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Multi-Way Conventional loudspeakers with crossovers

Cardioid Bass
Cardioid Bass
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Old 27th April 2008, 03:26 PM   #91
MaVo is offline MaVo  Germany
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I would think that the normal DIY guy will consider it to be fun to try different sub placements and to dial in the right numbers into the amps
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Old 27th April 2008, 04:16 PM   #92
Graham Maynard is offline Graham Maynard  United Kingdom
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Hi John,

I can see you are chewing over the kernel of an idea there, but I am puzzling to understand what it might be.
We should not alter the music in an attempt to correct a room response which arises after the loudspeakers have reproduced sound, especially as room modes are in three dimensions plus volumetric, whereas stereo has only two channels.


Cheers ....... Graham.
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Old 27th April 2008, 11:55 PM   #93
ScottG is offline ScottG  United States
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Quote:
Originally posted by FrankWW
Scot, why don't you let Earl and John sort each other out?

They get to some interesting things and I don't really care how they get there.

You are being "tiresome". The extra personal attack is unnecessary.
It wasn't intended to be a personal attack, rather stating a degree of displeasure with a type of forum "response".

As far as getting to some interesting things.. well, yes - but that was a couple pages ago. If you really enjoy things being "sorted out" I'd recommend the Enable "Technical" discussion thread.

If you find me tiresome, by all means make use of the forum's IGNORE LIST.
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Old 28th April 2008, 04:04 AM   #94
terry j is offline terry j  Australia
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recently I had to pull my system apart and hence put it all back together. Anyway, turns out somewhere that I had one of my bass drivers out of phase, what I mean is that when I fired it up the bass was obviously 'wrong' and a simple flick of the switch and it was fine and back in phase.

But the point I'd like to make backs up the observation made a page or two ago, that the diffuse bass soundstage given when out of phase WAS extremely enveloping and enjoyable in it's own right.

I'm sorely tempted to set up an extra sub or two, deliberately out of phase (and may even try the crossed 'x' mentioned earlier) and see if by judicious juggling of levels etc try and maintain the in-phase accuracy and imaging, yet superimpose upon it sufficient out of phase content to get the best of both worlds. It may even help by the distributed nature of the subs to iron out some of the FR anomolies.

I did try the Harman Kardon paper suggestion of distributed subs before, but found that it didn't really work for my ears. However, by lucky experimentation much later I think I found out why.

My theory to explain it (and it hasn't been touched upon here yet, so I'd love to see what others think) is that the 'trouble' arose because the subs were actually at different distances from the LP. So I figured that the dislike I experienced could have been down to the different arrival times from the different subs. You know, instead of one 'thump' it was kinda 'thump thump', or worse, At the very least, I spose it was 'smeared'.

On the lucky experimentation I mentioned before, I used a DCX 2496 to run the seperate sub channels, and could dial in reasonably closely I think the appropriate delay for each sub according to it's distance from the LP, with the aim that all the signals would arrive to coincide with the signal from the mains.

It certainly made a difference to my ears.

Anyway, assuming some quasi random placement of the subs, are there any comments on the audible effects of the different arrival times, or did I just manage to convince myself of the importance of something that is essentially unimportant?

I too would love to see a write up of the procedure that would help me do it properly, I already have had an interest in it.

And, I too would think it wonderful if you made available the HT writeup you speak of Earl, there would surely be a lot of valuable data in it.
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Old 28th April 2008, 07:17 AM   #95
Graham Maynard is offline Graham Maynard  United Kingdom
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Interesting.

Back in the mid 70's I made a pre-amp with extended LF response which did not roll off at 50Hz as per RIAA. Obviously the bass was something else, especially as I was using Celestion Ditton 66 loudspeakers at that time.

This pre-amp offered option for switching the primary of a miniature push pull driver transformer between channels at interstage points where the falling inductance could cross-couple the LF only to make the bass increasingly mono with falling frequency.

Thus when music was playing (loudly) and the bass notes were becoming extendedly boomy due to LF SPL feedback (even with a genuine brick wall mounted turntable) then the switch could be flicked and reproduction (disco partying) could continue.

The enemy had been the differential LF pressure waves energising room modes, NOT the overall LF response.

Thus I can now appreciate the validity of this out of phase woofer because it must reduce boomy LF room excitation, though, it might induce differential excitation at some frequency and thus positioning need to be careful arranged.
Also, if the LS 'suck' was not equidistant from the listener to the driven sources, then surely there might be additional 'thump-smear' as experienced by Terry.

Just a few thoughts.

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JohnK has optimised single driver cardioid bass, and there has been comment that it cannot be any better than monopole bass in relation to room modes.

My reason for not wanting to use the single driver bass is because I prefer the cleanliness of OB driver mounting even at LF; ie. no delayed damping.

John's last investigations have suggested that the radiating energy for either dipole, cardioid or monopole at LF does not match driver energies at higher frequencies, and (if I read correctly) he has already suggested a need for balancing this with a monopole.

So maybe extra monopole placements will be validated no matter what type of main drivers are being used, though I have noted that the distance between any Sub driver and listener can be critical unless frequency dependent phasing circuitry is introduced, even below 50Hz, and thus I prefer fully integrated main drivers only.

Cheers .......... Graham.
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Old 28th April 2008, 12:20 PM   #96
Fosti is offline Fosti  Germany
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Quote:
Originally posted by Graham Maynard
.........and thus I prefer fully integrated main drivers only.
Me too Especially for music to avoid unacceptable group delays at low crossover points. In HT systems I use a sub for the LFE.

Cheers,
Christoph
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Old 28th April 2008, 12:34 PM   #97
gedlee is offline gedlee  United States
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Quote:
Originally posted by terry j


Anyway, assuming some quasi random placement of the subs, are there any comments on the audible effects of the different arrival times, or did I just manage to convince myself of the importance of something that is essentially unimportant?

I too would love to see a write up of the procedure that would help me do it properly, I already have had an interest in it.

And, I too would think it wonderful if you made available the HT writeup you speak of Earl, there would surely be a lot of valuable data in it.

I'm inclined to think that time delays are not a big issue as audible events in and of themselves. The reason should be kind of clear. AT LFs these delays are only a small portion of the signal period. It just takes too long for our ears to detect a LF signal. We can't detect the presesnce of a LF signal in a few ms let alone have these kinds of delays be audible. Detection of arrival times is very complex, but no researchers that I know of have found any effect at LFs.

With several of subs arriving at different times the net result is a single tone which is the complex sum of the individual signals. Hence even small changes to the delays can have big changes to the net summation of the LF sources. So you are changing the FR at LFs when you change the delays or the phase to the subs and this can sometimes be quite a lot. As to its being an improvement or not only some measurements would sort that out.

I am going to post my HT book, a chapter at a time. I will review each chapter for updated data and then post it. It will take a while like this, but it will happen. Stay tuned.
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Old 28th April 2008, 12:37 PM   #98
john k... is offline john k...  United States
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Quote:
Originally posted by gedlee


John - I have said many times, but I guess that I'll say it again. Talking about directionality of the source in a frequency range of the room where the sound CANNOT travel in arbitrary directions is pointless. You can talk about LF sources in a free field or in a room, but the two things are completely different and there is no reason to believe that what happens in one will happen in the other. Thus, I think that your "test" is based on the false assumption that the free-field directivity will still hold in the closed room. It won't.

In response to these comments I spend some time yesterday and this morning preparing some calculation of the behavior of a dipole and a monopole source is a rectangular room when the dipole axis is aligned with one of the room directions. The results clealy show the effects of directionality of the source on excitation of the room modes in the direction aligned with the dipole and in the directions perpendicular to the dipole axis.


Enjoy
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Old 28th April 2008, 01:49 PM   #99
gedlee is offline gedlee  United States
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Quote:
Originally posted by john k...


In response to these comments I spend some time yesterday and this morning preparing some calculation of the behavior of a dipole and a monopole source is a rectangular room when the dipole axis is aligned with one of the room directions. The results clealy show the effects of directionality of the source on excitation of the room modes in the direction aligned with the dipole and in the directions perpendicular to the dipole axis.


Enjoy

John

I appreciate all your work, but I don't see where this really shows anything. Its ideal to make your point and I can show an example, not so ideal, which makes mine.

Do you deny that a sound wave in a room with widely dispersed modes (little modal interaction) can ONLY travel along the wave vector defined by that mode? This is the key because you either agree or disagree. If you disagree that this is true, then I can easily prove that it is and if you agree that its true then you cannot contend that directivity is a factor. Whats your position?

The two directions that you have choosen to look at in your example are aligned with the mode directions so of course this works in this case.

I am not promising anything as I have a lot to do, but maybe I will do a full frequency response simulation of examples of dipole cardiod and monopole. I will do several situations as one is never conclusive. This will show that, in general, all that one achieves by the dipole component of any source is a lower SPL, not a smoother SPL.

Do you agree that in a simulation like this a cardiod is modeled as two monpoles seperated in space, out of phase, with one twice the strength of the other? It also possible to do three points, but this is just more work and I wouldn't expect a much different answer.
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Old 28th April 2008, 03:10 PM   #100
john k... is offline john k...  United States
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Quote:
Originally posted by gedlee



John

I appreciate all your work, but I don't see where this really shows anything. Its ideal to make your point and I can show an example, not so ideal, which makes mine.

Do you deny that a sound wave in a room with widely dispersed modes (little modal interaction) can ONLY travel along the wave vector defined by that mode? This is the key because you either agree or disagree. If you disagree that this is true, then I can easily prove that it is and if you agree that its true then you cannot contend that directivity is a factor. Whats your position?

The two directions that you have choosen to look at in your example are aligned with the mode directions so of course this works in this case.

I am not promising anything as I have a lot to do, but maybe I will do a full frequency response simulation of examples of dipole cardiod and monopole. I will do several situations as one is never conclusive. This will show that, in general, all that one achieves by the dipole component of any source is a lower SPL, not a smoother SPL.

Do you agree that in a simulation like this a cardiod is modeled as two monpoles seperated in space, out of phase, with one twice the strength of the other? It also possible to do three points, but this is just more work and I wouldn't expect a much different answer.

My position is that you stated, more than once, quite emphatically, that directivity doesn't matter. The fact is that it does matter. This point has been raised in this discussion, by several people, and is related to Kate's and Salmi’s dipole work, etc. I say this, not to make any claim of which is better or worse, but only to show that there is a difference. Take a dipole, a cardioid and a monopole woofer; place them in a room on a Lazy Susan. How the different sources couple to the room, what resonances are excited, and by how much, and how they will sound will vary as the dipole and cardioid are rotated. This will not be the case for the monopole.

I do not agree that a cardioid is two monopoles separated in space, out of phase, with one having twice the strength. That will not produce a cardioid response.
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