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bobovox

Wammer
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About bobovox

  • Rank
    Wammer
  • Birthday 11/06/1972

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  • Location
    SE London, Europe
  • Real Name
    Robert

Wigwam Info

  • Digital Source 1
    Arcam CD73T
  • Digital Source 2
    RPi DIY Streamer
  • Integrated Amp
    Arcam A90
  • My Speakers
    DIY
  • Trade Status
    I am not in the Hi-Fi trade

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  1. Thinking about it a little more, I would suggest making a more conventional rectagonal enclosure for your experiments - you could oversize it and experiment with adding solid material to the enclosure to reduce the volume and determine your preferred Qtc for your design and take the measurements needed for crossover design. With most of the design done, you could then design and build the curved enclosure, knowing the size of the crossover you need to accommodate. There is a lot of wasted material with this form of construction, unless you can find a use for the pieces from the middle, or cut the two sides independently and the CNC time is high - I did look into it for one of my future projects and decided I would only do it that way when I was convinced I had the design fully bottomed-out and well tested before I would commit to that kind of expenditure.
  2. I’ve not seen that approach used before - dry joints and post-tensioning the laminations together, so not sure how good a seal you would get between the adjacent laminations and between the laminated box and the front baffle. The devil is in the detail, as ever. I warned against leaving the rods in on the assumption that you would be glueing the laminations together - it was based on a bit of an extreme example in DIYA a few years ago of a guy building a floor to ceiling line-array - he used metal rods to keep the stack of laminations straight but left them in place and sadly the speaker cracked at one of the glued joints. You can easily unscrew the bass unit from the front baffle to tweak the amount of filling material.
  3. Using plywood for this form of construction will give you an attractive finish on the curved sides that could be varnished and left exposed. I haven't actually done a stacked laminate construction but I expect you will end up with small irregularities on the sides due to CNC tolerances and tolerances in the lamination; you will want to sand these out. Sanding MDF is best minimised as the dust contains formaldehyde which is carcinogenic and its just not a very pleasant job. Alternatively, you could round-over the edges of the laminated boards to disguise the irregularities and make a feature of these, with a painted finish. If you use rods to align the pieces vertically, don't leave these in the final construction - differential temperature / moisture movement between the wood and the rods may lead to cracks between the laminations, especially if the speaker is tall. You could CNC horizontal internal braces to your desired curved shape and then layer flexible MDF between these to form the sides. There is less wasted material this way. Real woods are generally avoided in speaker cabinet construction due to dimensional stability; you may be OK with well seasoned hardwood but I can't be sure. Regarding the absorbing material, is your enclosure sealed or ported?
  4. I’m sure many will prefer the relative ease of downloading and flashing a prebuilt image for an SD card, however it’s actually not so difficult for a lay-person with a bit of experience with the command line to cut and paste the instructions in the README file on github into a terminal and do the install suggested by @Man in a van Using a Pi for computer audio is always a bit DIY - to a greater of lesser extent - and you don’t do DIY Audio as it’s the easy option, you do it as a project and maybe a bit of a learning experience.
  5. I wouldn't ever buy a product based on a promise of future features from a salesperson. I made that mistake with a mobile phone once... Speakers and amplifiers are durable items, I'm sure many of use are using and enjoying 10 or 20+ year old examples. Streaming, however, is a much less mature technology and having bought a commercially produced streamer I found it was quickly obsolete as firmware upgrades were not issued to allow it to connect to new streaming services. As Andrew says, if you don't mind doing a little bit of setting-up, a Raspberry Pi with freeware streaming software will do the computery bit for a modest outlay and it will likely remain upgradable well into the future. When it does eventually break or become obsolete the e-waste is minimal.
  6. Do scientists design hifi? For the most part it is scientist that discover the fundamental science on which hifi designs are based but I expect that the design is firmly within the realm of the engineer and industrial designer. Now, where would look on the internet for confirmation of that?
  7. bobovox

    crossover 'upgrades'

    Those Alcap electrolytic are peanuts from Falcon Audio: https://www.falconacoustics.co.uk/alcap-claritycap-solen-audio-capacitors/alcap-electrolytic-capacitors-low-loss-50v-100v.html?capacitor_series=213 Conceivably there may have been some drift over the years - even if it doesn't make any difference you will not lose much trying. The voltage rating is probably printed on the existing components.
  8. bobovox

    crossover 'upgrades'

    Agreed, different rather than necessarily better - for example if you change the iron cored inductor in the mid-bass part of the crossover to air core, you will likely have a different DC resistance which can have a significant effect on the bass response and will also attenuate the mid-bass differently, affecting the treble / bass balance. I have used resistors similar to the one shown in the photo and always found the inductance constant across the full audio band. The effects of changing different components are all predictable if you know the significant characteristics of each component you propose to use and have the impedance and frequency response curves for the drivers in the speaker and have suitable software (eg XSim) - if you really want to get into that. If you just wanted to tweak the level of the tweeter slightly you could just buy a few around the vale of the existing (photo and schematic show different values) and substitute each in turn and determine your preferred treble balance by ear.
  9. It sounds like they could be seriously improved with a proper crossover design. The crossover network, as well as dividing the frequency components between the drive units may also be used to compensate for irregularities in the frequency response and also the baffle-step - a 6dB drop in bass relative to the treble. Shorter wavelength (higher frequency) sound is reflected off the front baffle and radiates from the driver into a hemisphere in front of the speaker; whereas longer wavelengths radiate uniformly into the full sphere around the speaker and are therefore 6dB quieter in a forward listening position. Proper explanation here: https://sound-au.com/bafflestep.htm Depending on the size and shape of the speaker enclosure the baffle step will be accompanied by peaks and troughs in the treble response due to edge diffraction. Placing the speakers close to a rear wall will allow the longer wavelengths to reflect forwards and so the frequency response will be more balanced. Typical relative levels for a speaker of this size:
  10. Is that all there is? It looks like a first order high pass (the capacitor) with an L-pad (the two resistors) to attenuate the tweeter. I'm assuming that the wires at the base of the picture lead to the tweeter and those at the top of the picture are attached to the terminals? This combination of resistors would give about 6dB attenuation if the tweeter was considered as a constant 8ohm load. Real tweeters of course are not constant impedance due to the inductance of the voice coil. Therefore, the treble will tend to shelve upwards slightly, on-axis at least. The 4.7uF cap will give you a 1st order Butterworth high pass filter, again assuming a constant 8ohm impedance, with a corner frequency of just over 4000Hz. It may have been the builders intension to match the natural roll-off of the mid-bass, although this is usually a bit steeper than 1st order. Also, the baffle-step has not been compensated for based on what I can see in the photo. If you trace the wires from the mid-bass to the terminals is there nothing else lurking in the damping material?
  11. With the dimensions given, and allowing for the volume of the port and the cone and magnet assemblies of the two drive unit, were are looking at about 5.5litres internal volume. Using the driver parameters from the SEAS datasheet, the wide-baffle bass response looks like this: Allowing for the actual baffle width of 170mm (crudely) we get: Port tuned to about 47Hz. Depending on how the baffle-step and falling bass-response have been compensated for in the cross-over, the speakers will have a low sensitivity and will lack any deep bass - but physics is physics and there's only so much you can do with a 5.5 litre enclosure and 4" mid-bass, especially without any DSP assistance. Group delay is marginally above the audible threshold at port tuning frequency: I would expect what little bass there is to sound subjectively a little slow. A few health warnings on this analysis - the driver parameters vary with input level and the egg-box damping foam will effectively increase the volume of the enclosure. I have assumed a typical figure for box losses (leakage mainly) - depending on how well sealed the screwed-on front baffle is this can have a significant effect on the bass. Only measurements on the actual speaker will confirm the assumptions above. The screwed on baffles could be replaced if you wanted to use a different tweeter - I have a pair of the Scanspeak domes used in the current Tablette 10's in some of my DIY speakers and these have a 105mm diameter face plate whereas the Audax is a little less. However, the crossover would have to be modified for the impedance characteristics and sensitivity of the replacement tweeter.
  12. Thanks, Neds. I will have a look this evening and let you know what I think.
  13. I'm no expert but I have made a few DIY speakers. I'm quite curious about these speakers I must admit, having built some similarly sized speakers myself. I have done a quick simulation using the driver parameters published by SEAS. With a 35mm duct, 250mm long, you get a port tuning of 55Hz. The builder has had to put a bend in to fit the port within the enclosure. I tool a punt at the internal volume being about 3.5 litres - if you could tell me the external dimensions and cabinet wall thickness I can refine the analysis a bit. Have you looked at the crossover?
  14. Just looking at the T/S parameters in Tony's post, if my quick calcs are correct, the Super 10 Ferrite gives f3=55Hz in a 70 litre box, with the port tuned to 45Hz, so will be well down at 20Hz.