bobovox

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About bobovox

Personal Info

  • 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

    mini dsp 2x4 balanced vs dayton 408

    @rob4diy if you get a response from Dayton on the output voltage I would be interested to know myself - I had a look at the spec sheets for the DSP-408 a few weeks ago, with a view to using it for a three way crossover as it was quite a bit less expensive than the miniDSP4x10. That this information wasn't stated did ring alarm bells for me though.
  2. bobovox

    Your Brexit song

  3. bobovox

    Speaker terminal question

    Dunno but I imagine the answer was either: 1. Pure whimsey 2. CBA putting them in at the same level. Will this do?
  4. bobovox

    RIP Niki Lauda

    Sad to learn of his passing, he was a boyhood hero of mine for his bravery in returning to racing after the accident. RIP Niki.
  5. bobovox

    Tannoy 8" Dual Concentric active build

    Tony, out of interest could you post one of the impedance curves that you measured for the tweeters? I note the curves in the papers @cooky1257 linked to that the peak at resonance is not as pronounced as one might expect from a more conventional dome tweeter. I must confess I hadn’t spotted the type of tweeter and was a bit puzzled how a crossover frequency around tweeter fs was possible.
  6. Have been doing some playing around with 6th order assisted bass-alignments - keeping the lower port tuning and adding a high Q (1.4) 2nd order high pass filter to the bass is giving f3=56Hz, which is not bad from a 4litre speaker. It's effect is quite transformative on the sound - much more full-bodied. No adverse effect on group delay and it also limits cone-flap below port tuning frequency as well.
  7. Sitting in a café a few weeks ago I noticed the music was being played through some small Dali's that looked to be about the same size as the ones I built for use with the Beocreate. I noticed that the Dalis had more bass extension than my speakers, albeit, the speakers in the café were mounted on brackets and stuffed into the corners next to the ceiling. The original box tuning design was a crib of the published designs using the 12W/8524 midbass, although I did run some numbers through the Scanspeak toolbox spreadsheet to check that it looked reasonable before having the Valchromat cut. After completing the boxes, the measured port frequency was a little higher than the design (73Hz vs 65Hz) and I had come to wonder if that wasn't a bit high anyway. With the dust having settled after the Kegworth show, I have today tried blocking one port, lengthening the other slightly and adding a small amount of ballast to reduce the effective enclosure volume such that the speaker is in SBB4 alignment, with the port tuned to fs of the driver (52Hz). Whist the bass now rolls-off earlier than the original design, the initial roll-off is more gradual. The change has made a definite positive impact on the 'speakers ability to play orchestral music and bass-lines of rock music. Closing one port results in a significant increase in port velocity and the vent area to cone area is edging into the non-linear port behaviour region. However, the speakers will be used for near field listening from now on at moderate volume levels so I don't anticipate any problems from either. Next step is to investigate an assisted bass alignment using the DSP and have a copy of "Bullock on Boxes" on order. I have also put the board and the Pi in an aluminium enclosure (Galaxy from Audiophonics - popular choice at the moment ), pictured below. Unfortunately, with the top of the enclosure in place the on-board wifi on the Pi is unreliable so have ordered a USB wireless dongle with an aerial. The idea is to make a wooden stand and sit the enclosure vertically, with the speaker cables at the bottom.
  8. bobovox

    Isobaric Driver Arrangements

    I'm just using the basic equations relating driver f_s, Q_TS V_as with box volume Vc to give system Q_TC & f_c & f_3, put in a simple spreadsheet. The Linkwitz transform is extending the bass response by an octave. There is a spreadsheet on the MiniDSP website that will calculate the biquad coefficients and visualise the original and target roll-offs and the transfer function. The LT is adding around 6dB at 35Hz so amplifier power requirement is quadrupled. High power class D amps are relatively cheap these days but we need to take care with the power handling of the drive units. SBA are in the habit of quoting peak to peak Xmax - most manufacturers quote the amplitude (+/-) value. With +/-12mm and two drivers you get around 103dB at 1m.
  9. Why stop with just the windows? @Signs may get his wish yet...
  10. bobovox

    Isobaric Driver Arrangements

    Not isobaric, but my attempt to replicate the performance: D&D claim 106dB @1m from 35Hz; by my calculations, with two drivers of 8" this requires Xmax of 14mm. http://www.loudspeakerdatabase.com/Dayton/UM8-22 appears to fit the bill. 2 x Dayton Audio UM8-22 in a 30l enclosure (not isobaric) gives f_b=50Hz with Q_TC = 0.90. Apply Linkwitz transform in DSP to give Q_TC=0.71 & f_b = 25Hz. __ I now wait to be educated as to what I've done wrong.
  11. bobovox

    Tannoy 8" Dual Concentric active build

    For my two penn'orth, an 8" cone will be rather too directional at 3kHz to crossover that high. From the frequency response measurements, is there a peak from cone brake-up? Given the tweeter fs of 1.5kHz, I would suggest crossover from mid to tweeter around 2.3kHz as per the Tannoy passive design.
  12. 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.
  13. 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.
  14. 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.
  15. 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.