Basschat easy-build lockdown cab project

[stevie]

Phil's working on the cabinet assembly instructions at the moment and will post them as soon as he's sorted. Once I've retuned the cab, located the cause of the 60Hz resonance and measured the bottom end response, I should be able to sign off the tweeterless cab design. Then you can build to your heart's content.

The two-way version will obviously take longer.

Edited February 26, 2021 by stevie

[stevie]

Here are a few more measurements.

The first is the Pulse 10 at one metre. Unfortunately, I didn't calibrate the measurement, but from 200Hz to 1,7kHz it's 96dB. Between those frequencies it's really smooth - better than much more expensive drivers in fact. You can see the effect of the cone breakup between 2 and 3kHz. Not brilliant, but not as bad as your average Eminence.

The compression driver (second graph) works well with the horn - thank goodness. Celestion say it can be used down to 2.5kHz, which is really good for such an inexpensive HF unit, but our crossover frequency here will be dictated by the bass unit rolloff, which is higher than that. Crossing over at 2.5kHz would also require a more complex crossover than I'm aiming for here.

 

 

 

 

 

 

 

 

 

 

 

Edited March 7, 2021 by stevie

[stevie]

Sorry for the confusion with the graphs. It's not exactly easy to delete and replace images (although I finally managed to figure it out).

Edited March 7, 2021 by stevie

[stevie]

I decided to do a quick crossover hookup yesterday evening and managed to sort it out in an hour. You'll need three, cheap components, which is just what we wanted. The cab sounds surprisingly good too. More info and measurements to follow.

[Phil Starr]

Well done, that was quick given how late you got the cab and work demands. I'd better get on with the build write up

[stevie]

I've just come across Celestion's own published measurement of the Pulse 10 chassis. It's interesting to compare it with the one I took, as it looks like it's been smoothed slightly. I also measured 1dB more sensitivity.

[Mottlefeeder]

9 hours ago, stevie said:

I've just come across Celestion's own published measurement of the Pulse 10 chassis. It's interesting to compare it with the one I took, as it looks like it's been smoothed slightly. I also measured 1dB more sensitivity.

If they took one straight from the production line and tested it without running it in, would that account for the difference?

David

[stevie]

I doubt very much whether they'd do that, but it wouldn't account for the differences. Apart from the 1dB difference in sensitivity, which could be down to my mic placement and is neither here nor there, the main differences are in the size of the peaks and dip between 2 and 3kHz and the fact that my curve shows a dip at 6kHz. Other than that, they are remarkably close.

Peaks and dips can be minimised by using smoothing, a technique that's commonly used to make frequency response curves look a bit better.

It looks like Celestion has made some effort to tame the peak at 2.5kH and have turned it from one large peak into a less worrying twin peaks and a dip. Bear in mind that this is an inexpensive chassis and that virtually all bass guitar cabs have resonances at around this frequency, most of them much worse than what we're seeing here.

Edited February 28, 2021 by stevie

[stevie]

For comparison, here's an Eminence Basslite.

 

[nilebodgers]

11 minutes ago, stevie said:

For comparison, here's an Eminence Basslite.

 

That's pretty offensively large, would need some kind of parallel RLC trap in series with the driver to tame that.

[Mottlefeeder]

On 28/02/2021 at 21:49, stevie said:

For comparison, here's an Eminence Basslite.

 

This is the graph from the Eminence web site - where did yours come from?

 

Edited March 2, 2021 by Mottlefeeder
changed attached pdf to jpeg

[Beer of the Bass]

Could that be the graph from the 12" Basslite? I remember looking at those for my cabs and wondering if that spike would be offputting.  Most of the Eminence line have peaks around there and many of them can sound quite pleasing, but some models have it narrower and more pronounced than others.

[funkydoug]

It's not a bad bump to have. Our ears are much better at hearing stuff in that range than in the lows, so that bump helps bass cut through in a mix. 

Sansamp VT pedals call it 'bite' I think. Not everyone loves it, but then again not everyone loves salt on their chips...

[Chienmortbb]

17 hours ago, funkydoug said:

It's not a bad bump to have. Our ears are much better at hearing stuff in that range than in the lows, so that bump helps bass cut through in a mix. 

Sansamp VT pedals call it 'bite' I think. Not everyone loves it, but then again not everyone loves salt on their chips...

It is around the brightness range of many guitar amps. For pro sound it is a bad thing and Eminence have always been particularly poor at controlling those peaks. 
 

it would be interesting to see the specs that Emininence published at the same time as those Basslite plots above to see whether they changed the parameters of the driver or just “smoothed” the response. 

[Mottlefeeder]

5 hours ago, Chienmortbb said:

... it would be interesting to see the specs that Emininence published at the same time as those Basslite plots above to see whether they changed the parameters of the driver or just “smoothed” the response. 

This is the pdf I saved from the Eminence site in 2012

Basslite_S2010.pdf

[Alien]

On 14/02/2021 at 00:16, Downunderwonder said:

 Learning enough to solder a few wires is a thousand times easier than welding galvanised pipe with stick electrodes. 

Nailing jelly to the ceiling is easier than welding galvanised pipe.  My hat's off to you if you're any good at it!

 

A

[Downunderwonder]

21 minutes ago, Alien said:

Nailing jelly to the ceiling is easier than welding galvanised pipe.  My hat's off to you if you're any good at it!

 

A

It's 30 years ago now. I would be blowing holes in it left and right if you gave me a job today.

[Phil Starr]

13 hours ago, Mottlefeeder said:

This is the pdf I saved from the Eminence site in 2012

Basslite_S2010.pdf 644.06 kB · 6 downloads

It's quite interesting, I tend to print off the pdf's as I just find it easier. Eminence tend to be fairly stable producing the same models over very long periods. Fane on the other hand frequently change things around without changing the model no of the speaker. I've some  older 10-275  from Fane that were changed to 10-300 in the catalogue, all the Thiele Small parameters stayed the same except the power handling. It was the same speaker. Since then it has had more than one change of T/S parameters as it has been re-engineered but has kept the 10-300 designation. Celestion too have come out with the Pulse range a few years ago, which we are using but it was identical with a previous speaker. We try to recommend speakers that are easy to source and which we think will be available for several years and I try to watch out for changes which might affect performance. I suspect some of this at least is affected by the sourcing of components in China. 

Nowadays I keep all the old specs so I can double check for changes, and I rarely trust the database in WinISD not to have been overtaken by manufacturing 'updates'. It is ironic that paper still seems to be the best way of looking out for this stuff. My memory isn't any more

[stevie]

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.

 

Edited March 5, 2021 by stevie

[nilebodgers]

3 minutes ago, stevie said:

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.

 

Nice and simple. It’s handy it’s not a CD horn so doesn’t need correction.

[stevie]

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.

[nilebodgers]

6 minutes ago, stevie said:

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.

It's not completely obvious from the freq response though, I've seen horn responses where it is much more pronounced so they must be favouring the exponential response a bit more.

The CD HF response can be corrected by making the high pass look a bit like a 3rd order topology, but deliberately using the rising impedence of the driver to create a HF peak (the capacitor value nearest the driver is tweaked if I remember correctly). I found this trick in some commercial speaker designs and used it myself although it needs a lot of care to avoid the impedence dropping too low. (I used to use LspCAD and LAUD when I did some semi-commercial speaker design in the early 2000's)

[stevie]

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.

[Downunderwonder]

As an early morning brain exercise I am putting my non electrical third eye to work to build the chocolate block crossover. Through the fog I think it requires 4 screws each side?

[stevie]

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