Time Alignment on a flat baffle.....

[rabbitz]

1st order crossovers are much better with time aligned drivers so I'm looking for a solution so I can still have a flat and not a stepped or sloping (10-15°) baffle.

I saw this idea for the tweeter (see pic) but I'm not sure whether you'd get some horn loading and also diffraction problems with this. I'd also have to have the woofer protruding from the baffle by about 16mm (a round spacer the same diameter as the woofer). Is this a problem as currently it is flush?

Or is this going to cause more problems than it cures?

[Nuuk]

The truth is that many of these factors are just not audible in practise. While is is commendable to aim for perfection, it can sometiimes be a source of needless worry and wasted time

I had a speaker design with the tweeter mounted in it a separate housing which could be moved back and forward. I played around with it for ages but never did hear any difference.

[Bricolo]

why don't you want an angled bafle?

[Zappa]

With all my apologies, Nuuk, I presently prototype a 2 way with a mobile tweeter enclosure and it makes much difference to move it forth or back by 1/2 inch. Hint: you can easyly percieve the lobing from the listening position. The effect for a given move length of the driver (in this case, the tweeter) increase with the crossover frequency.

Rabbitz, given the crossover frequency is in the 2k range, I don't think any horn loading is to appear in your case.

[Guss]

With the woofers coil moving forth and back all the time is it really worth wasting some time to align the drivers to perfection???

[Bill Fitzpatrick]

Originally posted by Guss
With the woofers coil moving forth and back all the time is it really worth wasting some time to align the drivers to perfection???

Now that's a REALLY good question.

It seems that if nothing else, the excursion of the woofer will be responsible for "modulated lobing" and "modulated on axis frequency response" in the area of the crossover frequency.

Another good reason for a 2 way system actively crossed to woofers somewhere around 120Hz.

[5th element]

I was gonna say the same thing about doing a three way. But I have my tweeters in a separate enclosure and moving these back and forth doesnt seem to do much either to the sound. WHen simulating it makes a HUGE difference in the reverse null and a bit of difference in the non reverse.

I am all for time aligning but!, doesnt the amount you have to offset things differ with different crossover freqeuncies. I seem to remember linkwitz saying something about this, calculating time delay for the 4th order at the 1.5khz or so at with the orien.

Also how do you find out where the exact acoustic centres of drivers are? This need to be VERY accurate for LSPCAD pro altering things by half millimeters makes quite big differences.

[Bill Fitzpatrick]

According to Richard Heyser in one of his JAES papers, the acoustic center of a driver varies with frequency. This makes the time alignment solution much more difficult.

[Ken L]

Originally posted by rabbitz
have the woofer protruding from the baffle by about 16mm (a round spacer the same diameter as the woofer).

I would think that moving the woofer forward slightly is more likely to benefit than have a negative effect in regards to time alignment.Many "time aligned" designs place the tweeter slightly to the rear - moving the tweeter _forward_ is the way you wouldn't want to go.

this is not my area of expertise, however - I remember other posters making comments to the effect that the higher in hz you go the less important it is -

Again, if I remember correctly, this is only pertinent to within 1/2 of a wavelength (1/4 wavelength + or - a paticular wavelength)

Time wise, my guess is that you're OK.

I'm more concerned about protruding 5/8 of an inch - and don't really know, but I bet that's a little bit of a problem - whether it's audible or not, I just don't know, but that is something that probably needs to be looked at -

Regards

Ken L

[Nuuk]

With all my apologies, Nuuk, I presently prototype a 2 way with a mobile tweeter enclosure and it makes much difference to move it forth or back by 1/2 inch.

I bow to your superior hearing I guess it will also depend on factors like tweeter type/quality and crossover frequency.