I think you get a deal when you buy 2 of them. Not a bad way to beef up your main speakers if your worried about not getting enough power

 

[mtrycrafts]

I just upgraded my main speakers and would like to make sure that I am doing them justice from a power perspective. Everyone from the sales person who sold them to me to reviews of the speakers to other owner’s comments lead me to believe that I have purchased speakers that are “power hungry”. The specs on the speakers are:

Monitor Audio GR60
Frequency Response +/- 3dB 28Hz-30KHZ
Sensitivity (1W@1M) 90dB
Nominal Impedance (Ohms) 6
Power Handling RMS (W) 200

Is the 3805 capable of driving these speakers? If not, I am not opposed to purchasing a power amplifier to address this. I thought the Audioholics 3805 review gave me a quick and inexpensive way to address the power issue.

Several others and I have done the 3805 bi-amping and have had mixed results. In response to my questions about this, forum members have referred to this as “ghetto amping” and a “waste of wire” and recommended a separate power amp. There have been comments made about differences in the quality of the 3805 internal amps inferring that the zone 2&3 amps are inferior to the main zone amp but no data was presented to backup this assertion. Interestingly, there has been no comment from the review author on this subject nor was this addressed in the review. The only down side mentioned in the review was a reported but not verified low frequency hum generated by increasing the bass level several db’s.

I have to wonder if Clint still stands behind his “qualified” 3805 bi-amping recommendation and claim of 240 (2 X 120) watts power to the fronts (where you need it most) giving an additional 3dB headroom. It would be nice to hear a definitive statement as to the effectiveness of this procedure.

I understand that room acoustics and speaker positioning have a large effect on how the speakers sound and I am working on that but I would also like to get to the bottom of the bi-amping mystery. Is passive bi-amping pointless? Does this provide the 240 watts and 3dB additional headroom?

Sorry to keep carping on this, but before I spend $2K on 200 watts of power I’d like to know that what I already have cannot provide it.

Those speakers are not power hungry from the specs you posted. Just hope that it will not audibly distort well before the amp will give out at 110 dB spl.

 

[RMK!]

No need to spend 2 grand on a 200 watt amp, check out Outlaw Audio

http://www.outlawaudio.com/products/200.html

200 watt mono amp, only $299 each and I think you get a deal when you buy 2 of them. Not a bad way to beef up your main speakers if your worried about not getting enough power

Good idea but I have space limitations. There isn't much room in the AV cabinet for big amps so I'm thinking a used Sunfire Grand Cinema 200 5.1 would be a good fit (literally). I know the new version did not get a good review here but I have read good reviews elsewhere for the GC power amps, they run cool and will fit into the space.

 

[RMK!]

You're not really getting 3dB of headroom since the amp isn't being bridged to double power to the entire speaker. What you are getting is two amps driving a broken up reactive speaker load which can increase system linearity since each amp is only driving a portion of the loudspeaker and the back EMF from each portion of the system is not intermodulating with the same amplifier. Try it if you aren't running 7.1 and see if it works for you. Its effectiveness is dependent on your speaker load and listening conditions.

You know, I have been concerned about back EMF's and intermodulation with the amps...

Guess I should stick to posts in the Beginners and Audiophytes thread

 

[Buckeyefan 1]

Good idea but I have space limitations. There isn't much room in the AV cabinet for big amps so I'm thinking a used Sunfire Grand Cinema 200 5.1 would be a good fit (literally). I know the new version did not get a good review here but I have read good reviews elsewhere for the GC power amps, they run cool and will fit into the space.

Were you following this thread?
http://forums.audioholics.com/forums/showthread.php?p=78175#post78175

If you're looking to just power the bass in the speakers (biamped), you can get away with a massive $350 amp if it's going to be in a cabinet and you don't mind a little fan noise.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=23787&item=7333959612&rd=1&ssPageName=WDVW

 

[AVRat]

Bi-amping conundrum

Welcome to the confusing world of audio nirvana.

First off, the 3805 can defintely handle these speakers purely from the mono-amp perspective. The 3805 spec reads: 160 W + 160 W (6 Ω/ohms, 1 kHz with 0.7% T.H.D.) This a little ambivalent, I would more conservatively assume 150W across the freq. spectrum. BTW congrats on your purchase, those should be a sweet speaker. Even sweeter if bi-amped properly.

The problem is not as straight forward as it seems. And most trying it get it wrong. Based on the active bi-amping theory, which I'm not sure works for the passive but we'll assume it does, the crossover point between the LF and MF/HF is the important variable in this equation. Basically, the theory states that the crossover point (network) determines how power is distributed.

X-over Frequency (Hz) Power to Bass (%) Power to Mid+High (%)
250 40 60
350 50 50
500 60 40
1,200 65 35
3,000 85 15
5,000 90 10

This info is taken from an article at the following link: http://sound.westhost.com/articles.htm Its a little technical but well worth reading.

Unfortunately, Monitor Audio does not offer the crossover points on their website. Generally, speakers of this caliber have fairly low crossover points. But we see from this table that only a crossover point of around 350 Hz benefits from amps of equal power. If, however, your speakers have a crossover point of 250 HZ, then bi-amping the speakers based on their power capability results in required amps of 80W for LF and 120 for MF/HF.

If you use the 3805 to bi_amp the speakers, the LF receives 150W but the MF/HF requires 225W for proper balance. Basically, this equates to an amp rated at 180W @ 8 ohms. This is dependent on the amp. A Sunfire would only require about 120W @ 8 ohms. BTW, the Sunfire 200 actually gives you 300W into 6 ohms, which is OK. It just means that you don't have to push the amp as hard for great quality sound.

I may be way off base on this as I have never done it. What works in theory does not always work in reality. If there are any speaker designers out there, perhaps they could shed some light on this confusing subject.

Be sure to check specs and don't be afraid to ask questions. Many people on this site are more than willing to educate the uneducated.

 

[RMK!]

End of Bi-AMP Experiment (or is it)

Thanks to everyone who gave input. It was very educational.

I just purchased a Sunfire GC 200 5.1 off of AudiogoN and should get it in a couple of weeks effectively ending the Denon BI-amp experiment. I'm thinking of having the Sunfire power the mains and center and the Denon drive the surrounds. That leaves two channels available on the Sunfire to bridge and drive the fronts (400 watts). I'm just enough of a glutton for punishment to try it. So, as our esteemed Governor once said "I'll be back"

 

[AVRat]

Bridgeable???

The Sunfire GC is bi-wireable/ampable but I don't think its bridgeable. Remember you'll already have 300W into 6 ohms. I would try the bi-wiring option first.

You've got mucho dinero tied up in equipment to be playing around too much.

Did you check the specs on the speakers to see what the crossover points are?

 

[RMK!]

The Sunfire GC is bi-wireable/ampable but I don't think its bridgeable. Remember you'll already have 300W into 6 ohms. I would try the bi-wiring option first.

You've got mucho dinero tied up in equipment to be playing around too much.

Did you check the specs on the speakers to see what the crossover points are?

AVRat,

Good points. One of the reviews I read mentioned bridging the amps. I agree with you though and will try single wire first, bi-wire just for yucks, then depending how much extra time I have on my hands, do the bi-amp thing again. I could not find any detailed specification on MA's Website. I have e-mailed them asking for the crossover information.

Thanks again for the feedback.

 

[AVRat]

Bridging info

Since I'm not experienced with bridging, I did a search on the subject. What I found confirmed what I thought to be true.


Question:
How do I bridge my amp?

Response:
Bridging a stereo amplifier essentially turns two channels into one mono channel with greater power output. In order to bridge an amplifier it must have at least two channels and it must be capable of being bridged. Check your amplifier''s manual to determine if you can bridge your amp''s channels. If you do not have a manual, check your amplifier''s back panel for a bridging switch. Amplifiers capable of bridging will have a switch somewhere on the rear panel labeled ''bridge'' or ''bridge mode'' or ''mono'' or something similar.

Once you have established that your amplifier is capable of bridging consider the speaker load you will present to it. By bridging an amplifier you essentially halve the impedance it sees from a given speaker so an 8 ohm speaker looks like a 4 ohm speaker to the bridged amp. Be sure your amplifier is capable of delivering consistent power into the lower impedance without overheating or distorting before going through with the bridging process. In most cases you are better off to have a single more powerful amplifier than two bridged amps due to the excess heat and strain that can be induced.

Assuming your amplifier is capable of being bridged and you have decided it will work with your equipment, the actual process of bridging your amp is fairly simple. Turn off the power to your amplifier and disconnect your speakers. Most amplifiers will use the left input as the bridged mode input. Check the back of your amp for this information - the input to use for bridged operation should be marked in some fashion. Connect a single RCA cable from your pre-amp to this input. Run a strand of speaker wire from the positive (red in almost all cases) input on your speaker to the positive speaker-level output on your amplifier corresponding to the bridged input you just connected. Connect the negative (black in almost all cases) input on your speaker to the second POSITIVE (red in almost all cases) output on your amplifier. In most cases the wiring will work like this: a speaker wire connection will run from the positive (red) output on your amplifier''s left channel to the positive (red) input on your speaker and a speaker wire will connect the positive (red) output on your amplifier''s right channel to the negative (black) input on your speaker. Once you have made your connections, flip the bridging switch from stereo mode to bridged or mono mode and power the amplifier back up.

The important points to remember in bridging an amplifier are to switch the amp to bridged mode, use ONLY the amp''s positive speaker outputs, and be sure your amplifier and speaker will work well in bridged mode based on the speaker''s nominal and minimum impedance (halved) and your amp''s capability to operate into low ohm loads.

http://www.audiovideo101.com/learn/askus/displayaskus.asp?questionid=13&List=1

More info on bi-amping but doesn't discuss the issue of power distribution relating to crossover points. May have to start a new thread to see if we can clear this up.

Question:
How do I bi-amplify speakers that are capable of bi-amp/bi-wiring ?

Response:
Bi-amplification offers two main benefits over using a single amplifier to drive a speaker: (1) more power is delivered to the speaker and (2) the amplifiers used to drive the bass and midrange/treble portions of the speaker need not be the same and can thus be customized to work optimally in their individual areas. For instance, an amp that performs very well in the bass region can be used to drive the woofers while an amp with an open, sweet midrange and treble can be used for the higher frequency drivers.

There are two methods of bi-amplification - passive and active. Passive bi-amping is fairly simple: split the audio signal coming from the outputs on your pre-amp using a Y-adapter (some pre-amps may even have two outputs so a Y-adapter is not necessary), then connect one of the split connectors from each channel to one amplifier and the other split connector from each channel to the second amplifier, finally run speaker wire from your bass amp to the low frequency connections on your speaker using good quality speaker wire and do the same from the midrange/treble amp to the high frequency inputs on your speakers. Be sure you take off the connector plate or wire on your speakers that binds the high and low frequency inputs. In this type of arrangement you are using the passive crossover in your speakers to split the signals for the amplifiers thus the passive moniker for this form of bi-amping. Also, the amplifiers you use must have the same gain - this is very important, if the gain is different then the bass and midrange/treble will be amplified at different levels (one louder than the other).

The second more complex method of bi-amplifying is active in which you will not use the crossover built into your speakers. Instead you will use an active electronic crossover. This crossover should sit in the signal path between your pre-amp and your amplifiers. It will split the signal to high-frequency and low-frequency pieces sending only the highs to one amp and only the lows to another (in passive bi-amping each amplifier still receives the full frequency spectrum). You will also need to disengage the crossover network in your speaker, which may require you to take out the crossover and work on - this is best left to a professional A/V installer. Otherwise the connection method is the same from amplifiers to inputs. Active bi-amping allows you to set the crossover point you use, but be careful in doing so as the point used by the speaker designer was carefully selected. You may wish to simply use the same crossover point as the speaker designer did with your speakers but use the active setup to get the advantages of driving your amps with only a portion of the frequency spectrum and a direct connection from the bass amp to the bass driver(s).

http://www.audiovideo101.com/learn/askus/displayaskus.asp?questionid=246&List=5

 

[RMK!]

MA X-over

Welcome to the confusing world of audio nirvana.

First off, the 3805 can defintely handle these speakers purely from the mono-amp perspective. The 3805 spec reads: 160 W + 160 W (6 Ω/ohms, 1 kHz with 0.7% T.H.D.) This a little ambivalent, I would more conservatively assume 150W across the freq. spectrum. BTW congrats on your purchase, those should be a sweet speaker. Even sweeter if bi-amped properly.

The problem is not as straight forward as it seems. And most trying it get it wrong. Based on the active bi-amping theory, which I'm not sure works for the passive but we'll assume it does, the crossover point between the LF and MF/HF is the important variable in this equation. Basically, the theory states that the crossover point (network) determines how power is distributed.

X-over Frequency (Hz) Power to Bass (%) Power to Mid+High (%)
250 40 60
350 50 50
500 60 40
1,200 65 35
3,000 85 15
5,000 90 10

This info is taken from an article at the following link: http://sound.westhost.com/articles.htm Its a little technical but well worth reading.

Unfortunately, Monitor Audio does not offer the crossover points on their website. Generally, speakers of this caliber have fairly low crossover points. But we see from this table that only a crossover point of around 350 Hz benefits from amps of equal power. If, however, your speakers have a crossover point of 250 HZ, then bi-amping the speakers based on their power capability results in required amps of 80W for LF and 120 for MF/HF.

If you use the 3805 to bi_amp the speakers, the LF receives 150W but the MF/HF requires 225W for proper balance. Basically, this equates to an amp rated at 180W @ 8 ohms. This is dependent on the amp. A Sunfire would only require about 120W @ 8 ohms. BTW, the Sunfire 200 actually gives you 300W into 6 ohms, which is OK. It just means that you don't have to push the amp as hard for great quality sound.

I may be way off base on this as I have never done it. What works in theory does not always work in reality. If there are any speaker designers out there, perhaps they could shed some light on this confusing subject.

Be sure to check specs and don't be afraid to ask questions. Many people on this site are more than willing to educate the uneducated.

AV-Rat

MA finally responded to my e-mail with the following:

Your query has been passed onto myself for an answer, the GR60 is a 2 1/2 way design with the following Crossover Points as follows: -

Lower Bass Drivers approx 150Hz
Bass/Mid Driver 1500Hz
Tweeter 4000Hz

Regards Geoff Hill
Senior Acoustic Engineer

Based upon the information in the article, these numbers seem off a bit from the norm (if there is such a thing). They (MA) also referred to the GR60 as a 2.5 way design even though I have read reviews that describe the speakers as a "true three way design". There are three sets of binding posts and three distinct chambers for the Low/Mid/High. All very confusing. Comments?