bobovox

Wammer
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About bobovox

  • Rank
    Wammer
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  • Location
    SE London, Europe
  • Real Name
    Robert

Wigwam Info

  • Digital Source 1
    Arcam CD73T
  • Digital Source 2
    Pioneer N-50
  • Integrated Amp
    Arcam A90
  • My Speakers
    B&W684 + DIY
  • Trade Status
    I am not in the Hi-Fi trade

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  1. bobovox

    Measuring T/S parameters using REW

    As I remember, @orangeart organised a seminar with Dr. Scott Lindgren and he explained that T/S parameters are not constant with respect to signal level, perhaps this may explain some of the discrepancy? I look forward to reading about the new project.
  2. bobovox

    Measuring T/S parameters using REW

    Thanks for posting the comparison, Tony. The Qts figure for Bass 1 with REW looks like a rogue result and I have to agree the DATS results look more consistent. The fs & Re figures for the two methods are not too far apart. The Vas figures are quite alarmingly different between the two methods and also within the sample. If you do a box design using alignment tables the required box volume is proportional to the Vas figure for any given Qts. One might expect quite audible differences in the bass response from the sample in a given enclosure. Do Tanny publish any info about these drive units? I think I might consider the DATS for future projects.
  3. I can't comment on what is included in Linn Space Optimisation as I have no experience with this, however I have developed digital filters for some small DIY bookshelf speakers. I took the precaution of adding a high-pass filter to limit excursion of the mid-bass units when playing music containing significant low bass. Should these cones be driven beyond the linear excursion region due to the low bass, this will introduce audible distortion in the response of the mid-bass units at all frequencies. The high pass is easily implemented at no extra cost with a digital crossover or as @Nopiano states a decent phono stage should have a rumble filter - the line level components are cheap enough. The components, inductors in particular, would be physically large and prohibitively expensive to do this in a passive crossover, however.
  4. bobovox

    Speaker design software

    I have used the Scanspeak toolkit for modelling of closed box and ported enclosures. The simulated impedance and frequency response agrees well with measurements, albeit you need the box-loss factor QL and effective volume, which you can only ever estimate until you have built the box. It does baffle step but not edge diffraction modelling, open baffles or transmission lines. You need Excel; I haven't tried it with OpenOffice. For passive crossover design I have used XSim, which is free-form (not restricted to any specific topology). works extremely well.
  5. bobovox

    Measuring T/S parameters using REW

    Glad you have it working, Tony. I was using a Mac so didn't have the same issue. I suspect the REW documentation might be a bit out of date now as it seemed more straight forward a few years ago. If you get the DATS I would be interested to see some comparisons of results.
  6. bobovox

    Measuring T/S parameters using REW

    Tony, I have built one of those jigs to measure impedance vs frequency of drive units in some DIY passive speakers in have built. To test it, I have measured the impedance of some passive components across the frequency range and the measurements were close to the theoretical values (allowing for component tolerances). Having based passive crossover designs on the drive-unit measurements made with the jig and found the resulting measured frequency response very close to that predicted by XSim, I concluded that the jig was sufficiently accurate for it's intended purpose. I use a Behringer UCA222 USB interface. I take it you have tested the connectivity with the multi-meter and found it satisfactory, so it's probably something in the REW settings? I think the article was written with an earlier version of REW. When I used v5.X with it recently, I think I had to play with the left / right source settings in the measurement dialog box, which I think have changed since I first used REW. I can check which ones work for me but might not have a chance to dig all the gear out until tomorrow night.
  7. A safe space for classical would be very welcome. I'm signed-up. I mainly listen to classical at home but didn't play any on Sunday until gone 4pm when the visitor numbers were dropping off anyway and thought I would treat myself to some Rachmaninoff at volume levels that I can't at home, because neighbourliness.
  8. bobovox

    Rasberry Pi Streaming

    I imagine you will get as many different suggestions as responses - there are many ways to do computer audio and the Pi is very versatile. I know that you don't want to replace the Linn streamer but if you want to use it in the same location / network or have a familiar interface, the Raspberry Pis in both of my Kegworth systems were running a bit of software that emulates a Linn DS so that you can control it with Kinsky. It doesn't need an audio-specific OS - I just installed it on Raspian Lite (the OS distribution supported by the Pi Foundation). Install instructions here: http://petemanchester.github.io/MediaPlayer/ This can run on a Pi Zero W with an IQAudio DAC Zero (about £35 together, extra for a case). Although I didn't use it, as the Hotel wifi wasn't up to snuff in my room, I also had a Spotify connect client installed, instructions here: https://medium.com/eggbeard/spotify-connect-with-raspberry-pi-a3280893a076 I'm a linear power supply denier so I ran the Beocreate module from a 120W Meanwell power brick and the Pi Zero from a Pi wall-wart (an old 5V phone charger would do just as well).
  9. bobovox

    Kegworth 2019 - Suitcase Challenge

    Thanks to Tony @Tony_J and Ed @Ed Howarth for coming up with the idea and doing the judging - it was a great idea to open up the show to smaller, portable systems. Thanks to everyone else who took part in the challenge - each system different but each showing just what a good sound can come from small boxes. I must confess to having felt distinctly nervous as a first time exhibitor; thank you to everyone who took and interest or made kind comments - it was a genuine pleasure to met you all on the Saturday night and during the show.
  10. bobovox

    great show!

    Thanks and congratulations to Peter and everyone involved in organising and running the show this year and everyone who visited us in Room 109 during the show. Special thanks for your wonderful company and making a newbie exhibitor feel at ease to everyone we met on Saturday night especially Nial for the extended listen to the stunning JBL monitors. Robert & Patricia
  11. bobovox

    Jbl 4430 clones

    They look great - the red grille cloth is very striking. Will make a point of coming to hear these on Saturday night 👍.
  12. bobovox

    Leak Sandwich 250 Speakers an Active project

    Andrew, yes as Tony says above the higher the order of the filter, the steeper the roll-off, so: 1st order - 6dB / octave 2nd order - 12db / octave 3rd order 18dB/octave 4th order 24 dB / octave etc... Higher order slopes mean less overlap. Some people prefer the sound of shallower slopes, some prefer steeper - I haven't experimented enough to form a view. Generally, steeper slopes mean you need to do less to compensate for cone break-up etc, less comb-filtering and lobing and you can crossover to a tweeter lower without damage thereby minimising the effect of beaming. If you want to replicate the passive crossover then your approach should work fine - when testing the tweeter you will need to include frequencies some way below the crossover frequency as there is an overlap, the length of which depends on the crossover slopes proposed. Have you noticed any hiss from the tweeters in your previous projects? I am considering a late change to my Kegworth set-up to include an L-Pad or series resistor to do the bulk of the tweeter attenuation rather than doing this in the DSP - both to provide some protection to the tweeter as well as improve the gain structure.
  13. bobovox

    Leak Sandwich 250 Speakers an Active project

    I think there is a DIY speaker bug and it's bitten us both... I would offer that the crossover frequency that you choose for an active conversion doesn't necessarily need to be the same as that which the original designer chose, although it might be a good starting point, nor do the roll-off slopes - with DSP you can easily implement higher order crossovers that may have been prohibitively expensive to do with passive component for a commercial loudspeaker designer in the '70s. Just bear in mind the following: 1. The sound from drive units becomes increasingly directional at higher frequencies - the so called "beaming" phenomenon. This depends on the diameter of the drive unit (measured between centres of the surround) as explained here: http://www.troelsgravesen.dk/Beaming.htm 2. To avoid horrible distortion and potential damage to the tweeters you need to crossover well above the resonant frequency (fs) of the tweeter - how much above depends on the slopes of the crossover but at least 1 octave - so double the tweeter fs. LEAK, unlike KEF, are no longer a going concern so you are unlikely to get the same level of info, except from enthusiast sites. Looking at the drive units in the picture the high frequency driver look like cones s perhaps fs is low and perhaps not a problem with crossing over quite low at 900Hz. If you do get into doing impedance measurements, there are DIY alternatives to buying a DATS or other commercial rig - I knocked together one of these with twenty quid's worth of bits and it works with REW: https://www.avsforum.com/forum/155-diy-speakers-subs/1340740-lilmikea-s-diy-impedance-measurement-jig.html
  14. bobovox

    The Hi-Fi Pub (Cafe, Restaurant...)

    I happened to be passing RFH tonight and dropped in to Spiritland for a cheeky half on the way home. It’s at the back of the hall, accessed from its own entrance at street level. The narrow front bar has two large speakers at several metres separation (sorry no internal pictures taken). The dining room at the back has what I think are the Living Voice speakers. As with the KX venue, it seams a nice place to go for a coffee / drink / meal but with the general hubub of conversation it doesn’t strike me as a venue for serious listening to music on a fine system. Besides, if I travel to the SBC to listen to music it’s going to be the real thing in the concert hall. There did seam to be a DJ booth so perhaps some nights the music may be the main focus.
  15. bobovox

    Cable question (groan)

    When I first started making DIY passive speakers, out of curiosity I measured the impedances of a few 89p 10W wire-wound resistors and to all intents and purposes these were constant and equal to the stated DC resistances from DC to 20kHz. I see no reason to pay £25 + VAT for a Duelund resistor - irrespective of where they sourced the graphite from - cross-over components are not even conspicuous.