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Multi-Way Conventional loudspeakers with crossovers

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Old 1st October 2009, 04:34 PM   #21
WDYSUN is offline WDYSUN  Italy
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Hello dear,

thanks for contributing to this post so enthusiastically. I see your points guys. But as a mathematician/statistician I don't trust this graphs. These are based on models which only take into account 50% of the story, the other 50% is room (as mentioned before). I listen to music in my room, I don't need to sell my projects, so I just don't care what happens under anechoic conditions.

Today I and an expert with a CLIO we measured again this MCA15RCY on a 40cm baffle getting 90db at listening point (2.2mt distance, about 38 degree off-axis), the driver is mounted asymmetrically wrt the center of the buffer. The FR is flat (+/- some usual fluctuation) from 300Hz to almost 3K, I am sorry but this is what we measure. This is consistent with what Troel Gravesen has found. Moreover if I add two 5cm legs to the sides of the baffle (to form an U shape) with the these two sides internally covered with egg-foam the linearity becomes even better.

Anyway, my post started from a question which had nothing to do with FR. I am concerned about distortions caused by excursion. And the question was put an HP or to no HP at 300Hz in order to prevent excess excursion?

I tried to play 50Hz, 100Hz, 200Hz and 300Hz pure sine tones as suggested before in the thread. At low level I cannot hear any distortion or strange sound, at high level with the pure 100Hz I can hear some strange artifact which is probably distortion... now I wonder whether the same volume position will produce an insane pressure when a real music program is played. So I tried to play 500-2KHz white noise with volume in the same position when the 100Hz signal was dirty, I honestly cannot listen to this level, so I imagine it is insanely loud! So in absence of a distortion/excursion measures... I will probably keep the xover simple and let the midrange work without a high pass.

I have to say that while this MCA15RCY is considered a midrange it has a rather low resonant frequency, it seems more a mid-bass. The reason I love the sound of this driver is its transient behaviour, it is one of the most dynamic midrange I have ever heard... thanks to its large acceleration factor it has ( I mean the ratio BL/Mms*1000).

Best Wishes
Pierre
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Old 1st October 2009, 07:00 PM   #22
StigErik is offline StigErik  Norway
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You're absolutely right, you should also take the room into the equation! Room reflections affect the frequency response a lot more than the baffle shape, the worst being the first floor reflection, which is also the most tricky reflection to do anything about. Who wants a diffusor or absorber on their floor? I dont....
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Old 1st October 2009, 07:42 PM   #23
BudP is offline BudP  United States
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Go looking for automobile carpet underlayment. It is a mashed mess of kinked fibers, with a gradient to it's density. Place it as the carpet pad, rather than the usual foam, in front of the speakers. The floor reflections will all but disappear.

Bud
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Old 1st October 2009, 11:58 PM   #24
cuibono is offline cuibono  United States
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I haven't had the same experience - using all sorts of different treatments, combined with careful use of a microphone, I found nothing could effectively alter response below 250Hz. I tried absorbers, diffusers and reflectors up to 16" thick.
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Old 2nd October 2009, 12:27 AM   #25
gainphile is offline gainphile  Australia
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Quote:
Originally Posted by StigErik View Post
You're absolutely right, you should also take the room into the equation! Room reflections affect the frequency response a lot more than the baffle shape, the worst being the first floor reflection, which is also the most tricky reflection to do anything about. Who wants a diffusor or absorber on their floor? I dont....
The speakers need to illuminate the room uniformly to mask (not remove) its effect. The human hearing ignores second replicas of sound, but not if they're different. Thus smooth polar response is very important.

The smoothest polar response I've measured and heard is actually the omnidirectional Pluto. And in some area like imaging they are better than the dipoles I've built. They sound almost holographic. In this area the closest match I've got is using extremely narrow baffle (20cm).

I'm curious about your 250Hz suckout and I've never encoutered it after many builds. The only 'dip' I got is 100-200Hz which is easily solved with 100-200 shelving highpass as per Orion and Phoenix, and is due to half-space to full-space transition. Is it anything to do with U-Frame response?
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Old 2nd October 2009, 01:26 AM   #26
jamikl is offline jamikl  Australia
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After reading post no. 18 from Gainphile I can't help coming to the conclusion that a 10" or 12 coaxial, despite some drawbacks inherent in the type, might no be a better solution for the mids and the highs on an open baffle. Looks like its back to trying to find a PAudio 12 or two.
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Old 2nd October 2009, 01:58 AM   #27
gainphile is offline gainphile  Australia
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Quote:
Originally Posted by jamikl View Post
After reading post no. 18 from Gainphile I can't help coming to the conclusion that a 10" or 12 coaxial, despite some drawbacks inherent in the type, might no be a better solution for the mids and the highs on an open baffle. Looks like its back to trying to find a PAudio 12 or two.
jamikl
Hi, not sure what you meant. My finding is that the relative (not absolute) size of driver vs. baffle is the dominant factor.

In my earlier post, an 8" on 24cm baffle works as well.

I would guess a 10" driver on 30cm baffle may work too, but measurements will be needed to confirm.
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Old 2nd October 2009, 02:28 AM   #28
cuibono is offline cuibono  United States
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Quote:
Originally Posted by WDYSUN View Post

Anyway, my post started from a question which had nothing to do with FR. I am concerned about distortions caused by excursion. And the question was put an HP or to no HP at 300Hz in order to prevent excess excursion?

I tried to play 50Hz, 100Hz, 200Hz and 300Hz pure sine tones as suggested before in the thread. At low level I cannot hear any distortion or strange sound, at high level with the pure 100Hz I can hear some strange artifact which is probably distortion... now I wonder whether the same volume position will produce an insane pressure when a real music program is played. So I tried to play 500-2KHz white noise with volume in the same position when the 100Hz signal was dirty, I honestly cannot listen to this level, so I imagine it is insanely loud! So in absence of a distortion/excursion measures... I will probably keep the xover simple and let the midrange work without a high pass.
I guess the question is what driver you are using below the mid, and where are you crossing it in? Ultimately, you would want to measure the completed loudspeaker to make sure the two drivers are integrating well. Usually, 'anechoic' measurements are part of the process to make sure things are working as planned, but I always check in room measurements too - below 300Hz (generally), the room can cause a lot of problems.

White noise has a larger amount of high frequencies present, so it may sound a bit louder than music at the same volume (which generally has more low/mid frequencies).

Last edited by cuibono; 2nd October 2009 at 02:30 AM.
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Old 2nd October 2009, 02:51 AM   #29
MJK is offline MJK  United States
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Quote:
Originally Posted by gainphile View Post
Hi, not sure what you meant. My finding is that the relative (not absolute) size of driver vs. baffle is the dominant factor.

In my earlier post, an 8" on 24cm baffle works as well.

I would guess a 10" driver on 30cm baffle may work too, but measurements will be needed to confirm.
I was trying to resist getting into the narrow vs. wide baffle debate again. I do not buy into the importance of the relationship between driver size and baffle width and the potential negative impact on off axis performance if the baffle is wider then recommended.

So I ran an experiment. I took my MathCad model of the Fostex FE-103E and Eminence Alpha 15A two way passive OB design and calculated the response on axis, +/- 30 degrees off axis, and +/- 60 degrees off axis. I think this design violates most of the rules of the "cult of the narrow baffle" in that the baffle is very wide compared to the full range driver diameter and even worse the full range driver is offset closer to one edge.

I lined the plots up vertically from -60 degrees to +60 degrees in 30 degree increments and compared the responses, the on axis response is optimized to be as flat as possible. The responses were very close to symmetric with the biggest anomoly as a function of angle being the directional response of the FE-103E driver rolling off the high frequencies as you move off axis. But that effect is due to the driver geometry and not the relative baffle width, it would be present in any width baffle. The rest of the differences were not very big and nothing stood out. There were no big humps or severe dips as shown in some of the measurements, simulations of single drivers on a baffle, or SL's drawing that were presented in previous posts.

In my opinion, focusing on only baffle width as a function of driver diameter is ignoring many other more significant variables. If you design your OB system taking into account baffle size and shape, driver size and location, crossover frequencies and slopes between drivers then there is no reason not to expect a relatively symmetric smooth SPL radiation pattern that is free of significant humps and dips. You need to factor in all variables and not base the design on a plot produced by the EDGE and some guess work.

rule of thumb: baffle width <= 2x driver diameter is not meaningful
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Old 2nd October 2009, 03:16 AM   #30
cuibono is offline cuibono  United States
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In general, I would agree with Martin - baffle width is not the only thing to consider. But I fall in the 'narrow baffle' camp.

The point to remember is that above the baffle peak, off axis frequency response becomes irregular. Whether this matters is up to the designer. Also, my impression is that it is very difficult to accurately simulate the off-axis response, due to particulars of the driver's frame. I can say that all my measurements showed significant irregularity off axis above the dipole peak, and effect the mid, but especially the tweeter (if it is a dipole tweeter).
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