Enclosure tuning for HT speakers

[Rob41]

I just want to get some input on my ported enclosures for the home theater system I'm building. Although I've built speakers, this will be my first time building a ported enclosure without much to go on.


This will be my set up:
Receiver, Marantz SR7012, about 125wpc
(2) sealed UM18-24 Ultimax 18" subs in sealed enclosures
Behringer NX6000D for the subs


So far it looks pretty pedestrian, but I'm going unconventional for the LRC and surround channels. I am using Kicker 6 x 9 speakers with a silk dome midrange an silk dome tweeter. One per enclosure.


They are rated at 150 RMS and are 92db 1w 1m and are advertised for 30-21 kHz and are rated at 4 ohms. Aside from that, I have no Thiele small parameters whatsoever.



The enclosure interior dimensions for a 40 Hz tune ar 11" x 11" x 22". I figured in the area displaced by the 6 x 9 and a 3" diameter, 6" long port tube flared on both ends. It would be tuned to 36 Hz if I make the port tube length 8".


I plan on all my speakers being crossed at 80 Hz to allow the subs to take over below that. I guess my question is does this seem like reasonable plan to tune the enclosures to 36 or 40 Hz, or should I tune higher?

 

[Brett]

If by 'tuning' the Kickers you mean porting them to 36 or 40Hz, why if you're going to cross them at 80Hz? Run them sealed and cross them at 80Hz. How well this will work will depend upon you getting the T/S parameters and setting the box volume for that, or running a fairly large box volume for them, measure the final rolloff slope and work out what you need to do to get a good xover for both drivers at 80Hz.

 

[Rob41]

If by 'tuning' the Kickers you mean porting them to 36 or 40Hz, why if you're going to cross them at 80Hz? Run them sealed and cross them at 80Hz. How well this will work will depend upon you getting the T/S parameters and setting the box volume for that, or running a fairly large box volume for them, measure the final rolloff slope and work out what you need to do to get a good xover for both drivers at 80Hz.

Not "tuning" the kickers. The enclosure will be "tuned" based on internal volume, port diameter and port tube length.



I want the enclosure tuned to the lower 36 Hz as the drivers are capable of 30 Hz according to the manufacturer and I may want to use them stand alone at some point without the subs. If they are capable there, they should perform adequately at 80 Hz.


As I stated, I do not have any T/S parameters and can't find that information anywhere. As far as roll off slope goes, I'll be setting the type of slope and crossover point within the Marantz receiver.


I suppose I can just do some experimenting with the internal volume and take measurements.

 

[Brett]

Not "tuning" the kickers. The enclosure will be "tuned" based on internal volume, port diameter and port tube length.

Oh good grief. You're wanting to tune the Kickers to the enclosure volume. For which, you need the T/S.

I want the enclosure tuned to the lower 36 Hz as the drivers are capable of 30 Hz according to the manufacturer and I may want to use them stand alone at some point without the subs.

A small driver with limited Sd and Xmax is going to give poor LF output as it doesn't have enough volume displacement. However, without the T/S, how do you intend to tune it to anything? Also because of cabin gain in a car, which you don't get in a typical room, expect the specs to reflect that usage and expect the LF performance to be much worse in room.

I suppose I can just do some experimenting with the internal volume and take measurements.

Measuring T/S isn't hard nor does it require much so you should learn how to do it otherwise your project has little chance of decent performance.

 

[GM]

Yeah, if they still 'tune' [design] mobile audio drivers same as a couple of decades ago, Fs will be around 65 Hz with 30 Hz as much as -15 dB with ~0.6 Qts, so ~50 Hz Fb for vented with a ~100 Hz broadband mid bass peak to blend in with cabin gain.

Back then the 'FR' driver folks had a short fascination with RS, Pioneer mobile audio drivers and the few ovals measured required relatively huge MLTLs to get down to < 65 Hz, so as you noted, best overall in such an acoustically small cab with an 80 Hz XO is to run it sealed or at least semi-aperiodic by stuffing the cab and vent as required for smoothest overall response.

GM

 

[Rob41]

Yeah, if they still 'tune' [design] mobile audio drivers same as a couple of decades ago, Fs will be around 65 Hz with 30 Hz as much as -15 dB with ~0.6 Qts, so ~50 Hz Fb for vented with a ~100 Hz broadband mid bass peak to blend in with cabin gain.

Back then the 'FR' driver folks had a short fascination with RS, Pioneer mobile audio drivers and the few ovals measured required relatively huge MLTLs to get down to < 65 Hz, so as you noted, best overall in such an acoustically small cab with an 80 Hz XO is to run it sealed or at least semi-aperiodic by stuffing the cab and vent as required for smoothest overall response.

GM

Thanks for the info. I'll build an enclosure tomorrow so I can adjust internal volume and try both ported and sealed. The latter will no doubt be easiest to get right.

 

[Rob41]

A couple years ago when I built a pair of 7 1/2' tall open baffle line array speakers, I used a line of ribbon tweeters flanked on either side by 6 1/2" drivers. The overwhelming consensus on several forums was I should use 4' or smaller drivers because the combing effect would be terrible. While that may be true on paper, what I found was absolutely no audible combing at all.


While automotive 6 x 9 speakers with their relatively high qts, among other things, may not be considered ideal for home use, I found out today they will be ideal for my home theater LRC and surround speakers. I have yet to take measurements but I believe they are easily reaching 60-70 Hz at least and all I need them to do is get to 80 Hz.



After testing several interior volumes, (sealed) I settled on what sounded best to me. Then I decided to unscrew and remove the terminal cup of about 2" and wow! That really woke up the lower frequencies. Since this first test enclosure is my test mule, tomorrow I'm going to install a 3" x 6" long flared port tube. It's the only size I have on hand right now. We'll see how that works. Being they are intended for a virtual IB environment, the relatively large port may just work. I will play with the port more and maybe go "semi-aperiodic" as GM mentioned. I still need to add damping material to the enclosure as well.


Although not a true point source, I believe the less than one inch distance between the silk dome mid and silk dome tweeter will exhibit the same behavior as a point source which should make for some really good imaging. And given the drivers efficiency, they should be good for 99db or better in room which is plenty for what I need. The 18" Ultimax subs in sealed enclosures will easily bring up the bottom end.


Just about every thread I've read about someone wanting to use automotive speakers in home has been met with a laundry list of reason why it won't work, or will work poorly. I'm glad I decided to stay on track with this project, I was about to get a complete Polk HT set-up and I'm glad I didn't.


I'll break out my Umik microphone and REW as soon as I get a chance to provide some actual data, but for now my ears are liking what they are hearing.