Sloped baffle

Roy,

Thanks for your fantastic contribution here. We can only hope for more really knowledgeable folks like you to take the time and educate us hobbyists.

On the 1st or 2nd page I posted about a way I was intending to get at this. I have, at least for this purpose, the advantage of having only an optimized computer as audio source. My plan is to use Acourate software on the server, a multichannel DAC, and independent amps connected directly to each driver, without passive crossovers. Acourate allows the use of a variety of digital crossovers, and allows for time alignment of the drivers. BUT it is limited to a single time delay between any pair of drivers, much like the limitations you describe for DEQX (which I previously considered too, but a needlessly expensive option if the only source is a computer).
Clearly this will not solve 100% of the problem - something I learnt from you. But what's your very educated guess: will it solve maybe 80% of the problem vs a non-time-aligned 3-way speaker?

BTW, would love to get your thoughts about this XO white paper by Dr Uli Bruggemann, the guy behind Acourate.

As of now I'm using B&W 804S. Obviously not time-aligned. Probably not even phase-coherent. So the setup described above would first be used with these speakers. And eventually I'm thinking of building my own speakers using top-notch drivers, the Loudspeaker Cookbook as guide. I'm a mechanical engineer and handy building stuff. Assuming I do a good job selecting drivers and building the cabinets...sounds like I'll end up with very good speakers in terms of bang for buck...what do you think?

Bombaywalla, not trying to be a troll here. I restated my DEQX point because I already have speakers. However, as Lewinskih01 kinda alluded to above, the device may not be perfect ... for all the reasons Roy mentioned, but it may get me to a much better place.

Trying to arrange for a DEQX audition.

Kudos to Roy for his well written posts and dedication to our hobby.

Lewinskih01,
I took the time to read the XO White Paper by Dr. Uli. In many places he makes the same points that Roy is making i.e. lower order x-over ckts are better than higher order x-over ckts. He talks about the time delays getting worse with higher order x-over ckts - same point that Roy has made many times.
Dr. Uli talks about using minimum phase filters for the analog x-overs &
using linear phase filters (which are digital FIR filters. there is no equivalent in the analog domain) for his Acourate digital x-over software.
Dr. Uli makes a general statement that low-order minimum phase filters used in analog x-overs have limitations & create time distortions & cannot be used......
BUT he conveniently starts off with a 2nd-order x-over ckt while completely glossing over a 1st-order x-over ckt. Does the 1st-order x-over ckt have the same limitations as the 2nd-order x-over Dr. Uli discussed? Dr. Uli would like you to think so but I don't think so......

I created a simple 1-order network for a tweeter, midrange & woofer. I assumed a 6 Ohms resistance for each of the 3 drivers (totally arbitrary). I arbitrarily chose x-over frequencies of 300Hz & 2KHz. I simulated the frequency, phase & step responses of this 1-order x-over. I've labeled the curves in each of the 3 graphs so you can see which curve belongs to which driver. I've also put markers on various curves so you can see the phase shift at the x-over frequency.

For the frequency response - look at the sum of the frequency responses. There's only a 2dB hump at the x-over points.

For the phase response - look at the sum of all the phase responses/ There's a phase shift of only +/- 8 degrees over the entire audio band of 20Hz - 20KHz.

And, for the step response - you can clearly see that all 3 drivers act in unison to create unified step response (rather than the spikes you see in time-Incoherent speakers where the tweeter acts first, the mid second & the woofer third).
From these simulations, a 1st-order passive x-over looks quite good.
And, I don't have the music signal going thru somebody's DSP algorithm which is doing a great deal of signal processing to massage the music signal thereby imparting its sonic signature to the music signal.
Sure the passive x-over components are also imparting their signature to the music signal but by using top quality components I can minimize this.
In the DSP software, if I don't know what I'm doing, I can botch thing pretty badly because the music signal is so heavily modified by the DSP algorithm.

Here is the link to the simulations, if anyone is interested:
https://picasaweb.google.com/bombaywalla9/FirstOrderXOverFreqPhaseStepResponses?authkey=Gv1sRgCOz6xv6RnMDeUA#

In the XO White Paper, Dr. Uli says that "So the crossover has to be selected so that the good properties of the driver are used ! If the driver does not have a good behaviour we should not use it."
I am assuming the "good properties" of a driver are that it has flat freq response over its passband & rolls off at a frequency beyond the x-over freq chosen in Acourate by the user. BUT............
The degree that Acourate can compensate for any driver depends on how well you can characterize the driver. And, we of course, do not know if the drivers in our existing speakers have these "good properties" or not.....

Bombaywalla,

Not sure what to take away from your post. 1st order passive crossovers are better than any type of digital crossover? That would be in line with Roy's explanation. But I wasn't arguing otherwise...

I'll take as given that Roy's approach is the best one could hope for. My question to him is how close to that would my described approach get me.

Cheers!

hi Lewinskih01,
yes, with some engineering proof, that's what I was trying to say. And, the reason that seemed to make sense to me is that signal processing is happening correctly, real-time thru the passive x-over components without any intervention by a human-being. In a time-coherent loudspeaker with passive x-overs, drivers with "good properties" have already been selected & the x-over designed around them & the whole system would be working to benefit the user.

With digital x-overs the correction is as good as the skill of the user to characterize the drivers & to come up with the appropriate filter response to yield a time-coherent delivery. And, from reading Roy's letter to Six Moons - the link to which he provided earlier on - it's no easy feat to characterize a driver in the room. One cannot use 1 type of test tone, one needs to use many different types. And, one needs to measure the driver response in many ways to get an accurate characterization of the driver. Otherwise, the DEQX or Acourate correction will be (very) limited leading to less than stellar benefits.

I don't think that Roy can tell you how well DEQX or Acourate will solve your problem because the answer lies in how skilled you are in understanding the science behind how the driver response is affected by your room,
how skilled you are in DSP algorithms to come up with a filter that corrects for your room & your particular choice of drivers
how skilled you are in understanding the science behind reflections of drivers off the front baffle,
how skilled you are in understanding what the requirements are for selecting a microphone to do the driver characterization,
how skilled you are in compensating for this mic's own frequency response so that you don't misunderstand the mic's response to be that of your driver's,
etc, etc.

My understanding is that if you room correct like HT Receivers do & plug in the correction into some pre-designed filter in the software, you'll get a correction that's average at best & you might not like the results.
The thing that Roy has been saying all along is that we don't listen to test tones (which is what the room correction tones are) - we listen to music which is a bunch of partial wavelengths of various frequencies.
You use full cycle tones to characterize the driver then do the correction & then play partial wavelengths of various frequencies thru that driver - the correction to the driver, in my understanding, is invalid.
Of course, I could be totally off-base here....
FWIW.