Port resonance in a two way floorstander?

Guys I putting together a floorstander to use some car audio drivers I have, more as a test of the drivers against some more conventional home audio drivers than anything else.

The speakers in question are JL Audio C7 components, made in Germany by Kurt Muller and so aren't the usual crap one finds for making noise in cars but in theory good, hi fi drive units.

The common saying is that car audio components are overpriced, when good, compared to the usual home audio DIY brands and I would like to test this.

The advantage of using these is that they already come with an very good quality crossover all made up by the manufacturer, which simplifies things for a beginner I think.


Whilst I have modelled and built a few subwoofers and am comfortable with WinISD and Bassbox Pro, this will be my second attempt at speaker building with the first being a pair of bookshelf speakers using some other car audio drivers.

When porting a subwoofer I have always tried to keep the resonance frequency above the low pass filter crossover point, this seems impossible with a full range design and so how worried and what can I do about port resonances?


Should I try and push them down as low as possible, with a big port, or as high as possible, with as small a port as air velocity allows, or something else?
 
Thanks ‘Marley, I’ve read on baffle step compensation and I see where you’re coming from.

The crossover has some compensation built in terms of jumpers to change the tweeters level and midrange “presence”, I am hoping these might help?

I have no objection to building a crossover, i think I would go active with a DSP first to compare to the existing crossover.
 
If the port(s) are not too long, there is no problem with pipe resonances. A good modelling software can show the resonances. Low tuning in small boxes need long port, this is not much problem with low-passed subs as you described, but with fullrange box you need to choose wisely from the options.

Btw, car (mid)woofers are not planned to be used in boxes, those are for free-air application. The mentioned JL Audio stuff is not exception, the Qts of that driver is over 0.6, typical free air value. For vented box Qts 0.3-0.4, for closed box Qts 0.4-0.5 is the rough optimum. Of course this is just rule of thumb, it can be done more way, especially with active DSP.
 
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I can only tell you what I know...

Car speakers are usually 4 ohms or less to match the 12V power supply, and are usually designed for parcel-shelf mounting.

C7-650cw - Car Audio - Speakers - C7 - JL Audio

This means they have a highish Qts around 0.7. This is not reflex material which needs a Qts below 0.38. More infinite baffle.

Generally car speakers should be used in a car. Not in a home HiFi.
 
Thanks guys, I’m using these drivers as I have them on hand; they don’t fit my current vehicle.


On that basis I’m open to suggestions on what to do with them, seems a shame to leave them in a box. :)

Given their high Qts and being suited to being in a sealed enclosure better, should I model the box volume to result in a particular Q value?

I would have thought 0.707 would be the number to aim for?

Is there a reasonable way to use them free air in the domestic setting?
 
Qtc 0.707 is probably very impractical, you need a very large box to get that value with that woofer.
My advice is, use a box that is not too obtrusive visually Qtc 0.9, 1, 1.2 it does not matter too much.

Free air is a good option if you can flush-mount the drivers to the room's wall. Even the original crossover is designed for similar application as mentioned earlier.
 
That's the one, I'm not too worried about the low bass as I can easily add subwoofers. The sealed 38lt box seems interesting, I could make the subs tall and deep with the woofers on the sides and put the smaller 38 lt box on top.


If you're using a subwoofer you could go down to 15ltr sealed (Qtc - 0.86) with the advantage of a potentially higher SPL.

Looking at the dimensions, the mounting depth is only 70mm deep so you could build quite a shallow box.
 
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