Topic: Some single USB build pics (labsub midbass) (Read 17974 times)

Lasse Lukkari · « **on:** September 07, 2008, 10:13:36 AM »

I got these ready a week ago and have done some gigs already with them. Great speakers! I'm really happy about them. On smaller gigs they also work quite well on their own without any subs. But with 6 labsubs they really start to move some air. I would say that the USB is a perfect match for the labsub. A big thank you goes to David Trotter for the design.

Loaded with Celestion FTR18-4080FD

index.php/fa/17827/0/

Lasse Lukkari · « **Reply #1 on:** September 07, 2008, 10:14:05 AM »

Lasse Lukkari · « **Reply #2 on:** September 07, 2008, 10:14:39 AM »

Lasse Lukkari · « **Reply #3 on:** September 07, 2008, 10:15:20 AM »

Lasse Lukkari · « **Reply #4 on:** September 07, 2008, 10:15:55 AM »

Lasse Lukkari · « **Reply #5 on:** September 07, 2008, 10:16:17 AM »

jeffhtg (Jeff Kenney) · « **Reply #6 on:** September 07, 2008, 11:09:05 AM »

very nice!
now what exactly is it?

Lasse Lukkari · « **Reply #7 on:** September 07, 2008, 11:26:41 AM »

jeffhtg (Jeff Kenney) wrote on Sun, 07 September 2008 16:09

very nice!
now what exactly is it?

It's pretty much like half of this:
http://www.cs.helsinki.fi/u/ljlukkar/USBPLANS.jpg

Brian Alleyne · « **Reply #8 on:** September 07, 2008, 01:11:50 PM »

Nice build have the designs myself but am not a great carpenter have to start on something basic and work my way up.

Gino bruschini · « **Reply #9 on:** September 08, 2008, 06:23:51 AM »

hello im pretty new to this so please correct me if im wrong, but the picture with the driver installed, shouldnt the magnet be inside the compression chamber? or do you reverse polarity of the driver?? what differences would it make installing the driver how you have?
i only ask as ive seen usb's before and the driver was the other way round, Confused

great work none the less!! they look great!

Lasse Lukkari · « **Reply #10 on:** September 08, 2008, 07:07:12 AM »

Gino wrote on Mon, 08 September 2008 11:23

shouldnt the magnet be inside the compression chamber? or do you reverse polarity of the driver??

No. And the driver wouldn't even fit. Because it's a bandpass horn there is no need to reverse the polarity.

Ivan Beaver · « **Reply #11 on:** September 08, 2008, 08:00:50 AM »

Lasse Lukkari wrote on Mon, 08 September 2008 07:07

Gino wrote on Mon, 08 September 2008 11:23

shouldnt the magnet be inside the compression chamber? or do you reverse polarity of the driver??

No. And the driver wouldn't even fit. Because it's a bandpass horn there is no need to reverse the polarity.

What does that (bandpass) have to do with driver polarity not mattering?

Lasse Lukkari · « **Reply #12 on:** September 08, 2008, 08:10:24 AM »

Gino wrote on Mon, 08 September 2008 12:31

but if not reversing the polarity wouldnt the sound be driven into a sealed compression chamber?? i understand the sound should be driven thru the throat of the horn? i must be wrong...

I'm not sure if my English is good enough to explain this and I'm really busy at the moment but i'll try...

If you play one frequency, lets say 50Hz, the driver moves 50 times/second back and forward. If you now reverse the polarity it just changes the direction that the cone starts it's movement. It still moves 50 times/second. Because of long wavelenghts most of the time it doesn't matter much which way it is as long as you take into account the space the driver takes. But when you cross over the speaker to another you want them to be in the same phase or they will cancel each other on the overlapping frequency range.

And here is what David Trotter has said:

By making the USB to match the lab sub however, it was no longer possible to mount the drivers in the traditional forward firing configuration. It was therefore decided that the drivers would be reverse loaded and fire backwards through the magnet. In doing so, the front chamber has been made smaller, decreasing efficiency slightly around 60Hz, but the rear chamber is now larger, increasing sub bass response. Apart from this, there is no loss in output (as a driver acts like a piston) and there are actually some advantages:

1. The magnet now has a direct heat path to the outside and a cooling effect due to airflow over the magnet. This eliminates heat build up in the driver chamber, decreases power compression (loss in output due to heat) and allows for greater power handling.

2. The magnet acts like a phase-bung; to an extent, reducing path length differences and giving a much cleaner sound and flatter response.

3. Mounting the driver is a lot easier

4. There is protection of the paper cone due to the basket.

5. It is actually possible to reach round the horn and check on the magnet temperature!

Lasse Lukkari · « **Reply #13 on:** September 08, 2008, 08:20:23 AM »

Ivan Beaver wrote on Mon, 08 September 2008 13:00

What does that (bandpass) have to do with driver polarity not mattering?

Usually these kind of speakers need the phase to be reversed. I have measured this with HD15 (speakerplans.com) and with the USB. But because the driver is already backwards there is no need to do that with USB.

Elliot Thompson · « **Reply #14 on:** September 08, 2008, 12:33:16 PM »

Lasse, it is nice to see you on this side of the pond.

I've already seen your work on speakerplans (Or possibly freespeakerplans).

What is the frequency bandwidth of this box?

Best Regards,

Ivan Beaver · « **Reply #15 on:** September 08, 2008, 12:48:10 PM »

Lasse Lukkari wrote on Mon, 08 September 2008 08:20

Ivan Beaver wrote on Mon, 08 September 2008 13:00

What does that (bandpass) have to do with driver polarity not mattering?

Usually these kind of speakers need the phase to be reversed. I have measured this with HD15 (speakerplans.com) and with the USB. But because the driver is already backwards there is no need to do that with USB.

The actual polarity of the driver is determined by several factors. There is no "universal" polarity-except in direct radiators.

The actual polarity will be dependant on the particular path lengths between the loudspeaker in question (in this case the one in the thread) and others on either side of it's passband-and this will be determined by the particular freq of crossover-different path lengths for different freq.

There is no way to make a univeral statement about polarity, but rather one that depends on all the loudspeakers being used AT THAT TIME. Different loudspeaker combinations could very well result in different polarities for particular drivers.