Home » Sponsored » Pi Speakers » 4 Pi and 7 Pi bass response- More similar or different? (4 Pi VS 7 Pi )
4 Pi and 7 Pi bass response- More similar or different? [message #61567] Wed, 16 December 2009 22:57 Go to next message
Psychoacoustic is currently offline  Psychoacoustic
Messages: 75
Registered: May 2009
Viscount
G'day Gents,
I have 4 Pi derivative speakers made with JBL 4507 utility cabs (2226H), DE250, 4 Pi Eminence horn and 4 Pi X/O. The 4507 have all four ports open, which tunes the box to 40Hz.
When asked to comment on 4 pi VS 7 Pi Wayne wrote,
'The midhorn takes the load off the woofer, so it doesn't run as wide bandwidth. This reduces IMD and makes midrange smoother'.
Is this the main difference, or one of a few? I'm also curious to learn about how the two different sized cabinets and X/Os reproduce bass with the same model woofer; would you describe the bass produced as being more similar or different?
Thanks.

Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61568 is a reply to message #61567] Thu, 17 December 2009 09:44 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18727
Registered: January 2001
Illuminati (33rd Degree)

To me, they definitely sound more alike than different. All my speakers have basically the same tonal balance, and they're all designed to generate a uniform pattern. They all use the same tweeters and woofers, at least in "families" - three π and six π have the same woofers, four π and seven π do too. So when you compare, say a four π and seven π with JBL 2226 and DE250 drivers, you have two speakers that sound very much alike. They're exactly the same above 2kHz and depending on placement, exactly the same from 50Hz to 200Hz too. The only real difference is between 200Hz and 2kHz. Of course, that's a real important region, arguably the most important one.

To me, the π midhorn loaded with the Delta 10 has a real SET-like sound whereas the direct radiating 2226 sounds more like a very accurate FET. Without analyzing distortion or spectral balance, that's how I'd best describe them. The 2226 is very clear sounding when run through the midrange, no hint of breakup or anything like that. But the midhorn sounds silky smooth. Both are actually very low in distortion and smooth in response, so neither is a clear "winner" in terms of either metric. Both are excellent.

Remember too, the placement environment. That's actually the biggest thing, in my opinion, to influence the sound. Do a little experiment: Take a radio or speaker and listen to it when it is sitting out in the open, radiating into freespace. Now walk with it while still playing and sit it right next to the wall, perhaps on a window sill facing you. Listen to the difference in sound as you get close to the wall. Now take the same radio and sit it in a trihedral corner. Hear the big difference in sound? It gets louder, its tonal balance changes and even the ambient room "echo" is different.

When a speaker is put in the corner, it is louder overall and usually sounds like the bass is a bit more prominent. This is all a result of directivity, as the sound coming from the speaker is forced into a pattern set by the walls. It cannot radiate omnidirectionally, even at low frequencies, because the wall angles force it into the room, just like a horn. The smaller the speaker (baffle), the more pronounced the effect because on larger speakers, the baffle itself limits the radiating angle to at least half space, the larger the baffle, the lower the frequency before it becomes omnidirectional.

When a speaker is put in the corner, it is louder overall and usually sounds like the bass is a bit more prominent. This is all a result of directivity, as the sound coming from the speaker is forced into a pattern set by the walls. It cannot radiate omnidirectionally, even at low frequencies, because the wall angles force it into the room, just like a horn. The smaller the speaker (baffle), the more pronounced the effect because on larger speakers, the baffle itself limits the radiating angle to at least half space, the larger the baffle, the lower the frequency before it becomes omnidirectional.

The repercussions of this are profound. What it means is that when a speaker is designed to be placed in the corner, it should be voiced to compensate for the spectral shift that happens when placed in the corner, i.e. slight tilt upward in the bass. It also means that the sound at very low frequencies will have constant directivity all the way down, to the limits of the room. The room is the largest acoustic feature in the listening envirnoment, and you're usually "fighting it" to get response right. But in the case of the π cornerhorns, it becomes an advantage. Most modern (waveguide and) matched-directivity two-way speakers can only provide constant directivity above 2kHz but the π cornerhorn is CD fully a decade lower, all the way down to below 200Hz, limited only by the room modes below the Schroeder frequency.

Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61569 is a reply to message #61568] Thu, 17 December 2009 18:32 Go to previous messageGo to next message
tom-m is currently offline  tom-m
Messages: 56
Registered: December 2009
Location: Texas
Baron
Hi,
I may be building one of these soon. In your description of the midrange, what do "SET" and "FET" mean?

Thanks,
Tom
Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61570 is a reply to message #61567] Thu, 17 December 2009 19:16 Go to previous messageGo to next message
Psychoacoustic is currently offline  Psychoacoustic
Messages: 75
Registered: May 2009
Viscount
Wayne, thank you for taking the time to explain the design parameters. Answers my question... and more!
I'd also like some descriptive clarification on the difference between FET and SET. Detailed versus smooth?
I already have 7 Pi crossovers from you. All I would have to do is get the Delta 10s and build the cabs. I'm running a valve amp for the mains. A SS amp drives two 3 Pi subwoofers. Really satisfied with the 4 Pi bass response, but am curious what midwoofers would do for mids.

Merry Christmas to all.
Ant
Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61571 is a reply to message #61569] Thu, 17 December 2009 19:28 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18727
Registered: January 2001
Illuminati (33rd Degree)

tom-m wrote on Thu, 17 December 2009 18:32
I may be building one of these soon. In your description of the midrange, what do "SET" and "FET" mean?

SET is an abbreviation for single ended triode. FET is field effect transistor. I was trying to describe the difference as being like a high quality Class A tube amp compared with a high quality Class A solid state amp.

Psychoacoustic wrote on Thu, 17 December 2009 19:16
I'd also like some descriptive clarification on the difference between FET and SET. Detailed versus smooth?

Both are detailed, both sound very accurate. But I'd say the 2226 midrange is more towards the analytical, and the midhorn is more, well since I can't say "smooth" (both are smooth), so how 'bout "creamy". http://www.audioroundtable.com/emoticons/uhh.gif Maybe creamy-dreamy.

The midhorn isn't what I'd call laid back, nor is it forward. It's pretty neutral sounding. I dunno. Neither really add anything or take anything away and both can be played very soft and delicate or they can be run full tilt, balls out, louder than hell. They're both very detailed and accurate even when you put the power to them.

Psychoacoustic wrote on Thu, 17 December 2009 19:16
I already have 7 Pi crossovers from you. All I would have to do is get the Delta 10s and build the cabs. I'm running a valve amp for the mains. A SS amp drives two 3 Pi subwoofers. Really satisfied with the 4 Pi bass response, but am curious what midwoofers would do for mids.

Well, that's perfect. My setup is very much like that, Class A FET for the subs and Class A triode for the mains. I have four π's in my living room and seven π's in my office. Both have JBL 2226 woofers and DE250 tweeters. So I get to enjoy both often, daily, for several hours.

To me, they're both great. The big advantage of the seven π is its magic imaging, but you can get a lot of that with four π's if you set them up properly. Still, the reverberent field is perfect with the sevens, all the way through the audio range, even in the important midrange. So there isn't a bad seat in the house when you run sevens. Not that the fours lack anything in seat to seat coverage, but no DI-matched (waveguide) two-way speaker is CD through the midrange. The π cornerhorn is the only configuration I know of that delivers constant directivity through the whole audio range from the Schroeder frequency up. The downside is they need a specific room layout to use them properly. If you have the right room, they can't be beat. But if not, I'd rather have four π speakers than improperly placed sevens.


Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61572 is a reply to message #61567] Thu, 17 December 2009 21:12 Go to previous messageGo to next message
Psychoacoustic is currently offline  Psychoacoustic
Messages: 75
Registered: May 2009
Viscount
This helps to make an imformed decision. Unlike other speakers in the stable, I'm never wanting for anything for the 4 Pi's- just curious about the 7 Pi and in a situation to sate that curiosity. My guess is that my treated room would complement the 7 Pi's intended application. Please see photos:
http://audioroundtable.com/forum/index.php?t=msg&th=11661&start=0&
thanks again.
Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61573 is a reply to message #61572] Fri, 18 December 2009 09:09 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18727
Registered: January 2001
Illuminati (33rd Degree)

Looks like the first room (with drapes on the window) would be great for π cornerhorns. The second one (with blinds for the window) has an opening near the corner that would make them not work right.

Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61574 is a reply to message #61573] Fri, 18 December 2009 09:51 Go to previous messageGo to next message
tom-m is currently offline  tom-m
Messages: 56
Registered: December 2009
Location: Texas
Baron
Thanks for the info Wayne. I think I will go for the "creamy" sound of the midhorn. Very Happy

But with my room, I cannot do cornerhorns. I think I read somewhere that the midhorn and tweeter of the 7 pi could be used with a woofer in a bass reflex box, right? If this will work, I think this is what I will build. A 15" 3 way using your midhorn and tweeter. Would the 7 pi crossover work for this type of speaker?

Thanks,
Tom
Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61575 is a reply to message #61574] Fri, 18 December 2009 10:41 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18727
Registered: January 2001
Illuminati (33rd Degree)

Yes, that will work. But when not positioned in the corners, the speakers by themselves can't control the pattern to as low a frequency. The midhorn isn't large enough. Also bear in mind that the position and orientation of the speakers has a lot to do with their performance. For best results, set them up as described in the post below:

Re: 4 Pi and 7 Pi bass response- More similar or different? [message #61576 is a reply to message #61567] Fri, 18 December 2009 16:52 Go to previous messageGo to previous message
tom-m is currently offline  tom-m
Messages: 56
Registered: December 2009
Location: Texas
Baron
Is this the correct build specs for the midhorn?

http://www.audioroundtable.com/PiSpeakers/messages/14408.html

tom
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