ML-TQWT modelling the B102 question - Page 2 - diyAudio
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Old 8th October 2005, 02:18 AM   #11
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Wish I could get deeper response (F3 looks to be about 50 hz). Any suggestions?

Thanks.

Paul
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Old 8th October 2005, 03:13 PM   #12
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Try this on for size.

Click the image to open in full size.

The MathCAD worksheet looks like this

Bob
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Old 8th October 2005, 10:50 PM   #13
amt is offline amt  United States
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Bob, that looks pretty flat. I notice that the software version I have doesnt include the extra resistance field, and yours doesnt include the driver placement field. Where is the driver placed, or have I overlooked something?

Martin, so the BSC is really manditory for this drive, or else the frequency response will really be down by 3-4 db below 100hz or so?

Paul, Ive been eyeing this driver for a couple years, but once the Druid made its debut, I felt compelled to try and use it. A friend thats bass savy has said that they are a nice sounding speaker and has listened to the them numerous times. I will probably use a Fostex FT17H.

amt
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Old 8th October 2005, 10:52 PM   #14
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That looks great! Can you explain why a shorter box went deeper? Seems counterintuitive to me.

Also, will a 4" port be big enough? There's not much excursion going on, so perhaps chuffing will not be a problem? I figured I would use multiple ports.

Thanks!

Paul
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Old 8th October 2005, 11:33 PM   #15
MJK is offline MJK  United States
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The response looks much better.

Quote:
I notice that the software version I have doesnt include the extra resistance field, and yours doesnt include the driver placement field. Where is the driver placed, or have I overlooked something?
I think Bob just editted the original file. If you have a full version of MathCad you can set up the input area in any way that is convenient.

Quote:
so the BSC is really manditory for this drive, or else the frequency response will really be down by 3-4 db below 100hz or so?
Yes, I think some form of baffle step compensation will be needed to produce a balanced bass output.
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Old 9th October 2005, 02:46 AM   #16
GM is offline GM  United States
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Greets!

BB,

FYI, the Qts calc is wrong due to the need to subtract 'Rs' from 'Re' in the Qes field, so the additional formula should be either Re/(Re-Rs) or MJK's Re*(Re-Rs)^-1

GM
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Old 9th October 2005, 02:55 PM   #17
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Quote:
Originally posted by amt
Bob, that looks pretty flat. I notice that the software version I have doesnt include the extra resistance field, and yours doesnt include the driver placement field. Where is the driver placed, or have I overlooked something?

amt
I did indeed edit MJK's worksheet to add the Rs fields. Also, you can do calculations of the right side of the screen to confirm area, etc.

The driver placement is xo in the Closed End of Transmission Line section.

Quote:
Originally posted by Paul Ebert
That looks great! Can you explain why a shorter box went deeper? Seems counterintuitive to me.

Also, will a 4" port be big enough? There's not much excursion going on, so perhaps chuffing will not be a problem? I figured I would use multiple ports.

Thanks!

Paul
The whole combination of driver Fs/Vas, length, geometry and post size/length determines the shape of the FR plot. In general, a 40" straight MLTL or low taper TQWT will have F3 in the 40's.

The larger the port, the stronger the high order harmonics. You want the smallest port that you can live with before port noise becomes a problem. Given the low power levels this design will encounter before significant distorting sets in, 4" should be adequate.

BTW, one hint that your design needs some work is that you needed 0.6 lb/ft^3 stuffing to flatten out the humps and valleys. If you need more than 0.25 lb/ft^3, rethink what you are doing.

Understand that I spend maybe 15 minutes modeling this design. You should take this as a starting point and go from there.



Quote:
Originally posted by GM
Greets!

BB,

FYI, the Qts calc is wrong due to the need to subtract 'Rs' from 'Re' in the Qes field, so the additional formula should be either Re/(Re-Rs) or MJK's Re*(Re-Rs)^-1

GM [/B]
Oops!

Fortunately, the resulting plots are nearly identical. I've replaced the pdf.

Revised MathCAD worksheet

Bob
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Old 9th October 2005, 04:43 PM   #18
GM is offline GM  United States
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Greets!

FYI, since neither sections are 'locked', you can cut n' paste the 'X0 = L*x.xxx' into the 'ML TQWT Geometry......' section if you prefer.

Hmm, the way I calc them, I get the same FR plot except with a slightly smoother (though I imagine inaudible) HF BW with a much shorter straight ML-TL and slightly longer vent:

L = 26.1"
SO/SL = 171.434"^2
X0 = L*0.466
rp = 2"
Lp = 3.5"
same stuffing density/location as yours

Anyway, FWIW from my own stone age (minimal/coarse measurements) research I concluded that the pipe length basically just reduces the vent length, net Vb determining the shape ('fullness') of the FR/roff-off slope with driver location (and taper if applicable) determining the overall smoothness. This assumes the vent is near/at the bottom.

Hmm, I deleted both 'Qtd' calcs and the WS seems to work fine, with no obvious changes that I could see, so just brought it to your attention in case you/others used it for doing 'effective' Qts calcs.

GM
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Old 9th October 2005, 08:07 PM   #19
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Bob and Martin,

Thanks so much for your help. I'm learning some good info, here. I've got a lot of more general questions related to full range design (definitely, a novice). Since I don't want to hijack this thread, I think I'll take those to a new one.

There is one thing I'm curious about regarding the B102. An obvious difference between it and the driver used in the Druid is the aluminum phase plug. Ignoring the issue of making such a plug, is adding one something that can be done DIY? Also, what does such a plug buy you?

Paul
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Old 10th October 2005, 01:02 AM   #20
MJK is offline MJK  United States
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Quote:
Ignoring the issue of making such a plug, is adding one something that can be done DIY? Also, what does such a plug buy you?
I have no idea what the B102 driver is but I am sure a phase plug could be added in some form. Either a shaped plug or a socket head seems to be used most often. If you look in my gallery I added a picture of a homemade phase plug for a Lowther DX4 ML TQWT design. I have also seen people suspend a ping-pong ball in front of the driver, so suspending an object might be a method that does not require altering the driver if that is an issue.

I have experimented a little with phase plugs on my Lowther drivers. I have listened with no phase plug, the original bullet phase plug, the "shower head" phase plug from the DX4s, and a lightbulb phase plug from one of the horn applications. The light bulb phase plug seemed to degrade the high end sound. There was not much difference with the other three and if anything the original bullet sounded marginallly better then the other options. These are my opinions for my drivers in my room, your driver and situation might yield different results.
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