Help with ar.com kit from madisound

[Bobhof]

Hi everyone, I'm new here and very new to DIY audio. Hoping for some sound advice from the pros.

I have decided to attempt to build a madisound ar.com speaker pair with a sub with built in amp. It will be used with my computer for video editing as well as music and DVDs. At first I thought it would be as simple as building a box and sticking some drivers into it; but then I did some research and now I am having nightmares about standing waves and frequencey dips. So, before I start cutting, I would like to get some advice.

I have ordered the following parts:

ar.com kit: Peerless 850122 woofer, Peerless 812687 tweeter, pre-built crossovers, ports etc. (see http://www.madisound.com/ar_com.html)
Hi-Vi D8.8 9" woofer (http://www.madisound.com/cgi-bin/index.cgi?cart_id=1539839.2138&pid=1834)
Keiga KG-3100 2.1 Amplifier (http://www.madisound.com/cgi-bin/index.cgi?cart_id=9194221.18084&pid=1621)

Because the speakers will only be about 5" from the wall, I was advised to front port them. I also increased the volume of the design from madisound slightly. My design is as follows:

An externally hosted image should be here but it was not working when we last tested it.

Are the dimensions okay?
Is the port a good depth/width/height?
I do have a circular 6" port. Would that be better? If so, how should I place it?

I have designed the sub as follows:

An externally hosted image should be here but it was not working when we last tested it.

It's a sealed design (mostly because it's easier to build) and the amp is in a separate compartment at the back.

Does sealed mean totally airtight? Should I make sure there are no gaps where the wires enter etc?
Are these dimensions okay?
Would it be better to leave out the division and have the amp sticking into the main compartment?

Any other advice or comments will be appreciated. Sorry for all the questions, I have tried to research this but I quickly find myself out of my depth.

Thanks for any advice,
Rob

 

[Bobhof]

Material

Forgot to mention: I intend to build the enclosures out of 20mm pine. I could also use MDF with a thin layer of pine on the outside for appearance. Would MDF be better than pine or is it much of a muchness?

Thanks,
Rob

 

[Bobhof]

Vas, Qts, Fb, QB3 etc.

Sooo.. now I've found an online speaker dimension calculator thing (using a mac so can't run the software on my machine): http://www.linearteam.dk/default.aspx?pageid=newdriver

So I plug in the parameters for the above designs (speaker option 2, with the circular port):

SPEAKERS
Vas: 27.7
Qts: 0.38
Fs: 30

Vb: 13.5 liters
Fb: 25

SUB
Vas: 46.8
Qts: 0.38
Fs: 30

Vb: 17 liters

I plotted these two graphs on top of each other (results attached, sub in purple). What bothers me here is that the speakers seem to have an almost identical bass response to the sub. If that is the case, why do I need a sub at all?

 

[infinia]

Hi

what is the Mad kits desired box and tuning?


This is with WinISD box model program (see attached)
peerless 850122 8 liter with Fb=39
Swan D8.8 30 liter Fb= 36

 

[Bobhof]

what is the Mad kits desired box and tuning?

When I enter the speaker parameters and click the "optimum" button, the program calculates these values for the 850122:
Vb: 36.88
Fb: 33.67

And for the 8.8 (sealed):
Vb: 19.1

I assume that is what you mean by "desired". Unfortunately, 36 L is too big for me.

Thanks for the graph, could you redo one with the following parameters for the speakers (not sure if this tuning is ideal, feel free to change it if it is not good):

Vb: 13.5 liters
Fb: 25

 

[infinia]

Hi
No, I meant what Madisound suggested for their Kit. They did provide plans and drawings for them? ie box and vent sizes
How about Crossover schematics?
Good to get a baseline before you start changing things, yes?

 

[Bobhof]

Ah yes. They provide this box design: http://www.madisound.com/pdf/arcomcabinet.pdf. I wanted to make a slightly larger enclosure and front port because they will sit quite near a wall.

For the crossover they provide this schematic: http://www.madisound.com/efe_diy.html

 

[infinia]

Q1 Is this a nearfield monitor?
Q2 Is that a switch pad network on tweeter? If not what resistor is used in the design?
Q3 Most importantly. Where is the crossover for the Sub woofer?

 

[Bobhof]

Thanks for taking an interest Infinia.

Q1 Is this a nearfield monitor?
Yes and no. The speakers will be on a shelf on top of my desk to the sides of my monitors so mostly they will be used when I am close to them. However, my desk will be in my lounge so I will also use them for general listening and watching DVDs.

Q2 Is that a switch pad network on tweeter? If not what resistor is used in the design?
This explains the resistor:

EFE Technology has informed us a removable resistor (10watt) can be added at the tweeters positive terminal. This resistor allows the builder to tone the speakers according to personal taste or system. A male and female quick-disconnect (.110 red) can be crimped at each end of the resistor for quick removal and changing as necessary. The range recommended for this removable resistor is anywhere from 0.5 to 6.0 ohms. EFE recommends 2 ohms as the standard value for this add-on resistor.

Q3 Most importantly. Where is the crossover for the Sub woofer?
The sub crossover is built into the plate amp which will be attached to the sub: Keiga KG-3100 2.1 Amplifier http://www.madisound.com/cgi-bin/index.cgi?cart_id=9194221.18084&pid=1621

 

[infinia]

Q1 Is this a nearfield monitor?
Q2 Is that a switch pad network on tweeter? If not what resistor is used in the design?
Q3 Most importantly. Where is the crossover for the Sub woofer?

OK I played around with this design abit. Looks bad untill if figured it out. see attached plots

green=peerless baseline 8.0 liter Fb=53
blue=swan 8.8 30 liter Fb=36
yellow= swan 8.8 20 liter closed box Q=0.7

This is not a nearfield design. So what that means is they use the 3 dB midbass peaking and crossover's early midbass rolloff and padded tweeter for a baffle width compesation scheme. Answered my own Q's
A1) No
A2) end user adjust for taste.
A3) Forgot use a plate Amp built in cross over


My advice build it with no changes. Keep port design as is.
Sub woofer use ported design with walled off plate amp. Then add cooling vents for amp in its own chamber. Use MDF for SUB and a nice hardwood instead of pine.

Build it and enjoy it with your ipod. Come back a visit with pictures.
Cheers,

 

[Bobhof]

Thanks for taking the time to figure this out Infinia.

The speakers will only be about 15cm from the wall. I was advised to front port for this reason. If I build it as recommended will the rear porting not be a problem?

Looking at your diagram it does seem that a ported 30 L sub is much better than my sealed 17 L design. Can you advise me on port size and placement?

For the amp, I assume cooling vents are just holes at top and bottom to allow air flow.

I will try to find some decent hardwood or I will use MDF for all the boxes. Things should be done properly I suppose

Thanks,
Rob

 

[infinia]

Thanks for taking the time to figure this out Infinia.

The speakers will only be about 15cm from the wall. I was advised to front port for this reason. If I build it as recommended will the rear porting not be a problem?

Looking at your diagram it does seem that a ported 30 L sub is much better than my sealed 17 L design. Can you advise me on port size and placement?

For the amp, I assume cooling vents are just holes at top and bottom to allow air flow.

I will try to find some decent hardwood or I will use MDF for all the boxes. Things should be done properly I suppose

Thanks,
Rob

Hi
6'' of space between rear port and wall should be OK. Use smaller resistor on tweeter as bass frequencies build up as speaker gets closer to walls.
For Amp cooling more is better. Slots top and bottom are best use wire screen to keep critters out. If you choose holes the dia should be greater than panel width.
Use Madisounds recommended ported enclosure for the Swan 8.8. thats what I simulated in the plots.
These speakers should sound great on stands later on. So why not spend a little more and make em proud and loud.

 

[Bobhof]

Thanks! I think I will do as you advise but maybe make the speakers slightly larger using the same design. BTW, I found a neat excel worksheet that works on macs: it even draws the graphs. Not as neat as the program you used but useful nonetheless. I found it here: http://www.diysubwoofers.org/prt/ported1.htm

 

[infinia]

Little bigger box probably is good. Don't change the width too much thats figured somewhere in the crossover design. Wide sloted ports are harder to get right, as they are close to boundaries where pressure is highest. Stick with tubes away from box sides. Also when playing with tuning keep an eye on group delay as you change things. Lower GD is better for clean bass.
Have fun

 

[Bobhof]

Updated Design

Hi All,

I have updated my design as per above suggestions from infinia. I have not walled off the amp but may do so depending on how deep it is: I am worried about where I can put the vent if the amp is walled off. Here is my updated speaker design:

 

[Bobhof]

And here is my new sub design (please take a look and comment):