Speaker advice. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

RojDW48 · 20th May 2018, 9:02 pm

Nice work!

Techman · 20th May 2018, 10:55 pm

With a high demanding setup like that you can't have a central wooden bar across the front of the speaker like that. On loud guitar chords the speaker cone travel will cause it to come into contact with that bar and eventually smash the cone up. The only way round it is to either get rid of the wooden bar or make a deep spacer to set the speaker further back in the cabinet, but this may make it slightly directional in its sound dissipation.

I'll give you three guesses on how I know about this!

julie_m · 20th May 2018, 11:11 pm

You could easily take 10mm. or so off the back of that bar, maybe nearer 15, giving you a bit more clearance for the cone without weakening the cabinet too much. Go across the top and bottom ends with a ball-ended router bit to get a nice curve into the cut-out section, then use a standard flat-ended bit to remove all the rest of the material from in between. Lastly, round off the ends with a concave bit.

Techman · 21st May 2018, 12:12 am

Well, as you can guess, this happened to me and I've just spent the last half hour looking back through old photos to find some that I took of the event and eventually found them.

I'd had an old speaker cabinet that I'd been playing guitar through in years past for just use in the house, so nothing too powerful. I decided to open it up as I'd remembered that it had gone a bit rattly on louder settings - most of the time it would only have been powered by a Mullard 3-3 amplifier and sometimes a 5-10. I also wanted to modify the cabinet to house a 5-10 amplifier and pre-amp head unit for use as a general purpose all in one amplifier unit. I was shocked to find what had happened to the speaker when I removed it, but soon realised what had been happening.

As you can see from the pictures, I not only had to cut out the wooden bars, but also found that the 'circle' was actually slightly smaller than the speaker complete cone area, so as you can probably see, I had to get the pad saw and enlarge the entire hole by half an inch or so. I ended up fitting a 'convex' grill to the outside of the cabinet - this was a few years ago and I've still got it and no more trouble with shredded speakers.

Singlofty · 21st May 2018, 12:16 pm

Thanks for the info, I'll probably just fit some spacers to give the cone a bit more room.

Techman · 21st May 2018, 1:00 pm

I think that'll be the easiest solution. It'll need to be a complete ring, perhaps cut from a sheet of plywood and not just spacers at the four mounting points. You've certainly got the skills to do the job and it would be a shame to have to try to externally modify what you've made as it it does look really nice.

Techman · 24th May 2018, 1:15 pm

I forgot to comment on the modification suggested in post #23. While this suggestion would work, it doesn't take into account that there's a 'grill cloth' fitted in front of the speaker and this 'cloth' would no longer be able to be fitted if this modification was carried out.

That FAL speaker probably has quite a stiff cone, but being driven by a musical instrument amplifier, even of modest power, it's still likely to come forward enough to hit the woodwork on occasion.

When 'homebrewing' a speaker cabinet, it's easy to not appreciate certain things about the design of these things that professional manufacturers (hopefully) incorporate. You see a vintage radio with slats and cloth directly in front of the speaker and think the same can be used in a musical instrument cabinet. The thing is that the old radio probably struggles to put out a couple of watts at the most when flat out, so isn't going to have the sort of problems that an instrument speaker would have. I think that the speaker cabinet that I showed in a previous post was probably someones 'homebrew', although the woodworking was pretty good, and it had been made with the thought of protecting the cone of the speaker to the maximum. There was also a grill cloth of some sort originally behind the slats before I cut them out and increased the 'hole' size. I would have made a spacer to mount the speaker further back, but there just wasn't enough depth to the cabinet, also the speaker frame would have come into contact with at least one of the valves and some other parts of the amplifier, which I was going fit in the bottom of the cabinet - there was only just enough room as it was.

I was originally hoping to keep the 'vintage' look with 'patina' of the old cabinet, and I have to admit that I hadn't at first appreciated the serious design fault of the cabinet until I opened it up and removed the speaker. Once I'd thought about it properly, I could see that those wide, wooden bars would work more like a telephone earpiece than something to properly let the sound out. Thinking about it still further, it makes you wonder what sort of air turbulence could be caused in front of the cone with pressure waves rebounding from the wooden bars and back to the speaker cone, probably helping to contribute to the damage to the cone surround - the damage was actually worse than it looked in the picture and the cone had gone all the way round, with part of it having dropped out completely, as can be seen.

I would have liked to have kept the cabinet original with just the amplifier control head unit above the speaker, but it was no good as it was, so the little pad saw had to come out. If you look at all these professional musician speaker cabinets, none of them have grill or other obstructions such as decorative bars, directly in front of, or against the speaker. I ended up buying the most vintage looking modern grill that I could find from an on-line supplier of such things, and fitted that, and it does the job, although it perhaps doesn't look as nice as yours.

Singlofty · 25th May 2018, 9:17 am

The speaker cloth shouldn't be an issue as there's plenty of room in the cabinet to accommodate a spacer. As it happens I have an old cable drum with 10mm plywood rims so I'll probably knock up one from this.Incidentally I had a look on the YouTube channel mentioned in post #1as I'm starting to build a matching reverb unit and he has lots of vintage amps made by Valco, Electromuse, National etc, many of them with this type of cabinet design but no mention of this issue.
Cheers
Dave

Techman · 26th May 2018, 11:21 am

Quote:

Originally Posted by Singlofty

It sounds really well and clean at low volumes but breaks up as you drive it a bit.

The reason I brought up the problem with cone displacement at high volume causing it to come into intermittent contact with the woodwork was due to what you said in your quote above - or have you found another reason for this "breaking up" of the sound?

Singlofty · 26th May 2018, 1:29 pm

Sorry, I should have been clearer, I meant breaking up in a nice mellow overdrive way.

20th May 2018, 9:02 pm	#21
RojDW48 Nonode Join Date: Jun 2014 Location: Bristol, UK. Posts: 2,074	Re: Speaker advice. Nice work! __________________ '....don't go mistaking Paradise for that home across the road!' (Bob Dylan)

20th May 2018, 10:55 pm	#22
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Speaker advice. With a high demanding setup like that you can't have a central wooden bar across the front of the speaker like that. On loud guitar chords the speaker cone travel will cause it to come into contact with that bar and eventually smash the cone up. The only way round it is to either get rid of the wooden bar or make a deep spacer to set the speaker further back in the cabinet, but this may make it slightly directional in its sound dissipation. I'll give you three guesses on how I know about this!

21st May 2018, 12:12 am	#24
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Speaker advice. Well, as you can guess, this happened to me and I've just spent the last half hour looking back through old photos to find some that I took of the event and eventually found them. I'd had an old speaker cabinet that I'd been playing guitar through in years past for just use in the house, so nothing too powerful. I decided to open it up as I'd remembered that it had gone a bit rattly on louder settings - most of the time it would only have been powered by a Mullard 3-3 amplifier and sometimes a 5-10. I also wanted to modify the cabinet to house a 5-10 amplifier and pre-amp head unit for use as a general purpose all in one amplifier unit. I was shocked to find what had happened to the speaker when I removed it, but soon realised what had been happening. As you can see from the pictures, I not only had to cut out the wooden bars, but also found that the 'circle' was actually slightly smaller than the speaker complete cone area, so as you can probably see, I had to get the pad saw and enlarge the entire hole by half an inch or so. I ended up fitting a 'convex' grill to the outside of the cabinet - this was a few years ago and I've still got it and no more trouble with shredded speakers. Attached Thumbnails

21st May 2018, 12:16 pm	#25
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Speaker advice. Thanks for the info, I'll probably just fit some spacers to give the cone a bit more room.

21st May 2018, 1:00 pm	#26
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Speaker advice. I think that'll be the easiest solution. It'll need to be a complete ring, perhaps cut from a sheet of plywood and not just spacers at the four mounting points. You've certainly got the skills to do the job and it would be a shame to have to try to externally modify what you've made as it it does look really nice.

20th May 2018, 11:11 pm	#23
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Speaker advice. You could easily take 10mm. or so off the back of that bar, maybe nearer 15, giving you a bit more clearance for the cone without weakening the cabinet too much. Go across the top and bottom ends with a ball-ended router bit to get a nice curve into the cut-out section, then use a standard flat-ended bit to remove all the rest of the material from in between. Lastly, round off the ends with a concave bit. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

24th May 2018, 1:15 pm	#27
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Speaker advice. I forgot to comment on the modification suggested in post #23. While this suggestion would work, it doesn't take into account that there's a 'grill cloth' fitted in front of the speaker and this 'cloth' would no longer be able to be fitted if this modification was carried out. That FAL speaker probably has quite a stiff cone, but being driven by a musical instrument amplifier, even of modest power, it's still likely to come forward enough to hit the woodwork on occasion. When 'homebrewing' a speaker cabinet, it's easy to not appreciate certain things about the design of these things that professional manufacturers (hopefully) incorporate. You see a vintage radio with slats and cloth directly in front of the speaker and think the same can be used in a musical instrument cabinet. The thing is that the old radio probably struggles to put out a couple of watts at the most when flat out, so isn't going to have the sort of problems that an instrument speaker would have. I think that the speaker cabinet that I showed in a previous post was probably someones 'homebrew', although the woodworking was pretty good, and it had been made with the thought of protecting the cone of the speaker to the maximum. There was also a grill cloth of some sort originally behind the slats before I cut them out and increased the 'hole' size. I would have made a spacer to mount the speaker further back, but there just wasn't enough depth to the cabinet, also the speaker frame would have come into contact with at least one of the valves and some other parts of the amplifier, which I was going fit in the bottom of the cabinet - there was only just enough room as it was. I was originally hoping to keep the 'vintage' look with 'patina' of the old cabinet, and I have to admit that I hadn't at first appreciated the serious design fault of the cabinet until I opened it up and removed the speaker. Once I'd thought about it properly, I could see that those wide, wooden bars would work more like a telephone earpiece than something to properly let the sound out. Thinking about it still further, it makes you wonder what sort of air turbulence could be caused in front of the cone with pressure waves rebounding from the wooden bars and back to the speaker cone, probably helping to contribute to the damage to the cone surround - the damage was actually worse than it looked in the picture and the cone had gone all the way round, with part of it having dropped out completely, as can be seen. I would have liked to have kept the cabinet original with just the amplifier control head unit above the speaker, but it was no good as it was, so the little pad saw had to come out. If you look at all these professional musician speaker cabinets, none of them have grill or other obstructions such as decorative bars, directly in front of, or against the speaker. I ended up buying the most vintage looking modern grill that I could find from an on-line supplier of such things, and fitted that, and it does the job, although it perhaps doesn't look as nice as yours. Attached Thumbnails

25th May 2018, 9:17 am	#28
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Speaker advice. The speaker cloth shouldn't be an issue as there's plenty of room in the cabinet to accommodate a spacer. As it happens I have an old cable drum with 10mm plywood rims so I'll probably knock up one from this.Incidentally I had a look on the YouTube channel mentioned in post #1as I'm starting to build a matching reverb unit and he has lots of vintage amps made by Valco, Electromuse, National etc, many of them with this type of cabinet design but no mention of this issue. Cheers Dave

26th May 2018, 1:29 pm	#30
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Speaker advice. Sorry, I should have been clearer, I meant breaking up in a nice mellow overdrive way.