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Old 18th April 2004, 06:08 PM   #1
Merlin is offline Merlin  United Kingdom
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Default My Subwoofer Woes.

Hello,

This is my first post over here and I am a complete novice when it comes to building loudspeakers but am keen to learn.

My first project was a pair of 15" subwoofers, intended primarily for music listening. The cabinet design is a 115l enclosure vented and tuned to 27hz. The actual plans were supplied by a professional and I am generally very happy.

I do find however, that the bass is somewhat muffled at times (not sure if that's the right term), and lacks transient attack low down. I lined the interior of the cabinet with Dacron 1" thick and was wondering whether this might have something to do with the issue? Would removing the lining liven up the sound. I only ask as the drivers are 40lb each and it is not an easy job to remove them.

Any help would be really apreciated.
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Old 18th April 2004, 06:48 PM   #2
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Do you know what the drivers are?
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Old 18th April 2004, 06:55 PM   #3
Merlin is offline Merlin  United Kingdom
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Thanks,

It's the JBL 1500AL.

One other thought was to bung the port, but I don't know if this would be good for the driver.
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Old 18th April 2004, 07:10 PM   #4
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That amount of lining will probably make no noticeable difference to the sound of a subwoofer.

You could try bunging the port. If you do this, be aware that what you may percieve as tighter sound may well just be down to the fact that the response rolls off a bit higher.

What amp(s) are you using to drive the subs and where are you taking the feed from? This may make a bit of difference.
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Old 18th April 2004, 07:16 PM   #5
Merlin is offline Merlin  United Kingdom
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Thanks again.

I'm using a Crown K2 to power the subs in stereo mode. the feed is coming from a Rotel AV receiver which I konw isn't great, but simple inexpensive subs still seem to have more transient impact when fed from the same outputs.
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Old 18th April 2004, 07:42 PM   #6
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I don't think that the amps will be a problem The line-level drive should be OK too.

I suspect that what you are calling transient impact is not what good transient response actually is. It's quite common for people to think that a punchy bass is good transient response, where in actual fact it's a slightly peaky and underdamped response.

You may also be finding that your sub goes deeper than the cheaper smaller one you have tried, and with room gain you are getting too much energy, muddying the sound. What were your comparison subs?
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Old 18th April 2004, 07:45 PM   #7
GM is offline GM  United States
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115L/27Hz is an underdamped alignment. Try tuning it lower with a longer vent to get better damping and blend with the room's gain better.

GM
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Old 18th April 2004, 08:07 PM   #8
Merlin is offline Merlin  United Kingdom
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Thanks again.

The extension of the sub is actually not that great, it's about -3db at 50hz and -10db at 25hz according to the measurements. But you may well be right regarding the room gain. Would EQ be worthwhile and at what cost?!

GM, the designer did say that the tuning was underdamped ( I don't understand the implication I'm afraid), but felt that it would suit the room gain. I sadly cannot lengthen the port. It is 12" already and, being rear facing, nestles quite close to the drive unit as it is.

The Win ISD data shows a sealed cabinet of the same size gives the same output at 20hz, but slightly less between 80hz and 30hz. I have to admit I don't fully understand the implications of this! But the group delay is significantly less. Having said that the 1500AL was designed for a vented enclosure. So what information do you guys need to allow me to make the next move?

Thanks again

Michael
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Old 18th April 2004, 08:26 PM   #9
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If you cannot lengthen the port, try filling it with the stuffing you used to line the box, if you have any spare. Be very careful not to pack the stuffing, just put enough in to hold it in place.

How big is your room, BTW? 2x 15 inchers for music is one helluva lot of bass!
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Old 19th April 2004, 09:58 PM   #10
Merlin is offline Merlin  United Kingdom
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Thanks for that Ritchy,

I have bunged the ports loosely with Dacron for the time being, which seems to have had some of the desired effect.

The room is 20' x 14' x 9'. I like effortless bass. I don't seem to get that with small drive units.

When I get the chance I will try putting more stuffing inside the cabinets. Does Dacron do as good a job as anything else? I know that JBL line the cabinets with 1" fibreglass, but this was difficult to source. Some people tell me that it sounds better.
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