stevie

10 hours ago, Rich said:

BA55 TlT would be more fitting for me.

Oops.  I didn't realise this was a For Sale thread..... Comment withdrawn.

Sounds like a plan. What size of ports will fit on the baffle?

I reckon you have about 30 litres net. The tuning appears to be in the region of 80Hz, which is OK for a vocal cab or a guitar cab, but not good for bass. To make matters worse, as Downunderwonder correctly points out, the rear entrance to the ports is constrained. It looks like the designer didn't know what he was doing.

If you block one of the ports and open up the rear of the remaining port, you'll have a fighting chance. That will probably tune the cab to around 60Hz. It's difficult to be accurate here because the proximity of the ports to the rear baffle affects the tuning.

You might like to get hold of a Celestion 12BN-300S, which is claimed by many to be close to the EV you sold. No guarantees though.

On 03/03/2021 at 18:49, BassAdder27 said:

Who’s been setting their RM so to reduce the 240HZ control ?

Ive found that by running it around 9 o clock is a good setting 

I remarked in another thread about a year ago that I preferred the sound of the amp with the 240Hz cut - to about 9 o'clock if I remember rightly. So you're not alone.

Finally, a view of the front and rear of the cabinet. Builders can choose from a selection of feet, corners and handles from Blue Aran to finish the cab off.

And a photo showing the brace on the back of the baffle, which is simply glued on using three screws.

Here are a few more photos to help potential builders see what's what. The first is my port extension arrangement. This particular cardboard is ideal for the purpose because it entails going out and getting yourself a pack of beer.

Oh dear. Not sure what's happened but it doesn't sound good.

16 hours ago, Chienmortbb said:

What is the scale on the impedance curve @stevie?

It's on the left, John. Each horizontal bar is 5 ohms. Minimum impedance is around 7 ohms.

I forgot to mention -  gluing a piece of batten to the baffle just above the driver completely killed the 70Hz resonance, as can be seen from the impedance curve.

This should be the final piece of the puzzle from me. The port needs to be about 170mm long in total. So we have  to add 50mm to the length of our standard 120mm port using one of the techniques mentioned above - unless you can think of another way of doing it. There may well be 4" ports that are longer than the one we're using. If there are, they'll certainly be more expensive.

If you're not bothered about obtaining maximum output from this cab, stick with the tuning that the 120mm length gives you. It'll sound fine. But if there's any chance you might want to put the full 200 watts through it, be sure to add the extra two inches.

For internal damping, I'd line the cabinet with your damping material of choice, keeping it away from the port. Felt is my favourite nowadays, but use whatever you happen to have (or repurpose an old duvet).

I tested the cab with a variety of different recorded sources, including bass guitar (obviously) but also some recordings with voice. The cab is perfectly usable as a PA cab. The colouration between 2 and 3kHz is audible (on bass guitar also) but it doesn't jump out at you. It's a natural sound on voice and doesn't screech on female vocals like a lot of PA cabs do.

Here's the impedance curve without any damping material in the cab. It's a very easy amplifier load. Even @agedhorse would nod in approval (nasty amplifier loads are his pet peeve).

No, @JohnDaBasswhen I said more expensive components, I meant a lot more expensive. Their identity will remain a mystery at least for the time being.😊

While I've been doing this, I've been working on another 10" system that uses more expensive components and a much more complex crossover. This is what you can do if money's no object. No smoothing, by the way.

And here's a photo of my chocolate block crossover. It should be screwed to a convenient place inside the cabinet. Two screws in the chocolate block and one screw in the inductor - they must be brass or stainless steel screws. Keep all leadout wires as short as possible - the ones on the resistor should be shorter but I left them for clarity. You can tape the whole lot together if you like.

If you want to do a build without any soldering at all, you'll need to source three different sizes of connector because the 10" driver, HF driver and Speakon all use different sizes of crimp.

There's just enough room to fit some batten.

It's impossible to know whether the resonance is due to the narrowness of the wood between the main driver, horn and port or the thickness of the baffle - we're working with lightweight 12mm ply here. It could well be a combination of both. I did notice that the alternative 10" driver I tried, which has a thicker, cast aluminium chassis, reduced the severity of the resonance, although it didn't get rid of it. I'd guess that an 18mm birch ply baffle wouldn't have the same problem.

When I did more in-depth panel resonance testing on the Basschat MkIII cab (which used 15mm poplar ply),  I noticed that the baffle is by far the worst cuprit for undesireable resonances and that's why I always fit a figure-8 brace nowadays. But this is supposed to be an easy-build design. So I'm going to screw some batten to the back of the baffle and remeasure the impedance curve. If it's successful, I'll show you what the impedance of the system looks like.

The 70Hz resonance has been bugging me for a few days now, because it shouldn't be there and it's causing a noticeable dip in the frequency response at the same frequency. At first I thought it was an air leak and decided to seal all the battens on the back panel. It didn't make any difference. So I tried another driver and the resonance was still there. That ruled out the driver as the cause of the problem. It had to be the cabinet.

To cut a long story short, I eventually discovered that the impedance blip (or resonance) was caused by vibration of the baffle. The solution - and I'm sure Phil will include this in his drawings - is to fit a brace across the front baffle above the driver.

Here's the frequency response of the finished system with crossover.

22 hours ago, JohnDaBass said:

Hi @stevie & @Phil Starr, 

Internal dimensions of my 'no HF' cab are 375 X 340 X 291 giving a volume of 37Ltrs.  Am I correct that Phil has allowed 7litrs for Speaker, port and HF horn?

If I use a 100mm diameter port 120mm long will I still get close to your planned 50Hz tuning for my cab? 

The tuning with the standard port is in the upper 50s. The cab does works tuned to that frequency but power handling of the lowest frequencies is compromised. So I'd like to get it down to 50Hz - which means we need to lengthen the port.

There are a couple of ways of doing it. The first is to buy a second port (at £1.27 or what ever not really a problem), cut it to the extra length needed, and use plastic glue (the stuff you use to glue plastic drainpipe) to glue the piece of port to the main one. Support with gaffa tape. The second way is to cut some cardboard (Cornflakes packet, for example) and tape it to the existing port to extend the length.

Once I've tuned the system, I'll advise on the length of port needed.

19 hours ago, Downunderwonder said:

Hopefully not going to cause an amp to melt:

 

Yes, that's about the size of it.

I've got chocolate block crossover assembled and will post the info tomorrow. It'd be interesting to see what you''ve come up with, @Downunderwonder

LspCAD and LAUD are my current tools of choice too, although I have an Arta setup ready to go as soon as I have time to learn it. I'm not sure it will add much to what I have now but at least I'll be able to use a laptop instead of an MS-dos PC.

Dunno about that @nilebodgers, It looks like a CD horn to me. B&C say this: " Hyperbolic cosine geometry combines best of exponential and CD characteristics." The reason we can get away without CD correction is that the crossover frequency is relatively high (3.5kHz) and I'm not bothered about getting a flat response above 6kHz.

Still, the main thing is that we have a simple circuit that works really well and can be assembled in minutes.

Here's a diagram of the crossover. It doesn't get any simpler than this. I've assembled the circuit using a (chocolate block) terminal strip. So - no soldering needed. I'll post a frequency response of the finished system and of the assembled crossover later today.

The Pulse 10 is wired directly to the input and this circuit connects to the HF unit.

You live in Germany, @Si600, which is the centre of the universe for speaker kit building IMO. Check out the next issue of Hobby Hifi, available at your friendly kiosk in about two weeks' time. It should contain a complete design for an 'updated' version of the LS3/5a using modern components. I assume you speak German.

Falcoln and Wilmslow are stuck in the sixties, but IPL have some very nice transmission line designs, and Ivan knows his stuff.