Have a hot spot around 250 hz on my diy 4430's

[crtstudios76]

Built some 4430's out of 1 inch particle board, with 2235, 2425, and 2407 for the high freq. Triamping the drivers with a three way ashly electronic xover. I am noticing I have a hot spot around 250 hertz. The cab's are built like tanks, have been designed in a cab software to dimensions as similar to the 1x1.5x2.5 ratio. The back has been reinforced by a 2x4 along the length of the rear panel slightly off center to avoid any like area. The cabs have been insulated as well with typical pink fiberglass insulation along the top, bottom, sides, and rear. The front panel is not insulated. Any suggestions would be appreciated, and feel free to ask for more details if I missed something. I know my dad's 4430 stock from jbl didn't have this issue, so I doubt it's a driver issue..Thanks..

[boputnam]

I am noticing I have a hot spot around 250 hertz. How are you measuring this?

Could it be a room placement issue...?

[Beowulf57]

You could try this out and see where the problem frequencies reside in your room.

[Robh3606]

Why don't you try a slow impedence sweep to see if you have an anomaly where your peak is. If there is a box resonance you should be able to see it and excite it with the sweep.

Rob:)

[Loren42]

Built some 4430's out of 1 inch particle board, with 2235, 2425, and 2407 for the high freq. Triamping the drivers with a three way ashly electronic xover. I am noticing I have a hot spot around 250 hertz. The cab's are built like tanks, have been designed in a cab software to dimensions as similar to the 1x1.5x2.5 ratio. The back has been reinforced by a 2x4 along the length of the rear panel slightly off center to avoid any like area. The cabs have been insulated as well with typical pink fiberglass insulation along the top, bottom, sides, and rear. The front panel is not insulated. Any suggestions would be appreciated, and feel free to ask for more details if I missed something. I know my dad's 4430 stock from jbl didn't have this issue, so I doubt it's a driver issue..Thanks..

Either you have a room issue or diffraction step loss or both. How wide is your front baffle?

It would have to be less than 20" wide to get a 250 Hz step, but the step is downward in amplitude as frequency gets lower. The step will be somewhere from 3 to 6 dB.

[boputnam]

So, you've gone quiet...?

I'd suggest that perhaps your DIY resulted in an unintended cabinet resonance, and/or, your placement of the cabinets in the room has resulted in the same. Therefore, an easy solution is to use a graphic EQ and notch that frequency down - substantially - so that it does not excite the cabinet/room.

:)

[Mr. Widget]

If you can measure the impedance do a sweep and look for a possible resonance, but as others have posted, I'll bet it is a room/placement issue.

If you can't run an impedance sweep, temporarily drag the speakers into another room and give them a listen.


Widget

[grumpy]

better yet, outside. but if measurement capabilities are limited, an A/B
with your dad's 4430 might enhance or dispel this concern.

[crtstudios76]

Thanks for the input, guys!! A few details I left out..INTERNAL dimensions of my cabs are as follows: 20"width/14" depth/37" height. They are one inch partical board, and have a cross reinforcement 2x4 under the 2425 driver(for support) that is bolted to the sides securely. There is also One 35 inch 2x4 bolted to the rear panel from top to bottom maybe 8 inches from one side, and 12 inches from the other. There is a one inch build out plate on the top face of the cab (just like the 4430) to align the mid, and tweet I added (2407 w/ the cheapo horn). The ports are made of 4 inch thick cardboard carpet tubes, and have been cut to the prescribed length by my box/tuning program. The ports are located a little too close to the internal cab walls, but are cut into an angle (Like an "L") so where the port terminates inside of the cab is actually several inches from the internal wall.
I am measuring my findings by ear. I know a lot of you guys might be groaning now, but trust me..I'm a recording engineer by trade, and have years of experience hearing a frequency jumping out at me, and tuning it down. In this case, many cd's I play on that system have a little bit of "howl" in the mid bass of male vocals at certain moments that are not present on any of my other playback systems. I found the note that lights up, and went to my tone generator in my studio to find what frequency it was.
If you don't mind, Loren..Could you explain a little further "diffraction step loss"? I've never heard of that.

Indeed, I have been looking for an excuse to drag my system out doors to get a better feel for the cabs minus the room, but they weigh a absolute ton!!! It's nice out today, so I might give it a try!!

[crtstudios76]

Grumpy..Thanks for the advice. I do appreciate everyone's input. Unfortunately..My dad moved to Phoenix, and took his 4430's with him!!! I liked his so much, I just built my own!!! I do have a very good sense of what they sounded like, as they occupied the EXACT spot mine do now for a few years, while he lived here. I don't recall the issue I see now with his. That was what made me take notice. There was a difference.

[Beowulf57]

Grumpy..Thanks for the advice. I do appreciate everyone's input. Unfortunately..My dad moved to Phoenix, and took his 4430's with him!!! I liked his so much, I just built my own!!! I do have a very good sense of what they sounded like, as they occupied the EXACT spot mine do now for a few years, while he lived here. I don't recall the issue I see now with his. That was what made me take notice. There was a difference.

They occupy the exact same spot...but are the bass drivers the exact same distance from the floor and walls?

[crtstudios76]

They may not occupy EXACTLY the same spot, but I would say within a couple inches. Yes.. The driver in the cab is also mounted very similarly to how jbl did theirs in the stock 4430. I'm going to try, and plug the ports, to see if the issue continues. If it goes away, I'm thinking it's a port/cab issue. If it remains, I'm betting the issue is the room, or placement. That's the best I can come up with right now. Yesterday I moved the cabs a few feet forward in the room away from the rear wall, and did notice a little change. This thread might turn into a "how do I get my room in shape for professional listening?" thread!!

Also..Here are the room specs.. 18 foot width, 12 foot depth, and 8 foot ceiling. the left channel is about 3 feet away from the corner, and the right channel is about 4 feet from it's corner. they are backed up to the rear wall, but not touching. The room is also my main recording room. The walls have been 75 percent covered with acoustic panels I made that have completely killed any reflections off of the walls so as to have a cleaner, more focused sound to mic things in. This also had a dramatic impact of the clarity, and stereo imaging of my playback system. The ceiling is 90 percent covered with the same acoustic panels. I'm wondering if I have to make the rear wall more solid as it's a typical home wall....Drywall with 2x4's every 24 inches..Not very solid at all...

[Düse]

Built some 4430's out of 1 inch particle board, with 2235, 2425, and 2407 for the high freq. Triamping the drivers with a three way ashly electronic xover. I am noticing I have a hot spot around 250 hertz. The cab's are built like tanks, have been designed in a cab software to dimensions as similar to the 1x1.5x2.5 ratio. The back has been reinforced by a 2x4 along the length of the rear panel slightly off center to avoid any like area. The cabs have been insulated as well with typical pink fiberglass insulation along the top, bottom, sides, and rear. The front panel is not insulated. Any suggestions would be appreciated, and feel free to ask for more details if I missed something. I know my dad's 4430 stock from jbl didn't have this issue, so I doubt it's a driver issue..Thanks..
It is not a secret that the ports for Bassreflex can make trouble at 240..250 Hz. Have the ports minimum 1/3 of the surface of the Bassspeaker.
For the 2235 is the surface 804 cm2. 1/3 = 268cm2. The ports from the JBL
4341 is 86 cm2 x2 = 172cm2... but this is theorie from Dickanson.
Test it.

[daveobieone]

I hate to say this, but my factory original 4430's have some peaks in the 240-270hz area as well.

I have confirmed this using an RTA, in three different rooms, with vastly different sizes, and driven by different amps...first with the internal cross-over, and now bi-amped. Seems to be a little less of a problem bi-amped BTW. Perhaps better damping from the amp.?.

It's not terrible, but it is enough that you can notice it if you are sensitive to peaks in that area.

Dave O.

[Loren42]

Thanks for the input, guys!! A few details I left out..INTERNAL dimensions of my cabs are as follows: 20"width...

Here is the formula for calculating baffle step loss:

F3 = 4560 / 20" = 228 Hz

From 228 Hz and below you will see a roll off of SPL at somewhere between 3 and 6 dB per octave. This is due to the width of the front baffle (20")

Next, where are your crossover points? It could be that you are crossing over around 300 or so Hz and there is a SPL mismatch between the drivers where audio below 300 Hz is slightly higher than the audio above 300 Hz.

The result would give you a hump in SPL right around 250 - 270 Hz, or that would be the way it would appear.

Ideally, if you could set the crossover point at 228 Hz you could better compensate for the baffle step loss or even flush mount the speakers into the wall. You can always EQ the problem out, too.

Room placement will make substantial differences over ideal conditions, so none of the above advice is going to be exact, but when you stated a baffle width of 20" it raised the question if baffle step loss was a significant factor in what you heard and I suspect it was. However, I also would be quick to point out that it is probably not the only factor.

[crtstudios76]

Crossover points for the system are 1k, and 8k done with an ashly 3 way electronic crossover. The amp running the lows is a QSC mx1500a. I would like to think dampening would not be an issue. The porting is similar to how jbl did the 4430's originally: 2 4" ports per cab. I can't remember the length at the moment, but did use jbl's box tuning software, along with another one, both of with agreed on the proper length. I believe I tuned the cabs to right around 30hz.