Dual-500 king of the Castle

And this, this is full of good info too.
BTW, I have this and Bob Metzlers book in pdf if your email is fairly robust..
 

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The Powerful Difference said:
Lee,

Snagged the last one. (Only 1 I could find -- the law of Supply & Demand has conspired to make this a bit more dear...but given the lab I'm piecing together it's a relative bargain. (ie: It doesn't matter how much gear I've amassed, it's how many x how deep I have managed to test/fix/hotrod/WOPL/etc. And this book looks to be just the ticket to accelerate my "Zero to I got this" time. :0)

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Thanks again! When I said I wanted help spending my money, I meant it. And IMHO there's nothing like a small library of essential books at arm's length!

Stoked about this purchase!
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Believe me D3, I can spend other people's money....spent a LOT on location for our oil company..
 
The Powerful Difference said:
My last reply to this covered familiar ground having to do with the size & shape of the room vs. the physical wavelength of a given note.

But to better address your comment about room size vs. speaker size, (or more accurately, the speakers' ability to move a lot of air doesn't help make it sound better in a small room) I think I've got some additional insight to this phenomenon. My working theory is that when a system actually 'sounds loud' or 'congested' it's because we're not properly managing the energy that we are generating...and the higher the energy level, the more of a sonic mess all this becomes.

A better description would be that the energy we pumped into the room in the recent past is still decaying (that is, still audible) ...meanwhile, the right now energy is emanating from the loudspeakers on top of the old energy still bouncing back & forth in the 'smaller than optimal' room.

Before I continue, check out this short but very clear explanation of how they measure timing of the decay (reverberation) in a room.

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As an example, let's say that you are listening to me talk outside, with no nearby reflecting surfaces, and therefore no reverberation. My voice is clear against a quiet background. Let's say that we then walk inside and enter a large empty IMAX theater (spacious + all the surfaces are also treated acoustically) and I start talking again. Still no problem, for the words that I am currently speaking are not having to compete with the words that I said .1 / .2 / .5+ seconds ago.

Finally we walk into a 12' x 20' concrete block single-car garage with bare walls, floor, low ceiling, the doors are closed, & there's nothing else in it. Now, even though I'm speaking to you at the same loudness & enunciation that I used in the first 2 scenarios, now you are having intermittent difficulty in making out the words I'm saying. (Especially if I'm wearing a mask & you can't lip read.)

The problem is intermittent based upon the timing - that is, if I spoke a word louder (for emphasis) in the recent past, but right this moment I'm speaking softly, then (depending upon the distance from reflecting surfaces) the louder reverberation of the word that you've already heard washes out the softer word that you have yet to hear enough to recognize. Ergo, no loss in the quantity of sound, yet actual communication between us suffers. (!)

Q: So why does this problem worsen with increasing sound pressure level?

A: Because as you can see in the graph, the decay time is a constant, whether it's a 40db whisper, or a 100db musical transient. The thing is, 40db is a soft sound, so it will take far less time to decay to inaudibility (25db?) vs the time it will take for that 100db transient to decay to the same level of inaudibility. (Which will vary from person to person, plus the additional variable of how much each person's hearing has level-shifted due to how much sound that they have been recently exposed to.)

****

Check this out -- musicians are aware of this phenomenon, but look at how they discuss/debate what it's like to drive a room into 'compression'.

No wonder room acoustics are so difficult to discuss - we don't even share the same vocabulary when describing the same phenomenon, and to be sure both musicians and gearheads like us both want the quality with the quantity. :0)

One more thing to ponder. Let's say that in a small room you are playing a set of small monitors with very dense cabinets. So dense & braced internally in fact that the only sound emanating from them is coming from the drivers themselves -- no acoustic radiation from the cabs!

Now the well-behaved monitors are removed and a much larger set of '70's-era loudspeakers are brought in. The cabs are large yet made of 1/4" plywood. Unbraced. And they are *not* ported, so when you get that 15" woofer going, it really puts the pressure to the cabinet. And when you hit the resonant frequency of the large side panel(s) they 'talk'. It's actually been proven that with certain loudspeakers that the *cabinets* will emit more acoustic energy at specific frequencies than the drivers themselves. And guess what? That cabinet resonance is from the music that immediately precedes the music emanating from the drivers at that same moment in time. (!)

At this point in time I was going to talk about being able to quantify loudspeaker cabinet energy storage issues using MLSSA, but this is already too long, so I'll just embed the link and leave that as an exercise for the reader.

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Q: So, what does this all mean for you & I in our quest to have sound systems that just get bigger...instead of louder?

A: Most of us up 'til now only concern ourselves about how to best go about generating large quantities of clean, undistorted, acoustic power! But this is like building a car to accelerate very quickly to a high speed...but not worrying about if the brakes can haul it back down in an equally quick fashion.
So, in the land of audio, we have to make sure that whatever energy we create, we also give it a place to be attenuated/dissipated as quickly as possible. A quick example is that my speakers weigh 180 lbs each, but when I moved them into my house and they were sitting flat on the carpet, the bass was good at low listening levels, but with any real volume all the bass articulation/definition that helped me hear exactly which bassist I was listening to would disappear, and I would just hear a 'generic' bassist instead.

At first I thought it was a problem with the woofers, or maybe even my D500 amp running into trouble with the woofers...because I couldn't believe that 180-lb speakers would have an issue. As it turned out, I was talking to a fellow audio enthusiast at work, and he asked if I had tried the 'tiptoes'. "No, I didn't believe in them." So, of course he came down & together we put each speaker on 3 aluminum cones, flat edge on the bottom of the speaker, while the tip punched through the carpet & underlayment, and concentrated/coupled the entire weight of those speakers firmly into the 3/4" subfloor. Now, when the woofers really started working, the whole action/reaction thing now involved the solid subfloor in a 24'x24' room. (!)

Voila! The bass energy that was in the cabinet previously had nowhere to go, and so these large speakers were physically 'trembling' when sitting atop the carpet, smearing stuff up, but only when I turned it up towards 'life-sized' listening levels. Now, with the tiptoes installed, the speakers were able to 'sink' (ground) the old energy into the subfloor, and you could feel that the cabinets were much more stationary. And most importantly, the quality of the bass remained the same as I turned up the volume...

And the way that you make an entire room 'act' larger than it is, acoustically? That's where the bass traps in the corners, and acoustic treatments on the walls come into play. Because, if you do it right, it will help to mitigate the generation of standing waves in your listening room.

Apologies to anyone still wading through this, but if you are picking up what I'm putting down, then you may well find yourself listening to every room you enter for the next while. It's really interesting to do so. And finally, if you leave this post with more questions than you did when you entered, *perfect*. Because, the more I learn, the less I know. And I'm hoping that all this will spark some quality conversation...eventually leading to increased shared knowledge about this rather esoteric audio/acoustic theory.

"That's all I've got to say about that." - 3D gump
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3D, spot on.
I have experienced the same phenomena with speaker spikes but will say that the level of effectiveness depends on the subfloor and flooring. For example any carpeted room, spikes are a must. In rooms with suspended wood subfloors (second stories or peer and beam) using isolation plinths between the speakers and floors to reduce floor vibration is very affective. My current floors are 1/2 inch engineered solid wood, glued directly to the concrete subfloor, spikes have very little affect, in fact, I replaced my spikes with very dense felt pucks and could not tell the difference. My motivation for getting rid of the spikes was to be able to move the speakers without accidentally scratching the floors. Originally I had the type of spikes that have mating disks under the tips and are designed for hardwood floors but if while sliding them, one of the disks stuck to the floor a disaster could follow.
As to bass traps, yep they can be be extremely effective and anyone considering adding them should check out the many DIY videos out there, for very little money and time you can build and experiment with them.
On either side of my main system are two doorways, each opening into 12x10 rooms that turns out are the best bass traps you can have. The difference between having those doors closed versus open is amazing, closing the doors causes a spike at around 40hz, doors open, the room is pretty flat down to 25hz, then starts to roll off.
If I ever build a dedicated listening room, it will have a false wall with openings in each corner leading behind it into a space that is at least 5 feet deep and runs the width of the room. This is for two reasons, first the bass trap affect and secondly to be able to build audio racks into the wall so that my equipment is flush on the listening side and I have easy access the the cabling on the back side. A third advantage is that it naturally places the speakers out into the listening room without having anything between them. Ahh someday….
 
The Powerful Difference said:
My last reply to this covered familiar ground having to do with the size & shape of the room vs. the physical wavelength of a given note.
Click to expand...
“As a scientist Throgmorton knew if he were to ever break wind in the sound chamber he would never hear the end of it”. -from Bride of Dark and stormy, a book of worst novel opening lines...
 
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