Time alignment sanity check

[quickshift]

I'm in the process or trying to put together a design for a WMTMW and have a question about the optimum method of physically time aligning the drivers.

I think there are 2 main options, I can place a woofer and mid in the same plane and tilt them relative to the tweeter or offset the tweeter against the woofers and tilt only the mid (by about 10 degrees)

Which would be the best option please?

[MaVo]

without proper measurement or a really good simulation, time alignment is like shooting in the dark. you need to take into account that both the drivers and the crossover produce a frequency dependant time delay.

[quickshift]

OK, thanks MaVo.

I haven't found any (free) software that will give a complete full simulation of what I'm trying to design. I haven't seen anything that will deal with angled front baffles such as I'm proposing at all.

Have you got any suggestions of something I can use please?

I've used The Edge, Unibox, TPSD Multi and WinISD to put together what I have so far.

[MaVo]

I am also just learning about this stuff, but maybe you can find something helpfull here: http://www.pvconsultants.com/audio/frdgroup.htm

Much to expensive, but this will do it probably: http://www.linearx.com/products/soft...5/LEAP5_01.htm

[dlr]

Originally posted by MaVo
without proper measurement or a really good simulation, time alignment is like shooting in the dark. you need to take into account that both the drivers and the crossover produce a frequency dependant time delay.

The time delay to which you refer is not associated with the frequency-dependent delay. The latter is the minimum-phase response of the driver related to the transfer function of the driver as is the delay introduced by a crossover. The time alignment related to the acoustic center is a separate issue and as used in most CAD software is a fixed point, not frequency related, assumed to be the origin and specified in the model as such.

I believe that SoundEasy has the capability to create a model that incorporates driver axis rotation if desired.

Dave

[quickshift]

MaVo, I'd love a copy of LEAP but I think $1500 is pushing it a bit for someone with my low level of understanding of all this (at the moment) I wouldn't make the most of it by any stretch of the imagination

Thanks dlr. So it's "just" a case of physically aligning the drivers using the baffle shape that'll give me either the smallest amount of deviation of response or the deviation that is most easily compensated for?

I'll look at SoundEasy, thank you.

[dlr]

Originally posted by quickshift
Thanks dlr. So it's "just" a case of physically aligning the drivers using the baffle shape that'll give me either the smallest amount of deviation of response of the devation that is most easily compensated for?

I'll look at SoundEasy, thank you.

Yes, the alignment is an offset to align the two acoustic centers. The summed response target can be achieved much more easily when aligned. The individual drivers are designed to a target for each driver. When combined, the phase response of each leg of a crossover pair should be very close to the ideal so that little or no slope alteration is required to achieve the target summed response.

BTW, SoundEasy is not free software, but it's excellent for the price and is a complete package for almost any DIY efforts.

Dave

[quickshift]

I wonder if we could use a copy of SoundEasy to help with setting up the recording studio we are in the process of building at work... Seriously though, many thanks for your help. If SoundEasy will do everything I'm likely to ever need, I don't have a problem buying a copy.

[jzagaja]

How do you perform time alingment? We have several choices:

1) Curves (impulse, step) starts at one point in time domain (Manger et al)
2) Impulse maxima starts in the same time (popular)
3) Flattest response at crossover point
4) Something else

[dlr]

Let me suggest the following reference for some useful info:

John K's non-commercial Web Site

There's more than one alignment that may be desired. Time alignment (of acoustic centers) is not necessarily the single best goal. There can be reasons to align a bit differently, such as trying to align drivers with a crossover such that the phase at or in the crossover area is closer to optimal. This might be useful if there are limitations such as a difficult driver or a desire to minimize crossover components.

Most often I find that "getting close" is good enough because small deviations from ideal are almost not even noticeable in measurements. The exception to this would be transient-perfect types where the goal is to get close to accurate square wave reproduction.

All of this applies only on a single axis in any case.

Read John's pages, they should answer a lot of questions.

Dave