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Multi-Way Conventional loudspeakers with crossovers

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Old 2nd March 2010, 10:42 AM   #41
keyser is offline keyser  Netherlands
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Truly remarkable.
One question though: doesn't flat onaxis mean a lifted bass in-room due to the fact that the midrange is radiating in 4pi over its entire bandwidth, while the woofer operates in 2pi?
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Old 2nd March 2010, 03:10 PM   #42
cuibono is offline cuibono  United States
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That is a very good question - I've been looking into that a bit lately, but the answer is going to take some time to write up. Tomorrow maybe....
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Old 2nd March 2010, 04:15 PM   #43
parb is offline parb  United States
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i really like this thread, i learned a lot from you all! its also very inspirational reading!
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Old 9th March 2010, 04:29 AM   #44
cuibono is offline cuibono  United States
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So, one of the things I've done within the last few days is move the mid-tweeter XO point up to 2600Hz from 1700Hz. I knew for sure that this would deepen the off axis polar dip, but I did it mainly because several people were saying 1700Hz is too low for the Neo3pdr tweeter.

Here are the before and after polar measurements. As you can see, at 60deg off axis, the dip deepens by about 2dB.

Before:
Click the image to open in full size.

After:
Click the image to open in full size.

I assumed this would be audible, but, at regular listening levels, switching between the two settings showed the difference to be inaudible. That is good. I guess some amount of off axis irregularity is going to be inaudible - but I don't know where the transition is from audible to inaudible.

Similarly, at regular listening levels, I detected no difference in the sound at all - so I would surmise that nonlinear distortion is not an issue at modest SPLs. But that shouldn't be a surprise. I then listened at very loud levels. I didn't do A/B comparison switching, but I thought things might have been better maintained - there were fewer incidence of thinking 'whoa, thats too loud', which is where I would guess is where NLD is becoming an issue.

Good news all in all. I'll probably keep the XO point at 2600Hz because it is probably better for the tweeter, and no cost to the acoustics.
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Old 9th March 2010, 05:35 AM   #45
cuibono is offline cuibono  United States
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Here is a little more interesting rearrangement I've made recently too.

I suppose what got me onto this was thinking about one of the basic tenants of LR type crossovers - the two drivers working around the crossover must be equidistant from the listener to sum so that the vertical nulls are 'where they are supposed to be'. I then realized that my design, and all the other OB designs I could think of, have the same issue - the acoustic centers of each driver are different distances to the ear. The bass is particularly effected, being about 8% farther than the midrange from my ear.

Similarly, I kept having to adjust the EQ by ear, no matter how well I measured it - particularly, setting the woofer and tweeter level relative to the midrange. I usually had to boost the bass by several dB, and lower the treble by a couple dB. I didn't know why, but I could tell that even if my measurements were flat anechoicly, something wasn't right - what I had previously refered to as a need do final in room adjustments for the 'room curve'.

Well, then I realized that not only was the path lengths different, but the angle of radiation that I was listening on unequal - which leads to fairly significant in room radiated power imbalances.

The woofer is a good example - I have already had to boost its level by .7dB to account for the path length difference - so while the listening position may measure flat, the total woofer output has been boosted by that amount relative to the midrange. Additionally, I listen at 30deg off axis horizontally (because I sit in an equilateral triangle), and about 25deg vertically (because the woofer's acoustic center (AC) is 12" off the ground, while my ear is 44"), relative to the woofer's axis of radiation - this lead to at least 3dB, if not more, of level difference between the listening position direct radiation, and the total power response of the woofer, relative to the midrange. I think this is what made adjusting levels difficult - the direct radiation level and in room power were not scaling together. Additionally, the time of arrival is different between drivers, so their phase is not summing perfectly. Not an idea situation.

Drawings might make this more understandable (please excuse my drawings!). The first arrangement is where I had the AC's of the drivers arranged vertically:

Click the image to open in full size.

The second is my more preferable configuration, where things are arranged radially from the ear:

Click the image to open in full size.

There are two major differences between the two arrangements: first, each driver's AC is equidistant to the ear; second, each driver's axis is pointed directly at the ear. I am fairly certain that both of these conditions are necessary to ensure proper acoustic summing and power balance between all drivers.

After doing this, there were some pretty good improvements - the was a substantial increase in coherency through the whole frequency range; things sounded more punchy; there was both an increase in clarity and low level ambience. Things sound smoother and easier to listen to - more natural.

Also, the system required almost no adjustment after measurement - the only adjustment I made was to shelf the treble -1dB, which is probably due to my room being all hard surfaces, and listening relatively closely. I would conclude that this made a substantial improvement in the overall quality of the presentation, and highly recommend it. I would go so far as to say that any OB speaker that doesn't do this cannot both sum flat on axis and have a flat power response, say nothing of the phase response.

I should add one note though - previously, I had been measuring (outdoors) with each driver set so that the mic replicated the individual distances and angles of the listening position in room. I no longer do that - for this trick to work, each driver must be measured directly on the driver's axis (preferably at about 2m - at 1m or less, the driver's dipole cancellation is not fully seen). But this actually makes measuring easier.

Anyways, this is highly recommended.

Last edited by cuibono; 9th March 2010 at 05:38 AM.
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Old 9th March 2010, 06:55 AM   #46
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Really interesting project. Does this 2nd arrangement create a singular or smaller sweetspot for listening? Or can you gain the benefit in other seating positions?
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Old 9th March 2010, 12:21 PM   #47
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very interesting... what about imaging with the new arrangement? backwave is not only delayed this way
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Old 9th March 2010, 05:45 PM   #48
cuibono is offline cuibono  United States
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Quote:
Originally Posted by Antripodean View Post
Really interesting project. Does this 2nd arrangement create a singular or smaller sweetspot for listening? Or can you gain the benefit in other seating positions?
One of the big benefits to OB speakers is there are much much wider 'sweet spots' compared to boxed speakers - in fact, I hear very little to no change in the acoustics anywhere in the room, which is another thing that makes them very enjoyable to listen to. The only thing that changes by moving is the perspective into the soundstage - so, no, I don't find this new arrangement to be more limiting of the sweet spot. It seems to be the opposite, where the sound is more balanced everywhere in the room.

Quote:
Originally Posted by human.bin View Post
very interesting... what about imaging with the new arrangement? backwave is not only delayed this way
Imaging hasn't changed much - but there has been an increase in clarity and reverberant space, which helps reinforce the illusion of the soundstage.

I'm not sure what your trying to say about the backwave, but in my experience, the distances between the walls, speakers and listener(s) only changes the size of the perceived soundstage - similar to a 30" television versus a 70" projection. I haven't found any of the arrangements I've tried change the perceived frequency response.

I have measured reflection related peaks and nulls in the room - and I've tried EQing them. I've had varying results, but my most recent efforts suggest that it is best to leave them alone, presuming that the anechoic measurements were done well. I'll post some of the in room response measurements I've done, sooner or later, but still the bottom line for me was that reflections (either backwave or frontwave) sounded best left alone.
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Old 9th March 2010, 05:58 PM   #49
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Quote:
Originally Posted by cuibono View Post
I'm not sure what your trying to say about the backwave
nor am I. it's just that until now i thought of dipole cancellation as a planar 2d shape, orienting driver cone will make it a more complex 3d shape, but perhaps it probably is always like that just me not considering, and actually the mid-highs will just have the very same cancellation pattern just rotated a little, and at the crossover frequency with the woofers it will not be relevant... ok i don't know what i'm saying again thanks for a very instructive thread!
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Old 9th March 2010, 06:52 PM   #50
sqlkev is offline sqlkev  United States
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wow...impressive!!
i may just take up on that offer and make a drive there to audition this system
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