# Speaker cabinet/enclosure materials??????



## drf (Oct 22, 2006)

I have started this thread because over the last few weeks I have been looking into older P.A cabinet designs and I started to notice that a few of the original guitar amps and cab designs were made from chipboard (particleboard). It got me thinking about the sonics of chipboard as compared to MDF. I decided to look into the HIFI/HT. What I noticed (or more to the point what I had known all along but didn't really think about) was the amount of speakers built with chipboard yet that sounded amazing was quite intriguing.

I know some of you will say Duh, and others will be skeptical, many of my dealings centred on what materials to build enclosures with have ended with "use MDF or it will sound bad". 

these are some of questions I have used to get a "down to earth" understanding of cabinet material:

1, does the higher density of MDF give any sonic advantage over chipboard?
2, is "ease of use" an individual preference or is it generally accepted the MDF is easier to build with?
3, Assuming weight is not an issue, what advantage would ply have over MDF or chipboard?

over the next few weeks I hope the read as much as I can about specific material density, rigidity and resonance. 

What I already know:


High end speaker builders hate Chipboard and turntable restorers/builders hate MDF for exactely the same reasons. Resonance seems to be the major reasons quoted for timber selection.

I have built two small wedge monitors using chipboard. Each monitor is sealed with a 12" and a piezo tweeter. These I have used in small venues and a few with very bad accoustics, the general consensus was that these units were off suficient quality. whilst they are not high end monitors by any stretch of the imagination it would appear the general design and output quality is sufficient for professional vocalists.

My mains at home are also an older design, chipboard 4-way. After some serious positioning and crossover fiddling I have concluded (in this situation at least) that crossover design and driver alignment combined with room interaction is far more crucial than enclosure material. 

Whilst this is hardly a staistically accurate method for determining the sonic impact of enclusure material I have to start somewhere.


alternative thoughts:

this is an enclosure made from chipboard and polystyrene foam  

http://myweb.tiscali.co.uk/nuukspot/decdun/project.speakers2.html

Please post your thoughts no matter how much or how little experience you have. Right, wrong or just a gut feeling is all good as I would like to get as broarder base of opinions as possible. Also please post anything you think I have missed, got wrong or need to pay more attention to.


Cheers 
Dr. f


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## BoomieMCT (Dec 11, 2006)

He is my understanding;

MDF is denser and is therefore less resonant. This mainly comes into play on subwoofers.

Ply is stronger / lighter then MDF and doesn't chip as easy. Some ply has voids which affect the sound. 13 ply baltic birch should be as uniform as MDF.

I'm not sure what advantage chipboard has other then the fact it is cheap.


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## Darren (Apr 20, 2006)

MDF is more true and easier to machine. It holds an edge better, and has more surface area for a stonger bond. MDF is cheap and readily available, is more dense and therefore less resonant when braced accordingly. 

It's good stuff


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## drf (Oct 22, 2006)

It seems this debate could continue forever on the net, MDF v PLY v Chipboard.

I lifted this piece from: http://bellsouthpwp.net/l/j/ljfrank/Bracing.html



> This article is by Jim Moriyasu from AudioExpress (Feb. 2002) entitled, Panel Damping Studies:
> Reducing Loudspeaker Enclosure Vibrations. In it the author builds a test box with an 8" subwoofer, with a removable square panel and then clamps panels with various forms of bracing to the box. He then measures the vibration using an accelerometer and graphs the frequency and waterfall response. He first tests blank panels of MDF, particle board, and 7-ply birch plywood. His tests show that all three are very similar in the frequency and level of resonance, though MDF shows a 1 to 2 dB lower level of the primary resonances, but admits there's no major differences between the three. He decides to use the MDF panel for all the bracing tests. He then tests how much air vibration is cut down by stuffing the enclosure. He notes a 2 to 3 dB reduction in peak levels. He goes on to test multiple panel layers, applied damping materials, constrained layer damping, and bracing (as well as woofer isolation). He tried the following braces: 1 1/8" dowel rod cross-brace, 3/4" thick x 2 1/2" wide MDF brace (placed across the width of the panel), and various shelf (window) braces featuring square windows, oval windows, and a single large oval. His results favor the 3/4" x 2 1/2" wide MDF brace placed across the panel. He used a square panel so there is no distinction between widthwise or longitudinal. The window braces were next best with the oval windows outperforming the square ones. The single oval one was not quite as good as the other window braces. The dowel rod showed mixed results - some higher modes were reduced by 10 dB, but lower modes did not change much. The third mode was actually 5 dB higher in level than no brace at all. When I have time, I will chart his results for bracing as well as the other forms of damping he checked.


From this it would seem that thylantyrs' comments about designing specific to the material used is good advice. And good to note that all three id not differ greatly in resonance.

It makes me wonder if manufacturers like EAW aren't spinning a sales pitch when they say this:



> There are materials similar to MDF, such as chipboard or particle board, which EAW will not use. Made through the simple gluing together of castoff flakes, these materials have very low shear strength and are not consistent. These low density materials are prone to resonances that are difficult to control.


Although they state they use void free birch ply as preference, even that seems at odds with the speaker building internet majority (and personally abit like snake oil). 



All fostex had to say on the subject is that perticle board is harder to screw, nail or glue making it harder to workwith for the general public to process.

http://www.fostexinternational.com/docs/speaker_comp/overview_1.shtml


More to come, I'll try and filter out the sales rubbish or use it as an example of what not to believe.

If anyone has links I'd be glad to see them.

Dr F


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## Exocer (Apr 19, 2006)

Yes, this is an issue with many differing opinions.


I've read many discussions talking about MDF and how it is inherently good at dropping panel resonances below the intended FR of the speaker. Of course, if panel resonances are out of the speaker's operating range they will present little to no effect on the overall sound we hear.

The same goes with plywood and subwoofer building. Many believe enclosures made of plywood have the inherent ability of placing resonances out of the intended frequency range of a subwoofer. etc.

My experiences have proven plywood to be a wonderful wood to work with in comparison to MDF, which is messy and way tough on bits. In addition, if one chooses a plywood with a decent veneer from the beginning they'll have one less finishing touch to worry about when trying to make the speaker look aesthetically pleasing.


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## drf (Oct 22, 2006)

Anyone else have thoughts on this, or does everyone else just subcribe to the "MDF is industry standard so thats what I use" philosophy?


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## JCD (Apr 20, 2006)

Purely an educated gut response:

MDF is denser and uniform, both of which are going to be good for the cabinent resonance. It's also easier to machine to a desired shape than the other two choices given. Finally price -- it's only slightly more than chip board, but less than ply.

There are better, but you start getting into some seriously esoteric and hard to work with material (e.g., concrete is supposed to be really good).

JCD


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## drf (Oct 22, 2006)

Well, I am still scouring the net for more information. Here a a few more links I found:

http://www.speakerbuilding.com/content/1011/page_9.php

http://www.lautsprechershop.de/hifi/index_en.htm?/hifi/aka_tune_ls_en.htm

http://www.shadowworks.co.uk/SW/HTML/enclosures.htm

http://ldsg.snippets.org/sect-17.php

http://www2.abc.net.au/science/k2/stn/november1999/posts/topic6824.shtm


http://www.geocities.com/diyproac25/faq.htm

http://www.harbeth.co.uk/faq/index.php

If there is one thing I have found, it is that there are a lot of uneducated people on the net with funny ideas about enclosure design :coocoo: 

Now, I am no :nerd: maybe sometimes a little :dumbcrazy: but All the sites that specifically place MDF above chipboard accoustically show no tests or have any real theories to back the claim. In fact the sites that tell me chipboard and MDF are accoustically similar are the ones with nothing to sell and at least some form of research and testing to back there claim up. 


Anyhow, I am sure as I do more research I will find something a little more concrete to base such claims on.


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## drf (Oct 22, 2006)

I already have ply, MDF and chipboard in my shed from various projects. Just to clarify I did not start this thread to help me decide wqhat material to use for my next project, but to try and get an overall understanding of the prefered and scientific difference between all three. I am just not happy using or recommending one type of material over another simply because it is assumed to be better or generally prefered by the masses. Unfortunately I do not have the test gear required to scientifically check the resonance of each material nor do i want just one or two opinions onthe subject, that is why I am scouring the net for both. 

It is also a learning experience for me and hopefully if I get close to the bottom of it, others who are just starting out might also get something from this thread.


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## aceinc (Oct 24, 2006)

Don't you go messing around with one of my beliefs by talking facts, scientific principles and all that. 

MDF is heavy, heavy speaker is a good speaker, therefore MDF = good speaker.

Paul


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## JCD (Apr 20, 2006)

During my wanderings I found this site.

JCD


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## drf (Oct 22, 2006)

aceinc said:


> Don't you go messing around with one of my beliefs by talking facts, scientific principles and all that.
> 
> MDF is heavy, heavy speaker is a good speaker, therefore MDF = good speaker.
> 
> Paul


I don't think I will find anything that will debunk MDF as the cabinet material of choice. All the sites I have visited still confirm this, although what I am finding is that (for all intents and purposes) chipboard is accoustically identical. 

what I have also discovered is that chipboard will start to flake after about 5 years (personal experience), yet this doesn't effect DIY audio that much because no-one keeps there speakers that long before designing, upgrading then making a new pair.


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