GBShade684 Posted October 13, 2011 Share Posted October 13, 2011 First I will start with what I believe to be true about impedance...most of which will not be accurate so I am inviting correction... Impedance is essentially resistence on an AC circuit. DC circuits by their very nature have a steady DC voltage, and therefore a steady resistance. Impedance however will tend to vary based on the sinusoidal nature of AC power. After reading a few other posts, it seemed that the impedance dips were caused by exertions in frequency bands covered by multiple drivers. I suppose this is the capacitive impedance required to recharge capacitors to motivate multiple drivers at the same time, especially at peaks in movies/music. So while I think I have an answer to my first question, I am just looking for a bit of clarification or backing of my answers. Second question is how do you tell what type of impedance dips your speakers are having / will have? I ask this because the current draw is inverse to the impedance. So impedance dip = amperage spike. Amperage spike = possible clipping from the receiver... Last question is choosing an amp. I plan on getting an amp in about 6 months. I want to get a nice amp that will have plenty of headroom for my current speakers(RF82's), but will also be a good amp for future upgrades(which is not planned for multiple years...). Any thoughts? At a continuous rating of 150 RMS @ 8ohms, I would think an Emotiva(XPA-2) would be a good amp at a good price... Quote Link to comment Share on other sites More sharing options...
StephenM Posted October 13, 2011 Share Posted October 13, 2011 That's a complicated question, but the easy answer is that the impedance of a speaker is simply a product of the circuit a speaker presents (crossover components, the driver loaded into the box), and of course, the circuit design. A designer will of course use impedance to his advantage in evening out voltage sensitivity across the audio band. I suppose this is the capacitive impedance required to recharge capacitors to motivate multiple drivers at the same time, especially at peaks in movies/music. While there can be capacitors in a speaker's crossover, they aren't there to provide power for peaks; that comes from the capacitors within the amplifier. Second question is how do you tell what type of impedance dips your speakers are having / will have? 1. Measure it. 2. Hope that an audio rag has measured it. 3. Ask the manufacturer. I would think an Emotiva(XPA-2) would be a good amp at a good price... Presumably it can competently drive just about anything you put in front of it. I'd add Parasound to the mix as well; even their less costly Model 275 is rated down to a 2 ohm load, and their "little guy" Z-amp was tested by The Audio Critic into 1 ohm complex loads and managed to survive with some output (more than I can say for some other models). Quote Link to comment Share on other sites More sharing options...
willland Posted October 13, 2011 Share Posted October 13, 2011 Last question is choosing an amp. I plan on getting an amp in about 6 months. I want to get a nice amp that will have plenty of headroom for my current speakers(RF82's), but will also be a good amp for future upgrades(which is not planned for multiple years...). Any thoughts? At a continuous rating of 150 RMS @ 8ohms I recently picked up an Acurus A250 for a steal and could not be more pleased. This is my fourth Acurus amp I have owned and all I can say is wow. Very fast and punchy down low while very detailed up high. Build quality is simplistic(less is more) and very good overall and they can be found on the used market at very reasonable prices. Big toroidal transformer(1000va) to handle the low impedence dips. Very high performance/price ratio used and even when they were new. Not too fancy looking, like Emotiva's are, but it is the inside that counts most. My RF-63's have taken on a new persona with the addition of the Acurus A250. http://www.audiogon.com/cgi-bin/cls.pl?ampstran&1323464224&/Acurus-A250-Power-amplifier--2 If interested, offer seller $325.00 and see if he will take it. Bill Quote Link to comment Share on other sites More sharing options...
Don Richard Posted October 13, 2011 Share Posted October 13, 2011 A loudspeaker is an electromechanical device. The mechanical aspects of the loudspeaker such as cone weight and suspension stiffness cause the speaker to have a resonant frequency, the frequency where it vibrates naturally when excited. This motion causes the impedance to rise at that point. The windings in the voice coil have inductance that, when factored in with the DC resistance and the mechanical characteristics of the driver result in an impedance curve that varies with frequency. The box that contains the speaker also affects the impedance curve, mostly because the resonant frequency changes due to the box type (closed box, ported box, or horn loaded box) and box size. When multiple drivers are used for different frequency ranges each of them will also have an impedance curve. A crossover splits the frequencies and sends the appropriate frequencies to the correct driver. The crossover may also affect the resulting impedance curve. Quote Link to comment Share on other sites More sharing options...
Ski Bum Posted October 13, 2011 Share Posted October 13, 2011 Emotiva amps are outstanding values. My only concern with them is that they have comparably more gain than most amps. They get so loud so quickly that you don't have much wiggle room on the volume dial when using higher sensitivity speakers like Klipsch. And what they're fed had better be squeaky clean, cause it will all come through in magnified detail. Using Klipsch speakers and high gain amps is like aiming a compound microscope at everything up-stream. That being said, I would choose Emotiva in a heartbeat for less sensitive speakers. Great amps, and affordable. Quote Link to comment Share on other sites More sharing options...
altpensacola Posted October 13, 2011 Share Posted October 13, 2011 Any thoughts? At a continuous rating of 150 RMS @ 8ohms, I would think an Emotiva(XPA-2) would be a good amp at a good price... The XPA2 is 300 watts RMS x 2 into 8 ohms, 500 watts RMS x 2 into 4 ohms. and actually it has measured more. P.S. and My RF7 with the XPA 5 are dead quiet when they are supposed to be. Quote Link to comment Share on other sites More sharing options...
GBShade684 Posted October 13, 2011 Author Share Posted October 13, 2011 So...yeah...it's been a long day... Thank you Stephen and Don for clarifying the impedance sources and factors to take into consideration. Good information. Not an electrical engineer, but I work in the field. Talk about a confusing subject... Also thank you Ski, Bill and Alt for the info on amp selection. Unfortunately I am not in a position to expand any of my HT, but in the future I will keep the Parasound, Acurus, and Emotiva at the top of my craigslist and ebay searches... Quote Link to comment Share on other sites More sharing options...
moray james Posted October 13, 2011 Share Posted October 13, 2011 Somewhat OT but it would be worth an email to Emotive to ask for the necessary changes to adjust gain as it may well be something that you can do yourself (if you are handy with a solder sucker and an iron) or have a local tech do for a minimal cost. Best regards Moray James. Quote Link to comment Share on other sites More sharing options...
SuBXeRo Posted October 13, 2011 Share Posted October 13, 2011 you can use in-line attenuators which can reduce the gain i believe Quote Link to comment Share on other sites More sharing options...
StephenM Posted October 13, 2011 Share Posted October 13, 2011 Talk about a confusing subject... No kidding. Then you get into phase angles and having the voltage lead or lag the current. Quote Link to comment Share on other sites More sharing options...
GBShade684 Posted October 13, 2011 Author Share Posted October 13, 2011 Mmmmmm. Nothing like power factor talk to get a nerd all hot and bothered. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted October 13, 2011 Share Posted October 13, 2011 dips can result by overlaps in crossover frequency....through out the overlap range the impedance is lower ...peaks can result if there is a gap between crossover frequency...within the gap area the impedance is higher Quote Link to comment Share on other sites More sharing options...
russ69 Posted October 14, 2011 Share Posted October 14, 2011 Greg, Good amps are expensive but if you buy a really good one, you can use it for a lifetime. I'm not a big fan of mixing the lean sound of Emotiva with Klipsch loudspeakers but on the other hand they are not THAT bad. Quote Link to comment Share on other sites More sharing options...
GBShade684 Posted October 14, 2011 Author Share Posted October 14, 2011 Greg, Good amps are expensive but if you buy a really good one, you can use it for a lifetime. I'm not a big fan of mixing the lean sound of Emotiva with Klipsch loudspeakers but on the other hand they are not THAT bad. What do you mean by "lean sound"? Quote Link to comment Share on other sites More sharing options...
StephenM Posted October 14, 2011 Share Posted October 14, 2011 What do you mean by "lean sound"? Also curious on this since every Emo that I've seen measured has razor flat frequency response with very low distortion in the audible range and beyond. Moreover, if we're talking about something like the XPA-2, it would take a pretty ridiculous situation (with respect to the fact that this is a Klipsch forum, the land of high efficiency loudspeakers) to imagine it running short of power/current. Quote Link to comment Share on other sites More sharing options...
Ski Bum Posted October 14, 2011 Share Posted October 14, 2011 Yeah, Russ, I don't mean to be disagreeable, but I think you're off. Emo's are anything but "lean". Maybe "Mean" or "Clean". They laugh at impedance dips, and seemingly loaf along with ease on just about everything. They do, however, have voltage gain of 32db. That's higher than most amps I've seen. I checked one of the NADs I'm using, and it's gain is 29db, and even with that I've got it dialed way back (guesstimating about 19-20db gain) so I can more fully utilize the volume control, to kid proof it, and because more is just not necessary with Klipsch. If the Emos have a trim feature like that, I would use it. Emos can be pretty hot and zippy if you run them FWO. Quote Link to comment Share on other sites More sharing options...
GBShade684 Posted October 14, 2011 Author Share Posted October 14, 2011 Ski, Can you expound on the voltage gain of 32dB vs 29dB? Also on controlling this feature... What does a gain feature do exactly? My reciever has ± 3dB for all my speakers. What actually happens when you move it up or down. Are you driving more current? I think this comes back to me knowing enough to be dangerous...but I am looking for a more precise and technical explanation. I am also researching this as we speak...type. Google is a wonderful tool. http://www.ti.com/lit/an/sloa105a/sloa105a.pdf Quote Link to comment Share on other sites More sharing options...
StephenM Posted October 14, 2011 Share Posted October 14, 2011 Gain is a little different than the trim levels on a receiver. On your receiver, presumably the auto-setup adjusted the trims such that the combination of receiver output plus your speakers at 0dB would equate to a pre-defined reference level at your primary seating position. Gain on an amplifier tells you how much the voltage from the preamplifier/processor is being amplified. Variable gain lets you compensate for the differences in outputs among different preamplifiers/processors. For all practical purposes, it is a volume knob. Quote Link to comment Share on other sites More sharing options...
Ski Bum Posted October 14, 2011 Share Posted October 14, 2011 I'm not an engineer, but perhaps someone who is will chip in with the nuts and bolts of it. StephenM pretty much nailed it in general terms. An amp with higher gain will take whatever it's fed and raise it higher than an amp with lower gain, like a more powerful zoom lens on a camera. Klipsch speakers already take you closer to the music with their dynamic range and sensitivity, so high gain is not necessarily required. In the case of Emo amps, it's a significant amount of difference and should be considered when pairing with Klipsch. If there is no misbehavior upstream, e.g. an output stage somewhere between the source and amps that is clipping, then the results can be very good indeed, as attested to upthread. Emo amps certainly have no issues driving the weird load of Klipsch, but you better feed 'em right. [edit: that last comment is misleading, as 'crap in/crap out' applies more generally to audio. Regarding gain specifically, two amps with the same gain structure, level matched, assuming similar circuit topologies, should be indistinguishable; you don't lose any detail or resolution with lower gain, you just get less gain. I could be completely wrong here, but with a level matching gain control, you're not changing the gain of the amp per se, but it's input sensitivity; the Emo XPA-2 gives full rated power, full bandwidth, and within distortion limits at 1.1v input. If you reduce it's input sensitivity so that it takes 2v to come to full power, you haven't changed the gain, but you have increased the usable range of your volume control (or achieved whatever other practical goal your after). I use input level adjustments for a bi-amping situation where I have to match amps with quite different input sensitivities, which is a rather narrow situation.] Quote Link to comment Share on other sites More sharing options...
StephenM Posted October 14, 2011 Share Posted October 14, 2011 I'm not an engineer, but perhaps someone who is will chip in with the nuts and bolts of it. Not an engineer, but the easiest to understand description I've read of an amplifier is a simple relief valve controlled by an electrical signal. Basically, the valve controller (preamplifier) sends an electrical signal, the valve opens (the amplifier swings voltage) and lets steam (current) flow. The gain tells you the difference between the voltage the amplifier swings and the voltage from the preamplifier. Edit: For those interested, a 30dB gain indicates that the amplifier has amplified the voltage by a factor of 31.62. A 20dB gain indicates a factor of 10. Quote Link to comment Share on other sites More sharing options...
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