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| Re: 4pi build with stands finally realized [message #94427 is a reply to message #94426] |
Tue, 14 September 2021 07:04   |
Roger S.
Messages: 15
Registered: September 2021
Location: Norway
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Chancellor |
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Will try to do a soundcheck today, but work is calling, and I will be away 14 days. You see the rest of my system in the background. The 4pi's will be matched to the 21" subwoofers in the corner. They are Precision Devices PD2150 tuned to 18Hz, driven by a bridged Crown K2. I have used this setup for years now, and its a really fun combo. They are not flanking subs as they are positioned now, but I am going to try that when I come home. I have another K2 used for midbass duty on my former fully active setup, and a Crown Ct-4150. The plan is to run the woofer with the K2, and tweeter with 2 channels from the Ct-4150 as this has 10db better S/N ratio and it sounds really smooth. Proper gain matching between the amps will of course be done.
I have a minidsp Studio as preamp with Dirac. This is connected to minidsp 10x10HD, which will be used as dac for a while. Listening impressions and measurements will be posted when I find the time. The build started three weeks ago, and a lot of hours are spent. I am really looking forward to hear them, but from what I see from the measurements, rewievs and thorough documentation from Wayne, I am pretty confident they sound nice. Small adjustments in tonal balance can easily be done with dsp. Properly integrated drivers and good power response like in the 4pi is what I look for in a speaker. Poor engineering can not be fixed by dsp/room correction as some tend to believe. Tonal balance is easy.
Many thanks to Wayne and other builders for design and inspiration, and I hope this build will inspire others too.
I will be back with more when I have done some testing 
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| Re: 4pi build with stands finally realized [message #94536 is a reply to message #94535] |
Fri, 01 October 2021 08:38 |
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Wayne Parham
Messages: 18792
Registered: January 2001
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Illuminati (33rd Degree) |
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It's hard to say from your response chart, because it looks like a mix of on-axis and off-axis, e.g. power response. Were you measuring indoors, perhaps?
If so, measure outdoors or setup your equipment for a pseudo-anechoic measurement. Place the microphone directly on-axis around two or three feet away from the cone. Do this on a baffle or in a cabinet so reflections from the rear of the cone don't interfere with the sound emanating from the front of the cone.
To be honest, I'm worried about that notch at 1.3kHz because I see a lot of substandard cones get weird in that area. The aftermarket cones don't do well above 1kHz. But before we get worried about that, let's make sure you have good measurements because a lot of other things can cause that dip too. Could be self-interference from reflections or from the back-wave or both.
If you measure outdoors, or if you use gating to create a pseudo anechoic chart, what you should expect to see on-axis is rising response between 800Hz and 1.6kHz, and rolloff above that. On-axis, there's with a sharp dip around 2.6kHz. When you go far off-axis, at 45°, response starts to fall above 500Hz. It's down 3dB around 800-1000Hz and 6dB around 1.2kHz. Above that, it falls off rapidly, punctuated by a sharp dip around 1.3kHz.
The JBL spec sheet shows what you can expect to see from the raw driver:
And the four π loudspeaker measurements show what you can expect to see from the system:
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