Fair enough there might be some lobing even if XOed below 200Hz and side firing has it issues especially if one Xos above 200Hz.
BTW this is not my personal system. The SB 12.3 system is a friend's. Our discussion (over a few beers) was because we both have used 15" and 18" before and now use smaller woofers (12"). We realised that there are so many manfacturers using a vertical array of multiple (3-4) small (6-8") woofers. We wondered why these smaller woofers with their higher BL/mms ratio and smaller Le could not produce the slam of single big woofer having the same total Sd.
BTW if I ever build a new system I would be considering Ripole using Lambda Diople15s, Augies, DPL-15s or something similar (2 per channel stacked vertically) for the bass and OB for the mid/hf section. But that is the subject of another thread
Please read the links I posted. Then you'll realize that using 1 or 4 low frequency drivers at the same location is completely insignificant.
I did read the papers. However our observations are that a single large woofer provides a better sense of slam than multiple smaller woofers. Since these observations run contrary to research I was interested in the rationale (if there one) behind this difference. Or is it that the differences we observed are psychological or maybe even attributed to the vastly different woofers we were comparing (ported JBL Pro 15" and 18" woofers vs sealed ACI/SB Acoustics 12" woofers).
For example using multiple woofers in DIFFERENT locations we have also observed does smoothen out the bass response even if we do not have access to individual delay control.
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From measurements it is incontrovertable that multiple subs produce a smoother frequency response at the listener position than a single sub. If this does not "provide a better sense of slam than multiple smaller woofers" then that is simply a personal subjective impression, and not one shared by very many.
Of course if you are using several small poorly designed subs then that is going to be a problem as well. I have been shocked by how poor some of the smaller subs actually are. That is making me reconsider my position that one can use many "small" subs to replace "one big one". The subs need to be competent no matter how many there are. But multiple "competent" subs will always beat one "competent" sub.
Of course if you are using several small poorly designed subs then that is going to be a problem as well. I have been shocked by how poor some of the smaller subs actually are. That is making me reconsider my position that one can use many "small" subs to replace "one big one". The subs need to be competent no matter how many there are. But multiple "competent" subs will always beat one "competent" sub.
I think I have been misunderstood.
Earl (can I call you Earl or do you prefer Mr. Geddes?) , I have been an avid follower of your posts and have the greatest of respect for you opinion.
I agree that several subwoofers in different locations provide a smoother and more balanced presentation than one or 2 subs in one location. My observations match this theory.
However what I have observed is that multiple small subs do not have the same slam as one big sub if they are in ONE location.
Today many manufacturers are producing speakers that have 3 or 4 6-8" woofers in one cabinet topped by a midrange and tweeter. The question I was asking is why when these same cabinets are deep enough to accomodate a single side firing 15" which should provide more slam than a set of 3-4 small woofers. However the papers Markus presented in his links above show that in theory is should NOT matter if there are 3 8" or 1 15" in ONE location. It is here that my observations differ from theory and all I am looking for is why.
a. Is it because the 15"/18" woofers we observed were large ported boxes while the 12" woofer we observed were small sealed boxes?
b. Is it purely psychological - you see a big 18" cone and expect more bass
c. or is there some other theory or rationale behind what we have observed.
there is one other member who is also debating between using 2 10" vs 1 15" here
http://www.diyaudio.com/forums/subwoofers/158935-music-sub-2-sdx10-1-sdx15-2.html
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Following this line , you'll end in having a gigantic sub in your room (like the one in "Back to the future")...hey ,it exists ,it's the fostex with the tiny magnet ,in comparison to the diameter. But what that expensive design lacks is "competency" ,as Earl says , because of
weight-rigidity ratio. I think if such a gigantic monster (not to mention about magnetic action !) would be built ,we would be talking about neighborhood modes.
weight-rigidity ratio. I think if such a gigantic monster (not to mention about magnetic action !) would be built ,we would be talking about neighborhood modes.
LOL that (the FW800) reminds me a 30" EV subwoofer. I only saw a picture of it, never heard it; but a friend who clamed he heard it at some Audio show (in the 70s in Detriot) said they (The EV guys) were showing it off by plugging it into the 120V mains! Dont know if that was true or was he just ribbing me.
My friend had an EV30. They weren't bad - too expensive for what you got. Mostly bragging rights. And I was also at the Detroit audio show where they had a woofer connected to a 115 volt power cord. But it was a Cerwin Vega, and they declined to actually plug it in, although such a thing would not be impossible.
I understand your point now. No diasgreement that there will be audible differences. My only point would be that - in principle - I could make equal radiating areas of multiple drivers perform the same. Not that your examples did, by any means, its just that theoretically I CAN make it all come out the same.
But the key here is "competent" designs. Most of the stuff that you see is made over here (I'm in China at the moment) and "competent design" is simply not a requirement. Its all about low price, small size and good vinyl veneer. Sound quality? They have no idea what that even means.
I understand your point now. No diasgreement that there will be audible differences. My only point would be that - in principle - I could make equal radiating areas of multiple drivers perform the same. Not that your examples did, by any means, its just that theoretically I CAN make it all come out the same.
But the key here is "competent" designs. Most of the stuff that you see is made over here (I'm in China at the moment) and "competent design" is simply not a requirement. Its all about low price, small size and good vinyl veneer. Sound quality? They have no idea what that even means.
What is "slam"? How did you compare the two different subs? Did you measure the frequency response? Did they have the same free field frequency response?
If you change the location of a sub, you change their frequency response at the listening position. If the subs have a different free field frequency response, you will hear a difference. If one sub is louder than the other you might perceive more "slam".
That's the problem with subjective descriptions. They are meaningless in a technical sense but audio devices are solely technical devices. No room for subjectivism in how they are built.
I believe B&W has done a "test" on the subject and they concluded that one big woofer gives more "slam" than multi-smaller woofers with same total SD.
However, there is also the big issue of standing waves in room etc, ref. Gedlee, Harmand Kardon-white paper etc.
This might be a solution (depending on your room-size):
Use one 15" mid-bassdriver (e.g. AE TD15M) down to about 80 Hz (where room-modes might start to tamper too much of the sound quality), and use multiple smaller sub below (smaller because of WAF etc). A total of 4 subs (in mono) is suggested by Harman Kardon as "enough" subs, and either located in the 4 corners or (best) placed in mid-wall-location.
However, there is also the big issue of standing waves in room etc, ref. Gedlee, Harmand Kardon-white paper etc.
This might be a solution (depending on your room-size):
Use one 15" mid-bassdriver (e.g. AE TD15M) down to about 80 Hz (where room-modes might start to tamper too much of the sound quality), and use multiple smaller sub below (smaller because of WAF etc). A total of 4 subs (in mono) is suggested by Harman Kardon as "enough" subs, and either located in the 4 corners or (best) placed in mid-wall-location.
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If only it were this easy. Those "Harman 4 subwoofer setup" recommendations are only valid in rectangular rooms with rigid walls. Nothing you'll find in real life very often.
Unless your room is very big: forget my suggestion above.
I tried to simulate a room H: 2.4 m, W: 4.8 m, D: 7.0 m
Result: most of the standing waves will be above 80 Hz
Maybe dipole bass is the solution (at least partly) as some say dipole sub has less room-modes than monopole subs?
Edit: You are very right Markus76!
I tried to simulate a room H: 2.4 m, W: 4.8 m, D: 7.0 m
Result: most of the standing waves will be above 80 Hz
Maybe dipole bass is the solution (at least partly) as some say dipole sub has less room-modes than monopole subs?
Edit: You are very right Markus76!
I tried to simulate a room H: 2.4 m, W: 4.8 m, D: 7.0 m
Result: most of the standing waves will be above 80 Hz
Maybe dipole bass is the solution (at least partly) as some say dipole sub has less room-modes than monopole subs?
There are 11 modes below 80 Hz in that idealized room and that's the problem. At lower frequencies there are fewer modes and they are more spaced relative to each other. Each room has its own unique and fixed modal pattern. It's a property of the room and not of the sound source.
A dipol sub is not better or worse than any other low frequency source. It all depends on how low frequency sources are distributed throughout the room and where the listening position is.
IIRC a dipole sub is WORSE than a baffled sub for frequencies that are lower than the frequency corresponding to the longest dimension of the listening space. Dipole subs cannot operate in "pressure" mode, and this has nothing to do with room or listening position. A room can only sustain a "wave" of sound if it's wavelength fits in the room. Note that 10m is about the wavelength of 35 Hz. The typical dimension in a listening room is more like 5m, which is the length of a 70Hz sound wave. So, unless you have a very large room, stick with typical boxed drivers (sealed, vented, etc.) for the lowest octaves. Dipole definitely has some real advantages, but not for low frequency reproduction.
-Charlie
I thought everyone from Wavecor and SB Acoustics to Vifa and ScanSpeak was making their stuff there. Many of the owners/managers of these companies have worked with each other before so it makes sense that they all source in the same country.
I agree, there is a LOT of very average stuff coming out of China.
Well markus we conducted no measurements. We neither have the inclination not the equipment for this. I just relied on what I like to call "the goosebump factor".
Granted this is very subjective but music is subjective which is why the same piece of music offers different levels of enjoyment on different days.
Really? where? If you have a link it would be a great read. I would love to have some scientific validation for what I heard.
Which means that a dipole sub should NOT be used below say 70-80Hz. Thanks. I was considering dipole/ripole for my room (5m) some day.
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http://www.bwspeakers.com/downloadFile\technicalFeature\Sig_800_White_paper_Final_10.07.01.pdf
Page 12: there is indeed a discussion of 2 vs 1 drivers. I would not call that a "scientific validation", though, rather a practice report.
Interestingly, after choosing 1 driver in the Nautilus 801 flagship, B&W got back to 2 drivers in Signature 800
This extract from that PDF supports the points Loren raised way back in post 2 of this thread.
Now place the same two drivers in an environment with at least one near field boundary at a normal to the array. The two drivers now experience different driving point impedances. Their outputs will vary in magnitude and phase and the coherency of the wavefront is now further degraded
other observations
Extended experience showed that the Nautilus™801 thrived in larger rooms (especially those benefiting from a high ceiling) or highly damped rooms...
The fact that the smaller Nautilus™802, with its twin 8-inch bass drivers, could sometimes give preferable subjective results...
This twin driver approach was followed in the Signature™800, but with two 250mm (10-inch) units, which duplicate the radiating area of a single 350mm (15-inch) driver
These later observations lead me to believe that maybe, just maybe, if one was to compare the bass from a single 15" woofer vs a vertical array 2 similar 10" woofers like the woofers linked below (same links as post 1 reposted here for convience) one might well produce the same quantity and quality of bass at typical listening positions (3m from each speaker) in typical rooms (4mx5m or there abouts).
SB Acoustics SB42FHC75-6 15" Woofer from Madisound
SB Acoustics SB29NRX75-6 10" Woofer from Madisound
It might well be that the QUALITY of bass from a pair of 18" JBL 2245 in 2 10 cu. ft. ported box was very different from the quality of bass from 4 12" Audio Concpets DV12s in 2 5 cu. ft. sealed boxes and that given the room, listening postion and music used (we used Tchkaikosky, Mozart, Pink Floyd, Trilok Gurtu, etc..) the bigger ported box produced bass that was subjectively more dynamic.
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