# Backwards speaker design...



## aceinc (Oct 24, 2006)

Due to my woodworking skills, I want to use some Parts Express cabinets to build some speakers. My thought was to use two separate cabinets per side. For the bass, I was going to use these;

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=302-753

They have a 1 cubic foot volume. Using this cabinet, what is the best (lowest, cleanest, most efficient) bass I can get, using moderately priced drivers? I was thinking a pair of 8" or an 8"x12" speaker would work. My crossover from this cabinet would probably be in the 120hz-150hz range.

I don't believe that I need to be concerned about matching the mid/tweeter, as I intend to put L-Pads as part of each of the outputs of the cross over. That and it would be fairly hard to get a cabinet of this size to provide both low extension and high enough efficiency, as to exceed the rest of the components.

The final design will be a three way, but for the moment I am focused on the bass section. This is not quite a subwoofer design exercise, but comes close.

Paul


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## fusseli (May 1, 2007)

Sounds like a cool project. I'm picturing the bass cabs sitting on the floor and the smaller cabs sitting on top, connected with a stand of some kind. If I'm understanding, you essentially want a passive sub that will complete a 3-way speaker? Be careful in the size of the driver you select, I'm seeing that the baffle of those 1cuft cabs is only 7.5" usable width.

For efficiency and this size it sounds like a vented alignment is the way to go. Can you run 4 ohms or does it need to be 8?

At a glance, a quality 6.5" midbass http://www.parts-express.com/pe/pshowdetl.cfm?&DID=7&Partnumber=264-874&ctab=1#Tabs
Single one of those in 1cuft tuned to 35Hz gets an f3 of 39Hz, handles about 10W. Put an infrasonic filter on it and it handles full power which translates to 104dB. Pretty decent.

The TangBand 6x9" sub http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-837 doesn't extend as low in 1cuft, but would handle more power it looks like. Either would need a 2.5" vent or larger.


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## lsiberian (Mar 24, 2009)

You might consider asking a cabinet builder to build something for you. A sealed speaker is trivial for any cabinet builder.


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## fusseli (May 1, 2007)

Another candidate could be the 7" Dayton DA175-8. A single one vented plays real low, f3 of almost 30Hz! Just wouldn't handle much power. Two of them sealed would get decently loud, though. Here's the four configurations I've suggested so far, all at about what I'd say their limits before bottoming out. There's a wide range of LF extension and SPL.

I personally kind like the two cheaper dayton drivers in the sealed config. Shallowest rolloff and would play far tighter than the others (yellow). Advantage being you could also cross these up into the kHz range.

Also, the little TangBand sub http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-832 would extend to an f3 of 29Hz and a full 50W in a 0.75cuft vented box. That's probably the next best option, IMO (light blue). THis would probably go for the lower xover point the better.


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## aceinc (Oct 24, 2006)

Russ:

Thanks for the work. Think we could shoe horn two of the W6-1139SI into 1 cubic foot, to get better power handling & efficiency? Without sacrificing too much bottom end?

Yes, my thought is to build a full 3 way in two separate cabinets, with the smaller cabinet crosed over in the 120-150 hz range. The two cabinets would be connected with some sort of stand. I haven't thought through the design completely, as I need to get a relatively good bass subsystem first, or the rest really doesn't matter.

Paul


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## 1Michael (Nov 2, 2006)

Two of these http://www.parts-express.com/pe/showdetl.cfm?Partnumber=295-374 or the 8Ohm version, in that box, is what I have for my Modula MTM's, sealed. I think they sound pretty good but if you get into the vented thing, be aware that it is quite the pain in the back side to install the port. Check out the Modula thread for directions on how to do that...


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## aceinc (Oct 24, 2006)

Any idea what kind of response curve you get? I haven't looked at WinISD yet to see what it says.

Paul


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## 1Michael (Nov 2, 2006)

http://www.htguide.com/forum/showthread.php4?t=11321


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## fusseli (May 1, 2007)

Two W6-1139SI work well in 1cuft but need at least a 3" port (gray/100W), it appears. They also would handle lots of power since they have a huge xmax.

The Dayton RS180's (green/40W) of the Modula MT wouldn't play nearly as low as the cheaper DA175's (yellow/20W) in a sealed config, but would handle more power. Neither would do well in 1 cube vented.

From the looks of it, the little TangBand subs are what you're probably looking for if you want LF extension and max power handling. Those with baffle step would only be around ~80dB of sensitivity though, when integrating into the rest of the speaker system. The bright side being that they'd handle enough power to make up for that. 











Will you have a sub also? If these are for HT and not music a rumble filter might be a safe idea still for stuff below 25Hz. Otherwise if it's music only, I'd call them safe.


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## aceinc (Oct 24, 2006)

I do not understand how you came up with 80 db sensitivity on the tang band option.

The specs say that the driver is 83 db, I am using two which should yield an additional 3 db. The cabinet is ported which should provide another 3 db. My rough calculation would be 89db. How am I going wrong?

Paul


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## fusseli (May 1, 2007)

aceinc said:


> I do not understand how you came up with 80 db sensitivity on the tang band option.
> 
> The specs say that the driver is 83 db, I am using two which should yield an additional 3 db. The cabinet is ported which should provide another 3 db. My rough calculation would be 89db. How am I going wrong?
> 
> Paul


The port only adds LF end of things, since we're tuning low it won't boost the entire output of the speaker. The two TBs would be 86dB together, BUT, you are integrating them into a passive 3-way speaker where baffle step will need to be accounted for. Thats what will eat up probably another 4-6dB of sensitivity.


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## aceinc (Oct 24, 2006)

My understanding on baffle step is that it boosts frequencies much higher than what this cabinet would be designed to output. 

Are you saying that the specs provided by PE are based on putting the driver in the center of a very large baffle? If not, I do not understand how placing these drivers in this cabinet would yield a loss of 3db below the published specs (assuming they are honest specs of course).

Paul


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## fusseli (May 1, 2007)

aceinc said:


> My understanding on baffle step is that it boosts frequencies much higher than what this cabinet would be designed to output.
> 
> Are you saying that the specs provided by PE are based on putting the driver in the center of a very large baffle? If not, I do not understand how placing these drivers in this cabinet would yield a loss of 3db below the published specs (assuming they are honest specs of course).
> 
> Paul


Baffle step doesn't boost highs, it cuts lows. This is because low frequencies below baffle step radiate in all directions rather than beam straight forward like high frequencies, meaning the sound radiating all around is lost acoustic power unless you put the speaker in a corner, or against/in the wall. And yes to my understanding 99.99% of all driver data is measured from a very large baffle.

I've run the BSC simulation with the published data for the TB driver, two series in the vented Dayton 1cuft cabinet, the results are below. Do you have Excel 2007? That's what all of the Jeff Bagby software that I use runs in. Looks like two of those in series is even lower sensitivity than I thought, would probably be looking at a 75dB/1W 8ohm speaker system. If you run 100W of good power though, 100dB of SPL is still a reality. Finding a tweet and midrange to handle that power shouldn't be an issue, either. 

The only way to increase this would be to get a bigger LF cabinet and driver, or consider making it a 2.5-way. E.g. my own 3-ways are 85dB final, and that's with a 12" woofer. Sensitivity drop due to BSC is an issue with any full-range speaker design. Small drivers that reach low are often low sensitivity, so I think this is pretty typical. In my opinion this is looking great. The RS180s and other drivers would have higher sensitivity as we've seen, but they can't touch the LF extension these TB subs get in that small of a box.

I'm going to write a thread now on my own lessons learned in BSC, hopefully that will illustrate some things better.


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