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Old 14th December 2001, 01:01 PM   #1
pkgum is offline pkgum  Australia
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Default SPL good enough?

Running through the t/s parameters of a 15" Blueprint 1503 driver in computer software(winISD) told me that if the Blueprint was put into a 120L sealed 0.5qtc box it would produce the following approximate SPL at 1000W power without room gain:

10Hz - 95Db
15Hz - 102Db
20Hz - 105.5Db
25Hz - 108Db
30Hz - 110Db
40Hz - 112.5Db
50Hz - 114Db
60Hz - 115Db

The driver has a EXCEPTIONAL Xmax of 25.86mm

Is the driver being used to its full SPL potential in a sealed box or can it be better?
If a driver has that much excursion it should produce alot more SPL than what I have listed. Or is this the limit in SPL of a BP1503 in a sealed enclosure?
Heard that a PR box using a 12" peerless xls driver achieves identical SPL but the Blueprint has TWICE THE AMOUNT OF EXCURSION OF THE PEERLESS plus its displacement can swallow up the displacement of 2.5 peerlesses anyway

NOTE: Don't suggest to me to use a ported or PR..etc box....the piont is that I'm trying to extract maximum SPL from only a sealed box from the BP1503
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Old 14th December 2001, 01:04 PM   #2
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It is likely that at some point along that plot you will have exceeded Xmax ... you will need to check that by simulating it in software.

Also is that Xmax you quoted one-way or peak to peak?
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Old 14th December 2001, 03:27 PM   #3
Wizard of Kelts
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Gum:

Your quote: "Heard that a PR box using a 12" peerless xls driver achieves identical SPL but the Blueprint has TWICE THE AMOUNT OF EXCURSION OF THE PEERLESS plus its displacement can swallow up the displacement of 2.5 peerlesses anyway".

The Peerless is in a Passive Radiator box. The reason we have ported and passive radiator boxes-essentially the same principle-is that the action of the port or passive radiator REPLACES the excursion of the cone.

There is a reason that designers recommend that the passive radiator have AT LEAST twice the displacement of the driven speaker. You have just discovered it.

In fact, in most well built ported boxes, at resonance the speaker is moving only ONE FOURTH the distance it would have to move if it had to produce the same frequency without a port or passive radiator. Passive radiator boxes operate on similar principles to ported boxes.

Put a speaker in a sealed box. Measure the excursion at a given bass frequency and a given spl. Now, vent the box and tune to that frequency. Adjust the power so the SPL is identical to the sealed box. Your excursion will be between one fourth and one half of the excursion of the same speaker in the sealed box.

If the sealed box is operating at max excursion, the ported box will have between 2 and 4 times more travel to go before it hits max excursion. Passive radiators are similar.

AudioFreak: That 25 mm, (1 inch), excursion is one way for the Blueprint 1503.
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Old 14th December 2001, 10:32 PM   #4
Wizard of Kelts
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Gum:

Something seems amiss with those numbers that WinISD gave you for the SPL the Blueprint 1503 can give you at various frequencies.

For example, at 15 Hz, the SPL that a 1000W amp can achieve with it in a 120 liter sealed box is 102 dB. At 30 Hz-one octave higher-it is 110 dB. The difference is 8 dB.

Even if the speaker/box combo was flat all the way down to 15 Hz, instead of beginning to roll off, these numbers would appear suspicious. With the rolloff factored in, the situation is worse.

If a speaker is at 102 dB at max excursion, then when it goes one octave higher, it should be able to crank out 12 dB more. That is because it takes only one fourth the air volume moved to produce a sound that is one octave higher at the same SPL. Since the speaker, at 30 Hz, only needs one fourth the excursion to maintain it's SPL level that it needed at 15 Hz, when it goes to it's max excursion at 30 Hz it will produce 12 dB higher SPL.

4 times the air displaced equals either:
a) the same SPL at one octave lower frequency
or
b) 12 dB higher SPL at the same frequency .

Moreover, since the output at constant voltage is rolling off from 30 Hz to 15 Hz, the output at 30 Hz from a 1000W amp should be much more than 12 dB higher than it is at 15 Hz.

Something appears wrong.
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Old 15th December 2001, 05:04 AM   #5
pkgum is offline pkgum  Australia
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something is wrong....I'm not on the right track? This post is to make sure I'm using the software the right way
here are the details of the driver

Click the image to open in full size.


someone plot the stats from the DUMAX report into their loudspeaker design software
(Your software has to be capable of graphing the SPL at max power)

choose a sealed box then modify the box so it is at 0.5qtc

power handling should be 1000W RMS

Note the max SPL graph....anything different...if so PLEASE POST IT HERE

If the SPL readings are the same as the ones I've posted here then I know that I'm on the right track.
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Old 15th December 2001, 05:15 AM   #6
Wizard of Kelts
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Just thought I would throw in that the volume of air to achieve 112 dB at 15 Hz is about 295 cu inches, or 4600 cubic centimeters. Do not forget to convert 25 mm excursion into 2.5 cm excursion when you figure Vd if you use Metric.

Also at 112 dB:

20 Hz = 129 cu in. or 2015 cc
25 Hz = 100 cu in. or 1560 cc
30 Hz = 74 cu. in or 1155 cc

At 106 dB:

15 Hz = 147 cu in. or 2304 cc
20 Hz = 64 cu in. or 1009 cc
25 Hz = 50 cu in. or 781 cc
30 Hz = 37 cu in. or 578 cc

These figures apply no matter how powerful your amp is. These amounts of air must be moved if these SPL's are to be achieved in a sealed box. These Vd, (Volume of Displaced air) are calculated using the center-to-peak figure of the max excursion. Divide peak-to-peak excursion in half to get that figure.
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Old 15th December 2001, 05:34 AM   #7
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The Vd of the 1503 = Sd X Xmax, (one-way) which is:
804 cmsq X 2.5 cm Xmax, (one-way) equals : 2010 cc.

The Vd of the 1503 = 2010 cc.
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Old 15th December 2001, 05:45 AM   #8
pkgum is offline pkgum  Australia
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kelticwizard,

I know that in sealed cabinets the response drops 12Db/octave after F3 (I think)

But I can't help it. Maybe Win ISD is wrong......I'm here just asking to make sure that I designed a proper sealed enclosure for the 1503......an enclosure that can harness its full potential with fastest group delay and extreme SPL
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Old 15th December 2001, 06:09 AM   #9
Wizard of Kelts
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The max SPL is limited by the efficiency of the Blueprint and it's rolloff characteristic rather than lack of Vd.

I ran a frequency response chart on Boxplot for 107 liters, (Boxplot suggests you allow for making box 10% larger than the printout), which will give me a response for a box that 120 liters, sealed.

At 15 Hz, the 1503 in a 120 liter box plays at 75 SPL @ 1 Watt/Meter. So at 1000 Watts, you raise the SPL 30 dB to 105 dB. Actually , that coincides with it's Vd of 2010 cc approximately.

These other frequencies are not limited by the Vd of the 1503.
All are 30 dB above what the 1 Watt/Meter reading is. That is what 1000 watts delivers-30 dB above the 1 Watt reading.

20 Hz = 109 dB
25 Hz = 112 dB
30 Hz = 114 dB
40 Hz = 116 dB
50 Hz = 118 dB

These are somewhat higher than your program allows. Room gain is NOT taken into account.

Check your frequency response chart at 1 Watt readings. Is the 1503 30 dB down from these figures at the appropriate frequencies? Remember, the 1503 sensitivity if 91 dB@ 1 Watt. If it is not, we have a conflict on our programs.
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Old 15th December 2001, 06:55 AM   #10
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winISD can handle high power without a problem and it's results agree with boxplot and WinSpeakerz the trouble is in the accuracy of the driver database which comes with these or other such programs.... upon looking at them i have gotten 3 different sets of data from 3 different database entries in different programs............
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