I dont understand why a bridged amplifier changes the percieved ohms of the speaker. I thought the increase in power was due to the two seperate amplifiers working as one. |
""That is because a REAL 4 ohm speaker would EFFECTIVELY be seen as a 2 ohm load by the bridged amp. Only BEEFY amps can run bridged at 4 ohms. If an amp can run bridged with a 2 ohm load, you KNOW that it is built BETTER than a tank.""
Since my ML speakers are real 4 ohm speakers, the Bel Canto must be a pretty beefy amp, build like a "tank" |
Sean,
You have done a very credible job of explaining the complex loads that electrostatic hybrids represent, and I thank you for your effort and all the good information.
One additional point I'd like to bring up is that while tube amps generally excel as voltage amplifiers (which is why many use them to drive ESL panels) they do not deal with low impedances as well as solid state designs. So in the typical ESL panel, where you have that low impedance dip at high frequencies, the power that most tube amps can deliver falls off rapidly. However, in such designs, sometimes a bit of high-frequency roll off is perceived as a good thing by listeners.
This was one of the biggest problems I had in finding a suitable amp to drive my InnerSound Eros, which dip to 2 ohms in the high frequencies. The tube amps I tried, although they sounded nice in the midrange, noticeably rolled the high frequencies. Even the highly-respected Clayton Audio M70's, a solid-state, high-current design that exhibited wonderful high frequency reproduction with many other speakers, failed to maintain its level of treble performance on the Eros. With such a load it cannot be taken for granted that every high-current, solid-state amp will be up to the task, and many that I tried were not.
The InnerSound amp, which is stable to under 1 ohm and delivers 1200 Wpc into 2 ohm loads sounds utterly unrestrained, detailed, and airy. At the same time, it is also quite adept at providing plenty of punch, extension, and control in the bass. Of all the amps that I've tried with the Eros so far, the InnerSound Amp and the Monarchy Audio SE-160 hybrid monoblocks have provided the best performance. |
I'll jump in here for Bob and he can add / change as he sees fit. Others are always welcome to do the same as i am not above making mistakes. I would rather be corrected and get "spanked" in public than to spread "disinformation".
When you bridge an amp, it effectively sees HALF of what the actual loudspeaker load is. In other words, what appears as an 8 ohm load to an "unbridged" amp now looks like 4 ohms to a bridged amp. If you doubt this, take a look at what an amp is rated at per channel into four ohms and combine the output of the two channels together. You will then have what the amp is rated at in bridged mode ( in MOST cases ) with an 8 ohm load.
A common figure for a pretty decent sized amp would be 250 X 2 @ 8 ohms / 400 X 2 @ 4 ohms. Bridging the two channels together would typically result in a rating of 800 X 1 @ 8 ohms with 4 ohm loads not recommended by most manufacturers. That is because a REAL 4 ohm speaker would EFFECTIVELY be seen as a 2 ohm load by the bridged amp. Only BEEFY amps can run bridged at 4 ohms. If an amp can run bridged with a 2 ohm load, you KNOW that it is built BETTER than a tank.
The reason that the damping factor is reduced has to due with the reduction in effective impedance that the bridged amp sees. If you look at the spec sheets, damping factor is based on a specific load impedance and frequency. Most amps have a lower damping factor at higher frequencies. As such, a common place to rate them is at 1 KHz and, even if not specified, typically at 8 ohms.
Damping factor is based on the difference between the output impedance of the amp and the impedance of the load. The greater the variance between the two results in a higher damping factor. Damping factor is typically thought of as how tight of a grip the amplifier has on the speaker i.e. commonly referred to as "control" of the drivers. Since going from an 8 ohm load to a 4 ohm load effectively halves the difference in impedance, the damping factor is now cut in half and "control" is reduced by appr 50%. Whether this is noticeable or not has to do with how high the damping factor was to begin with.
The opposite occurs as you go up in load impedance. Using a speaker rated at 4 ohms and then switching to an 8 ohm load effectively doubles the damping factor. Going from a 4 ohm load to a 16 ohm load QUADRUPLES the damping factor. This typically results in notably tighter bass reproduction.
All things being equal, a lower impedance speaker is tougher to control for ANY amp. This is true even though the amp may be able to generate more power due to the lower resistance. In this specific case, more power does NOT necessarily mean more control over the drivers and you might actually end up with "looser" or "sloppier" low frequency output.
As a general rule, solid state ( SS ) amps have a MUCH lower output impedance ( typically way below 1 ohm ) than tube amps ( sometimes as high as 1 or 2 ohms ). This is one of the reasons why many folks prefer to run higher impedance speakers with tube amps. Not only does it pull less current from the tubes ( which are more at home producing high voltage rather than high current ), the damping factor is increased. In a comparative analysis, a SS amp with an output impedance of .5 ohms and a speaker load of 4 ohms is equivalent in damping factor to a tube amp with an output impedance of 2 ohms and a speaker load of 16 ohms. This is why many tube amps are said to suffer from "mushy" or "round" bass when running low impedance speakers. The damping factor or "control" over the drivers is drastically reduced.
Given the specifics of the speakers in question ( ML hybrids ), i can see quite a dilemma. Whereas the mid and high frequency section is electrostatic ( prefers high voltage and can be quite reactive ) and the woofers are dynamic ( prefers high current ). You really need a top notch amp(s) for speakers like this to perform at their potential. While tubes typically are thought of as being "voltage amplifiers" and seem well suited to the drive characteristics of an E-stat, they typically do not like the low impedance drop that ALL E-stat's exhibit at high frequencies. Obviously, poorly built and designed tube amps need not apply for this job. On the other hand, the woofers need a lot of current making them more suitable for use with a beefy SS amp. Only problem is that they typically don't generate the higher voltages that really make E-stat's sing.
In order to achieve optimum results with ONE amplifier driving this type of load, you would need something that offered very high voltage capabilities along with something that was of a high current design. Sounds like the best of both worlds, right ??? Now you know why some people running "hybrid" speakers run tubes on top and SS on the bottom end. Hybrid speakers with a hybrid amplifier arrangement. Do i hear Detlof's name coming up ??? : )
The only alternatives that i know of using a similar approach would be amplifiers designed around some type of high current / high voltage switching power supplies. The Bel Canto MIGHT fall into this category. I don't know enough about it to say one way or the other. Some others that would APPEAR to be well suited to this type of application might be the aforementioned Innersound amp and the Sunfire amps. Both of these two amps run high rail voltages and are quite stable into low impedances. This is evidenced by the "doubling down" of power output as impedance is halved. It is quite possible that the larger Bel Canto's also fall into a similar category.
I know that Perreaux's have also been known to drive VERY reactive loads ( i.e Apogee's ), even in bridged configuration. While they are also of a high rail voltage / high current design, they make use of a more standard power supply arrangement. This means that they run WAY hotter, are WAY heavier and WAY less efficient in terms of power consumption. Some Krell's might also be suitable candidates but also fall into the "big clunker" category like the Perreaux's. Whether any of these compliment the tonal balance of the rest of the system or your personal taste is anybody's guess though.
With all of that in mind, i would suggest following the "K.I.S.S." principle. Instead of running four amps and the associated cables, i would look for one or two amps of equivalent or higher power and quality that could do the job. While doubling up on your amps would obviously give you more of what you already have, you might be able to achieve even greater results AND keep it simpler for about the same amount of money. Otherwise, i can see you moving into an active crossover and doing major mods to the internals of the speakers ( i.e. bypassing the crossovers ) to achieve what you are looking for.
Hope this helps and keep us posted with what you decide to do. Sean
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Bob, Tell us more about what you said. Explain how a bridged amp has less control over the speakers then the same two amps running in stereo. |
Tek you might as well try the vertical passive biamping: it sounds like you're presently bridging the stereo amps, which halves their damping factors resulting in degraded control of the speakers by the amps. |
Tekunda,
I never said that you needed an external active crossover to bi-amp. You can just use the passive crossovers in your speakers. Going to the vertical bi-amp configuration should improve your sound noticeably without you having to buy anything else.
Later, down the road if you feel you want to go to an active external crossover you can always do that and it will likely improve the sound even more. You can get a decent active crossover used for under $500. The hardest thing will probably be taking your speakers apart to disconnect the passive internal crossovers (lethal voltages may need to be discharged too) but the folks at Martin Logan would be able to advise you of just what is involved to accomplish that. They could also advise you as to what crossover frequency and slopes to use. It could be a fairly simple, straight-forward operation, so it wouldn't hurt to give them a call just so you'd have a complete view of all your options (before you rush out and buy the crossover and then find out that it's not a job you'd care to tackle). Happy listening! |
My suggestion, would be to definitely bi-amp. Then when you can afford it, purchase an external electronic crossover to actively bi-amp the speakers.
As "Mgottlieb" mentioned, I have had the B&W800's for years and just recently actively bi-amped them (with Krell amps and crossover). It was the biggest improvement that I have ever made to my system!
Richard |
I also think that for the costs of four amplifiers and two sets of speaker cables you would be better off selling your amps, combine that money with the money for the second set of amps, and buy yourself one great amp.
Power is important but the quality of parts are even more important. I would buy the best amp you can and then down the road on your next upgrade buy a second one. |
You don't have to use an external crossover if the speakers are set up for bi-amping. The sound will be better with the external crossover but since good ones aren't cheap, I would just plug 'em in and use the passive crossover in your speakers instead and later figure out if you want to go active! |
You are right. I am not bi-amping, but monoblocking right now.
But why must I use an external cross-over when trying your vertical bi-amping suggestion? Could't I use the internal speaker cross over in my speakers, like Martin Logan suggests?
And since I bi-wire my speakers anyway, I would not have to invest in extra speaker cabling. |
I'm not familiar with Martin Logan crossovers, but you may well need to remove all or certain components of your speakers' internal crossover if you go to "active biamping" with an external crossover. Check with the manufacturer and see what they advise.
Good luck ... I haven't done this myself yet, but if you use a good external crossover "active bi-amping is supposed to be an terrific way to go . BIG gains in clarity and effective power from your existing amps. |
Thinking about how many pairs of speaker cable that you will need.It cost you alot of the money for just the cable.
Try Bryston 4b .It may help.Good luck. |
I second Plato's vertical bi-amping suggestion -- before you invest any further. Use an (external) electronic crossover b/ween pre & amp, and check out the sound.
Good luck! |
As a slight correction to earlier comments, Tekunda's current configuration is not really what is considered bi-amping, rather, it is bridging or monoblocking since one amp drives each speaker full range. This further complicates the impedance issues by effectively halving the already low impedance presented to the amplifier...
That's why my suggestion of putting the amps back to stereo mode and vertical bi-amping makes a whole lot of sense in this case. |
I can't comment on your speaker-amp combination, but years ago I tried it with 2 pair of the original BEL 1001s and a pair of B & W 808s, and even thogh the speakers were quite efficient, there was a noticeable gain in clarity in the midrange and control and definition in the bass, |
Tekunda, another thing to try before you buy anything else would be to use the Bel Canto amps in their stereo mode to drive the ESL panel and bass section of each speaker separately. This is the configuration for vertical bi-amping -- right now, with the amps in mono you are horizontal bi-amping. My guess is that vertical biamping would result in better quality sound -- not louder -- but better. Try that and let us know what you think. If that still doesn't float your boat then you may want to consider my previous suggestion of going to the InnerSound amps. I doubt that using two pairs of the Bel Canto amps will give you what you are looking for. |
If you really want to improve your sound sell the Bel Cantos and buy an InnerSound ESL amp. The ESL amp was specifically designed to drive the complex loads that electrostatic hybrids present, and a single stereo ESL amp will give you just as much power (if not more) than the 4 bridged Bel Cantos you are considering. If you did a vertical bi-amp with two ESL amps you'd have more power/volume than your ears could possibly stand and better sound to boot. |
