Dear all,
I've built a part of 2-way Synergy-style horns, and am currently musing on how to manage the crossover/delay requirements of the speaker as a single unit.
I saw in this thread that opamps or bucket bridge devices could potentially be used in an analogue setting, but I wanted to ask to see what other designers and builders have done, with success.
For this, I'm looking for a small delay, somewhere between 0.4 and 0.6 milliseconds.
While it's relatively easy to do this using a PC-based DSP, additional system latency is a factor, so I thought I'd try looking at an analogue solution to minimise that.
Thanks in advance for your help and thoughts!
I've built a part of 2-way Synergy-style horns, and am currently musing on how to manage the crossover/delay requirements of the speaker as a single unit.
I saw in this thread that opamps or bucket bridge devices could potentially be used in an analogue setting, but I wanted to ask to see what other designers and builders have done, with success.
For this, I'm looking for a small delay, somewhere between 0.4 and 0.6 milliseconds.
While it's relatively easy to do this using a PC-based DSP, additional system latency is a factor, so I thought I'd try looking at an analogue solution to minimise that.
Thanks in advance for your help and thoughts!
I've never designed anything like that, but considering the short delay and the poor signal-to-noise ratio of bucket brigade devices, I'd go for an all-pass filter with Bessel pole positions.
Just being curious: how come you use British spelling while you live in the USA?
Just being curious: how come you use British spelling while you live in the USA?
Thanks for the tips! I'll do some searching 🙂 Do you have any examples that you can recommend? I'm very new to this part of audio processing.
I originated from Great Britain, but moved to the USA, and so some of my spellings are British out of habit 🙂
The old bucket brigades are long gone, besides they did not sound very nice. These days it is more often done in the digital domain. Some have done passive ladder filters, but they have very high loss and other problems. Time alignment is better managed by physical offset and phase. Google "all pass filter" and see what you get.
That would normally be the case, but these speakers are within a single enclosure. It's a 2-way design, where the ~70-500Hz are handled by woofers firing into the horn from the sides, and a full-range driver running from 500Hz upwards at the apex/throat of the horn. For coherence, a delay needs to be used.
0.6 millisiemens?
Actually if you replace the air in the room by helium the problem will be much less severe as the speed of sound in He is 3 times faster, so a 0.2m offset is only 0.2ms rather than 0.6ms.
You will have to recalculate all the speaker parameters though, and wear breathing apparatus. But hey!
More seriously I think this means you could extend the bass of a speaker by using a dense gas to effectively increase its acoustic size (in wavelengths)... Hmmm perhaps that is even feasible for a sealed or passive-radiator enclosure?
Sadly, they aren't. (Or are back.)
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The Bear is retiring this year, and I bet his fans will buy all his stock.
BBDs appear on other outlets but fraud is rampant.
And no, I would never put good audio through a BBD. (And these longer ones won't clock down to half-mS.)
That seems simple enough! 😀
It certainly would seem possible! However, not with the build quality I'm currently reaching 😀
I've been googling around, and I've found a couple of avenues. The allpass filters seem to end up pointing to circuits that alter phase.
Given that I'm looking for a 0.4ms delay, that would have to be considered at a single frequency, correct? If so, I'd probably have to calculate the phase 'angle' of 500Hz based on a 0.4ms delay, which is where I plan to crossover between the two speaker circuits. Is that correct?
That's a good tip. Thanks PRR! That appears to be the general consensus about BBDs.
That is the definition of an allpass filter...
The group-delay plot for the filter is what you want, tells you how constant the delay is across the band. In an active crossover the band of interest is often not the whole audio band making it easier to construct allpass filters that approximate constant group delay
Some instructive graphs here:
analog - ALL PASS Filter-Why the name filter - Electrical Engineering Stack Exchange