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Multi-Way Conventional loudspeakers with crossovers

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Old 20th October 2010, 07:26 AM   #1
thadman is offline thadman  United States
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I am aware that if you invert one driver, wire it in opposite phase, and place it in the same plane as another driver, you will cancel even order distortion.

This is exactly what Linkwitz uses for the OB bass section of the Orion with the XLS woofers.

However, does it actually produce a notable difference or is it simply good in theory? I've heard the difference is subtle, but with OB woofers the improved distortion performance may be non-negligible. I'm debating whether it would be worth it in the midbass and upper bass. Aesthetically, it is a very undesirable option.

Thanks,
Thadman
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Old 20th October 2010, 09:21 AM   #2
StigErik is offline StigErik  Norway
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Noteable? yes
Subtle? no way!

I run all drivers except the tweeter (there's only one...) push-pull, even the midranges in my 4-way system.

The difference is in my opinion very obvious measurement-wise. Subjectively, there is a noteable difference - it sounds cleaner, tighter, better defined.
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Old 20th October 2010, 09:25 AM   #3
CLS is offline CLS  Taiwan
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Quote:
Originally Posted by thadman View Post
...

I've heard the difference is subtle, but with OB woofers the improved distortion performance may be non-negligible. I'm debating whether it would be worth it in the midbass and upper bass. Aesthetically, it is a very undesirable option.
...
So, what's the debating?

You can try it yourself any time after the baffle holes are cut. The effort is only turning several screws, isn't it? I won't bother myself. I can't stand the looks anyway.

Some drivers do have handsome rear view - those functional beauties, but if this is the case, I'd like to show all drivers with the same side, and then it's still no benefit in distortion cancelling.

OTOH, the force cancellation in W-baffle type of mounting is indeed significant. It supresses vibration very effectively. Then again, it's not pretty, either.

Do you consider mounting the drivers with swings? It can be beatifully done and very little vibration issue. As to the distorion of the drivers themselves, just never mind.
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Old 20th October 2010, 10:40 AM   #4
Rudolf is offline Rudolf  Germany
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Don`t we have to consider two rather different cases?

First the "bass" region (up to 500 Hz): In this region I have never seen a difference in frequency response between front and back of a driver. But you can get different response if the front and back volumes of the housing are as different as in a W frame a la Linkwitz. I would prefer a symmetrical position of the drivers in the "Ripole" style.
If you really want to cancel even order distortion, only the H configuration would do that perfectly - but without impulse compensation.

Second the region above 500 Hz: When drivers develop different radiation patterns to the front and rear, it is always a good idea to mount paired drivers in opposite directions. Whether the notion of "sounds better" is the result of distortion compensation or of better symmetry in the frequeny response (or the combination of both), I would not dare to judge.

Rudolf
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Old 20th October 2010, 03:02 PM   #5
Saurav is offline Saurav
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I think I saw a post by Linkwitz somewhere where he said he's measured a 15dB reduction in distortion by using the reversed mounting technique on the woofers. The new Orion 4.0 prototype uses a different mounting technique to achieve the same thing, I think.

http://www.diyaudio.com/forums/multi...ml#post2337403
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Old 20th October 2010, 06:46 PM   #6
LineSource is offline LineSource  United States
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I favor a speaker's front cone sound over the rear cone, and I do not inverse mount woofer or midrange speakers. A W-frame with counter mass vibration balancing is the only execption for me. Personally, I still favor the sound of an H-frame with front facing woofers despite higher vibration problems then a W-frame, but H-frames demand isolated mounting of midrange and woofers.

I noticed that Linkwitz's latest Orion 4 uses a horizontal orientation W-frame instead of the previous H-frame. This is an engineering decision to accept the gravity cone sag on horizontal speakers in order to remove cabinet frame vibrations.


Many woofers and midranges employ some type of rear cone and/or motor air venting for cooling and/or to vent the dust cap air. I can hear this air noise, and so I send it to the back wave where is it less noticable. Most speakers are designed for closed box operation where the vent huffing can be contained. Speakers with phase plugs, even large woofers like the Lambda TD15D, often have the lowest air noise.
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Old 20th October 2010, 08:27 PM   #7
twest820 is offline twest820
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What Rudolf said.

Quote:
Originally Posted by thadman View Post
I'm debating whether it would be worth it in the midbass and upper bass.
Midbass and above, yes. Upper bass, maybe, depending on driver selection and what exactly upper bass means to you. My solution was BG Radia Neo10s. Real nice drivers, even with their vertical directivity limitations.
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Old 21st October 2010, 08:47 PM   #8
thadman is offline thadman  United States
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I have 4 NS15s I would like to use for dipole midbass. I have been following StigErik's thread as well as a few others and would like to achieve something similar.

However, I'm not sure how high in frequency they should be taken. The primary cone resonance is ~2.2KHz, which corresponds with the first impedance aberration. Frequency response is flat to 500Hz and is down 6dB by 1KHz. Distortion decreases with frequency up until about 500Hz (-55dB), but is below 1% until ~8KHz.

http://www.aurasound.com/public/pdf/NS15-992-4A.pdf

My intuition is suggesting a ~2nd order FIR filter at ~150Hz.

How would you "suspend" these woofers? I was thinking of using a vertical arrangement with the lower woofer inverted. These really are beautiful woofers, so it should be relatively aesthetically pleasing. Could I mount the woofers to a minimalist frame and suspend this? I have a feeling their frames should be coupled in order to maximize harmonic distortion cancellation.

I'd like to incorporate them into a linear phase multi-way system. A Duelund XO with a=2 could be nice. If the interdriver spacing is minized, a=sqrt(3) could be very interesting.

I've been trying to understand the minimum driver layout constraints in order to be able to assume quasi constant directivity. If we force the lower range driver to be -20dB as its interdriver spacing approaches distance/wavelength=.5, we might get some interesting results. Any thoughts?

Honestly though, a 3-way simply will not be able to work without significant sacrifices if constant directivity dipole behavior is desired. A 5-way could be very interesting, but a 4-way would probably be much easier (monopole subwoofer <50Hz would make it a 4+1 or 5+1 way). Has anybody used a higher order Duelund?

Also, I'd like to avoid symmetrical driver layouts (ie WMTMW, MTM, etc). Waves expand as spheres. If a linesource is used, the wavefront will distort as it transforms into a spherical wavefront in the nearfield. If we assume the listener is in the far field, then by going with a symmetrical layout we have reduced the amount of possible surface area within the plane where the waves sum constructively.

Between ~800Hz and ~1.6KHz, human hearing transitions from ITD to ILD. As a result, we might compromise (ie minor lobes) the response above 4KHz in order to allow for some design flexibility below 1.6KHz by extending the response of an upper midrange driver into the lower treble. John K appears to have achieved success in using this technique in his Nao Note loudspeaker.

Phase is not that significant above 4KHz, so a BG Neo3 might be added as a supertweeter. The SS 10F will afford the opportunity for 1 wavelength driver spacing at ~3.8-4KHz. If we machine the drivers frame off and mount it by the magnet, we might be able to push this up to ~4.2-4.5KHz.

I have access to a machine shop, so driver modifications and metal fabrication are possible. A custom aluminum dipole waveguide would be within reason. I'm not sure if a torus (controlled response) would be superior to no baffle (closer spacing)? I assume there is some ratio between the ID/OD of the torus and the driver diameter which minimizes the dipole peak, of course the depth of the waveguide should be <1/4WL at the highest frequency.

Push/Pull NS15 --> W22EX --> W15CH --> SS 10F ------> BG Neo3

A waveguide for the SS 10F could be interesting since it will assume a relatively wide bandwidth. John K seems to think so. However, I'm not sure how to optimize the waveguide. The velocity distribution at the throat must be known in order to determine and optimize the far field response. Any thoughts on how to estimate or measure this? I'd assume it will be non-trivial considering the modal contributions of the cone have to be considered and the fiberglass cone isn't exactly homogeneous.

Push/Pull NS15 --> TD15M --> W22EX? --> SS10F w/ WG ------> BG Neo3 ???

I have a pair of TD15M Apollo lower midrange drivers, but they don't quite fit into this constant directivity dipole design if the NS15s are used. However, I'd really like to incorporate it (linear phase must be satisfied) into the system if its possible. It really needs to be highpassed at 150Hz, since I'd like to limit RMS excursion to <1mm, but it can't be used above 500Hz due to the dipole peak. Perhaps some insight can be gained by simulating a higher order Duelund.

I'm quite fascinated with the Duelund crossover topology, but the math is a bit terrible. Could anyone recommend any links so I can solve these equations myself? Also, what is the usual mathematics software that is used for crossovers?
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Old 21st October 2010, 09:14 PM   #9
thadman is offline thadman  United States
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Quote:
Originally Posted by Saurav View Post
I think I saw a post by Linkwitz somewhere where he said he's measured a 15dB reduction in distortion by using the reversed mounting technique on the woofers. The new Orion 4.0 prototype uses a different mounting technique to achieve the same thing, I think.

http://www.diyaudio.com/forums/multi...ml#post2337403
Interesting. That would indeed cancel vibration and distortion. It would appear the woofers pump air in and out of those chambers, similar to the functioning of an AMT. Would that be a correct visualization?
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Old 21st October 2010, 09:20 PM   #10
Davey is offline Davey  United States
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The Orion 4 configuration is the same setup as the Phoenix woofers but with the enclosure rotated 90 degrees. The only possible issue here would be cone sag, but I'm sure he's investigated and is comfortable with the Seas drivers in this respect.

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Dave.
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