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radiogram

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  1. Al: Thanks for offering me your time to speak with me on the phone. It is prettly late now (India time 12 AM) and I just about hitting the sack. I will try calling you Sunday your up time. Thanks
  2. Greg: 1. Based on your test report I figured that you had compensated all tweeters for their sensitivity differences before evluating them. Is that not correct? 2. Also, this is my personsal experience - As we go higher in frequencies we cannot rely on the ear to tell differences in output. I can easily tell a 1000Hz tone at 90db from a 93db tone at that freq. But at tweeter territories I find it hard to detect levels and at 16KHz (the limit of my current hearing) I cannot distinguish a 90dB one Vs 93db One. So in my opinion particlualry at higher frequencies we should rely on the meter rather than the ears. Again this is my opinion and I could be wrong.
  3. Al: I went thru your website after some hiatus due to some other posts that led me to download you DOS Filter software. I was quite surprised with your updated website that talks abour Cornscala and advocating use of crossover higher than 400Hz (600-700Hz) since the K33 or its clone by themselves can easily handle those frequecies. This is surprisingly in line with my expereicnes in the PDF I had posted about "Whether to Cornscala or not"where I had questioned the need for a a K55/K400/401 that can go down as low as 400Hz when a Cornwall Bass Bin can well go up to 700H and my personal experience in preferring a higher crossover for the woofer and using a K53/K701 instead of K55/K400 at 400z.
  4. Greg: You may want to very explicitly HIGHLIGHT the different crsoover slopes you used in evaluating these tweeters. I recently made a reply post to a Hersey Upgrade post regarding my opinion of CT125 stating that it is a mimatch with low order Hertitage crossovers as there will be more overlap in the upper midrange to lower treble because of the CT125's ability to go lower than the K77. It seems some people have misunderstood me and taken it unnecessarily personal, as to having bad mouthed CT125. Hardly the case. All I pointed out was that the CT125 is a good tweeter provided one uses high slope crossover but with stock low order netwroks it will be a mismatch due to overlap with the squawker. I still stand by it unless techically proven otherwise. In your tests you had indictaed that with the CT125 the midrange might sneak thru and hence you used 18dB slope for Ct125. This is imporant and in line with my opinion. Hence I feel it is important you very explicitly Highlight the slopes you used in your favourable impressions of all tweeters. Cheers
  5. Gill, Lee: What is your take on this ? Please look at Posts Dated 08.28.10 9:12 PM thru 10:31PM Thanks
  6. Al: This still does not answer my quesion or rather I cannot comprehend and infer answer for my questions regarding: 1. if I decide to subtract Le from L2, then should I not be be designing the T Section for Re (not nominal impedence) and then subtract Le from the L2 value obatined based on Re? 2. Conversely if I choose to use some nominal impedence around crossover instead of Re,and compute the T Section paramters (L1,C,L2), I have then by defintion already taken into account the inductive AC resistance and hence I will just use compued L2 as is (no subtraction)? Thanks
  7. Reagrding my previous Post that relates to my question on compensating for Voice Coil Inductance (Le) in the filter design, I have made some important corrections for better clarity. So, if you care to respond to that, please re-look at the post and do not go by what you saw before or what you saw in the email you got. Thanks
  8. Al, Gil: I am confused yet again. (For clarity in my terminology below: L2' is some Inductance <> L2; L2" is some inductance <> L2 or L2). The circuit model for the Load is: ----------- | Re Le | ----------- The effective load impedence Rz (freq) = Re + The Inductive Resistance(freq) In order to compensate for the varying impedence we have two approaches: 1. Implement a Zobel and make the effective impedence to some constant R, forget about the Le and then design the T section for that R. OR 2. Incorporate Le as part of the T filter by compensating Le from L2 and then the network model becomes as follows: ----L1--------L2(=L2'+Le)-- | | C Re | | --------------------------------- Where, L2 = Some L2' Plus Le. Since we have incorporated Le in the filter we have taken care of the varying AC Resistance component introduced by the Le. Thus what we have left for the Load is only Re. Should'nt that dictate then if I use the L2'=L2-Le appraoch I have to then design the T Network for Re and not the impedence around the crossover frequency since AC component introduced by Le has been taken into account? Let us say if we design a T Section for Re=3.7 Ohms and get L2 for the right most inductor. So for our case the actual value of the right most inductor then becomes L2' = L2-Le?'. By designing a T section for say 7 Ohms and then again subtracting Le from L2 seems like a double compensation to me. If we design for 7 Ohms instead of Re=3.7, then by definition we have already taken into account the inductive resistance, so further making L2' = L2-Le seems double error. It seems to me that if we use nominal impedence of 7 Ohms, that being equal to (Re+Some Average Inductive Resistance), then we should forget about Le or use Re for designing the network and then incorporate Le by doing L2'=L2-Le. Where is my analysis wrong if so? Thanks
  9. Ok, based on Xover freq=630 and imp=7.7 (imp at the Xover freq), I get the following values: L1 = 2.92mH; C=43.6uF; L2=.97mH. If I deduct the 1mH voice coil from L2, L2 goes out the door leaving only L1 and C for the final network. If I move up the crossover freq then L2 starts getting less and less and for e.g. if I want over at 700Hz L2 comes to .90 and L2-1 = -0.1mH. Upto how much mH difference we can ignore?
  10. Al, I am bit confused here. We have two values 1) Average or Nominal Impedence and 2) Impedence at the Crossover Freq of interest. Based on my measured impedence (see attached measurement spreadsheet) in 0-800Hz (the bandwidth of interest), the average impedence excluding the two peaks comes to 6 Ohms. At freq of say 630Hz (the chosen crossover freq) the impedence is 7.7 Ohms. Now, if I design the network for the Nominal Impedence I should use 6 Ohms, on the other hand if I design based on Gil's suggestion to use the value at the Crossover freq, then I have to design for 7.7 Ohms. Can you please clarify why you suggest 6-7 Ohms. Thanks CS1526C_Imped_Measurement.pdf CS1526C_Imped_Measurement.pdf
  11. Ok. The DC Resisitance as I measured with multimeter is Re=3.7 Ohms At 700Hz based on my measurements and little extrapolation the Impedence @ say 700 Hz will be about 8 Ohms. So, 8 minus 3.7 = 4.3 Ohms by which the Imp is higher at 700Hz. Ok, so the extra 4.3 Ohms is attributable to the inductance of the voice Coil. I am with you so far, but after this step I am stumped. Please help me more. Thanks
  12. Alk, Gil: I appreciate your feedback and sharing info. Thanks. Are you guys suggesting strongly that I should build a Zobel? If, I do not, what will be the side effect and how bad it will be? BTW, the AL-4 network has a T Section ( I am not sure if it is butterworth/Chebyshev) but does not use a zobel. I am not defending that but this is just FYI. Thanks
  13. Correction - The planed Network for the woofer is a T section and Not PI Section.
  14. This question is for the likes of ALK / Lee and the likewise network experts. I am planning on building a custom crossover for the woofer section of my Cornsey Speaker (i.e. Cornwall Bass with Crites CW1526C Woofers, Hersey Mid & High - K53/K701 and K77). The mid and high section will be pretty much like stock i.e first order where the K53 is crossed over at about 710 Hz. The only difference between the stock Hersey network and mine will be that the input cap in my case will be 4uF instead of 2uF since for Cornsey the squawker is moved one tap above at the Autoformer to accommodate for the higher sensitivity of the Cornwall bass bin. The plan for woofer section is a 3 pole PI Filter with two series inductors and a parallel cap in the middle as follows (I want a steeper network for the woofer than 1st order): -----L--------L------- | C | The crossover freq will be around 620Hz or so. In order to compute L & C, I only need the value of Crossover Freq and load Impedence. The Re of the Crites Woofer is 3.7 Ohms. I measured the actual in cabinet impedence response at various frequencies using a dividing network with a known Resistor value and using voltage division theorem, and I have attached measured impedence plot here. So my question is to do with what Load Impedence value to use to calculate L & C. As you can see, if we ignore the two impedence peaks around 20Hz and 65Hz (typical of a Ported speaker), the average impedence between 30Hz – 600Hz is around 5.7 Ohms. At the chosen crossover freq of say 620 Hz is it is about 7.7 Ohms. So my question is to design the 3 Pole PI network for a Fc of 620Hz, should I use the Load impedence value as Re (i.e 3.7 Ohms) or the Average (i.e 5.6 Ohms) or the impedence at the crossover freq (i.e 7.7 Ohms) ? Thanks
  15. I would first suggest replacing the Stock Caps with Audiocap Theta (from my experience) or Auricap (from others' experience). In addition if your Hersey is the same as what I have (K22, K53/K701, K77, E2 Network), then I will have some additional suggesstions.
  16. Replacing the tweeter with CT125 with the stock crossover is to be approached with some caution as it is technically not a direct drop in replacement for the Hersey and due its consequent end result. A "drop in" replacement driver by definition is one that has to satisfy the following criteria: 1. Same sensitivity 2. Once dropped in and integrated to the given crossover, its net acoustic response output shall have quite similar (if not exactly the same) acoustic bandwidth and roll of rates as the one it replaces. While the CT125 is a good tweeter in some absolute sense, it is a mismatch with the Hersey or any heritage speakers that employ K77 with a 1st order filter and a squawker section that is just high pass and not bandpass, like TypeA and some Conrwalls. These networks in a sense "sort of" get away with it due to the natural roll off of the K77 below 4000Hz. Replacing it with any tweeter that has an extended response below 4000Hz to as low as 2000Hz will end up with exaggerated lower treble overlapping with the squawker’s full passband. And given that the CT125 has sensitivity that is lower anywhere from 3db - 5dB, what you may get is relatively muted output above 5000Hz and exaggerated output in the lower range. Now one may be able to match the sensitivity by moving it up the T2A tap, while this will restore the high freq balance it is going to accentuate the lower freq overlap even more. Forget all the technical stuff, I compared the K77 in my Hersey tweeter network, with the CT125 by listening to the tweeter alone disconnecting the woofer and the squawker and played a Bob Seger CD. With the K77 I could barely hear his voice, but with the CT125 his voice was well audible and clear. This part of the spectrum is already in the full passband of the squawker reproduced at full 0dB. So what you have is a different sonic signature from the original. Now one may like that is an entirely different story, but I would hardly call this transparent driver swap. Transparent by definition means one should not notice the swap. The words “drop in” replacement by definition implies that when the replacement driver is mated with the given network its acoustic passband corners and roll off rates are very similar (if not exact) to the original. Within the passband it may have different performance aspects (distortion, different dips or peaks, smoother response, etc) that may lead one to choose over another. Nevertheless to be a drop in (meaning no change to crossover) it has to have similar passband corners and roll off rates and of course same sensitivity. If one likes the sound subjectively I have no argument for that, but objectively it is not correct unless the crossover is steep enough to mitigate this by providing enough attenuation as to making it audibly not much perceptible or the squawker network is modified to be band pass with appropriate high frequency limit and slopes. Having said these, I think the CT125 may be better suited with speakers using higher order tweeter sections like the TypeAA, Type AK3 and higher, with the following caveats: 1. There is still a lower sensitivity matching issue to deal with 2. The CT125’s sonic signature is very different from the K77, where its lower tones seem to dominate the higher tones, which whether you will like or not only you can be the judge.
  17. The part number for the 4mH inductor on the E2 is 2304 (made by Universal Transformer Company), as was confirmed by Bob for my E2 network. Also in E-2, it is important to note that the 4mH is to be used in conjunction with a 33uF bypass cap across the woofer, without which the woofer response will extend into the sqauwker range. Regards
  18. Mcintosh C15 Preamplifier ----- This post is probably a bit late to do and maybe less relevant now, as I should have shared this many years ago when I experienced it and also the fact that the model in questions is pretty outdated. However, there may be people considering purchasing them in used market, and I feel it is important that I share the following, only to make them aware of certain truths so that they do not get misled the way I was and spend their money thinking that they are buying a true Mcintosh. Besides I was never a member of any forums until recently, so I never had a chance to express these. The Mcintosh C15 is not really a true Mcintosh just like its matching MR7084 Tuner. I bought one from Audigon a few years ago (I believe in 2001) and after listening to the C15 I was very much disappointed. The sound lacked transparency, it was mushy with no definition or impact in the bass. It did not sound much better than using a Sony TV as a preamp. No kidding - I really did that comparison. Completely bewildered, I compared it with 2 other preamps that were retailed around $600 – Yamaha CX-2 and NAD-C160. Both outclassed the C15 in transparency and definition. I was at a total loss and out of curiosity I opened all the three chassis. What a shocking disbelief I was in for!! C15 – Here is a preamp that retails for $1500 from a prestigious company known for making excellent high quality High End electronics and even known for over engineering. 80% of the chassis was empty. Other than the quality switching relays, the rest 20% was made up by really cheap integrated circuitry. I do not have anything against Op Amps or ICs, but I certainly did not expect this at this price point and worse it was really inferior circuitry, parts and OpAmps. Now take the Yamaha / NAD – Both preamps retailing around $600-$700 and considered only Mid-Fi. The entire chassis filled with All Discrete high quality Class A circuitry, beefier power supply, advanced and superior Power section circuit. I soon sold the C15 to Audio Classics in NY and surprisingly got a good price for it! I also lost respect for Mcintosh for betraying my trust. Later from other sources I learnt that the C15 and the matching MR7084 Tuner, were products that were a result of corporate pressures from Clarion Merger to offer products at a certain lower price point with higher margins. This was a time before the big economy boom when high end sales were really struggling. So for the C15 and MR7084, Mcintosh was forced to use Clarion like cheap circuitry and stuff into Mcintosh Clothing. Fancier knobs and heavy metal chassis cannot make up for inferior guts inside.
  19. Has anyone done comparison of dispersion characteristics between a K55-K400 with a K53-K701? The reason I am asking is when I did my Cornscala (Cornwall Bass Bin, K55-K400, K77), I seem to prefer the Cornsey instead i.e Cornwall Bass bin and Hersey top section (which I have explained in my Post under my cornscala experiences @ http://forums.klipsch.com/forums/p/137054/1389045.aspx#1389045). I did on axis measurements (that I had posted under my cornscala experience) and while it explains to some degree the tonal difference and the fact that I find the K53-K701 a bit more detailed in the lower treble and presence region with a bit more tactile expressiveness in that region, I do not think that alone explains my impression that the K53-K701 seems more open and more balanced in filling the room as I turn up the volume. I am hence curious to know about the dispersion aspects between the K55-K400 Vs K53-K701 if anyone has done any such measurements. Thanks
  20. Al, Lee: That seems perfect. Pro Build is a welcome bonus as well. Thanks
  21. I need to convert some analog cassette recordings to CD and also some old vinyl. For a budget up to $500 can someone suggest a good CD recorder? The important thing of course is the Quality and resolution of the ADC. I prefer single box solution and not computer based ones. Thanks
  22. Al: There is one thing I may have overlooked here. In my B&W 801 Example I have given, the impedence is not that of just the driver, it is with the crossover and driver as a whole. So while my calculation that at 100Hz, 6.5 times more power is being fed is correct, it is power fed into the crossover. Does it necessarily mean the same power is being drawn by the load (Driver) ? Is it possible that the power consumed by the network @ 100Hz is more than that at 35Hz and what is at the load @ 100Hz is actually not higher by 8dB but lower ? In other words, is it possible the crossover network can be consuming different power at different frequencies and somehow this needs to be taken into account?
  23. Lee: Please ignore previous post. Issues with New Line when I post which Preview does not show. ]That is quite interesting and makes some sense now. While it is not clear to me regarding mathematical relationship of impedence vs speaker efficiency, there has to be some truth in what you are saying, since otherwise many speakers with wild swinging impedence curves will sound utterly terrible with modern sold state amplifiers which are closer to a voltage source. Now let us look at this with some numbers taking the example of a B&W 801N speaker. I have taken the values as was published by Stereophile measurements. I am completely ignoring the impedence phase here. Impedence = 19.5 @ 35Hz; Impedence = 3.0 @ 100Hz. Driven by a Voltage Source Amplifier – Let us for practical purposes assume its source impedence is 0 since many SS amps have impedence as low as .01 ohms. Source Voltage Freq Load Impedence Power at Load (Watts) 2.83V 35 19.5 0.41 2.83V 100 3.0 2.67 So, the power delivered is 6.5 times (8dB) at 100Hz compared with at 35Hz.Now, if the speaker had the same efficiency or sensitivity based on Watts at all frequencies, it will have an acoustic output at 100Hz that will be about 8 dB louder than at 35Hz. Now this cannot be really the case as the 801s supposed to sound good driven by SS Amps. Now, if we assume that in reality the speaker’s real efficiency at same power is actually between +/- 5dB across the frequency spectrum and if we further assume what you said that real efficiency will be higher at higher impedences, then let us make an assumption that at 35Hz its true efficiency is 5dB higher than at 100Hz - and in the end the net effect when driven by the same voltage, becomes a difference in acoustic output at 100Hz being more by 8 – 5 = 3 dB compared with 35Hz, which is a lot better than a difference of 8 dB. But again it is a huge assumption that at 35Hz its real efficiency at same power is 5dB more than that at 100Hz. Now let us take an Amp with a high source impedence (like a Tube Amp) and let us assume it has an output impedence of 3 Ohms and let us increase the source voltage so as to have the same power at the load at 35Hz (0.41 Watts) as in the above case. Source Voltage Src Imp Freq Load Impedence Total Imp Current (I) Power at Load 3.26V 3 35 19.5 22.5 .145 .41 Watts 3.26V 3 100 3.0 6.0 .543 .885 Watts Now, while the voltage freq response at the load will track the impedence curve of the load and not be flat like a voltage source solid state, LOOK at the power response at the load. The power difference is only 2.16 times i.e. 3.35 dB and not 8 dB between F1 & F2. Now, if SPL were a function of purely Watts, does it mean DEPENDING on the speaker’s true efficiency differences at various frequencies, a high source impedence amp MAY actually result in a subjectively flatter acoustic output?
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