Sub Cabinet

[Alex Avakian]

Hey,

So I came across this semi-old PA loudspeaker by Peavey that didn't work well so I took it apart and decided to turn it into a subwoofer. I took everything out, sanded it down, repainted it, and went out and bought a Gemini XGA-4000, a Peavey 15" Low Rider Subwoofer for it; then I bought a 80 Hz Low Pass 8 Ohm Crossover from Parts-Express. I just put everything together and it doesn't feel like a 700 watt should feel, my friend bought a 500 watt sub from Behringer and that feels more powerful than mine. Did I mess up by assuming I could use any cabinet for a subwoofer? Any help or information is appreciated as I'm very much still learning about audio.

Thanks,

Alex

 

[j_garcia]

Power does not determine the capability of a sub. The design does - selection of the driver and correct design of the cabinet to accommodate that driver for what you want to do. Slapping a random driver into any old cabinet will rarely give you great results and that driver may be geared toward output rather than extension, so it depends on what you were after?

 

[Alex Avakian]

What do you mean geared toward output rather than extension?
And, to fix this would I just have to find a cabinet that would work with mine?
Another thing I forgot to mention was that I have the amplifier inside the cabinet with the sub under it.

 

[William Lemmerhirt]

What do you mean geared toward output rather than extension?
And, to fix this would I just have to find a cabinet that would work with mine?
Another thing I forgot to mention was that I have the amplifier inside the cabinet with the sub under it.

What he means is it's geared to be super loud vs playing super low frequencies. PA subs usually are rolled off by about 30hz. Not good for HT but since a lot of music above that range, pa subs are made for a lot of output above that range. To appropriately design the enclosure, you'll need the TS parameters. Is it sealed?

 

[Alex Avakian]

Rolled off at 30Hz? The sub's usable frequency is as low as 30Hz if thats what you mean.
I don't know what HT is, and I don't think I bought a PA sub (I could be wrong though).
And as for if its sealed, I'm gonna say no, since it has 4 vent holes in the front, and a couple squares on the back that were used for control panels.
Again, I'm sorry if you need to explain anything more than you would normally like to. I'm a rising junior Mechanical Engineer so I should be able to understand anything you tell me, but I also had almost zero knowledge about audio before I started this (so a few weeks).

Thanks again

 

[William Lemmerhirt]

Hey no problem. I take for granted knowing audio terms. My bad. Yes, roll off is where the frequency response starts to be less, and less or "roll off".
HT would be short for Home Theater and I should've asked what the intended purpose is. So the cab is ported. You should look up the TS(Thiele/small) parameters. That will tell you how to best build an enclosure to the drivers potential. For example, if the fs of the driver is 35hz, there's not much sense in tuning the cab to 22hz.
The diy section should have some good articles on building subs.

 

[Alex Avakian]

So this is going to change how much air the sub is able to push out which is going to change how it sounds and feels? And this is just for personal use.
And so if it doesn't feel as powerful as it should, do you think from the information Ive given you that the enclosure is too big?
I will definitely check out that section though, and thank you for your help.

 

[William Lemmerhirt]

Hard to say from the info above without researching each component, which I just don't have time for at the moment. Is that personal for music? Or movies?

 

[j_garcia]

Need the driver parameters, which will give us an idea of the kind of box it was intended for. That is sometimes specified when looking at drivers, but some manufacturers just expect you to know what specs you are looking for for a given speaker design. As mentioned, a bass driver good to 30Hz won't give you any low end response if that's what you're looking for, but it might give you a lot of output in the right box. You may be able to use that box by installing an extra wall inside it to achieve the correct internal volume if it needs less, which might be the case. Hard to say without the parameters.

Like Will said, are you looking for DEEP bass or LOUD? That driver probably won't give you deep bass.

 

[Alex Avakian]

I just want to be able to feel it more. I'm fine with the 30Hz because I think I should be able to feel it more. I would also be using it for personal use, which just entitles playing music from Spotify or Youtube, not live sound. My friend's Behringer is a 18" with a 25Hz low end, but its 500 watts, that's what I think I should be able to feel mine more because I have more wattage, but he also does have the right cabinet as he didn't try to and build it himself.

 

[William Lemmerhirt]

Well your friend has a few advantages. Designed and built as a system for one, and the other is 18" is a lot more surface area to excite air waves with. I can't remember the percentage off hand but given the same excursion, the 18 will be moving much more air. J is right too. You should be able to modify the enclosure BUT you should find the driver specs first.

 

[Alex Avakian]

So I found the driver specs (just in the manual), and I found the specs for the Peavey HDH 244 which is the enclosure I'm using. It does say its Tuning Frequency is 60Hz, and its Low Frequency Limit is 55Hz. It doesn't however give the internal volume of the enclosure, so I think I'm gonna have to do some geometry to figure out how I can get the internal volume to in-between 2 and 5 cubic feet (56.6 to 141.6 liters) and vent tunings from 34 to 45 Hz, because this is what the manual said for the sub.

 

[lovinthehd]

You can utilize software like winisd (or others) to model the driver/box possibilities using the T/S parameters. As to whether the 500 watt amp spec is even equivalent to your 700 watt amp spec we'd need more info about the specific amps (are they both rated using the same parameters, particularly impedance?); largely the sensitivity spec of the system will determine how the watts translates into spl (sound pressure level).

 

[Alex Avakian]

The amp I bought was 4ohm to each channel with a peak power less than the RMS of the sub I bought, the sub is 8ohm, and so I bridged the amplifier to work with it. I also just calculated the internal volume of my enclosure and its 3.5 cubic feet, which is a full cubic foot smaller than it should be. Which is quite disappointing considering refurbishing the enclosure was the second thing I did in this project after buying the amp and sub.

 

[lovinthehd]

Curious, what do you have invested in this (aside from your time)?

ps What brand/model amp did you get?

 

[TLS Guy]

So I found the driver specs (just in the manual), and I found the specs for the Peavey HDH 244 which is the enclosure I'm using. It does say its Tuning Frequency is 60Hz, and its Low Frequency Limit is 55Hz. It doesn't however give the internal volume of the enclosure, so I think I'm gonna have to do some geometry to figure out how I can get the internal volume to in-between 2 and 5 cubic feet (56.6 to 141.6 liters) and vent tunings from 34 to 45 Hz, because this is what the manual said for the sub.

So what is that Peavey driver you bought? If you tell us what it is we can see if it is even possible to make a sub with it. We need to find the T/S parameters. The T/S parameters define the precise relationship of the weight of the cone and its area to the springyness of the suspension and the magnetic motor characteristics. Then you can design an appropriate enclosure. It is almost never possible to reverse engineer a different driver for an existing enclosure. That way you don't get a sub, but the "Dog's Dinner" you have created.

 

[Alex Avakian]

The sub I bought is the Peavey Low Rider 15" (00560310) which was around $200, the Gemini XGA-4000 amp I bought was around $200, and then I've prob spent a little more than $100 on parts to refurbish the enclosure.

I've also heard I can fill the inside with Poly fill or some material that essentially makes the space seem larger to the sub, will that work well for my case so I don't need to scratch everything I've done so far?

 

[lovinthehd]

Article on sub stuffing http://www.data-bass.com/data?page=content&id=79

 

[William Lemmerhirt]

I'm gonna try to look at this later. But iirc, you mentioned 55hz as the low end frequency response. Was that just the driver? Or is that the cabinet literature? 55Hz is pretty high, and I'd guess is the driver is for a guitar cabinet.

 

[lovinthehd]

FWIW the specs for the driver here https://assets.peavey.com/literature/specs/116625_13679.pdf