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Cabinet weight and sub output question
Cabinet weight and sub output question
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Old 6th February 2019, 01:09 PM   #1
bvdd is offline bvdd  United States
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Default Cabinet weight and sub output question

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.
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Old 6th February 2019, 07:08 PM   #2
GM is offline GM  United States
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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
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Old 6th February 2019, 09:29 PM   #3
bvdd is offline bvdd  United States
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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.

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?
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Old 6th February 2019, 10:12 PM   #4
mark100 is offline mark100  United States
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Originally Posted by bvdd View Post
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
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Old 6th February 2019, 10:14 PM   #5
bvdd is offline bvdd  United States
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Originally Posted by mark100 View Post
Yep.

I've read if you can squish a sub between enough sandbags, you can gain 3 dB...hope to try this someday


thanks

guess you don't like my example
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Old 6th February 2019, 10:22 PM   #6
GM is offline GM  United States
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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
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Old 6th February 2019, 10:27 PM   #7
bvdd is offline bvdd  United States
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Originally Posted by GM View Post
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

I had no idea this was a real thing -
I thought you guys were just giving me the business.
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Old 6th February 2019, 10:40 PM   #8
GM is offline GM  United States
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Originally Posted by bvdd View Post
Is that the idea simplified?
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
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Old 6th February 2019, 10:51 PM   #9
bvdd is offline bvdd  United States
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Originally Posted by GM View Post
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.
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Old 6th February 2019, 11:22 PM   #10
GM is offline GM  United States
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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
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Last edited by GM; 6th February 2019 at 11:24 PM.
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