Lets us assume you have a fairly simple 2 way stand mount speaker. Something like a 6.5" mid bass and dome tweeter. I'm using one example, Mission 761.
Let's assume that you keep the original speaker units and crossover, and just "upgrade" the cabinet. What kind of upgrades would be likely to improve the sound without too many negative side effects?
... doubling the thickness of the front baffle
... adding an extra layer of thin wood or aluminium to the sides, top, bottom, back, front
... adding internal bracing
... Increasing the cabinet size a little if it's a sealed box
... making a new cabinet using typical Troels Gravesen cabinet designs and materials.
... something else?
One answer is going to be "leave it because it will never sound as designed", of course. But how about some more creative and imaginative answers......?
.
Let's assume that you keep the original speaker units and crossover, and just "upgrade" the cabinet. What kind of upgrades would be likely to improve the sound without too many negative side effects?
... doubling the thickness of the front baffle
... adding an extra layer of thin wood or aluminium to the sides, top, bottom, back, front
... adding internal bracing
... Increasing the cabinet size a little if it's a sealed box
... making a new cabinet using typical Troels Gravesen cabinet designs and materials.
... something else?
One answer is going to be "leave it because it will never sound as designed", of course. But how about some more creative and imaginative answers......?
.
It's difficult to predict what you'll have to do after you reduce the cabinet resonances. You may end up with a boring sound you need to liven up. You may produce a cleaner sound and you need to tone everything down around it. You may unmask disturbing distortions you have to track down.. It is a step in the right direction if you do plan to take that next step.
Thin constriction layer damping of front baffle. 2-4mm bitumen and 4mm hardboard glued to the front. With double fornt panel you can get tunnel effects from the woofer cutout if you do not chamfer.
Read about cross brace Dr.Geddes used to make
https://www.diyaudio.com/community/...ing-to-absorb-bass-geddes.351376/post-7981499
Hi there,
a friend of mine many years ago swapped the existing DIY speaker to a new enclosure that was really acoustically dead double walled filled with sand, it was a really heavy weight but the bass performance was at a different level
- Stefano
a friend of mine many years ago swapped the existing DIY speaker to a new enclosure that was really acoustically dead double walled filled with sand, it was a really heavy weight but the bass performance was at a different level
- Stefano
Imo the only thing you could with a 2 way w/o to waste its design is to make it heavier from the outside without touching the front at the cost of dead-end looking with no assurance of sound improvment as you voiced your hifi with the original sound of your Mission.
Let's illustrate it : it could be like if you add Porsche big wheels to a Lada Niva (could drive at 50 Mph still but needing just one way instead twos to drive straigth).
Or isolating your house from outside : migth work at the cost of loosing the soul of the House and his aesthetic to winn 1.5 C° !
Better not to waste good wood and build a new loudspeaker from a proven kit design, there are tons good public domain one.
What you coulld do to play is to change the amount of internal damping and its composition,, because it is reversible. Find better values with your filter if some lythics drifted, change a sanded resistor by a MOX to learn if you hear a difference. Play with all sort of decoupling with the stands, etc.
Let's illustrate it : it could be like if you add Porsche big wheels to a Lada Niva (could drive at 50 Mph still but needing just one way instead twos to drive straigth).
Or isolating your house from outside : migth work at the cost of loosing the soul of the House and his aesthetic to winn 1.5 C° !
Better not to waste good wood and build a new loudspeaker from a proven kit design, there are tons good public domain one.
What you coulld do to play is to change the amount of internal damping and its composition,, because it is reversible. Find better values with your filter if some lythics drifted, change a sanded resistor by a MOX to learn if you hear a difference. Play with all sort of decoupling with the stands, etc.
Cheap commercial speakers?
Add fibre damping, fibreglass or polyester or even egg crate foam. Bingo job done
Perhaps glue blocks at every panel intersection too.
Add fibre damping, fibreglass or polyester or even egg crate foam. Bingo job done
Perhaps glue blocks at every panel intersection too.
can play with melamine sponge inside as damper on the top and/or sides & base to free some space, but be aware the amount of internal damping can be a factor to change the Vas of a sealed cabinet
first, find out what is wrong. Some speakers benefit from extra bracing or thicker cabinet walls, others not. And the biggest improvement is mostly on the filters, as many speaker builders skip corners on that or did not have the knowledge to do it right. Room correction can also fix a lot (but not all).
But it start with an analisys (including measurements) of what you have and where the problems are. Without that you are shooting in the dark.
But it start with an analisys (including measurements) of what you have and where the problems are. Without that you are shooting in the dark.
..........lacking analysis and considering the lower the cutoff the wider its BW; I long ago had some fun 'killing two birds with one stone' by tacking on a much larger baffle cut in an organic shape based on golden room ratios.
Yes, I would be taking the opportunity to make a larger baffle, but this may call for crossover adjustment and OP did talk about keeping the original crossover. A little EQ would do, and I use EQ regardless so that seems normal to me..
Hard to get inside the box to add decent bracing, and it reduces cabinet volume. The latter not a big issue with sealed boxes.
Adding aluminium to panels is an interesting. Really stiffen the panels while adding minimal mass.
Even just the sides. Run a threaded rod from side to side and put them into tension by tightening up just a bit (GM trick)
Stiffening the front baffle should not hurt … 3mm Al shouldn’t cause the issues Allen mentions.
You can do a better cabinet than Troels. But the radical approach is to just rebuild the box.
dave
Adding aluminium to panels is an interesting. Really stiffen the panels while adding minimal mass.
Even just the sides. Run a threaded rod from side to side and put them into tension by tightening up just a bit (GM trick)
Stiffening the front baffle should not hurt … 3mm Al shouldn’t cause the issues Allen mentions.
You can do a better cabinet than Troels. But the radical approach is to just rebuild the box.
dave
Except of adding internal bracing (if it is really needed), nothing else. All other suggestions are gigantic waste of time and money, with unknown results. For example, you couldn't possibly know whether doubling the thickness of the front baffle would be beneficial, or not. It is true that some loudspeakers have smaller cabinet than optimum, but building larger enclosure is not logical - it is far better to sell that loudspeaker and with the money intended to "improve" it you will have enough money to by (or build) much better loudspeaker.
No money in selling Mission 761s I'm afraid...
I can't do woodwork in my city apartment so choices are
... have a box made (expensive and I think unjustified, unless a friend can do it)
... use a larger and better "donor" cabinet off ebay (quite possible)
... buy a different used speaker (that's a different subject)
... improve the existing cabinets, which is the subject of this thread.
I can't rebate the front baffle which is one issue, but this could exist in a donor cabinet.
I can't do woodwork in my city apartment so choices are
... have a box made (expensive and I think unjustified, unless a friend can do it)
... use a larger and better "donor" cabinet off ebay (quite possible)
... buy a different used speaker (that's a different subject)
... improve the existing cabinets, which is the subject of this thread.
I can't rebate the front baffle which is one issue, but this could exist in a donor cabinet.
But without measuring what is wrong you don't know ifwhat the issues are, so you're doing random things.
I do know that those mission cabinets are made out of not so thick mdf without bracing. But as it's a small speaker it's not necesairly a big issue. You could rebuild the cabinet with bracing, but a bit larger (to make up for the space), but that will also need an adapted crossover (as the cabinet changes). Idem with changing the front or using a donor cabinet. And for that you need a whole leap of other tools and skills...
So if you don't have the tools to measure or do woodworking, there is not much you can do that will improve the cabinet. Then you better spend money on better speakers and skip the diy part.
I do know that those mission cabinets are made out of not so thick mdf without bracing. But as it's a small speaker it's not necesairly a big issue. You could rebuild the cabinet with bracing, but a bit larger (to make up for the space), but that will also need an adapted crossover (as the cabinet changes). Idem with changing the front or using a donor cabinet. And for that you need a whole leap of other tools and skills...
So if you don't have the tools to measure or do woodworking, there is not much you can do that will improve the cabinet. Then you better spend money on better speakers and skip the diy part.
I didn't realize that you actually own Mission 761, because you wrote "one example, Mission 761".
So, you have Mission 761... and what is wrong with it?
Measuring (and modifying) several models of well-known hi-fi loudspeakers, I found that almost always the main problem was the crossover. Modifying the crossover will always make bigger improvement than any messing with the enclosure. Only the cheapest loudspeakers have meagre enclosures, where additional bracing will indeed bring improvement.
Here is one example what can be done for improving the vintage Mission 753 Freedom.
This is the measured frequency response of the original (with separate freq. responses of the drivers, shaped by their filters):
And this is with modified crossover (midrange low-pass filter only) which, surprisingly, is cheaper than the original one!
Resonance at 200 Hz was eradicated with a simple lump of foam placed in the canal behind the midrange enclosure.
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A nearly 50 year old modest 2 way likely worth under £50 in reasonable condition and worth less if modified makes no sense financially. So the intention is to spend a bit of money having some fun with DIY?
The drivers and cross-over components are normally out of spec in 50 year old speakers. Addressing this is likely to bring the biggest improvements in sound quality. Internal stuffing can also degrade depending on the material and this can also be worth fixing.
A competently designed cabinet in a small 2 way contributes little to sound degradation. Some people like bracing cabinets but unless this is done to address a known issue there is every chance it will make things worse by moving the main cabinet resonances higher in frequency where they are perceptually more intrusive. Increasing the stiffness of the baffle is safe in that in itself it won't make things worse and might have a very tiny beneficial effect. However, the side effects in terms of different cabinet shape, internal volume, etc... may degrade things more. Increasing the damping of the walls is also a modification that in itself won't make things worse and might make a tiny improvement. But again the side effects of pinching some volume might degrade things more.
As others have said, to reliably make improvements in technical performance you will need to identify the weak spots with your speakers (usually by measurement but it is also possible with simulations or a combination) and then to introduce modifications to address these identified weak spots. Making modification based on feelings or random suggestions on forums is more likely to make no effective difference or degrade the technical performance rather than improve it. On the other hand, a fair few audiophiles trust that particular modifications suggested by those with high audiophile standing will bring improvements in sound quality without needing guidance and confirmation from things like measurements or (mainstream rather than audiophile) engineering/physics. If you are inclined this way then "trust your ears" and go for it.
The drivers and cross-over components are normally out of spec in 50 year old speakers. Addressing this is likely to bring the biggest improvements in sound quality. Internal stuffing can also degrade depending on the material and this can also be worth fixing.
A competently designed cabinet in a small 2 way contributes little to sound degradation. Some people like bracing cabinets but unless this is done to address a known issue there is every chance it will make things worse by moving the main cabinet resonances higher in frequency where they are perceptually more intrusive. Increasing the stiffness of the baffle is safe in that in itself it won't make things worse and might have a very tiny beneficial effect. However, the side effects in terms of different cabinet shape, internal volume, etc... may degrade things more. Increasing the damping of the walls is also a modification that in itself won't make things worse and might make a tiny improvement. But again the side effects of pinching some volume might degrade things more.
As others have said, to reliably make improvements in technical performance you will need to identify the weak spots with your speakers (usually by measurement but it is also possible with simulations or a combination) and then to introduce modifications to address these identified weak spots. Making modification based on feelings or random suggestions on forums is more likely to make no effective difference or degrade the technical performance rather than improve it. On the other hand, a fair few audiophiles trust that particular modifications suggested by those with high audiophile standing will bring improvements in sound quality without needing guidance and confirmation from things like measurements or (mainstream rather than audiophile) engineering/physics. If you are inclined this way then "trust your ears" and go for it.
Andy, with your demand of sound quality, the best thing you can do with your Mission is paint it green and throw it away/
Have a look at my recent conversion. I started with exactly the same objective: use existing cabinets to avoid/minimise woodwork. And I also ignored advice. Lesson learned: it was actually more woodwork. less (simpler, easier, quicker) woodwork if building from scratch.
Still, enjoyed immensely and learned a lot.
Thread '3-way to active - Hypex FA253 - learning project'
https://www.diyaudio.com/community/threads/3-way-to-active-hypex-fa253-learning-project.421061/
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