Sub: Volume of Enclosure with Amp

[bigkid]

Hi,

I am about to make my first attempt at building a sub, well its my first attempt at anything made of wood since I made a coat hanger in woodwork at school. I am using the Shiva in the Adire designed 54 litre enclosure. I'll be using a Redgum 180 watt sub amp. Down the track I'll add a Linkwitz Transform to improve bass extension.

I have managed to pick up from the forum that bass extension is a function of enclosure volume (amongst other things). What I haven't been able to work is whether there is anything 'special' about particular volumes. Do Adire use 54 litres because it has some special mathematical relationship with the Shiva or is it just a convenient size likely to get spousal approval and without too much compromise in bass response? I note it has a Qtc of .707.

The reason I ask the question is that I intend to put the amp into the rear of the enclosure. It will take up less than 2 litres of volume. I was wondering how critical my measurements would need to be to extend the enclosure to accommodate the additional volume of the amp. Can I just approximate it or does it need to be exactly the volume of the amp (which is an irregular shape and my calculus ain't what it used to be). I was planning in just adding an extra 15mm to the enclosure length. Are slight variations in overall Qtc noticable?

One other question. If I add a linkwitz transform circuit later on, can it be in a separate box in the path between the preamp and the sub power amp using RCA connections or must it be an integral part of the amp? This is just not stated anywhere that I can find, even on the linkwitz pages. Apologies if this is just a plain dumb question.

Thanks for your help.

[pinkmouse]

Hi Allen

Try downloading one of the free graphical box design packages, it is much easier to see Q changes than to describe them, and it will also give you an idea of why Adire chose the box they did.

Normally, you can get away with about 10% variation in box volume before you have problems with response, so putting your amp in the box should be no problem, ( but make sure it is in a seperate compartment!).

Yes, you can add the LT circuit in later at line (signal) level.

Good luck with your project

[bigkid]

Hi pinkmouse,

Thanks for your help. Can I just ask a couple more to make sure that I have it. When you say "( but make sure it is in a seperate compartment!)", does it need to be completely sealed from the rest of the sub enclosure, say to the extent that there needs to be some sort of sealant around the cable hole?

Can you take the time to explain why a separate compartment is necessary?

Also, when you say "you can add the LT circuit in later at line (signal) level", this means that I can run "Sub out" on my preamp to an RCA input on the circuit, RCA output from the circuit to RCA input on the amp (ie. but not to a speaker level input).

Thanks again.

[pinkmouse]

Originally posted by bigkid
Hi pinkmouse,

Thanks for your help. Can I just ask a couple more to make sure that I have it. When you say "( but make sure it is in a seperate compartment!)", does it need to be completely sealed from the rest of the sub enclosure, say to the extent that there needs to be some sort of sealant around the cable hole?

Can you take the time to explain why a separate compartment is necessary?

Well, thats the way I would do it anyway. The extra compartment basically helps to isolate the vibration sensitive circuitry of the amp from the speaker compartment. It also means you do not have to make sure all your heatsinks, input panels, sockets etc. are sealed. You need to seal that compartment in order so as not to upset the volume of the main box.

Also, when you say "you can add the LT circuit in later at line (signal) level", this means that I can run "Sub out" on my preamp to an RCA input on the circuit, RCA output from the circuit to RCA input on the amp (ie. but not to a speaker level input).

Yup, you got it

[pinkmouse]

Originally posted by bigkid
Hi pinkmouse,

Thanks for your help. Can I just ask a couple more to make sure that I have it. When you say "( but make sure it is in a seperate compartment!)", does it need to be completely sealed from the rest of the sub enclosure, say to the extent that there needs to be some sort of sealant around the cable hole?

Can you take the time to explain why a separate compartment is necessary?

Well, thats the way I would do it anyway. The extra compartment basically helps to isolate the vibration sensitive circuitry of the amp from the speaker compartment. It also means you do not have to make sure all your heatsinks, input panels, sockets etc. are sealed. You need to seal that compartment in order so as not to upset the volume of the main box.

Also, when you say "you can add the LT circuit in later at line (signal) level", this means that I can run "Sub out" on my preamp to an RCA input on the circuit, RCA output from the circuit to RCA input on the amp (ie. but not to a speaker level input).

Yup, you got it

[bigkid]

Thanks pinkmouse. Appreciate you taking the time to respond.

[pinkmouse]

No probs, just post some pics when you're done, ok?

[bigkid]

Will do.

[Kanga]

Hi Allan

Sounds like you are on the right track.

Where are you getting the Redgum amp from and at what price?

Mick

[bigkid]

Hi Mick,

I got it from John Woodhead at Accoustic Concepts in Victoria. He does the base model RGSW-1 for A$395 and $17 freight. He emailed me a detailed price list for the amps and Adire speakers. If you email me I will send a copy to you.

Audio Concepts are here: www.acousticconcepts.com.au