A Detailed Look at the Importance of Proper Loudspeaker Cabinet Bracing

mtrycrafts

mtrycrafts

Seriously, I have no life.
Here is a quote (edited the first part out because it doesn't apply to this topic) from Dr. Sean Olive that I found applicable to this thread.
It looks like he was in a discussion with someone on a forum. Do you have that link? It be interesting to read.
 
haraldo

haraldo

Audioholic Spartan
Perhaps my previous remark was a bit different than what I intended......

Something like 15 to 20 years ago Celestion made some top notch mini monoitors, they were very clean and revealing with a truly uncolored lively genuinely pleasing and natural sound, no trace of resonances and they could play quite loud without any sign of harshness or feeling of being pushed. Really made it enjoyable to listen to music through them.

I had the pleasue of attending a presentation by the chief designer of Celestion at that moment (I just don't remember his name) and this was very interesting, the design goals at that time was to make the cabinets as stiff and properly brased as possible and at the samt time minimize the weight of the cabinets as much as absolutely possible, in order to minimize the amount of stored energy that could be entered into the cabinet walls... The chief designers clear thoughts about this is that the less weight, the less stored energy and less ringing... When we talk about their speakers at the time is must have been working because the products were sensational :-D
 
N

Nuance AH

Audioholic General
So if I understand all of these articles and studies correctly, am I wrong in taking away from them that the quality and/or amount of bracing, along with the proper placement of said bracing is extremely important while the thickness of the cabinet walls takes a back seat?
 
haraldo

haraldo

Audioholic Spartan
So if I understand all of these articles and studies correctly, am I wrong in taking away from them that the quality and/or amount of bracing, along with the proper placement of said bracing is extremely important while the thickness of the cabinet walls takes a back seat?
I think it's not what's stated here.... both is extremely important.... thickness of cabinet makes panels stiffer, which decreases vibrations... so increased thickness and bracing works together in union :p
 
N

Nuance AH

Audioholic General
I think it's not what's stated here.... both is extremely important.... thickness of cabinet makes panels stiffer, which decreases vibrations... so increased thickness and bracing works together in union :p
Then what of Dr. Olive's sources and their study/findings? I would, of course, prefer a proper combination of sturdy cabinet walls and bracing, but Lipshitz and Vanderkooy's findings suggest that we may be putting too much importance into it.

Here's a portion of his quote for reference:

"Lipshitz and Vanderkooy concluded that you could get away with loudspeaker cabinets that were relatively light-weight and flimsy as long as you had adequate bracing judiciously placed etc to make the resonances fall below their detection threshold. "

I don't know how long ago their testing was, but I'd love to see this subject re-tested by professionals such as Dr. Olive or Lipshitz and Vanderkooy using the most modern technology and tools. I imagine things have changed quite a bit since their findings... I appreciate what Audioholics' team has done here, so don't take my statement the wrong way. Applying such findings to how it correlates with human detection would be nice, though. Perhaps a "Part 2" could be completed? :)
 
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mtrycrafts

mtrycrafts

Seriously, I have no life.
...

I don't know how long ago their testing was, but I'd love to see this subject re-tested by professionals such as Dr. Olive or Lipshitz and Vanderkooy using the most modern technology and tools. I imagine things have changed quite a bit since their findings... I appreciate what Audioholics' team has done here, so don't take my statement the wrong way. Applying such findings to how it correlates with human detection would be nice, though. Perhaps a "Part 2" could be completed? :)
It seems they did it before 1988 when Tool published his paper you referenced above.
I searched AES for a paper by him but didn't see one if it was published or I just didn't see one that could be it.

Thanks for that link to Olive's posts.

It would seem to me that with more bracing and thinner walls the resonance frequency would be going up and most likely of reduced amplitude to place it below the thresholds of detection or perhaps out thresholds are higher with frequency of this nature?
 
tonmeister

tonmeister

Audioholic
It seems they did it before 1988 when Tool published his paper you referenced above.
I searched AES for a paper by him but didn't see one if it was published or I just didn't see one that could be it.

Thanks for that link to Olive's posts.

It would seem to me that with more bracing and thinner walls the resonance frequency would be going up and most likely of reduced amplitude to place it below the thresholds of detection or perhaps out thresholds are higher with frequency of this nature?
The Lipzhitz et al. paper "An Investigation of Sound Radiation by Loudspeaker Cabinets" was written in 1991 -- 3 years after Floyd Toole and I published our paper on the detection of resonances, "The Modification of Timbre by Resonance: Perception and Measurement"

In re-reading the Lipshitz paper they conclude that some of the cabinet resonances on the worst-case speakers may be audible or "borderline audible" on certain signals based on our predictions of audibility of resonances.

The audibility of a resonance depends on its amplitude, Q, frequency and the signal exciting it (steady-state versus transient). The audibility of a resonance at a given level increases as the resonant frequency increases, and the Q decreases. So shifting the resonance up in frequency and lowering its Q will increase its audibility -- all things being equal.
 
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gene

gene

Audioholics Master Chief
Administrator
The Lipzhitz et al. paper "An Investigation of Sound Radiation by Loudspeaker Cabinets" was written in 1991 -- 3 years after Floyd Toole published our paper on the detection of resonances, "The Modification of Timbre by Resonance: Perception and Measurement"

In re-reading the Lipshitz paper they conclude that some of the cabinet resonances on the worst-case speakers may be audible or "borderline audible" on certain signals based on our predictions of audibility of resonances.

The audibility of a resonance depends on its amplitude, Q, frequency and the signal exciting it (steady-state versus transient). The audibility of a resonance at a given level increases as the resonant frequency increases, and the Q decreases. So shifting the resonance up in frequency and lowering its Q will increase its audibility -- all things being equal.
That assumes the amplitude remains the same which it doesn't as can be seen in David's analysis when adding more braces. You also need to look at more than a single point on the cabinet to see how the resonance modes change when stiffening is added.

Aside from simulations and analysis, I know from personal experience that I've never heard a boomy speaker that was well braced but I have heard many boomy speakers that had little to no bracing in them.
 
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lsiberian

lsiberian

Audioholic Overlord
That assumes the amplitude remains the same which it doesn't as can be seen in David's analysis when adding more braces. You also need to look at more than a single point on the cabinet to see how the resonance modes change when stiffening is added.

Aside from simulations and analysis, I know from personal experience that I've never heard a boomy speaker that was well braced but I have heard many boomy speakers that had little to no bracing in them.
I think the real question and one I want answer is how much bracing is enough to be high quality sound. Wood may be cheap, but simplicity in construction is always preferred over complexity that nets no audible benefits.

David's Analysis is helpful for addressing the effects of bracing on a cabinet in a pure motion sense. What is the audible threshold when adding another brace makes no audible difference?
 
gene

gene

Audioholics Master Chief
Administrator
I think the real question and one I want answer is how much bracing is enough to be high quality sound. Wood may be cheap, but simplicity in construction is always preferred over complexity that nets no audible benefits.

David's Analysis is helpful for addressing the effects of bracing on a cabinet in a pure motion sense. What is the audible threshold when adding another brace makes no audible difference?
Agreed and it really depends on the cabinet size, driver compliment, and output levels sustained within the enclosure. Most loudspeaker engineers choose to stiffen the cabinet enough to push resonance out of the bandwidth of the woofer to make it less audible.
 
tonmeister

tonmeister

Audioholic
I think the real question and one I want answer is how much bracing is enough to be high quality sound. Wood may be cheap, but simplicity in construction is always preferred over complexity that nets no audible benefits.

David's Analysis is helpful for addressing the effects of bracing on a cabinet in a pure motion sense. What is the audible threshold when adding another brace makes no audible difference?
That's the key question: at what point does the bracing/cabinet no longer contribute towards an audible improvement?

If the cabinet resonances are below the masked detection threshold, then you are over-engineering the speaker. Remember that for resonances at higher-medium Q-values, the level of the cabinet resonances must be almost as high as the output of the transducers to be audible.

So to answer the question, you need to apply a psychoacoustic model to the FEA output of the speaker cabinet to determine if the bracing produces audible changes.
 
gene

gene

Audioholics Master Chief
Administrator
That's the key question: at what point does the bracing/cabinet no longer contribute towards an audible improvement?

If the cabinet resonances are below the masked detection threshold, then you are over-engineering the speaker. Remember that for resonances at higher-medium Q-values, the level of the cabinet resonances must be almost as high as the output of the transducers to be audible.

So to answer the question, you need to apply a psychoacoustic model to the FEA output of the speaker cabinet to determine if the bracing produces audible changes.
Thanks for the clarity Sean and I agree though I suspect audibility is also highly dependent on what frequency range the problem exists too.

Since when is overdesigning a product a bad thing? Heck if it were, we wouldn't have Ferrari sports cars or any cars than can run a 1/4 mile faster than a turtle :)

Down the road, I'd love to build up some cabinets and do this type of analysis but I know many loudspeaker companies already do this when designing their product so its more practical (at least for now) to converse with them and see if they will share their data for a followup article.

I appreciate your feedback in this thread as always.
 
GranteedEV

GranteedEV

Audioholic Ninja
Sean, i've got a slightly off topic, slightly on topic question.

I've been trying to set up a pair of bookshelf speakers on a desk top for the last couple days. I'd wager they're pretty damn sturdy and cabinet resonances are not audible. My question is - Is transfer of energy through the underside of the speaker to the desk going to create issue? Is decoupling necessary when the speaker is atop a resonant structure such as a desk?

WHen I press my hands against the desk it does seem to be excited by the bass energy (msot likely transmitted through the air but maybe through the underside) but i'm not sure if this is affecting the sound quality to any appreciable extent (i'd imagine the room being the primary contributor to bass SQ). I haven't cranked the speakers loud enough to really excite anything meaningfully though.
 
Alex2507

Alex2507

Audioholic Slumlord
Sean, i've got a slightly off topic, slightly on topic question.

I've been trying to set up a pair of bookshelf speakers on a desk top for the last couple days. I'd wager they're pretty damn sturdy and cabinet resonances are not audible. My question is - Is transfer of energy through the underside of the speaker to the desk going to create issue? Is decoupling necessary when the speaker is atop a resonant structure such as a desk?

WHen I press my hands against the desk it does seem to be excited by the bass energy (msot likely transmitted through the air but maybe through the underside) but i'm not sure if this is affecting the sound quality to any appreciable extent (i'd imagine the room being the primary contributor to bass SQ). I haven't cranked the speakers loud enough to really excite anything meaningfully though.
Don't be so cheap and just get the MoPads already. You know you want to. :)
 
gene

gene

Audioholics Master Chief
Administrator
Sean, i've got a slightly off topic, slightly on topic question.

I've been trying to set up a pair of bookshelf speakers on a desk top for the last couple days. I'd wager they're pretty damn sturdy and cabinet resonances are not audible. My question is - Is transfer of energy through the underside of the speaker to the desk going to create issue? Is decoupling necessary when the speaker is atop a resonant structure such as a desk?

WHen I press my hands against the desk it does seem to be excited by the bass energy (msot likely transmitted through the air but maybe through the underside) but i'm not sure if this is affecting the sound quality to any appreciable extent (i'd imagine the room being the primary contributor to bass SQ). I haven't cranked the speakers loud enough to really excite anything meaningfully though.
sticky rubber feet can be bought at home depot for $3-4 per set of 4. I installed these under my desktop speakers and it was beneficial to my ears.
 
its phillip

its phillip

Audioholic Ninja
just get the cheap alternatives from the foam factory :)

my desk is a 6' plastic table, and the mopads do help me (plus they were handy for angling the speakers up). it wasn't so much that the speakers sounded bad on the desk, it was that the desk sounded bad with the speakers on it :D
 
Alex2507

Alex2507

Audioholic Slumlord
sticky rubber feet can be bought at home depot for $3-4 per set of 4. I installed these under my desktop speakers and it was beneficial to my ears.
Maybe if you cut Tom's salary a little you'll be able to swing the MoPads from the Audioholics Store.

I'm leery of that foam store but that's a different discussion.
 
lsiberian

lsiberian

Audioholic Overlord
Since when is overdesigning a product a bad thing? Heck if it were, we wouldn't have Ferrari sports cars or any cars than can run a 1/4 mile faster than a turtle :)
I'd say when you need a forklift to move it up the stairs. :D

I didn't know you had a Ferrari. :D
 

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