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Discussion Starter · #1 ·
Hi all,

I am wanting to build a compact 100 liter ported sub, I already have a 18mm ply enclosure suitable for a 15" driver. This enclosure has two slot ports which are 5 1/5" by 1 3/4" is size cut out on the front baffle. Yes it's a PA bass cab which is sitting unused so I am thinking I can use it for another budget sub that's compact and easy to move around.

The enclosure is an old Peavy, internal measurements are 22 3/4" wide + 18 1/2" high + 16" deep.

I would like to do a simple modification to this, I can if required seal up the ports and fit another, but I was wondering if I could fit a passive filter to cut bass below 25Hz and if this would affect any through put?

I have a JBL GTO-1502D 15" car audio bass driver for using with the above enclosure.

It does look like I could tune it to 25Hz with a single 3.23 + 8" port and by keeping program material below 200W cone excursion looks fine if I use a 25Hz Butterworth High Pass filter. Can I add this filter as a passive crossover type component?

Edit; Cab tuning to 19Hz with a 19Hz high pass also looks possible?

Any opinions or tips on this?

Many thanks guys,
Steve
 

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Hi all,

It does look like I could tune it to 25Hz with a single 3.23 + 8" port and by keeping program material below 200W cone excursion looks fine if I use a 25Hz Butterworth High Pass filter. Can I add this filter as a passive crossover type component?
The problem you run into would be the large size of coils, capacitors and dummy load = not cheap. :spend:
Then you have to consider the dummy 8Ω load needed for the sub 25Hz content.
If you are running 500 Watts it needs to be able to dissipate the 500 Watts in a worst case scenario.

As Mike says, do the filtering before the power amp, easier and cheaper. :T
 

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Discussion Starter · #4 · (Edited)
You would be better off using an electronic device like the Reckhorn B1 or B2. What are you using for an amp?
Hi Mike,

Do the Reckhorn units have adjustable or pre-set/switcheable rumble filters? I plan to use it from the mono sub out of an AV amp. Power amp will either be a Classe CA-100 bridged, or a PA power amp which I can't remember the name of, Samson I think.

The cab in question is around 100L I think, not well braced, a single narrow port looks like it will have very high port velocity, how may this affect the sound?

The 25Hz tuning with a high pass at 25Hz looks the best option for cone excursion and power. I am not sure what two 51/5" by 1.3/4" ports equate to tuning wise, I guess around 70Hz?

Edit; Is there a difference between the B1 and B2? Edit; High Cut!

Edit would an electronic crossover be useable as a rumble filter type unit, such as a Behringer model?
 

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Hi Mike,

Do the Reckhorn units have adjustable or pre-set/switcheable rumble filters? I plan to use it from the mono sub out of an AV amp. Power amp will either be a Classe CA-100 bridged, or a PA power amp which I can't remember the name of, Samson I think.

The cab in question is around 100L I think, not well braced, a single narrow port looks like it will have very high port velocity, how may this affect the sound?

The 25Hz tuning with a high pass at 25Hz looks the best option for cone excursion and power. I am not sure what two 51/5" by 1.3/4" ports equate to tuning wise, I guess around 70Hz?

Edit; Is there a difference between the B1 and B2? Edit; High Cut!

Edit would an electronic crossover be useable as a rumble filter type unit, such as a Behringer model?
1 3/4 is much to narrow. I know of no driver on the planet that should be ported that way. Get bigger ports or seal the thing. 1 3/4" will get you nothing but port noise and distortion.
 

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Discussion Starter · #6 · (Edited)
Hi Lsiberian, the cab was a PA cab, Peavey Bass Flex with a blown driver hence the ports.

I think I will put a new port in,

A couple of 15mm mdf corners can fill up the slot ports with ease, I am thinking of adding a couple of batton or dowel braces? I have it lined with foam egg crate type stuff. Was thinking of putting a bed pillow in each too?

Problem is I need a 4" port 20" long and do not have much room to play with, so I guess I need some sort of bend or flexability to snake it around inside the cab?

Any ideas what I can buy such a 4" port within the UK?
 

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Discussion Starter · #8 · (Edited)
Well the box is already constructed, and there are two 5.5" + 1.75" slots in the front baffle which dont seem suitable.

Due to the small size of the box WinISD states a required length of 59" for a 6" diameter port? With a 25Hz tune I can keep cone excusion within limits with a 12.5" long 4" port which keeps port velocity under 20ms.

I can also use a single slot port 5.5" wide + 1.75" tall with a length of 10" to tune to around 24Hz/25Hz with a peak port velocity of 24.5mz. Should the port length be from the front of the baffle?
 

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Discussion Starter · #9 ·
Well I have got some port tubing from an old paper mill.

76mm internal diameter, 10mm thick and pratically MDF like in construction. So I will use 76mm diameter porting.

The cab is 18mm ply with an 18mm MDF front, internal dimensions are 23.75" wide, 18.5" high 16" deep. which equates to 115.201 Litres of cabinet. there is a 1" by 18mm strip along the back panel and each side panel. Taking this minimal bracing into account gives a 114.5 litre cab.

I have made little mdf plugs the exact shape and size of the slot ports, and used them to fill in the slots so there is now no slot ports and I can fit a new port.

I can use a single port from 9.5" to keep port velocity down, I am aiming to tune between 18Hz to 25Hz.

Now a single port is simpler, it takes up a lot less cab space, but the relevant tuning means I exceed Xmax by 1mm to 1.5mm with 300w signal and a 25Hz HP filter.

In comparison a 25Hz tune with a single port leads to high port velocity, and two ports reduce this but take up a lot of cab space. Two ports would be 12.74" long in a cab only 16" deep putting them around 4" from the rear panel.

I am thinking a single port 10" long would be better even though it means a little over excursion of 1mm from target? It would give me an 19.74Hz cab tune and port velocity would peak at 24.227ms around 20hz, though I would use a 25Hz hp.

Does this extra over excursion sound OK? and does the cab sound like a couple of battons would be beneficial for bracing?

Edit, is it ok for the open rear end of a port to be 3" to 4" from the back of the cabinet?
 

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Discussion Starter · #10 · (Edited)
Well I built two of these 106.5 Litre subs, both with a single 76mm port which around 12.5" long with a corner brace holding the rear of the port.

I had got the amp model wrong that I was borrowing, it was a W-Audio DA-1300 power amp which is rated at 650w per channel into 4ohm £200 retail. It can be run in stereo, mono parallel and bridged mono. http://prolight.co.uk/images/media/...df?PHPSESSID=4cde525b5af4dadbfe5cbe3c801c11df

So I had a single JBL GT-1502D in each cab, with the DVC wired in series to give a 4ohm load.

At this point I still don't have a rumble filter.

So we had a movie night, AV amp sub out connected with an RCA to XLR to the DA-1300 amp which was ran in mono parallel to both subs, these were sitting next to each other between the left and centre speaker.

I have to say I was a little disapointed with the result, punch, weight and depth were not as big as I hoped.

May still have to play around with set up and levels, what we did was do auto calibration on the Sony AV amp then later a quick manual small mains set up.

Still wonder if the 103db 8ohm sensitivity of the Cerwin Vega V152's used for the 7 main speakers is still difficult to match? The JBL driver is 93db 4ohm.

So not sure what the problem or answer is here, I expected a good kick at least, on paper the power amp looks reasonable, but I do wonder if the wattage is a little ambitious? It was not the last word in sound quality when I tried it with the Cerwin Vega's.

I was also wondering if there could have been a phase issue or some cancelation, could a port cause such? Or if it was plain old lack of volume ability? I tried a single Cerwin Vega and single 106L JBL sub with the DA-1300 to see what difference there may have been in levels, I used the front panel volume potts, with the bass attenuation up full the Cerwin Vega was drowning out the bass box at a quarter attenuation!

Any opinions or thoughts? Does the amp sound worthwhile? Are the subs just too small and insensitive?

I did think the plots on WinISD looked reasonable considering I was throwing a couple of subs together with old bits and bobs.

PS, I didn't think too much of the PA power amps bass impact, as I found this lacking with the CV's in comparison to the likes of my Classe and Krell home amps? Could this be due to the amplifier topology or my perception/expectations?
 
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