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Multi-Way Conventional loudspeakers with crossovers

Front Ported Tarkus?
Front Ported Tarkus?
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Old 15th September 2020, 12:37 AM   #1
BlindMelon7 is offline BlindMelon7  United Kingdom
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Default Front Ported Tarkus?

Hey all,

I'm looking into building a pair of Tarkus as I'm going to be off work for a while longer (I work in live sound).

I have a question regarding the port location. Most of the speakers I've owned are front ported. I'm wondering if it might be advantageous to move the port to either the front or possibly the bottom of the speaker? (I was planning to raise them up a little anyway)

Would love some insight on this is.

Thanks,
BlindMelon7

Edit: might it even be possible to make them Aperiodic? Pretty much all of my current speakers are either transmission line or sealed so I'm a little worried about "boominess"

Last edited by BlindMelon7; 15th September 2020 at 12:40 AM.
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Old 15th September 2020, 03:34 AM   #2
jReave is online now jReave  Canada
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No problem at all to front port it. Look at Paul's page for that speaker and you will see more than a couple of versions with front ports.

No problem either for a bottom port. B&W is (was?) fond of doing it that way. Rule of thumb I think is to give an amount of clearance equal to the port diameter. I'm sure someone will correct me if I'm wrong.

A whole lot of people have been very happy with Paul's design but if you are worried about boominess you could go sealed depending on your room size (small would be better) and tastes. Sealed F3 is about 48Hz in 60L which if I remember correctly is about right for the Tarkus. I'm not sure aperiodic would offer any advantages here.

Another approach would be to start with the port about 3" longer than suggested. Listen and then shorten by about an inch repeatedly until you like what you hear. I will say though that when I model what the Tarkus is doing with that Peerless woofer, the knee of the rolloff is already more gentle than normal which is what you want to do to avoid boominess when F3 is quite low.
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Old 15th September 2020, 03:43 AM   #3
AllenB is offline AllenB  Australia
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Front Ported Tarkus?
Quote:
Originally Posted by jReave View Post
Rule of thumb I think is to give an amount of clearance equal to the port diameter.
Sounds sensible. If you consider the I/O in a cylinder head, the valves don't open far, it's the diameter that makes it significant.
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Old 15th September 2020, 10:14 AM   #4
fatmarley is offline fatmarley  England
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That woofer works well in a sealed enclosure, so I can't imagine there would be any problem experimenting with aperiodic.
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Old 16th September 2020, 12:28 AM   #5
BlindMelon7 is offline BlindMelon7  United Kingdom
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Thanks for the replies! I guess the beauty of DIY is I can always change it if I don't like it. I think I'll start with a longer port placed at the bottom and experiment from there as jReave suggested.
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Old 16th September 2020, 12:49 AM   #6
BlindMelon7 is offline BlindMelon7  United Kingdom
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While I've got you, do you guys mind casting an expert eye over my crossover components? My main concerns are:

Is the 0.71mm cable suitable for the inductors.
Is it a bad idea to run two parallel pairs of 2ohm resistors to make up a 4ohm resistor? I'm not entirely sure what the downsides are to it, but I'm struggling to find 4ohm resistors.

My final question (for now) is regarding the cabinet damping. Paul Carmody suggests egg crate foam in the bass cabs and polyfill in the tops. Is there an alternative to egg crate foam for the bass? It's surprisingly expensive, and in the acoustic treatment world it's generally considered ineffective (although it might be different in this scenario).

Apologies for all the questions - this is my first build so I'm probably overthinking things.

Edit: shopping list attached
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Old 16th September 2020, 01:30 AM   #7
DeLander is offline DeLander
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Your shopping list is missing the Peerless midranges.
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Old 16th September 2020, 01:42 AM   #8
AllenB is offline AllenB  Australia
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Front Ported Tarkus?
The resistance of the larger inductor being over 2 ohms is likely to have a small but noticeable effect on the response. In addition this resistance will probably make the inductor warm when used for bass duty, possibly too warm.
Quote:
Is it a bad idea to run two parallel pairs of 2ohm resistors to make up a 4ohm resistor?
That's OK, 2 in series will make 4 ohms. You should be able to find 3.9
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Old 16th September 2020, 02:27 AM   #9
BlindMelon7 is offline BlindMelon7  United Kingdom
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Quote:
Originally Posted by DeLander View Post
Your shopping list is missing the Peerless midranges.
Well spotted, Falcon don't sell them so I'm getting those elsewhere. I don't think it would sound very good without those.
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Old 16th September 2020, 02:33 AM   #10
BlindMelon7 is offline BlindMelon7  United Kingdom
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Quote:
Originally Posted by AllenB View Post
The resistance of the larger inductor being over 2 ohms is likely to have a small but noticeable effect on the response. In addition this resistance will probably make the inductor warm when used for bass duty, possibly too warm.
I suspected as much. It might have to be a ferrite core as the lower resistance air core version is way out of my price range. Is the extra distortion likely to be noticeable?
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