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I happened to stumble across the following page which has some frequency response plots of single full range drivers. Some of them have off axis measurements as well. See: http://melhuish.org/audio/response.htm You can see how their output off to the sides is dropping relative to on axis as the frequency increases (and the wavelength is decreasing). Shawn

Robert, " Where does IM (intermodulation?) distortion come from a single driver?" Do you have the Dope from Hope papers, it is explained there. IM distortion is basically distortion that occurs from the doppler shift of a moving speaker cone that is producing more then any single tone. As the cone is moving in and out to reproduce the lower frequency tone that will effect the reproduction of the higher frequencies the same driver is reproducing. I think PWK gives the example of 60 (or 30hz) on a regular woofer also producing 400hz. The 'source' of the 400hz tone will be moving closer and further away from the listener at the frequency of the lower tone. How much this effects playback will depend on how much the cone needs to move for the lower frequencies... so higher efficency helps to reduce the effect. How much of an effect it will be will also depend on the frequency difference between the two tones. On say a K'Horn a 60hz tone wouldn't effect a 4000 hz tone at all since they will be reproduced by different drivers. Ditto the 60hz and a 10k hz. Also because the efficency is higher the drivers won't be moving much anyway. With a single driver speaker the 60hz tone will effect everything. "With dispersion you mean the output as a function of the frequency?" Output off axis from the driver. Because we listen in rooms the room has an effect on what we hear from any speakers. Having a smooth off axis frequency response (or a very controlled full range off axis frequency response) is thought to help keep a smoother frequency response at the listeners position even if the listener sits on axis as the rooms contribution to the sound will be flatter. Any typical non horn loaded drivers off axis frequency response is basically determined by the size of the driver as compared against the wavelength of the sound it is reproducing. When the wavelength of the sound is longer then the size of the driver its dispersion is wider/broader. As the wavelength gets shorter then the size of the driver the drivers gets to become 'beamy' in that its sound is more focused straight ahead, which means off to the sides its output is dropping. This is why a woofer which reproduces long wavelengths is bigger then a midrange which deals with shorter waves, which is in turn is bigger then a tweeter which is reproducing shorter waves yet again. To keep your off axis response good on a multiway speaker you want to be crossing over to the next speaker before the driver gets beamy. When you have but a single speaker reproduce everything you can see that at lower frequencies its dispersion will be much wider then its dispersion at higher frequencies. Because it is one driver as you go up the frequency range the dispersion is just going to get narrower and narrower. Shawn

Russ, "ok guys..... take it outside...." Good idea, not worth continuing that discussion. "i recently got a used dynaco amp and at the same time bought one of these devices.....$40 seemed a nice insurance policy to protect my tubes....." Yes, and it really helps protect all of your amp as it is making the turn on surge smaller. If you ever get bored it would be interesting to see if that box uses just a thermistor or if they take a different approach. An other common way of doing it is to put a large power resistor in parallel with a NO relay. Upon powering the device you close the relay XXX amount of time later. The resistor initially lowers the current surge into the amp then the relay closes which basically bypasses the resistor. Plus side is you have more control of the limiting and that when it isn't limiting you have no added resistance in the line. Downside is it is more complex/expensive (thermistors are cheap) and takes up more room in the chassis. People take it further too. Welborne Labs made a box that acted like a Variac to ramp up the voltage slowly to your amp over a user settable amount of time. http://welbornelabs.com/ac.htm Shawn

Craig, "What the resistance is cold has no bearing on this..." You yourself called the parts by their correct name earlier. They are inrush current limiters. If you don't think the resistance of the heaters hot/cold has a bearing on what we are talking about I'd suggest you re-read ohms law. For everyone else I = V/R I = current V = voltatge R = resistance So if you hold voltage constant and the resistance gets higher then the current drops. There is a current spike on turn on. As far as why you would want to slow this spike down Marantz and McIntosh both used this method on the incoming AC lines of their tube equipment. If you don't think they knew what they were doing that is you deal. Shawn

Craig, "I don't want to insult you but do you know what the heaters actually do ? They never see any voltage spike from inrush current !" Measure the resistance of the heaters when they are cold. After they warm up measure their resistance again. If you don't think they have a current spike when they are cold ( lower resistance then when they warm up) you are crazy. The filaments (heaters) are very similiar to any light bulb you have in your house. When do they burn out? Shawn

Craig, "The Scotts and even most of the Dynaco's use a 5AR4 which employs its own soft start to safe guard the tubes there really is no benefit to the tubes at all." The 5AR4 is a soft start for the B+ for the tubes. It doesn't do a thing about the heaters. Besides, it certainly doesn't soft start itself. Shawn

Craig, "With Scott amps this really is not a issue the voltage just doesn't spike high enough to endanger the components." I'd still put them in the Scott amps too. The softer start is better for the tubes too. How much will depend on how they are rectified and by what tube if tube rectification. It may only help the heaters but it may do more. And the parts are so inexpensive it really isn't a big thing to add them. Just think about when a light bulb burns out. Some companies also used small neon bulbs as an additional soft start for their tubes. My old Quicksilver pre-amp did and I know Marantz used them on some tube products. Shawn

"Would it just be soldered across the ac poles? " No, that would short out your AC and could cause a fire if the circuit breaker doesn't kick in quick enough. The thermistor goes in line with the hot lead of your AC equipment. I put it between the fuse and the power switch on my St-70. " I'm assuming it would be just as effective if it installed somewhere in the line source, as in an outlet box... right?" Better to do it in the equipment you intend it to be active for simply because that way you won't accidentially overload the thermistor and again potentially have a fire issue. They have power limits to how much they can handle. Shawn

Robert, "but also lower the efficiency when music is played. I thought that speaker efficiencies are measured INCLUDING the xover." It is including the xover. What they may be talking about is the inherent efficiency of the drivers themselves. On a single amped system if you have a three way system your end efficiency will basically be no better then around the point of your lowest efficency driver. Reason being is the xover has to scale back the other two drivers to have a balanced system. For example your tweeter is 100dB/w/m, midrange is 105dB/w/m but your woofer is only 85dB/w/m. For these drivers in a system with a relatively flat FR at best you are going to have a speaker that is 85dB/w/m efficent. This is what the transformer is doing on the squaker in the La Scalas. The squaker is more efficent then the tweeter or the woofer so to balance that out you have to in effect lower the efficiency of the squaker. This is an advantage of a multi-amped system that moves the crossover ahead of the amplifiers and has the amps directly connected to the drivers. Now all your drivers can run at their normal efficiency and to balance the system out you just lower the volume going into the amp that runs the more efficent driver. On a single driver speaker you only have the one speaker so there is no balancing needed. As such it runs at whatever its efficiency is. Of course a single driver speaker has all sorts of other problems like IM distortion, very uneven dispersion (which is a function of wavelength and. driver size on conventional driver non-horn systems) and so on. Shawn

Dee, Yes, for tube equipment that sort of thing is a good thing. McIntosh and Marantz both used NTC thermistors in the incoming AC line to their equipment as a sort of soft start. On initial startup they added around 25-50 ohms of resistance to the AC line. As the thermistors warmed up their resistance drops to under an ohm. That helps to limit the AC surge on turn on. I have added 49 ohm NTC thermistors to my Dynaco tube amps for exactly the same reason. If you can handle soldering it is a DIY mod to something like a Dynaco or whatever if you can find appropriate thermistors. Shawn

"If it were not so, most every speaker in the world would be unlistenable." If you amp has a low output impedance it doesn't interact with your speakers impedance to nearly the same degree. Back in the days of tube power only companies like AR specifically added impedance compensation to their networks because of this. In the days of SS power amps it isn't as much of an issue. The FR changes aren't theoretical. The Audio article I mentioned earlier measured the changes to the same speakers frequency response based on the interaction with the amp that was driving it. When the amps were measured by themselves into a non reactive load their FR didn't show the same changes as seen when plugged into the speakers. They interacted with each other. No one here claimed not to go with what sounds best. I was just curious about the modeling Al has done with his networks. Shawn

Al, "I suspect the frequency response is not the factor that would be upset by a strange load." Actually it is exactly what gets effected if the speakers impedance varies by frequency and the amp itself has a highish output impedance. See: http://www.transcendentsound.com/amplifier_output_impedance.htm and http://www.stereophile.com/showarchives.cgi?810 "No, every amp is different. Some don't care what load you connect to them. Others do" Exactly, and part of what that is from is the output impedance of the amp. E. Brad Meyer and someone else (can't recall the name) wrote an article for Audio magazine explaining this in the late '80s or early '90s. One of the tests they did was double blind ABX tests of two different amps (one tube with a high output impedance, one SS with a low impedance) on two different speakers. One speaker had a benign/flat impedance curve, the others varied widly. On the benign speakers the amps were indistinguishable from each other when level matched and blind folded. On the speakers with the widly moving impedance the amps were easily distinguished due to the differences in FR caused from the interaction of the tube amps output impedance and the speakers impedance compared against the much smaller changes in FR with the low output impedance SS amp. Bob Carver says this is where a large portion of the 'tube' sound comes from. In some of his amps he literally offers an output connection which basically has a large 1ohm power resistor in series with the output to cause the same FR type deviations. Shawn

" The production units actually measure 8 Ohams +-1 Ohm with a phase angle of less than +-15 Degrees form pure resistive impedance (that's "polar" impedance)." That is really flat. Have you ever modeled the difference in FR a user with a highish output impedance amp (tubes) would see with the stock crossover compared against yours? Yours would obviously be flatter through the 1-6k range. "The modes you propose sound ok to me." Thanks, glad to hear it. "Fliping the proposed squawker level switch with the amp on shouldn't casueany problems." Cool, that should make it easier to find the setting I like. I don't think I want to wire up five of those switches. Shawn

Al, "Here is the computer simulation of the AA network input impedance. " Do you have one for your network? BTW, just waiting on the transformers and I'll be starting to build five of them. All the other parts are ready and waiting to go. I'm doing it slightly differently though. First I'm making the boards a little longer and wider so I can put the terminal strip on the short side so when it is installed in a La Scala the terminals will be facing the opening on the speaker. The little bit extra size means I can move the coils a little further apart while still keeping the same orientation. Second, I'm going to add the poly switch tweeter protection and maybe make that switchable in and out of the circuit. At least on one so I can easily hear how much of an audible effect that will have. Third, I may wire the autoformer on one up to a 2 pole rotary selector switch so I can quickly switch between taps to see how I prefer the midrange setting. The poly switch has about 1/2 ohm of resistance so that is going to drop the tweeter level a little, so dropping the midrange slightly more might balance that out better. With your swamping resistor on the squaker crossover do you think it would be a problem using a break before make rotary switch to change taps while the amp is on/playing? BTW, thanks again for sharing the plans for this for us DIYers. Shawn

" (or are there other 300B amps out there?). " Yes, lots of them. That was the tube that sorta started the whole SET craze going. Shawn

What was the input signal? If it was a single pulse the plain horns response doesn't look so good. But on the flip side I'm not sure that says much since the SPL out of each of the tweeters will vary since they all received the same voltage input. Might be more interesting to see how they compare playing at the same relative SPL. Shawn

I'm going to refinish the cabinets on my '76 La Scalas. They started life as raw birch which was stained at some point in their life. They have small chips and are missing small amounts of the veneer. What does everyone recommend to use to fill in the wood? I think I read the HDBRbuilder recommends staying away from the Elmers filler products. I'll probably be restaining these after they are filled/sanded down so whatever filler needs to be stainable. Thanks, Shawn

"I was always told by the khorn delears that a lot of pipe organ tuners use khorns as they were the only speaker that could reproduce the low c in its full on compressed range." Are you sure you aren't thinking of piano tuners? I think low C on them is 33hz. Check out the pipe organ section here: http://www.infrasonicmusic.co.uk/background.htm According to that there are a few pipe organs that can hit just over 8hz. Shawn

Tom, "The movie affects for sure. I'm with you on the need for subs, which I have three in my HT system." Yup, I use three as well. "For two channel I just don't feel the need. I don't believe there is that much going on in those lower registers with the music I listen to." Sure, that makes sense. The bass they do have is very nice, they just aren't the last word in extension and loose about the last octave. I'm crossing them to my L/R subs at 60hz right now which is working well. Shawn

Alan, "then go for the Belle Klipsch the Belles could not be transported so easy along time ago, so Paul built a smaller version called the Heresy." I thought the Heresy came out much earlier then the Belle? Shawn

Tom, OK, we are talking about two different things then. Pipe organs have a 16hz note (low C) on them... try the 2001 theme, I think it starts with low C. My system does double duty for music and movies and there are plenty of movie effects that low and lower. Shawn

Tom, "I don't buy the bass is lacking statement, thats BULLSH*t, people conclude to this due to specs, which don't hold water when your sitting there and the bass is knocking you in the chest like your there live!" The resonant frequency of your chest is somewhere in the 75-125hz range. So chest pounding bass isn't a very good indicator of deep bass response. When you get into the deepest range (my big sub is -3dB at 14hz) and energizing the room the air all around you gets to feeling like it is pulsating. For some deep bass material check out this list: http://smr-home-theatre.org/Sub-woofer-Set-Up/How-Low.html I only have the Telarc CDs from that list but they are good. Be careful as the depth and range on some of those can seriously overdrive woofers. Shawn

" Dropped like a stone below about 45 / 50 cycles." I've only had my La Scalas for a little over a week but I agree with this. I forget what I was listening to but there were definitly a few places where some bass lines were all but inaudible. This isn't an issue for me since I always use subwoofers anyway. I was running them full range just to see what they could and couldn't do. I ended up crossing the La Scalas over to a pair of ACI Titans fourth order at 60hz. That seems to work very well in my setup. By preventing the La Scalas from trying to play the deepest bass (which was mostly inaudible on them) reduced the resonation of the sides of the bass horn quite a bit. And it would also reduce IM distortion that PWK talks about frequently in the Dope from Hope papers. Shawn

" By this I mean is one of the horns meant to point towards the front of the room?" That will depend on if the two horns are wired in phase (for a bipolar type dispersion) or wired out of phase (for a dipolar dispersion) with each other. If they are in phase they wouldn't have a front or rear. If the horns are out of phase they typically should have a front to them so that the front horn would be wired in the same phase as the matching Klipsch speakers from that line. Of course different amps between channels or whatever can invert phase so it is a good idea to run a phase test on something like AVIA anyway. Having a 'front' on a dipolar speaker is also needed if you use 4 surrounds. In that case you put your sides with the fronts pointing to the front but your rears you swap so their fronts are pointing at the rear. That is so the area between say the left side and the left rear is in phase which each other. Shawn

" shouldn't be too far from MA." I'm near the Ma/RI border so it would be a pretty good haul but doable. If you were going to pick up the Cornwalls I could meet your somewhere. Or I could possibly bring the Cornwalls up to you or meet you in the middle somewhere. Shawn