83 posts
Chris,
Yes, I think you may have too much in there. That's why I suggested starting with only a layer on the back, then going from there. You may have deadened it too much. In hi-fi, that's always good. In guitar, it's "to taste." Start with a little. Add more til you don't like it anymore then back off a little to what sounded best. This should vary from cab to cab, speaker to speaker.
FB, The differences will always be FAR greater in closed back cabs, followed by open back cabs with small openings. Your amp has a LARGE opening, making the damping properties of the insulation have far less effect.
A good example of an "open back" cab that could really benefit is the Avatar. It has a small oval opening, so it has a great deal of back panel reflection.
You know, now that I think about it, it sounded a lot better as an open back cab. I'm gonna try it with just the back pad (closed) then without a back at all or maybe a half back. I'll let ya know...
cgtrox 8-)
"And now for something completely different!" ;D
Yeah, no doubt it will sound DIFFERENT with an openback cab. Different in every room, different every time you move it a few inches closer too or farther from the wall, etc...
Both cab types have their advantages. Closed back is just more consistent and controllable in more situations. And has tighter and deeper bass with smoother rolloff. If you like tight, punchy, chunky bass, and like to palm mute, a closed back cab with "some" insulation is the best case scenario with almost any cab/speaker combo.
Do you think it also has something to do with "gig" level vs. apartment level? I'm sure it does. I also put a 4" tape square on the inside of the grill cloth as a beam blocker.... I left that out. :-/
cgtrox 8-)
Chris, absolutely! But, it should HELP more at gig level than at bedroom level. At lower levels, there isn't nearly as much SPL bouncing around inside the cab to start with, so the insulation won't make as much difference. If you loved it at lower levels, and didn't like it at higher ones, that would tell me you put too much of it in the cab.
#2, the tape instead of beem blocker thing has mixed results. People say that since it just blocks those higher freqs. that come out the middle, but doesn't redistribute them (ala the beam blocker) that it causes high freq. standing waves in front of the speaker and does more harm than good. They say it smears the highs some, rather than just blocking the "beam zone" for the ice picks. Again, some say it works. Depends on what "works" for you, and your speaker, and where you are listening from (position-wise) when you hear the differences.
Hey Howie, I tried insulating one of my cabs by burying it underground about five feet down. Although the noise levels are down to nothing, I can't seem to hear any highs, or lows... Do "they" think that this might be due to the levels? :D
Craig, when I haven't tried something, I will still relay the things I've heard others say. I've never tried tape in front of the speaker dust cap. SRV did. That doesn't make it good. It was a crude solution for someone who played in many smaller to mid sized clubs with LOUD BRIGHT Fedner amps.
Next time I talk to "them," I'll try to get some feedback on burying the cabinet. I think this could be the ultimate dead iso cab thing that Deano was working towards.
p.s. Is it waterproof? Have you thought about potential termite damage? Did Alice In Chains write a song about being in your speaker cab?
DreamTheaterRules — Mar 17, 2009 I've never tried tape in front of the speaker dust cap. SRV did. That doesn't make it good. It was a crude solution for someone who played in many smaller to mid sized clubs with LOUD BRIGHT Fedner amps.
Well, it works! Pretty damn good, too. :)
cgtrox 8-)
When I was in high school (78-81) I can still remember SRV playing local gigs at small clubs in town and the surrounding area. I NEVER went to see him as I was into Priest, Maiden, Saxon, etc. I could kick myself now... >:(
cgtrox 8-)
I only saw him twice, but they were big venues. And he was the opening act...
This was back when he was headlining, also. But he was the ONLY act playing, too.... :D Some of these places were just hole-in-the-wall types. Then after he "made" it, my brother showed me a couple of DVD's and I was just floored!!
cgtrox 8-)
Get "El Mucombo" (sp) It is killer! Best SRV I've ever seen and I have 4 of his DVDs.
Will do, thanks bro! :)
cgtrox 8-)
thank Sheep. He's the one that turned me onto that one.
Thanks Sheep!! :D ;D
cgtrox 8-)
Well, I took out the "extra" padding and it sounds very nice! I left the padding on the back panel ONLY and it seems to have worked! Very nice, all is zen again...for now! :D
cgtrox 8-)
that's great news. This is what I expected, but let me know once you've had more time with it. And, where the heck I can find some dacron! LOL I'm ready to do a google if I don't find it at this place I found and we are going this weekend.
Now I KNOW you have to have some kinda arts and craftstore over there in Ohio! That's where I found mine. It's about an inch thick and very fluffy. Hell even check out WalMart, I know they have a fabric dept. Good luck bro...
cgtrox 8-)
I looked at Wal Mart and Hobby Lobby. Hobby Lobby had some stuff, but it was polyester and I prefer Dacron. I was going to try it, but it was $18, and I keep hearing you can get Dacron (better) for $4-$5. So I'll keep looking. If I don't find some soon, I'll search online.
I got mine from some obscure crafts store, it had it on sale, too! It wasn't a big name chain. Try just a mom n pop fabric store.
cgtrox 8-)
Hey guys, I also built a half-back panel with two jacks. I put the padding on the inside of that one, too. I haven't tried it yet, but it gives me the option for a closed back or open back cab, depending on the music and venue! I have them both setup up with the detachable connectors on the speakers so I can interchange them in about five minutes.
cgtrox 8-)
my Lopo is open/closed back convertible. Nice option to have if you play different styles/tones.
Hmmm, I guess I could build that 2nd part and just remove THAT back and forth, eh? Will do... :-[ :-[
cgtrox 8-)
I've seen several styles of convertible cabs. One was top half/bottom half, with the top being removable. The other was thirds, with the top and middle being removable, so you had 3 options. Closed, top open, top and middle open. The third one I've seen was thirds approximately... the middle appeared smaller than the top and bottom), with only the middle section being removable.
If I was building one, I'd build the thirds style with either middle only, or top and middle removable. I don't like a ton of open space back there (like most combos have) because the more back wave you introduce into the room, the more potential for phase and other issues. Might sound better in one room, bad in another, etc. What I'm saying is, in general, the more open back the cab is, the more room influenced the sound will be.
Too late, I made the two piece. It's not that big of a cab anyway, so I don't think a 3 piece is doable. It's gonna be cool to be able to change it by removing only five screws! Cool! Thanks for all the help and input Howie!
cgtrox 8-)
hey, no problem with that. The two piece will work great and is closer to what a normal openback combo is. Glad to help. You'll dig the convertible option.
Hey!! We had a gig last Saturday night and the "convertible" worked great! ;) I get to the venue for the soundcheck, crank it up to gig level, tried it both ways and ended up with the closed cab on this one. It's just really cool to have that option available. It's almost like having another amp to choose from! :)
cgtrox 8-)
OK folks... I know, I'm in/out very infrequently, these days. Lots of things going on at work, can't post so much any more. :'(
Couple of things about this... there are MANY factors that affect the cabinets "sound" and the overall effectiveness of a material that you put into the cabinet to "absorb" the sound/reflections/modes.
So, let's get to it, shall we... the cabinet itself has dimensions which are rectangular, in nature. The opposite walls of the cabinet create what are called standing waves, modal resonances and/or eigentones. The frequencies that these are at can be calculated using the following formula:
565 / L
Where "L" = distance in feet from wall to wall. An 18" value = 1.5 feet... 24" = 2 feet, etc.
Let's say the cabinet is 18 x 15 x 12. The standing waves, inside the cabinet, will occur at the following frequencies:
12" - 565Hz
15" - 452Hz
18" - 377Hz
These resonances WILL occur no matter how well the cabinet is designed/made, just so you know. If the cabinet is "poorly constructed" (using that in quotes because some very "poor" designs sound very good (i.e. Fender's "floating baffles", etc).
These "primary resonances" really define the "sound" of the cabinet. These resonances continue to "ring" after you've stopped playing, for roughly 50-100mS. A Marshall 4x12 cab will resonate at a frequency much lower than that. (226 Hz - on the 30" sides, and 565Hz on the 12" side).
Now... beyond the primary resonant modes (standing waves) that exist, every time a frequency emanates from the rear of the cone it bounds off the side, top, bottom and back walls and, of course, just plain buggers right through that flimsy paper cone. These reflections, from the cabinet walls, hit the microphone both in/out of phase w/ the primary sounds emanating from the speaker.
If the cabinet is made of wood, most of these reflections are pushed right back at the speaker and go through it. MDF and/or plywood both absorb about 5-7% of the energy hitting them. The 93 to 95% of the reflected energy will head out the speaker. Because the distances are relatively short, much of that energy will hit the mic... these reflections will cause a certain amount of comb-filtering, mainly in the higher frequencies. Depending on how well/poorly the cabinet is constructed these can cause some "smearing" of high frequency energy right in that range we use with our brains/minds to determine concepts like "clarity" and "presence" and etc.
If the back/front baffles flex, as they many times do because most manufacturers use low-grade, 3/8" plywood (many use grade B/C plywood which has a lot of pits/air spaces and isn't quite solid), there can be low frequency emanations as a result of cabinet flex that further "smear" and "blur" the final result. Good quality 3/8" panels should resonate, sympathetically and relatively in-phase with the sound.
So... all that said, let's look at acoustical materials. There are several things that determine acoustical material efficiency and/or effectiveness. First, that absorbent NEEDS to be able to pass gas - I mean air MUST be able to flow through it. If it can't, then it's not an effective damping material, at all. It's just stuff. If you're using foam it MUST be open-cell foam! If it's closed-cell foam, it is primarily reflective, not absorptive.
Moving on - the next thing that determines foam effectiveness is density - usually expressed in pounds per square, or cubic, foot. Quality foam, will have a high density (i.e. 2-3 lbs per sq. foot, or 5lbs per sq. ft. etc). The denser the foam, the more effective it is at lower frequencies. Those open-cell foams you get from Wal-Mart (egg crate bed pads), have a density of about 1/4 to 1/2 lb per sq. foot. They are effective, because of that, at frequencies above about 5-6kHz - just a tad beyond what your guitar speaker(s) reproduce well. So not too effective.
To give you an idea of the differences in quality - SONEX (standard) runs 2-3lb / sq. ft. density. AURALEX runs about 1lb / sq. ft. and the difference in capability is expressed in the NRC ratings. NRC ratings typically have a few values:
125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz 8000Hz
.025 .014 .100 .57 .98 1.25 2.00
.100 .574 1.000 1.25 1.50 2.00 2.10
So, the above, has NRC values for two different things. I made them up, but they're kind of close to Owens Corning 705 (2") and standard pink foam from Wal-Mart.
Under 125Hz, the foam (top line) absorbs 2.5% of 125Hz. The rigid fiberboard absorbs 10% at the same frequency. Thus it's much more effective at 125Hz. Above 4kHz (top) and 500Hz (bottom) the absorbent actually absorbs 100% + of the sound (complete absorption). I have yet to understand how it can absorb more energy than is pushed at it, but that's just part of acoustics. Whenever you see the value of 1.0 coefficient of absorption, you've got 100% of the sound energy hitting the absorbent, absorbed.
Let's say that you want to keep some of resonance (6dB down from what it is now), but not all of it. So, if you look at the frequencies, above, for that 15 x 18 x 12 cabinet, again:
12" - 565Hz
15" - 452Hz
18" - 377Hz
The "center" frequency (average) of all of these is roughly 465 Hz. The "loudest" will probably be 565Hz (12"), next loudest should be 15" (452) and the lowest level will be the 18" (377Hz). SPL decreases as a function of the square of the distance. :-) So, that's why they'll be at different levels. But you have to damp, for something, so you typically damp for the average.
So, what you'd look for then, is a foam/material that has an absorption coefficient of about .5 (50%, or 6dB SPL) at 500Hz. More than that will damp more than 6dB, less than that will allow the cabinet to "ring out" more.
Now, the next step, then, above the control of modal resonances is the control of reflections off the back of the cabinet. Absorbents (i.e. Auralex panels, dacron, etc) suck at absorbing low frequencies. You'd need to look for a 1.50 number in the 125Hz region for it to be effective. Thus, the low frequencies are going to be reflected out. Because the wavelengths of those frequencies are so much longer than the distance the wave has to travel it'll be mostly supportive (in-phase) w/ the speaker movement. So, you should be OK, there.
Reflections are going to be above the 465Hz region... these are mainly high frequency reflections/noise that interfere w/ the clarity of the signal and, many of these (above 1kHz) are going to be out of phase with the signal from the speaker! OOOOOHHHHHHHH!!!!! Out of phase. How do you know which those are? 1130 ft / second / 1 foot = 1130Hz. Anything with a wavelength smaller than 1 foot (1.13kHz and above) will be out of phase with the speaker movement. So, taming those reflections will help, in overall clarity of the high-end of the output.
On the 15" side, reflections above 905Hz and on the 18" side reflections above 755Hz will also be out of phase. So, to "tame" these you're looking for an absorber that would range from about .75 (500Hz) to 1 (1kHz). That should get roughly 90% of the 755Hz issues (which is WELL below what would cause issues w/ a mic on the other side) and all of the reflections above that point. This should "clean up" the sound of the cabinet.
Now, all of that said... that is the THEORY behind how this all works. It's up to you to decide whether or not this really makes the difference you want in practice. The reason I say this? 99.99999% of the guitar tones we're used to listening to, both live and on recordings DO NOT have absorbent located in the cabinet. All those phase issues, reflection and modal issues ALL exist in those tones. Thus, the end-result MAY NOT be anything that you're looking for. It'll be relatively "different..."
To that end, what you end up with, then, is a cabinet that still has the primary modal resonances damped to some extent, but still there to provide "body" and "fullness" to the overall-end result. Because you've steeply attenuated the highs you need to have some attenuation on those lows to keep the end-result relatively "balanced".
You've also, then, built a cabinet that more "accurately reflects" the tone of your amp in combination with the speaker (driver) in the cabinet. Again, that will either be good, or bad, depending on your perspective and your overall musical tastes/objectives. Again, you have to be the judge.
By putting in something like Dacron, which IS NOT a very good material as it's non-breathable plastic, you're damping SOME of the resonances, probably under 5% (0.05) and you're damping SOME of the high-end reflections (around 30-40% - 0.3 to 0.4 values) to the 2-4kHz region. This will reduce the overall volume of the noise reflected from the cabinet without it being to oppressive. That'd get you about 30% of the "way there" but it'd be a cheap way to determine if you like the "quieter" more "damped" internals.
Anyway... there you have some of the theory, how to read the specs of the absorbent materials, etc. Let me know if you have questions.
If you have real questions PLEASE email me directly at: kornowsd@zeecon.com. I'll get to them much faster than here.
Dar
:o I should have had you write it up, then. That took a lot of work... :'(
Dar
Sorry, I forgot to add the tags. :D
I tried running your description through Alta Vistas Babelfish translator, but it just caused my PC to smoke... ;)
First, that absorbent NEEDS to be able to pass gas - I mean air MUST be able to flow through it.
Craig knows a way to measure that and has a nose for it. :)
