I've built a ported 82L box for my 12" I had lying around (JBL GT3-12), and I seem to be getting annoying group delay. It's not massive, but I notice it.
Initially reading around people seem to mention underdamped boxes will give a similar effect, but more of a "sloppy" bass sound. The sound from it actually sounds quite nice, but delayed. I've heard worse.
I've also read people mentioning it shouldn't be audible until at least 20ms or so. WinISD puts GD @ 50Hz somewhere around 6ms and 10ms @ 30Hz, however I'd be curious to know what effect filters and all that rubbish have on it (AVRs filter, the filter on the plate amp that has no bypass switch etc).
Would it be likely those two filters would have significant effect? Would I be right in assuming a typical filter could delay by up to 1 whole wavelength? At 50Hz isn't that around 20ms itself?!?!
None of my mates can hear it, but it drives me mad. One of them has a setup with terrible delay and he hears no problem, so probably not the best person to ask haha. Either that or I'm far more sensitive to it than most I'm gonna try delaying all the other channels from the AVR and see how it goes.
No stuffing in the box btw. Would that have any effect anyway?
Initially reading around people seem to mention underdamped boxes will give a similar effect, but more of a "sloppy" bass sound. The sound from it actually sounds quite nice, but delayed. I've heard worse.
I've also read people mentioning it shouldn't be audible until at least 20ms or so. WinISD puts GD @ 50Hz somewhere around 6ms and 10ms @ 30Hz, however I'd be curious to know what effect filters and all that rubbish have on it (AVRs filter, the filter on the plate amp that has no bypass switch etc).
Would it be likely those two filters would have significant effect? Would I be right in assuming a typical filter could delay by up to 1 whole wavelength? At 50Hz isn't that around 20ms itself?!?!
None of my mates can hear it, but it drives me mad. One of them has a setup with terrible delay and he hears no problem, so probably not the best person to ask haha. Either that or I'm far more sensitive to it than most I'm gonna try delaying all the other channels from the AVR and see how it goes.
No stuffing in the box btw. Would that have any effect anyway?
Also I walked around the room a bit listening to some music and I think it might just be the location within the room.
If I'm in a fairly low-volume (low-resonance?) location of the room and turn the sub up a bit more it sounds kind of delayed, but if I'm in a higher-volume location within the room and turn the sub down to match it actually sounds good.
I'll figure it out in a month, we just bought a house so it'll be a whole new setup. I dunno about you guys but I never seem to be happy with what I make - I can see this one going downstairs in the 'workshop' with some basic speakers and building myself a new one for the lounge, hehe
If I'm in a fairly low-volume (low-resonance?) location of the room and turn the sub up a bit more it sounds kind of delayed, but if I'm in a higher-volume location within the room and turn the sub down to match it actually sounds good.
I'll figure it out in a month, we just bought a house so it'll be a whole new setup. I dunno about you guys but I never seem to be happy with what I make - I can see this one going downstairs in the 'workshop' with some basic speakers and building myself a new one for the lounge, hehe
rabbitz said:
The trouble with this is one could still attribute a change in something else to group delay.
phreeky82 said:Also I walked around the room a bit listening to some music and I think it might just be the location within the room.
If I'm in a fairly low-volume (low-resonance?) location of the room and turn the sub up a bit more it sounds kind of delayed, but if I'm in a higher-volume location within the room and turn the sub down to match it actually sounds good.
I'll figure it out in a month, we just bought a house so it'll be a whole new setup. I dunno about you guys but I never seem to be happy with what I make - I can see this one going downstairs in the 'workshop' with some basic speakers and building myself a new one for the lounge, hehe
Sounds like your sub is exciting some room modes, and your listening position is in an anti-node. If practical, try experimenting with sub woofer placement (even if only temporarily) and see if the problem is helped. Alternately try making comparisons outdoors, or in some environment where room modes come into play. Next step i'd take would be to find someone with a SPL meter or a mic and measure the room response using roomEQWizard or similar. If your room is particularly bad and optimal placement doesn't help, then the next step could be a BFD or similar parametric eq (it might be more sensible than building another sub and still having problems, assuming the sub itself is fine).
Yep I will do, but like I said I'll probably leave it till I move house anyway. I put a small bloody dent on the paint within a few hours of setting it up (agrhrgh), and the side panels are just MDF for the time being (would like to do using real timber for the side panels, but just used MDF for the time being): http://www.clubpoint.net/bluebird/stereo/Img_4325cr.jpg
Underneath: http://www.clubpoint.net/bluebird/stereo/Img_4329cr.jpg (that's just dust etc on the paint and mat)
Note: I just place carpet between panels to remove vibrations as they're bolted on.
Underneath: http://www.clubpoint.net/bluebird/stereo/Img_4329cr.jpg (that's just dust etc on the paint and mat)
Note: I just place carpet between panels to remove vibrations as they're bolted on.
rabbitz said:
Yep, the GD would change, but so would a number of other things, such as port noise or low frequency extension, which might mean a particular room mode isn't excited as much for example. IMHO there are too many other changes to experimentally determine if group delay is the problem, of if it is something else.
I have seen instances where people plug ported boxes, then proclaim how tight the bass is, only to find out that their boxes are rolling off at 80hz or higher and the tightness is just an outright lack of bass. My point is that in many cases the associations made between what is heard and what is happening can be wrong, so its not a good idea to make assumptions.
edit: That said, stuffing the ports might help narrow down the problem, just not solve it.
FYI the sub sounds nicer in other but really inconvenient locations. So leaving it where it was, I played with the delays in the receiver (delaying the other speakers a bit) and it sounds pretty bloody good at the moment. Unfortunately I'm not exactly sure how much it is delaying them by because the settings are changed by specifying the number of metres they are from the listening position.
edit: btw I'm going to live with this for the time being - almost everything will be getting packed up for moving in a couple of weeks anyway, and then I'll have a whole new room to setup (including a massive workshop area)
edit: btw I'm going to live with this for the time being - almost everything will be getting packed up for moving in a couple of weeks anyway, and then I'll have a whole new room to setup (including a massive workshop area
)Box volume stuffing is in my opinion often not needed for well-braced ported subsystem that have a bandwidth up to 80 Hz.
Fs/Qes for JBL GT3-12 car driver is about 46-47 and the driver Qts is > 0.5 giving a strong indicator it’s a driver designed for closed enclosures but not for unstuffed ported designs if using small volumes.
The driver can only be tamed to sound good in a ported box if sufficient volume is used to bring the driver sensed box Qt down to allow the design to fall within recommended design alignments, or is driven by a negative impedance (positive feedback-) amplifier or by using any of the acoustic damping methods described by R. Small.
Howe to use `Negative impedance`: http://sound.westhost.com/project56.htm
A couple of pictures to consider:
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Well TBH some of those graphs are a little beyond me, at least without some indepth reading (which I don't really have time for at present).
I understood the driver doesn't have a great response curve @ 82L (I was actually originally going to buy a cheap JBL GT4-12, which gave a much nicer response), but thought I'd give it a crack anyway - I didn't know it would "sound poor" for the response it did have, if that's what you're trying to illistrate to me.
I understood the driver doesn't have a great response curve @ 82L (I was actually originally going to buy a cheap JBL GT4-12, which gave a much nicer response), but thought I'd give it a crack anyway - I didn't know it would "sound poor" for the response it did have, if that's what you're trying to illistrate to me.
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