Warning.... Kappalite 3015 NOT designed for Bass!

[Bassman Rich]

2 hours ago, Phil Starr said:

Hi Rich, without the Thiele Small parameters you won't be able to calculate a port length with any reliability and if the cab wasn't ported originally the speakers may not be suitable for a ported cab. Your best bet would be to simply cover the hole with a piece of plywood, so long as it is properly airtight the cab is restored to it's original design as far as the speakers are concerned. If you did want to port the cab I'd probably risk tuning it to 50Hz as the resonant frequency of the speakers will probably be around that area, no guarantee though.

 

Ashdown are probably the best though when it comes to after sales and they might cough up the Thiele Small figures if you email them. Equally they might not want to share that information as it would be potentially commercially sensitive.

 

Part of me wanting to remove the tweeter, was to get a bit more ooomph out of the cab, and removing the tweeter, effectively front porting was a 'win win' way of both doing this, and lightening the cab.

 

Also, as the front speakers and port will be behind the snazzy new silver grill Ashdown use for the RM III models, it wont need to be a pro finish visible job, just do the business audiably

[Bill Fitzmaurice]

If you remove the tweeter and don't replace it with a port of the correct length and area you'll likely make things worse. Getting it right requires modeling, not just to find the correct tuning frequency but also acceptable port air mass velocity. This assumes the driver will work well in a ported cab at all. Many drivers are compatible with both sealed and ported alignments, but those which are ideally suited for the one are not suitable for the other. 

[Phil Starr]

2 minutes ago, Bill Fitzmaurice said:

If you remove the tweeter and don't replace it with a port of the correct length and area you'll likely make things worse. Getting it right requires modeling, not just to find the correct tuning frequency but also acceptable port air mass velocity. This assumes the driver will work well in a ported cab at all. Many drivers are compatible with both sealed and ported alignments, but those which are ideally suited for the one are not suitable for the other. 

Exactly this, without the parameters you are down to guesswork. There are drivers designed for ported enclosures and drivers that won't work well plus a few 'general purpose' drivers that will work in either, the problem is that without the specs you can't do the modelling. It's possible Ashdown didn't match their speakers to the cab but more likely that they did.

 

The things that can go wrong with mis-matched drivers are well explained in the previous six pages of woe and blown speakers. Power handling is reduced in a mismatched cab. It could be OK but no-one can be sure so you'd be taking a bit of a risk. If you really want to do this then your cab is just over 50litres and  10CM dia port 11cm long would tune it to 50Hz. You might be better off selling the cab and buying one that sounds the way you want but if you are a tinkerer then I know no advice will stop you from trying it. Good luck, you might like the result but message me if you do blow the speakers and we can look to see if we can find replacements

 

[Bassman Rich]

19 minutes ago, Phil Starr said:

Exactly this, without the parameters you are down to guesswork. There are drivers designed for ported enclosures and drivers that won't work well plus a few 'general purpose' drivers that will work in either, the problem is that without the specs you can't do the modelling. It's possible Ashdown didn't match their speakers to the cab but more likely that they did.

 

The things that can go wrong with mis-matched drivers are well explained in the previous six pages of woe and blown speakers. Power handling is reduced in a mismatched cab. It could be OK but no-one can be sure so you'd be taking a bit of a risk. If you really want to do this then your cab is just over 50litres and  10CM dia port 11cm long would tune it to 50Hz. You might be better off selling the cab and buying one that sounds the way you want but if you are a tinkerer then I know no advice will stop you from trying it. Good luck, you might like the result but message me if you do blow the speakers and we can look to see if we can find replacements

 

Ooh thanks ever so much. I don't really want to hack the cab about, so can't really increase the port diameter from 7.5cm. I don't suppose you could advise on port length for that diameter could you?? 

 

Pics of cab added. 

 

Ps The upstairs loo has stopped flushing, and the bedroom TV broke on Monday (after absolutely years of service, it's a 23" one) new one arrives this afternoon, so might not get to experiment with cardboard tubes for a day or two.... 

[DGBass]

Ashdown used a lot of Sica stuff in their 2x10 300w  and 4x10 600 watt cabs, 10" 150 watt 8 ohm and 16 ohm variants. This link might give you a basic idea of parameters you could try when modelling a ported solution. The Sica BP10/150 is probably as near as you'll get to the OEM version Ashdown used in some cabs, assuming Ashdown can't supply you with the parameters of the drivers in your RM cab. Again, its only a rough guide and no guarantees as OEM drivers could be specified differently from retail versions. The Ashdown Sica's of the time look identical( but probably aren't exactly the same) to the BP10/150 but with the blue ashdown label on the back.

 

https://sica.it/wp-content/uploads/2021/02/ZJ05820.pdf

[Bassman Rich]

55 minutes ago, DGBass said:

Ashdown used a lot of Sica stuff in their 2x10 300w  and 4x10 600 watt cabs, 10" 150 watt 8 ohm and 16 ohm variants. This link might give you a basic idea of parameters you could try when modelling a ported solution. The Sica BP10/150 is probably as near as you'll get to the OEM version Ashdown used in some cabs, assuming Ashdown can't supply you with the parameters of the drivers in your RM cab. Again, its only a rough guide and no guarantees as OEM drivers could be specified differently from retail versions. The Ashdown Sica's of the time look identical( but probably aren't exactly the same) to the BP10/150 but with the blue ashdown label on the back.

 

https://sica.it/wp-content/uploads/2021/02/ZJ05820.pdf

Hey, fantastic response, they look almost the same. 

[Bassman Rich]

17 minutes ago, Bassman Rich said:

Hey, fantastic response, they look almost the same. 

The magnet is not quite the same size as on your Jenson spec sheet, about 130mm full width ot the outside of the magnet, as far as I can measure with a ruler.. 

Edited September 11 by Bassman Rich
Incorrect info

[DGBass]

1 hour ago, Bassman Rich said:

The magnet is not quite the same size as on your Jenson spec sheet, about 130mm full width ot the outside of the magnet, as far as I can measure with a ruler.. 

Yes, OEM stuff can often be variations of retail drivers and as the vendor says, specifications can also change. Worth speaking to Ashdown about your RM cab. They are usually very helpful.

[Bill Fitzmaurice]

2 hours ago, Bassman Rich said:

 I don't really want to hack the cab about, so can't really increase the port diameter from 7.5cm. I don't suppose you could advise on port length for that diameter could you??

That diameter is far too small, so you'd end up with port air mass velocity that's too high, resulting in port noise. For two tens in an average size cab with 50Hz tuning the minimum required port diameter is 12 cm, or a pair of 8.5 cm. 

[Phil Starr]

Again Bill has got there first. I've just checked the port velocity, you aren't too far short of a sonic boom I was pushing it at 10cm.

[Bassman Rich]

1 hour ago, Bill Fitzmaurice said:

That diameter is far too small, so you'd end up with port air mass velocity that's too high, resulting in port noise. For two tens in an average size cab with 50Hz tuning the minimum required port diameter is 12 cm, or a pair of 8.5 cm. 

Great stuff Bill, however disappointing. Thanks so much to you and @Phil Starr, you guys really know your stuff. 

 

I guess thats why my ABM 1 x 15 speaker has two 75mm ports on the back.

[Bassman Rich]

50 minutes ago, Phil Starr said:

Again Bill has got there first. I've just checked the port velocity, you aren't too far short of a sonic boom I was pushing it at 10cm.

 

My other half often complains about my rear port velocity, and sonic booms, better not upset the apple cart any more  😉

[Bassman Rich]

Ps all, I did enjoy watching this guy, tuning his cab with rice, sounds like fun !!

 

 

[Bill Fitzmaurice]

The video points out that at the tuned frequency cone movement is at a minimum, while port output is at its maximum. However, one cannot assume that 41 Hz gives the best result. That you determine with modeling software. With most bass cabs the best result is around 50-55 Hz. He also gave the manufacturer too much credit on the port sizing. They're much too small. His methodology is off as well. To find the exact tuned frequency you use a sine wave generator, slowly sweeping the frequency until the cone movement is at its minimum.

[agedhorse]

With OEM drivers, you can't assume that it has anywhere near the same TS parameters even if it looks "identical". The differences can be huge, thus impacting any modeling accuracy you hope to achieve.

[Bassman Rich]

3 hours ago, Phil Starr said:

Again Bill has got there first. I've just checked the port velocity, you aren't too far short of a sonic boom I was pushing it at 10cm.

But, just in case I get the fiddle about itch, what length single tube at 75 mm would I use, to possibly get sonic booms?? It sounded OK ish, but uneven, when trying it with no port attached, just the hole, but could just be my ears playing tricks, hearing what they want to hear... 

[Bill Fitzmaurice]

As best I can tell the cab internal volume is about 60 liters, so a 75 mm ID tube 35 mm long would give roughly 50Hz tuning. But the port velocity is off the charts. You need two, 120 mm long. 

[agedhorse]

2 hours ago, Bill Fitzmaurice said:

As best I can tell the cab internal volume is about 60 liters, so a 75 mm ID tube 35 mm long would give roughly 50Hz tuning. But the port velocity is off the charts. You need two, 120 mm long. 

Yeah, that would turn an electric bass into a tuba at those velocities

[Phil Starr]

On 11/09/2024 at 20:51, Bill Fitzmaurice said:

As best I can tell the cab internal volume is about 60 liters, so a 75 mm ID tube 35 mm long would give roughly 50Hz tuning. But the port velocity is off the charts. You need two, 120 mm long. 

Rounded off it's 57 litres, I calculated based on 53 litres allowing 4l for the volume of two speakers and the port plus any bracing. I also assumed the wall of the port was 2mm. I also looked at the tuning with no port and the 75mm hole. It's tuned too high but you still have the problem of port velocity and it just changes the point where the cone goes into over excursion. Hence your experience just trying it as it is.

 

On 11/09/2024 at 23:36, agedhorse said:

Yeah, that would turn an electric bass into a tuba at those velocities

Love this 😂

 

If you are playing with this cab at home and at reasonable volumes then just enjoy having some fun with it, try creating a cardboard or even papier mache tube of 35mm and listen to the difference. Just don't take it to a gig and crank it. If you decide it's your dream tone then the two port solution Bill suggested will give you that tone and probably will be reliable but you'll have to take a saw to the cab. You could add some bracing to it at the same time and experiment with damping, it's all good fun but it won't be as saleable if you do modify it.

 

If you want to do the rice test you can also try putting a 50hz signal through the speaker with the volume right down and gradually turn it up listening to the noise from the port, you'll hear the port noise at a remarkably low power and that is effectively your new maximum volume.

Edited September 23 by Phil Starr

[Bassman Rich]

8 hours ago, agedhorse said:

Yeah, that would turn an electric bass into a tuba at those velocities

 Oh yes, I love this too, I am the new Herbie Flowers, two instruments for the price of one session guy, available for rent, cheap prices, easy action baby....

[Bassman Rich]

54 minutes ago, Phil Starr said:

Rounded off it's 57 litres, I calculated based on 53 litres allowing 4l for the volume of two speakers and the port plus any bracing. I also assumed the wall of the port was 2mm. I also looked at the tuning with no port and the 75mm hole. It's tuned too high but you still have the problem of port velocity and it just changes the point where the cone goes into over excursion. Hence your experience just trying it as it is.

 

Love this 😂

 

If you are playing with this cab at home and at reasonable volumes then just enjoy having some fun with it, try creating a cardboard or even papier mache tube of 35mm and listen to the difference. Just don't take it to a gig and crank it. If you decide it's your dream tone then the two port solution Bill suggested will give you that tone and probably will be reliable but you'll have to take a saw to the cab. You could add some bracing to it at the same time and experiment with damping, it's all good fun but it won't be as saleable if you do modify it.

 

If you want to do the rice test try putting a 50hz signal through the speaker with the volume right down and gradually turn it up listening to the noise from the port, you'll hear the noise at a remarkably low power and that is effectively your new maximum volume.

 

I cannot emphasise enough how much I appreciate all this effort you guys, Phil and Bill especially, have put into this quest of mine, but thanks again.

 

As I have 3 other gigable cabs, I think I'm going to do the 'tuba tube port' experiment, will order a port today (blue aran do them cheap as chips) , try it out, and post the results. Can I post a video with sound on here, just so you can all giggle at my playing, and the tuba sounds ?? !!

 

When all said and done, if I blow the speakers, I can then hunt for some new ones that will match my big deep bass trouser flappy desires in a shallow box that fits the boot of the car dreams !!

[Bassman Rich]

Quick update. 

 

Thanks to the brilliant guys at Ashdown, I had a long chat about this with their chief designer, Dave Green. 

 

He has been trying to do this for quite some time too. 

 

Got some experiments to do with a bit of cardboard tube, so it just might work. 

 

BTW the speakers are not the Sica/Jensen ones we thought they were, and the parameters are not accurately known. 

[Phil Starr]

It is possible to measure the behaviour of your speakers and then calculate the Thiele Small parameters using software like REW https://www.roomeqwizard.com/ It is moderately complex and you'll need to make up some test leads but perfectly feasable at home. The results will probably be as/more accurate than the manufacturers tests as published. As usual You Tube is your friend.

 

[Phil Starr]

Btw one of your photo's illustrates the problem you have. At the relevant tuning frequency all of the sound from a ported cab comes from the port and theoretically none from the speaker cones which almost stop moving. You are asking tht little port hole to shift as much air as those two big speakers. 20" of speaker v's 3" of port. Roughly speaking that is a ratio of 50:1 in area so the port air is moving 50x faster than the speaker cones!

[Bassman Rich]

On 24/09/2024 at 07:31, Phil Starr said:

It is possible to measure the behaviour of your speakers and then calculate the Thiele Small parameters using software like REW https://www.roomeqwizard.com/ It is moderately complex and you'll need to make up some test leads but perfectly feasable at home. The results will probably be as/more accurate than the manufacturers tests as published. As usual You Tube is your friend.

 

Thanks for that Phil, sadly, I don't have any focusrite type interface, but after retiring from being an electronic engineer for nearly 40 years, and having my kit provided, I have bought myself a Fluke 75, the Fender USA P bass of test meters.