2235H Project Help

[Loren42]

Greetings,

I am trying to understand what might be the problem with my speaker system. The issue is lack of bass.

The 2235H is in a 6 cubic foot ported enclosure with two 4" diameter ports 6" long tuned to 32 Hz. This is the frequency plot at 1 meter:



This i the near-field of one of the ports:



The box appears to be tuned correctly, but for whatever reason at about 55 Hz the bottom falls out of the bass and I don't know why.

Is that all I can get out of a 2235H?

Any thoughts?

[Robh3606]

Can you measure the FS of the drivers?? Can you run an impedence plot with the woofers in the boxes?? When I got my pair with new recones they were actually a bit under 20Hz. I have a pair in 5 cubic ft and a third in the 4.5 cu ft B380 box. Either set-up works just fine. What happens with a sine sweep?? No phase issues for a stereo pair?

Rob

[Loren42]

Can you measure the FS of the drivers?? Can you run an impedence plot with the woofers in the boxes?? When I got my pair with new recones they were actually a bit under 20Hz. I have a pair in 5 cubic ft and a third in the 4.5 cu ft B380 box. Either set-up works just fine. What happens with a sine sweep?? No phase issues for a stereo pair?

Rob

Can be done, but 55 Hz seems like a pretty big error. I could do a test in the box and I could also pull one and do a free air impedance test in a day or so.

I am just testing one cabinet set in the middle of the room facing a sofa with a mic on a micstand to do the tests. The program to run the sweep does a pretty good job of canceling room artifacts and the plots are a log sine sweep. I ran multiple plots at near and far field and they come up essentially the same. The plots confirm what my ears tell me; no bass.

So, how far down does your bass extend for you?

[Robh3606]

Do the impedance in the box. That will verify the box tuning. The FS should be 20Hz on the raw drivers do that last after you make sure everything else is OK. The best thing to do is go through your whole set-up and look for a high pass filter in line and verify speaker phase if you are running a pair. If it's phase simply disconnecting one will tell you.

Rob

[Loren42]

Do the impedance in the box. That will verify the box tuning. The FS should be 20Hz on the raw drivers do that last after you make sure everything else is OK. The best thing to do is go through your whole set-up and look for a high pass filter in line and verify speaker phase if you are running a pair. If it's phase simply disconnecting one will tell you.

Rob

I can't imagine phase being an issue. there is only one 2235H in the cabinet and I am only testing one speaker, so the second channel is disconnected.

[Robh3606]

I am just testing one cabinet set in the middle of the room

Worst place, try moving it to where you plan on setting them up. Could just be room placement issues although to loose the whole bottom is a bit odd.

So, how far down does your bass extend for you?

Solid to below 30hz about 25hz or so for the pair. For the sub a little lower with the BX-63.

Rob

[Ruediger]

If You measure at a distance of one meter You measure speaker and room influence.

You could do a nearfield measurement where the direct signal is magnitudes larger than the reflected one.

There is an article from D.B. Keele about this, available at http://www.xlrtechs.com/dbkeele.com/papers.htm,
"Low-Frequency Loudspeaker Assessment by Nearfield Sound-Pressure Measurement".

Ruediger

[grumpy]

You appear to be using Fuzzmeasure (Mac software)... there are instructions
for assembling a simple impedance measurement cable/setup with it.

Both Rob's and Ruediger's help should...er help.

A 3 year old nearfield plot of two 4430 systems (albeit with the low pass filter in place)
are here with comparable (with yours) graph ranges and smoothing:

[Loren42]

You appear to be using Fuzzmeasure (Mac software)... there are instructions
for assembling a simple impedance measurement cable/setup with it.

Both Rob's and Ruediger's help should...er help.

A nearfield plot of two 4430 systems (albeit with the low pass filter in place)
are here with comparable (with yours) graph ranges and smoothing:

So, you think I am in the ball park?

I did a slew of different measurements with both speakers in near-feld, far-field, and 1 meter with the cabinets placed in various positions in the room and pointing in various directions.

After doing all those tests I found that the rolloff begins at about 40 - 45 Hz and drops at least 15 Hz per octave.

A simple sine wave generator on my Mac and a voltmeter tells me I have a box resonance tuned at about 25 Hz. I need to confirm that because that seems too low for the cabinet volume and two port dimensions (3.95" diameter 6" long).

Here is the crossover:

http://www.mdbq.net/pyramid/LEAP.pdf

Here is a picture of the cabinet:



Stuffing is 1" polyfill on about 85% of the wall surface. I also have one sheet stretched across the internal bracing about 6" behind the woofer that subdivides the internal cabinet space.

While it looks like the ports are clogged in the picture, that sheet is about 6" behind the ports. I think I may pull that sheet out and recheck the port tuning and frequency sweep when I get some more time to play with it.

[Loren42]

If You measure at a distance of one meter You measure speaker and room influence.

You could do a nearfield measurement where the direct signal is magnitudes larger than the reflected one.

There is an article from D.B. Keele about this, available at http://http://www.xlrtechs.com/dbkeele.com/papers.htm,
"Low-Frequency Loudspeaker Assessment by Nearfield Sound-Pressure Measurement".

Ruediger

That link does not seem to work, even when copied and pasted into the address bar.

[grumpy]

chop off the first http:// ... and take a look at the nearfield paper (#6)

[4313B]

A simple sine wave generator on my Mac and a voltmeter tells me I have a box resonance tuned at about 25 Hz. I need to confirm that because that seems too low for the cabinet volume and two port dimensions (3.95" diameter 6" long).

Check the tuning frequency without any internal stuffing. If your tuning frequency is 25 Hz instead of your targeted 32 Hz and your ports are correct then you have a whole lot more volume than the six cubic feet you built for.

After doing all those tests I found that the rolloff begins at about 40 - 45 Hz and drops at least 15 Hz per octave.

Measure the driver nearfield and then the port nearfield and sum the response. Response should be solid to ~ 30 Hz and roll off from there. If they sound thin then it's your room.

I suppose you could also have 2234H's instead of 2235H's...

The 2235H is in a 6 cubic foot ported enclosure with two 4" diameter ports 6" long tuned to 32 Hz.

The 2235H really shines in 4.5 to 5.0 cubic feet (tuned in the 26 Hz to 30 Hz range). I know people build six cubic foot boxes for them (and I did a few too) but... whatever...

[Loren42]

Measure the driver nearfield and then the port nearfield and sum the response.

I have two ports, so do I add 3 dB to the port measurement and then sum with the nearfield of the woofer?

[Robh3606]

I suppose you could also have 2234H's instead of 2235H's...

I was thinking the same thing. They have been refoamed as well so we don't know what the driver FS is.

Rob

[pos]

I have two ports, so do I add 3 dB to the port measurement and then sum with the nearfield of the woofer?

+6dB at these frequencies