Some speakers slant, some don't. Why?

[Keith_W]

Jud, it is because time alignment by driver alignment and analog crossover are able to do it within a narrow band only. The actual crossover itself plays havoc with the phase, which introduces delay. There is only so much an analog passive crossover can do before it becomes incredibly complicated and starts introducing losses. After all, if you think about it, an analog passive crossover is lossy enough already. It is powered by ... of all things ... your music signal. 

 

DSP is able to accomplish all this within the digital domain, where the losses are comparitively small. Also, with modern computing power, DSP units (like my setup) are able to achieve time alignment to within 1/1000 of a second. 

 

When I first heard the theory of DSP driven crossovers, I was totally won over by it. The reality is somewhat different (isn't it always!!!). The reality is - doing a DSP driven crossover means that YOU (or ME), as a complete speaker design novice, is tasked with designing what my friend (a speaker manufacturer) calls, "the heart and soul of the speaker". And to do this without training, or if you are like me, only a high school understanding of maths. I have learnt plenty, and I have achieved plenty (my speakers already sound better than they did from the factory), but I have a long way to go. 

 

In short, if the DSP is handled by someone who knows what they are doing, the results can be phenomenal. Ask a twit like me to do it, and the results are ... variable. 

[Keith_W]

5 hours ago, Jud said:

 

Yes, no way I'd try this by ear.  You should ask Keith, I think, because I have no experience using digital crossovers.  I'm sure you can *tune* digital crossovers using mics, but I don't know if there are crossovers that auto tune by microphone (I understand this to mean the crossover would tune itself using a connected mic).

 

I also wonder (Keith?) whether the tuning that one can do oneself extends not only to frequency but to measurements of group delay and phase.

 

Hi Jud, as I understand it the first question pertains to whether there is such a thing as an "auto-tuning" DSP? As far as I know, there is no such thing as a crossover that can tune itself with DSP. With all products I have tried, you MUST start by inputting the desired crossover configuration - crossover point, crossover order, and configuration (Butterworth, Linkwitz-Riley, etc), symmetric vs. asymmetric, etc. To even know these things, you need to have an understanding of the Thiele-Small parameters of your drivers, your enclosure, etc. 

 

There are DSP products which are able to do room correction of the entire corrected speaker at the push of a button. Lyngdorf/Tact, and a few companies. Including one company with a fancy looking microphone that looked like an alien villain's anal probe whose name I forget. 

 

The DSP that you do yourself can do nearly everything if you have software which is powerful enough, sufficient processing power, and enough brains to interpret your results. I have plenty of the above with the exception of the latter. Correcting group delay and phase is considered bread and butter for crossover DSP software. At the very minimum, they should be able to do it. However, how much correction can be applied depends on how much processing power you have. 

 

Just an example of what DSP can do. You may have heard of a double bass array. The idea is that your front wall has four subwoofers panel mounted (i.e. infinite baffle) at locations precisely defined by some equations. The bass frequency will emerge almost as a flat plane (rather than a point source) and sweep across the room until it encounters the back wall. The back wall has another array of similar subwoofers, only that the back wall has been controlled by DSP to cancel reflections from the incoming front bass wave. 

 

You can even do a "virtual" double bass array with DSP. Rather than have an array of subwoofers in the back wall, you can set your front subwoofers to produce the cancelling frequency at the same time it is producing the audible frequency. CA member akcheng has described exactly this method in his blog. 

 

There are still quite a lot of things that DSP can not do. It can not control speaker directivity or off-axis response. It can not force drivers to do what they don't want to do. 

BTW I hope that you don't think I am some kind of DSP guru, because I am not. It just seems as if CA's real DSP gurus don't seem to be around very much these days, which is a bit sad considering the whole reason I joined CA in the first place was to learn from them.