8" 'sub' and plate amp advice - diyAudio
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Old 12th April 2007, 01:45 AM   #1
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Default 8" 'sub' and plate amp advice

hey all, so I am trying to fit a sub into an existing enclosure that I found (vol = .812 cuft).
as the enclosure is a cylinder I don't have much room to mount the plate amp, the largest rectangle I can fit on the bottom of the box is about 8.5" x 10.5" (depending on the LxW ratio).
have been looking for suppliers and so far I have found madisound, parts express and apex jr, any of these I should steer clear of or others I am missing?
I have been doing some looking at the above suppliers web sites and my choices have come down to these:

speakers:

1. Apex Jr Super 8 Subwoofer ($39.95)
fs = 47.75 Hz
Qes = .552
Qts = .5140
Qtc = .707

F3 = 33.5894 Hz
Fb = 37.2682 Hz?
Vb = .8364 cuft
1.5" dia port L = 2.8771"

Ref eff. = 85.0153 db/w
EBP = 86.5

2. Peerless 8" CSC-X Woofer ($50.05)
fs = 28.2
Qes = .29
Qts = .27
Qtc = .707

F3 = 50.5191 Hz
Fb = 42.5250 Hz?
Vb = .7442 cuft
1.5" dia port L = 2.3192"

Ref eff. = 89.6687 db/w
EBP = 97.2414

1. Dayton QT210-4 8" Quatro series subwoofer ($49.75)
fs = 36 Hz
Qes = .42
Qts = .4
Qtc = .707

F3 = 36.4467 Hz
Fb = 36.3141 Hz?
Vb = .7973 cuft
1.5" dia port L = 3.3043"

Ref eff. = 85.9084 db/w
EBP = 85.71


Amplifiers:


Dayton SA100 plate amplifier ($94.34)

W @ 4 ohm = 100
W @ 8 ohm = 75


Dayton SA70 plate amplifier ($52.59)

W @ 4 ohm = 70
W @ 8 ohm = 45

any way I would appreciate any advice you could give me. thanks for your time.
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Old 12th April 2007, 08:26 AM   #2
Shaun is offline Shaun  South Africa
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I have used the ApexJr Super8 driver. It is quite good for the price. It is, however, a true sub in that it has a very much rolled-off top end. So it does not integrate well with mini satellite speakers because it leaves a hole in the system response between the two units.

As far as the low end is concerned, some T/s modelling will tell you which unit is better. I like this driver for what it does and what it costs. PM me with your email address, and I'll send you my design for a slotted BR box.
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Old 12th April 2007, 02:50 PM   #3
tinitus is offline tinitus  Europe
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Obviosly not easy o find a cheap true 8" sub driver with low Fs

But I think this Hivi D8.8 looks quite nice with 4" voice coil and Fs=30hz - but its a 9" and cost a little more

http://www.madisound.com/cgi-bin/ind...28009&pid=1834
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Old 12th April 2007, 03:02 PM   #4
Shaun is offline Shaun  South Africa
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I agree. When you start by defining the woofer size, you automatically place a restriction on low frequency extension. But it comes down to what you want from the sub. Have realistic expectations, and you won't be disappointed.
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Old 12th April 2007, 03:27 PM   #5
tinitus is offline tinitus  Europe
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Question is if it would be better to choose a nice driver and build the right cabinet
Then it would make sense later on to build another sub
With 8ohm drivers they could both be driven from the same subamp

To start with the cabinet and then try to find a driver that will ALMOST work, is not the ideal situation and could be waste of money that could have been spend better
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Old 12th April 2007, 07:32 PM   #6
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thanks again, i understand the limitations of trying to fit components to an existing box but i am willing to take the risk cuz the box is just so damn cool. i plan to use the sub to complement a full range stereo system (not that i have the stereo speakers yet but figured i would start small).

so...

T/s modelling?.... is this just using using the various free web based calculators to find the optimum box volume given my speaker specs such as Qes, Qts and Qtc, or is there something more i am missing?

Don't know if this is a dumb question, but... i cant seem to find the nominal resistance of the super 8, the Re is 2.653, is this not low even for a nominal R of 4?

Similarly, the power handling info also seems to be missing, can i extrapolate this info from the T-s characteristics, or am i just supposed to know?

if i go for the super 8 then with a 1.5" port the recommended volume is .8364 cuft and i found that in fact my box is .7498 cuft, could the addition of damping overcome this discrepancy?

on the other hand if i seal the port the recommended volume is .4215 cuft, this seems like the better option as i assume the volume of the speaker itself and any volume taken up by the plate amp need to be subtracted from the .7498 (plus getting rid of the port tube in the base would allow me to use a bigger plate amp).

Shaun, what sort of amp did you use with the super 8?

any one else have any good, cheap amp suggestions?

sorry, i am kinda just thinking out loud here, thanks for the help.
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Old 13th April 2007, 12:40 PM   #7
Shaun is offline Shaun  South Africa
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Quote:
Originally posted by 1234567890
so...
T/s modelling?.... is this just using using the various free web based calculators to find the optimum box volume given my speaker specs such as Qes, Qts and Qtc, <snip>?
Yes. It will tell you how (or if) you can use the volume you intend using as an enclosure

Quote:
Originally posted by 1234567890
Don't know if this is a dumb question, but... i cant seem to find the nominal resistance of the super 8, the Re is 2.653, is this not low even for a nominal R of 4?
It is OK. The 4 ohm rating is more of an impedance (Z, not R)category than a spec.

Quote:
Originally posted by 1234567890
Similarly, the power handling info also seems to be missing, can i extrapolate this info from the T-s characteristics, or am i just supposed to know?
No. My guess is it's anywhere between 70W and 100W

Quote:
Originally posted by 1234567890
if i go for the super 8 then with a 1.5" port the recommended volume is .8364 cuft and i found that in fact my box is .7498 cuft, could the addition of damping overcome this discrepancy?
No, unless you're using a sealed box. Model the system with the actual enclosure volume minus the displacement of the driver and port. It may still be OK.


Quote:
Originally posted by 1234567890
on the other hand if i seal the port the recommended volume is .4215 cuft, this seems like the better option as i assume the volume of the speaker itself and any volume taken up by the plate amp need to be subtracted from the .7498 (plus getting rid of the port tube in the base would allow me to use a bigger plate amp).
Yes. But the sealed version would have a higher cut-off frequency.

Quote:
Originally posted by 1234567890
Shaun, what sort of amp did you use with the super 8?
ApexJr had a 100W Cerwin-Vega! amp available a while back. That's what I used
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Old 14th April 2007, 12:36 PM   #8
AJinFLA is offline AJinFLA  United States
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This amp should fit MCM 100w
My driver choices would be W8740p W81363 or GTO804 available here Sonix .
The 740 puts you near $100 total cost, the 1363 reduces weight and the GTO804 would probably me my choice for overall performance in a small sealed enclosure.

cheers,

AJ
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