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funkydoug

Port tuning and velocity

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Bill's right here. What's necessary is to make the best choices so that the compromise can be lived with.

 

Looking back at your first post, are you SURE that your port velocity is being calculated correctly. for a 75mm diameter port, I would not expect that much velocity from a single 10" driver. I'm starting to think that there is an error somewhere... since you are using WinISD, that's the first place I would look. Buggy software is a charitable way of saying it.

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Ok, I just ran the numbers and I think you may have gone down a rabbit hole.

If the internal dimensions of the box are really 41 liters, a 3" diameter port 2" deep is going to be fine at 100 watts RMS. If you go to a 4" diameter port, the depth will increase to 4" and you will increase the power handling to a little over 150 watts RMS (a better choice).

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Posted (edited)

Morning all,

Really appreciate your engagement and the time you've given.

I measured the cab and the internal volume of the box is 42.3 litres.

I'll need to deduct the driver itself from that but there are no handles or braces (unfortunately!) to deduct.

I'll revisit the modelling given what's been said. Is there an alternative to WinISD that is less 'buggy'? 

One other consideration I have is that the cab/combo needs to be able to play nicely with an extension cab. The extension cab will be a vented 210. Do I need to tune this box the same as that one to avoid wierdness?? Maybe that's one reason to keep it sealed, so that it doesn't mess with what's happening with a vented extension?

I'm open to all options, all speaker upgrades and even keeping it sealed and for now will keep experimenting in the modelling realm when I can. As I said in the OP, this is as much about learning as it is about the result, so although some might think I'm over thinking it, that's kind of the point! I clearly don't understand this stuff very well yet, but that's why I'm asking.

That said, it's a busy family bank holiday weekend with young kids, so there's not a lot of scope for geekery today!

 

Edited by funkydoug

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17 hours ago, Phil Starr said:

Why not put in the components we used in the Lockdown Easy Build project? You'd end up with a really nice sounding combo for a modest cost

This is looking like a great idea. Will very closely re-read the thread. Thanks

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19 hours ago, Phil Starr said:

Why not put in the components we used in the Lockdown Easy Build project? You'd end up with a really nice sounding combo for a modest cost.

+1

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I entered the Celestion Pulse 10 and the Sica driver into my modelling program and the Celestion performs marginally better in the 41-litre cab, but I'd persevere with the Sica rather than going out and buying a another driver. My software recommends a slightly longer port than @agedhorse. The standard length of the usual 100mm ports is 115mm. According to my software, that would tune your cab to around 52Hz, which would be fine. 

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IME WinISD isn't buggy. It has some idiosyncrasies, but they're mainly related to user experience with the program. HornResp is considerably more sophisticated, but it gives the same results. As for the cab volume, remember to deduct for the space taken up by the port.

Quote

One other consideration I have is that the cab/combo needs to be able to play nicely with an extension cab. The extension cab will be a vented 210. Do I need to tune this box the same as that one to avoid wierdness?? Maybe that's one reason to keep it sealed, so that it doesn't mess with what's happening with a vented extension?

Using two non-identical cabs is always a crap shoot, no matter what their configuration.

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11 minutes ago, Bill Fitzmaurice said:

Using two non-identical cabs is always a crap shoot, no matter what their configuration.

If the drivers are identical in the both cabs, do they also need to tuned identically?

 

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Ideally, but it's not as critical as using the same drivers in very close to the same box volume per driver. That way you avoid the most common mish-mash mess, as typified by the 410/115. That combination by and large doesn't work as intended, as the 410 will usually have higher thermal and mechanical power capacity than the 115, when it needs to be the other way around.

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I've been wondering why Ashdown got the cabinet volume so wrong. It looks to me like they specified the width of the cab to match the width of the amp, which is logical. I suppose they specified the depth of the cab so that the amp would fit in there too. Makes sense. And then they specified the height of the cab so that a 10- inch driver would fit with enough space for the grille surround.

 So that's how the professionals do it! 😁 (Present company excepted, of course).

The lack of a port remains a mystery. Especially as their published description claims it's ported.

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Posted (edited)

Ashdown DIDN’T get the volume so wrong. It was simply a design choice. 
 

By any chance was that tweeter ADDED to the cabinet in the existing port???

Edited by agedhorse
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2 hours ago, stevie said:

I entered the Celestion Pulse 10 and the Sica driver into my modelling program and the Celestion performs marginally better in the 41-litre cab, but I'd persevere with the Sica rather than going out and buying a another driver. My software recommends a slightly longer port than @agedhorse. The standard length of the usual 100mm ports is 115mm. According to my software, that would tune your cab to around 52Hz, which would be fine. 

Again, just a design choice/preference.

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2 hours ago, stevie said:

I entered the Celestion Pulse 10 and the Sica driver into my modelling program and the Celestion performs marginally better in the 41-litre cab, but I'd persevere with the Sica rather than going out and buying a another driver. My software recommends a slightly longer port than @agedhorse. The standard length of the usual 100mm ports is 115mm. According to my software, that would tune your cab to around 52Hz, which would be fine. 

At this point it might look like, as in the words of the song "logical advice get's you in a whirl" but actually I think we are quite close. The Pulse would work well in your cab and isn't too expensive. If you went for it you have the advantage of a well worked out matching horn and crossover, if you went for porting the Sica the crossover/horn Stevie designed wouldn't match but you could get an acceptable result with the right tuning, (around 52-55Hz looks good for that solution) and you'd save the cost of the Pulse. That's kind of a choice for you as it's your money and time.

There are of course a number of other drivers that would work well in  a 40l cab, I only picked out the Pulse because we used it in a recent design and I know that it works well in a cab your size.

I too wondered if the cab you have is as original, it's an odd driver to choose for a sealed cab and that piezo does not look right, it might be worth pinging an email across to @Ashdown Engineering and asking. They are really helpful people.

I think you probably need to sleep on everything and then make the design choice. If you decide not to go for the two way design then of course it may not be worth spending money on a new speaker.

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These are the responses you'd get with those two drivers in 40l. the Sica is in green. I've tuned them to give the flattest response each will give

 

image.png

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I don't know if these things still happen or if it was an early days thing, but I get the impression Ashdown would sometimes stick whatever driver was in stock into a combo rather than necessarily the one they designed and spec'd it with. Certainly my old Mag 200 tilt back combo in about '99 came with an Eminence driver that wasn't very well suited to the small sealed cab, rather than the custom spec Celestion they advertised and listed in the spec sheet.

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Posted (edited)

That's possible, and you can't assume that any design was arrived at by scientific means. Marketing departments have a habit of specifying target dimensions, driver sizes and wattage ratings with little regard to how well it works, because they're interested in how it will sell. For instance, at one time the Kappa Pro Ten was a popular driver in 'boutique' cabs, mainly as its 500 watt rating could be advertised as a step up from the usual. However, it was designed for PA midbass/midrange, so with electric bass it worked no better than a 250w rated Beta 10 that cost and weighed half as much.

Edited by Bill Fitzmaurice
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Posted (edited)
2 hours ago, agedhorse said:

Ashdown DIDN’T get the volume so wrong. It was simply a design choice. 
 

By any chance was that tweeter ADDED to the cabinet in the existing port???

Interesting suggestion. If the cab originally had a port where the piezo currently is, that would explain a few things. Ashdown's literature says:

"Handmade in the UK, Ashdown introduces the ABM-NEO-210 Combo and NEO-115 combo and now a C110 1 x 10 combo, both the 210 and 115 are fitted with Ashdown high-frequency horns and custom Italian Sica Neodymium drivers..."

No mention of a tweeter on the 1x10. Unless they thought it best not to mention the piezo. The plot thickens. 

I can't find any photos of the cab with the grille off, but there are descriptions of the combo elsewhere on the internet that claim it has a horn. 

Mind you, that's all academic. Fitting a port to the cab will certainly improve its performance. And that's what matters to the OP.

Edited by stevie
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Posted (edited)

AFAIK it is the original driver and the piezo was also factory fitted. I studied the few photos of them online and came to the conclusion that despite Ashdown's blurb, this one never had a port or a posh tweeter. I also noted the deliberately ambiguous product description you spotted Stevie. Not the first time I've come across Ashdown being inaccurate when it comes to accurately providing details of different amps / cabs across a given range. I'll let them off, the amps are great.

Ok, I've got a few really good options here for adding a port which I'll think more about. I'm leaning towards a large rear facing port, as it'd avoid cutting more out of the baffle to the point where it starts to lose stiffness. Once I've got the design right I'll just need to avoid making a mess of the tolex.

The piezo has a 77mm cutout. I'd need to find a same size upgrade I reckon, as expanding that cutout would be difficult (for me!). 

Off to re-read the easy build 10 thread ... 

Edited by funkydoug
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3 hours ago, Beer of the Bass said:

get the impression Ashdown would sometimes stick whatever driver was in stock into a combo rather than necessarily the one they designed and spec'd it with

That's my conclusion too. The power and eq flexibility in the amps mean that we don't notice until we open them up! 

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On 02/05/2021 at 17:03, Phil Starr said:

These are the responses you'd get with those two drivers in 40l. the Sica is in green. I've tuned them to give the flattest response each will give

Hi Phil - any chance you could enlighten me on how you achieved this flat response down to about 55-60hz? And are these charts taking Xmax limitation into account?

Thanks again, Doug.

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The how is really simple, suck it and see. I tried the frequency response at 40,50,60 and 70Hz which brackets the range of tunings which were likely to work. Then I knew 50 was too low and 60 too high. Halve again and try 55 then try the in between again until you are happy. Too low and you get a shelving response, too high and you get a big peak just above tuning.

It's best in WinISD to open a second project by clicking on new and then loading in the same driver then you can actually see what difference it makes when you make a change

I'm sorry I didn't save the actual values when I re-booted my computer but from memory at 100W there were no excursion problems above 50Hz

If you decide to build I'm happy to check your values

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Hi Phil, 

just a quick one to say thanks for the message above. I'm still in the planning rather than doing phase - this thread has been extremely helpful.

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Posted (edited)
2 hours ago, funkydoug said:

Moving at a snail's pace here...

This 10cm port seems to be ideal: https://www.bluearan.co.uk/index.php?id=MON126660&browsemode=category 

Only issue is it needs a 103mm cut-out. My hole saw has a 100mm 'blade' but don't think i'd want to try to squeeze the tube in there. Is there a 103mm hole-saw anyone recommends for it?

I would just use the 100mm hole saw you have, hole saws will normally cut "oversize" a tad and you could just ease the hole with sandpaper to achieve a nice snug fit.

Edited by JohnDaBass
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