| Compact version of 6Pi / 7Pi [message #98714] |
Sat, 21 June 2025 07:38  |
Henner
Messages: 4
Registered: January 2024
Location: Sydney Australia
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Esquire |
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Dear Wayne,
Thank you for your great service to the DIY community!
For me, the holy grail are low-distortion constant directivity corner-horns for all the reasons you've already explained very well. Matured designs are very rare to find, and yours are by far one of, if not the best!
I have a few questions regarding the 6/7Pi, as well as modifications.
1) I'm trying to decide between the 6Pi and the 7Pi, each configured with the best drivers you have as options. My current listening room is relatively small at 20m². In the future we plan to move, but I don't expect a room larger than 40m². I primarily listen at low to medium volume levels. My main power amp is a 25W FirstWatt F5.
Which one do you recommend, the 6Pi or 7Pi? And what's the reason for your recommendation?
2) Most of us have partners with low tolerance for large speakers in the living room—so does my wife. Her aesthetic requirements are fairly basic though. It has to be relatively low in height and square in shape, at least square when covered by acoustic fabric. In addition, she'd like to put things on top of it, possibly even a similar-sized shelf.
As I like keeping my wife happy and I'm also an engineer, I thought I'd try to modify the 6/7Pi to make them wife-compatible. I started this a couple of years ago, then my work got busier and the project stopped. Today I have a free day and here I am. Back then I asked Wayne some basic questions on modification and he gave me the OK as long as I keep the internal volumes the same. I've gotten a little further since then and have more questions. I thought I'd post this in the forum as others might find it useful.
My first questions focus on the bass horn of the 6/7Pi.
The 1st image shows the 6/7Pi. The 2nd and 3rd images show the original bass horn and its floor print. In blue is the reflex chamber. The 4th and 5th images show the modified bass horn with floor print. Again, the reflex chamber in blue. I followed the edge of the wall to create a square. This extended the cross-section of the reflex chamber (blue) by 25%. This allowed me to lower the height of the bass horn by 25% while keeping the chamber volume unchanged. Good—wife is 25% happier.
2a) My first question relates to the opening of the mouth of the bass horn. Now it is 25% shorter, thus 25% smaller in cross section. The width and all other angles remained the same. Will that affect the frequency response in a noticeable way? If yes, should I adjust the mouth's width, or do I have to revert back to the original height?
2b) The front of the bass chamber changed from flat to pointed. Will that make any notable difference to the frequency response? I assume not, but I thought I'd ask to be sure.
2c) I noticed that the section between the driver and the horn's mouth (the section that sits in the room's corner) is not increasing consistently towards the mouth. It appears to be a front chamber rather than just an expanding horn. I indicated in red what I would have expected the section to look like. Was this "front chamber" intended for acoustic reasons, or was it a design simplification to make things easier for the person who builds the enclosure? If it was for acoustic reasons, what does the "front chamber" do? I ask because I failed to simulate it with Hornresp.
2d) I made two variations of the 6/7Pi that have the compression driver positioned between the mid-horn (top) and the bass horn (bottom).
(I am aware that the compression driver is best positioned at the ear level of the listener. Yes, I might run into trouble with furniture between a sitting listener and the horn.)
Kindly tell me which of the following versions would be preferable and why.
Version A allows the unused volume around the compression driver to be added to the reflex chamber of the bass horn. That would allow a potential further reduction in overall height by keeping the reflex chamber's volume unchanged. However, the mouth of the bass horn and the mid-horn would be separated by 16cm. This affects the overlapping vertical radiation lobes of course. Would that be noticeable?
Version B sacrifices the previously added volume to the reflex chamber (from the unused volume around the compression driver) to allow for more mouth height of the bass horn. Thus eliminating the previously described separation between the mid-horn and bass horn.
3) If I were able to scale up your compression horn to the size of the mid-horn and use that instead of the one with flat sides as in your drawings, would that give any advantages?
To the members of the forum: Once I refine the design a little more, and Wayne gives his OK, I can make the CAD file available for everyone to use. 
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Attachment: VersionB.jpg
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Attachment: VersionA.jpg
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Attachment: 2c.jpg
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Attachment: image 1-5.jpg
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