Tannoy R-GRF

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izzy wizzy
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#1 Tannoy R-GRF

Post by izzy wizzy »

I'm having to down size the speakers as the next house, however temporary is not going to accomodate the corner York enclosures. So the plan is to make rectangular GRF enclosures which are still not small but will be easier to accomodate. Bit over 1m high, 600mm wide by about 460mm deep. They're rear horn loaded sort of.

Original plans are for flimsy wood. A chap on the Audio Nostalgia forum, Magna Audio https://fosworld.wixsite.com/magna-audio/tannoy makes them from 24mm birch ply so that seems a good idea. Found a Sketchup model for something like the original so I've altered it for 24mm ply, the Baltic Birch seems to be the way to go.

My other 'arf is very encouraging of this move, probably in the hope that I come up with something domestically acceptable and suggested getting the parts CNC or laser cut to save a whole heap of time. So she found Peter Bensen Plywood https://www.peterbensonplywood.co.uk/ and they do CNC cutting. My question is, has anyone used such a service and if so where and how?

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#2 Re: Tannoy R-GRF

Post by chris661 »

I believe our-Colin uses those guys to get the wood cut for his builds.
I do wonder if there are any better cabinet designs around, though. Is this for the 15" Monitor Golds?

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#3 Re: Tannoy R-GRF

Post by Scottmoose »

Well, it's basically a trad. pro-audio style scoop-bin, which can work well enough, although are usually targeting gain through the mid & upper bass region (as you'd expect given the context & purposes for which they were developed) so outright LF extension is usually limited.
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#4 Re: Tannoy R-GRF

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My other 'arf is very encouraging of this move, probably in the hope that I come up with something domestically acceptable and suggested getting the parts CNC or laser cut to save a whole heap of time. So she found Peter Bensen Plywood https://www.peterbensonplywood.co.uk/ and they do CNC cutting. My question is, has anyone used such a service and if so where and how?
As Chris mentioned above I have used Peter Benson Plywood exclusively for all my speaker builds for quite some time now. They provide an excellent service and can deliver to your home. Not sure though if there flat bed CNC router table has a 3-axis head cutter to do angled cuts, they may only be able to do 90-deg vertical cuts. You'll have to ask. If you do contact them mention me (Colin Topps) and say I have recommended you.
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#5 Re: Tannoy R-GRF

Post by izzy wizzy »

It's good to know Bensens is a known quantity, thanks. I'll mention you Colin when I enquire again. I asked whether they could do the angle cuts and the bloke on the phone couldn't tell me but there's only a few of them so hopefully not a big deal for me. Just got to get my Sketchup cutting plan model into dxf file smaller than 170Meg to send them.

I'm going in to this realising the bass might not be as optimal or go as deep as the Yorks. I believe it was designed to be a smaller version of the corner GRF when stereo came along so rooms could accomodate two speakers so it's quite an old design.

However at this stage, I would also welcome other ideas from the speaker builders around here. I've never built anything other than the Corner Yorks. My limit is 600mm wide for the 15" Tannoys. There's many varying reports of the R-GRF. Some good, some not so I'm taking a risk not having heard some. Part of me wants something a bit different to a vented box hence this route.
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#6 Re: Tannoy R-GRF

Post by IslandPink »

With a limited size, anything other than a vented box is going to give you less bass. This seems to be one of the cruel laws of speaker design.
How about selling the 15's and buying a pair of 12"-ers ?
I will now find something large to duck down behind ... :)
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#7 Re: Tannoy R-GRF

Post by Toppsy »

Now if you were to go with a 12" driver as suggested by Mark you could build a pair the 12" Monacor SP-312CX coaxial MLTL speakers as featured in the thread below? These will certainly deliver the bass lacking in the proposed Tannoy cabinets. I know they are a vented cabinet design of which you'd rather avoid but the gains in lower end performance justify the box design.

Pity you live so far from me otherwise you could borrow my pair of the 12" coax speakers to live with for a week or two and see if they gain approval from your other half and yourself. Still the offer is there and Peter Benson Plywood can supply you a full set of CNC machined panels. I have a ready available CAD file your welcome a copy.
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#8 Re: Tannoy R-GRF

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Well, I suspect the 15" Tannoys will do bass just fine.
... Just not in the cabinets proposed above which, as Scott notes, aren't optimised for deep bass.

I'd be looking at a low-tuned ML-TL or ported box, aiming for an EBS alignment, which should sit well with room gain.
I'd also consider a big-ish sealed box for the same reason.

Got any measurement gear?

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#9 Re: Tannoy R-GRF

Post by izzy wizzy »

chris661 wrote: Fri Feb 21, 2020 7:03 pm Well, I suspect the 15" Tannoys will do bass just fine.
... Just not in the cabinets proposed above which, as Scott notes, aren't optimised for deep bass.

I'd be looking at a low-tuned ML-TL or ported box, aiming for an EBS alignment, which should sit well with room gain.
I'd also consider a big-ish sealed box for the same reason.

Got any measurement gear?

Chris
OK, none of that means anything to me so will have to go do some homework. If there's a dummies guide I can be pointed at for all those acronyms, MLTL, EBS, room gain I'd appreciate it. And how big is a big-ish sealed box? The original Lancaster box for 15" is "aperiodic" they say whatever that is and is about this kind of size.

I just got given an IMP Audio Analyser gizmo that works in DOS so will fire up an old laptop to use it.

The thing that kinda confuses me is all the scoop boxes I've seen have a whopping great space behind the speaker while this one has what looks more like a compression chamber. There's a mod that sticks a teardrop baffle at the entrance to the "horn". Maybe I could model it with something or other to give me an idea as to how the thing responds in theory?

A 12" driver isn't really an option especially a Tannoy. They go for too much money. I'm not really interested in other drivers. Frankly I've not heard anything that makes me go oooh. I've only owned two speakers in 40 years and the other was Acoustat ESLs.
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#10 Re: Tannoy R-GRF

Post by izzy wizzy »

Toppsy wrote: Fri Feb 21, 2020 2:59 pm Now if you were to go with a 12" driver as suggested by Mark you could build a pair the 12" Monacor SP-312CX coaxial MLTL speakers as featured in the thread below? These will certainly deliver the bass lacking in the proposed Tannoy cabinets. I know they are a vented cabinet design of which you'd rather avoid but the gains in lower end performance justify the box design.

Pity you live so far from me otherwise you could borrow my pair of the 12" coax speakers to live with for a week or two and see if they gain approval from your other half and yourself. Still the offer is there and Peter Benson Plywood can supply you a full set of CNC machined panels. I have a ready available CAD file your welcome a copy.
Thanks for the offer Colin. Part of my historical problem is I don't get to experience many other systems nor get much feedback on my efforts so kinda live in a bubble and have to take a punt on things.

The Yorks were only an experiment and were never meant to be more than that and here I am 15 years later :)

What just occured to me was the start of the 813PP amplifier thread. The opening comments were "why are you starting with them". Seems I'm doing it again and look where that one ended up. No 813s, no 46s, VCCS filaments etc. You guys are dangerous ;)
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#11 Re: Tannoy R-GRF

Post by chris661 »

izzy wizzy wrote: Fri Feb 21, 2020 7:23 pm
chris661 wrote: Fri Feb 21, 2020 7:03 pm Well, I suspect the 15" Tannoys will do bass just fine.
... Just not in the cabinets proposed above which, as Scott notes, aren't optimised for deep bass.

I'd be looking at a low-tuned ML-TL or ported box, aiming for an EBS alignment, which should sit well with room gain.
I'd also consider a big-ish sealed box for the same reason.

Got any measurement gear?

Chris
OK, none of that means anything to me so will have to go do some homework. If there's a dummies guide I can be pointed at for all those acronyms, MLTL, EBS, room gain I'd appreciate it. And how big is a big-ish sealed box? The original Lancaster box for 15" is "aperiodic" they say whatever that is and is about this kind of size.

I just got given an IMP Audio Analyser gizmo that works in DOS so will fire up an old laptop to use it.

The thing that kinda confuses me is all the scoop boxes I've seen have a whopping great space behind the speaker while this one has what looks more like a compression chamber. There's a mod that sticks a teardrop baffle at the entrance to the "horn". Maybe I could model it with something or other to give me an idea as to how the thing responds in theory?

A 12" driver isn't really an option especially a Tannoy. They go for too much money. I'm not really interested in other drivers. Frankly I've not heard anything that makes me go oooh. I've only owned two speakers in 40 years and the other was Acoustat ESLs.

Happy to have a go at a quick dummies guide.

- ML-TL = Mass Loaded Transmission Line. The towers that Colin (Toppsy) has been working on (with the 10" and 12" Monacor coaxials) are an example. The idea is that you set off with a transmission line, and add a port (the air inside the port is the "Mass"). Between the quarter-wave action (vertical standing waves) and the mass of air in the port, you have quite a lot of flexibility on low-frequency tuning.
- EBS = Extended Bass Shelf. You take the bass reflex enclosure that WinISD (or whatever) would suggest, and then make it bigger and tune lower. The bass response then goes lower, but not as loud - looks like a shelf, hence the name.
- Room gain is more tricky, because it varies room to room. It's how the room responds to low frequency sources. In my room, for instance, there's a lot of boost at 35-40Hz and some at 70-80Hz. So, if I was to make a speaker that was flat (simulated) down to 35Hz, my room would add, say, 10dB there, resulting in boomy bass. It would be better to use a speaker that had less output at 35Hz (ie, a sealed box that rolls off gradually) so that I avoid the boomy bass.

Here's what my (sealed box) speakers do in my room. Being sealed boxes, you'd expect a gradual rolloff towards the bass. In my case, that should be happening below about 60Hz.
Image
As you can see, the room totally dominates the resulting response. What I do for those is apply some EQ to cut down those low-frequency peaks.

REW is free software that's great for measurements. I did a bit of a thread about it here - http://www.audio-talk.co.uk/phpBB3/view ... f=9&t=7555

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#12 Re: Tannoy R-GRF

Post by izzy wizzy »

Thanks Chris. I remember reading the rew thread and just did so again. From a measurement point of view, I should see if the IMP thing I have works with what I have already and see if it correlates with what I think I'm hearing as a sort of baseline.

I guess in some ways I should start again with what I'm trying to do. I've done a bit of homework since. From what I understand I should just dump my preconceived idea about a vented box and work towards having one as that seems to be what most Tannoys end up in so that must be for a reason. Maybe coz that's what they work best in.

So my limitation is 600mm wide, about 450mm deep would be handy and around 1m or so high. Would this sort of size be OK? And if so, is there some kind of vented box sim that will lead some design thinking?
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#13 Re: Tannoy R-GRF

Post by Scottmoose »

I'm not Chris, and I generally hate working with old Tannoy DCs because (assuming they haven't drifted over time) they often want smaller enclosures than many of their owners believe. To a point this depends on intended location in the room and amplifier output impedance; be that as it may, a lot (not all, but a lot), rather like the Altec 604 variations nevertheless don't require huge enclosures. Depends which model they actually are. (?) But from your perspective, you may be in luck since you aren't wanting / necessarily expecting a titanic cabinet.

As far as vented boxes go, 90% of the dodgy reputation they have in some quarters is due to poor design -usually some variation on blindly creating a mathematically flat anechoic alignment with no consideration for anything else e.g. positioning, room gain &c., which only becomes worse if it's tuned narrowly. If you want to know how to design a rubbish vented box, all you need to do is ignore how the speaker will be used, and aim for a QB3 or whatever other max-flat alignment option will give you a really narrow vent tuning. That'll do it, and you too can enjoy the on-off / one-note bass boom so many people object to. ;)
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#14 Re: Tannoy R-GRF

Post by izzy wizzy »

Scottmoose wrote: Sat Feb 22, 2020 8:55 am I'm not Chris, and I generally hate working with old Tannoy DCs because (assuming they haven't drifted over time) they often want smaller enclosures than many of their owners believe. To a point this depends on intended location in the room and amplifier output impedance; be that as it may, a lot (not all, but a lot), rather like the Altec 604 variations nevertheless don't require huge enclosures. Depends which model they actually are. (?) But from your perspective, you may be in luck since you aren't wanting / necessarily expecting a titanic cabinet.

As far as vented boxes go, 90% of the dodgy reputation they have in some quarters is due to poor design -usually some variation on blindly creating a mathematically flat anechoic alignment with no consideration for anything else e.g. positioning, room gain &c., which only becomes worse if it's tuned narrowly. If you want to know how to design a rubbish vented box, all you need to do is ignore how the speaker will be used, and aim for a QB3 or whatever other max-flat alignment option will give you a really narrow vent tuning. That'll do it, and you too can enjoy the on-off / one-note bass boom so many people object to. ;)
OK there's a whole bunch of pitfalls I'd like to avoid but I will be working with Tannoys. And yes, they may have drifted somewhere. Narrow vent tuning doesn't sound good so let's avoid that.

I've just been reading about unassisted flat alignments and an example of how to calculate stuff from speaker parameters. But isn't this easier to sim?

I've also read that all this is fun until its built and then after measurements/listening a revised box has to be made coz unintended/non modelable box losses.

Although they will sit against a wall, plan is to have them on casters so can move them out if necessary.

Am I heading in the right direction?
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#15 Re: Tannoy R-GRF

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izzy wizzy wrote: Sat Feb 22, 2020 9:45 am OK there's a whole bunch of pitfalls I'd like to avoid but I will be working with Tannoys.
Yes, but which type? If you can tell us, we should be able to help. You've probably mentioned it elsewhere, but I don't often get chance to look at all the threads.
Narrow vent tuning doesn't sound good so let's avoid that.
A good start. ;)
I've just been reading about unassisted flat alignments and an example of how to calculate stuff from speaker parameters. But isn't this easier to sim?
Yup.
I've also read that all this is fun until its built and then after measurements/listening a revised box has to be made coz unintended/non modelable box losses.
Complete nonsense fortunately. ;)

A straightforward vented loudspeaker is not mysterious & if it's built correctly, there should not be any non-modelable losses. You will never have 'the perfect' alignment given that room modes will always have an impact on LF behaviour in particular (anything above that is nothing to do with the cabinet), and we all live with a degree of that; even massive DSP can never fully compensate & in most cases it wouldn't be a bright idea to try that anyway. What you can do is design a decent alignment that accounts as far as possible for room positioning, avoids unwanted eigenmodes if it's a conventional design rather than a QW, also avoids excessively narrow vent tunings, ensures air velocity in the duct is kept sensible while minimising unwanted losses & keeps the length down to avoid self-resonant modes. Providing the cabinet is built properly, you shouldn't have unwanted air-leaks, audible panel modes etc. and damping isn't a big deal to account for either.
Although they will sit against a wall, plan is to have them on casters so can move them out if necessary.
Good plan.
Am I heading in the right direction?
Well, I think so.
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