Of late I have had discussions with friends about moving a lot of air gently vs moving a lot of air vigourously. This stemmed from comparing modern small (10" and less) high BL and Mms woofers with huge motors and Xmax (12mm+) to the older larger (15" and more) woofers that did not have such large Xmax or motors (lower Le) but often sound more musical.
The arguement put forward by the high BL, Mms, Xmax camp was that the smaller woofers had better WAF. Point taken. WAF (we agreed) for apartment dwellers means a floorstanding loudspeaker that is less than 12" wide and occupies less than 1.5 sq. ft. of floor space (plinth and feet included).
We sorta also agreed that this WAF speaker's internal box volume (after bracing, etc..) would not exceed 4 cu. ft. If we were to fit a 3 way into this box the woofer system would have about 3 cu. ft.
So we compared 8", 10" and 15" woofers. A 10" being as big a woofer one can fit into a box that is 12" wide (atleast on the front baffle) and a 15" being the biggest woofer we can fit on a box 18" deep. Any wider or deeper and WAF would be compromised.
The most recent system we had built was the Zaphaudio SB12.3. John Krutke of Zaph Audio seems to like SB Acoustics so we decided to see how much bass we can produce from 3 cu. ft. using simple woofers from SB Acoustics. Obviously we did not have access to these woofers (we live in India).
Would the bass from a 15" woofer be more musical than from 2 10" or 3 8" woofers? The Sd of a 15" woofer is about the same as that of 2 10" or 3 8" woofers (650cm2).
Has anyone compared the 15", 10" or 8" woofers from SB Acoustics?
Madisound lists an F3 of 45Hz for the SB42, a F3 of 48Hz from the SB29 (in less than half the volume of the SB15) a similar F3 from the SB23 is also possible. Room gain would push the in room F3 to the mid 30s - adequate for almost all music at sane SPLS save some large scale organ works and maybe hip-hop.
SB Acoustics SB42FHC75-6 15" Woofer from Madisound
SB Acoustics SB29NRX75-6 10" Woofer from Madisound
SB Acoustics SB23NRXS45-8, 8" Woofer from Madisound
Now we are not related to SB Acoustics, I am sure SEAS's Prestige series or ScanSpeak's Discovery series woofers would perform similarly (neither SEAS nor ScanSpeak have a 15" in their portfolio though). We just chose SB Acoustics so that our discussions were based on real world drivers and not any hypothetical drivers.
The arguement put forward by the high BL, Mms, Xmax camp was that the smaller woofers had better WAF. Point taken. WAF (we agreed) for apartment dwellers means a floorstanding loudspeaker that is less than 12" wide and occupies less than 1.5 sq. ft. of floor space (plinth and feet included).
We sorta also agreed that this WAF speaker's internal box volume (after bracing, etc..) would not exceed 4 cu. ft. If we were to fit a 3 way into this box the woofer system would have about 3 cu. ft.
So we compared 8", 10" and 15" woofers. A 10" being as big a woofer one can fit into a box that is 12" wide (atleast on the front baffle) and a 15" being the biggest woofer we can fit on a box 18" deep. Any wider or deeper and WAF would be compromised.
The most recent system we had built was the Zaphaudio SB12.3. John Krutke of Zaph Audio seems to like SB Acoustics so we decided to see how much bass we can produce from 3 cu. ft. using simple woofers from SB Acoustics. Obviously we did not have access to these woofers (we live in India).
Would the bass from a 15" woofer be more musical than from 2 10" or 3 8" woofers? The Sd of a 15" woofer is about the same as that of 2 10" or 3 8" woofers (650cm2).
Has anyone compared the 15", 10" or 8" woofers from SB Acoustics?
Madisound lists an F3 of 45Hz for the SB42, a F3 of 48Hz from the SB29 (in less than half the volume of the SB15) a similar F3 from the SB23 is also possible. Room gain would push the in room F3 to the mid 30s - adequate for almost all music at sane SPLS save some large scale organ works and maybe hip-hop.
SB Acoustics SB42FHC75-6 15" Woofer from Madisound
SB Acoustics SB29NRX75-6 10" Woofer from Madisound
SB Acoustics SB23NRXS45-8, 8" Woofer from Madisound
Now we are not related to SB Acoustics, I am sure SEAS's Prestige series or ScanSpeak's Discovery series woofers would perform similarly (neither SEAS nor ScanSpeak have a 15" in their portfolio though). We just chose SB Acoustics so that our discussions were based on real world drivers and not any hypothetical drivers.
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While that article does discuss the polar patterns and how it changes and even why we need 4 drivers to effectively and effciently cover 10 octaves it does not discuss if, how, and why a single woofer having an Sd of say 600cm2 should sound different from 3 similar woofers each having an Sd of say 200cm2 (total Sd being the same). After all with even mm of movement (Xmax) one is moving the same volume of air with 3 x 8" woofers as one is with 1 15" woofer right?
That said I think the author forgot about modern wide range drivers (Fostex, Feasterx, PHY, Visaton, and Lowther) as well as smaller 'fullranges' (Jordan, CSS, Alpair, etc..) when he discussed the '3 octave rule'. Many of these wide/full range drivers can be linear over 5 octaves (200-6kHz) needing only a subwoofer (3 octaves) and helper tweeter (2 octaves).
For one thing you assume that all three smaller woofers move the same. Theoretically, they might, but driver-to-driver variation will produce somewhat different results out of each. Ideally, they should be in independent chambers to minimize effects from each other.
Polar dispersion, both horizontally and vertically, is not something you can just throw off the table, either. It impacts power response.
When you add multiple drivers they interact with each other's dispersion pattern, which causes lobing.
You also introduce different diffraction patterns from multiple drivers and different baffle sizes, so you really do not have an apple to apples comparison.
Lastly, the large woofer is a different driver than the smaller one. Again, you are not comparing apples to apples, just combined cone area, which is just one attribute of very many for a loudspeaker.
Polar dispersion, both horizontally and vertically, is not something you can just throw off the table, either. It impacts power response.
When you add multiple drivers they interact with each other's dispersion pattern, which causes lobing.
You also introduce different diffraction patterns from multiple drivers and different baffle sizes, so you really do not have an apple to apples comparison.
Lastly, the large woofer is a different driver than the smaller one. Again, you are not comparing apples to apples, just combined cone area, which is just one attribute of very many for a loudspeaker.
Why? Wouldn't having them in the same chamber couple them more closely and reduce the differences in the output (assuming that's even a problem)?
There's a very interesting thread about this by Geddes.
Loosely speaking, he finds that multiple subs at different positions sort of 'average out' the room modes leading to more balanced reproduction at any listening position. Although, beyond 4 woofers in a room, you get into diminishing returns.
jd
Loosely speaking, he finds that multiple subs at different positions sort of 'average out' the room modes leading to more balanced reproduction at any listening position. Although, beyond 4 woofers in a room, you get into diminishing returns.
jd
This is unlikely. The transient part of the music is reproduced by the tweeter. I don't see how the woofer can have any impact on that.
jd
If I am reading the original question correctly, it looks like this is multiple drivers in the same full-range enclosure, not subwoofers.
I agree with the Dr. Geddes on the multiple sub approach, but that wouldn't apply here.
I think that the transient response is really a non issue for lower bass. You might loose some mid bass transient response with a large woofer, but that was one of the points for adapting a 4-way approach as pointed out by Lenard Audio.
You hit one of the reasons why a multiple bass driver approach would be preferred in the first post. That is aesthetics. It just depends where your requirements lie and what you are willing to trade off.
Hum, you cannot reproduce drum's impacts a with a tweeter
Some instruments have their frequency range for from the treble. The frequency range of a snare drum is 90-1.6k
General Acoustics
Large woofers could have some problems with some high bass and low mid transient.
The ideal case is a 4 ways approach but a little complicated. In general it is possible to achieve successful designs with a 3 ways
. The multiple small woofers approach might simplify the design towards a 2 ways.
This is not correct. You want to place all the drivers in the same chamber, as long as the signal sent to each one is the same. Even in the case of manufacturing variations (e.g. 20%) in the various parameters (compliance, etc.) when you put them in the same chamber the result is a "lumped" response that is the combination of all three. Unless the parameters are very different (e.g. you use three completely different brands, models, etc.) then you should end up with a single equivalent response.
-Charlie
Hum, you cannot reproduce drum's impacts a with a tweeter
Some instruments have their frequency range for from the treble. The frequency range of a snare drum is 90-1.6k [snip].
OK, so what you are saying is that that transient part of up to 1.6k has to be delivered by the woofer. Hmm, sounds reasonable.
So, that means that you should select a woofer for the LF range you want in your speaker, iow don't select a 15 inch one if you want to cross over above 1kHz?
jd
navin
You're asking the wrong questions. The low frequency region is dominated by the room, not by the source. So it's solely a matter of where the source and the listener is located and how many low frequency sources there are.
Please see
mehlau.net > audio > multisub
http://www.harman.com/EN-US/OurComp...p/Documents/Scientific Publications/13680.pdf
Best, Markus
1. The woofer system (either 1 15", 3x 8" or 2 x 10") would be only producing the bass (sub 200Hz). At 200Hz the wavelength of sound is 1.7 meters (about 5 ft.). All 3 drivers (if we are considering 3 x 8") if in a linear array as used in most multi woofer systems would fit inside a 5 ft wavelength. While these 3 drivers would act like 3 different sources; at the wavelengths they are reprducing wont they effectively act like one soruce (now I am from the single big driver camp but am playing devil's advocate here).
2. One reason we looked at real world drivers from SEAS (Prestige), ScanSpeak (Discovery) and SB Acoustics was to compare all their attributes like Bl, Mms, Le, etc..
Oh yes one can understand this. But what if the multiple drivers are in a vertical array as used in most multi woofer 2 way and 3 way tower systems?
The question is that why are so many manufacturers using 2 8" woofers instead of a 12" or, to extend this argument, further 4 6" woofers instead of 1 15". WAF maybe one reason but most of these systems are suffciently deep for a 15" to be slapped on the side.
My gut tells me that a 15" gives better impact than 3 8" or 2 10" but there must be a scientific reason to this that goes beyond just plain driver specs (lets assume that 3 8" woofers have a combined Le, Mms etc.. of a 15"). Is it only psycological? You see a 18" woofer and expect more bass than say 2 12" woofers?
In my pre WAF days my bass system consisted of 2 JBL 2245 woofers in 2 10 cu. ft. B460 ported bass bins (top end was MTM using Focal 8N515s and Morel MDT33s) each channel powered by a bridged Adcom 555 (BGW 75 for the tweeters and 150 for the mids). When WAF got involved (and my SPL needs reduced) I switched to 4 12" DV12 ACI woofers (2 per cabinet) in 2 5.5 cu. ft. bass bins (top end was MTM using ScanSpeak 8546 and 9900) powered by a single Carver M1.0t (a home brew B&K ST140 derived amp for the top end)
Although the 2x12" woofers have the same Sd are a single 18" and can really pump, the visceral impact of the 18" (even at lower SPLs) was missing. Maybe it was the ported box, maybe it was psychologial, maybe Dr. Bose was right all along - all you really need is a 5" in a band pass box.
Transient response for me is for the entire system - woofers, mids, tweeter, amps, source and room.
I agree so lets assume the room is your average 350-400 sq. ft. (25' x 15' ok with everyone?) living room with say a 9ft ceiling and that the 2 sources are
a. Tower speaker with a 15" woofer (either on the front or side)
b. Tower speaker with 3 8" or 4 6" woofers.
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a 15 or a 18" may scientifically ,physically impress firstly , because it can represent optically a large wave . The height of that WL is given by the power
mainly , so from now we're talking about magnets,heat and air pressure.
Newer subwoofer speakers are projected to allow high temperature rises in the coil and magnet ,thou allowing higher power to be managed.Higher air pressure in the box will do the counter part ,striving the mechanical side of the driver to return to an ENTROPY state
and wasting currents from the amplifier. In the meantime , room air would be forced to resonate to those frequencies ,well ... we hope not , just letting them spread all over . In this case multiple subs may take a more authoritative control on air volume displacement.
mainly , so from now we're talking about magnets,heat and air pressure.
Newer subwoofer speakers are projected to allow high temperature rises in the coil and magnet ,thou allowing higher power to be managed.Higher air pressure in the box will do the counter part ,striving the mechanical side of the driver to return to an ENTROPY state
and wasting currents from the amplifier. In the meantime , room air would be forced to resonate to those frequencies ,well ... we hope not , just letting them spread all over . In this case multiple subs may take a more authoritative control on air volume displacement.
No sense in this case below 200Hz, any sub >10" can do well the job better than any smaller drivers. I never use n x 8" with a crossover lower than 500Hz. The real advantage is to handle big bass and a clean midrange. You add a tweeter and you obtain a 2 ways with high bass capability.
2.The question is that why are so many manufacturers using 2 8" woofers instead of a 12" or, to extend this argument, further 4 6" woofers instead of 1 15". WAF maybe one reason but most of these systems are sufficiently deep for a 15" to be slapped on the side.
Although the 2x12" woofers have the same Sd are a single 18" and can really pump, the visceral impact of the 18" (even at lower SPLs) was missing. Maybe it was the ported box, maybe it was psychologial, maybe Dr. Bose was right all along - all you really need is a 5" in a band pass box.
Transient response for me is for the entire system - woofers, mids, tweeter, amps, source and room.
These are link. Transient response for the entire system if all frequencies in the system are stimulated. With real music, only with big classical orchestras.
In an entire system you could have some slowness for example in a bass reflex system, the bass is very slow.
You use a smaller driver in the bass because it is faster but to be faster have less subjective impact. If you want impact the speaker must be slower and must deliver a high SPL bass, must be bigger. You might find the good compromise. I prefer a fast bass instead a slow bass.
Note bass impacts are very close recording not very true in real concert.
If you want impacts, a close box is perfect because the box also plays boom boom.
No, they do not act as one true point source, even if they are close together (< 1 wavelength).
You still get cross interference with multiple radiation sources. The lobing issue just gets much, much better when they are ganged close together, but it never totally disappears. That doesn't mean you can't use it to your advantage, but you need to model or build it and see the effect.
Lastly, integrating two or thee drivers in place of one is more challenging with respect to the crossover design due to impedance.
All fine drivers.
Side firing has its own problems. They are not horrible and can be done (have been done), but still have their issues. Everything is a compromise to one degree or another.
True, but the decision for a woofer compliment of 8", 10", or 15" does not impact transient response much beyond the crossover point. So, it is useless to discuss the mid and high frequency transient response at this point without discussing the rest of the driver complement.
If you cross that low, then you probably will never hear a difference. Particularly if it is a vented enclosure.
Personally, I like the 15" drivers because they are simpler to integrate, have a near ideal width for polar response, and are capable of moving large volumes of air. I use a JBL 2235H in my home loudspeakers and will be doing some experiments with Acoustic Elegance's TD15Hs when they arrive.
Your application may say otherwise based on cosmetics or personal preferences, but you still should be able to get fine results with a thoughtful design regardless of the architecture. Just look at what others are doing and their results.
You could also make the mains pretty small and add some small active subs if you have the power amps. I've seen some active designs that pack a 15" into a small sealed box and produce mountains of bass with the right driver. Results are flat to 20 Hz with a very high transient response and low phase shift due to the sealed architecture. Two or three of those in a room would be a better arrangement than a single 15" mounted in the mains cabinet and provide better management of room modes, which you will have.
Here is one example.
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