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In general, larger port diameter will cause less port noise and power compression issues.
 

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Elite Shackster
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There is a tab in WinISD to look at port air speed.

Slowing the air speed is good, but you also need to monitor port resonance, so if changing to 6 inch ports slows the air giving a positive affect, but port resonance drops within the subs usable/audible range, it might actually be worse to use a 6 inch port. You need to look at all the variables to ensure the ports are working at their optimum in your sub design.
 

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Discussion Starter · #7 ·
What I am coming up with is really what you recommended initally :)

Either a 9cu ft box or and 8cu ft box.

I am modeling with a high pass of 18Hz and a low pass of 110Hz.

You came up with this and said it was within Xmax, but I dont know how to check it. Here is what I am seeing. Is it right?

I am figuring it with 750 watts (amp will do 850 watts) DCX2496 for filters and eq.

Am I within port speed rules and good resonance?

Am I missing anything?

Thanks!!!!!
 

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Elite Shackster
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You came up with this and said it was within Xmax, but I dont know how to check it.


Thanks!!!!!
As long as the driver your modelling has had the xmax input, then the red line on the cone excursion graph is the xmax. If xmax had not been input the red line would not be showing. No part of your graph is showing excursion beyond xmax so your good. Thats basically all there is to checking the xmax :T.

If you remove your HPF, you should be able to see the excursion exceed xmax below the port tune (frequencies along the bottom of the graph). You can then see from that where you need to target your HPF.
 

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Discussion Starter · #10 ·
Ok I actually think I am starting to get this with all of your help.

Thank you ever so much!!!

How does this look?
Again, am I missing anything?

If I am not mistaken this is modeling very good for car subs, is it not?

The ever grateful
Bop
 

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Discussion Starter · #14 ·
So considering what we know now.
Built with 1in MDF then covered in 1/2 in Cocobolo wood, braced heavily.

Eq'ed with the DCX2496 and placed in the room properly.

How do you think it will sound in your best guess? Not holding anyone to anything.

Thanks

Bop
 

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You don't need your highpass filter to keep your WinISD excursion tab completely under the xmax of the driver - that's wasting a lot of potential. This method is flawed for many reasons:

xmax is not the mechanical limits of the driver, it's only the point at which Bl linearity drops by 30%

peak excursion use is only appropriate if you plan on listening to sine waves or extended signals - most bass in music and movies are short, multifrequency pulses or bursts. Try changing the unit to rms for a different perspective.

the suspension of the driver will stiffen as you approach its mechanical limits, so you won't actually achieve the amount of excursion WinISD predcist for a given amount of power - you will achieve less



I'm not sure where this extreme caution to the point of degredation is coming from on this forum, but I'm seeing more and more of it. If you're paying full price for a driver, you may as well get full performance from it. I suggest you use more powerful amp (if possible) and drop the center frequency of the highpass.
 

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True, Xmax is not the mechanical limit of a sub, but it is the point where distortion increases when exceeded. Modeling in peak as opposed to RMS has shown its accuracy in many of the builds in the Database. Push a sub past the predicted modeling has resulted in reports of "the sub is making noise", "I hear the sub clanking", etc. I agree you want to get the most performance from a sub, but I don't consider it "extreme" caution when the goal is to a recommendation to a new member to get the best sound from a sub and years of trouble free performance. Since the Staff here are in a position of people taking what we say to heart, we tend to err on the side of caution to achieve those goals. Obviously we each have our own opinion, to each his own.
 

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Discussion Starter · #18 ·
Now look what you have created!! lol

This is a comparison of adding a third driver to the mix.
The volume of the box goes up to 13cu ft. to get it to tune as flat as I can.
The wattage also goes up kinda high (1100 watts, wow).

The big question???
Is the performance gain going to be enough to be worth the added cost of a third driver and higher wattage amp?
As well as a kinda huge box.

What say ye gentlemen?

Bop
 

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The wattage also goes up kinda high
Not quite, 2 DVC 4 ohm subs can be wired for 4 ohm load which your modeling is based on. The options for 3 subs is either 2.6 ohms or 6 ohms, the power input required will change when either of those options are used and the amp has to have the required capabilities.
 

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Discussion Starter · #20 ·
I see what you mean. If I run them @ 2.66 ohm's then getting the power is within the amp I am considering's power range.
I was going with Crown or QSC but the more I read most of the guys are using Behringer amps for their subs. More bang for the buck I guess.
So the Behringer amp I am looking at now is The EPX3000 rated at:
2 x 1500 watts into 2 ohms; 2 x 900 watts into 4 ohms; 3000 watts into 4 ohms (bridge mode) RMS
The Crown or QSC in the same price range won't run 2 ohm's. Or put out as much power.

Is there a mesurable difference in sound quality between running 2.66 or 4 ohm's?

I am assuming I have driver power handling right to:
Question: How can a 600watt RMS driver handle 1100watts?
Answer: The increased dampening effect of the large cabinet and proper port tuning allows the driver to handle and use added power.

Again I ask is the increase in performance worth going to the 3rd driver? 117dB to 120dB?
Keep in mind I am building a pair of either. As well, how often will the wifey let me crank it up that high :)

Bop
 
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