No need to wax lyrical about Synergy-type horns. Lots of advantages obviously.
My question: why are midrange ports not more common on flat baffle speakers, i.e. speakers with 180-degree waveguides? The same caveats apply, such as minimizing midrange chamber volume, avoiding internal resonance and phase cancellation, etc. But I could see various situations where the use of port-fired mids would significantly reduce c-c distance to the tweeter, compared to conventionally-exposed direct-firing mids.
Of course, one big downside: midrange drivers are often physically delayed vs the tweeter right from the get go, so you're almost forced to use DSP to correct the time delay if hiding the mids behind the baffle... besides that and additional cost/complexity, what else? You can fit larger, more sensitive, higher power-handling, lower distortion drivers for the same c-c distance, generally speaking, not to mention achieving c-c distance that would otherwise be impossible.
My question: why are midrange ports not more common on flat baffle speakers, i.e. speakers with 180-degree waveguides? The same caveats apply, such as minimizing midrange chamber volume, avoiding internal resonance and phase cancellation, etc. But I could see various situations where the use of port-fired mids would significantly reduce c-c distance to the tweeter, compared to conventionally-exposed direct-firing mids.
Of course, one big downside: midrange drivers are often physically delayed vs the tweeter right from the get go, so you're almost forced to use DSP to correct the time delay if hiding the mids behind the baffle... besides that and additional cost/complexity, what else? You can fit larger, more sensitive, higher power-handling, lower distortion drivers for the same c-c distance, generally speaking, not to mention achieving c-c distance that would otherwise be impossible.
There are a number of disadvantages:
1) Tweeter has to play lower due to mids bandpass
2) There is no dispersion control, Synergy-type horn the radiation is constrained by the horn but in the flat baffle it's constrained by the aperture size
3) Acoustic issues with the bandpass arrangement: compression, port noise, resonances
4) Mids are physically further away from each other than in a horn making (1/3)(lambda) spacing at crossover harder to achieve
In the right design the benefits could outweigh the disadvantages but the arrangement is less advantageous that in the Synergy scenario. The Small Syns design uses a unity horn and slot loaded woofers behind the baffle. A related idea to reduce c2c distance is produced by Martin Audio.
1) Tweeter has to play lower due to mids bandpass
2) There is no dispersion control, Synergy-type horn the radiation is constrained by the horn but in the flat baffle it's constrained by the aperture size
3) Acoustic issues with the bandpass arrangement: compression, port noise, resonances
4) Mids are physically further away from each other than in a horn making (1/3)(lambda) spacing at crossover harder to achieve
In the right design the benefits could outweigh the disadvantages but the arrangement is less advantageous that in the Synergy scenario. The Small Syns design uses a unity horn and slot loaded woofers behind the baffle. A related idea to reduce c2c distance is produced by Martin Audio.
1) Agreed, for the most part. But to minimize c-c distance this is a given anyway.
2) I'm not sure I understand this, on a flat baffle you're not expecting any dispersion control anyway other than half-space radiation above baffle step.
3) Yes, exactly the same as in a Synergy horn. Readily mitigated.
4) Agreed, however, in the concepts I've investigated the ports are still closer to each other and to the tweeter than if the mids were fully exposed as on a conventional baffle.
Also, if you have a rigid-cone mid that has a strong resonance above passband, you can attentuate acoustically by using the chamber volume to low-pass. Might be more of an academic exercise than a practical approach, but still an interesting idea I think.
Regarding 2) the effective piston diameter of the midrange constrains the radiation, this is reduced to the port diameter in the bandpass
For sure.
But if we are not using a waveguide on the tweeter - which we are not, because this is a flat baffle and not a Synergy horn - then the tweeter will be fully half-space, why try to "neck down" the radiation pattern of the mid? Would be quite strange IMO to have a bottleneck shape in the off-axis contours.
Sorry if I misunderstand.