ML-TQWT modelling the B102 question - diyAudio
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Old 7th October 2005, 09:04 PM   #1
amt is offline amt  United States
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Default ML-TQWT modelling the B102 question

Ive been fooling around with Martin Kings ML-TQWT program and have come to an impass. The below output is as optimal as I have gotten thus far. I would like to flatten the response out a bit more but cant seem to get the parameters dialed in to do so. Does this look about as good as can expected or can it still be manipulated further?
As if so, what combination will do this?

Thanks, amt
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File Type: jpg mltl b102.jpg (36.3 KB, 441 views)
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Old 7th October 2005, 09:44 PM   #2
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You have left us a little short of details to make any recommendations. I would like to see the entire input section and at least the driver/port spl plot. Without any details, my guess is that you are trying to tune the pipe way too low.

Bob
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Old 7th October 2005, 09:47 PM   #3
MJK is offline MJK  United States
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From the plot, it looks like a very low Qts driver. Have you considered adding some series resistance to tame the rising SPL response?
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Old 7th October 2005, 10:44 PM   #4
amt is offline amt  United States
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Great! I conjured up the experts.

Since I cant save the work, Ive had to write down the parameters and so here they are. I havent added any series resistance and to be honest, hadnt thought of doing so.

Fs 45
Re 5.66
Le .67
Bl 13.8
Sd .0449 m2
Vas 73.51 liters
Qe .24
Qm 7.07
Qt .23

L = 52
driver position = .4
So = 1
SL = 3
Density = .25
rPort = 2
lPort = 5.5

Im more concerned with efficiency than lowering the response.

amt
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Old 7th October 2005, 11:45 PM   #5
MJK is offline MJK  United States
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For that low value of Qts, I don't think a ML TQWT or ML TL is going to work well without a serious correction circuit. Remember that you still need to account for an additional 3 - 4 dB of low end loss for the baffle step which is not included in the MathCad calculated SPL response.
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Old 8th October 2005, 01:16 AM   #6
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I, too, am interested in this driver. I was able to model the attached response. Perhaps a bit of an improvement?

My parameters where:

L = 50
driver position = .45
So = 1
SL = 3
Density = .6
rPort = 4 (don't want any port noise or compression)
lPort = 6

I notice from the published frequency response that there is a dip between around 300 and 700 hz. Perhaps that would even out the response a bit.

I wonder what the response would look like in this enclosure above 1k.

BTW, I've always been uncertain about the driver position. Is it the % from the closed end? As in (50 x 0.45) = 22.5 inches from the closed end?

Thanks.

Paul Ebert
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Old 8th October 2005, 01:23 AM   #7
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amt,

Are you considering doing something with this driver?

After hearing the Druids (and, unfortunately, anticipating that I will not be able to afford buying a pair ), I'm thinking about giving it a go.

I'd probably add a suitably high efficiency tweeter. Probably a ribbon.

Paul Ebert
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Old 8th October 2005, 01:38 AM   #8
MJK is offline MJK  United States
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Quote:
I wonder what the response would look like in this enclosure above 1k.
Probably very close to the driver's measured response o a spec sheet.


Quote:
BTW, I've always been uncertain about the driver position. Is it the % from the closed end? As in (50 x 0.45) = 22.5 inches from the closed end?
You have it correct.

I still think that the comments in my second post hold. Paul's design is better but is still down about 5 dB from the response at 1 kHz. I think that without a correction circuit the bass will be very weak.
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Old 8th October 2005, 01:58 AM   #9
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Martin,

I simply increased Re by 2.4 (for a total of 8.06) and got the attached plot. Looks pretty good to me.

Is that all there is to it (adding 2.4 ohms)? Or, would I want to add more to deal with BSC?

Thanks!

Paul
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Old 8th October 2005, 02:09 AM   #10
MJK is offline MJK  United States
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Quote:
Is that all there is to it (adding 2.4 ohms)? Or, would I want to add more to deal with BSC?
That looks much better. But you still need to deal with the baffle step in some way. For my Lowther systems, I end up using an 8 to 10 ohm parallel resistor in the correction circuit to overcome baffle step and the low Qts of the different Lowthers drivers. I use SS amps, a tube amp would require a lower value of resistance. You can use a circuit, try room placement, or some combination of the two to get a flat response and decent bass.
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