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Old 2nd January 2010, 01:25 AM   #11
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Thanx for the Reply Mark...it just so happens that i've got everything including a spare set of MCM guides so i was thinking to forge ahead with my TDFC's instead of the outlay for the DXt tweeters. I've got a pretty good method of adapting the tdfcs to the waveguide that involves gluing wellnuts into the guide with epoxy and then screwing the tweeter on to the backside of the guide. Subsiquently i fill all of the voids with epoxy which increases the density of the guide. Well i'm sure you can understand my hesitance to spend more $$$ as this is DIY..Wadda you think?
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Old 2nd January 2010, 12:24 PM   #12
DIFORCE is offline DIFORCE  Australia
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Thank you for the reply mark. I think i'll pass on the wall padding then.. But i still find it wierd how you came to that conclusion ,while most people leave the poly and aggresively pad the walls instead ,like in most zaph's designs ,The sr71 also use the er18rnx and he does not mention poly fill ...Wish i could know why . On the side note ,Mark you kinda miscalculated the total cost on your site ,the woofers and tweeters are 259.40 $ while at the total cost they are 159.40 $ so total cost without cabs is less then 500$ not 400$
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Old 2nd January 2010, 03:52 PM   #13
ucla88 is offline ucla88  Tahiti
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Originally Posted by mayhem13 View Post
Thanx for the Reply Mark...it just so happens that i've got everything including a spare set of MCM guides so i was thinking to forge ahead with my TDFC's instead of the outlay for the DXt tweeters. I've got a pretty good method of adapting the tdfcs to the waveguide that involves gluing wellnuts into the guide with epoxy and then screwing the tweeter on to the backside of the guide. Subsiquently i fill all of the voids with epoxy which increases the density of the guide. Well i'm sure you can understand my hesitance to spend more $$$ as this is DIY..Wadda you think?
If you have the MCM waveguide and don't mind mating it to the tdfc, this is a good way to go. That would be sort of a cross between Zaph's waveguide and Jon's ER18MCM project-

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It would have the potential to be very good.

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Originally Posted by DIFORCE View Post
Thank you for the reply mark. I think i'll pass on the wall padding then.. But i still find it wierd how you came to that conclusion ,while most people leave the poly and aggresively pad the walls instead ,like in most zaph's designs ,The sr71 also use the er18rnx and he does not mention poly fill ...Wish i could know why . On the side note ,Mark you kinda miscalculated the total cost on your site ,the woofers and tweeters are 259.40 $ while at the total cost they are 159.40 $ so total cost without cabs is less then 500$ not 400$
Ooops! I did chisel off $100. Oh well, it's worth it

As far as the stuffing-The rationale for the stuffing the way it is-

Most folks just follow the standard convention of stuffing a sealed box and lining a ported one. It works.

But I've had good success using Martin King's mathcad sheets to model stuffed ported boxes. I wouldn't call the box a TL, but the reality is that TL and ported boxes are along the same spectrum and martin's software can model stuffing a ported box very well. The net result of stuffing a ported box is some slight reduction in bass output which martin's software lets you model nicely and compensate for, and the flip side is markedly decreased internal reflections which can affect midrange/low treble FR significantly.

All my ported boxes over the last couple of years have been with Martin's software and I've always been satisfied with the balance of bass output and midrange clarity.

But, yea, people think it's really weird to stuff a ported box significantly...
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Old 3rd January 2010, 08:58 AM   #14
DIFORCE is offline DIFORCE  Australia
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Are there any options available like baffle step compensation ? If i dont have a huge room ...
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Old 7th January 2010, 09:29 PM   #15
DIFORCE is offline DIFORCE  Australia
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Says the 2'' precision port is being used. It does not say how much should I cut it and where ... Or what is the final tuning freq ...
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Old 8th January 2010, 02:45 PM   #16
ucla88 is offline ucla88  Tahiti
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Originally Posted by DIFORCE View Post
Says the 2'' precision port is being used. It does not say how much should I cut it and where ... Or what is the final tuning freq ...
I had a number of different lengths I was trying. I can't recall off the top of my head what I settled on. I'll double check this over the weekend and let you know.

I'll try to post a sim of Martin's nearfield low end response also when I get a chance. I'm always loath to quote an exact F3 because I think this misrepresents actual bass performance. Many ported designs use poor performing woofers, with a slightly exaggerated hump around the tuning frequency. This gives the initial impression of bass, but it ends up being a bit monotonous as the driver can only cleanly reproduce bass around the tuning frequency. On paper, the F3 looks good, but in reality the overall bass performance is not realistic. The ER18DXT is tuned to sag a bit, without any hump. The actual F3 is in the mid to high fourties, but the rolloff is a bit more gentle with the tuning and stuffing. There is meaningful bass output, maybe down 5-10dB to 35-40Hz.

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Old 8th January 2010, 06:19 PM   #17
DIFORCE is offline DIFORCE  Australia
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Thanks , I though I would look into zaph's SR71 design as it uses the same driver and enclosure size but I think there are changes , so I didnt.
Edit : Looking into the tuning freq he made ... and copying it , No need to do it now.

Last edited by DIFORCE; 8th January 2010 at 06:27 PM.
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Old 8th January 2010, 10:56 PM   #18
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Originally Posted by ucla88 View Post

Again, the main benefit of this two way, as opposed to any other well executed two way, is that it does have much a much smoother power response.

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I fully understand the benefit of (very) low distorsions in the low-treble and the global smooth power response on the fr range up to very high fr.
However I wonder about this huge 2.5 - 3.5khz energy (equal from 0 to 45).
At first thought I would not tell this "smooth power response" in such a sensitive area...Am I wrong?
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Old 8th January 2010, 11:30 PM   #19
DcibeL is offline DcibeL  Canada
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I don't see any problem between 2.5 and 3.5kHz...

Click the image to open in full size.

Btw, absolutely excellent work Mark! This is definitely a well thought out design, everything taken into account. I am curious about the transfer function though, since you have valleys in the tweeter transfer function at 1.5kHz and 6kHz, I would expect to see a tweeter roll off that is not as smooth as it is. I'm not saying you've done anything wrong, it's just interesting how that transfer function creates such a smooth frequency response.
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Last edited by DcibeL; 8th January 2010 at 11:36 PM.
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Old 9th January 2010, 01:58 AM   #20
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Originally Posted by DcibeL View Post
I don't see any problem between 2.5 and 3.5kHz...

Btw, absolutely excellent work Mark! This is definitely a well thought out design, everything taken into account. I am curious about the transfer function though, since you have valleys in the tweeter transfer function at 1.5kHz and 6kHz, I would expect to see a tweeter roll off that is not as smooth as it is.
I don't believe it either, but have to admit at what was measured, maybe the phase (from both drivers) is playing a role here (would like to see matching phases to understand) what, also, is not very easy. The speakers look very good. Congratulations Mark.
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Last edited by Inductor; 9th January 2010 at 02:00 AM.
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