Stevie’s 12” FRFR Cab Build Thread (Basschat Cab v3)

[Phil Starr]

Fly screen mesh is a new idea, just a quick look shows they do fibreglass mesh in black and grey as well as aluminium mesh plus polyester https://www.flyscreen.com/mesh/standard-rolls-for-cladding-and-screening/

[LukeFRC]

11 hours ago, Phil Starr said:

Fly screen mesh is a new idea, just a quick look shows they do fibreglass mesh in black and grey as well as aluminium mesh plus polyester https://www.flyscreen.com/mesh/standard-rolls-for-cladding-and-screening/

Fly screen and pet mesh is a fairly common idea in some of the old Fearful builds. Pet screen would probably work better than my fly mesh. I stole the idea from @2x18 of this parish who has used it to great effect on his fearful

[funkle]

Good morning all

I was testing the cab out further again a bit yesterday evening and today. I’ve had to cancel some gigs due to a family member being unwell, which led to a little extra time alone at home.

Everyone else was out of the house, so I cranked the GK’s gain and volume up. I noticed a metallic ‘clank’ noise when I got everything up to about the 12 o’clock on both, which is moderately loud but not excessive. I hadn’t noticed it previously in testing the cab (hint: my previous higher volume testing was done with the grille off...). It seemed to come at notes hit hard around ‘G’ on the E string or below; it was only present during volume spikes, not when I played softer. It seemed pretty odd to happen at what was well within the cab’s capabilities previously.

This was obviously concerning, but I soon worked out the cause. I was afraid it was the voice coil hitting the back plate with a voltage spike with the low notes. Or the woofer cable hitting the back of the woofer. Neither was the case. It’s the grille. 

I screwed my grille in fairly firmly, and iI think the cone is hitting it when I slapped or accented lower notes. I took the grille off and worked my way up to max on both the gain and volume controls. Pretty intense testing....insane volume....no metallic ‘clank’ noise any more. Whew.

(I could still make the woofer distort a little if I push it that hard/at that volume, or cranked in more bass. That seemed normal to me, every cab has its limit somewhere.)

My conclusion. At very high volume transients it appears to be possible to get the woofer to touch the grille, currently.

(The alternative explanation, that the grille simply vibrated a lot with those spikes, didn’t seem to be the case when I pressed on it or checked the fit again.)

I will need to perhaps add another layer of foam to the battens and experiment.

As context. The GK MB800 is a very powerful amplifier, and the Faital woofer is rated at 300W AES (max 600W). I double checked the bench test output from the GK from Bass Gear Magazine and I attach the info below for context. The GK delivers continuous power at near max handling of the driver, and burst power beyond it. (Dependent on THD %)

 

 

Edited September 13, 2019 by funkle

[stevie]

This is excellent work, and just goes to show that you can calculate till the cows come home but nothing beats a practical test. I carried out lots of tests on the cab (including using it live) but didn't carry out any stress tests.

The obvious solution to the problem is to increase the height of the picture frame grille support. The "lip" around the cab is 25mm - so we have plenty to play with. I looked for some suitable batten ("stripwood") and found some from Wickes. I believe Wickes has a national distribution network - so it shouldn't be too difficult to source. You can always try your local timber merchant, of course.

Wickes have 10 x 18mm and 12 x 21mm batten, which will raise the grille by an additional 3mm or 6mm.

https://www.wickes.co.uk/Wickes-Pine-Stripwood-Moulding-PSE---10mm-x-18mm-x-2-4m/p/121255

https://www.wickes.co.uk/Wickes-Pine-Stripwood-Moulding-PSE---12mm-x-21mm-x-2-4m/p/121260

I suspect that 3mm will be plenty but will wait to see what Pete discovers in his tests.

Both Pete and I now have the 15mm batten installed in our cabs. So we're going to have to figure out what to do now. Foam strip might work but there is the problem of the foam poking through the holes in the grille, which we want to avoid. The alternative is some neoprene rubber sealing strip, which is available in a variety of thickesses from Ebay for about £6 delivered. That is enough to do two cabs. Ebay item no. 261725424586.

Pete, if you can figure out what thickness of strip we need, I'll order some and send half of it on to you.

 

Edited September 13, 2019 by stevie

[stewblack]

Rubber 'feet' or door stoppers? 

[stevie]

The kind of grille Pete has needs to be supported all round - otherwise it could rattle. Rubber feet would work but only on a heavy grille.

[funkle]

50 minutes ago, stevie said:

The obvious solution to the problem is to increase the height of the picture frame grille support. The "lip" around the cab is 25mm - so we have plenty to play with. I looked for some suitable batten ("stripwood") and found some from Wickes. I believe Wickes has a national distribution network - so it shouldn't be too difficult to source. You can always try your local timber merchant, of course.

Wickes have 10 x 18mm and 12 x 21mm batten, which will raise the grille by an additional 3mm or 6mm.

https://www.wickes.co.uk/Wickes-Pine-Stripwood-Moulding-PSE---10mm-x-18mm-x-2-4m/p/121255

https://www.wickes.co.uk/Wickes-Pine-Stripwood-Moulding-PSE---12mm-x-21mm-x-2-4m/p/121260

I suspect that 3mm will be plenty but will wait to see what Pete discovers in his tests.

Both Pete and I now have the 15mm batten installed in our cabs. So we're going to have to figure out what to do now. Foam strip might work but there is the problem of the foam poking through the holes in the grille, which we want to avoid. The alternative is some neoprene rubber sealing strip, which is available in a variety of thickesses from Ebay for about £6 delivered. That is enough to do two cabs. Ebay item no. 261725424586.

Pete, if you can figure out what thickness of strip we need, I'll order some and send half of it on to you.

 

Thanks @stevie  

I agree, I’ve been thinking about solutions and the best is to add more batten height. I’ll strip out the foam I’ve got and install some more batten.

The current batten is probably going to be very hard to remove, so I might have to look for very narrow strips to glue on top of the existing batten.

Don’t sweat sending me anything, I’m just going to measure everything again and then hit either B&Q or Wickes to buy something suitable. 

Edited September 13, 2019 by funkle

[stevie]

Make sure you don't wreck your driver. It looks to me like you're hitting 10mm excursion. If you hit 17mm, the driver dies. I'd expect the suspension to stiffen up before you get to 17mm, but 500 watts of bottom E string is a lot for a single 12.

Edited September 13, 2019 by stevie

[funkle]

16 minutes ago, stevie said:

Make sure you don't wreck your driver. It looks to me like you're hitting 10mm excursion. If you hit 17mm, the driver dies. 500 watts of bottom E string is a lot for a single 12.

Agreed. I’m listening carefully for signs of distress. The most I’ve been able to cause by stressing the driver so far is woofer distortion. Thankfully no other worrying sounds...

I’m interested in knowing the cab’s limits before it hits a gig. I definitely do stress cabs. But as carefully as I can.

When I can, it will come to a rehearsal space with me, as basically I’ve found a smallish room with loud musicians is often more intense volume wise than many gigs. Lol...

The only driver that has taken every form of abuse I can hit it with is the 3012LF. That thing caused my (500W into 8 ohm) power supply to cry for help. I never heard the driver ever distort with that power level. Slapping a B string with max bass boost on amp and bass; it never sweated. Insane. But of course it lost midrange sensitivity because of that LF performance, and to my eye needs crossed over to another driver around 1.5kHz (maybe 2kHz if you can live with the spike in response).

I never asked, but at what frequency does the crossover shift things between the drivers?

Edited September 13, 2019 by funkle

[stevie]

I have a couple of those 3012LF drivers here - so I'm quite familiar with them, although I've never pushed them to the limit. It's probably the best driver Eminence makes. They're fairly insensitive and need a large cabinet (and a separate midrange driver) but they do extend low, handle oodles of power and sound very dynamic.

The crossover on your cab is 2kHz - 24dB per octave.

 

[funkle]

Found what I need at B&Q. It will add another 6mm depth to the battens in one easy move. It’s 6mm deep and 11mm wide (in fact it’s probably 10.5mm, they just round up for some reason). Same width as what I already have.

https://www.diy.com/departments/smooth-stripwood-t-6mm-w-11mm-l-2400mm-pack-of-1/1793539_BQ.prd

Just a teeny bit more building and painting work now. 

Edited September 13, 2019 by funkle

[stevie]

Right, I'll see if I can get hold of some of that too.

[RichardH]

Most of the DIY sheds have a section with various profiles like that - usually at the end of an aisle with them all racked up end on. Wickes are usually pretty good for that sort of thing too.

[Chienmortbb]

That is a powerful amp and it can clearly push the cabinet to and beyond its limits. However it must have been incredibly loud when you turned  it up. 

I was testing my MK 2 once with the grille off. Heard a horrible noise when plaint Open E. The guitar cable had twisted and was testing on the cone!

As for the 3012LF, the clue is in the LF. It is a low frequency driver with not much above 2kHz. In addition the peak above 1.5KHz is nasty. In not opinion it needs to cross over well before 1.5KHz. 

[Phil Starr]

I nearly said that the reason I worried about this is that I've had to stop gigging with my 2x10 until I sort the grilles. I'm still using those horrible round grilles that are widely available and the cone's are reaching them at certain frequencies. They aren't really designed for high Xmax speakers. 

If you are slapping with an amp with no HPF or limiting/compression it won't matter which string you hit, the initial hit will be below the speakers resonant frequency and excursion will get out of hand fairly quickly

bad luck though and easily sorted.

Edited September 13, 2019 by Phil Starr

[stewblack]

Thanks again @funkle for putting the cab through hell so we don't have too!!

[funkle]

40 minutes ago, stewblack said:

Thanks again @funkle for putting the cab through hell so we don't have too!!

No problem. I want to know before a gig what I can expect. Not during it...running out of enough cab is an unpleasant experience. Or suddenly finding that low G and below gives a horrible click every time you hit it at moderate volume, because the grille is just a smidge too close. 

1 hour ago, Chienmortbb said:

That is a powerful amp and it can clearly push the cabinet to and beyond its limits. However it must have been incredibly loud when you turned  it up. 

No kidding. The mugs shook on the shelves, the windows rattled, I could hear walls vibrate. I felt a strong breeze from the port on low notes. On open A at max power, I actually watched the cab walk itself backwards an inch or two. My wife came in from the front of the house en route to somewhere else and said she could hear it out front (quietly). That is through a few stone walls and was about 40 ft away. This is clearly a capable cab.

Eventually, when more cabs are built, you know someone, somewhere, will do this without knowing what they are doing...better to know how it behaves with borderline or outright improper use.

As a side note. The preamp on the Celinders is legendary for putting out mega treble. I messed with it this morning and flicked the switches that give boosts in both lower and upper treble, just to see what it was like through this cab. Then cranked the volume up.

Indescribably piercing. I’ve never had so much treble, ever, at that volume. It was a very clear, even treble, but just too much.

I turned those switches off smartly. As it is, even without the boosts, both Celinder Updates I have (Jazz 4 and PJ4) need the treble rolled off a bit to be manageable through this cab. 

Running cab sims from the Zoom B3 into the cab, I am struck by how many of them clearly roll off the upper end, quite significantly. 

[LukeFRC]

1 hour ago, funkle said:

No problem. I want to know before a gig what I can expect. Not during it...running out of enough cab is an unpleasant experience. Or suddenly finding that low G and below gives a horrible click every time you hit it at moderate volume, because the grille is just a smidge too close. 

No kidding. The mugs shook on the shelves, the windows rattled, I could hear walls vibrate. I felt a strong breeze from the port on low notes. On open A at max power, I actually watched the cab walk itself backwards an inch or two. My wife came in from the front of the house en route to somewhere else and said she could hear it out front (quietly). That is through a few stone walls and was about 40 ft away. This is clearly a capable cab.

Eventually, when more cabs are built, you know someone, somewhere, will do this without knowing what they are doing...better to know how it behaves with borderline or outright improper use.

As a side note. The preamp on the Celinders is legendary for putting out mega treble. I messed with it this morning and flicked the switches that give boosts in both lower and upper treble, just to see what it was like through this cab. Then cranked the volume up.

Indescribably piercing. I’ve never had so much treble, ever, at that volume. It was a very clear, even treble, but just too much.

I turned those switches off smartly. As it is, even without the boosts, both Celinder Updates I have (Jazz 4 and PJ4) need the treble rolled off a bit to be manageable through this cab. 

Running cab sims from the Zoom B3 into the cab, I am struck by how many of them clearly roll off the upper end, quite significantly. 

You’ve seen this site? http://www.zinfanus.com/zoom_b3/cabinets/index.htm

 

out of interest - and Stevie May be able to tell us having designed the cab and done the maths - but if you use the HPF on the B3 can you dial out the knocking sound by taking out the subs? Ie is it the power of the amp or subsonics that cause the high excursion?

[funkle]

I have experimented with the HPF in the Zoom B3 Fishman Preamp sim. It works great as usual at tidying up the lows, although to be honest turning down the bass knob on my instrument or the amp seemed just as good. I have had much more profound effects on other cabs with the HPF than on this one.

I didn’t experiment it with trying to take the ‘click’ of the woofer hitting the grille. It might work, but I suspect the woofer just needs to have a certain amount of movement. The ‘clicking’ happened at very moderate volumes when I accented notes or slapped; I suspect a compressor set as a brick wall limiter would have been a better tool than the HPF, perhaps.  

TLDR; I think it was the power of the amp rather than any subsonics causing the cone travel. 

[funkle]

40 minutes ago, LukeFRC said:

You’ve seen this site? http://www.zinfanus.com/zoom_b3/cabinets/index.htm

Fascinating graphs. Look at the frequency responses of those classic cabs. Anything but FRFR...

[tauzero]

On 11/09/2019 at 23:05, stewblack said:

I am toying with the colour scheme for mine too. One idea is to get a little green in there - homage to my beloved Trace Elliot heritage. Maybe mix the paint to get a deep greenish black. I have several old TE grills I could use - assuming they would fit. 

Just put some green LEDs behind the grille. Or go wild and multicoloured, like I did with a Berg AE112.

[Phil Starr]

1 hour ago, LukeFRC said:

You’ve seen this site? http://www.zinfanus.com/zoom_b3/cabinets/index.htm

 

out of interest - and Stevie May be able to tell us having designed the cab and done the maths - but if you use the HPF on the B3 can you dial out the knocking sound by taking out the subs? Ie is it the power of the amp or subsonics that cause the high excursion?

First of all thanks for the link, really interesting, probably worth a thread on it's own

To answer your question it's very simple. As you reduce the frequency the speaker has to move further to produce the same volume. To make things louder the speaker moves further as you turn up the power. The HPF simply reduces the power below a certain frequency. It's the combination of high power and low frequency that creates the greatest excursion.

(This is a little more complicated if you have a ported cab. At high frequencies the air in the port doesn't move so the cab is in a practical sense sealed. As the frequency approaches the port tuning frequency the plug of air in the port starts to vibrate. This creates a back pressure on the speaker and reduces it's movement until at the tuning frequency it isn't moving at all and all the sound is coming from the port. Below this frequency the back pressure falls away very quickly and the air in the cab exerts no pressure on the speaker and it is effectively flapping around in free air. Excursion will become extreme at very low frequencies even with just a few 10's of watts because of the inherent design of all ported cabs)

 

 

[LukeFRC]

6 minutes ago, Phil Starr said:

First of all thanks for the link, really interesting, probably worth a thread on it's own

To answer your question it's very simple. As you reduce the frequency the speaker has to move further to produce the same volume. To make things louder the speaker moves further as you turn up the power. The HPF simply reduces the power below a certain frequency. It's the combination of high power and low frequency that creates the greatest excursion.

(This is a little more complicated if you have a ported cab. At high frequencies the air in the port doesn't move so the cab is in a practical sense sealed. As the frequency approaches the port tuning frequency the plug of air in the port starts to vibrate. This creates a back pressure on the speaker and reduces it's movement until at the tuning frequency it isn't moving at all and all the sound is coming from the port. Below this frequency the back pressure falls away very quickly and the air in the cab exerts no pressure on the speaker and it is effectively flapping around in free air. Excursion will become extreme at very low frequencies even with just a few 10's of watts because of the inherent design of all ported cabs)

 

 

I think what I was thinking is that if you high pass it around the tuning freq you can test if the high excursion is because the power of the amp is really good with transients, or if there is something going on below thetining freq which is giving the high excursion. 

 

[stewblack]

9 hours ago, tauzero said:

Just put some green LEDs behind the grille. Or go wild and multicoloured, like I did with a Berg AE112.

Are they sound activated? 

[Chienmortbb]

As Phil says, in a ported cabinet,below the tuning frequency the speaker is uncontrolled and will move a large amount for a few watts. Not only can this be dangerous, with the excursion approaching XLimit/XDamage but when the Voice coil is beyond the magnet, any signal has no effect on the cone,  but still heats up the voice coil.

So apart from potential causing damage to the driver, you could also be adding a lot of distortion to your sound. The extra heat may also contribute to power compression. As with most resistors, the voicecoil’s resistance rises as it heats up and it heats up with power. This could reduce the acoustic output by 3 dB or more. That has the effect of halving your output power. 

 

Edited September 14, 2019 by Chienmortbb