2269H Optimized Port Tuning Help

[theriam]

Greetings Group!

I'm in need of some tuning advice for a project I'm wrapping up.

I have a JBL 2269H 18" sub that I'm loading to an empty JBL 4648A-8 enclosure that I've had laying around to be used as part of a home theater project. The net internal volume when subtracting internal bracing is 7.3 cubic feet. I've run several on-line simulations (speaker box lite) and I'm not confident with it's results. I'm planning to run dual 6" flared ports.

Can someone run this driver with their design software in configuration above to help me with an optimized port length recommendation?

Since this box is only 15 1/4" deep internally, I can accommodate longer internal port lengths using 90 degree elbows. This sub will be powered by a Crown DCi 2/2400 amp than includes DSP. It also has custom tuning for the SUB 18 that might be helpful.

The balance of the system has the JBL Master Reference 708i Monitors for the LCR channels. Those are powered by a Crown DCi 8/300 (each bi amped) using their custom DSP tuning to support them.

Thanks in advance for your help!

Mike

[RMC]

Hi Mike,

Quickly as i'm busy.

You're the second guy i see here not having too much faith in speaker box lite results. What you ask for is not that easy, and the fact nobody else replied confirms this.

First, your net box volume is incomplete at 7.3 CF. You need to subtract also volume displaced by driver (.3 cf for an 18" according to JBL), and volume displaced by the ports in the box which is unknown at this time due to Lv. So you'll likely be under 7 CF net.

Flared ports are not a piece of cake. The real science on these is from Harman Engineers Salvatti, Devantier and Button, Maximizing port performance, in the JAES, it holds the copyright on it, and its not free to acquire. Very heavy stuff and unless you're a scientist or a mathematician i wouldn't touch it, written by Engineers for Engineers... (original version paper about 62 pages, and JAES printed version around 40-50 pages)

I know someone posted before a small flared vent program, and flared vents come out of China plants like hot muffins, with no specs given, but the credentials of both of these are really unknown: good, bad, ugly? Its mostly a leap of faith.

I modeled before the 2269 in a box with single flanged 6" port @ 600W and it showed port compression (some chocking). So two flared ones might make sense, as long as one understands the mathematics involved... Plus one needs to remember there is a relation between SPL output and vent size. At low drive its less critical, but at high drive things become more serious.

One thing is sure from Salvatti and al, the flared ends reduce the tube length requirement. How, by how much etc. well that's part of the heavy stuff in that article.

As a shortcut, what i suggest is the following:

- model the conventional way with flanged vents, see the vent length you get

- then knowing that flared vents result in a shorter tube, i would try a shorter flared tube and see if it meets your requirements in terms of Fb, F3 and response. Example only, flanged gave you 10" Lv, then try a flared 8" Lv. Don't forget that you need to have a good space inside the box between the flare and the back wall for "breathing".

You're pretty much on your own in this unchartered territory, you may have to go by trial/error testing a few ports, unless you switch to flanged ports. Sorry but that's the best i can do for you at this point.

Richard

[theriam]

Richard,

Thanks for the response. I'll play around with those suggestions when I get back from Vegas.

By the way, do you have a favorite software you prefer to use? Let me know and I'll order it.

Thanks!

Mike

[RMC]

Mike,

I have both Win ISD from linearteam.org and WinSpeakerz from trueaudio.com

Download free Win ISD latest edition (2016), you may want to avoid their prior editions, still available, but they had some bugs. The driver database in ISD is poor having very few drivers only. You can add yours at will.

WinSpeakerz is not a free download , just $40., has a 1,570 driver database, including a number of older JBLs, but certainly not all of them, e.g. 2269H being absent, however here too you can add any you want in the database along with their parameters in order to model driver/box duos.

Each has its pros and cons, i tend to like WinSpeakerz because its fast and easy, plus it includes some things the other doesn't have. So you pay a small amount for WinSpeakerz and get the other free, then you have two speaker design softwares for the price of one, and you can compare their results, usually close when things are done correctly (e.g. using the same QL box loss number).

I don't remember if they can do flared ports, don't think so, only flanged? Even if they did flared ones i doubt these would be properly scientifically based...

Richard