T48 Response Plot

EQ guys are using on their cabs/systems. A good starting place if you don't have your own RTA.
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KORTH
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T48 Response Plot

#1 Post by KORTH »

Image

The above is a frequency response plot of one of my T48’s. The cabinet is 25.5 inches internal width, loaded with 2 Delta 12LF’s. Pink noise from an O1V was sent through a dbx dr260, setup to function as a crossover only, no other processing was used. The crossover filters were set to about 26Hz and 2.5kHz. The signal sent to the cabinet was about 2V as measured with a voltmeter across the output terminals of the amp. The mic was a dbx RTA placed about three ft in front of the cab and about 2 ft above the ground. The mic fed into an old Behringer 8000 DSP to display the response. This was done indoors, so room size and placement probably had an influence. Two things caught my eye, though. The first was how closely the response matches what's advertised in the plans, especially from 60 to about 100hz, and the second was the upper range output. In practice, cut a few db around 125hz, and boost a bit between 40 and 50hz. They are used with either DR280’s or a pair of recently built OT12x2’s. If ever needed, I think the crossover could run up to 250Hz, but usually it's set to about 110-120Hz with the OT12's or to about 95 Hz if using the DR280's.

Mark Coward
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Re: T48 Response Plot

#2 Post by Mark Coward »

KORTH wrote:They are used with either DR280’s or a pair of recently built OT12x2’s. If ever needed, I think the crossover could run up to 250Hz, but usually it's set to about 110-120Hz with the OT12's or to about 95 Hz if using the DR280's.
What drivers & tweeter arrangement did you use in the OT12's, and how would you compare them to the DR280?
Mark Coward

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Bill Fitzmaurice
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#3 Post by Bill Fitzmaurice »

When taking pics of a display the best method is to put the camera on a tripod, switch the flash off, and use the self-timer to eliminate jitter with the long shutter time that comes with existing lighting.

KORTH
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#4 Post by KORTH »

Ok, thanks for the tip!

Drivers in the OT12 are Delta Pro 12's (x2) and I'm having a hard time deciding on tweeters. I've used compressions drivers (2x Eminence PSD 2002-16) and the same 1016 x10 array I have in the DR280's, both sound good. I started off building the OT12's because folks in my band, and other bands I work with, complained about the "look" of the piezo's on the 280's. The lower crossover point of the 2002's and the flexibilty of a three way system were contributing factors in deciding to build them, as was the thought of the OT12 being a louder cabinet than the 280. That was a pipe dream, I can't tell a difference in loudness, even though there are two twelves versus one in the DR. The DR's are better in terms of spl, HF dispersion, amp load, and driver cost per cabinet, which is what many others have been saying all along. Also, the DR's low end is superior compared to the OT12's. Overall, the 280's sound better with 1016's and the right eq. I'm probably going to take David Perry's advice to reload the 280's and put some sort of grill on the front to satisfy all concerned. The OT12's sound good, are a much easier build, and fit my pack space better, but based on the above, I can't justify building more of them.

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DAVID_L_PERRY
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#5 Post by DAVID_L_PERRY »

Your eyes are the worst set of ears you have...

When I tried my new DR280's in place of my DR290's I didnt tell the band I provided Pa for, they could not tell, becuase the cabs are identical and both have grills, but it was clear that the sound was superior outfront, not only that, but one less amp working...

Its not worth the time to argue the piezo corner before the gig as people know they sound crap, its great to tell people after the gig who have commented on the quality sound.

Grills with foam are your answer for the "look at that police"...

Korth, once you have your DR280's eq'd post the results so we can see another eq curve. Mine has been tweeked a little over the last few gigs, but only slightly from that shown on this forum.

Dave

KORTH
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#6 Post by KORTH »

I finally got around to taking photo's of my 280's eq settings for a flat response...

http://www.frappr.com/?a=viewphoto&id=3 ... myphotos=1

For some reason, I have a fairly significant dip around 1.6Khz that requires almost a 10dB bump on the eq. Could be the crossover region between the woofer and tweeters, or maybe a room interaction?? I see on your posts a dip around 1.25Khz that requires a correction of about 5-6dB. My HF section from about 3Khz to 6Khz is weaker than yours for some reason, I remember you mentioning you had twelve piezo's, I have ten, but I wouldn't think it would be that drastically different. It does sound rather bright, so I'll look at my measurement setup sometime this week and re-post if it is much different.

Also, I added a front grill, specifically for those with ears on the front of their head instead of on the sides. It looks pretty good, my only concern is how durable it will be.

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DAVID_L_PERRY
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#7 Post by DAVID_L_PERRY »

KORTH wrote:I finally got around to taking photo's of my 280's eq settings for a flat response...

http://www.frappr.com/?a=viewphoto&id=3 ... myphotos=1

For some reason, I have a fairly significant dip around 1.6Khz that requires almost a 10dB bump on the eq. Could be the crossover region between the woofer and tweeters, or maybe a room interaction?? I see on your posts a dip around 1.25Khz that requires a correction of about 5-6dB. My HF section from about 3Khz to 6Khz is weaker than yours for some reason, I remember you mentioning you had twelve piezo's, I have ten, but I wouldn't think it would be that drastically different. It does sound rather bright, so I'll look at my measurement setup sometime this week and re-post if it is much different.

Also, I added a front grill, specifically for those with ears on the front of their head instead of on the sides. It looks pretty good, my only concern is how durable it will be.
I use transit covers on my grills made from 10mm MDF. They work well and keep the grills looking in as new condition. All my grills on my subs still look as new thanks to these cheap little covers. Best part is that you can stack stuff on them without worrying about denting the grills:-
http://www.frappr.com/?a=viewphoto&id=1 ... myphotos=1

They are just held in place when vertical using 4 small strips of velcro.

My EQ curve is for a single DR280
I have the very same excessive single eq bump (although 1.25k) and was pretty sure it was room related, perhaps not.
This is the eq curve and shows the 1.25k bump:-
http://www.frappr.com/?a=viewphoto&id=1 ... myphotos=1

Regarding the output of the piezo's, I obtained them from a UK supplier called CPC.
8 of these CPC piezo's outperformed 12cut and glued piezo's of an alternate UK suppliers cheaper brand (WLE) in both SPL and freq response.

Dave

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Bill Fitzmaurice
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#8 Post by Bill Fitzmaurice »

KORTH wrote:For some reason, I have a fairly significant dip around 1.6Khz that requires almost a 10dB bump on the eq.
A dip that severe at one frequency almost always indicates a phase cancellation. I wouldn't think it's caused by the tweeters at that low a frequency, but you never know, so I'd switch polarity of the tweeters just to be sure. It also could be caused by a reflection path in the measuring process, and even insufficient damping inside the box is a possibility, as a quarter wavelength at 1.6kHz is only 2.1 inches. In any event if you can't get rid of it I'd manually back off the correction there by 3-4dB and see how it sounds.

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James R
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#9 Post by James R »

I have a question, I've seen the eq for the tops and one for the subs what about when they are combined as they wil be used?
" Everyone Has a Photographic Memory, Just Not Everyone Has Film In The Camera"


4 x T48 24.5" 3015LF
8 x 112 Otops


NEXT 2 x DR280's

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Bill Fitzmaurice
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#10 Post by Bill Fitzmaurice »

KORTH wrote:
For some reason, I have a fairly significant dip around 1.6Khz that requires almost a 10dB bump on the eq. .
I've narrowed down the source of that dip, and a cure is in the offing. Expect it within a few weeks.

KORTH
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#11 Post by KORTH »

James R - I don't have pics of the full system response. Seems I've always focused on one component at a time when testing. I'll check the whole system next time I setup to take response measurerments, maybe in a couple of weeks, per Bill's note...

Bill - Excellent, can't wait to try it out!

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James R
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#12 Post by James R »

No problem, I was just curious I never realyy saw any eq settings for the whole system. It always seemed to be the tops or the bottoms.


Thanks,
Jim
" Everyone Has a Photographic Memory, Just Not Everyone Has Film In The Camera"


4 x T48 24.5" 3015LF
8 x 112 Otops


NEXT 2 x DR280's

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