Ok, so I lied.
It's not a simple thing to design so that you get good results.
The simple part is understanding what the main design issues are. The front horn loading, the problem of driver selection WRT sensitivity & LF extension and how to meet the HF section.
To break it down further. That design with the sub added in (soulsheiksan's)?
Well, that is certainly an interesting option. But it's no longer an A7 except in terms of the visual impression. We can take that design as a way to analyze the A7, by separating the parts: HF (horn), Mids (front loaded horn/dynamic driver), Bass section.
IF you divide the box physically and make the front loaded horn ONLY run the mids up to the HF horn, the design equation changes dramatically since you no longer need to balance the parameters and frequency response of a single "mid/bass" driver for best results. This is an advantage but it is no longer actually an A7. Potentially much better than an A7, but more expensive (probably) to put together.
Now you can concentrate on the midrange driver, you can select the ideal rear volume and construction. The mid can now be a screamingly high output driver with a FLAT response out to >800Hz. They do exist. You'd likely want one that loaded will have an F3 >~100Hz, and has a response that USES the 140Hz horn flare rise to get a flat response (a little up at the LF limit is not all bad...) (also, this driver is likely not one that has a flat response, just a smooth response, when mounted in a flat baffle)
The problem then switches to matching the bass section successfully, and this may be more problematic since typically for subs to match the perceived "texture" of "fast" drivers is not easy, and also depending on what you do and how you build it, there may be an issue with the subs lagging the rest of the drivers in time. You can get a flat frequency response with great LF extension, but things like a bass drum hit may be somewhat amorphous to a critical listener as a result. Mounting the bass driver on the front will help to some extent... but again this is NOT an A7
You can think of this as a sub box, mid horn box, and a HF section box, but the LF and mids are in one enclosure for aesthetic reasons.
All in all, with a tri-amp or biamp system, it might be pretty nice doing it this way.
(the choice of the mid driver is hyper critical for best results...)
It's not a simple thing to design so that you get good results.
The simple part is understanding what the main design issues are. The front horn loading, the problem of driver selection WRT sensitivity & LF extension and how to meet the HF section.
To break it down further. That design with the sub added in (soulsheiksan's)?
Well, that is certainly an interesting option. But it's no longer an A7 except in terms of the visual impression. We can take that design as a way to analyze the A7, by separating the parts: HF (horn), Mids (front loaded horn/dynamic driver), Bass section.
IF you divide the box physically and make the front loaded horn ONLY run the mids up to the HF horn, the design equation changes dramatically since you no longer need to balance the parameters and frequency response of a single "mid/bass" driver for best results. This is an advantage but it is no longer actually an A7. Potentially much better than an A7, but more expensive (probably) to put together.
Now you can concentrate on the midrange driver, you can select the ideal rear volume and construction. The mid can now be a screamingly high output driver with a FLAT response out to >800Hz. They do exist. You'd likely want one that loaded will have an F3 >~100Hz, and has a response that USES the 140Hz horn flare rise to get a flat response (a little up at the LF limit is not all bad...) (also, this driver is likely not one that has a flat response, just a smooth response, when mounted in a flat baffle)
The problem then switches to matching the bass section successfully, and this may be more problematic since typically for subs to match the perceived "texture" of "fast" drivers is not easy, and also depending on what you do and how you build it, there may be an issue with the subs lagging the rest of the drivers in time. You can get a flat frequency response with great LF extension, but things like a bass drum hit may be somewhat amorphous to a critical listener as a result. Mounting the bass driver on the front will help to some extent... but again this is NOT an A7
You can think of this as a sub box, mid horn box, and a HF section box, but the LF and mids are in one enclosure for aesthetic reasons.
All in all, with a tri-amp or biamp system, it might be pretty nice doing it this way.
(the choice of the mid driver is hyper critical for best results...)
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Bear, Soulsheiksan, and others, thanks for the pictures and guidance. Today I had the idea of setting up a pair of active subs (Pioneer SW-8MK2) on a separate channel to get a practical sense of where I need to go as far as LF. I definitely need to expand the lower reach and if the unit adjustments are to be an indicator, at least down to 50Hz.
Bear, you gave me a lot to digest and I appreciate your time and expertise. I haven't studied TS parameters in over 30 yrs, but there are some really bright folks on this sight that do a great job of explaining them.
BTW, are there modeling/simulation software pkgs that are suited for enclosure like these? I see many that have the simpler enclosures sans waveguides.
Bear, you gave me a lot to digest and I appreciate your time and expertise. I haven't studied TS parameters in over 30 yrs, but there are some really bright folks on this sight that do a great job of explaining them.
BTW, are there modeling/simulation software pkgs that are suited for enclosure like these? I see many that have the simpler enclosures sans waveguides.
The only part you need to simulate is the same as any ported box enclosure.
(except for the rise from the front loaded horn, which you can simply draw onto the curve of prospective drivers to see what
they do... from about 140Hz up until it ceases to do much... so figure two octaves?)
I don't have a suggestion, but there are many freeware that do this. There's nothing to "study", you just drop in values and see the response. Your Vb is more or less fixed, unless you decide to partition, in which case change that constant. You'll see the trends pretty quickly when you vary Fs, Qt and VAS.
You are looking to identify potential parameters of existing drivers that might work in the enclosure.
For example a low Qt, high VAS driver will certainly require a very low Fs to get bass out.
Then if you increase the Qt, and or lower the VAS, you'll see the curve change, with more LF output.
Then also you'll see "peaking" of the response both across the passband and at the rolloff depending again on the
choice of these parameters PLUS the frequency you pick for the PORTs in the simulation.
If you like "deep bass" then 35Hz @ ~-3dB (or 4, 5, 6 dB) is a very good target. There is often "room lift" at the bottom, but not always... 40Hz. is a safe bet. A lot depends on the rate of rolloff below that point - with a ported system, that's usually pretty fast.
It's difficult to get high sensitivity and low bass, especially in this box size, but if you do not need high sensitivity because you will be using a high power amp, then you can do more with the design, including EQ.
If you want a "purist" and high sensitivity system to use with low power tube amps, then your design issues are different entirely from the above case.
(except for the rise from the front loaded horn, which you can simply draw onto the curve of prospective drivers to see what
they do... from about 140Hz up until it ceases to do much... so figure two octaves?)
I don't have a suggestion, but there are many freeware that do this. There's nothing to "study", you just drop in values and see the response. Your Vb is more or less fixed, unless you decide to partition, in which case change that constant. You'll see the trends pretty quickly when you vary Fs, Qt and VAS.
You are looking to identify potential parameters of existing drivers that might work in the enclosure.
For example a low Qt, high VAS driver will certainly require a very low Fs to get bass out.
Then if you increase the Qt, and or lower the VAS, you'll see the curve change, with more LF output.
Then also you'll see "peaking" of the response both across the passband and at the rolloff depending again on the
choice of these parameters PLUS the frequency you pick for the PORTs in the simulation.
If you like "deep bass" then 35Hz @ ~-3dB (or 4, 5, 6 dB) is a very good target. There is often "room lift" at the bottom, but not always... 40Hz. is a safe bet. A lot depends on the rate of rolloff below that point - with a ported system, that's usually pretty fast.
It's difficult to get high sensitivity and low bass, especially in this box size, but if you do not need high sensitivity because you will be using a high power amp, then you can do more with the design, including EQ.
If you want a "purist" and high sensitivity system to use with low power tube amps, then your design issues are different entirely from the above case.
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Put this another way.
IF you pick a port frequency (that being the volume and length of the ports), which the software will "design for you", then you will see that that resonance does not move, but the response for any give driver will alter depending on its parameters.
Sometimes you find that by altering the port freq a bit, you get a potentially "flatter" LF response... but when things are badly misaligned, you'll see a big slope down to the port/box frequency. Potentially this can be corrected with active EQ, big amps, and a super high power high output driver - but that is often the most expensive and difficult way to get things to work, and may or may not sound good to you.
Similarly, you can get a big "boost" up above this frequency, often in the 75Hz+ range. Again, this MAY or may not work into the overall design depending on the whole picture. That too is due to a different set of TS parameters.
etc.
try dorking with a simple bass box simulator
_-_-
IF you pick a port frequency (that being the volume and length of the ports), which the software will "design for you", then you will see that that resonance does not move, but the response for any give driver will alter depending on its parameters.
Sometimes you find that by altering the port freq a bit, you get a potentially "flatter" LF response... but when things are badly misaligned, you'll see a big slope down to the port/box frequency. Potentially this can be corrected with active EQ, big amps, and a super high power high output driver - but that is often the most expensive and difficult way to get things to work, and may or may not sound good to you.
Similarly, you can get a big "boost" up above this frequency, often in the 75Hz+ range. Again, this MAY or may not work into the overall design depending on the whole picture. That too is due to a different set of TS parameters.
etc.
try dorking with a simple bass box simulator
_-_-
No, Vas is the driver's compliance spec while the vent [to the first approximation] is part of a Helmholtz Resonator, which the driver's specs don't influence, i.e. one can design the vent without them: https://en.wikipedia.org/wiki/Thiele/Small
https://en.wikipedia.org/wiki/Helmholtz_resonance
That said, the 800/825/828 cabs small VoTT cabs are crude mid-bass BLHs if one leaves off the vent baffle boards, so a simple T/S box calculator will be off a bit, though unless tuning to the driver's Fs to get max bass efficiency when coupled to a high output impedance amp, box tuning [Fb] becomes a 'what sounds best overall' scenario where small errors aren't obvious due to both our poor hearing acuity down low combined with room modes dominating a speaker system's frequency response.
GM
Yes, perhaps I was not clear - the vent/port frequency is independent of VAS.
The driver's response is not. (as GM said)
We're all on the same page? 😀
_-_-
One thing I was not clear on, is that I replace the big open "vent' with a baffle board, sealed that includes 4 large diameter ports... this way they can be tuned.
The driver's response is not. (as GM said)
We're all on the same page? 😀
_-_-
One thing I was not clear on, is that I replace the big open "vent' with a baffle board, sealed that includes 4 large diameter ports... this way they can be tuned.
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