Anyone plug their ports for music? (1 Viewer)

[PaulDF]

Does anyone often plug or unplug the ports on their subs, depending whether they are listening to music or HT?

I have gotten into the habit of doing this, to avoid the high group delay with my large vented Tempest. Modelling in WinISD I see that the GD is much lower, but the max power also drops a lot below 30hz. Respectively, the cone excursion goes VERY high below 30hz.

Am I risking damage when I plug my ports? Or is 150+ liters just too large for a sealed enclosure?

 

[David Giesbrecht]

Am I risking damage when I plug my ports? Or is 150+ liters just too large for a sealed enclosure?

I wouldn't worry about damaging a Tempest with that large of an encloser, each one of my sealed Tempests is 230 liters and I have yet to bottom them out. I am using a QSC RMX 1450 for an amp (450 watts x 2 @ 4 ohms) and I've clipped the amp before but never bottemed them out ever.

 

[George W]

Hey Paul,

I plug my ported 85L shiva often for music and I've never run into any problems with it. Does seem to tighten the sound up nicely.

George

 

[PaulDF]

Well, I am debating whether to build a smaller enclosure or change my tuning. (to suit my amp more safely). I was leaning toward shortening my ports to change the tune from 16 hz to 20. This way, I would not lose any SPL or extension, and keep the excursion down, and up the power handling.

But, the group delay increases by a substantial amount, so for music this is not good. At least as far as I can tell. So, if plugging the ports is a safe way of lowering my GD, then this alteration might just work.

Until I get tired of plugging and unplugging. And realizing AFTER I watch a boombastic DVD that I forgot to pull the plugs. And, that what I thought was a flat response through my BFD was really who knows what because the plugs were still in! (Actually, I wonder what would really happen in this case? perhaps nothing other than loss of lower extension. I have yet to plot the curve of my sub sealed...)

My wife can sense money going up in a cloud of musical smoke, the minute I start playing test tones!

 

[Jack Gilvey]

but the max power also drops a lot below 30hz. Respectively, the cone excursion goes VERY high below 30hz.

Yup, standard vented vs. sealed trade-offs.

 

[Chris Popovich]

Good point there Jack - how much of a difference do you really hear?

When I've plugged the port on my designs, I didn't hear that much of a difference. Of course, most people won't say that because we're "supposed" to be able to hear 1ms of difference in something like group delay or +1dB at 16Hz... and it isn't like that.

On the other hand, if it makes you rest easier, then by all means go for it. Any vented/PR design I've made has alwasy been tuned below 20Hz, and especially for music, there justisn't that much info down there, especially high level info. You aren't going to *hear* much GD at 20Hz no matter how bad it is -I'd be more concerned with 30hz on up.

Sealed designs are simple and great, but I'd put my Tumult/PR box up against any of 'em.

Cheers,
Chris

 

[PaulDF]

Jack, you are right. I didn't actually mention the difference in sound that I heard while in use. And afterall, this is my main concern... how it sounds!

When I plug my ports, I do notice the bass a little bit tighter, and also less boomy. Of course most of this could be psycological because I've read "this is the way it is...", but it could also be legit.

I've been trying to understand group delay for a while, but it seems the best way to learn about it is to play with it a lot.

So what about my original idea to shorten my ports to bring the tune to 20hz? All else is better on paper, but GD goes up. Should I make this mod, or redesign from square one?

 

[Jack Gilvey]

So what about my original idea to shorten my ports to bring the tune to 20hz? All else is better on paper, but GD goes up. Should I make this mod, or redesign from square one?

Could you post the exact specs for your Tempest sub, and what amp you're using? In general, raising the tune will result in less excursion at the peak, protect the driver a little better above Fb, but leave more room for overexcursion below. The aural difference on music will likely be minimal if audible at all.
Would it be tough to try...is everything glued together? My ports are held together with duct tape, so I can experiment with different Fb's.

 

[Brian Knauss]

My thoughts:
The sound might be tighter, but the enclosure is far from optimal for a sealed box.

You have less chance of hurting a sub in a sealed box than a ported box. With a ported, the vent allows for higher excursion at the lower end and this might cause a problem if the sub goes into over-excursion.

 

[Jack Gilvey]

You have less chance of hurting a sub in a sealed box than a ported box.

Depends...a vent protects the woofer around Fb. Can overload easily below Fb, but this is well-known and a good amp will provide a filter.

 

[PaulDF]

Jack - thanks, its good to hear you are quite pleased with the EBS alignment! I also now understand that the changes I/we are seeing here with GD and FR are pretty minimal, and perhaps really not that noticable.

The Tempest I built is 360l, tuned to 16 hz. The amp is the AVA 250 with a filter at 18hz. The baffle might come off, with some work. I'd rather not try it though. The ports are caulked into place (PVC), so they might come out. I think I have a plumber friend who has an internal PVC pipe cutter, it should reach 10 or so inches inside.

 

[Jack Gilvey]

Looking at that in WinISD pro, I'd leave it just the way it is, nice looking curve.

 

[PaulDF]

Well thankyou. But isn't 250 or 270 watts a little much for it? A 200 watt amp would have been a little "safer" in my opinion.

 

[Jack Gilvey]

That's about a 1dB difference, I wouldn't worry too much.

 

[PaulDF]

Yes, Jack, but I was talking more in terms of excursion and power handling... WinISD shows that 200 watts would have been "safer" for my enclosure and tuning. I'm just trying to avoid potential damage, as at times I push it quite hard!

 

[ThomasW]

Since a Tempest can handle ~750 watts to the driver (both VC's driven) you'll clip the amp long before you overdrive the woofer

 

[Jack Gilvey]

WinISD shows that 200 watts would have been "safer" for my enclosure and tuning.

Yup, and 100 watts would be even "safer". I'd rather have the headroom above 30Hz than worry about possible overexcursion in a narrown band just above tuning.

 

[PaulDF]

Okay, thanks Jack. I'll leave it be.