[josh358]

J Gordon Holt is right when he says that when a recording is made on site the ambience of the locale is already in the recording.  At least it is in analog made recordings.  This is what has kept me away from Maggies for so many years, but I'm trying to hear some 1.7's locally to see what I think in actual practice.  JohnR is calculating the delay as the time it takes to hit the wall and the time it then takes to reach the plane of the speaker coming the other way*.  I can give the speakers 5' off the wall and nothing more.  So, to calculate the time delay should I multiply the distance to the wall behind times 2?

Next question.  How low should the crossover point be to a single bass panel?  The reason I am asking this is because I would try to get by with one panel if the signal is undetectable as mono.  Or, is that even possible?

Thanks.

*Is that right, JR?

But note that all loudspeakers produce delayed reflections in the listening room. Maggies are no different in that regard, in fact, as dipoles, they dump 4.2 dB *less* energy into the room than omnis for the same direct level. And for this reason all speakers image best when out from the wall.

You're right that you double the distance in feet (round trip) to get the approximate delay in milliseconds. Five feet is fine, about the minimum that works well with dipoles. That's because a 10 ms delay is about the point at which reflections start contributing to a sense of ambiance rather than causing image shift. At five feet, you can expect massively spectacular imaging, e.g., wall melting away to open on a vast concert hall. It's just that at 15 feet, it's even more massively spectacular.

The main differences are this. Dipoles dump most of their energy front and back, and will give you a great sense of depth. True omnis like the MBL's radiate 360 degrees, and will give you a strong sense of depth, and of width. Most conventional boxes are omni in the low frequencies and cardioid in the highs, because the box blocks the high frequencies and keeps them from reflecting off the front wall. This is bad. It makes them image poorly. However, they do send a fair amount of sound to the sides, so generally have more apparent width (outside of the stereo speaker spread) than dipoles, but not omnis. In all cases, you want to obey the five millisecond rule in the directions that they radiate, e.g., it's critical to keep an MBL 5' from a side wall but not a Maggie, because being a dipole it doesn't radiate much there.

By the way, Holt wrote a column in which he explained why we needed these reflections with stereo recordings. It was quite a few years after his 901 review and it's up on the Stereophile site. His thesis as I recall was that the ear doesn't detect ambiance as ambiance if it comes from the same direction as the direct sound source, e.g., the speakers themselves. If you *don't* want the speaker to add reflections, you can always use absorption at the reflection points, but having spent many years in relatively dead recording studios I can tell you that you probably don't really want to. It just doesn't sound real on recordings made in a real acoustical space. It can sound uncannily real on individual voices and instruments, though, there have been times I turned around because I thought someone was talking to me in the control room when it was actually someone talking into an open mic.

[JohnR]

I can give the speakers 5' off the wall and nothing more.  So, to calculate the time delay should I multiply the distance to the wall behind times 2?
...
*Is that right, JR?

Generally that's about right. To get an exact figure, this is a handy calculator: http://mehlau.net/audio/floorbounce/

(Turn it on its side for the walls.)

[josh358]

Aha, Google image search reveals all:

I also found http://www.avguide.com/review/magnepan-s-mini-maggie-speaker-system-revisited-playback-53?page=1, which says "DWM uses a planar magnetic mid/bass panel that, by design, features dual conductors or “voice coils” (one set for the left channel of the Mini-Maggie system, the other for the right channel). Note, however, that while the DWM panel can be used with two-channel inputs, it also works fine with a single-channel input."

Great find!

[jimdgoulding]

Thanks Josh and John for your replies.  Nicely comprehensive.  I understand.  Cheers.  Because I listen mostly to acoustic music made on location I am excited to demo the 1.7's at my earliest.

Think I can get some improvement with one bass panel?  I know two would be better but that's not the question.  Should the bass panel be out from the wall, too?  Is it bi-directional like the main panels?  Thanks in advance.

[josh358]

Thanks Josh and John for your replies.  Nicely comprehensive.  I understand.  Cheers.  Because I listen mostly to acoustic music made on location I am excited to demo the 1.7's at my earliest.

Think I can get some improvement with one bass panel?  I know two would be better but that's not the question.  Should the bass panel be out from the wall, too, and is it bi-directional like the main panels?  Thanks in advance.

The general rule is that bass is non-directional for most people below 80 Hz. A single panel is used with the MMG setup and it gives good results even though it's crossed over higher, but in the case of the 1.7's you'd be running the DWM's in parallel so I think you would want two DWM's, one for each side. But you'd have to ask Wendell to be sure, I'm just guessing here but he's the one who's actually tried them.

The bass panels produce the most bass against the side wall. They should be out from the front wall like the mains, if that's what you mean. They have to be the same distance from the listener as the mains, less 12" or the phasing won't be right.

They do radiate to both the front and back, like the mains.

[jimdgoulding]

Thanks, Josh.  I remember now seeing the recommended way the panels are set up at the Maggie's site and that would work well in my room.  Where ya'll put all these amps?  I have two monoblocks for the main speakers.  Other than those, I would be outta pocket some more moola.  I don't suppose they are active? 

[josh358]

Thanks, Josh.  I remember now seeing the recommended way the panels are set up at the Maggie's site and that would work well in my room.  Where ya'll put all these amps?  I have two monoblocks for the main speakers.  Other than those, I would be outta pocket some more moola.  I don't suppose they are active?

Luckly, if your amps can drive a 4 ohm load as I'm sure they can, you don't usually need extra amps. You just hook them up in parallel with your main speakers, usually with a resistor to reduce the level a bit. The resistor keeps the impedance from falling too low.

[jimdgoulding]

Luckly, if your amps can drive a 4 ohm load as I'm sure they can, you don't usually need extra amps. You just hook them up in parallel with your main speakers, usually with a resistor to reduce the level a bit. The resistor keeps the impedance from falling too low.

Oh, wow.  That's certainly what I would try.  My amps are Kenwood L07M's rated at 150w into 8ohms.  I don't know how stout they are at 4.

[josh358]

Oh, wow.  That's certainly what I would try.  My amps are Kenwood L07M's rated at 150w into 8ohms.  I don't know how stout they are at 4.

See if you can find current specs for your amps. If not, you can check to see if the specs double into 4 ohms, that's a sign of good current headroom and chances are if they can do that they'll be OK with 3 ohms or whatever you'll end up with after you put in the resistors (hard to say for sure since you select the resistors to match the bass level to your room and system).

[jhm731]

Oh, wow.  That's certainly what I would try.  My amps are Kenwood L07M's rated at 150w into 8ohms.  I don't know how stout they are at 4.

See:
http://www.thevintageknob.org/kenwood-L-07M.html

[jimdgoulding]

See:
http://www.thevintageknob.org/kenwood-L-07M.html

Power :

1x 150W (20Hz...20Khz, 8 Ohm, 0,008% THD) 0,007%THD

Continuous power :

1x 150W (8Ohm, 1Khz)

Dynamic power :

1x 200W (4Ohm, 1Khz)

1x 300W (4Ohm, 1Khz) 1x 250W

Well, what do you guys think of these specs from the link provided by most cool jhm ?  Help me understand the bit on the end of the following-  1x 300W (4Ohm, 1Khz) 1 x 250W (?).  Thanks.   

[Don_S]

Take a closer look at the original spec page.  Notice some specs are in yellow and some are in white.  The specs refer to two different versions of the amp.

Most of the specs are yellow and for the L-07M.  Where the specs are different for the MII they are in white.

Per the website: L-07M (L-07MII in off-white)

Power :

1x 150W (20Hz...20Khz, 8 Ohm, 0,008% THD) 0,007%THD

Continuous power :

1x 150W (8Ohm, 1Khz)

Dynamic power :

1x 200W (4Ohm, 1Khz)

1x 300W (4Ohm, 1Khz) 1x 250W

Well, what do you guys think of these specs from the link provided by most cool jhm ?  Help me understand the bit on the end of the following-  1x 300W (4Ohm, 1Khz) 1 x 250W (?).  Thanks.

[jimdgoulding]

Thanks, Don.  If I'm reading the bottom line right, the power doubles into 4 Ohms, 150w to 300w for the LO7 and 250w for the Mark II.  The line just above, however, reads only 200w but what the difference is, is unclear to me.  Any guesses as to why there is a difference?  And if I were to hook up a bass panel in parallel with a main panel to the amp, what if anything happens to the dynamic output?  Still capable of 300 watts?  Thanks.

See:
http://www.thevintageknob.org/kenwood-L-07M.html

And, do the 1.7's require a lot of damping factor to control the panels?  100 (8 Ohms) enough?  Is more desirable?

[Don_S]

Jim,

I understand your question. I did not see that discrepency before. I can't make sense out of that part of the data either.  It almost looks like a typo and the last line was supposed to be for 2Ohms although I see the speaker usage rating is 4-16Ohms.  Yes, definitely 

Thanks, Don.  If I'm reading the bottom line right, the power doubles into 4 Ohms, 150w to 300w for the LO7 and 250w for the Mark II.  The line just above, however, reads only 200w but what the difference is, is unclear to me.  Any guesses as to why there is a difference?  And if I were to hook up a bass panel in parallel with a main panel to the amp, what if anything happens to the dynamic output?  Still capable of 300 watts?  Thanks.

See:
http://www.thevintageknob.org/kenwood-L-07M.html

And, do the 1.7's require a lot of damping factor to control the panels?  100 (8Ohms) enough?  Is more desirable?

[josh358]

Thanks, Don.  If I'm reading the bottom line right, the power doubles into 4 Ohms, 150w to 300w for the LO7 and 250w for the Mark II.  The line just above, however, reads only 200w but what the difference is, is unclear to me.  Any guesses as to why there is a difference?  And if I were to hook up a bass panel in parallel with a main panel to the amp, what if anything happens to the dynamic output?  Still capable of 300 watts?  Thanks.

See:
http://www.thevintageknob.org/kenwood-L-07M.html

And, do the 1.7's require a lot of damping factor to control the panels?  100 (8 Ohms) enough?  Is more desirable?

Hard to make sense of those specs. "Dynamic power at 1 kHz" doesn't really mean much. The damping factor is well past the point of overkill with any speaker: the driver coil and speaker cable will be the limiting factor here.

[jhm731]

"What's the difference between Continuous RMS and Dynamic Power?

Many people confuse these specifications, so I will try to give you a simplified, non-technical explanation. Continuous RMS Power, is the spec that really tells you how powerful an amplifier is. RMS power is expressed in watts. A typical specification might read 100 watts RMS into 8 ohms from 20Hz-20KHz at .01% THD. What this means, basically, is that the amplifier will deliver 100 watts into an 8-ohm speaker from 20Hz to 20Khz? This frequency range is basically the entire audio range that an individual can hear. The THD spec stands for Total Harmonic Distortion: This is the amount of distortion the amplifier will introduce into the original signal. Any high quality amp made today has extremely low distortion ratings. The human ear cannot hear anything under 2%. For the most part, when you are considering purchasing an amplifier, you can disregard the THD specifications. Dynamic Power, is a little more difficult to understand. This is a test of the amplifier's ability to go beyond its continuous RMS power for a very short time period. We are not talking minutes or even seconds here. We are talking milliseconds or thousandths of a second. A musical transient peak, such as a cymbal crash lasts only a very short time. Dynamic power is usually measured into 8 ohms, but specifications are generally also published for 2, 4, and 6 ohm loads as well. To keep things from getting too complicated, we will concentrate on the 8-ohm figures. To measure dynamic power, an amplifier is fed a 1000 Hz signal for 20 milliseconds then allowed to rest for 480 milliseconds. The amplifier volume control is turned up until the amp reaches the clipping point. At that point, the amp has reached its instantaneous peak or dynamic power output. Like the continuous power rating, dynamic power is expressed in watts. The figure is usually significantly larger than the RMS power rating, and should not be confused with the continuous power ratings of the amplifier. A dynamic power rating into a figure such as 1 or 2 ohms does not mean that the amplifier can drive a speaker with a 1 or 2 ohm rating continuously. If you attempt that, the amplifier will either go into the protection mode or possibly cause damage."

,

[josh358]

Thanks Josh and John for your replies.  Nicely comprehensive.  I understand.  Cheers.  Because I listen mostly to acoustic music made on location I am excited to demo the 1.7's at my earliest.

Think I can get some improvement with one bass panel?  I know two would be better but that's not the question.  Should the bass panel be out from the wall, too?  Is it bi-directional like the main panels?  Thanks in advance.

Jim, I asked Wendell about whether you could use one panel, and he emailed back to say, "One might be too much, or too little. That is the beauty of a modular approach." So try a single one first!

As he keeps emphasizing, this is about tuning to the room rather than making up for a bass deficiency in the speakers, which are tuned to have flat bass response in an average room.

I also asked him about whether a single panel wouldn't make the image lopsided since the DWM's go above 80 Hz, and he said "A 1.5 mfd inductor in the attenuation jacks will give a faster rolloff. Buy two and don't worry about it. They aren't expensive."

[SteveFord]

http://www.theaudiobeat.com/ces2013/ces2013_jimmy_awards.htm

[SteveFord]

This is probably the most in depth review of the show to date:

http://parttimeaudiophile.com/2013/02/05/las-vegas-2013-magnepans-big-bass-boogie/

[SteveFord]

Wendell sent me their new ad so here it is before it hits the magazines:




Judging from all of the press, it looks like he came up with something pretty special.