Time aligning planar tweeter and 15". Help please!

SAC · 12th August 2009, 11:36 AM

The tweeter (BGneo 3 pdr open baffled) is crossed to the 15" (alpha 15a OB) just below 2khz with a first order Xover. I read that time alignment at 2khz is worthwhile to within 4.5cms at this frequency.

1. Is it worth the bother?
2. At what point in the 15" driver should I aim? The acoustic centre or thereabouts?

Admittedly, I will incur diffraction problems in the event I move the tweeter back although your answers may help me weigh up the pros and cons.

Thanks

gainphile · 12th August 2009, 12:26 PM

My method which seems to work:

1. Measure woofer on-axis 20cm. Get impulse and record gated phase

2. Measure tweeter on-axis 20cm (exactly!) same thing.

3. Compare phase, build delay circuit then play around until the phase matches (0 deg if LR4) at the xo point. (physical offset is a good starting point)

You'd find out that the acoustic centre is *not* the voice coil.

You're crossing alpha 15 at 2kHz? ... very brave

SAC · 12th August 2009, 01:11 PM

Gainphile, your method is way beyond my means. I use a test CD with frequency sweeps to get an idea of the flatness. It is a rough design as you noted. I am relying on Audyssey auto-eq to resolve as many problems as possible. Emerald physics CS2 do a similar thing.

With regards to alpha 15 at 2khz;
I had the B200 crossed to a single and also two alpha 15s.
Also had neo3 pdr crossed with the same cross over to the B200. The four remaining alphas acted as a sub.
In conclusion, the best sound was when I crossed the tweeter to the single alpha in an experiment. Realistic treble and soundstaging for the first time. I have to give up on the B200s perhaps due to my inability with crossovers, the necessary chokes, and so on. Wooden phase plugs didn't even help much with that uncomfortable high end response.

12th August 2009, 11:36 AM	#1
SAC diyAudio Member Join Date: Feb 2007 Location: London	Time aligning planar tweeter and 15". Help please! The tweeter (BGneo 3 pdr open baffled) is crossed to the 15" (alpha 15a OB) just below 2khz with a first order Xover. I read that time alignment at 2khz is worthwhile to within 4.5cms at this frequency. 1. Is it worth the bother? 2. At what point in the 15" driver should I aim? The acoustic centre or thereabouts? Admittedly, I will incur diffraction problems in the event I move the tweeter back although your answers may help me weigh up the pros and cons. Thanks

12th August 2009, 12:26 PM	#2
gainphile diyAudio Member Join Date: Dec 2007 Location: Melbourne the sunny city!	My method which seems to work: 1. Measure woofer on-axis 20cm. Get impulse and record gated phase 2. Measure tweeter on-axis 20cm (exactly!) same thing. 3. Compare phase, build delay circuit then play around until the phase matches (0 deg if LR4) at the xo point. (physical offset is a good starting point) You'd find out that the acoustic centre is not the voice coil. You're crossing alpha 15 at 2kHz? ... very brave __________________ http://gainphile.blogspot.com

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
time-aligning a super tweeter	cporada	Multi-Way	26	8th September 2006 12:03 AM
Time aligning LCY ribbon tweets on baffle	j.burtt	Multi-Way	1	25th September 2005 04:29 AM
Time aligning subs, mains, etc.	tiroth	Multi-Way	16	24th December 2004 04:28 AM
planar tweeter	joz	Planars & Exotics	0	31st March 2003 04:25 PM
Time Aligning Questions	mrfeedback	Multi-Way	1	6th May 2002 01:49 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

12th August 2009, 01:11 PM	#3
SAC diyAudio Member Join Date: Feb 2007 Location: London	Gainphile, your method is way beyond my means. I use a test CD with frequency sweeps to get an idea of the flatness. It is a rough design as you noted. I am relying on Audyssey auto-eq to resolve as many problems as possible. Emerald physics CS2 do a similar thing. With regards to alpha 15 at 2khz; I had the B200 crossed to a single and also two alpha 15s. Also had neo3 pdr crossed with the same cross over to the B200. The four remaining alphas acted as a sub. In conclusion, the best sound was when I crossed the tweeter to the single alpha in an experiment. Realistic treble and soundstaging for the first time. I have to give up on the B200s perhaps due to my inability with crossovers, the necessary chokes, and so on. Wooden phase plugs didn't even help much with that uncomfortable high end response.