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Bass driver vs room size
Bass driver vs room size
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Old 21st July 2017, 10:53 AM   #1
JRKO is offline JRKO
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Default Bass driver vs room size

My listening area is 15ft 6in long, 11ft 3in wide and 7ft 6in high. I like the sound of big speakers and before I move forward with the bass section of my 3-way (1.4in CD with 10in mid) need more info about drivers vs room size. Btw I'll be using minidsp to bring the room under control.

Larger drivers couple with the room better and I'd happily have a 18in driver but was wondering: Is it better or is there any harm/benefits to have more bass capability than is needed for your room and dial it back? Is there any sort of bass driver/multiple driver total radiating area vs room size correlation?
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Old 21st July 2017, 02:23 PM   #2
Cask05 is offline Cask05  United States
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Quote:
Originally Posted by JRKO View Post
Larger drivers couple with the room better...Is it better or is there any harm/benefits to have more bass capability than is needed for your room and dial it back? Is there any sort of bass driver/multiple driver total radiating area vs room size correlation?
When you come from the perspective of minimizing distortion, larger woofer areas move less for a given SPL at low frequencies. The types of distortion that are prevalent include the familiar harmonic distortion, of which it's been shown that only the higher harmonics are typically audible (i.e., 4th-10th harmonics, etc.). But those harmonics also turn into higher frequencies that modulate with the fundamental frequencies, producing non-harmonic sideband peaks. For woofers, the predominant type of modulation distortion has shown to be AM distortion, i.e., not Doppler--otherwise called FM distortion--which is the predominant modulation distortion type for higher frequency drivers: midrange, tweeters (see Klippel's paper on modulation distortion measurements, also Nelson Pass's article on distortion in amplifiers, pg. 6ff). AM distortion is due to nonlinear properties of the much greater woofer diaphragm motions than midrange/tweeter diaphragms.

So larger is better in order to reduce distortion during music peaks and low frequency impulses, like kick and bass drums. The penalty of using smaller woofer areas is not being able to turn the SPL up to anything much above fairly low listening levels, and having to ignore those modulation distortion bursts during LF transients (which people that haven't been exposed to live instrument sounds have learned quite well to ignore).

The best kind of bass, IMO, is horn-loaded, because the AM and FM distortion products move about 15-20 dB lower than the same drivers used in direct radiating mode. That's why horn-loaded bass sounds as good as it does (when done well).

I once had the opportunity to listen in-room to direct radiating ported cabinets having 1, 2, and 4 (15" diameter) woofers per side, and also a very good corner-loaded fold horn cabinet. The single and dual woofer cabinets had a definite "edginess" and artificial quality to their sound, while the quad woofer cabinet had a much more natural sound, albeit with the sound of "splintering wood" when driven hard. The horn-loaded cabinet sounded like the real thing.

So to address your question: there are no limits to woofer area/size of room, although at some multiple of woofer area size, the effects of direct radiation begins to disappear, except for the impulsive transients. Larger total woofer areas are better.

The tradeoff, of course, is a lower high-frequency roll off of larger diameter woofers, and the need to cross to the midrange drivers at a lower frequency. One way to get around this is to use multiple smaller woofer drivers, but then the 1/4 wavelength separation distance between the drivers playing at their highest frequencies start to create polar lobing issues. The other part of the tradeoff is size.

So the discussions about room coupling are mostly related to the small size of the diffuse region of the room (which is at a quite high frequency in a small listening room). I look at this situation differently: at what frequency do you need to start adding extra surround channels to add apparent spatial width/depth, and how many absorption panels to control early reflections around the loudspeakers themselves? The type of acoustic absorption panels used by virtually everyone however don't have much effectiveness below 100 Hz (and about 70 Hz for bass traps). This is the real limitation of smaller listening rooms--controlling early reflections, and usually not at the lowest woofer frequencies, i.e., usually above ~100-200 Hz for small rooms practically.

So my experience is to use as much "woofer area" as is tolerable in-room. For horn-loaded woofers that means horn mouth size: the larger, the better to control AM distortion and to lower the effective "Fc" of the room-loudspeaker array.

YMMV.

Chris

Last edited by Cask05; 21st July 2017 at 02:26 PM.
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Old 21st July 2017, 03:58 PM   #3
Godzilla is offline Godzilla  United States
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Hi JRKO - bigger is better, IMO. Which tweeter and 10" are you planning to use?
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Old 21st July 2017, 04:35 PM   #4
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Hi JRKO - bigger is better, IMO. Which tweeter and 10" are you planning to use?
I have this CD for 1500hz and up FaitalPRO | HF Drivers | HF144 and this for mids 150-1500hz ish http://www.bcspeakers.com/products/l...0/8/10md26.pdf
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Old 21st July 2017, 04:38 PM   #5
Cal Weldon is offline Cal Weldon  Canada
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Bass driver vs room size
James Rupert Kingsley Oborne. Did I remember correctly?
Yes, as the others said even if you don't need a huge woofer to satisfy, there are advantages to having more or larger...


...to a point.
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Old 21st July 2017, 04:43 PM   #6
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Originally Posted by Cask05 View Post
The best kind of bass, IMO, is horn-loaded, because the AM and FM distortion products move about 15-20 dB lower than the same drivers used in direct radiating mode. That's why horn-loaded bass sounds as good as it does (when done well).

Chris
Thanks for the reply! So are we talking something like THAM15 & Tuba? Any design recommendations to get me going?
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Old 21st July 2017, 05:02 PM   #7
freddi is offline freddi  United States
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Bass driver vs room size
fwiw I'll have a little midbass horn scaled from the old University Classic which will run a surplus 8 ohm Eminence 10 with 2" coil and 56oz magnet - don't know if it will play well or not. It sims ~110dB 2.83v 1pi 1M

THAM15 is a small tapped horn - Tuba have long path for bulk and mouth size. Short path bifurcated horns like La Scala and Peavey FH1 roll off below ~110Hz outdoors.

I think John Inlow feels that folded horn carrying mids will never be as uncolored as properly designed straight horns.

135 hz Mid Bass Horn - The Paper Horn by Inlow Sound

the old Karlson K15 (designed in the summer of 1951 - debut 1952 HiFi show) shows 10dB or more two-tone sideband reduction vs reflex with some 15 inch speakers. I choose Karlson as front loaded midbass horn alternative. A "K12" is about as small as a traditional Karlson should be made.

lets say you have a BP4 bandpass box with good 12" woofer and 4 or 6 in ch port - its a 4 or 6 inch speaker directivity wise?
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Old 21st July 2017, 05:07 PM   #8
Godzilla is offline Godzilla  United States
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Looks like it will be an amazing sounding speaker! I have a B&C DE250 plus the smaller FaitalPRO horn - smooth!
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Old 21st July 2017, 05:10 PM   #9
Cask05 is offline Cask05  United States
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There aren't really that many instances of good horn-loaded bass out there, especially that will integrate aesthetically with the room size that you've identified. I think a La Scala-style bass bin (perhaps with djk's ported bin extension on the bottom to extend a little below 70 Hz) coupled with some version of a Fitzmaurice-designed FLH (if you can get them all into the room). The University Classic horn-loaded bass cabinet (single mouth instead of dual on the La Scala) would actually work a little better in terms of maintaining wider midrange polars.

Sometimes you can get away with a smaller DR sub that's pretty clean in terms of phase/group delay and harmonic distortion figures in the size room that you've identified, depending on your typical music choices and your ideas about how much true low bass (e.g., double bass and kick drum, or conversely pipe organ, etc.) that you prefer. I know that a lot of people are not really into accurate bass below ~40 Hz. I'm one of those that prefers to have flat FR and clean bass down to at least 30 Hz or lower (20 Hz is much better) but this gets more problematic in smaller listening rooms.

Chris
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Old 21st July 2017, 05:15 PM   #10
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Quote:
Originally Posted by Cal Weldon View Post
James Rupert Kingsley Oborne. Did I remember correctly?
Aw man! You remembered my full name Now it's out there again . Must have made some sort of impression.......

Quote:
Originally Posted by Cal Weldon View Post
Yes, as the others said even if you don't need a huge woofer to satisfy, there are advantages to having more or larger...


...to a point.
More vs larger? 12x2 vs 18x1?
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Last edited by JRKO; 21st July 2017 at 05:27 PM.
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