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Tannoy Chatsworth 12" MG rebuild advice.

Glad to see it's not me going mad then.

Interestingly, I found you can fix the problem by adding an aperiodic vent to the cabinet (just model the same 160ltr cabinet with 2 x 4" ports, but with a leak). Would be interesting to hear how that compares to a smaller cabinet. As you say though, it has a large peak in the group delay, so perhaps the smaller cabinet is the best way to go.

I've not tried that, trouble with leaks is their unpredictability in a practical/ executional sense.
 
I've made a few diy speakers using an aperiodic enclosure, they really are only of use when using a driver in a cabinet that should be too small (the Q peak is too large). These are of use with higher Qts drivers, pretty much the opposite of older Tannoys which usually have a Qts of 0.2-0.3 IIRC, it will also flatten the impedance peak at the tuning frequency, handy for valve amps.
The cabinets are easy to build, and forgiving as you can play with the stuffing/restive vent to tune with the room.

I used an aperiodic design for some Goodmans Axiom 201s, with a Qts of ~0.7 it works well, the same with some Supravox 165-2000 drivers, Qts ~1.1 it was excellent. When I tried it with a Supravox 285GMF, much lower Qts of ~0.35 IIRC, it was much better in a standard sealed box.

I'm not saying it won't work but is likely to be less than optimal for those Tannoy drivers.
 
I've not tried that, trouble with leaks is their unpredictability in a practical sense.

Yes it would be difficult to work out exactly how much of a leak you would need. Just noticed Willys hifi sell the Scanspeak variovents, they are adjustable IIRC. Not cheap though...
 
I've made a few diy speakers using an aperiodic enclosure, they really are only of use when using a driver in a cabinet that should be too small (the Q peak is too large). These are of use with higher Qts drivers, pretty much the opposite of older Tannoys which usually have a Qts of 0.2-0.3 IIRC, it will also flatten the impedance peak at the tuning frequency, handy for valve amps.
The cabinets are easy to build, and forgiving as you can play with the stuffing/restive vent to tune with the room.

I used an aperiodic design for some Goodmans Axiom 201s, with a Qts of ~0.7 it works well, the same with some Supravox 165-2000 drivers, Qts ~1.1 it was excellent. When I tried it with a Supravox 285GMF, much lower Qts of ~0.35 IIRC, it was much better in a standard sealed box.

I'm not saying it won't work but is likely to be less than optimal for those Tannoy drivers.

An aperiodic vent in a Tannoy would just be a quick fix for a badly tuned (Peaky) reflex port.

What I'm saying is someone could build the RFC enclosures, and if they found them to have too much bass, an aperiodic vent would be an easy fix.
 
An aperiodic vent in a Tannoy would just be a quick fix for a badly tuned (Peaky) reflex port.

What I'm saying is someone could build the RFC enclosures, and if they found them to have too much bass, an aperiodic vent would be an easy fix.
I guess it could but would be a bit of a waste to start cutting up the enclosures. Just stuffing the ports would give you a leaky closed box but much larger than ideal and the Q tuning may end up being to under damped (based on the original cabinet being tuned for ported Q of around ~0.707)
 
Yes it would be difficult to work out exactly how much of a leak you would need. Just noticed Willys hifi sell the Scanspeak variovents, they are adjustable IIRC. Not cheap though...

The ScanSpeak Variovents are just glass fibre insulation sandwiched between two plastic holders. I found playing around with lots of drilled holes or whole large vents, using various density foam to tune it.

Just as an illustration, two different densities of foam makes a big difference on the smoothness of the impedance plot. (not Tannoy but you get the picture)

Driver in Free Air:

Supravox 165-2000 (2)
by Robert Seymour, on Flickr

Aperiodic with pillow stuffing and a foam absorber


Supravox 165-2000 (2-A2 in cabinet - Open Back with Pillow and Bass Foam V2)
by Robert Seymour, on Flickr

Aperiodic with pillow stuffing and 2x layers of 36mm foam

Supravox 165-2000 (2-A2 in cabinet - 2x Layer 36mm foam & Pillow)
by Robert Seymour, on Flickr
 
I guess it could but would be a bit of a waste to start cutting up the enclosures. Just stuffing the ports would give you a leaky closed box but much larger than ideal and the Q tuning may end up being to under damped (based on the original cabinet being tuned for ported Q of around ~0.707)

That wouldn't work. As soon as you stuff ports it kills the output over the whole range, not the problem area. The best way would be an aperiodic vent combined with the ports. Or just the correct sized enclosure in the first place.
 
That wouldn't work. As soon as you stuff ports it kills the output over the whole range, not the problem area. The best way would be an aperiodic vent combined with the ports. Or just the correct sized enclosure in the first place.

That's what I was getting at, Aperiodic really is for when you need to use a much smaller than ideal enclosure size, for Tannoys that does not make sense to me unless you needed to fit a 15" HPD into a 50 Litre box for example.
A small Sealed, correctly designed ported or horn enclosure seem the best designs for Monitor Golds. In my experience, an Aperiodic design offers no advantage over a Sealed/Closed box, if you can accommodate the correct sized enclosure.
I only used them as both the Goodmans and Supravox drivers would require 150 Litre+ enclosures to avoid a large peak at the tuning frequency due to their high Qts.

With the 11" 285GMF drivers, putting them in Aperiodic Vs Sealed offered no advantage, both in measurements or listening. The Sealed was tighter and sounded more extended in the bass, and better definition too. I did not try ported, only Open Baffle but thats another ball game.
 
That's what I was getting at, Aperiodic really is for when you need to use a much smaller than ideal enclosure size, for Tannoys that does not make sense to me unless you needed to fit a 15" HPD into a 50 Litre box for example.
A small Sealed, correctly designed ported or horn enclosure seem the best designs for Monitor Golds. In my experience, an Aperiodic design offers no advantage over a Sealed/Closed box, if you can accommodate the correct sized enclosure.
I only used them as both the Goodmans and Supravox drivers would require 150 Litre+ enclosures to avoid a large peak at the tuning frequency due to their high Qts.

With the 11" 285GMF drivers, putting them in Aperiodic Vs Sealed offered no advantage, both in measurements or listening. The Sealed was tighter and sounded more extended in the bass, and better definition too. I did not try ported, only Open Baffle but thats another ball game.

We're just looking at different things. You are correct that aperiodic is traditionally used to lower the impedance peak and/or bass peak in a high Q, sealed speaker. The Tannoys are very low Q, but in an enclosure that is far too large, and this causes a peak at the port tuning frequency. The aperiodic vent lowers the peak, but without lowering the overall port output.
If you put a Tannoy HPD in a very small enclosure it wouldn't produce any bass, and would probably sound like a large Linn Kan. An aperiodic vent on top of this would only make things worse.
 
As regards to this: https://www.hilberink.nl/tannoy2/paulc/paultannoy315hpdproject.pdf

I don't know if the published thiele small parameters are wrong for the HPD 315A or if it's my software, but with a 160ltr enclosure and 100 x 225 port - When modelled, I get a 3db peak in the low frequencies centred around 33hz (or it could be a dip centred around 55hz depending on what the crossover is doing). How that sounds subjectively, I don't know. Obviously It also depends on the room.
I have the rubber surround MG 12s, not HPDs. And I measured the bass resonance at 20Hz, not the published 27.85Hz. I assume the suspension has softened over the years, But I will re-measure with a different sig gen. In the Chatsworth cab it is at 50Hz.
Where I have to sit in my room, close to the back wall, there is a peak at around 30Hz, so I will have to try to balance the speaker's output to ameliorate that.
BTW, what software do you use? I always have trouble with software; I can't figure out LTSpice and can't input speaker data to BoxSim.
 
WRT adding aperiodic vents, changing the front (or rear) panels isn't something I regard as a problem. Making the lower section removable to play around with would suit my limited software skills. Measuring the actual response with REW is do-able for me, and I may even manage to set up the impedance measurement aspect. One of my laptops has separate mic and headphone sockets, so I should be able to make up the wiring for that.
 
WRT adding aperiodic vents, changing the front (or rear) panels isn't something I regard as a problem. Making the lower section removable to play around with would suit my limited software skills. Measuring the actual response with REW is do-able for me, and I may even manage to set up the impedance measurement aspect. One of my laptops has separate mic and headphone sockets, so I should be able to make up the wiring for that.

For Impedance Sweeps & T/S Parameters, I use a basic Dayton DATS (V3 IIRC) which works well.
 
Can't understand how to use winISD, and on this laptop boxSim won't open as it used to on a Windows 7 laptop. I simply don't understand the everyday usage of computers, sadly.
 
Can't understand how to use winISD, and on this laptop boxSim won't open as it used to on a Windows 7 laptop. I simply don't understand the everyday usage of computers, sadly.

Do you have a set of T/S parameters already for the MG12 drivers? I could have a look later on some sims to do a quick run-through if you like?
 
Can't understand how to use winISD, and on this laptop boxSim won't open as it used to on a Windows 7 laptop. I simply don't understand the everyday usage of computers, sadly.
Plenty of sims available that will run on your browser. Easiest is build a 75L sealed box.
 


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