working from Thiele-Small parmeters, what rules (and parameter constaints) might one go by to have an effective aperiodic alignment so result not too large nor too small?
a removable vent panel on cleats might be nice for adjustments
btw - can't even get WindISD to run - Bullock's DOS stuff will run but screenshot seems impossible (?) with WinXP
Freddy
ps - old GE article on Distributed port - sorry for old huge scans
http://img95.imageshack.us/img95/2271/disportre1ii7.jpg
http://img95.imageshack.us/img95/2391/disportre2ja5.jpg
http://img95.imageshack.us/img95/7002/disportre3gw2.jpg
http://img95.imageshack.us/img95/7849/disportre4pz5.jpg
http://img95.imageshack.us/img95/903/disportreplansev5.jpg
a removable vent panel on cleats might be nice for adjustments
btw - can't even get WindISD to run - Bullock's DOS stuff will run but screenshot seems impossible (?) with WinXP
Freddy
ps - old GE article on Distributed port - sorry for old huge scans
http://img95.imageshack.us/img95/2271/disportre1ii7.jpg
http://img95.imageshack.us/img95/2391/disportre2ja5.jpg
http://img95.imageshack.us/img95/7002/disportre3gw2.jpg
http://img95.imageshack.us/img95/7849/disportre4pz5.jpg
http://img95.imageshack.us/img95/903/disportreplansev5.jpg
It may interest you to know that you can view and print out a full copy of British patent GB 696 671 which contains six pages, on a free internet website called 'Espacenet'
The full address for this website is;
http://gb.espacenet.com
When you reach the homepage of the site choose the option for the 'Advanced Search' and click on it, this will take you to the search page. At the top of the search screen under 'Advanced Search,' you will see '1. Database.' Choose the 'Worldwide' search option, (you can select this by using the drop down arrow.)
Enter the patent number that you have exactly like this 'GB696671' (but without the quotation marks) into the box marked 'Publication Number' then scroll down to the bottom of the page, and click on the 'Search' option.
The next screen you will see will show you the 'Result List' click on the title of the patent, and you will see the bibliographical data for the patent. If you then click the place that says 'Original Document, 'provided you have Adobe acrobat 6 .0 on your machine, the full specification will be displayed. You can then print out a copy if you wish, by clicking on the 'Print Option.'
I should warn you that printing from this database is on a page by page basis, laborious but it is free.
The full address for this website is;
http://gb.espacenet.com
When you reach the homepage of the site choose the option for the 'Advanced Search' and click on it, this will take you to the search page. At the top of the search screen under 'Advanced Search,' you will see '1. Database.' Choose the 'Worldwide' search option, (you can select this by using the drop down arrow.)
Enter the patent number that you have exactly like this 'GB696671' (but without the quotation marks) into the box marked 'Publication Number' then scroll down to the bottom of the page, and click on the 'Search' option.
The next screen you will see will show you the 'Result List' click on the title of the patent, and you will see the bibliographical data for the patent. If you then click the place that says 'Original Document, 'provided you have Adobe acrobat 6 .0 on your machine, the full specification will be displayed. You can then print out a copy if you wish, by clicking on the 'Print Option.'
I should warn you that printing from this database is on a page by page basis, laborious but it is free.
Hi gang,
I started work on my second set of APs, or more to the point, modifying existing cabinets. These are 59L ducted port, supposedly tuned to 35Hz housing a standard pair of Wharfedale Super Ten RS-DDs.
In the ducted port:
DC 10R8
203 Hz 11R9
152 Hz 12R1
76 Hz 20R7
48 Hz 18R7
21 Hz 25R6.
It's quite obvious the port is too short, or the cabinet too small.
Stuffing the port with a foam filled sock, with the calf of the sock wrapped around the foot to fill the port produced:
203 Hz 11R9
152 Hz 12R1
107 Hz 13R8
60 Hz 25R1
38 Hz 22R
30 Hz 22R4
20 Hz 18R
A few things here. The stuffed port sounds smoother in the lower bass region. Looking at the figures, you can see that stuffing a port a aperiodic does not make. The port is too small in area. Jigsaw or drill time.
Interesting comparing the 29 Litre cabs with these. The best sound is with both sets running. It's a bit hard doing a-b testing due to the apparent 10db difference in SPL.
Also see:
http://www.diyaudio.com/forums/showthread.php?threadid=57670&goto=newpost
Cheers,
Geoff
I started work on my second set of APs, or more to the point, modifying existing cabinets. These are 59L ducted port, supposedly tuned to 35Hz housing a standard pair of Wharfedale Super Ten RS-DDs.
In the ducted port:
DC 10R8
203 Hz 11R9
152 Hz 12R1
76 Hz 20R7
48 Hz 18R7
21 Hz 25R6.
It's quite obvious the port is too short, or the cabinet too small.
Stuffing the port with a foam filled sock, with the calf of the sock wrapped around the foot to fill the port produced:
203 Hz 11R9
152 Hz 12R1
107 Hz 13R8
60 Hz 25R1
38 Hz 22R
30 Hz 22R4
20 Hz 18R
A few things here. The stuffed port sounds smoother in the lower bass region. Looking at the figures, you can see that stuffing a port a aperiodic does not make. The port is too small in area. Jigsaw or drill time.
Interesting comparing the 29 Litre cabs with these. The best sound is with both sets running. It's a bit hard doing a-b testing due to the apparent 10db difference in SPL.
Also see:
http://www.diyaudio.com/forums/showthread.php?threadid=57670&goto=newpost
Cheers,
Geoff
Geoff H said:
Greets!
Right, damping the vent is for fine tuning the cab, damping the driver is required to make it ~aperiodic and to do that requires the cab be tuned above Fs since adding stuffing lowers Fb, so tuning to ~Fs/Qts with a cab Vb = ~sealed max flat and stuffed with 1-1.5 lbs ft^3 fiberglass acoustic insulation works well, ergo as Vb rises above this point the vent area rapidly increases to where it becomes baffle size and why either using a stuffed to suit open back cab or just a flat baffle with insulation stapled loosely over the back of the driver has historically been the DIYer's default aperiodic alignment.
GM
GM said:
Hmmm.... Seems like that would give a very peaky response around the tuning point, at least in a normal box. Maybe best done with a driver of moderate Q - like 0.6, to keep the tuning low?
What sort of port are you talking about here? A damped one?
Reminds me of a harmonica platyer I used to know. He played thru a guitar amp with the rear of the driver stuffed with foam rubber - between the basket and the cone! Worked for him.
Greets!
Yes you do, its this extra vent damping that gets shifted downwards in frequency to damp the driver's Fs peaking, so it doesn't matter what the Qts is as Fs/Qts will give you the tuning frequency that's required to null it out. For Qts >0.707, the tuning frequency gets low enough that it's best to design a classic TL since the cab's Vb, vent will be so large.
Typically it will just be a baffle thickness reflex vent. All the damping will be internal, which will include the rear of the vent, so it may need a screen or similar retainer depending on the material used and level of cosmetics and/or child, pet protection desired.
Right, all he wanted was an inexpensive harmonics passband PA unit.
GM
Yes you do, its this extra vent damping that gets shifted downwards in frequency to damp the driver's Fs peaking, so it doesn't matter what the Qts is as Fs/Qts will give you the tuning frequency that's required to null it out. For Qts >0.707, the tuning frequency gets low enough that it's best to design a classic TL since the cab's Vb, vent will be so large.
Typically it will just be a baffle thickness reflex vent. All the damping will be internal, which will include the rear of the vent, so it may need a screen or similar retainer depending on the material used and level of cosmetics and/or child, pet protection desired.
Right, all he wanted was an inexpensive harmonics
passband PA unit.GM
Thanks for your input Greg. The classic TL and aperiodic tend to be low in efficiency due to all the damping material. I am trying to avoid that.
The 29L cabs have a piece of fibrefill following the shape of the 2 walls and baffle. The 59L has a 500mm x 600mm covering the sides and rear panel.
If you have a look at the 2nd set of figures for the first cab, I don't think it's worth sacrificing sensitivity for what may be a flatter curve.
I have replaced the whizzer dampers on the drivers in the larger cabs, which has made them gentler on the ear. Pulling the ducts has moved the Bf to 60 Hz, where it peaked with it stuffed.
Cheers,
Geoff.
The 29L cabs have a piece of fibrefill following the shape of the 2 walls and baffle. The 59L has a 500mm x 600mm covering the sides and rear panel.
If you have a look at the 2nd set of figures for the first cab, I don't think it's worth sacrificing sensitivity for what may be a flatter curve.
I have replaced the whizzer dampers on the drivers in the larger cabs, which has made them gentler on the ear. Pulling the ducts has moved the Bf to 60 Hz, where it peaked with it stuffed.
Cheers,
Geoff.
Hi Greg, I am not disputing your response, just stating I am heading into an area between BR and AP. Not just critically damped BR, as the box freq is much higher.
It probably does warrant a new thread, but what do you call it? Hence my original question.
What this concept needs now is applying it to more readily available drivers, hopefully I can do that in the not to distant future.
In the mean time, bench racing (my term, different to yours) these two.
Regards,
Geoff.
It probably does warrant a new thread, but what do you call it? Hence my original question.
What this concept needs now is applying it to more readily available drivers, hopefully I can do that in the not to distant future.
In the mean time, bench racing (my term, different to yours) these two.
Regards,
Geoff.
Just finished measurements/calcs on the 59L cabs with 1x90 mm and 4x45mm ports, giving a bf of 105 hz. The damping material is 30mm 200 GSM polyester covering the ports. The first z is one layer, the 2nd figure is the change with 2 layers.
200 Hz 12r
126 hz 13r
84 hz 16r5
56 hz 17r4
32 hz 27r4 25r6
25 hz 30r 27r
20 hz 23r 22r8
16 hz 18r7 17r5.
Felt may be a better material here. Any one have any clues as to what's happening at 16 - 20 Hz? There's more effect at 16 than 20.
So far it looks pretty safe to choose a port size to resonate the box where the z in free air approaches the rated z.
Regards,
Geoff
200 Hz 12r
126 hz 13r
84 hz 16r5
56 hz 17r4
32 hz 27r4 25r6
25 hz 30r 27r
20 hz 23r 22r8
16 hz 18r7 17r5.
Felt may be a better material here. Any one have any clues as to what's happening at 16 - 20 Hz? There's more effect at 16 than 20.
So far it looks pretty safe to choose a port size to resonate the box where the z in free air approaches the rated z.
Regards,
Geoff
what about lower Qts drivers?
in the 1950's Karlson used saw-blade-width slits in K12 and flanked 1960's x15's port with 3/4" holes which de-Q-ed tone. GA Briggs had dual a dual chamber box with an "acoustic filter" placed before a reflex port.
in the 1950's Karlson used saw-blade-width slits in K12 and flanked 1960's x15's port with 3/4" holes which de-Q-ed tone. GA Briggs had dual a dual chamber box with an "acoustic filter" placed before a reflex port.
An externally hosted image should be here but it was not working when we last tested it.
Greets!
Remember that low Qts drivers were medium Qts once hooked up to a typical tube amp of the day, which usually had adjustable DF that could jack it up to >1 to boot. If driven with SS, then aperiodic would roll them off above 100 Hz, just like a T/S max flat sealed cab. Indeed, that's basically what an aperiodic cab is, a ~T/S max flat sealed alignment except the driver's impedance peak is damped to near flat. For SS amps this is a waste of driver BW IMO, but driven with a SET tube amp you'll get a much flatter/'tighter' response.
GM
Remember that low Qts drivers were medium Qts once hooked up to a typical tube amp of the day, which usually had adjustable DF that could jack it up to >1 to boot. If driven with SS, then aperiodic would roll them off above 100 Hz, just like a T/S max flat sealed cab. Indeed, that's basically what an aperiodic cab is, a ~T/S max flat sealed alignment except the driver's impedance peak is damped to near flat. For SS amps this is a waste of driver BW IMO, but driven with a SET tube amp you'll get a much flatter/'tighter' response.
GM
Yeah, I went over the Goodmans ARU again, and noted the resultant Z curve was like my small cabs before I loaded the ports, so I pulled the stuffing and rechecked. Z peaks at 25 Hz at 23 ohms. The ARU example shows 80 ohms (16 ohm system). The ARU cabs are not stuffed, only lined.
Also, the 16 hole port offers more resistance than a single port of same cross sectional area, so if proportioned correctly, may not need additional resistance.
The bigger cabs are producing glorious bass. Still low in midrange.
Freddy, those cabs look familiar. I had a pair with upward firing 10" Richard Allen dual cones.
There are some comments about slits in the ARU article. Also comments about aperture ports in front of drivers. I think Mr Jordan was being polite. I could never get decent sound from them, hooked up to pp 6bq5s.
Cheers,
Geoff.
Also, the 16 hole port offers more resistance than a single port of same cross sectional area, so if proportioned correctly, may not need additional resistance.
The bigger cabs are producing glorious bass. Still low in midrange.
Freddy, those cabs look familiar. I had a pair with upward firing 10" Richard Allen dual cones.
There are some comments about slits in the ARU article. Also comments about aperture ports in front of drivers. I think Mr Jordan was being polite. I could never get decent sound from them, hooked up to pp 6bq5s.
Cheers,
Geoff.
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