sub to set up?


Active Member
After weeks of waiting for the parts for my sub they finally arrived and i finished it today.
Put nemo on where the girl taps the glass,"Bllody hell" my son complained his bedroom on the opposite side of the house was's a 7cu^ft box with a 15"dvc speaker and 250w amp.
It's loud so no problem there,but how do i set it up correctly?
How do i use the phase knob?.I bought 3.5in angled ports which extend but now they are installed how am i supposed to adjust them? and what am i suppose to be listening for if i could adjust them.
I have never heard a good quality sub so i have no reference to judge whether mine sounds right or if it's "tight".
there is a picture attached (i would put a couple more on but don't know how)i get a lot of bass where the doors are but because of the size of the sub don't have many options to move.


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Well done Panny, that is one fantasic looking sub! With regard to setting up the ports you normally just put a couple of screws into the plate amp to hold it in position, take a reading and then remove the amp to get access to the ports to make an adjustment. To setup you need to either use a computer with a tone generator program or a CD with some test tones on it. You then measure the response with an SPL meter.

The phase control is to set the sub 'in phase' with your main speakers so that you are not 'cancelling out' the bass from your mains. This shouldn't be too much of a problem because you should set the sub to roll off at the frequency you main start to roll off, look up the F3 point for your speakers on the manufacturers website, you want your sub to be rolling off just below their F3.

The position of your sub looks to be about half-way along a side wall which should give an 'even' response, if you put it in a corner you will get more response which may be overpowering, the ideal position for a 'tight', 'even' response would be between your mains.
Looks like Gary has covered the phase and level which just leaves the port question:

Originally posted by panny300
I bought 3.5in angled ports which extend but now they are installed how am i supposed to adjust them? and what am i suppose to be listening for if i could adjust them.

Well the longer the reflex port the lower the tuning of the enclosure is. Think of the big pipe organs in the churches for an example, the longest tubes in the set are the lowest notes.

So in otherwords: longer tubes = lower bass

But this would only be in a perfect world and we of course, don't. The longer tubes and lower bass are at the expence of SPL or loudness and you also can only make a realistic length of tube given the size of a living room friendly enclosure, it would be nice if you could slap a great 1m long drainpipe in your sub but it would of course be stupidly big.

Another interesting point is the fact that you have use 2 ports rather than one and whilst this is great for minimising port noise, it does mean that you have to make both ports roughly twice as long as an enclosure with a single port to obtain the same tuning frequency.

Get along to and download WinISD,

1. Then find your subwoofer driver in the list
2. Choose a ported type as the enclosure
3. Enter the capacity of the cabinet in litres
4. Finally enter the parameters of the ports ie. diameter, number of etc.

After this you can change tuning frequency of the box and note how long the ports have to be to obtain this.


Active Member
Thanks for the info ,but can you be a bit more specific?
what is the procedure for measuring the response?
how do i make the sub roll off at the same freq as the main speakers?if the main speakers go down to 40hz how do i roll the sub off at this and also 20.4hz which is the speaker fs


I posted a length reply and lost it so here's the 'abridged' version.

Your main speakers go down to 40hz so you want to set the crossover on your sub to match so that when a 40hz tone is played the output from both your sub and main speakers combines to a flat response.

Take a look at the graph here where the sub integrates with the main speakers to produce a flat response.


Active Member
You can easily work out if your sub is in phase or out of phase your speakers by placing the sub face and the main speaker face "face-to-face" (if you see what I mean). Then play some music which is very bassey and adjust the phase button so that you get the highest amount of bass.

The theory is that frequencies that are the same but out-of-phase cancel each other out and same frequencies in-phase are amplified.

Let me know what peoples experences are with this as if you think about it there perhaps shouldnt be an overlap between your subs frequency range and your main speaker range so *maybe* you want them to cancel out giving a linear frequency respence.

I guess its one of those things (like cable) etc where the correct and best way is the way which sounds best *FOR YOU*.


Active Member
thanks.when setting the sub up how high do i turn the volume on the sub amp?
I have just made a disk with freq from 15hz to 40hz in single steps then 40hz to 100hz in 5hz steps,do i play this and take spl readings noting the results at each step?,and what setting should my meter be on?
I have set all the speakers using the test tones alright,but when i used the above disk on the sub the meter went off the scale so i had to turn the volume on the sub down why was the volume ok on the ve test disk test tones but not the disk i made?.


Don't worry about the absolute levels or the meter setting it's not important at this stage, all you're interested in doing is plotting the frequency response of the sub so pick a level that's comfortable for your ears, not too loud and not so quiet that the reading are affected by external noise. Try and get a setting which has the meter reading in the middle of it's range so that you have plenty of scale left should you have a peak or a null. The main point is not to adjust the volume after you've started. Take a meter reading on each sweep and then at then at the end plot a graph to see what the response of your sub was.


Active Member
Hi gary,i started to do the test but the readings are all over the place.
Do i disconnect all other speakers?
Set the denon volume to 00 same as setting speaker levels?
I set the meter on 80db?
Which freqs do i use to set the level on the sub amp 16hz or 100hz?
I tried at various freqs and adjusted volume on the sub until the needle was around 0 but as i went through the test the needle would go off the range,so i tried lowering the volume on the sub at the freq that went off the scale and started again but the lower freqs were way too quiet. whats wrong?


Initially you want to plot the frequency response of just the sub so that you can see how it's reacting with the room and also see how it's responding with the port tuning you've set.

Given that your reading go off the scale at both ends you will need to do a couple of quick sweeps to find the 'mean' level at which the needle is in the middle of the meter for the most part of the test.

If you still get wildly swinging readings with just the sub playing then you might want to try changing it's location to see if you can 'smooth' out the response, after that we're into all the fun and games of a BFD equaliser and/or room treatment to 'even' out the response.

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