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

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43 minutes ago, Chienmortbb said:

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. 

 

I’m not being facetious - but how do you avoid this? 

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1 hour ago, LukeFRC said:

I’m not being facetious - but how do you avoid this? 

Firstly this is general advice and not specifically aimed at this cab. Really low frequencies muddy the sound and use vast amounts of amplifier power as well as over exerting the bass driver.  So

  1. Don't use any sort of low bass boost such as an octaver
  2. Don't use too much  bass control on the amp.
  3. Don't use too much bass on any onboard pre-amp (does not apply to passive basses).
  4. The best way is to use an HPF.

Some amps have an HPF built in but there are some good external ones available. In my opinion you need one the operates about 30-35Hz and with a 24dB per octave slope. One often mentioned is the Thumpinator. My only worry is that there are no specs on any of the models. However they do seem to work.

FDeck on the other site, has a few designs and they are very versatile. Some multi effects units have them but the slope is usually too small. I think maybe I should do a separate thread on HPFs.

 

As a rule of thumb, any needed frequencies will move the cone too fast for you to see. So if you see large s;ow come moveent, that is the stuff we want to avoid.

Edited by Chienmortbb
added last paragraph
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1 hour ago, LukeFRC said:

I’m not being facetious - but how do you avoid this? 

Just to back up what John has said the only real way to avoid this is to use an HPF. remove the frequencies you can't really hear anyway. If your speaker is tuned to 50 Hz then filtering below 40Hz at 24dB/octave makes sense. Eminence recommend this for a lot of their speaker designs, not because there is anything wrong with their speakers but because they know their stuff.

the other thing I'd say would be don't slap the bass without using compression or a limiter. Not all amps produce much in the way of really low frequencies but it's possible to make an amp that goes all the way down. If you did then when you pushed the strings down it wouldn't make a note but the cone would follow that movement. If you slap the strings you are pushing them down as far as they go so that represents an extreme movement The initial movement is relatively slow compared with say the 80 cycles per second of the main component of low E so this represents something going on below the resonant frequency of you cab.

It's possible that Funkle's amp is one with a relatively low cut off, most have a bit of HPF baked in. Combine that with slapping and inadvertently he's invented a new obstacle course for speakers :)

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Heh. I’m certainly trying. 

I’m not sure if the GK MB800 has an HPF built in. There’s nothing in the manual and I can’t find mention of it on Talkbass. 

I experimented with the Zoom B3 HPF and cannot see much difference playing into the GK front end with the cone movement with or without it. That implies there is some kind of baked in HPF in the head? (Edit. The other possibility is that the Zoom HPF doesn’t do as much as it should.)

Nonetheless, I have attempted abuse of the woofer in other ways. Mainly dialling in huge bass boost to see how it reacts. 

Slapping is an excellent test of speaker cabs. It has a huge transient, plenty of low frequency information...and just about every bassist will do it when stressed, lol

Edited by funkle

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Phil is 100% correct. I think the other thing to stress is that an HPF helps with the headroom of  an amp. 

Also slapping sounds better when used with a compressor. 

As for the amount of treble available from the cabinet, you will soon get used to it and miss it when you try other cabs. Those with a simple crossover to a piezoelectric tweeter will sound really harsh. That is not to say that Piezo’s sound harsh. It is often the way they are used.

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2 minutes ago, Chienmortbb said:

Also slapping sounds better when used with a compressor. 

As for the amount of treble available from the cabinet, you will soon get used to it and miss it when you try other cabs. Those with a simple crossover to a piezoelectric tweeter will sound really harsh. That is not to say that Piezo’s sound harsh. It is often the way they are used.

How do you set up the compressor? As a normal compressor e.g. 4:1 with fast attack/release, or as a brick wall limiter (to protect the speaker)?

I really like the treble from this cabinet and how it is presented.  Not harsh. 

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Yeah Stevie spent a lot of effort in firstly choosing a nice driver for the horn and then taking out some of the irregularities out of the frequency response. It was really noticeable when we did the comparisons with other speakers at the SW bass bash and we had a chance to listen properly late on. It would be really interesting to try them as PA speakers.

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On 14/09/2019 at 13:16, Phil Starr said:

If you slap the strings you are pushing them down as far as they go so that represents an extreme movement The initial movement is relatively slow compared with say the 80 cycles per second of the main component of low E so this represents something going on below the resonant frequency of you cab

 

This has been bugging me all weekend. There's no reason why the cone should have touched the driver on Pete's cab. There was a gap of 4mm between the driver frame and the grille, which means the speaker was moving 4mm beyond the frame. That's quite a lot of movement, to put it mildly.

It's worth mentioning that exceeding xmax isn't necessarily a disaster, and exceeding xmax on transients is probably something we all experience regularly when we're playing loud. However, it shouldn't have happened in this instance because Pete says he wasn't playing at an outrageous volume. I can think of two possibilities, which are not mutually exclusive.

The first is that sub-E-string frequencies were being sent to the cab. This is what Phil has suggested and it makes a lot of sense. The port has been designed to support the frequencies 40 to 80Hz, which is the bottom octave of the bass guitar. Below that, power handling reduces quickly, causing quite severe movement of the cone.

The second possibility is that the amp's frequency response wasn't flat during the test. The  specs on the GK amp review Pete posted mentioned +/-7bB. So I decided to take a look at the original review, which is here: <https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwj1n8-e-dTkAhWoRhUIHe0eCYMQFjAAegQIARAC&url=https%3A%2F%2Fbassgearmag.com%2Fwp-content%2Fuploads%2F2017%2F07%2FIssue8.pdf&usg=AOvVaw03uQIy_EsBJQP-iYWC1vxL>

Go to p. 74. Unfortunately, the graphs are a bit pixellated, but I'd say that, with its controls at noon, the amp  has a baked-in bass boost of about 4dB at 50Hz and a strongly rising treble (+7dB at 10kHz). That could also account for the excess treble Pete noticed. It looks suspiciously like a Trace Elliot "smile" in fact. Optimally flat settings for the amp are Contour off, Treble 10 o'clock, Bass 10 o'clock, Hi-mid one o'clock and Lo-mid one o'clock.

Back to the grille. I found some 3mm foam strip in my workshop and have decided to use that instead of adding batten. As long as I don't fully compress the foam, it doesn't poke through the grille. That gives me an additional 3mm of clearance. If the cone hits the grille now, it will be doing so at twice xmax, which is plenty - and just 4mm short of xlim. Perhaps a warning that you're about to reach xlim isn't a bad idea.

I'll alter the Parts List for the batten accordingly.

 

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On 14/09/2019 at 14:21, funkle said:

How do you set up the compressor? As a normal compressor e.g. 4:1 with fast attack/release, or as a brick wall limiter (to protect the speaker)?

I really like the treble from this cabinet and how it is presented.  Not harsh. 

I'm not an expert on compressors, but as far as I can see, you need to set the compressor to catch and squash that initial transient.

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On the question of a HPF on the GK, the measurements show that there is one but it's quite mild and is negated by the bass boost. It looks better with the tone controls set to optimally flat.

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Thanks @stevie

When I started testing, I did set the controls to optimally flat to start off with, and proceeded from there with bass boost etc. The Bass Gear Magazine article is very helpful indeed, in many ways, and learning how to set the GK flat properly was one of them.

I’m trying to recall if there was a modest bass boost or not when I was getting the driver to hit the grille with moderate volume when playing G or below. I can’t reliably recall, so will simply have to re-test, with and without a HPF. 

I added the extra 6mm batten in last night and re-fitted the grill today. 

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5CA3240F-2E40-41FB-8276-1430B5BE895A.thumb.jpeg.b52be457ca600eb15e7bf2fe6a6e34a3.jpeg

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I did a dry run before doing any glueing and determined that the grill would be a very close fit indeed after adding the foam. The photos above demonstrate that well; it is just about flush fit now. 

So I have 21mm of batten installed now with 1mm of foam. 22mm total. That should be plenty of space. 

I’m not sure when I can next stress test; I’m all tied up with looking after an unwell relative at the moment. I’ll do some controlled testing when I can and report back. I’ll also be more methodical when I test as well. 

Edited by funkle
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Did some quick pics of the cab in its current state before I left this morning. Just for fun. 

6B5DF138-0313-4ADA-A4A8-80B15F15475D.thumb.jpeg.5b91a5ee80c7943ad7f2a94abbef9fe4.jpeg

3468B8B2-2EF0-4C1A-99F2-957A1AD30641.thumb.jpeg.3a496effc8eb023e27916ffe95488341.jpeg

51E5DEA2-F0EA-4292-84A1-F4FDFE5B55FE.thumb.jpeg.bb0d315084d8fc9c288ebeb289d7cc29.jpeg

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That looks the business - and certainly outshines some commercially built cabs. "What, you built that yourself? You're kidding me!"🤩

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But just wait till you see my grey one with the aluminium grille.......

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3 hours ago, stevie said:

But just wait till you see my grey one with the aluminium grille.......

We are waiting!

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5 hours ago, stevie said:

That looks the business - and certainly outshines some commercially built cabs. "What, you built that yourself? You're kidding me!"🤩

That has always been the goal. I’m pleased.

I have wondered about other tweaks as I have built. One was whether there is enough wood to allow the handle to be routed out to be flush mounted?

Getting the grille right is another critical key to the look. I like my one. But I’d suggest taking time on the aluminium one to get it perfect. 

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Flush mounting the handle is a nice idea but I think it looks best surface mounted because the edges are rounded rather than straight - you'd have an odd gap.

I thought about fitting rear wheels and a retractable handle, but they cost the earth.

 

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5 hours ago, stevie said:

That looks the business - and certainly outshines some commercially built cabs. "What, you built that yourself? You're kidding me!"🤩

 

I have to agree.

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4 hours ago, stevie said:

I thought about fitting rear wheels and a retractable handle, but they cost the earth

And probably weigh as much as the cab!

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17 hours ago, LukeFRC said:

We are waiting!

Best I can do right now, as the grille's not finished.

 

844154304_IMG_4394(Medium).thumb.jpeg.831b358ed5cd6397b16ef2817ffb2556.jpeg

Edited by stevie
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 That's the finish you get from the foam roller without trying too hard. (The badge looks great!)

The shine on the bottom left is from the flash.

Edited by stevie

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Regarding the finish, after achieving the leather effect, do you think it would be possible to remove the shine of the tuff-cab simply by scrubbing it with steel wool?

@funkle, could you please try this, if you have some steel wool at hand, in one of your test blocks?

If it works it may give a more convincing leather look without any shine.

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46 minutes ago, Ghost_Bass said:

Regarding the finish, after achieving the leather effect, do you think it would be possible to remove the shine of the tuff-cab simply by scrubbing it with steel wool?

@funkle, could you please try this, if you have some steel wool at hand, in one of your test blocks?

If it works it may give a more convincing leather look without any shine.

Thing is the smoothness is part of what means dirt won’t cling to it easily

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Hmm. Now I’m confused what to try. Lol

I threw away my original tester blocks after I finished the paint job. But will experiment when I can. Unfortunately my relative is now in a hospice and my time is fully occupied for a while. 

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