Question about Speakers vibrations

echelion

Member
2015-12-07 11:49 am
Dear all!

In first place, i want to say hi to all the comunnity. You have the best forum in the world about diy audio and its a gorgerous resurce for absolut dummies because your rigurosity. Im from Malaga, south Spain, and its very difficult found resources in spanish with rigurosity and good quality info.

However and before of entry in the matter of this post, i want to say sorry for my english, its not my mother tongue.


Few months ago, i build four scoops thats lather i converted in two 2x15. I dont follow any planes and started from scracht. I committed a lot of errors in that desing, but i dont care, i learn a lot about that errors (with help of your forum and anothers) and i solve the major part with sucesive mods.

At day of today, im very happy with that subwofers. Has good "wooob woob" and are so louder for 2x15' 50€ 300w speakers.

But for finish them, i have this problem: I use MDF of 16mm and the wood has loads of vibrations. I put a lot of screws. I want to ask you posible solutions about this problem.

I focused in this options, but i dont know if its better doing one, some or all the options and i want your advice.

1) Break the linearity of the flat bottom with a curve wood
2) Put foam or other absorbent material inside
3) Reinforce all the walls with another layer of wood (this will make heavy for the low power of that boxes)
4) Seal all the unions of the wood with Sicaflex, silicon or something similar

Sorry for the looong text!!

Very big hug and gratitude for all!

[IMGDEAD]https://scontent-mad1-1.xx.fbcdn.net/hphotos-xaf1/v/t1.0-9/1915668_635977719876625_4388726663014773588_n.jpg?oh=50aac5316ba0248909def2a072788032&oe=57BAF3FC[/IMGDEAD]

PD: Are the bottom subwoofers (black and red)
PD2: Another day, i want to publish my other desing, the 2x 6x9 speakers. And although not believe me, they sound great for plywood boxes only 75w and 15€.
 

turk 182

Member
2012-10-26 3:03 pm
well MDF is not the right material for sub boxes that are going to be worked hard in a DJ rig.

baltic birch (furniture or marine grade) with multiple plies is far superior(but costs more sorry in this case you get what you pay for) and sealing all adjoining pieces is a must (leaks can severly reduce output)
as far as "rounding" over fold areas it will increase higher frequency output ( not really what you want coming from a sub) stuffing or damping is useful but is not a cure all.
internal bracing such as 1x2 glued and scewed at odd angles can help reduce the vibration of large panels.
 
Last edited:
Another chance: dipol.
The backward sound is not cased and does not pump the casing. And you would not need big casings. And, pa, you could tune by filling with any stuff - all different circumstances.
To stiffen "closed" mdf-casings is very elaborate. You have to connect the opposite planks all 8 - 10 cm!
"Closed" casings I would fill up - not pressed, but full - with textile, like t-shirts, stockings,-) No wool, no foam, no expensive speaker-damping. Everything else and unfilled, or sparsely filled does rumble and roar (the inner sound comes through the membranes, modulates the correct-phasing sound, as example).
...
 
1) Break the linearity of the flat bottom with a curve wood
2) Put foam or other absorbent material inside
3) Reinforce all the walls with another layer of wood (this will make heavy for the low power of that boxes)
4) Seal all the unions of the wood with Sicaflex, silicon or something similar

None of the above. The boxes likely need to be cross-braced internally.
 
A dipole is as pressure stressed as any bass reflex cabinet, the fact that is open does not change this ṕhenomenon. Try an open baffle and feel the vibrations. The whole point of baffle is to separate the front and backwave (of oppoiste pressure) to cancel out each other.

Imagine that the cone is moving forward. A positive pressure wave will propagate radially in front of the driver, and an equal negative pressure wave from the back of the cone. The pressure waves are separated by a wall be it in a box or baffle. Both are subjected to Newtons third law with respect to the cone movement and to the pressure differerenses.
 
A dipole is as pressure stressed as any bass reflex cabinet....

Strange physics!

A moment's thought will reveal that the ghostly effects of phase cancellation around the back (which monumentally disturbs members of this forum) are nonsense. Yes, for steady-state sine waves there will exist certain points, lines, and contours in space where complete cancellation will exist in an anechoic chamber. But instead, think of a music bouncing off six surfaces.....

Using dipoles for decades over 140 Hz, I've never observed or measured any such cancellation. Likewise, when I had a gigantic open baffle sub with a 20 Hz driver, the room eigentones swamped any cancellations too.

Ben
 
Theory and experience,-)
FULLRANGE! 12 x 12". Even in front of a wall they play subs - but ugly in general, cause all reflexions and resonances of the (big) casing are reflect. But with some, or a lot, place, a dream. Clean! Clean! Clean! - relative to "closed" big casings. A dream. Never I would use separate subs, big horns or br or bp for big performances again.
And cheap,-!
 

Attachments

  • WIN_20160118_100358.JPG
    WIN_20160118_100358.JPG
    144 KB · Views: 97
  • WIN_20151230_102258.JPG
    WIN_20151230_102258.JPG
    185.8 KB · Views: 97

just a guy

Member
2006-05-12 6:59 pm
Another chance: dipol.
The backward sound is not cased and does not pump the casing. And you would not need big casings. And, pa, you could tune by filling with any stuff - all different circumstances.
To stiffen "closed" mdf-casings is very elaborate. You have to connect the opposite planks all 8 - 10 cm!
"Closed" casings I would fill up - not pressed, but full - with textile, like t-shirts, stockings,-) No wool, no foam, no expensive speaker-damping. Everything else and unfilled, or sparsely filled does rumble and roar (the inner sound comes through the membranes, modulates the correct-phasing sound, as example).
...

Theory and experience,-)
FULLRANGE! 12 x 12". Even in front of a wall they play subs - but ugly in general, cause all reflexions and resonances of the (big) casing are reflect. But with some, or a lot, place, a dream. Clean! Clean! Clean! - relative to "closed" big casings. A dream. Never I would use separate subs, big horns or br or bp for big performances again.
And cheap,-!

This is a pro sound application. Dipole losses are very real and suggesting a dipole subwoofer for a prosound application is ridiculous, it won't work.

Looking at your pictures, it appears that you have 12 drivers that are at least 12 inch, maybe 15 inch drivers in a very small room. THIS is exactly why a dipole subwoofer for a prosound application simply isn't going to work.

The lean and clean sound of dipole comes at the very real cost of dipole cancellation. In a small room dipoles can do well if designed properly but only above the Schroeder frequency. Below the room's modal region it's impractical to use dipoles, as dipoles don't produce any room gain.

In an open space prosound environment where there is no Schoeder frequency, no room modes, no reflections, dipole simply makes no sense. You would need to spend a fortune on drivers and it still would never be loud enough. You could fill the entire stage with dipole subs and it would never be loud enough.
 

just a guy

Member
2006-05-12 6:59 pm
Strange physics!

A moment's thought will reveal that the ghostly effects of phase cancellation around the back (which monumentally disturbs members of this forum) are nonsense. Yes, for steady-state sine waves there will exist certain points, lines, and contours in space where complete cancellation will exist in an anechoic chamber. But instead, think of a music bouncing off six surfaces.....

Using dipoles for decades over 140 Hz, I've never observed or measured any such cancellation. Likewise, when I had a gigantic open baffle sub with a 20 Hz driver, the room eigentones swamped any cancellations too.

Ben

The dipole cancellation phenomena is well understood, well documented, and very real. Anyone who has actually used a dipole speaker or subwoofer should know very well that they are output limited below the baffle step frequency due to cancellation. Using them in a small room will obviously net some benefit above the Schroeder frequency due to reflections and modes but dipole cancellation is very real and it does take a huge toll below the baffle step frequency.

With regular normal placement in a room the dipole cancellations will happen right at the edge of the baffle, long before the waves ever get to the boundary reflection points. So whatever is left after the cancellation can be reflected and can cause room modes but in any normal situation the cancellation occurs long before the waves ever reach the walls of the room.

It may be an inconvenient fact for you, but measurements do match the math on this subject and it can all be easily simulated. I have a wealth of experience with dipole speakers and subs, the measurements don't lie, they directly support the theory.

Your 1 meter square dipole panels are no exception. Due to their huge size the baffle step frequency is quite low. This is a baffle diffraction profile of a 1 meter square baffle with the entire surface area radiation source, like your ESL panels.

sv4bgg.png


As you can very clearly see there ARE no losses until you get lower than 140 hz. THIS is why you didn't notice or measure any losses in the panel's passband when only used above 140 hz. The theory isn't wrong, you just don't understand it. The losses below 140 hz, below the baffle step frequency are significant.

Maybe ask yourself why you chose 140 hz as a lower limit to use these panels. Was it a manufacturer's recommendation? Was it because they don't do well below 140 hz? It seems strangely convenient that you chose 140 hz to use as a crossover point when the theory indicates that 140 hz is the lower limit to the diffraction profile's flat response and below 140 hz the diffraction profile takes a nosedive into very low spl territory. This can't be coincidence. This is dipole cancellation theory in full effect providing real world measurable results that match the theory.

As for your dipole subwoofer, it's a unique case of a massive baffle size located parallel and only a few inches from a wall. It's not a true dipole in that sense, it's actually just as similar to a bandpass as a dipole because it does have an acoustic load on the cone provided by the air between the massive baffle and the wall.

The theory is not wrong, the measurements match the theory and the sims match the measurements. The problem is that you don't understand the theory.
 
Last edited:
I would furthermore recommend:
Your sum: In rooms no problems. Further: Including a lot of stuff and people ... One drawback: Rumbling and roaring not everywhere. Dipols play a bit focussed.
Open air: A chance for the neighbourhood not to get everything and not to play subsonics. Nobody wants +/- 0 dB, 20 or 40 Hz. Your mesurement under "ideal"-) circumstances shows - 3 dB, 100 Hz, -6 dB, 80 Hz. Square 1 meter. 15" drivers end in 1,50 meter or more. And it is simple to extend locally. Or by filling a bit (as described) to get an other relation front - back - sonic. And including a lot of stuff and people around...
Than: The most never listened clean subs. They listen per Dynaudio or Sonus Faber, per Marshall or HK. Clean subs, clean tones at all, require stone or any synthetics. No chance to get per wooden-material. The most misunderstand rumbling and roaring casings as subs. A little chance are dipols. Required decoupled and clamped drivers, as every driver has to be, and tuned ...
I would furthermore recommend.

But: cause the most never listened clean subs, may be they would miss rumbling and roaring. A problem that I know. And: The most want bawl, bellow, cry, not listen good music well or get real rhythm to dance,-)
 
I would furthermore recommend:
Your sum: In rooms no problems. Further: Including a lot of stuff and people ... One drawback: Rumbling and roaring not everywhere. Dipols play a bit focussed.

In room it IS a problem. If you want to play flat lower than the baffle step frequency the driver qts (or eq) has to provide the extra gain to keep the response flat. This comes at the HUGE price of MASSIVE excursion below the baffle step frequency. MJK's open baffle papers show this clearly but don't focus on the excursion required to keep the response flat below baffle step. http://www.quarter-wave.com/OBs/OB_Design.pdf
This is all very simple to simulate too, and measurements match the sims.

Open air: A chance for the neighbourhood not to get everything and not to play subsonics. Nobody wants +/- 0 dB, 20 or 40 Hz. Your mesurement under "ideal"-) circumstances shows - 3 dB, 100 Hz, -6 dB, 80 Hz. Square 1 meter. 15" drivers end in 1,50 meter or more. And it is simple to extend locally. Or by filling a bit (as described) to get an other relation front - back - sonic. And including a lot of stuff and people around...
Than: The most never listened clean subs. They listen per Dynaudio or Sonus Faber, per Marshall or HK. Clean subs, clean tones at all, require stone or any synthetics. No chance to get per wooden-material. The most misunderstand rumbling and roaring casings as subs. A little chance are dipols. Required decoupled and clamped drivers, as every driver has to be, and tuned ...
I would furthermore recommend.

This is ridiculous, of course you want flat response (+/- 0 db) down to the low knee regardless of whether you are inside or outside. And the low knee frequency should be determined by the lowest frequency of the tracks you play.

A dipole played outside is not going to do what you suggest. The figure 8 dispersion pattern will throw as much sound backwards as it does forwards. The only cancellation area is to the sides. So the neighborhood people directly behind the stage will get the same spl as the audience in front. The neighbors to the side will receive less due to cancellation.

Dipole cancellation is a HUGE issue. You can use U or H baffles to try to extend the effective baffle width but you can only make the cavities so deep before the cavity resonances push down into the passband of a subwoofer. MJK's U and H frame examples are only 7.5 inch deep cavities, and even with cavities this shallow the cavity resonance shows up around 200 hz, limiting the passband to a 200 hz high end. http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

You can stuff the cavities of a U or the back cavity of an H frame. The more stuffing you use the more the dispersion pattern will stray from dipole and become more and more cardiod. At some point, with enough stuffing you can completely block the back wave and the sub will operate more similar to a sealed box in terms of dispersion pattern.

They physics and theory of all this stuff is very well known and has been for several decades now. Pure dipole flat baffle, dipole U and H frames, stuffed U and H frames all have significant dipole cancellation losses and will never have as much spl as a simple sealed box. This is fact.

In pro audio sealed boxes don't have enough spl so going dipole or cardiod makes no sense at all. You need MORE spl than a sealed box not less.

But: cause the most never listened clean subs, may be they would miss rumbling and roaring. A problem that I know. And: The most want bawl, bellow, cry, not listen good music well or get real rhythm to dance,-)

As I said I have extensive experience with dipole speakers and subs. They do indeed sound very lean and clean. It's an experience that everyone should try. But it's only efficient ABOVE the baffle step frequency. BELOW the baffle step frequency there are huge losses.

These losses can be countered with high driver qts or eq BUT this comes at the cost of massive driver excursion. And below the Shroeder frequency there's no point to dipole at all.

This is EXACTLY why you have a dozen 12 or 15 inch drivers in your very small room. A single horn loaded 12 inch driver could produce more output than all 12 of your dipole subs and it can do it with very low distortion. The sound will be completely different but when spl matters dipole is NOT the way to go.
 
My last horns were 160 kg things,-) Not just wooden-rumblings. Believe, I would not listen these. No chance,-) To get the same max. output, the same "room under pressure", the same rumbling and roaring ("distortions"-!) - the common measurement does not show - would not be my aim.
All common theory and measurement is just a minimal extract. As example: A 1000 W complementary-pp. Good measurement, clear theory - for the most - but unacceptable in sound. Horrible. The most would prefer,-) Every little se beats easy, cause less stages, less parts, indifferent parts...
The most do never "understand"-), cause they do use may be perfect flat frequence response, less "distortions", somehow fine time-resonance, but rumbling and roaring speakers. Never listened - cause never compared. Never clean.
Speaker-building is at moment in fledging stage. Too much is not regarded. Simplest physicially ideas not regarded: as to clamp. Did anybody, did you ever? And there is much much more to regard.
My suggestions furthermore: Try a lot, make your own experiences, be not frighten by common measurements and common theories.-) Extend and supplement these.
Or remove,-)
 
Dipole subs aren't going to work for PA applications.
Example - I put a pair of Beyma 15P1200Nd on OBs, one per side. EQ'd to 20Hz, cone excursion got to 30mm p/p and they were pulling around 300w per driver. Decent listening volume, but not excessive.
The same drivers in small sealed boxes make the house (old, solid stone walls) make complaining noises, and go louder than you'd ever need in a domestic environment.
The OB setup was a little cleaner at low volumes - next to no room interaction meant that the LF there was very very good. Headroom was a huge problem, though. As I said, 30mm p/p travel on peaks at LF when turned up a bit. Linear travel is 19mm p/p, so the peaks were likely being compressed.


Back on-topic, which is fixing the 2x15 subs.

I'd recommend gluing triangles into the joins where the cabinet walls meet. Do lots of them. You'll increase the strength of the joints hugely.
Putting cross-bracing inside a constructed cabinet will be difficult, but not impossible. This will help stop the panels bending.

Use good wood glue, and (if you haven't done already) go along all the joins in the wood you have already. Use lots and wood glue - its very strong.

Chris
 
My last horns were 160 kg things,-) Not just wooden-rumblings. Believe, I would not listen these. No chance,-) To get the same max. output, the same "room under pressure", the same rumbling and roaring ("distortions"-!) - the common measurement does not show - would not be my aim.

There's no need for horns to be anywhere near 160 kg.

Common measurements show exactly what you would expect. Resonances cause time decay issues, these can be seen in any number of different measurements - waterfall, impulse response, phase, etc. There's nothing here that isn't measured or completely understood.

Resonances can boost output by an incredible amount. But you can also design for minimal resonance and have a ported box that sounds like a sealed box but has more max spl.

All common theory and measurement is just a minimal extract. As example: A 1000 W complementary-pp. Good measurement, clear theory - for the most - but unacceptable in sound. Horrible. The most would prefer,-) Every little se beats easy, cause less stages, less parts, indifferent parts...
The most do never "understand"-), cause they do use may be perfect flat frequence response, less "distortions", somehow fine time-resonance, but rumbling and roaring speakers. Never listened - cause never compared. Never clean.
Speaker-building is at moment in fledging stage. Too much is not regarded. Simplest physicially ideas not regarded: as to clamp. Did anybody, did you ever? And there is much much more to regard.

The notion that enclosure design is at a fledgling stage is so ridiculous I can't believe I even have to respond to this. The theory has been established 100 years ago or so. There have been VERY few innovations in enclosure design in the last few decades.

There's a difference between max flat alignments (of the sealed, ported or other varieties) vs flat in room response. Flat in room response is ALWAYS the goal (unless you prefer a bit off boost like bass boost or a bit of cut in certain ranges, like a BBC dip).

MANY people find sealed, ported, and other types of enclosures that were designed to have a "max flat" anechoic response to sound boomy, loose and bad in room. That's because a "max flat" design is NOT flat in a room.

I have no idea what you mean by "clamp".

My suggestions furthermore: Try a lot, make your own experiences, be not frighten by common measurements and common theories.-) Extend and supplement these.
Or remove,-)

I have tried a lot. I've tried a lot of OB speakers and subwoofers too. I know how to design them properly and I know the pros and cons of OB. I also know the pros and cons of other alignments because I have tried a lot of them too. And I know how to design them for any given performance goals.

There's a very good reason you don't see more OB speakers being used. They are only efficient above the baffle step frequency and there's no reason at all to use them below the Shroeder frequency. What you end up with is a situation like your pictures - a dozen 12 or 15 inch subwoofer drivers in a very small room. Assuming placement a couple feet from walls, the subwoofer ends up taking up a large percentage of the room. It's a nice clean sound but it's incredibly inefficient below the baffle step frequency.

The "common measurements and common theories" are not wrong. I agree, everyone should try it. But not many people will find the compromises worth the physical realities of inefficient bass reproduction.
 
I don't know anything at all about those speakers and I'm not going to look them up any further than to see that the first appears to be a small ported 2 way speaker and the second appears to be a raw woofer, so I'm not even sure what you are asking.

I make decisions based on system goals. Based on the brand name I can pretty much guarantee that I wouldn't choose either of those speakers for pro sound use, which is the intent of this discussion.