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In Reply to: RE: As An Observation, Looking at Your Rig - Not With Your Speakers... posted by Doug Schroeder on October 19, 2010 at 07:09:14
Doug,
I appreciate what you've said, but what I haven't added to my system's description is the fact that I'm presently using a pair of 15" Hawthorne Audio OB "Augie" woofers in my system to cover from 100Hz and lower. In addition to that, in the past I've had Hartley 24" woofers and still have a single Harley 18" woofer at present. So I've "heard" what I believe to be bass.
Perhaps I wasn't very clear in my OP, but it's not a matter of what I believe I hear as much as it's a matter trying to understand how a room that's physically smaller than the size of the wavelength of a note I'm trying to produce can actually produce that note. To my perhaps misguided way of thinking that's sort of like trying to fit an elephant into a closet.
Thetubeguy1954 (Tom Scata)
SETriodes Forum -- Central Florida Audio Society -- Fullrange Drivers
==============================================================
"The man that hath no music in himself nor is not moved with concord of
sweet sounds is fit for treasons, stratagems and spoils."
- William Shakespeare
Follow Ups:
So, philosophically, replying to the inquiry, my thought would be, "How much of an elephant does it take to fill a room? Let's say you have an 8'x8' room (small, I know, but necessarily so for illustrative purposes). A mature bull elephant would likely fill this room and some to spare. If the entire beast's back end filled the room then it still might be said that you had an elephant in your room.
Likewise, just because the entire wave does not fit into the room unmolested by walls does not mean the wave cannot emanate from the driver/source and extend naturally until it hits a wall.
If music traveled through a solid medium then you would be correct. However, since it propagates through air the size of room restriction does not apply. Thus, the good analogy of headphones.
I think most will accept that it is possible to obtain deep low bass in a small room, even a car. But I have found that while bass quantity is relatively (too) easy to obtain (maybe especially in a small room), that the impediments to quality bass are found more numerous small rooms. Invariably, I have found that larger rooms or smaller rooms that have immediate and largely unfettered access to an adjacent larger space have a chance at audibly higher quality bass (less boomy, for example)as perceived by the listener. This is a generalization. There are plenty of exceptions, I'm sure.
Robert C. Lang
Hi
“I'm presently using a pair of 15" Hawthorne Audio OB "Augie" woofers in my system to cover from 100Hz and lower. In addition to that, in the past I've had Hartley 24" woofers and still have a single Harley 18" woofer at present. So I've "heard" what I believe to be bass.”
I am sure you heard something BUT…..
An open baffle cannot couple to your room gain slope by virtue of the fact that the larger the wavelengths get, the closer the two phases are and more completely they cancel out. The Hartley woofers were impressive…once. Now one can easily exceed their performance in a smaller space.
A suggestion for a DIY project.
Take your rooms longest dimension, find the frequency where that distance is 1 / 2 wl (sound travels about 1132 feet /sec).
Look for 12 or 15 woofer with a low Fs and large Xmax (like 10mm or more. DO NOT consider power handling, brand or studly looks.
Model each of these in a sealed box of a volume you would accept in your room (some people don’t mind a refrigerator in the corner).
Pick the one that gives the low corner knee nearest your theoretical room number and nicest shape. If you have a giant volume, try two drivers.
Overlay these, it is easier to see the figure of merit for each when you consider the model predicts at a given voltage or power, so the area under each curve is what you want. An alignment that is say 6dB higher along the low roll off slope with a lower overall or upper range sensitivity may be what fits your room better, your looking for LOW bass now, part of that is the roll off slope.
IF you have a suitable crawl space or an opening into another space you can use, then mount the driver in the wall or floor. With a much larger volume behind the speaker, it is much easier to get the Fb close to Fs in line with a large room.
What may not be optimal here is the Q or shape of the low corner. If one has an amplifier where you can adjust the output impedance (was often a damping factor control), then one can easily raise the Q to result into a optimally flat response.
Alternately, a series R will have the same effect although throws away some power.
The goal being that you align your low corner with the rooms estimated lowest mode. This makes the speakers roll off compliment the room gain in the smoothest way. If you can do this with “enough” capacity, the effect is not subtle and you will likely find there is vlf content you have never heard in many things. Understand this frequency extension IS NOT anything like "Turning the subs up"
It is true real rooms do not have the theoretical 12 dB / octave rise that a sealed concrete bunker has, the rooms I have measured tended to be more like 3 to 9 dB per octave. Still, the more one can take advantage of the room gain, the less volume you must displace to have a meaningful signal. By meaningful, I mean that until one reaches and exceeds the threshold of hearing, and then masking, there is no point is even producing the very low frequencies.
Without sufficient fundamental capacity, one produces much too much upper harmonic spectrum often leading to the conclusion that adding a subwoofer muddies the sound. Well, in that case, it does but not from the low frequency output but rather the much more audible harmonic distortion.
Lastly, cross this into your system as high in frequency as possible as the lower the crossover F and or greater slope, the greater the crossover delays involved are. Given what your crossing into doesn't have a defined / measured phase response i have seen, trial and error listening should govern the selection.
With TEF measurements a passive or with a loudspeaker controller, an exact electronic crossover solution is possible.
Best,
Tom
Tom,
I deeply appreciate you're taking the time from what must be your very busy schedule to help me with this! I would definitely like to try this experiment, and I will if you'll first help me comprehend some things that are apparently self-evident or self-explanatory to you, but are lost on me, ok?
1) You said "Take your rooms longest dimension, find the frequency where that distance is 1 / 2 wl (sound travels about 1132 feet /sec)."
My audio room is 15.5' L. So if I'm understanding what you're asking me to do. The frequency I want is 37.5Hz whose wavelength is 30' and hence was a 1/2 wl of 15' So is 37.5 the wavelength I'm looking for in #1?
2)Look for 12 or 15 woofer with a low Fs and large Xmax (like 10mm or more. DO NOT consider power handling, brand or studly looks.
I have a pair of 15” Woofer that were built to spec by TC Sounds for Jon Lane Design. These have cast four-legged frames, 3.5" flat wire coils, heavy copper Faraday motors with underhung geometry and precision machined gaps, vented poles, hard paper cones, cloth surrounds, flat lead-in wires woven into the rear suspension. Xmax is 10+ mm. The rest of the specs are:
NomR: 12 ohms
Revc: 9.2 ohms
BL: 25.75 TM (!)
SPL: 94.25 dB
Qms: 6
Qes: .27
Qts: .25 ik
Vas: 355 litr.
Cms: 350 uM/N
Mms: 130 Gm.
Fs on these is under 25Hz.
Will these suffice?
3) Model each of these in a sealed box of a volume you would accept in your room (some people don’t mind a refrigerator in the corner).
Well I don't really want refrigerator sized boxes, but would 4'x3'x2' be sufficient enough or will they need to be bigger? After that I'm DIY illiterate and don't know how to even begin modeling these? Heck I even have to pay someone to build the cabinets to put them in.
4) Pick the one that gives the low corner knee nearest your theoretical room number and nicest shape. If you have a giant volume, try two drivers.
This is where I start getting really lost! I have no idea of what the "Low corner knee is" and what is the "theoretical room number" you're refering to? I suppose you can see how it gets even more confusing for me after that. I still appreciate your trying to help me, though..
Thetubeguy1954 (Tom Scata)
SETriodes Forum -- Central Florida Audio Society -- Fullrange Drivers
==============================================================
"The man that hath no music in himself nor is not moved with concord of
sweet sounds is fit for treasons, stratagems and spoils."
- William Shakespeare
Hi Tom
Answer one , yes. The lowest room mode is usually in the neighborhood of that ½ wl frequency.
From your driver spec’s and tolerable box size, there is a combination which looks promising and smaller than you upper limit.
Make one ten cubic foot cabinet for box drivers –or- make two five cubic foot enclosures for one driver each. I say 10 cubic feet with a loose tolerance, 9 to 11 works fine too.
Brace the walls, a thumb rule, no more than about 10 inches of un braced panel (using Baltic birch). There is no need to go crazy or overboard with bracing either but some is required, the larger the panels, the greater the number of braces. Cross bracing to an opposing panel is also very effective.
Be sure to brace the baffle board around the driver mounting, that is where the drivers inertial component is felt. Cover the interior walls of the box with fuzzy but don’t fill it.
Perhaps, one could make towers that “hid behind” the main speakers?
Now, tuning into your room. If you measured the response as is, one finds a somewhat over damped sealed box response with an Fb about 37Hz. This would probably sound pretty good and tight as is with a good sensitivity.
IF these were subjectively too loud or on a separate amplifier (where you could adjust level separately) then one can add say 2 Ohms (use 2X25Watt) in series with each driver. This lowers the overall sensitivity BUT produces a response “knee” more in line with the knee in the room gain slope. Once at the correct level, this alignment will have more deep bass, also if separately driven, one can add an equalizer to help smooth the rooms LF response..
Once you have something you can listen to and measure, you can zero in on the “low pass” xover filter. If you feel or measure that you would like a little more vlf content, then fill the enclosures with fiberglass. That will shift the Fb where the response knee is, downward a bit.
This should get you squarely into the VLF realm, potentially single digits.
Best,
Tom Danley
Thanks Tom! I'll inform whoever builds my boxes about the 10" bracing rule and I'll definitely cross-brace, I'd rather over-brace than under-brace anyway. I'll be using a seperate solid state power amp for these sub-woofers, so I'll definitely have control over their volume vs the Sachikos. I'd like to ask a couple more questions, if you don't mind. You said either make one a ten cubic foot cabinet for both drivers –or- make two five cubic foot enclosures for one driver each. Am I mistaken in believing those are minimum dimensions? In other words can I make these boxes too big?
The reason I ask that is I actually wanted to make the cabinets for these woofers as close as possible to the size and shape of the Sachikos and place them just to the outside of them. The Sachiko's measurements are 72"H x 12.5"W x 19"D and I was originally thinking of making the woofer cabinets 72"H x 18"W x 18"D Is that possible or will I ruin something? Sorry Tom I honestly don't know about DIYing speakers and I'm attempting to learn. Now speaking of the woofers enclosures, I thought that Fb was a tuning frequency of a ported enclosure. So are these woofer enclosures you've mentioned sealed box or ported enclosures?
I really don't see needing the subwoofers to be used any higher than 100Hz, but you previously said "...cross this into your system as high in frequency as possible as the lower the crossover F and or greater slope, the greater the crossover delays involved are" so what frequency do you think I should cross over at? Maybe this will help. When my friends did a frequency test of the Sachikos with the FE208ES-R drivers installed as the test continued dropping down in frequency from 200Hz to 160Hz to 125Hz to 100Hz all was fine. However at 80Hz it was 3dB. then from 63Hz to 50Hz it was down 6dB, and finally by 40Hz the bass output was down a full 12dB! I have a chance to purchase a used Velodyne's SMS-1 (Subwoofer Management System)that a friend who originally purchased two, is offering to sell me. All it's different functions tested & reviewed at the link below.
Finally my audio room is 15.5'L x 12.5'W with a ceiling that slopes from 8' (where the speakers are) to 10' (where I sit) on the 12.5 wall. The only thing that seperates the audio room from the 12.5'L x 12.5'W kitchen is a wall that juts out 3' and extends from floor to ceiling on the side where the ceiling is 10'H. On the other end of the kitchen the only thing that seperates my kitchen from the 9.9'L x 12.5'W dining room is another wall that juts out 3' and extends from floor to ceiling on the opposite side where the ceiling is 8'H. Finally believe it or not nothing seperates the dining room from my 15.5'L x 12.5'W living room. So I "think", but I've been told I'm wrong that my speakers will "see" that entire space! However "if" I am correct in that case the length that a bass wavelength can "see" is now almost 54' in total. I added the length of the audio room 15.5 + the kitchen length 12.5 to the width of the dining room 12.5 to the width of the living room 15.5 because they form an L on it's side altogether
Thetubeguy1954 (Tom Scata)
SETriodes Forum -- Central Florida Audio Society -- Fullrange Drivers
==============================================================
"The man that hath no music in himself nor is not moved with concord of
sweet sounds is fit for treasons, stratagems and spoils."
- William Shakespeare
You're falling into the (very common) intuition trap. It is indeed possible, and you only need to consider the example of the headphone to realize this. .5" is a pretty short wavelength :)
Bass is supposed to sound big. 6.5" is not a woofer size.
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