Dual JBL GTO 1014 TH design - constructive critisism required please - AVS Forum
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Old 08-19-2012, 01:33 PM - Thread Starter
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Hi

First serious build-related post in the forum and looking for constructive criticism and a few answers to (probably silly) questions……

I’m looking to build a TH. I live in the UK so modestly priced subs with reasonable specs are hard to come by and having spent many an hour playing with different drivers and configurations in hornresp I have settled, I think, on the JBL GTO1014, or most likely 2 x JBL GTO1014’s! ---- or maybe 4 if the 1st TH turns out ok ;->

I have attached my hornresp model and would be very grateful if someone could check that I haven’t made any silly errors with parameters etc. I am not quite sure I follow what values I should enter in “Eg” to check max displacement etc given my configuration to 2 x 4Ohm drivers in parallel (do I put, say, “300” and “2” in the box to give an Eg of 24.49??)

Anyway, maybe I should just list what I think I have done and then you can all correct me !!! tongue.gif

What I think I have modelled is:
- 2 x JBL GTO1014 TH wired in parallel
- representing a 2Ohm load (to be run off of 1 channel of an EP4000)
- pretty flat from low corner of 23Hz to 70Hz
- big spike to EQ at 80Hz and back down @100Hz mark
- 213 litre horn (about 7.6 sq ft)
- 95dB @ 2.83 in halfspace
- ~125dB corner loaded with eg of 24.49 (xmax under 12.5)

Questions:
- Is this correct / any good (will I go deaf biggrin.gif ) and what have I missed?!
- If I build another and then wire together for a 4Ohm load for the EP4000 that would work ok wouldn’t it and yield comparable results?
- any recommendations for a cheap EQ to deal with the 80Hz peak and also the sub 23Hz and over 100Hz? Is the miniDSP what I need for this?

I’m not going to start (try) folding until I know it’s worth doing!!

Thanks in advance!
Simon

1014jblx.txt 0k .txt file
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Old 08-19-2012, 02:13 PM
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i downloaded your file and took a look.

the pmax and xmax figures in the file are low, but i'll assume that you entered the other parameters correctly.

i'm getting the same result that that you describe.

"I am not quite sure I follow what values I should enter in “Eg” to check max displacement etc given my configuration to 2 x 4Ohm drivers in parallel (do I put, say, “300” and “2” in the box to give an Eg of 24.49??)"

yes, for 300 watts and 2 drivers in parallel, but one channel of an ep2500 will give you more power than that into 2ohms.

"What I think I have modelled is:
- 2 x JBL GTO1014 TH wired in parallel
- representing a 2Ohm load (to be run off of 1 channel of an EP4000)
- pretty flat from low corner of 23Hz to 70Hz
- big spike to EQ at 80Hz and back down @100Hz mark
- 213 litre horn (about 7.6 sq ft)
- 95dB @ 2.83 in halfspace
- ~125dB corner loaded with eg of 24.49 (xmax under 12.5)"

that is what i am seeing too.

"what have I missed?!"

s2 is the cross section area in front of the driver. the sd of the driver divided by s2 gives you the compression ratio. with 2 drivers it will be double. so you are net 4:1. i don't know what a good rule of thumb is for long term survivability at high spl. just thought that i'd point it out.

"- If I build another and then wire together for a 4Ohm load for the EP4000 that would work ok wouldn’t it and yield comparable results?"

no need to wire together, just use the other amp channel.

"- any recommendations for a cheap EQ to deal with the 80Hz peak and also the sub 23Hz and over 100Hz? Is the miniDSP what I need for this?"

that is probably your best bet. it will also have the highpass filter that you can use to protect your driver below the bottom corner.

overall, in my opinion, you have done your homework and have a nice tapped horn plan.

cone hits minimum at right around 20hz, so that is where i would call its tuning.

if that is low enough for you...go for it.

Listen. It's All Good.
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Old 08-19-2012, 04:31 PM - Thread Starter
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Thanks very much for your post.
Quote:
Originally Posted by LTD02 View Post

i downloaded your file and took a look.
the pmax and xmax figures in the file are low, but i'll assume that you entered the other parameters correctly.

Thanks. I didn't change those (not sure where to in hornresp!). I assume, since the plotted xmax is below the driver spec, that it doesn't matter?
Quote:
Originally Posted by LTD02 View Post

s2 is the cross section area in front of the driver. the sd of the driver divided by s2 gives you the compression ratio. with 2 drivers it will be double. so you are net 4:1. i don't know what a good rule of thumb is for long term survivability at high spl. just thought that i'd point it out.

I was looking out for this, but it probably drifted a bit as I was 'tweaking'. I've increased S2 to 190 which has a minimal impact on the output but drops the ratio to 3.5. Good enough for me rolleyes.gif
Quote:
Originally Posted by LTD02 View Post

"- any recommendations for a cheap EQ to deal with the 80Hz peak and also the sub 23Hz and over 100Hz? Is the miniDSP what I need for this?"

that is probably your best bet. it will also have the highpass filter that you can use to protect your driver below the bottom corner.

I'll look into that, thanks.
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Originally Posted by LTD02 View Post

if that is low enough for you...go for it.

It'll do for now tongue.gif
(two reasons for getting an EP4000 - 1) more headroom for the future (I started a sealed 21" build as was looking to import a 21" Mal-X mad.gif), and, 2) they seem to be in better supply over here)

OK..... sketchup here we come!

v2 attached for anyone interested. v2 model 0k .txt file

biggrin.gif
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Old 08-19-2012, 05:14 PM
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after the frequency response is plotted, if the "maximum spl" is selected, power and excursion numbers are required. i suspect that is where pmax and xmax are grabbed, but i'm not certain.

the only other thing that comes to mind is that one channel of your amp into two ohms will give more than 300 watts (900 or so? is my guess), so if you hit them really hard around 25-30hz, you might damage the drivers. the drivers can handle more than 12mm, but it gets difficult to predict how much power will actually damage them.

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