Opinions on this HT-sub design please.

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For the DIY home theatre, I'm building a 5 channel amplifier and five TL-speakers with *almost-full range* drivers ;)
And a sub, of course...

This sub would be 680l internal volume and be tuned at about 25Hz.
Am I doing something that will be less then satisfying compared to this size?
It would be a pity to waste all the material and work, if it is doomed to fail.
So please, some advice would be appreciated.
An externally hosted image should be here but it was not working when we last tested it.
 
Thanks for the reply.
Yes, if tuned at 18Hz, it has a -3dB point at 18Hz and it's quite flat then. But is this better just because it is flatter?...

I thought the hump might compensate for the hearing loss that occurs when getting that low and that sound lower then 30hz is not around a lot of the time anyway.

I'm not the expert, so more thoughts and comment is welcome!
 
it is common practice to try to achieve a flat response. bumps such as this are usually described as "boomy, one note, sluggish etc. bass". but since your room modes will certainly mess with the response much more than a 4db peak does, one could say, that under real life conditions, it wont be a problem. from an audiophile point of view, such a peak would of course be an utter sin.
 
MaVo said:
it is common practice to try to achieve a flat response. bumps such as this are usually described as "boomy, one note, sluggish etc. bass". but since your room modes will certainly mess with the response much more than a 4db peak does, one could say, that under real life conditions, it wont be a problem. from an audiophile point of view, such a peak would of course be an utter sin.
It's not at 50Hz or 60Hz, so 'boomy' would not really be a good name for it. But I know what you're saying. The room is about 10m, so at 34Hz it will go up, but at 30Hz it will be lower again and that is the bump I've put in the tuning.
 
These 4 woofers, configured as two times iso-baric, take only the space in a bass reflex enclosure as if it would be one driver only.
The ideal volume, according to WinISD, would be 853l, so building more then one sub could only mean building two subs, each having an iso-baric configuration, otherwise it would take up double the space. :xeye:
One box of 680l is already very large, even if it takes just one location.
A second box would take to much of my wife's good will. :D

I had a quick look at that PDF-file, can't do that even if I would want to.
It's not about sound quality as in HI-FI, it's for home theatre and occasionally a bit of music.
The five other satellite speakers will not be much of high quality either and these woofers have been laying in the garage for a lot of years now, time to design something with them, even if they have a large VAS, I can't just chuck them out and buy others.

The lower F3 is very appealing but with 680l it's not really optimal.
I am tempted to take the lower F3 anyway though. tuning frequency=17.9Hz F3=16.7Hz :bigeyes:

The specs: (don't laugh ;) )

Radio Shack 15" 40-1301
Fs: 20Hz,
VAS 21.0Ft^3,
QMS: 6.45,
QES: 0.485,
QTS: 0.45,
CMS: .564x10^-3,
Xmax: 0.694",
D: 13",
Area: .0856m^2

I don't know if all this is correct, it's the best I could find on the web, it's not even measured. :ashamed:

Can't do measurements, too bad...
 
I don't know if all this is correct, it's the best I could find on the web, it's not even measured.

Hi, Some simulations (3) using Radio Shack 40-1301 T/S parameters fond in document:

A Digital Approach to Actively Controlling Inherent Nonlinearities of Low Frequency Loudspeakers

Paul R. Williams General Motors Corporation Flint, Michigan
David G. Meyer School of Electrical Engineering Purdue University, West Lafayette, Indiana
Presented at the 87th AES Convention 1989 October 18-21 NewYork

Re = 5.6 ohms,
fo = 20 Hz,
Vas = 21.0 ft 3,
Qms = 6.45,
Qes = 0.485,
Qts = 0.45,
peak linear excursion = 0.347 inch,
gap flux density B = 8.0 Gauss,
power handling = 100 watts (peak),
voice coll diameter = 1.5 inches.

Expanded to suite MJK:s programs with Re = 5.6 Ohm,BL = 12.732 N/A, and SPL/1m/1W = 91.8 dB.

b

1(3)
 

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Greets!

FYI, the factory specs are somewhat different than those published here and RS was notorious for changing vendors/specs without updates, so I recommend designing based on a worst case scenario to ensure you have an adequately large cab: http://support.radioshack.com/support_audio/doc14/14173.htm

Anyway, you imply a ~5 m longest room dimension where a theoretical +12 dB/octave room gain curve begins and while few rooms achieve this over a wide BW, I don't understand why you think it will begin flattening out so quickly by ~30 Hz. If true, then some peaking at Fb is desirable IMO. Regardless, movies today typically have enough < 20 Hz content to justify at least a ~16 Hz Fb.

GM
 
… the factory specs are somewhat different than those published here…

Ok, Take my simulations with grain of salt i.e. they are probably overestimating the SPL capacity as I used the peak excursion when simulating.

The SPL readings should be lowered with 3 dB, the input power cut in half and excursion reduced by dividing with sqrt(2).

If the Radio Shack specifications is more reliable with: Peak-to-Peak (Maximum) Linear Excursion = 3.8 mm, the SPL curves must be reduced with about 16.4 dB which make the use of these drivers for HT subs very doubtfully and only if JND whispering levels are convenient.

b

1(1)
 

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Right, a worst case is making a very large, low tuned vented cab and still needing enough room gain to keep it linear down low and while it would barely make it to DD/DTS reference levels using all four drivers, it will still be loud enough for most folks.

Still, better IMO to use these as car trunk IB 'subs' as originally intended and get some high Xmax drivers better suited to HT.

GM
 
Maybe it's better not to go with bass reflex?

_______________________________
I know this is not the ideal driver for HT, because of the box size needed.
Using 4 is better of course, but still... ±800l ?!?

I do have the 1.7m length space that I can use, one meter high and about 40cm wide or a bit more.
I read a bit about transmission line's today and maybe that would be better, don't know. :xeye:

What if I made a Tline of about 5.5m, tapered smaller towards the end?
I'm not familiar with software for simulating TL, so if anyone can help me out...
(I'll look if I can sketch something with Google sketch-up)
 
Do you have said drivers already? If not I'd go with something else. After seeling the T/s params....I doubt these would work well at all for HT applications.

Maybe a 6th order bandpass. That will reduce excursion at 2 frequencies. Try it in WinISD, aim for a flat BW from 20 to 80Hz(or higher depending on your mains, crossover, etc) for movies.
 
Yes I have them already , that's just the reason why I would go for 2x iso baric. :xeye:

I had a long look at the HouseWrecker from Decware but I doubt that it would be good either with these drivers, don't know for sure of course.
It's kind of a 6th order bandpass.

Any thoughts on this TL?
Or is this set of woofers doomed to get thrown out:confused:
(TL not correct, just a sketch)
 

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If I can jump in here for a second (albeit a few months late)...

We are discussing two different drivers here. the Radioshack 40-1301 was not the same driver as the 40-1301A.

The 1301 (without the A) has an Xmax of .694 inches. Also lower Q values and higher efficiency.

I am looking at the spec sheet for the 1301 and it shows the following parameters:
Re = 5.6 ohms
Fs = 20 Hz
Cms = .564x10-3
Vas = 21.0 cubic feet
D = 13.0 inches
Sd = .0856 m3s
Mms = 113.5 grams
Qms = 6.45
Qes = 0.485
Qts = 0.45
Power = 100 W
Xd = 0.694 inches
SPL (1w@1m) = 90dB

Not a great driver, and somewhat limited in power handling, but certainly better than the 1301A.

I have a pair, and have been planning on building something with them, but they will still require a BIG box.

I suspect I will end up with an isobaric design because of the volume requirements.
 
WayneM,

Isobaric was also what I thought of building, even two of them or one big one with all four in there.
But even one isobaric enclosure is still very big for our little house, so now I have made a final decision.
Actually made this decision more then a month ago but I forgot about this thread myself. :rolleyes:

A bit more work but the linkwitz transform subwoofer it will be!
http://sound.westhost.com/project48.htm
http://sound.westhost.com/project71.htm
In my opinion this is the only good way if you need your space for other things then subs AND you get tight bass!

B.

→Now I just need to have some spare time...
 
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