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Posts posted by drboar

  1. Plywood for sure is far more sturdy than MDF for mobile use, bumps and scratches and the occational rain shower. For a stationary indoor loudspeaker however, it appears that bracing and damping/lamination to be more important. There are differences but they are not that huge. Here is a test conducted by the German magazine Hobby & HiFi.

    The setup is a dual chamber box with a driver in bisecting wall.


    A board to be tested was  placed in front of the driver and both soundpressure in front of the box (compared to no board) as well vibrations of the board was measured


    Vibrations to the left and reduction in sound level to the right. The referense was the 19 mm MDF at the bottom. That result is inserted in the other graphs for comparison.


    Not much difference between 16 mm MDF, 19 MDF and 18mm Plywood.  Fire retarding concrete chipboard 20mm is better but hard to come by.


    28 mm MDF is better but not by that much, 20mm stone is way better, 19mm chipboard is slightly worse than MDF and 19mm blockwood a bit worse than chipboard.


    These measurements were made in the frequency -amplitude domain, I have seen measurement in the time domain and they show most effect of bracing and lamination more than the instrinsic qualities of the board.


  2. At resonable temperatures the speed of sound is lineary proportional to temperature, in Kelvin that is.

    If we imagine the air above the fire as a hot cylinder, hotter in the center.  If a wavefront hits this cylinder the wave in the middle will accelerate more than the wave hitting the cylinder off center as the path lenght is longer and the air hotter through the center.  So the   wave will become more circular in the horizonal plane  and less sound energy will reach the listener in  front of the speaker. So the heat cyliner will work as a lens. The lens action works when the pathlenght through the hot cylinder is a sizable fraction of the sound wavelenths.


    If the rising air is to deflect sound the soundwaves has to be lifted a significiant amount during the less of 1/100 of a second it passes through the heat cylinder.


    As there is a vertical heat gradient in the air column that gradient will deflect the soundwaves upwards in a similar to the previous description.

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  3. I am quite sceptic to the value of very expensive cables. However, good long time quality is important. in 1988 I bought two loudspeaker cables. Some booring looking Supra 2.5mm2 cables and some Monster cable copies shiny and fat. 2-3 years later the latter had the copper turning green, probably due to reactive components in the plastic. If I peal of the plastic of the supra 30 years later it is still coppery and shining! So head for Madisound and Supra! There are many other brands that I am sure ar good as well, but as a Swede and a happy customer I want to push Supra a Swedish brand🤔

  4. I bought some vintage Ortophon speakers (In Sweden).They contained Scan-Speak drivers. A site in Japan offered to buy them at a very good price. However, I had to pay for the shipping (expensive !) and they would give me their final price after inspecting the drivers. All in all at maximum price  a would make a small profit otherwise I would make a loss at the sale...

    So the point is value depend on were you have someting. So the vintage Dalies would probably go for less than 500 USD here. If you can fill a container with similar goods you could make a profit selling to Japan but not with single speakers.

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  5. The LS have a peak that seem hard to get rid of.  If one used a HH chamber or a pipe resonator to reduce that peak things would be better for home use of the LS. In PA use I can imagine that any contraption that reduce effiency is a bad thing but at home were the LS hardly goes on at full blast hours on endThe LS has that midbass?

  6. Per pound fiberglass is the most cost effective if you need a lot of it. However for a small box polyfill from cheap pillows from IKEA, a DIY store or what is nearby is cheaper as you can get a smaller amount than fiberglass. I newer use fiberglass ( and I have spare  insulation in the attic for "free") as polyfill and the like is so much nicer to handle.


    Avoid covering the crossover with insulation, even if the losses is only a watt or two if well insultated the components can get really hot. My guess is that the horn is padded down with resistors and if they get really hot they can overheat, they can also heat  up the capacitors. For electrolytic caps you can estimate that for every 10 degrees C (roughly 22 F) increase in temperature the lifespan of the cap is halved.


    There is recycled denim and biodynamic hemp fiber and what not, but dont overdo it.

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  7. If you are using just caps then you have first order high pass filters. With no filtering in lowpass mode for the woofer and midrange.

    A cap will give you 6 db/octave for a resistive load only. say 8 Ohms,  If the impedance deviate substantially from a constant load so will the filter slope!


    To get a resonable  6db filter crossover at 600 Hz the bassdriver has to have a flat impedance to at  least 2400 Hz (doable with a Zobel) and a flat response to 2400 Hz as well otherwise the slope will shift around for the lowpass.  The same hold true for the midrange horn that should be flat down to 150 Hz!

    So adding a cap in series with the midrange and a coil in series with the woofer, is low slope crossover, and first order in one sense of the word but still not a "true" 6dB filter with that phase and frequency response of a theoretical filter. IRL it will be a hybrid filter with various slopes and orders where it counts, in the accoustic domain.

  8. There are many that use aircore  coils for woofers. They just become larger and more expensive than iron core for a given inductance and resistance. 2.5 mH is not that large either so a breif look at parts express going from 18 and 16 AWG what ever that is in mm2 air ( 0.9 ohm and 0.45 ohm) drops to  0.3 and 0.15 ohm). Try to measure the losses...

    I have a pile of woofers and various 2.5mH coils, if I just could find my Dayton Woofer tester :) 

    I could try measure the accoustic changes,. Going from 1 ohm to close to 0 should be possible to measure.

  9. Regarding a cone driver Faital Pro M5N12-80. 

    In my experience the lowpass functions of the horn may or may not follow the calculated curve.so you could try crossing over higher than 400 Hz and then things like Faital Pro LTH142 crossed over at 500 Hz or so (in a domestic setting) is possible. 


    The fact that the basshorn may have output to 1 kHz does not have to equal good sound up to 1 kHz so, test! An old analog active crossover where you can slide the crossover point around with a twist of a knob is handy ;)

  10. As far as smoothness goes it is strongly impacted by curves "in the nude" or smoothed curves. In my setup I can diplay cuves au naturel warts and all. smoothing over 1/12 octave all the way to smoothing to running averages over octave windows.


    The overall response is then dependent on which horn that is used with the driver.

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