Hi all,
I build Thiele design 15" cabinets using 3/4 plywood for subs which work great for what I do.
On stage, I use two cabinets crossed over at 100hz, powered by a Crown XLS 1502 in bridge mode - 1500w @ 4 ohms.
Cabinet size is roughly 24" x 22" x 19". No feet - plywood bottom sits flat on the floor.
Now, I've noticed that some 3/4 plywood weighs noticeably more than others.
Would the lighter vs. heavier plywood weight difference affect the bass response and perceived volume of the cabinet?
I have always assumed that a heavy cabinet 'connects' with the floor better and would yield better results than a lighter cab - given same speakers and dimensions.
Is this true ?
Thanks.
I build Thiele design 15" cabinets using 3/4 plywood for subs which work great for what I do.
On stage, I use two cabinets crossed over at 100hz, powered by a Crown XLS 1502 in bridge mode - 1500w @ 4 ohms.
Cabinet size is roughly 24" x 22" x 19". No feet - plywood bottom sits flat on the floor.
Now, I've noticed that some 3/4 plywood weighs noticeably more than others.
Would the lighter vs. heavier plywood weight difference affect the bass response and perceived volume of the cabinet?
I have always assumed that a heavy cabinet 'connects' with the floor better and would yield better results than a lighter cab - given same speakers and dimensions.
Is this true ?
Thanks.
It does and why I recommend adding weight to the tops of regular speakers to preload them so to speak to the floor. If have any doubt, just stand on one.
In prosound the goal is to brace them well and keep them as light as practical and stack them to gain weight and/or when practical, hard mount them to the floor, walls like was done with the CV Earthquake subs.
Another option is to make bipoles, so they ~ cancel out their rocking motions.
As for using lighter plywood, you gain some weight back due to increased bracing requirements, but stiffness is gained quicker via bracing than material thickness, so worth the effort overall in weight/cost reduction.
GM
In prosound the goal is to brace them well and keep them as light as practical and stack them to gain weight and/or when practical, hard mount them to the floor, walls like was done with the CV Earthquake subs.
Another option is to make bipoles, so they ~ cancel out their rocking motions.
As for using lighter plywood, you gain some weight back due to increased bracing requirements, but stiffness is gained quicker via bracing than material thickness, so worth the effort overall in weight/cost reduction.
GM
So if I understand you correctly, a really simple way to make a difference in sound when using a cab with lighter plywood (with plenty of bracing), would be to ad some weight right on top of the box - like for example, a concrete block.
Just an example of course.
Is that the idea simplified?
Yep.
I've read if you can squish a sub between enough sandbags, you can gain 3 dB...hope to try this someday
It can definitely require a lot, especially a poorly constructed one as this fellow found out when deciding to make it strictly temporary:
Mass Loading ALTEC A7 VOTT 825 enclosures - drlowmu - High Efficiency Speaker Asylum
High Efficiency Speaker Asylum
Ideally they needed to be set in a massive sandbox, but one can only do so much in a given situation.
GM
Mass Loading ALTEC A7 VOTT 825 enclosures - drlowmu - High Efficiency Speaker Asylum
High Efficiency Speaker Asylum
Ideally they needed to be set in a massive sandbox, but one can only do so much in a given situation.
GM
Correct, see extreme real world example since no added bracing [he didn't want to destroy its poorly performing originality].
Others have used their huge vinyl collection, money change in jars, boxes, wicker baskets, etc., marble, slate, cast concrete, etc., 'plates', large planters [my fave for a bit of carbon dioxide 'scrubbing', damping around the speaker], even built a few into the cab top. Anyway, you get the picture
.Note that with tall, skinny cabs either a more massive and/or wide base is required if any chance children, pets, the elderly with balance problems, etc., can potentially topple them. I used outriggers, though in retrospect if there's enough room to trip over them, someone will eventually [and did].
GM
Correct, see extreme real world example since no added bracing [he didn't want to destroy its poorly performing originality].
Others have used their huge vinyl collection, money change in jars, boxes, wicker baskets, etc., marble, slate, cast concrete, etc., 'plates', large planters [my fave for a bit of carbon dioxide 'scrubbing', damping around the speaker], even built a few into the cab top. Anyway, you get the picture
GM
Well, maybe you can offer some insight on my specific issue.
I have one cab that weighs about 12 lbs more than the second one.
Same exact specs, speakers, bracing.
The older one is the heavier one and the one I built yesterday was apparently made with lighter plywood. I didn't notice anything until I was done and picked them both up.
Again, I run them in parallel, 1500w bridged @4ohms (not that it matters)
How concerned should I be that the new one will sound weak by comparison?
I appreciate your time, GM.
You're welcome!
Depends on the ratio of weight difference, box frequency pass-band, i.e. if the heavy one weighs at least a 100 lbs, then probably no big deal; but as a general rule, typical speakers, and especially high aspect ratio [tower, etc.] cabs need it, so would add identical weight to both [at least 50% of the heavier speaker] and if curious enough, do an A-B test with them side by side with a frequency that's the mean of the cab's box loading pass-band; basically near enough to [Fs*[2*Fs/Qts]]^0.5
GM
Depends on the ratio of weight difference, box frequency pass-band, i.e. if the heavy one weighs at least a 100 lbs, then probably no big deal; but as a general rule, typical speakers, and especially high aspect ratio [tower, etc.] cabs need it, so would add identical weight to both [at least 50% of the heavier speaker] and if curious enough, do an A-B test with them side by side with a frequency that's the mean of the cab's box loading pass-band; basically near enough to [Fs*[2*Fs/Qts]]^0.5
GM
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My bet would be that with well braced 24" x 22" x 19" cabinets, the 12 pound heavier (probably birch) cabinets would have no more than 1 dB more upper bass (around 100 Hz) and no more than 1/4 dB more low bass (around 40 Hz), and variations from speaker to speaker would be more than that difference, making a speaker swap needed before the difference could be determined.
If I'm doing the hauling, my vote is for a lighter, well braced cabinet.
Art
Hi, it's not just weight that matters.
It's more about keeping the box panels from flexing.
So, distributed weight will help more...hence surrounding with sandbags, etc.
Or more realistically to reduce flex.....as Art says..... well braced
Will work if you build a wall of sand bags.
Does weight matter at all?
Isn't it all about containing pressure, so no flex?
If you would build a stronger box with lighter and stronger wood, wouldn't it be a better box?
I.e. Okoume ply is 5/7 of the weight of birch ply at same thickness and is often used for boats.
Or go more extreme and build round as a round bucket (or boat) has hardly any flex compared to a square one.
When the point of bracing is to stop the panels vibrating, then the corners aren't the most effective place to put the braces. The corners are already relatively stable because of the joint to the adjacent panel anyway.
You really want the bracing near the centre of the panels, but offset a bit so you don't just create 2 smaller sub panels of identical shape & size.
The attachment was posted a few years ago on another forum by the principal of MM Acoustics, and is a pretty well braced box.
HTH,
David.
Attachments
Attached drawings of JBL Kit (year 1970). They reinforce the vertices, the center of the panels and an bracing of generous dimensions between the deflector panel and the rear panel. Everything helps to lower resonances.
I've always built my cabinets like that.
Attachments
It is clear that as the speakers and amplifiers have increased the power, the same happens with the number of reinforcements of the boxes.
Here is an example:
Supra Sub - www.pcpaudio.com
So I decided to also reinforce the missing vertices of the upper and lower panels of my current construction.
Here is an example:
Supra Sub - www.pcpaudio.com
So I decided to also reinforce the missing vertices of the upper and lower panels of my current construction.
Attachments
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