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7pi plans [message #69855] Sat, 22 October 2011 19:37 Go to next message
jgoodd8050 is currently offline  jgoodd8050
Messages: 28
Registered: February 2010
Chancellor
I think I'm ready for a copy of the 7pi plans.

Thanks very much.
Re: 7pi plans [message #69864 is a reply to message #69855] Sun, 23 October 2011 08:22 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18787
Registered: January 2001
Illuminati (33rd Degree)

You've got mail!

Re: 7pi plans [message #69904 is a reply to message #69855] Wed, 26 October 2011 21:59 Go to previous messageGo to next message
jgoodd8050 is currently offline  jgoodd8050
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How important are the verticle pieces that form the 45 degree angle at the back of the corner horn? Is the corner formed by the walls enough?
Re: 7pi plans [message #69906 is a reply to message #69904] Wed, 26 October 2011 23:08 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18787
Registered: January 2001
Illuminati (33rd Degree)

Those pieces are there for structural integrity. The back is just a positioning device.

Re: 7pi plans [message #70284 is a reply to message #69855] Fri, 25 November 2011 09:49 Go to previous messageGo to next message
jgoodd8050 is currently offline  jgoodd8050
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Registered: February 2010
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What is the low frequency cut off like for the 7pi? I'm trying get an idea of how low they go.

Thank you.
Re: 7pi plans [message #70286 is a reply to message #70284] Fri, 25 November 2011 11:16 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18787
Registered: January 2001
Illuminati (33rd Degree)

It's totally room dependant. The room sets the response below about 200Hz. And since they are designed to be used in corners, there is really no way to decouple the room response from the speaker response.

If you wanted to know how they would sound in an anechoic environment, you can look at the four π response curve. The problem is that this is probably pretty meaningless. There is a huge difference in the way a speaker acts in free space compared to the way it acys in eighth space. It is different in SPL, response and directivity.

To get a feel for the difference, listen to a portable radio set out in the open. Hold it in your hand and stand in the middle of the room. Listen to the tonal balance and the volume level. Now, walk over to the wall and set it on a countertop, table or shelf where the radio is sitting in a tridedral corner. You will notice an immediate and obvious increase in volume level, and the bass and midbass is made fuller. This is how corner loading affects the cornerhorn too.

None of that was as specific as I think you would like. The problem is I can't really be more specific than that. The response down low is too room dependent. I can only say that the bass is made fuller and the corner sets the directivity to a constant 90° above the Schroder frequency. It actually starts getting that pattern above about 100Hz, and is very well defined above 200Hz.

I think what might be more important to you is whether or not to use subs. I would suggest using them, yes. Even though the constant directivity cornerhorn increases bass output, it could still use some extra extension at the lowest bass frequencies. These are high-efficiency speakers, after all. And also, while directivity is constant above the Schroeder frequency, room modes influence bass coverage below that. A couple dedicated subs placed in opposite corners or at the center of the side walls will give increased bass extension and smooth the lower frequency room modes.

The constant directivity cornerhorn is really great down to about 100Hz or so, because the upper frequency room modes (100-200Hz) are mitigated by blending between the woofer and midhorn. The woofer is snuggled tightly into the corner, so there is no self-interefence notch from either adjacent wall or the floor. These two things really help maintain smooth response in the 100-200Hz range, which is such a problem for other loudspeaker configurations. But below 100Hz, the axial room modes dominate. So subs placed as mentioned above are ideal, providing increased extension and modal smoothing.

Re: 7pi plans [message #70289 is a reply to message #69855] Fri, 25 November 2011 11:52 Go to previous messageGo to next message
jgoodd8050 is currently offline  jgoodd8050
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Registered: February 2010
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I'm working on building the cabinets now so I'll have to test them out after completion. Maybe we can address the bass system when I have a better idea of what the room might need. Subs are definitely part of the plan.

Re: 7pi plans [message #70333 is a reply to message #70289] Wed, 30 November 2011 13:10 Go to previous messageGo to next message
tom-m is currently offline  tom-m
Messages: 56
Registered: December 2009
Location: Texas
Baron
Hi Wayne,
A few 7pi questions.

1. Eminence or JBL woofer. The polarity connection to the crossover is different for these 2 woofers. Their red and black terminals are opposite of each other? Meaning a positive voltage applied to the red terminal of each woofer, one cone would have outward movement, the other would have inward movement? I see in the doc, "We consider positive polarity to be that which creates positive pressure from a transducer when positive voltage is applied." So from your diagram, it looks like the JBL red and black are backwards, considering your statement. I just want to be clear as I will be using a different woofer.

2. Were do you put the speaker binding posts? I may put mine on the side of the cabinet.

3. Should be midhorn be attached to the bass cabinet, or just sitting on the bass cabinet?

4. Is the crossover mounted inside the bass cabinet? If so, we would need to run the wires for mid and tweeter back out the cabinet to the drivers.

Thank you.
Tom
Re: 7pi plans [message #70342 is a reply to message #70333] Wed, 30 November 2011 19:07 Go to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18787
Registered: January 2001
Illuminati (33rd Degree)

Answers by numbers:

1. The JBL 2226 is connected weird, in that positive voltage applied to the black terminal creates forward cone movement (away from the magnet). See "Notice for JBL Transducer Users" for more information.

2. There are two connection methods most commonly employed, and I've done both. One way is to mount the crossover in the bass bin along with the binding posts to connect wires to the amp. The outputs to the midhorn and tweeter then exit the bass bin, usually through separate connectors. The other method is to put the crossover and amplifier connection panel in a separate box which has outputs for the bass bin, midhorn and tweeter.

3. Some mount the midhorn permanently or semi-permanently atop the bass bin. I personally like to pin mine, using the same hardware that is used for dining table leaf inserts. See "Finishing details" for more information.

4. You can put the crossover in the bass bin or in a separate box. Either way, I like to run the wires out using speakon connectors or binding posts.

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