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Old 22nd October 2013, 03:55 AM   #1
tcpip is offline tcpip  India
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Default The Darbari: new speaker project

Hi all,

Am starting a new project, and would welcome comments.

My initial thoughts on the Darbari are on this page.

After the Asawaris, am hoping that this will be a system I can live with for my own use (all the Asawaris have gone to friends).

This will be a three-way with Dayton RS woofer and mid, and Seas TBFC/G tweeter. Drivers were bought a few years ago. Enclosure building will start soon. Crossover has been ordered. And in case you are wondering how the hell does one order a crossover before even the enclosures have been built, please read the attachments.

Wish me luck.
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File Type: pdf box-plan.pdf (13.7 KB, 95 views)
File Type: pdf box-internals.pdf (13.8 KB, 40 views)
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Old 22nd October 2013, 01:42 PM   #2
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Well, good luck !!

There are some ( most of them ) faults in the reasoning that I found while reading the darbari project. I start from the bottom : the 6" will have an equalization like LT ?? Why ? (I would scale all the dimensions : 6 " woofer; 4" midrange and 3/4- 1" tweeter ); cone papers are floppy ? Why ? You're meaning that the cone doesn't follow the VC pistonic movement and changes in dispersion are uneven because only the very center emits the higher frequencies ? Well, paper is a very old material and of course there are better ones, but for other reasons (!?!).
The reasoning at the beginning about the reproduction of the voice might be true, but also slopes of the various drivers must be considered, e.g. 80 Hz Fc having 6 dB/oct slope would still play till 300 Hz (!?). Talking about vibrations and the way to confine them to inaudible levels, the only effective one is the one I exposed in the 'floating speaker enclosure' Thread
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Old 23rd October 2013, 07:48 AM   #3
tcpip is offline tcpip  India
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Quote:
There are some ( most of them ) faults in the reasoning that I found while reading the darbari project. I start from the bottom : the 6" will have an equalization like LT ?? Why ? (I would scale all the dimensions : 6 " woofer; 4" midrange and 3/4- 1" tweeter );
If a driver is put in a sealed enclosure, you don't know exactly how it will behave at the bottom end of its SPL curve, and what its F3 and Q will be. One either calculates this by box modelling and accurate sizing of box to get the desired Q and F3, or one designs an approximate box size and then uses LT to get the desired Q and F3. I am doing the latter. Nothing very revolutionary there.

After the 6" driver is fitted to the enclosure, I will take impedance measurements and get the "natural" Q and F3 of the driver in the enclosure. I will then plug these into the LT to get a Q of 0.7 and the F3 I want (I will probably go for 100Hz). This will give me a 2nd order high-pass at 100Hz. I will then add another 2nd order highpass at the same F3 to get a 4th order rolloff. As I said, nothing revolutionary here.

Quote:
cone papers are floppy ? Why ? You're meaning that the cone doesn't follow the VC pistonic movement and changes in dispersion are uneven because only the very center emits the higher frequencies ? Well, paper is a very old material and of course there are better ones, but for other reasons (!?!).
I think paper cones have higher second-order harmonics because they are not stiff and pistonic as much as hard metal cones. The fact that most paper cone drivers have higher low-order harmonics is quite well known, I believe.

Quote:
The reasoning at the beginning about the reproduction of the voice might be true, but also slopes of the various drivers must be considered, e.g. 80 Hz Fc having 6 dB/oct slope would still play till 300 Hz (!?).
Absolutely right. To address this, I intend to do 4th order acoustic for most of the slopes, if not steeper. This will minimise those problems, I feel.

In general, I don't know how people build first-order crossovers unless they are using full-range drivers. I much prefer higher-order unless I have a good reason to use lower-order slopes.

Quote:
Talking about vibrations and the way to confine them to inaudible levels, the only effective one is the one I exposed in the 'floating speaker enclosure' Thread
Yes, I guess such approaches are really excellent, but I am trying to get to 90% of that level with 20% of the effort.

Last edited by tcpip; 23rd October 2013 at 07:54 AM.
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Old 23rd October 2013, 11:56 AM   #4
Dissi is offline Dissi  Switzerland
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You know what you are doing and I wish you luck with your 3-way project. Just a little thing to consider. Maximum excursion of the drivers limits the low frequency extension of woofer and midrange. Thus 25 Hz and 100 Hz seems to be a little optimistic, I would rather expect 40 Hz and 200 Hz. However that's still fine IMO.
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File Type: jpg MaxSPLDaytonRS225-8.jpg (118.7 KB, 365 views)
File Type: jpg MaxSPLDaytonRS150-8.jpg (117.0 KB, 360 views)
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Old 23rd October 2013, 03:28 PM   #5
tcpip is offline tcpip  India
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Quote:
Originally Posted by Dissi View Post
Just a little thing to consider. Maximum excursion of the drivers limits the low frequency extension of woofer and midrange. Thus 25 Hz and 100 Hz seems to be a little optimistic, I would rather expect 40 Hz and 200 Hz. However that's still fine IMO.
You're probably right, but the question really is about the limits at a given SPL, isn't it? I may not have problems reaching low frequency levels at 5W and 10W power outputs, where I will listen at home.
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Old 7th November 2013, 02:17 AM   #6
tcpip is offline tcpip  India
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The building of enclosures has started. The woofer enclosure has good bracing, built as a separate assembly out of 20mm plywood, and inserted into the enclosures. The side walls will be clamped tightly to the bracing using screws and Araldite.

You can see some images of bracing here. These things are pretty impressive to look at, being about three feet tall.
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Old 23rd November 2013, 03:09 AM   #7
tcpip is offline tcpip  India
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Default Woofer box construction

The woofer enclosures are turning out well.

Click the image to open in full size. Click the image to open in full size.

The front baffle is being constructed out of three sheets. I am chamfering each sheet so that the cutout for the driver widens inside the box, creating as little reflections of the back wave as possible. (I guess this will be a much bigger issue for the midrange driver than for this one, since this one will have a a high-pass at 100-150Hz.)

Click the image to open in full size. Click the image to open in full size. Click the image to open in full size. Click the image to open in full size. Click the image to open in full size.

More details on my page here.

Last edited by tcpip; 23rd November 2013 at 03:13 AM.
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Old 23rd November 2013, 03:17 AM   #8
tcpip is offline tcpip  India
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Default The amplifier side of things

Am aiming to use Panson Audio's compact amplifier module for my six channels of amplification. LME49811-based modules with one pair of ThermalTrak OPS devices per channel. Am hoping they will serve this application well. They are a bit underpowered for my taste -- would have loved it if they just had two pairs of OPS devices instead of one, but then I have to make do with what I am getting.

I will also be adding speaker protection and amplifier soft-start modules to the amplifiers. I am thinking of making two chassis, with four amplifier channels in each chassis. (I need three per side; the fourth will be free for now.)

When the left channel and the right channel have completely separate circuits, can one call them "dual mono", even if three amp channels share a common transformer?
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Old 8th January 2014, 06:41 PM   #9
tcpip is offline tcpip  India
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The enclosures are almost ready.
Click the image to open in full size.
Click the image to open in full size.

I have yet to start work on the amplifiers. Am getting a new measurement mic (calibrated Dayton Audio mic) from Cross Spectrum Labs, and a new Behringer 302USB, for SPL measurements. Let's see how they work out. Am sure I will have to suffer a lot of pain figuring out how to configure this stack -- my old mic and USB sound card worked well but did not support XLR mic inputs, so could not use it with any of the calibrated mics available.

More details of construction on this page
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