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HD15 Time Alignment

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Andrew View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Andrew Quote  Post ReplyReply Direct Link To This Post Topic: HD15 Time Alignment
    Posted: 05 September 2004 at 2:40pm

Just used a HD15 / Bose 802 system.  The 802's were set on poles which are at the centre point of the HD15.

I just wanted to check if I got the time alignment right, 6.55mS, which seems quite long, considering the tops are sat at about the mid point of the unit, and not on the front edge.

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whitehousejamie View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote whitehousejamie Quote  Post ReplyReply Direct Link To This Post Posted: 05 September 2004 at 3:44pm

Hi Andrew,

I use a system 4 times per week for Karaoke consisting of 2 x Bose 802s and 1 x Short Horn (simular to HD15) using the Bose Processor and it sounds great. Normally put the horn so that its front is about 1ft infront of the Bose and it works fine. Used to use a Bose 302 before, which never had the kick that this horn does, plus it was damn heavy too.

System is run off a Crown MT2400.

Jamie

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JD01 View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JD01 Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2004 at 10:41pm
6.55ms is okay. It's not only the length of the horn you have to compensate but some other factors too. If you place the HD15 in a corner or in smaller rooms you will have to raise the delay even more.
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loophole View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote loophole Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2004 at 3:38am
could you please outline some of these other factors? does it depend on the air mass/volume coupled with the speaker or something?
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Dave Slater View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave Slater Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2004 at 11:25am
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Andrew View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Andrew Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2004 at 12:48pm
The HD15s were in a large and tall room, but were adjacent to the side walls.  How does this change the effective horn length?
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whitehousejamie View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote whitehousejamie Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2004 at 1:48pm
How many HD15s and 802s do you use?
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Andrew View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Andrew Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2004 at 2:20pm

One of each per side. 45-254Hz, 290-16.5k, 6.55ms delay, and a little 2dB cut around 125Hz.  Power was equal for top and bottom.  Used amps with volume at 12 o'clock position.  This was a visually small but subtle rig.

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loophole View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote loophole Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2004 at 3:27pm
Originally posted by dave dave wrote:

http://www.speakerplans.com/page88.html


cheers for the reply, but this doesnt explain anything other than normal reasons for delay, plus a bit about temp/humidity
jd01 suggested that the space in which the bin was placed made a difference to the delay needed
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Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JD01 Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2004 at 4:00pm
The HD15 like any speaker has a group delay which is caused by mechanical and electrical components of the speaker and the enclosure. Yes, the air mass is also involved. Of course the length of the horn is also part of the group delay of that box. It's the overall time the box needs to bring the electrical signal to the air. Even without the horn this would take some time....
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loophole View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote loophole Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2004 at 4:18pm
so effectively it has a lot in common with the transient response? is there any easy-ish way of calculating the g.d. for certain speakers or is it something that should just be measured using SMAART or something similar?
thanks
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JD01 Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2004 at 4:38pm

No, it's not automatically the transient response. A system (in this case a speaker or a box) can have a group delay of x ms but the transient response is very good. That means the signal is delayed by x ms but after that time the signal comes out of the box like it went into the box. Just some ms later...

But a bad transient response can contribute to higher group delay....

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