Hi All,
I recently gifted away a pair for Wayne 4Pi Speaker Cabinets and in return, the person gifted me a vintage set of ITT LPKM 130/50 2" mid-domes.
Look through my driver inventory, I realized I had a pair of Dayton Audio RS225S-8 (vintage shielded version) and Peerless DX20BF00-04 tweeters.
With the parts on hand, I proceeded to build a ATC lookalike mini-monitors, with offset dome mid and offset tweeter.
As I take measurements of the ITT (using sweeps via ARTA) - I hear some sort of resonance / odd tune to the sweep between 100hz -700hz, and thereafter the sweep sounds more normal. It sounds tube-y - if that makes any sense. Perhaps I can record in on my phone and upload it to Youtube if that helps. Almost as if the diaphragm is ringing at certain frequencies. One would have to listen for it using headphones.
The mid's resonance frequency is approximately 250, but despite crossing the mid at 800hz - I still hear it. I've even tried including a parallel LCR circuit to suppress the resonance, but I still hear it.
Can fellow forum members help me troubleshoot the issue? Let me know what measurements I can provide (e.g., distortion, near-field with and without LCR, CSD, etc.).
I recently gifted away a pair for Wayne 4Pi Speaker Cabinets and in return, the person gifted me a vintage set of ITT LPKM 130/50 2" mid-domes.
Look through my driver inventory, I realized I had a pair of Dayton Audio RS225S-8 (vintage shielded version) and Peerless DX20BF00-04 tweeters.
With the parts on hand, I proceeded to build a ATC lookalike mini-monitors, with offset dome mid and offset tweeter.
As I take measurements of the ITT (using sweeps via ARTA) - I hear some sort of resonance / odd tune to the sweep between 100hz -700hz, and thereafter the sweep sounds more normal. It sounds tube-y - if that makes any sense. Perhaps I can record in on my phone and upload it to Youtube if that helps. Almost as if the diaphragm is ringing at certain frequencies. One would have to listen for it using headphones.
The mid's resonance frequency is approximately 250, but despite crossing the mid at 800hz - I still hear it. I've even tried including a parallel LCR circuit to suppress the resonance, but I still hear it.
Can fellow forum members help me troubleshoot the issue? Let me know what measurements I can provide (e.g., distortion, near-field with and without LCR, CSD, etc.).
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Do the mid drivers exhibit the same distortion with tone sweeps out of the cabinets and are they identical between the two drivers?
I believe that you may have a resonance at round about 900Hz. This can be seen in the filtered FR of the mid and the crossover filter's response. I recommend you look at getting rid of the sharp roll-off knee there. Use target curves to compare how close to ideal you are.
What back enclosure and damping is at the rear of the dome? And is it firmly mounted? What about the other units, can there be some panel resonance causing this?
Can you do an impedance sweep with ARTA or LIMP of the bare unit?
Can you do an impedance sweep with ARTA or LIMP of the bare unit?
IMO the response used to design the crossover was incorrect, clearly not matching the real deal for one reason or another. (Baffle step not taken into account perhaps?) Simulation shows the same acoustic output level at about 900 Hz and 2.8 kHz or so, however the XO's midrange section is up by about 2 dB while the driver's acoustic response drops by ~5 dB in the same range.
"Tubey" sound is likely to be a result of high 2nd harmonic as a result of excursion, something quite typical for traditional domes (a distortion sweep should show it). With its little waveguide this should fare better than an average 2" dome, but it still won't defeat the laws of physics - excursion quadruples for each octave lower.
"Tubey" sound is likely to be a result of high 2nd harmonic as a result of excursion, something quite typical for traditional domes (a distortion sweep should show it). With its little waveguide this should fare better than an average 2" dome, but it still won't defeat the laws of physics - excursion quadruples for each octave lower.
While adjusting this, try raising the cross point to 1k. That quarter octave will help with excursion and 'tubey' or 'honky'ness without screwing up your phase too much.
Otherwise, you'll still have to go steeper on the high-pass.
If everything worked the first try, it would be a boring hobby.
Otherwise, you'll still have to go steeper on the high-pass.
If everything worked the first try, it would be a boring hobby.
Try to rule out components, does the sweep have the "tubey" sound with the mid or woofer disconnected? It is coming from one of the drivers or the enclosure, unless your drivers are damaged, it is probably not coming from them, from the information shown, your crossover looks fine, do you have the ability to view the electrical transfer function (curves) of the the crossover alone, a super high "Q" crossover could be audible but from the looks of things, this is not the case. if possible , run an impedance sweep of each driver in the enclosure without the crossover, if there is a driver or box resonance issue, is should show up as a small "hiccup" in the graph. Your waterfall (spectral decay) graph shows something going on but I doubt that this is audible at least in the way you are describing. Welcome to Loudspeaker design!
Geoffrey
Geoffrey
Have a look at the graph titled "Filter" in the first pic. This is the crossover transfer function. As it appears the mid filter does have a high-ish Q on both ends. However, only the knee on the lower end is of consequence in my view, as it comes through in the final mid response.