Has anyone been able to get a tuned port to work with success in a 2way MEH? I know danley uses them on his 3 way units, but then at the same time Iv been seeing folks on this forum not to happy with ports performance in their designs.
To be clear im not talking about the entry ports for the drivers but using the back phase of the speaker like a a hemholtz resonator to get extra low end, but with without the tube.
Seems like a waste to not use that energy.
What am I missing?
To be clear im not talking about the entry ports for the drivers but using the back phase of the speaker like a a hemholtz resonator to get extra low end, but with without the tube.
Seems like a waste to not use that energy.
What am I missing?
Any advice on specs to target?
In my simple understanding:
Are you implying the that desired port frequency should match the Fs of the driver?
In my simple understanding:
- tune the port and box to the desired lowest cut off
- place the port 1/4 wave away from that from the midway entry port cut off?
Are you implying the that desired port frequency should match the Fs of the driver?
I had reasonable success with the bass reflex output in the SynTripP MEH, but failure in terms of out-of-phase cancellations in the upper passband of the woofer due either to upper port resonance or leakage.
Sold the cabinets before noticing the difference in the upper response "with and without" ports in the early testing.
In a three-way, the woofer is usually crossed over below the problematic port resonance or leakage, so the above problem does not exist.
The actual port length may be increased by it's proximity to the cabinet sidewalls, making it more difficult to predict with simulations.
The conical horn-loaded output phase is shifted from a direct radiator, so the bass reflex alignment is different.
For example, the DSL SH-50 Fb (box tuning) appears to be at 90Hz (the lower impedance minima in the "imp mag" graph) which would normally be the -3dB point, while the low frequency "bump" maxima is at 70Hz.
The Fb that would be predicted with four round port holes only the depth of the horn wall (~18mm) in the net volume of the SH-50 would have a different "end correction" if placed elsewhere in the cabinet. The sidewall braces to the left and right of the ports in the above photo also increase the effective port length.
Lots of "moving parts", it won't be so simple, model using Hornresp MEH simulations for a starting point 😉 .
Art
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It's my understanding that it's a 6th order alignment with conical vents of differing flare frequencies, so as Art noted, 'lots of moving parts'.
OK
No, depends on the desired LF BW/response
So "leakage" is essential the upper and lower roll of frequencies of the port tuning, causing phase cancellation as it overlaps with the main drivers? If thats the case then wouldnt there be cancellations regardless of if the system on 3 way vs 2 way? or is there a timing situation where the (2) identical frequencies some how never "touch" in a 3 way system?
Is there any possibility of using some kind of "bucket" inside the box to phase cancel the offending frequency? or a 12db high pass cut at the main drivers at the offending frequency in a 2way, kind of allowing the port to take over below that cutoff?
you guys may have to dumb this down a little for me to fully grasp this.
Is there any possibility of using some kind of "bucket" inside the box to phase cancel the offending frequency? or a 12db high pass cut at the main drivers at the offending frequency in a 2way, kind of allowing the port to take over below that cutoff?
you guys may have to dumb this down a little for me to fully grasp this.
Not really following this 'leakage' bit in that my interest ended once I 'grokked' Tom's cryptic description of his new invention in a PM that became the Unity Horn and helped a bit here when folks were really struggling, so with that limitation and using it as a baseline plus from experience preferring a two octave 'subwoofer' limit for tapped horns:
200/2^2 = 50 Hz Fc
sqrt(50*200) = 100 Hz Fb BP6, so near enough 90 Hz with real world acoustics and the fact that the SH50 is rated @ 50 Hz proves the old adage of 'don't fix what ain't broke'.
200/2^2 = 50 Hz Fc
sqrt(50*200) = 100 Hz Fb BP6, so near enough 90 Hz with real world acoustics and the fact that the SH50 is rated @ 50 Hz proves the old adage of 'don't fix what ain't broke'.
By "leakage", I meant reflections from within the cabinet emitted through the port. The reflections may be in phase (constructive) or out of phase (destructive) or somewhere in between.
If a 12dB crossover at 400 Hz was used, any out of phase "garbage" emitted from the woofer through the port would be ~-12dB at 800 Hz, it won't cause much of a cancellation.
If the crossover was 800Hz, the 800 Hz garbage could cause a much deeper null.
Sealed mids have a "bucket" behind them, none of their rear energy is released through a bass reflex port.
You would have to give me some LF and HF driver and HP & LP frequency examples for me to understand what you are trying to achieve.
I may be using the wrong term. By "bucket" I meant a kind of resonant trap or tuned chamber inside the box, that i think creates an intentional standing wave of a certain frequency, that is then directed to the port. I think I ran across the concept in a transmission line thread.
--
BMS 4550
Cheap 8" or 10" Dayton level drivers, +-60HZ Fs but this may need to change
800Hz cut off
25"x25" +- horn mouth, 25" deep
+-77d primary angle with a transition to small 90d
Hoping my calcs get me down to a 140hz
--
So my thinking is: a high pass filter at 120hz+- on the woofers, and tuning the back wave port at 90Hz. But are we talking upper harmonics of the fundamental that are getting through the port also? Or unrelated random psycho waves?
I would prefer to be a purist, but would a traditional PVC pipe fitted to the port reduce the leaks? Or are harmonics inherent ?
--
BMS 4550
Cheap 8" or 10" Dayton level drivers, +-60HZ Fs but this may need to change
800Hz cut off
25"x25" +- horn mouth, 25" deep
+-77d primary angle with a transition to small 90d
Hoping my calcs get me down to a 140hz
--
So my thinking is: a high pass filter at 120hz+- on the woofers, and tuning the back wave port at 90Hz. But are we talking upper harmonics of the fundamental that are getting through the port also? Or unrelated random psycho waves?
I would prefer to be a purist, but would a traditional PVC pipe fitted to the port reduce the leaks? Or are harmonics inherent ?
Band stop filters, but it won't solve comb filtering if that's the problem.
That said, 'we' discussed this problem in the form of round Vs slot ports and their location with Tom obviously using round ports to get max gain; but for HIFI/HT, it in theory seems better to me to use one slit on each side designed to get a ~critically damped output.
That said, 'we' discussed this problem in the form of round Vs slot ports and their location with Tom obviously using round ports to get max gain; but for HIFI/HT, it in theory seems better to me to use one slit on each side designed to get a ~critically damped output.
The 10" would make it to ~700Hz before the 24dB/octave acoustical LP, 8" might make it to 800Hz.
The BMS 4550 will be ~-12dB in the 800Hz region.
Sealed, the woofer response will be ~-12 dB at 140Hz compared to the upper response peak near the acoustical LP.
The bass reflex port may increase response 3- 6dB around and above Fb, a HP at 120Hz would remove that gain.
"Psycho waves", sounds like a Hitchcock/Spielberg homage..
Speakers and bass reflex ports don't generate (much) harmonic distortion until driven past their linear range of operation.
Ports have an upper pipe resonance related to their length which is independent of the Fb resonance.
The pipe resonance may be in or out of phase with the speaker output.
Reflected internal waves of any frequency may also pass through the port, also in or out of phase with the speaker output.
Pipe resonance are inherent with ports regardless of the material they are made from.
The percentage of leakage of upper passband through a large port diameter relative to speaker output is greater than a smaller port.
A ducted port in a MEH may have no more sonic problems than a front-loaded BR cabinet.
Ahh, I need the error in my thinking.. And also seeing why this is such a challenge. Ill probably just stick to the basics for this first attempt at a MEH.
I got it to work with this one.
I needed 8" mid-low drivers to make f-6 @ 100Hz, to reach standard 100Hz sub cross target.
Right or wrong, I figure the ports work somewhat similar to any reflex design........
that some size air duct creates a Helmholtz resonance, and the air volume/cabinet volume determines strength of the resonance.
Just my simple way of thinking about how it works...
Anyway, I played with PVC pipe for ports, but ended up using wood ducts. Easy because a lid seals up both the driver chamber and posts.
Ended up with this before finishing/painting.
Here's the raw response of the 8"s. I don't remember how low the 8"s reached without the ports, just that they didn't get near close enough to hit my sub 100Hz target without adding the reflex ports.
I also tried adding PVC tube ports to a big MEH that had dual 18" for lows (as well as 12"s for mid-lows).
The ports were solely for the 18"s which were isolated from all other drivers. It failed miserably, I think because their wasn't enough box volume to allow the ports to work.
You might want to find Scott Hinson's MEH project...pretty sure he put in rearward facing reflex ports.