Port placement for a twin subwoofer box?

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Mobile audio drivers are normally horn drivers spec wise, so inverse tapered TQWT stuffed to 'taste' is the best overall vented alignment for wide range apps and TH or TTL for 'sub' woofer apps and above a ~0.71 Qts', using a Fs/Qts' to find its tuning [Fp] is generally the better performing overall.

Qts' = Qts + any added series resistance [Rs]: mh-audio.nl - Home

GM

edit: FWIW, here's a HT app 20-80 Hz TH woofer I just did for a neighbor that meets THX reference [simmed] with a cheap [~$40 local one day sale], high Qts JBL, not too shabby performance wise and further lowered overall cost since he has enough scrap from another neighbor's rehab to build it:
 

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I've decided to finalise the ported box and have built a sealed box to do the comparison with.

Before I glue it all up the final question is how long to make the port length.

With the drivers and volume used a WinISD predicted a tuning frequency of 33Hz at a port length of 41.3cm.

The actual tuning frequency is around 31.5hz.

I want to aim for a 30hz tuning frequency.

If the port is going to be consistently 1.5hz lower in tune than the software predicts then can I model for 31.hz and be reasonably confident that the calculated port length will result in a 30hz tune?
 
You should try GM's TH! Your sealed and ported boxes can't compete against it in SQ or SPL.
 

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If the port is going to be consistently 1.5hz lower in tune than the software predicts then can I model for 31.hz and be reasonably confident that the calculated port length will result in a 30hz tune?

Frequency scale is 1/f = exponential, so guessing it's exponential, but I imagine you could use WinISD, etc., to figure out a usable scale by simming Fb with a number of 10 Hz different tunings to find the progression rate.

GM
 
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Frequency scale is 1/f = exponential, so guessing it's exponential, but I imagine you could use WinISD, etc., to figure out a usable scale by simming Fb with a number of 10 Hz different tunings to find the progression rate.

GM

I understand, will do.

The reason I’m keen to sort the port out is that my sealed boxes sound much better to my ear when heavily braced.
 
Big bass requires big enclosures!

Well, I’m not sure it does necessarily.

My first impressions of a ported box are that the attack of the notes are softened and the decay is lengthened.

I’m not sure I like it for classical, acoustic or rock music but it suits electronic dance music very well.

I think this is because I have seen classical concerts live and so want absolute fidelity if the orchestra and auditorium when listening to this. I prefer Telarc recordings, for example, even using a digital telarc recording of danse macabre and night on bare mountain as one of references.

Rock and acoustic music are similarly referenced back to gigs where the musician’s amps and cabs are very close to the audience kind of sound

Dance music is referenced to the PA sound of night clubs and so I can see how that sort of music would sound “right” with the ported box’s signature.

On balance however I am thinking that unless a tapped horn is as tight and fast as a highish Q sealed box then I may just end up getting a couple of 15s in a sealed box and playing with massive power amps and DSP eq
 
With the drivers and volume used a WinISD predicted a tuning frequency of 33Hz at a port length of 41.3cm.

The actual tuning frequency is around 31.5hz.

That can happen when using those programs. Try simming the box volume and vent dimensions in Hornresp to see if Hornresp provides a more accurate result.

Also, bear in mind that Fb can be lowered if the if the entrance to the vent inside of the box is close to one of the internal walls.
 
Well, I’m not sure it does necessarily.

On balance however I am thinking that unless a tapped horn is as tight and fast as a highish Q sealed box then I may just end up getting a couple of 15s in a sealed box and playing with massive power amps and DSP eq

Big (LOUD and low) bass requires a big box.

Multiple speakers and DSP is cheating. A sealed box with 2 speakers is not going to produce the same SQ and SPL as a single speaker in a TH. If a speaker moves, it distorts. Per a given watt input, a speaker in TH moves less than a speaker in a sealed enclosure WITHIN the TH's passband. Because that speaker moves less, more wattage can be applied to the TH.

You need to model your two 15's in a 30hz sealed enclosure and then model 1 of those 15's in a 30hz TH. Compare the voltages at 2.83 in HR.
 
Whilst I fail to see the problem with cheating if the result is good, I am intrigued by your comment about excursion and distortion.

I understand that subwoofers have a given extent of linear excursion and that pushing the sub beyond this causes distortion.

Is there are further sub-limit on linearity and how would I go about researching this?
 
By the way, I have a single 15" negative flare 23hz tapped horn in my mancave that has cracked walls in the mancave and the master bedroom doorway wall with less than 200 watts from an old analog Yamaha AVR. Negative flare is the least efficient and smallest of the 3 types of TH's.
 
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