Port length question

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#21
It should be pointed out that the Drone Cone, (Passive Radiator) system was invented for this-when the port becomes unwieldy due to size.

Essentially the Passive Radiator act the same as a port. It is not like a sealed system at all.

There is a price to be paid. The Passive Radiators cost something, although members here have made them themselves. The rolloff becomes slightly sharper, therefore the transient response not as good. Thomas W himself comments on the AS-15 project web page that he liked the bass better with the port than in a similar project using the Drone Cones.

However, Thomas was using an enclosure that was almost twice your volume. Therefore, he could use a port that was considerably smaller than one a 4 cu ft box would require.

When the size of the port gets out of hand, the Drone Cone, even with it's limitations, is there to make the thing work for you.
 
#23
Thanks Kelticwizard,

I too don't want to spend money on something that people think is substandard to a cheaper option. But I understand it is an option. Being mischievous, I'm happy trying to do what hasn't been done yet, if applicable.

Michael
 
#25
pinkmouse said:
If you want a small box to go that low, I think you might be better looking at a sealed box with a Linkwitz transform circuit, it would be much easier in construction, and in my experience, small boxes with big ports are never very satisfactory.
Click to expand...

Or build a high Q sealed box and make it aperiodic. Not having the T/S for the driver you are talking about i can't make any suggestions.

I do know that John Stryke uses Dual (at least) PRs with the sub he does with the HE15 (i'd have to go look, but i think we are talking about a 22" cube).

You can mount the port externally like Joesph Audio does.

Or you make the port even bigger and longer, damp it and end up with a Daline-like TL.

And DO NOT disregard room gain. Far too many subs get designed for flat anecohic response and get real boomy and lumpy when placed in the room. For this very reason i like a sub to roll off slowly and early (F10 is more important than F3 in this situation).

dave
 
#28
Hi Thomas,

The ported design looks to be much the same design as your AS-15, using the comparable driver. Did you tune it the same? Port Length?

What were your impressions of the ported sonotube, compared to your AS-15?

Did you ever do anything with that port software from Polk? It looked interesting enough, wondered if you thought it could be a valid way to shorten these ports, allowing smaller (ported) enclosures to be utilized.

Michael
 
#29
Re: Hmmm, Room Gain

masterp2 said:
Can you speculate where room gain will be +3db? 40HZ? 30HZ?

What would dB gain be around 16HZ?
Click to expand...

The +3dB point will depend on the size & how "sealed" it is, but typically the effect starts between 100 & 250 Hz. And from there you can get anywhere from a couple to many dB/octave of gain.

So if you had a big room that started at 100 Hz and you got only 3 dB/octave, you would be up about 11 dB at 16 Hz.

If you do a net search on Tom Nousaine you might get some papers on the subject

dave
 
#32
masterp2 said:
So can someone suggest what port length would be too long, using a 120l or 140l box tuned to around 20HZ? Would 40" be annoying, barely perceptible etc?

Michael
Click to expand...
Based on my limited, but seat-of-the-pants experience, if you have a box that big 😎 a 120mm diameter port for 20Hz would need to be about 110 to 120m long approx.
 
#33
Krykie,

I'll have to measure it on the rugby field, mate. Just for ***** and grins, tell me more. I'd love to hear your rationale. Sorry, I'm being a louse. Just tell me you made a math error and the seat of your pants got a little wet.:scratch:

I'm just kidding really.

Cheers
 
#34
this doesnt really apply, since you are talking about HT, but i have a 1503 in a 3.8cuft box tuned to 25hz in my car. i did not use a round port bc it has to be too long with multiple ports in order to reduce the vent mach, so i made a slot port, which is cheaper and also easier to calc volume after displacement.. my slot port is 15.5"x2"x30"long. my 1503 is getting 600watts continous from a jbl amp and the highest vent mach ism 23m/s @ 22hz, which is a bit high for HT, but you can solve this by making a larger port area... just an idea.. ive always preferred slot ports..

-chris
 
#35
Thanks Chris,

That is the way I am leaning, smaller is better if I can deal with the compromises. 3.8 ported, hmmmm. Can you detail the box and port specs for me? What was your inspiration? What would you do different? Can you tell me, have you played with the 1503 sealed? Comparisons? Just wondering.

Michael
 
#36
well since it is in a car, not a house, you can hjave a much higher vent speed and not notice if.. if i were to build this for a house i would shoot for 10m/s or lower... also, it would have been nicer to make the box a bit larger, but the 1503 reacts well to this size box.. it is in a car, so i cant make a 10cu ft enclosure 😀 ... i have a hatchback (ford focus), so the cabin gain starts at about 50hz.. this is the free air freq resp curve

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


the following are construction pix... its all 3/4mdf, NO BRACING.. no wood glue used, just caulk for sealing and drywall screws for construction, and carpetting... alot of people insist on bracing, but once again in a car, going 70mph, any noise or problems caused by an unbraced box will go unnoticed. it is getting 600w continous form a jbl 1200.1 and the output is too much.. if i crank it all the way it hits 140db @ 40hz, which is too loud for any music reasonably, and this is tuned low... its very common for peple to tune to 60-65hz and throw a HPF at 40hz and make a box just for slamming... they sound lke crap though.

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

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

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


if you do a slot port and round the wall like i did, you should put in order peices in order to make the port width uniform throughout the turn, however i neglected it, once again, since its in a car ...

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


i used winisd pro alpha for all my graphs and stuff

-chris
 
#38
not sure if the flaring woudl reduce noise, but it is not noticable.. when i am in the car in the front seat, you cannot hear port noise.. it highest around 20-30hz, otherwise its very low, and at 20-30hz at full volume (where it makes enough air for port noise), you cant hear anything. but it does give a nice back massage 😀
 
#39
An externally hosted image should be here but it was not working when we last tested it.


at 40hz the speed is 7m/s, which, from personal experience, is good for HT setups... you cant really hear it unless your ear is withing 1-2' of the port and you are listening for it... and this is when JUST bass is playing.. combine it in a musical or HT environment and its perfect... anyways, as far as the peak goes, the bass drowns it out.

again if u are going HT or home stereo and u really care about quality, go for 10m/s at your peak.
 
#40
Michael

The BP-1503 is a drop in for the AS-15 cabinet and it's ~18Hz port tuning.

Using the 1503 in a ported cab it likes no less than 200watts/VC, 400 watts is better. It also needs some parametric EQ to flatten the hump in the output caused by the somewhat high Le of the voice coils.

Using the 6" AeroPort flares allows house shaking SPLs with absolutely no port chuffing

Going sealed increases the power requirements and one doesn't get the nice boost below the driver Fs from the port
 
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