DrWho Posted June 1, 2011 Author Share Posted June 1, 2011 lol Mark, you are more than welcome to share your wonderful experiences on other forums - make sure you piss on their products while you're at it... This is the first time I've really set out to be super complete in all of my measurements. We're probably at well over 200 measurements before being able to post the plots I've shared. I simply can't fathom anyone building anything without any real level of validation. This beast sounded "fine" when we first fired it up, but we brought it to whole new levels when we used the measurements to track down things that didn't sound right. It is flat out impossible to finesse something without having tools to show you where the problems are at. All this horse crap about "refined listening" is just ignorance or insane arrogance... Here's a few more pics for your viewing pleasure: Vertical Polars: Horz Polars (new xover): Horz polars with old xover: Impedance Response (no stuffing): Painted: Sitting on its rigging in a double doorway (on a dolly to move it around): Quote Link to comment Share on other sites More sharing options...
seti Posted June 1, 2011 Share Posted June 1, 2011 That is a fine looking horn. Quote Link to comment Share on other sites More sharing options...
jwc Posted June 1, 2011 Share Posted June 1, 2011 Bentz, Cool stuff. What are your thoughts on what the impedance is starting to do above 500Hz. BTW. I don't believe Mark was criticizing your horns....but being sarcastic that someone else may make an improvement of your horn. jc Quote Link to comment Share on other sites More sharing options...
mark1101 Posted June 1, 2011 Share Posted June 1, 2011 Some doctors are too smart to figure out the easy ones. Quote Link to comment Share on other sites More sharing options...
Moderators dtel Posted June 1, 2011 Moderators Share Posted June 1, 2011 Looking at the size of that room how long is it, we can see part of the width, looks like about the size of a basketball gym. Quote Link to comment Share on other sites More sharing options...
DrWho Posted June 2, 2011 Author Share Posted June 2, 2011 Cool stuff. What are your thoughts on what the impedance is starting to do above 500Hz. Do you see something you don't like? We can see the suspension ripple at ~2kHz. The slow rise is corresponding with the mass corner and lines up with the falling frequency response. It only took ~6dB of CDEQ to bring things flat on-axis. I think these drivers in a Jub LF wouldn't need any boost since there's some extra DI at 1kHz. Btw, the impedance was measured in nearly full space. You see the horn ripple reduce a bit when there are more boundaries nearby. Regardless, the crown XTi really chokes on the impedance minimums. BTW. I don't believe Mark was criticizing your horns....but being sarcastic that someone else may make an improvement of your horn. Ya, I know. I was suggesting he be a minion to promote products for me (another sarcastic angle agreeing with other implications behind Mark's post). I guess my sarcasm wasn't as clear...he would be bashing the products of the other company. Epic fail on my part it seems, haha. Quote Link to comment Share on other sites More sharing options...
jwc Posted June 2, 2011 Share Posted June 2, 2011 Oh no.....nothing I don't like. Just wanted your explanation of the impedance. So. Where is the crossover point? Are you using them out to 1000Hz? Where is the 6dbEQ? Looks like the polars hold up "well" to 1000Hz? My tractrix straight bass horn droops after 550-600Hz....but not doing EQ. I should run an impedance curve on mine. Quote Link to comment Share on other sites More sharing options...
DrWho Posted June 2, 2011 Author Share Posted June 2, 2011 Adding the EQ allowed the electrical and acoustical xover frequencies to both be exactly 1kHz. This means the natural rolloff of the drivers are not being used as part of the xover slopes. We started off with a 4th order L-R, but it was causing some suckout in the horizontal polars as shown above. I'd like to go to a 3rd order Bessel (ideal for MTM, or D'appolito arrays), but the XTi amps don't offer that option. I wonder if the new XTi2 amplifiers do? I should do another round of measurements where we do the polars of the bassbin and tweeter separate from each other. I think it would also be good to get a plot of the before/after EQ that is normalized to the input voltage (so that true sensitivity can be derived). Getting absolute SPL measurements is going to require a new soundcard interface - that I'll probably just build to make my life easier. Anyways, that should provide a better view of how much EQ is used and all that shnazz. Coming up next is a custom tweeter (and hopefully we can improve on its polars below 2kHz). The tweeter really wants to be crossed at 2kHz, but I'm not sure we can push the bassbin that high. I think I might try it though just to see what it sounds like. My guess is the suspension will create unpleasant artifacts at 2kHz. Quote Link to comment Share on other sites More sharing options...
aj01 Posted June 24, 2011 Share Posted June 24, 2011 I've been looking at building a mid-bass horn and have been working through fc, throat area and expansion contours. How do you calculate what the high frequency is going to be? Quote Link to comment Share on other sites More sharing options...
Edgar Posted June 24, 2011 Share Posted June 24, 2011 We started off with a 4th order L-R, but it was causing some suckout in the horizontal polars as shown above. I'd like to go to a 3rd order Bessel (ideal for MTM, or D'appolito arrays), but the XTi amps don't offer that option. The denominator polynomial for a 3rd order Bessel filter is: s3 + 6s2 + 15s + 15 This can be decomposed into the cascade of a 2nd order section and a 1st order section: (s2 + 3.67781464537391s + 6.45943269348336)(s + 2.32218535462609) The 2nd order section has a Q of 0.69105, which is really close to the Q of a Butterworth filter (0.70711). So you could construct a very close approximation to a 3rd order Bessel filter as the cascade of a 2nd order Butterworth and a 1st order filter. You just need to figure out the cutoff frequencies for the constituent filters. Greg Quote Link to comment Share on other sites More sharing options...
Ironsave Posted June 24, 2011 Share Posted June 24, 2011 Mike, Congrats on a fine build. The Church is very lucky; and I am sure they appreciate all of the hard work. A+!!!! Quote Link to comment Share on other sites More sharing options...
Deang Posted June 24, 2011 Share Posted June 24, 2011 Dag gone Mike, you be all grown up and stuff. Way cool dude. Wow. Quote Link to comment Share on other sites More sharing options...
gistofit Posted June 25, 2011 Share Posted June 25, 2011 Link to video of testing of the Horn. First time stuck together in the gym. Long video 45+ minutes! Set aside a day! Quote Link to comment Share on other sites More sharing options...
DrWho Posted June 26, 2011 Author Share Posted June 26, 2011 I've been looking at building a mid-bass horn and have been working through fc, throat area and expansion contours. How do you calculate what the high frequency is going to be? Keele has some good equations on his website, but a more iterative approach would be to punch numbers through hornresp to feel out how things behave. Quote Link to comment Share on other sites More sharing options...
DrWho Posted June 26, 2011 Author Share Posted June 26, 2011 We started off with a 4th order L-R, but it was causing some suckout in the horizontal polars as shown above. I'd like to go to a 3rd order Bessel (ideal for MTM, or D'appolito arrays), but the XTi amps don't offer that option. The denominator polynomial for a 3rd order Bessel filter is: s3 + 6s2 + 15s + 15 This can be decomposed into the cascade of a 2nd order section and a 1st order section: (s2 + 3.67781464537391s + 6.45943269348336)(s + 2.32218535462609) The 2nd order section has a Q of 0.69105, which is really close to the Q of a Butterworth filter (0.70711). So you could construct a very close approximation to a 3rd order Bessel filter as the cascade of a 2nd order Butterworth and a 1st order filter. You just need to figure out the cutoff frequencies for the constituent filters. Greg The problem is that the XTi amps only give you a single xover....so no cascading options. I'm thinking it may be possible to incorporate a PEQ with a 4th order to make it behave 3rd order. Quote Link to comment Share on other sites More sharing options...
Edgar Posted June 27, 2011 Share Posted June 27, 2011 The problem is that the XTi amps only give you a single xover....so no cascading options. I'm thinking it may be possible to incorporate a PEQ with a 4th order to make it behave 3rd order. If they offer a 1st order filter after the crossover, then you can cascade a 2nd order Butterworth crossover with a 1st order LPF in the woofer path and with a 1st order HPF in the tweeter path. Greg Quote Link to comment Share on other sites More sharing options...
Edgar Posted June 27, 2011 Share Posted June 27, 2011 More detail, with an example: If you need, say, a 100Hz 3rd order Bessel crossover, then create a 144 Hz 2nd order Butterworth crossover. In the woofer signal path, insert a 132 Hz 1st order lowpass filter after the crossover. In the tweeter path, insert a 132 Hz 1st order highpass filter after the crossover. The combination of the 2nd order Butterworth crossover and the 1st order filters will create a very close approximation to a 3rd order Bessel crossover. For cutoff frequencies other than 100 Hz, just scale accordingly. In general, this technique does not work for higher order Bessel crossovers. It just happens that a 3rd order Bessel filter contains a 2nd order section that is very close to a Butterworth characteristic. Greg Quote Link to comment Share on other sites More sharing options...
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