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In Reply to: RE: IIIa Frankenpan Active X-Over points? posted by computerman on February 23, 2015 at 14:29:43
When you alter crossover settings from textbook settings, you certainly will create holes in the response.....but in the electrical summation of the slopes, not necessarily in the acoustic response. Nearly all speaker systems (Maggies too) use non-textbook electrical responses to create proper acoustic crossovers. This is the essence of crossover design....but it's not fully appreciated by many users.
-3db simply means that's the frequency at which that electrical filter rolls off to -3db from the passband response. It's confusing though when programming DSP units because different crossover alignments designate different cutoff points depending upon their type. Butterworth crossovers have adjacent filters equal at -3db, Linkwitz-Riley crossovers have adjacent filters equal at -6db, etc, etc.
Cheers,
Dave.
Follow Ups:
Thanks first for the posts. I presently set the crossover points to unlinked and as neolith suggested as the stock crossover points. If they need tweaking, I will experiment with them. Once I am satisfied with them, I will try exploring the DCX further and learn more about delay, time alignment etc. I studied this in the past when I was thinking of going to a full computer based crossover system, but it has been a while, so i need to brush up. This forum is a great place to learn things. I am very impressed with the level of knowledge of "inmates" and hope to be in a position to contribute more myself as I learn. I do have a Behringer mic for calibration so I will give that a try as soon as time permits and report back.
I also run a business which keeps me real busy so I cannot get back here as often as I would like, so please forgive delays in responses from me if that matters at all. I just learned that my new apartment is ready and inspected. I have been waiting patiently for this as it means that I will have a much more spacious area to use for the Maggies. It will not be a dedicated listening room, but it will be quite an improvement. The room is approximately 14' by 13' 6". The Maggies and equipment will be on the 14' wall. There will be very little furniture in the room and it will be placed against the far wall facing the Maggies. Hope it all works out well. The apartment walls are sound proofed so I do not have to worry about disturbing the neighbors. They did an awesome job with the construction. They included ethernet cabling in the walls as well. As an IT Consultant/Network Analyst, that means a lot to me.
Just a little warning for the Behringer microphone, it really need to be calibrated.
http://www.cross-spectrum.com/audio/newgifs/ecm8000_frequency_response_large.jpg
https://www.hifi-selbstbau.de/images/stories/Messraum/MicCal1000/MicCal_ECM8000a125.png
https://www.hifi-selbstbau.de/images/stories/Messraum/MicCal1000/MicCal_ECM8000b129.png
I have read that it is difficult to get this mic calibrated, and that it is best done by a company that specializes in calibration, is that true, or could one just use REW to do the calibration?
Not sure if Cross Spectrum will do a calibration but they do sell calibrated microphones.http://cross-spectrum.com/measurement/calibrated_umik.html
http://cross-spectrum.com/measurement/calibrated_umm6.htmlminiDSP directly from the manufactor:
http://www.minidsp.com/products/acoustic-measurement/umik-1I like the ones connecting through USB, no need for an additional preamp.
Measuring techniques need to be studied too! A microphone need to be understood, it is not as sofisticated as our ears (+brain).
Edits: 03/02/15
I ordered a MiniDSP. I think that the USB connection is definitely a plus, and it is calibrated. Not bad for under $100. I just hope it performs as well as the reviews say. Do you have any experience with this mic? I could use it on my iPad as well. Shouldn't the Behringer be able to be used for the Auto-Align" feature in the DCX? Or does it also have to be calibrated for this use as well?
No, I have no experience of the miniDSP UMIK. Auto-align is often a bad idea. Can you chose a target curve? If not, it is really a bad idea. A straight line (a linear response) is not what is wanted, more a tilted curve dropping towards higher frequencies. A microphone cannot separate direct and refected sounds as our ear and brain can.
Roger would you know what the phase of each of the drivers should be in relation to one another?
The phasing of the drivers depends on the order of the filters. For instance, if you change from first to second order, phase need to be changed too. In the end, you need to measure the frequency response of the speaker. The crossover will also influence the dispersion charateristics of the speaker. There will be a main direction of "throw" from the speaker depending of the chosen crossover/phasing. Yes, this is complex....
Can you find the original phasing of the drivers? Think you need to start from there. Maybe some guys can run simulations on some crossovers? A good start is to measure the frequency response of each driver without crossover. A warning, it is easy to damage the ribbon tweeter that way. Maybe a large capacitor in series with it gives some protection?
I would have to do more reading on the auto alignment to see if a target curve can be done with the DCX2496. I do not recall seeing anything referring to this but I will check further. Thanks for the advice.
Roger what do you think of the crossover points I am using? Also thanks so much for your guidance in the choosing of the correct foil for the mids. Magnepan was very cooperative and installed as you suggested. Awesome sound so far. They used the same foil you are using for your T-IV build as far as I know, I did not measure it. I would love to be able to hear your T-IV's once finished. I just entered the crossover values, suggested by neolith, and I heard an immediate improvement. I do not have the T-1 D's in the picture yet, and will not until I move. I also have a sub which is an AR with Sunfire amp, crossing that over via the Sunfire TGP-5 Pre/Pro at 50 Hz, and using it's LFE input with speaker size set to large which means the signal is available at all times to the sub with an additional "Enhanced Bass" setting in the TGP-5. I think it might be a good addition with the IIIa's by themselves, but will take it out of the picture when I add the T-1D's.
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