Home » Sponsored » Pi Speakers » 4 Pi and 7 Pi bass response- More similar or different? (4 Pi VS 7 Pi )
seven π photos [message #61723 is a reply to message #61722] Thu, 14 January 2010 19:32 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18297
Registered: January 2001
Illuminati (33rd Degree)

Here's a photo of a seven π cornerhorn at a regional audio show:

http://lonestaraudiofest.com/2007/Photos/DSCN2857.JPG


A close-up view:

http://lonestaraudiofest.com/2007/Photos/DSCN2934.JPG


Another close-up:

http://lonestaraudiofest.com/2007/Photos/DSCN2935.JPG


At an angle:

http://lonestaraudiofest.com/2007/Photos/DSCN2937.JPG

Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61726 is a reply to message #61722] Fri, 15 January 2010 15:31 Go to previous messageGo to next message
tom-m is currently offline  tom-m
Messages: 56
Registered: December 2009
Location: Texas
Baron
Hi Psychoacoustic,

That is a fun mix of music you have listed. Smile

The 15" woofer I will be using is the AE TD15M. I purchased a pair about 6 months ago. I knew I wanted a 15" 3-way using pro woofers and compression drivers, but did not know the exact design. Also, because I do not have measuring equipment, I would be hard for me to design a crossover from scratch. So after a lot of research, I think a modified Pi 4 would work well for me. And I can purchase the Pi 7 crossovers from Wayne.

Wayne, the high res pictures of the Pi 7 is helpful to see how you finished out the mid horn. Thanks.

Tom
Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61727 is a reply to message #61567] Fri, 15 January 2010 16:55 Go to previous messageGo to next message
Psychoacoustic is currently offline  Psychoacoustic
Messages: 75
Registered: May 2009
Viscount
Understand your hesitation to build a crossover without a reliable measurement system. Have been in the same predicament.
Can you compare response graphs between the woofers you have and those used in the 7 Pi design? Perhaps that would help?
A complete guess- integrating a woofer in a three-way system might be easier than a two-way?
Questions for the experts.
Best luck with it!
Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61728 is a reply to message #61567] Fri, 15 January 2010 22:01 Go to previous messageGo to next message
tom-m is currently offline  tom-m
Messages: 56
Registered: December 2009
Location: Texas
Baron
Wayne,
With the mid horn being 24" wide, but not using it in the corner, What is the lowest frequency that the horn will control the directivity? I have no idea, but my guess would be about 600-700 Hz?
Cornerhorns and constant directivity [message #61729 is a reply to message #61728] Fri, 15 January 2010 23:50 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18297
Registered: January 2001
Illuminati (33rd Degree)

You're about right. I wouldn't expect much directivity control below 500Hz in freespace. The corners set the pattern for a couple octaves below that. In my opinion, this is the biggest benefit from corner placement: It gives the loudspeaker designer the opportunity to create a pattern having constant directivity all the way down to the Schroeder frequency.

On a related aside, I love good horn loaded loudspeakers and have always built them. But it cracks me up to watch people talk about cornerhorns and focus on the acoustic loading of a truncated basshorn. To me, that is trivial compared to the possibility of constant directivity. To build a loudspeaker designed to be placed in a corner and fail to incorporate constant directivity horns or waveguides is a huge mistake. The biggest benefit of a cornerhorn is how it directs the sound field above the Schroeder frequency, not below it. A good cornerhorn is probably the only configuration I know of that can provide constant directivity all the way down to the Schroeder frequency, approximately 100Hz or so.

Re: 4 Pi and 7 Pi bass response- More similar or different? [message #62060 is a reply to message #61567] Sat, 13 March 2010 04:56 Go to previous messageGo to next message
Psychoacoustic is currently offline  Psychoacoustic
Messages: 75
Registered: May 2009
Viscount
Just curious- the 7 Pi is shown on the Pi website as a '600 watt speaker'. Is there any potential at loud volume levels to damage the DE-250 ('120 watt continuous program power capacity')with amps rated over 200 W RMS per channel? Also, is there any problem with heat dissipation when the crossover is mounted in a small, sealed box? Thanks.
Crossover considerations - power handling, frequency, slope, etc. [message #62061 is a reply to message #62060] Sat, 13 March 2010 10:35 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18297
Registered: January 2001
Illuminati (33rd Degree)

All of my speakers, and the components used within (crossovers, drivers, etc.) are rated to take the full listed power. One of the things I take as a design requirement is that the crossover deliver signals that the drivers can handle with respect to bandwidth, crossover slope, etc. I never publish a design that requires a driver or component to be derated due to power - instead, I design the system so it can be used to its maximum potential. Not only does this help protect them, but it also usually makes them sound better because they aren't stressed. Distortion is usually much lower and the overall sound is better when the system is designed this way.

I've examined this in some detail, various crossover types (first through third order, with and without compensation, Zobels, notch filters, etc.) and I've shown an analysis of the voltage (power) levels across each component in the document below:
Drivers usually have to be limited on the lower end (frequency and slope) to protect from overexcursion. Through the passband and approaching their upper range, drivers are more vulnerable to thermal overload, getting so hot the voice coil adhesive fails, unwinds and begins to rub or buzz. Another thing I consider a design requirement is that the components used in the crossover have sufficient voltage and current capacity to handle the full rated power. This usually means selecting capacitors with sufficient voltage limits and choosing resistors with appropriate power ratings. Coils aren't usually an issue, because if they aren't large enough to handle the current, they'll modify the transfer function due to excessive resistance. Most times, if the coil is large enough to sound good, it is large enough to take the current.

To answer your specific question about the DE250, or any of the compression drivers used in my designs, there are two issues to consider where power handling is concerned and my loudspeaker designs address them both quite fully. One is the thermal limit, set by passband power level, and the other is the maximum excursion, usually occuring near the lower cutoff point.

The passband power level is reduced 10dB by the crossover, mostly to match sensitivity with other drivers and to allow passive equalization for mass rolloff. A side effect of this is that it means power input to the loudspeaker system can be 10dB higher than the driver alone could handle. When the loudspeaker system is presented a signal at ~2kHz that would result in 600 watts across an 8Ω load (approximately 70v), the crossover network splits this signal out to the tweeter and sets the level, ultimately presenting a much lower signal that dissipates approximately 60 watts in the tweeter. So it is quite safe, nowhere near its limits.

The lower frequency excursion limits are a little more complicated, in that the horn provides acoustic loading and this sets the lower limit to some degree. At frequencies high enough that the horn is providing acoustic loading, excursion is reduced. Below that point, excursion rises rapidly and one thing compression drivers cannot handle is excessive excursion. The diaphragm will literally hit the phase plug and begin to make a clacking sound, sometimes even shatter. Long before that occurs, distortion goes through the roof, so this isn't something you want.

Even where the horn loads the diaphragm, excursion still rises as frequency goes down. So even though the horn is providing acoustic loading, even if it is used above cutoff, this is still not a guarantee that the driver won't reach its excursion limit. Excursion limits are so small many compression drivers rate them as having 0mm xmax, which isn't really the case, of course, they have to move to make sound. But the point is they are designed to move very little.

It is important to design the crossover so the crossover point is high enough and the slope great enough to reduce low frequency energy. This is what limits excursion - don't allow low frequency signals to be developed across the compression driver. You can get away with first-order slopes on a dome tweeter with wide surround, it has relatively large suspension travel (for a tweeter, anyway) and no phase plug to hit. But you really can't do this with a compression driver, at least not if you plan to ever use more than 10 watts. Granted, 10 watts is plenty loud on a driver like this, but still, I think it's important to design a speaker to allow it to reach its full potential. It lets you crank it up without fear, and even if you never do that, it still is better with respect to distortion.

Of course, all this has to be juggled with other competing priorities. The crossover isn't there just to protect the driver. It also has to achive flat response on-axis, and to provide the right phase relationships between sound sources to put the forward lobe and vertical nulls where you want them to be. Getting all these things right simultaneously is not trivial. But it is possible, and really should be done, in my opinion. Anyone can throw together a crossover that works, but to build a really great loudspeaker, you have to pay attention to all these details, to get them all right.

Re: 4 Pi and 7 Pi bass response- More similar or different? [message #62067 is a reply to message #61567] Sat, 13 March 2010 17:38 Go to previous messageGo to next message
Psychoacoustic is currently offline  Psychoacoustic
Messages: 75
Registered: May 2009
Viscount
Sensei- Thank you for taking the time, once again, to answer a question so informatively.
Re: 4 Pi and 7 Pi bass response- More similar or different? [message #62111 is a reply to message #61567] Tue, 16 March 2010 17:54 Go to previous messageGo to next message
Infrasonic is currently offline  Infrasonic
Messages: 17
Registered: March 2010
Location: Clovis, CA
Chancellor
Hi Wayne. 2nd time poster, long time lurker.

I have done tons of research on your site and I am getting close to ordering a trio of Pi4's (DE250+2226H) for new LCR's in my home theater. Similar to what some other recent posts have wrote.

I saw this thread and had a couple questions. For HT use would there be any benefit using the Pi7's over the Pi4? I won't be using any cornerhorns. Unfortunately, I don't have that option right now. I saw this pic and thought it was really cool:

index.php?t=getfile&id=140&private=0


Could the Pi7 work with a forward firing woofer section? I know the JBL has nice midrange though so I am unsure. I don't want to complicate my build anymore than it needs to be but if there are benefits I'd like to know.

Thanks.
Re: 4 Pi and 7 Pi bass response- More similar or different? [message #62114 is a reply to message #61567] Tue, 16 March 2010 18:29 Go to previous messageGo to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18297
Registered: January 2001
Illuminati (33rd Degree)

If you have the right corners, then sure, seven π cornerhorns are better, definitely.

They have two big advantages, first is the corner sets the pattern constant all the way down in frequency, clear down to the Schroeder frequency. This is where room modes begin to take over, making pockets that sort of overrule the launch directivity. Standing waves within the room modify the wavefront that would have existed outdoors or in a very large room. But from about 150Hz up, the cornerhorn makes a pattern with constant directivity, and I know of no other configuration that can do this. The second advantage is you split up the mids and bass, which improves IMD and also gives some smoothing of the upper modal region.

So if you have the right corners, use them. But if you don't, the DI-matched speakers are very close, especially when combined with multiple subwoofers. More info at the link below:

Previous Topic: Three Pi sub
Next Topic: 4Pi Plans please.
Goto Forum:
  


Current Time: Mon Jun 27 13:03:47 CDT 2022

Sponsoring Organizations

DIY Audio Projects
DIY Audio Projects
OddWatt Audio
OddWatt Audio
Pi Speakers
Pi Speakers
Prosound Shootout
Prosound Shootout
Smith & Larson Audio
Smith & Larson Audio
Tubes For Amps
TubesForAmps.com

Lone Star Audiofest