mechanical grounding systems in speaker cabinets

[SB99ACR]

Hello all, I am new to this forum and relatively new to this subject.
I am interested in building a 2 to 2 1/2 way speaker for 2 channel music.
I plan on using scanspeak drivers and all dueland crossover components.
I want to use the best materials and components that are available.

My main questions is.... have any of you built speakers with a true mechanical
grounding system?

I plan on constructing the cabinet from Finnish Birch plywood 1" thick front baffle and 1/2" and 3/4" on remaining surfaces and braces. I don't want a "dead" speaker. I want a lively sound but of course void of resonance and coloration to the extent reasonable.

I was going to use a very substantial grounding system built into the cabinet
in an effort to send vibrations to ground.

Fortunately I have access to cnc routers, gantry mills, waterjets and many other pieces of equipment to complete this project.

I would be very interested in hearing opinions of the effectiveness of this type of system. I have seen it done on very expensive speakers and want to try the concept in a smaller slim freestanding approach.

Thanks

 

[annunaki]

Technically speaking, using constrained layer damping, extensive bracing, decoupling the drivers from the cabinet, and use of acoustically absorbent material internally should make such a system uneeded. The above solutions push any form of resonance well below audible levels and when done properly render the enclosure acoustically inert.

 

[Swerd]

Welcome to the forum!

My main questions is.... have any of you built speakers with a true mechanical grounding system?

I plan on constructing the cabinet from Finnish Birch plywood 1" thick front baffle and 1/2" and 3/4" on remaining surfaces and braces. I don't want a "dead" speaker. I want a lively sound but of course void of resonance and coloration to the extent reasonable.

I was going to use a very substantial grounding system built into the cabinet
in an effort to send vibrations to ground.

I have built several DIY designs, but I have never run into this concept of a mechanically grounded cabinet, other than using the typical spiked feet. Can you describe this further, or provide a link that does?

Don't confuse a "dead" sounding speaker with a resonance-free cabinet. In as much as is practically possible, the cabinet should not contribute sound to the speaker. There are a variety of construction methods that attempt to minimize this, but none are perfect.

I am interested in building a 2 to 2 1/2 way speaker for 2 channel music. I plan on using scanspeak drivers and all dueland crossover components. I want to use the best materials and components that are available.

Of course, we want more details about your speaker design .

There is nothing wrong with Scanspeak drivers, but there is considerable debate and controversy within the DIY speaker building world on the benefit of high-priced crossover components, especially capacitors and resitors. Opinions abound on this subject, but there is little or no solid evidence that high-priced capacitors or resistors provide an audible benefit. There seems to be nothing better than standard metalized polypropylene capacitors such as the relatively inexpensive house brands sold by Parts Express or Madisound. The same is true for the exotic "non-inductive" audio-grade resistors. I'd save your money on these components and put it into drivers, crossover design, and cabinet construction.

 

[avaserfi]

What type of floor are you planning on placing these speakers on? If it isn't of sufficient mass, like concrete, by grounding the speaker to the floor you are potentially transferring energy to the room. Rather, if you decouple the speaker from the ground you will prevent any transferred energy.

 

[R-Carpenter]

Hello all, I am new to this forum and relatively new to this subject.
I am interested in building a 2 to 2 1/2 way speaker for 2 channel music.
I plan on using scanspeak drivers and all dueland crossover components.
I want to use the best materials and components that are available.

My main questions is.... have any of you built speakers with a true mechanical
grounding system?

I plan on constructing the cabinet from Finnish Birch plywood 1" thick front baffle and 1/2" and 3/4" on remaining surfaces and braces. I don't want a "dead" speaker. I want a lively sound but of course void of resonance and coloration to the extent reasonable.

I was going to use a very substantial grounding system built into the cabinet
in an effort to send vibrations to ground.

Fortunately I have access to cnc routers, gantry mills, waterjets and many other pieces of equipment to complete this project.

I would be very interested in hearing opinions of the effectiveness of this type of system. I have seen it done on very expensive speakers and want to try the concept in a smaller slim freestanding approach.

Thanks

What will you be using to measure speaker cabinet resonances, driver FR, distortions and so on?
Are you going to be doing all the woodwork yourself?

 

[highfigh]

Hello all, I am new to this forum and relatively new to this subject.
I am interested in building a 2 to 2 1/2 way speaker for 2 channel music.
I plan on using scanspeak drivers and all dueland crossover components.
I want to use the best materials and components that are available.

My main questions is.... have any of you built speakers with a true mechanical
grounding system?

I plan on constructing the cabinet from Finnish Birch plywood 1" thick front baffle and 1/2" and 3/4" on remaining surfaces and braces. I don't want a "dead" speaker. I want a lively sound but of course void of resonance and coloration to the extent reasonable.

I was going to use a very substantial grounding system built into the cabinet
in an effort to send vibrations to ground.

Fortunately I have access to cnc routers, gantry mills, waterjets and many other pieces of equipment to complete this project.

I would be very interested in hearing opinions of the effectiveness of this type of system. I have seen it done on very expensive speakers and want to try the concept in a smaller slim freestanding approach.

Thanks

If the floor system is lumber and somewhat flexible, energy transferred to the floor can influence the perceived speaker output. De-couple ot from the floor, but make the cabinet inert, as others have recommended.

If you don't care about cabinet weight, look into the Wharfedale speakers that used a space around the woofer's enclosure that was filled with sand. That's a good way to make it inert and if you leave a way to remove the sand, moving day won't be a problem. I had an uncle who built a pair of octagonal speakers with a table top on them, with down-firing woofers, one mid and two tweeters (90 degrees apart), in the late 1950s. They sounded really good and we discussed how he built them when I was working at a stereo store. With two young kids, he didn't have a big budget, so he used what he could get but as a technician at AC-Delco and having worked on the guidance system for Apollo, measuring the response, tweaking and getting similar response from both with mis-matched drivers wasn't hard.

Because Birch plywood isn't particularly dense, I would use MDF and avoid a lot of the bracing by bonding two pieces for anything that could resonate. Heavy and stiff beats light and stiff for performance, IMO.

 

[avaserfi]

If you don't care about cabinet weight, look into the Wharfedale speakers that used a space around the woofer's enclosure that was filled with sand. That's a good way to make it inert and if you leave a way to remove the sand, moving day won't be a problem.

Using the method you describe the sand will act as a decoupling layer, not a constraint layer. Because of this the drivers would need to be decoupled as well to take proper advantage of the sands implementation. Additionally, a cabinet within cabinet approach would be required for proper decoupling characteristics. While it is possible to compress the sand such that it does act as a constraint layer there are easier methods to mitigate resonances. The most simple effective way to build an inert speaker using a viscoelastic constraint layer and dense bracing would be far easier to properly implement.

Because Birch plywood isn't particularly dense, I would use MDF and avoid a lot of the bracing by bonding two pieces for anything that could resonate. Heavy and stiff beats light and stiff for performance, IMO.

Ply is not as dense as typical MDF products, but it is far more stiff. Due to this quality, cabinet grade, ply would be less resonant than MDF. Now, if the OP can find HDF or a composite material with density greater than 100lb^3 the situation would change, but such materials are extremely hard to find.

 

[TLS Guy]

Hello all, I am new to this forum and relatively new to this subject.
I am interested in building a 2 to 2 1/2 way speaker for 2 channel music.
I plan on using scanspeak drivers and all dueland crossover components.
I want to use the best materials and components that are available.

My main questions is.... have any of you built speakers with a true mechanical
grounding system?

I plan on constructing the cabinet from Finnish Birch plywood 1" thick front baffle and 1/2" and 3/4" on remaining surfaces and braces. I don't want a "dead" speaker. I want a lively sound but of course void of resonance and coloration to the extent reasonable.

I was going to use a very substantial grounding system built into the cabinet
in an effort to send vibrations to ground.

Fortunately I have access to cnc routers, gantry mills, waterjets and many other pieces of equipment to complete this project.

I would be very interested in hearing opinions of the effectiveness of this type of system. I have seen it done on very expensive speakers and want to try the concept in a smaller slim freestanding approach.

Thanks

I would recommend a two and a half way. Are you doing the speaker plans, tuning and crossover design? If this is your first project we will be happy to check your calculations. What actual drive units are you planning to use? I ask this as the first step is to pick drivers that will hand off well to each other, without a huge component count in the crossover and a lot of consequent insertion loss. Just because drivers come from the same manufacturer does not mean they are the best match for the job at hand.

As far as caps are concerned, I have used Solen caps, which are cost effective, and have given no trouble. For inductors in the signal path use 16 SWG air core, unless you need a resistance in series with an inductor, and then you can sometimes save a component, by using a lower gauge of wire, and coming out right. Wire wound resistors are fine. The real trick is designing the most elegant crossover with the flattest response across the crossover region.

I agree, that there would be no benefit coupling a speaker rigidly to the floor, and it could be deleterious.

 

[SB99ACR]

Thank you all for your responses

Here is more about the planned speakers
Drivers planned are Scanspeak silk dome tweeters, Scanspeak revolater 6.5"
for mid drivers and audio technology 8" base drivers (two per speaker).

Tweeter and Mid drivers are enclosed with openings on backside.
Base drivers are chambered and ported.

As far as the Mechanical grounding goes...
Top of speaker will be 1/2" 353 brass, Front baffle will have a 3/8" thick
x approx. 10" wide brass band mounted to 1" Birch Plywood. Drivers will be mounted to the brass band. Brass band is approx 51" Vertical.
Band will connect to Brass top and will engage to 1/2" thick brass bottom plate with 5 axis machined traingulated feet approx 3" dia x 2.5" tall.
To complete the circuit there will be a 2.5" dia rear "spline" running vertically
from brass top to brass bottom. Wood back will be split into to pieces with each side into machined grooves in spline.

Bracing will be aluminum or brass precision machined with expanding panels allowing for precise tensioning of all sides of cabinet. Braces will mount to the massive rear spline.
The hope is this dynamic cabinet system will allow "tunning of the speaker to the desired effect.

This cabinet will involve extensive machine work and woodworking to make this combination perform in a cohesive harmonic manner.

Spline will have turned brass rods running through motor of mid driver and bass drivers to apply precise tensioning of the drivers. Tensioning rods will
be fastened to Phase plugs mounted to these drivers after dust covers are removed.

Weight per speaker to be approx 175-200 pounds per unit.
Internal dampining will be kept to a minimum.

The tensioning principle is also an important concept in addition to the mechanical grounding.

I should also mention that the cross overs will be remote on a complimentary brass base sitting behind the base for the main speaker cabinet.
As I mentioned the crossover will be constructed with duehlan capacitiers, inductors and resisters. Having heard "change outs" on other speaker cross overs to duehlan componets I belive there is something to their natural approach to producing their products that result in better sounding speakers.


I belieive My cost for these will be approx $15,000.00 - $20,000.00 doing much of the work myself. I think they will perform to the ability of speakers costing $40,000 - $75,000

For clarification these are not large "hulking" speakers.
Front dimensions approx 12" horz. x 51" vert. Depth approx 15".

Over all height with base to be approx 54". Center of tweeter to be approx
41.5" above finished floor.

I would appreciate any feedback or opinions. I have extensive design and manufacturing experience in a number of areas but my speaker building expereince is minimal and certainly much less than the more experienced builders on this site.

Please if you think this is ridiculus please say so.
I posted this in this forum because it indicated that it was about getting to the truth in the realm of High end audio.

I belive these ideas are supported by physics and will result in a superior speaker.

 

[WmAx]

There is no reason to have a 'tunable' cabinet. The cabinet should in fact be producing no audible level of acoustic energy from it's panels if you want a true state of the art enclosed cabinet speaker system. Since you are stuck on doing all of this machine work, consider this, which will result in an absolute inert cabinet: 1/4" inner metal cabinet, with bracing in every axis, every 4" or so. Another 1/4" to 1/2" outer metal cabinet, with a 1/4" channel between the two. Use a relatively low weight metal such as aluminum. The channel between the two cabinets will be filled with a viscoelastic dampening material such as Dynamat. This will give you a cabinet with no audible acoustic panel output.

I am concerned that you want to "keep internal dampening to a minimum". This sounds like a sure fire way to result in coloration. If anything, I recommend using far more effective acoustic dampening materials than are commonly used in speakers.

With this budget, I wonder why you want to use a passive xover at all. Superior performance can be had with a fully active system.

Driver selection is critical, and please realize, high cost does not mean a driver is in any way best for any specific application. Sometimes an optimal driver for a specific application may be expensive, but this is not always the case.

Can you actually define your target response goals for this speaker? What exactly are you trying to accomplish? Is their a specific commercial speaker you have heard that you are trying to emulate or best?

BTW, my area of expertise in this hobby is perceptual research and how it relates to human reaction to specific measured behavior(s) as they relate to loudspeakers.

-Chris

 

[SB99ACR]

WMax thanks for your response.

The general intent is to attempt to "drain" vibration to ground very quickly
Getting rid of resonance without having to dampen the cabinet heavily.

I realize that traditionally you can produce a close to inert cabinet however
I am trying to do it more mechanically.

I am not sure of all the terminology but my listening experience seems to favor what I can only describe as a more lively sound. My testing thus far
with MDF versus birch plywood with some dampening indicates a preference
for the birch plywood.

The interest on my part is to attempt to do it differently. If I just wanted to acquire a good 2 -2 1/2 way speaker I could easily do so in the $10,000 - $20,000 range.

I also find the look of the turned and brushed metals with combination of nicely finished wood to be a treat to the visual senses as well.

I believe it all contributes to a satisfying experience.

I have also found that using brass provides a variance in sound that is unavailable with different materials. I have produced very high end brass stand systems in conjunction with some major speaker manufactures and it improved
the sound of their speakers.

I have also produced Amp chassis using massive brass bottoms feet and stands for units approaching $100,000 dollars and the manufactures were always impressed with the improvement. These are private label products so i am not at liberty to discuss the OEMs involved. I just thought I would share a bit so you don't think I am totally crazy.

BTW have any of you ever tried using Hardy board for speaker cabinet manufacture?

 

[WmAx]

WMax thanks for your response.

The general intent is to attempt to "drain" vibration to ground very quickly
Getting rid of resonance without having to dampen the cabinet heavily.

Not feasible. The large, resonant panels will be excited appreciably during the vibration drain to ground, causing substantial acoustic output from the panels in the process.

I am not sure of all the terminology but my listening experience seems to favor what I can only describe as a more lively sound. My testing thus far
with MDF versus birch plywood with some dampening indicates a preference
for the birch plywood.

13 ply high grade birch ply is actually superior to MDF in terms of panel output. The birch is far stiffer material.

I guess you need to decide if you want the highest fidelity/most realistic speaker, or one that is intentionally colored, that will not meet the same level of realistic effect. Making speakers colored is by far the most common thing done today in DIY and high-fi. So if you actually try to go true hi-fidelity, then you will be doing something very different from most.

The interest on my part is to attempt to do it differently. If I just wanted to acquire a good 2 -2 1/2 way speaker I could easily do so in the $10,000 - $20,000 range.

I also find the look of the turned and brushed metals with combination of nicely finished wood to be a treat to the visual senses as well.

It's completely feasible to build the cabinet as I described above, and this would yield a nice challenge for you. In addition, you can machine voids to be fitted with various hardwood accent pieces. This would seem to fulfill your cosmetic purpose.

I

have also found that using brass provides a variance in sound that is unavailable with different materials. I have produced very high end brass stand systems in conjunction with some major speaker manufactures and it improved
the sound of their speakers.

Building the speaker to be inert in the first place, it matters not what material is used to accomplish this feat, so long as the execution is properly done to accomplish the effect. Another option is a complete de-coupled inner and outer construction. This is by far the most difficult to accomplish properly, even though it sounds simple at first.

I have also produced Amp chassis using massive brass bottoms feet and stands for units approaching $100,000 dollars and the manufactures were always impressed with the improvement. These are private label products so i am not at liberty to discuss the OEMs involved. I just thought I would share a bit so you don't think I am totally crazy.

This goes purely into the realm of psychological, it would seem.

BTW have any of you ever tried using Hardy board for speaker cabinet manufacture?

Yes, I have used this re-enforced concrete material as an inner speaker shell, with a channel of visco-elastic dampening between the concrete and outer speaker shell. For bracing on the concrete, I adhere steel L angle to the full length of the concrete, every 3" span, and use steel square tube to connect opposing walls, anchored to the L angle. This combination yields an extremely low resonance cabinet system.

-Chris

 

[SB99ACR]

Chris

what size were these speakers that you used the hardy board in?
That sounds very interesting to me.
Do you have any photos?

 

[WmAx]

Chris

what size were these speakers that you used the hardy board in?
That sounds very interesting to me.
Do you have any photos?

I used this method recently in a modification job to a commercial speaker, as one step, in improving the unit for someone that wanted to radically improve the speakers. It was a 2 way speaker with a 6.5" midbass. Ascend CBM-170SE.

To make it clear what you see in the photos: I have cut the rear off of the speaker cabinet. I have installed 1/8" thick of Dynamat type visco-elastic material on the MDF. I have adhered 1/2" HardiBacker concrete to the aluminum side of the visco-elastic material. I have adhered oak pieces to the corners of the cabinet, and an oak runner across the center of the baffle between midbass and tweeter. I have adhered steel angle to the oak also, to re-enforce it further. I adhered the same L angle to the walls and used steel tubing, using metal to metal epoxy for the steel tube to L angle adhesion points. To adhere the steel to concrete, the best adhesive I found was PHL premium polyurethane construction adhesive. Super adhesive - far superior to liquid nails, gorilla glue, etc.. for this purpose.

New back.

If you are interested in just how much attenuation this produced. Here is a graph of accelerometer readings before and after, center side wall, same SPL:

-Chris

 

[annunaki]

I used this method recently in a modification job to a commercial speaker, as one step, in improving the unit for someone that wanted to radically improve the speakers. It was a 2 way speaker with a 6.5" midbass. Ascend CBM-170SE.

To make it clear what you see in the photos: I have cut the rear off of the speaker cabinet. I have installed 1/8" thick of Dynamat type visco-elastic material on the MDF. I have adhered 1/2" HardiBacker concrete to the aluminum side of the visco-elastic material. I have adhered oak pieces to the corners of the cabinet, and an oak runner across the center of the baffle between midbass and tweeter. I have adhered steel angle to the oak also, to re-enforce it further. I adhered the same L angle to the walls and used steel tubing, using metal to metal epoxy for the steel tube to L angle adhesion points. To adhere the steel to concrete, the best adhesive I found was PHL premium polyurethane construction adhesive. Super adhesive - far superior to liquid nails, gorilla glue, etc.. for this purpose.

New back.

If you are interested in just how much attenuation this produced. Here is a graph of accelerometer readings before and after, center side wall, same SPL:

-Chris

Beautiful inside they are not. Effective the process is for sure!

It is impressive how well this method works through the midrange. There is approximately a 35db reduction near 1.8Khz!

 

[TLS Guy]

WMax thanks for your response.

The general intent is to attempt to "drain" vibration to ground very quickly
Getting rid of resonance without having to dampen the cabinet heavily.

I realize that traditionally you can produce a close to inert cabinet however
I am trying to do it more mechanically.

I am not sure of all the terminology but my listening experience seems to favor what I can only describe as a more lively sound. My testing thus far
with MDF versus birch plywood with some dampening indicates a preference
for the birch plywood.

The interest on my part is to attempt to do it differently. If I just wanted to acquire a good 2 -2 1/2 way speaker I could easily do so in the $10,000 - $20,000 range.

I also find the look of the turned and brushed metals with combination of nicely finished wood to be a treat to the visual senses as well.

I believe it all contributes to a satisfying experience.

I have also found that using brass provides a variance in sound that is unavailable with different materials. I have produced very high end brass stand systems in conjunction with some major speaker manufactures and it improved
the sound of their speakers.

I have also produced Amp chassis using massive brass bottoms feet and stands for units approaching $100,000 dollars and the manufactures were always impressed with the improvement. These are private label products so i am not at liberty to discuss the OEMs involved. I just thought I would share a bit so you don't think I am totally crazy.

BTW have any of you ever tried using Hardy board for speaker cabinet manufacture?

I don't think you can drain vibrations to ground. You can't direct how sound will travel through the walls of an enclosure. That whole theory sounds bogus.

 

[SB99ACR]

The intent is not to direct energy through cabinet but to do so with the heavy metallic circuit built into the cabinet which transfers energy much much faster than the cabinet. Mass from top to bottom to base plate to floor.
This metal mass is substantial.

You can control and direct energy through mettalic shapes very effectively.

I agree with WmAx that connecting panels could be excited during this energy transfer. This condition will need to be looked at carefully. More so in the rear spline.

Could you guys tell me the best way to measure resonance to a specifically directed area of speaker? Is an accelorometer the best way and if so what set up would you suggest? Based on my research I believe this system will
be effective but I don't want to try to fool myself ! I want to be objective
in evaluating this system.

Any advice about the best way to do this would be appreciated.

Thanks

 

[annunaki]

I believe the point Chris is trying to get across, is this: Why try to ground the potential resonances when they can be (almost completely) removed with the enclosure techniques described in previous posts?

Your method sounds like more of a band aid to the issue at hand as opposed to the solution. If the cabinet is inert to begin with, the system you propose is completely unnecessary. The only "tuning" required can then be done with a high quality EQ/signal processor where it makes the biggest difference (really mattters).

Any "sound" one desired could be theoretically possible, assuming quality, well complementing drivers would be used. If one were to do a completely active system with such a cabinet design (as proposed), the results would be amazing. The sound could be completely custom tailored to the listening room for maximum performance & realism.

Chris's reference towers he is planning will be of such a design. I am not at any liberty to discuss them however.

 

[SB99ACR]

clearly you guys are very intelligent and passionate about truth in audio.
My limited experience in manufacturing products in this realm (a very small part of our business) is build it and market the hell out of it.

I want to try this process because I believe it does work when done right
which I want to approach objectively and I like the sound which of course is subjective.

I have a pair of speakers built similar to the ones I described and they sound very good. But I am going to take the concept further. It is simply another way to do it. If it doesn't work to my satisfaction, oh well it won't change my life.

I don't disagree with any comments I have heard except the ones that said it won't work. Will it result in coloration maybe but its a very musical and lively sound with no audible distortion. Its a very articulate speaker and very easy to listen to. Later next week I will bring in some traditional very high end 2 and 3 way speakers to compare it to. I lack the ability to simply listen to speakers at different times and make accurate comparisons. I can only do it back to back (even thats difficult).

Can one of you help me with this question? What is the best system or instument for measuring resonance or vibration in a speaker like this.
I have listened to different parts with a stethesope and can pick out areas that need work but would like to measure and graph it like the speaker rebuilt shown earlier today. Its hard to arque with data like that.

I appreciate the comments

 

[TLS Guy]

clearly you guys are very intelligent and passionate about truth in audio.
My limited experience in manufacturing products in this realm (a very small part of our business) is build it and market the hell out of it.

I want to try this process because I believe it does work when done right
which I want to approach objectively and I like the sound which of course is subjective.

I have a pair of speakers built similar to the ones I described and they sound very good. But I am going to take the concept further. It is simply another way to do it. If it doesn't work to my satisfaction, oh well it won't change my life.

I don't disagree with any comments I have heard except the ones that said it won't work. Will it result in coloration maybe but its a very musical and lively sound with no audible distortion. Its a very articulate speaker and very easy to listen to. Later next week I will bring in some traditional very high end 2 and 3 way speakers to compare it to. I lack the ability to simply listen to speakers at different times and make accurate comparisons. I can only do it back to back (even thats difficult).

Can one of you help me with this question? What is the best system or instument for measuring resonance or vibration in a speaker like this.
I have listened to different parts with a stethesope and can pick out areas that need work but would like to measure and graph it like the speaker rebuilt shown earlier today. Its hard to arque with data like that.

I appreciate the comments

If you really want to know, you need an accelerometer.