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Mike's speaker thread

External crossovers would be my approach, although it is more theory rather than measured results. I first mounted pssive crossovers at the rear of the cabinets (they had 5/6mm steel dished plate as the rear panel and I thought this would reduce the speaker magnetic field influencing the crossovers, plus limiting vibration. It does require extra space, and in effect pushes the speakers away from the wall. Subsequently I managed to aquire a pair of active amps which were mounted on an adjacent chimney breast wall, the cases were quite simple to make, speakers are about 300 to 400 mm from the amps, unlikley that they could be wired directly as the six terminals are a give away. However the downside is your fear, they are not elegant and caused some domestic grief. The six speaker wires in flexible trunking are also hard to hide.
I'm re-jiging some old tannoy gold cabinets made years ago, and have a 'plan' to mount the crossovers in the stands, some careful thought is still needed!! Good luck
 
h.g. and westsea, thank you very much for your contributions to this thread, I appreciate it.

I've been thinking about it today and I've decided to go down the external passive crossover route.

Going external will allow me to make changes to the crossover much more easily.

As mentioned previously I'm considering upgrading the tweeters which will almost certainly necessitate tweaking the crossover. Furthermore, with external crossovers I can also experiment with the 6dB mid-range roll-off if I want with minimal hassle.

I'm not worried about affecting the resale value of the speakers as I don't plan on changing them in the foreseeable future and I've already got approval for the extra boxes from my other half.

h.g.

I will follow the build instructions and add bitumen sheets to the walls of the cabinet before covering with absorbent materials. Thank you for your thoughts on this.

I'm thinking to do the lower chamber on all walls above the transmission line pipe. I can't access the pipe anyway so going below this isn't an option. For the pipe itself I'll just stick with the PAF as that's what is there and that's what the build instructions call for. It sounded good before and if it ain't broken....

For the upper chamber I'm thinking to put bitumen panels on the sloping floor, the ceiling and both side walls.

On top of the bitumen and on all surfaces I was thinking I would use some wool underfelt. The existing felt inside the speakers which I have removed was 12mm thick. I've found a supplier that sells this felt in 8mm, 10mm or 15mm thicknesses. Any thoughts on this h.g.?

After the bitumen and felt I was going to add some extra wadding. I already have several packs of monacor MDM-3 wadding left over from a previous project which I think should be suitable. I'm not sure yet if I'll stuff the compartment loosely or add a layer of wadding on top of the bitumen sheet and felt. General wisdom for ported cabinets seems to be to coat the walls and leave the air space empty but (as far as I understand) the build instructions seems to call for stuffing the upper compartment loosely with balls of wool fibre stuffing.

h.g. yes the upper chamber was tightly stuffed completely blocking the port at the back. Sorry, I'm not sure I fully followed your comments regarding this, are you saying that blocking the port could be a good thing? I thought it was generally accepted good practice to not block the port.

At any rate, the amount of stuffing in the upper chamber can be easily adjusted later after listening and/or measurements. I just need a sensible starting point.

With the above I would be quite accurately following the build instructions with regards to the damping materials and compared to how the speakers were I would be adding bitumen sheets to reduce the cabinet resonances and maybe reducing the amount of stuffing in the upper compartment.

If anyone has any advice/thoughts different to the above please let me hear it. Other options include acoustic foam panels or more extensive use of PAF.
 
Mike P said:
I've been thinking about it today and I've decided to go down the external passive crossover route.

Going external will allow me to make changes to the crossover much more easily.
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Most of my DIY loudspeakers had external crossovers. But once you are satisfied with them, they are better internalised. I've done this to my baby E-IX and giant E-X, and will do the same to my E-IIIR when I can be bothered lugging them out of the spare room.

You might like to consider a way of re-internalising the XO, perhaps in a false plinth underneath the loudspeaker.

Mike P said:
As mentioned previously I'm considering upgrading the tweeters which will almost certainly necessitate tweaking the crossover. Furthermore, with external crossovers I can also experiment with the 6dB mid-range roll-off if I want with minimal hassle.
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Tweaking the XO by ear will be an exercise in frustration, particularly if you are changing a driver with materially different parameters. I tend to tweak by ear only once I know the FR is measurably in the right ball-park, and then I tend to adjust component values +/- 10% max.

It's also not a simple matter of changing the roll-off slope of a driver without considering how it will interact with its complementary driver. The common mistake most DIYs make is they assume FR is purely summative. It's not. Relative phase between them will dictate whether they sum, detract or somewhere in between. If the relative phase tracks in different directions over the crossover range, then all bets are off.

If you want to do this properly, get hold of a measurement microphone and measurement-based XO modelling software. I used to use LspCAD, but I'm not sure what's favoured these days. Or, ask someone who has the kit to take measurements and model for you.
 
Mike P said:
For the upper chamber I'm thinking to put bitumen panels on the sloping floor, the ceiling and both side walls.
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It won't do any harm to add the damping pads to the internal panels but it is the large areas that radiate sound into the room that will benefit most.

Mike P said:
On top of the bitumen and on all surfaces I was thinking I would use some wool underfelt. The existing felt inside the speakers which I have removed was 12mm thick. I've found a supplier that sells this felt in 8mm, 10mm or 15mm thicknesses. Any thoughts on this h.g.?
Click to expand...
What is the felt meant to do? It is not stiff enough to have a noticeable effect on the damping of the walls. It is in the wrong place to damp the sound inside the enclosure. To be effective the damping material needs to be a quarter of a wavelength away from the wall because the particle velocity is zero at the wall and damping works by the squeezing air at high speed through narrow gaps.

The "transmission line" is a bit different because the sound is travelling along the wall and not normal to it. It also requires a small but precise amount of damping. Sticking foam on the walls is a nicely controlled way to get the right amount of damping. A loose amount of wool like stuff teased out into the line tends to have issues with settling which then changes the amount of damping and the tuning.

In the midrange chamber damping needs to be in the centre in order to effectively damp the lowest frequency modes. Damping material is a lot less effective at low frequencies and so if you can sort the lowest frequencies the high frequencies will look after themselves.

Mike P said:
h.g. yes the upper chamber was tightly stuffed completely blocking the port at the back. Sorry, I'm not sure I fully followed your comments regarding this, are you saying that blocking the port could be a good thing? I thought it was generally accepted good practice to not block the port.

At any rate, the amount of stuffing in the upper chamber can be easily adjusted later after listening and/or measurements. I just need a sensible starting point.
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Like sticking thin amounts of foam/felt on walls, using a port on a midrange chamber is something audiophile enthusiasts might do while those with a more technical background won't. By adding a lot of stuffing to the chamber (which is needed because the chamber is big introducing low frequency internal modes that need to be damped) it will suppress most of the port resonance. Plugging the port would make sure.

If you want to keep the port resonance then you will have to experiment with introducing enough damping in the centre to adequately reduce the lowest cabinet modes while not too much to reduce the port resonance. I would suggest the sensible starting point is lots of stuffing like it is at present.
 
Yeah, mount the crossovers externally at first. Mount them on some plywood. Once you are 100% happy with them, chuck them inside the cabinets. Screw them down, job done.
 
I would be wary of changing values in the xover. There is an awful lot to analyse in a 3 way speaker as it includes the acoustic roll-offs of the drivers in their boxes, and frankly most people haven't got the time, even if they find it interesting. If the xovers are external you need to think of some tidy connections on the back or is there 3 x binding posts? Binding posts are probably not reliable enough as you should never run 2nd order x overs without the drivers connected at any normal volume. It could hurt your amp and the xover caps. The advantage of external xovers is that you can build another from the ground up and swap it over when it is finished, which will take a fair time, allowing a quick comparison and no disruption to the music flow. This is how I have done it for diy. The downside is I have a lot of large xpensive passive components, which I will have to pass on when I give up building soon..

Your bass section is 2nd order LP which is about -3dB at 250Hz

The mid is 2nd order HP and 1st order LP at the treble end.
 
The mid driver bass roll off is 2nd order below 176Hz [Q~1] with a peak of about +1dB at about 300 Hz. You could short a link across the 2.7uF cap. This will take a bite out of the upper bass at about 200 Hz and will lower the input impedance in the mid a bit to about 5 ohms. With this shorted, you can safely disconnect 1 leg of the 12mH, then it has a gentle 1st order bass roll off below about 300Hz. Easy to reverse if it's not better.
 
Mike P said:
If you can spare a few minutes please take a look.
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I had looked earlier and it prompted me to introduce the business about the differing views of audiophile enthusiasts and those guided by technical knowledge about the subject. The discussion of the speaker is clearly intended to appeal to audiophile enthusiasts and the speaker shows some signs of having been designed by audiophile enthusiasts. For example, price rather relevant technical performance is used as an indicator of quality, appeals are made to the better sound of components without linking it to what has changed in the sound field, technical reasoning and evidence is almost wholly absent although they do refer to partial measurements without discussing them, etc... Compare with this presentation of a large DIY home speaker.

Changing the slope of the crossover will make audible changes to the speaker. Whether it sounds better, worse or just different is perhaps for individuals to judge. Whether it moves the sound towards a more neutral sound or a more characteristic sound could possibly be judged if we had the on and off-axis response of the speaker. The cost to make the change is likely to be significant and so would only make sense if you get pleasure from the process.

Changing a good 1" aluminium dome tweeter for a good 1" beryllium tweeter is going to be expensive and likely to make little difference to the sound of the speaker if used in the same way. Again, the cost could make sense if you want the experience of modifying crossovers and/or place value in using a beryllium tweeter.
 
Thanks h.g. I appreciate your input and I sympathise with the tone of your post.

Until just a few months ago I also owned a pair of IMF RSPM IV which I'm sure you'll agree is a very highly regarded transmission line design. I had both sets of speakers side by side for about 6 months. To my ears the Studio 100's bettered the IMFs' in every way other than the IMF's possibly going a touch lower in the extreme low bass. A few other forum members here have heard them and they've been equally impressed.

They must be doing something right, 'audiophiles' or not. ;)

I think the sensible approach is going to be to rebuild the speakers with the existing drive units but with the crossovers external. If I then decide to try different tweeters or make any changes to the crossover it'll be much easier to implement (and reverse if necessary).

I've been shopping online today for various materials and have just had a very helpful chat with thewoodveneerhub.co.uk about the veneer replacement.

Must go, 'real' work beckons.

Cheers, Mike
 
Mike P said:
Until just a few months ago I also owned a pair of IMF RSPM IV which I'm sure you'll agree is a very highly regarded transmission line design. I had both sets of speakers side by side for about 6 months. To my ears the Studio 100's bettered the IMFs' in every way other than the IMF's possibly going a touch lower in the extreme low bass. A few other forum members here have heard them and they've been equally impressed.

They must be doing something right, 'audiophiles' or not. ;)
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You wouldn't expect differences when comparing a speaker that is decades old using standard range drivers from 40 years ago with one that is fairly new using current exotic drivers and components? The IMF is also likely to be out of spec due to age. There has been some development in driver performance over that time.

I lack the information to determine if the person/people behind your speakers are 'audiophiles' themselves or are simply designing and marketing for the 'audiophile' market. Perhaps there is a mix of total 'audiophiles' and partial 'audiophiles'?

Whatever, your speaker uses very expensive drivers and components that perform well technically. They are not boutique audiophile components that are very expensive and perform poorly technically. The configuration is OK but open to some small improvement: active crossover, a smaller midrange, better directivity control between tweeter and midrange, a quieter cabinet,... The main criticism seems to be that because of audiophile enthusiasms rather than technical understanding the modifications being mooted (different tweeter, different crossover slope) appear to be both expensive and not much of an improvement in a technical sense though not necessarily in an audiophile sense.
 
I have external crossovers on my wd25tex speakers connected via Neutrik speakons and Van Damme 4 core Black. I placed them as near as poss to the amp because LesW suggested they might sound best that way. I tried both ways and think I agreed with his findings. I hate external crossovers because they make it so easy to ask yourself "What if ..... " and chop and change so I’m forever pissing about changing caps and coils and size of components is no handicap. My latest bass/mid circuit are with Russian teflon FT3, PIO MGBR and jantzen wax coils and if you´re not careful your crossovers may cost more than the actual speakers. Who mentioned V-caps ?
 
They are great connectors, I recommend them to all my customers, although mostly they end up with binding posts anyway.
 
I use Speakons exclusively, except for my Yamaha NS-1000Ms. I'm contemplating a custom-made rear plate to take a single NL4MP.
 
There are a few families of speakons and I think only the best type is easy to solder with heavy wires. Some are screw only and I can't solder to the nickel or chrome grips. There is a 2 and 4 wire version. The pros use the 4's for both 2 and 4 wires as they are an easier design. Personally I will go back to XLR next time as they are more than enough.
 
Veener update:

When I stripped off the old veneer it came away leaving a layer of sticky, gummy contact adhesive on the MDF cabinet surface.

Initially I hoped that I might simply be able to apply some fresh glue over the top and then put the new veneer on. However, after getting some advice it became clear that the old glue would have to be completely removed to leave a totally smooth surface on which to apply the new veneer. Any surface imperfections whatsoever would telegraph through the new veneer.

Attempts to sand this glue off proven futile, the glue is so gummy that it almost immediately clogs the abrasive paper you are using and rather than being removed just gets smeared across the surface. Damn!

After a bit of contemplation and experimentation I arrived at the following technique:

1) Wipe the surface with a rag soaked in cellulose thinners. To soften the glue.
2) The glue can then be scraped away with a Stanley knife blade held firmly and dragged across the surface (like a cabinet scraper).
3) Repeat the above until all the glue is removed.
4) Finish by sanding with 180 grit abrasive paper.

It's rather tedious work but has given me a really nice smooth surface to work with.

20171017_141714[1] by Michael Pickwell, on Flickr

20171017_141855[1] by Michael Pickwell, on Flickr

20171017_151458[1] by Michael Pickwell, on Flickr
 
Just ordered some veneer samples and some cellulose sanding sealer to seal the porous MDF surface prior to applying the veneer.
 
Hi Mike,

I recently went trough upgrading the crossovers in my speakers with same value but "better component" varieties from the Mundorf range.

The greatest difference of a break-through kind was via replacing the inductors with copper foil ones. eg. CFN zero ohm style 6,8mH on the woofer, air core ones for the smaller values.

The Mcap caps you have in your speakers are very basic. The Mundorf range has several with quality above them.

As to picking your replacements: More money will get you a better part, with diminishing returns of course. I would set my budget and buy what I can get for it. In the cap department from mid-range on, go for something with oil in it!

If the Clarity cap on your woofer is foil, then keep it.

Cheers,
Achim
 
Achim said:
As to picking your replacements: More money will get you a better part, with diminishing returns of course.
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Really? The evidence to support this seems to be remarkably difficult to find in the literature that is openly available. This is not like cables where there is no relevant technical difference between competent examples. Crossover components can be significantly nonlinear which is the main reason why active crossovers perform better by getting rid of them. So why aren't the technical differences presented and discussed? Why bang on about their sound as if they were cables? It seems something of a missed opportunity to add credibility to a subject that is treated by many in the same way as cable differences. I expect there is a reason that I can't see. Anyone?
 
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