| Vivek |
Hi all,
I have built two subwoofers with Infinity car drivers for HT. Each driver is rated at 300W RMS, 4 ohm and 90dB. Vas is 78L and I have put them in 62L sealed boxes.
Some people say since they are 90dB, they are pretty efficient and do not need too much amplifier power. On the other hand, if I use a lower powered amplifier, it may be driven into clipping in case I drive them too hard. Could anyone give some inputs as to how things really work?
Thanks,
Vivek. |
|
|
| GM |
Greets!
Both are true statements, so the variables are what peak SPL is desired and/or how much power is required to use up its ~linear cone travel.
For example, if 110 dB/m peaks are enough, then the sub only needs 2^(110-90/3.01) = 100 W and hopefully it has enough ~linear excursion to handle this amount of power. With two subs acoustically close together and wired in parallel, then you only need ~50 W/sub since they are ~3 dB more sensitive. This will require an amp rated at 2 ohms though if only one amp is used.
FYI, the DD/DTS LFE channel reference peak SPL is 115 dB at the listening position and if all the other other channels are set to 'small', then in theory it needs to be able to handle another ~7 dB or ~122 dB plus any losses over distance.
Bottom line, when in doubt, better to have too much power than not enough.
GM |
|
|
| Vivek |
Hi,
The woofers have an Xmax of 12mm. I have been using them with 70W amplifiers till now. The problem is that I have to crank up the bass boost on the LFE channel all the way up to get some thump. That was what set me thinking about how much power may be needed.
Now if you are saying for 110dB peaks, only about 100W may be enough, then I suppose I do not have to go for very high powered amps. I think getting 110dB peaks can be pretty loud, don't you think?
Vivek |
|
|
| GM |
Every time you add +3 dB of boost, amp power requirements double and excursion increases ~1.4142 times for that BW, so you may need a lot of power to keep from clipping the amp. Of course if your amp has a clipping indicator and it never lights up, then it's powerful enough.
GM |
|
|
| AndrewT |
Hi,
I think that 90dB to 110dB sensitivity/SPL conversion is for mid band.
Do you subtract the response droop of the speaker/box combination at low frequency from the 90dB sensitivity?
If the box/driver is 10dB down at 30Hz then you need another 10dB of drive to get your 110dB of SPL.
That would equate to 1kW not 100W.
Which is right?
Taking your actual drivers specs of 90db/2.8v/M and a 62L sealed box for a 78l Vas. The response will be dropping from around Fb (50 to 70Hz) all the way down through the bass range.
Then use EQ (Linkwitz transform) to bring the response back up to the desired "shape".
This is where the big power and big Xmax get used up.
If 115dB at the listening position is the target, then 122dB at 1m is the SPL required. That is a further 12dB above the 1kW input. Now we are talking 16kW for a sealed box that has Fb=~60Hz to get 115dB at 30Hz. |
|
|
| Vivek |
1KW? 16KW? I understand that in theory this is needed.
Maybe I should go for the bigger power amps (about 300W) or so to be on the safer side.
Is there an option that I build a lower power amp and LT the subs to get the desired shape? The idea is to try and build an amp that is not very complicated.
Vivek |
|
|
| AndrewT |
It's the LT that causes much of the problem.
Sealed virtually demands LT and that in turns demands big power and big Xmax.
There are much more efficient ways of getting there but all have a downside, just in different forms.
Based on the very rough guessimates I gave as an example, 300+300W give 14dB less than 1.6kW.
That gets you to 101dB at the listening position for 30Hz and considerably louder as the frequency rises.
GM,
was my arithmetic correct and my assumption on midband sensitivity?
BTW,
I measured the voltage delivered to a vented bass speaker and compared that to the mains. The bass was running at more than 3dBV below the main amps even though the crossover was at 150Hz. |
|
|
| Vivek |
| So you are saying I just need to go for ample amount of power rather? |
|
|
| AndrewT |
You need to balance cost against size (volume) against sensitivity, against power against Xmax against box (driver loading method).
The car audio folk thought power was more important and see where it got them. |
|
|
| Vivek |
| Looks like I am better off looking for home audio sub drivers. It could be a big task in India, where the DIY market is very small and we do not get drivers like in Europe or the US. |
|
|
| Vivek |
| Andrew, I assume you are a fan of Colin McRae and David Coulthard. I saw that you are interested in motorsport. I am a sports writer and cover motorsport. |
|
|
| nunayafb |
| quote: | Originally posted by Vivek
Looks like I am better off looking for home audio sub drivers. It could be a big task in India, where the DIY market is very small and we do not get drivers like in Europe or the US. |
No, no, no - let's back up.
The speakers that you have are fairly high efficiency compared to other home/car subs, they have decent power handling and xmax, you don't need to replace them.
I personally disagree with the approach that GM and AndrewT have taken here. While technically accurate, and directly answering your question I feel that the numbers stated misrepresent what your situation is. The highest wattage you need to be concerned with is 300Wx2 rms @ 4ohms or 600Wx1 @2 or 8 ohms(assuming single voice coil). You are limited by your woofers here, and your question appears to be about power to achieve "acceptable" spl. Lt's and other eq's are designed to flatten out the frequency response, and as stated the power requirements for an eq'd woofer can be quite high. Due to the power handling of your speakers, eq'ing them will not require more power it will lower your peak spl.
The highest dB peaks you need to pursue are up to you, yes 110dB peaks are loud, and I don't think that 122dB is realistic or necessary. I typically aim for 90-95dB when watching movies, and yes I used to sit there with an SPL meter until I "calibrated" my ears. Like I said max spl is up to you, pick up a meter and measure your current system. Determine the difference in spl between 1m and at listening point to assess room gain/loss-check several bass frequencies.
With the cheap price of amps today I am curious what is being debated here. My first thought when I read your post was what is your budget for this amp? If $300 is acceptable then you can get an amp with enough power to blow apart 4 of these woofers, turn the gain down for now and if (when) you upgrade woofers you will have the power.
Looking at parts express I don't see any single amp that can power two 4ohm drivers (series or parallel) at or very close to their rms rating except for the Behringer EP1500($300 ref. above).
As GM said it is better to go bigger... |
|
|
| Vivek |
nunayafb, I think you got what I was trying to ask. I have never measured the SPL so I don't really know how much I would need. What I need is "acceptable" amounts of SPL. I feel what I am getting now is not really acceptable because I am having to use the bass boost on the receiver.
For example, I love the movie U-571 and the scene where the guys are depth-charged. During the explosions, my subs do not have that punch. That is why I was thinking I may need more power.
The question here is simply about how powerful an amp I need to build. There are many in the 100W range, while there are others like the PA-300, ETI466 or Quasi's 300W amps which I could try out.
Currently, I am using two 70W amplifiers with the subs. Is is that I am not integrating the subs properly with the rest of the system? I could tell you guys one thing though. When I use the current sub setup, it still is far better than having no sub. I was just trying to see if I could improve things. |
|
|
| AndrewT |
| quote: | Originally posted by nunayafb
I personally disagree with the approach that GM and AndrewT have taken here..................... You are limited by your woofers here, and your question appears to be about power to achieve "acceptable" spl. Lt's and other eq's are designed to flatten out the frequency response, and as stated the power requirements for an eq'd woofer can be quite high. Due to the power handling of your speakers, eq'ing them will not require more power it will lower your peak spl. |
| quote: | Based on the very rough guessimates I gave as an example, 300+300W give 14dB less than 1.6kW.
That gets you to 101dB at the listening position for 30Hz and considerably louder as the frequency rises. |
is exactly the same thing as lower your peak SPL (aspirations).
We are not in disagreement. |
|
|
| Vivek |
I suppose 101dB should be loud enough.
Andrew, take a look at post no 11. |
|
|
| AndrewT |
| quote: | Originally posted by Vivek
Andrew, take a look at post no 11. |
off topic.
I do enough of that already.
But, what of the other hundred or more famous Scots involved in international motor sport. |
|
|
| Vivek |
| quote: | Originally posted by AndrewT
off topic.
I do enough of that already.
But, what of the other hundred or more famous Scots involved in international motor sport. |
Point taken. Sorry. And I know there are more. |
|
|
| GM |
| quote: | Originally posted by AndrewT
Hi,
I think that 90dB to 110dB sensitivity/SPL conversion is for mid band.
Do you subtract the response droop of the speaker/box combination at low frequency from the 90dB sensitivity?
If the box/driver is 10dB down at 30Hz then you need another 10dB of drive to get your 110dB of SPL.
That would equate to 1kW not 100W.
Which is right?
If 115dB at the listening position is the target, then 122dB at 1m is the SPL required. |
Greets!
Could be, it would depend on the design. It was just an example, not meant to define a sealed cab's HT system's power requirements per se.
Well, in theory you would, but a sealed cab's Vb is an acoustic limiter, so while the driver might can handle 1 kW and the Xmax it requires, it won't play any louder than the cab allows, ergo beyond this point it will mostly just heat up the VC and increase its Qts/Qtc (thermal power compression), so doing a sim (or the math) of the design to find its max power handling requirements seems the obvious thing to do. That, or just buy an amp that has at least as high a rating as the driver, which is what most folks do AFAIK.
While SPL falls at 6 dB/doubling of distance in large venues, making your 115 dB example 121 dB/2 m, 127 dB/4 m, etc., LF falls off at only 3-4 dB on average in a typical HIFI/HT app due to room modes, so the power requirements are much less. Still, if you design based on theory, then your system tends to be lower distortion, though judging by what folks buy, this is a very low/no performance priority.
Yeah, if you want your HT system to play at DD/DTS reference levels (most folks don't for a variety of reasons and why I listed it as an FYI) requires a whole lot more than one or two small sealed cabs no matter how powerful the amp or how much Xmax/power handling the driver has.
GM |
|
|
| GM |
| quote: | Originally posted by AndrewT
BTW,
I measured the voltage delivered to a vented bass speaker and compared that to the mains. The bass was running at more than 3dBV below the main amps even though the crossover was at 150Hz. |
OK, is it fed from a LFE channel and at the same nominal impedance during a movie or.....?
GM |
|
|
| GM |
| quote: | Originally posted by Vivek
Looks like I am better off looking for home audio sub drivers. It could be a big task in India, where the DIY market is very small and we do not get drivers like in Europe or the US. |
It all depends on what your HT performance goals are. I mean as a rule-of-thumb (ROT), if you want to use a sealed alignment for the LFE channel, then until you've met the DD/DTS reference level requirements there's no such thing as too low a driver's Fs or too high an Xmax, thermal limited power handling, but due to room/SAF/cost/neighbor variables, few can/want to 'afford' the luxury of a cinema experience the producer envisioned in their home.
Indeed, AFAIK most folks buy HT receivers, speaker systems based on size/price/ high power handling claims, then set it up by ear based on their distortion level tolerance, which due to the various component's actual performance specs tends to be well below DD/DTS reference. Ditto HIFI systems.
GM |
|
|
| GM |
| quote: | Originally posted by nunayafb
The speakers that you have..........
I personally disagree with the approach that GM.........the numbers stated misrepresent what your situation is. The highest wattage you need to be concerned with is 300Wx2 rms @ 4ohms or 600Wx1 @2 or 8 ohms(assuming single voice coil).
I typically aim for 90-95dB when watching movies......... |
Apparently I'm the only one here not familiar with Vivek's driver, so what is the model #, specs since they offer more than one?
Interesting, I didn't realize I had an 'approach' other than to answer Vivek's Q and toss out some facts to get the thread going.
Without knowing either the details of the driver's build or the manufacturer's music power rating (if any), or best, a measured VC thermal power curve, there's no way to determine whether its RMS rating is the only one to be concerned with, so we'll have to disagree on this point since some drivers can only handle a small percentage (or much more) of its RMS rating before it audibly compresses on transients.
Hmm, 90-95 dB peaks/listening position/LFE channel equates to a 60-65 dB average or about as loud as near-field conversational speech, which is fine for late night while others are sleeping and/or where there's ~intolerant neighbors on the other side of the wall, but hardly loud enough to convey a cinematic experience, which is what HT is all about, at least as originally envisioned.
Indeed, even the TV movie broadcast standard's average is considerably higher at 79-82 dB/channel/listening position since the typical viewer supposedly watches regular TV programming at 70-75 dB, so I guess if I were to make an 'approach' for folks to potentially disagree with, it would be to measure your average TV viewing SPL and add 4-7 dB to it as a minimum baseline to calc the LFE's SPL/power requirements, unless of course this is higher than the DD/DTS reference levels.
GM |
|
|
| zobsky |
| quote: | Originally posted by Vivek
nunayafb, I think you got what I was trying to ask. I have never measured the SPL so I don't really know how much I would need. What I need is "acceptable" amounts of SPL. I feel what I am getting now is not really acceptable because I am having to use the bass boost on the receiver.
For example, I love the movie U-571 and the scene where the guys are depth-charged. During the explosions, my subs do not have that punch. That is why I was thinking I may need more power.
The question here is simply about how powerful an amp I need to build. There are many in the 100W range, while there are others like the PA-300, ETI466 or Quasi's 300W amps which I could try out.
Currently, I am using two 70W amplifiers with the subs. Is is that I am not integrating the subs properly with the rest of the system? I could tell you guys one thing though. When I use the current sub setup, it still is far better than having no sub. I was just trying to see if I could improve things. |
I suggest re-examining your current designs, rather than looking at things purely from the perspective of efficiency / power . I understand the audio market in India is wretched for DIYers.
1. Firstly, can you obtain and post the T/S parameters or at least model numbers of your subwoofers.
2. Depending on (1), maybe porting your enclosures will give you what you want in terms of extension and impact. A few years ago, I built a sealed enclosure for my adire shiva and was singularly unimpressed with it. The same driver in a 135 liter sonotube ported enclosure was much better , driven off between 50 - 100 Watts. I used an EBS alignment to get down below 20 Hz in room.
In my case, that design was succeeded by a couple of horn subwoofers. Why? When you hear a horn subwoofer, you'll understand.
3. See if your driver models well in a tapped horn . If it does, that should give you what you want in terms of extension, efficiency and will probably work better with a low power amplifier. Of course, the driver has to be suitable for use with that enclosure.
FWIW, the table tuba I use now runs off a cheapo 100 W amp that doesn't even get warm after 8 hours of use. In room extension down into the mid 20 Hz .
If you can't get a hold of the T/S parameters, you can estimate them (at least at low levels) by using readily available software . I built a cheap jig and documented my procedure here
http://zobsky.blogspot.com/2008/01/...nt-jig-for.html |
|
|
| Vivek |
So reaching the DD/DTS reference levels is what will give me the performance I want. In that case, the fact that I am trying to use car audio subs looks like a big compromise since these drivers were not meant to be used for HT in the first place.
Or like zobsky has said, maybe a change in approach in the box type could be the answer.
Attached is the spec sheet of the driver. The company recommends a volume of 56L for a ported box.
Here is a link to the driver specifications.
http://manuals.harman.com/INF/CAR/B...ech%20Sheet.pdf
I also checked EBP and it is 58 for the driver I have. Should I try and convert the enclosure to a ported one? |
|
|
| zobsky |
Alternative 1: A quick calculation with WinISD Pro (after entering the parameters you supplied ) yield a fairly large EBS ported enclosure (red) that should get you down to just under 20 Hz (with a 14" port), if that's what you want .
Alternative 2 (since you have a pair of these drivers) would be to mount them in an isobaric arrangement (grey) to cut the enclosure size by half (and use a 4" x 30.4" port) .
With the EBS, enclosure, you're depending on the room gain to help you fill in some of the low bass.
Alternatives 3 & 4:
Likewise, here are 2 more sims of an SC4 ported alignment normal and isobaric (yellow and pink) . The isobaric enclosure (pink) is around the same size as your sealed box and is tuned to 25 Hz . If you're willing to sacrifice one box, you might be able to get it to work.
Another thing you want to check is if your amp can handle 2 drivers in parallel in an isobaric arrangement. Alternatively, you could connect them in series for a nominal 8 ohm load. How are you currently driving both your subs? Off a single plate amp, a stereo amp or what ?
 |
|
|
| GM |
| quote: | Originally posted by Vivek
I feel what I am getting now is not really acceptable because I am having to use the bass boost on the receiver.
For example, I love the movie U-571 and the scene where the guys are depth-charged. During the explosions, my subs do not have that punch. |
You need a lot of gain BW (more and/or bigger, lower tuned subs) and power to 'experience' all that a movie like U-571 has to offer. Scroll down to U-571 and look at the various ETF plots to see that ideally you need a multiple driver I.B. system capable of near DC extension with DD/DTS reference SPL output down into the low 20s. Ditto many other movies: http://www.svsound.com/questions-faqs.cfm#moviedemos
The dark side though is that if your house or separate standing dedicated HT isn't extremely well built to handle these VLFs they can seriously damage foundations, walls, etc.. Been there, done that and still have a lot of repairs to do yet, so as long as I live in this house, my system will stay rolled off below ~25 Hz for HT. :(
That said, 'punch' implies a strong mid-bass which are the harmonics of the explosions rather than the ultra low fundamentals that pound your chest/shake the house, so if you're happy with the amount of the sub's low LF 'rumble' factor, then the sub's alignment is probably fine as is.
That said, I'm a bit confused WRT what you're actually boosting and what you feel is lacking since boosting apparently isn't hard clipping your existing amps or receiver since you're not complaining about it, so do you mean you're increasing the mains/CC/surround's bass tone control, which has no affect on the sub's frequency response, or increasing the LFE channel's level setting, which changes the level WRT the other channels? When properly set, the LFE channel should be +10 dB referenced to any one channel and there should be no need to boost anything.
Or I wonder if you're trying to fill in one or more room nulls, which can't be done by using electrical EQ, so for all we know you may just need to either relocate and/or adjust the phasing of your subs, so still too many Qs to even begin to figure out if any more power is required.
GM |
|
|
| zobsky |
| quote: | Originally posted by GM
You need a lot of gain BW (more and/or bigger, lower tuned subs) and power to 'experience' all that a movie like U-571 has to offer. Scroll down to U-571 and look at the various ETF plots to see that ideally you need a multiple driver I.B. system capable of near DC extension with DD/DTS reference SPL output down into the low 20s. Ditto many other movies: http://www.svsound.com/questions-faqs.cfm#moviedemos
The dark side though is that if your house or separate standing dedicated HT isn't extremely well built to handle these VLFs they can seriously damage foundations, walls, etc.. Been there, done that and still have a lot of repairs to do yet, so as long as I live in this house, my system will stay rolled off below ~25 Hz for HT. :(
That said, 'punch' implies a strong mid-bass which are the harmonics of the explosions rather than the ultra low fundamentals that pound your chest/shake the house, so if you're happy with the amount of the sub's low LF 'rumble' factor, then the sub's alignment is probably fine as is.
That said, I'm a bit confused WRT what you're actually boosting and what you feel is lacking since boosting apparently isn't hard clipping your existing amps or receiver since you're not complaining about it, so do you mean you're increasing the mains/CC/surround's bass tone control, which has no affect on the sub's frequency response, or increasing the LFE channel's level setting, which changes the level WRT the other channels? When properly set, the LFE channel should be +10 dB referenced to any one channel and there should be no need to boost anything.
Or I wonder if you're trying to fill in one or more room nulls, which can't be done by using electrical EQ, so for all we know you may just need to either relocate and/or adjust the phasing of your subs, so still too many Qs to even begin to figure out if any more power is required.
GM |
If he lives in typical indian dwellings, the construction will most probably be concrete / plaster, so not much chance of serious structural damage. More change of damage from irritated neighbours, if he lives in an apartment complex though.
Vivek. ... GM has a point, are you missing low bass, mid-bass, or both ? FWIW, I've had car audio drivers before that worked well in car, but sounded weak in home. |
|
|
| GM |
| quote: | Originally posted by zobsky
3. See if your driver models well in a tapped horn . If it does, that should give you what you want in terms of extension, efficiency and will probably work better with a low power amplifier. |
It does model well, though probably a bit too large at 361+L, but using both drivers in isobaric loading drops it down to 264+L and using the existing 70 W amps for each driver should meet the DD/DTS ~122 dB 'worst case' requirement if the published specs are reasonably accurate without using up all its Xmax until ~16 Hz (assuming no room gain, so will probably be a bit lower):
GM |
|
|
| Vivek |
| quote: | Originally posted by zobsky
If he lives in typical indian dwellings, the construction will most probably be concrete / plaster, so not much chance of serious structural damage. More change of damage from irritated neighbours, if he lives in an apartment complex though.
Vivek. ... GM has a point, are you missing low bass, mid-bass, or both ? FWIW, I've had car audio drivers before that worked well in car, but sounded weak in home. |
Yes, houses in India are constructed with cement blocks or bricks and plastered. I stay in an apartment so irritated neighbours are something I have to be careful about.
When I play the test tone on the receiver, stuff in the house rattles. But when the movie is on, that 'punch' is missing. What I mean to say is that the bass kind of sounds very loose. It looks like the cone is flapping around for nothing.
Like you said, it could just be the case of the car audio subwoofers sounding bad at home.
| quote: | Originally posted by GM
That said, 'punch' implies a strong mid-bass which are the harmonics of the explosions rather than the ultra low fundamentals that pound your chest/shake the house, so if you're happy with the amount of the sub's low LF 'rumble' factor, then the sub's alignment is probably fine as is.
That said, I'm a bit confused WRT what you're actually boosting and what you feel is lacking since boosting apparently isn't hard clipping your existing amps or receiver since you're not complaining about it, so do you mean you're increasing the mains/CC/surround's bass tone control, which has no affect on the sub's frequency response, or increasing the LFE channel's level setting, which changes the level WRT the other channels? When properly set, the LFE channel should be +10 dB referenced to any one channel and there should be no need to boost anything.
Or I wonder if you're trying to fill in one or more room nulls, which can't be done by using electrical EQ, so for all we know you may just need to either relocate and/or adjust the phasing of your subs, so still too many Qs to even begin to figure out if any more power is required.
GM |
Mid-bass is probably what I am missing if it is what gives that feeling of punch. But I also read somewhere that such harmonics are what most people who put in tons of money to buy HT equipment mistake for true bass. True low end thump is certainly better, isn't it?
I am referring to the channel volume on the LFE channel when I say I am boosting it to +12dB.
I have tried moving the subwoofers around. They sound better when kept in a passage which leads to a bedroom. But that is a rather inconvenient place to keep the subs, right? My wife hates the sound of these things already and I have been forbidden to buy more speakers.
I did think of Isobaric even before I built these boxes. But then I thought that these are car audio drivers and I should not try complicated stuff with driver which are not meant for home audio in the first place. So I thought sealed would be the simplest thing to try out first. |
|
|
| zobsky |
| quote: | Originally posted by Vivek
Yes, houses in India are constructed with cement blocks or bricks and plastered. I stay in an apartment so irritated neighbours are something I have to be careful about.
When I play the test tone on the receiver, stuff in the house rattles. But when the movie is on, that 'punch' is missing. What I mean to say is that the bass kind of sounds very loose. It looks like the cone is flapping around for nothing.
Like you said, it could just be the case of the car audio subwoofers sounding bad at home.
Mid-bass is probably what I am missing if it is what gives that feeling of punch. But I also read somewhere that such harmonics are what most people who put in tons of money to buy HT equipment mistake for true bass. True low end thump is certainly better, isn't it?
I am referring to the channel volume on the LFE channel when I say I am boosting it to +12dB.
I have tried moving the subwoofers around. They sound better when kept in a passage which leads to a bedroom. But that is a rather inconvenient place to keep the subs, right? My wife hates the sound of these things already and I have been forbidden to buy more speakers.
I did think of Isobaric even before I built these boxes. But then I thought that these are car audio drivers and I should not try complicated stuff with driver which are not meant for home audio in the first place. So I thought sealed would be the simplest thing to try out first. |
1. Are you sure that you don't have a leak in your boxes ? Maybe run an impedance sweep.
FWIW, My sealed sub behaved exactly like that (plenty excursion, with relatively less output below 30 Hz). I hated that enclosure with a vengeance.
2. This is important. Do you have the box stuffed / have you experimented with the quantity of stuffing?
Well, the harmonics "fatten" up the sound . Maybe that's what you're missing . Some people like them, some don't . Generally speaking, horns tend to have less harmonics and tons more impact, at the cost of size / placement issues but let's not get off topic.
If you can afford to hack up one of your cabinets, I suggest you port it and run those two subs isobaric . Or if not, can you get another cabinet built to test out the ported / isobaric alignment. Double check any calculations before cutting anything.
If you can live with a 7 ft tall / small footprint monolith (and a major room mode is not the cause of your issues), I'd guess the tapped horn will solve most of your issues. You could tune it a bit higher and thus, a bit smaller.
Okay, so everyone understands, you are boosting the subwoofer channel output, not Eq'ing the bass contour itself.
Here's a screen of isobaric sealed vs isobaric ported in around a 60 liter box.
 |
|
|
| Vivek |
1. I have checked the terminal cup and the area around the woofer. Both seem to be sealed properly. The inside joints are all sealed with wood glue. I did that thrice after the previous sealing dried up. Just to double check I will smear the edges around the terminal cup once again.
2. I have lined the inside walls with polyfibre material. No other kind of filling etc. And I have not experimented with any kind of filling.
The only subs I can compare with the ones I have are commercial ones. Do commercial subs have harmonics which make them accepable to my ears at least?
If you are saying a horn, are you talking something like a sonotube sub or PVC pipe stuff?
The ported isobaric looks good in the graph you have posted. Maybe I should build a new box to try it out.
But if I have to hack up one of the boxes, I think I will just have to make a cut on the rear of one of them and fit the woofer there, right? |
|
|
| zobsky |
| quote: | Originally posted by Vivek
1. I have checked the terminal cup and the area around the woofer. Both seem to be sealed properly. The inside joints are all sealed with wood glue. I did that thrice after the previous sealing dried up. Just to double check I will smear the edges around the terminal cup once again.
2. I have lined the inside walls with polyfibre material. No other kind of filling etc. And I have not experimented with any kind of filling.
The only subs I can compare with the ones I have are commercial ones. Do commercial subs have harmonics which make them accepable to my ears at least?
If you are saying a horn, are you talking something like a sonotube sub or PVC pipe stuff?
The ported isobaric looks good in the graph you have posted. Maybe I should build a new box to try it out.
But if I have to hack up one of the boxes, I think I will just have to make a cut on the rear of one of them and fit the woofer there, right? |
Good . I'd think you need more than just lining for a sealed enclosure. From what I remember, you'd usually want to STUFF a sealed enclosure. I don't remember the exact rules needed to determine the quantity of stuffing, but google around, .. or maybe more knowledgable folks will chime in :) Regardless, I don't think that is the source of your problems, .. but maybe something to try. Stuffing might "flatten" your response curve (simulating increasing the box size) but more likely won't get louder.
Re. isobaric, I mean't something like this (not my images):
which will end up looking like this in real life:
IF you wanted to modify your existing enclosure, it should be a relatively small matter to use the "cone-to-cone" isobaric mounting.
Regarding leaks, I was more concerned about leaks along the joints.
Regarding horns, sonotube subs are usually ported enclosures. I meant stuff like
http://www.cowanaudio.com/hornsubjr.html and
http://www.cowanaudio.com/th.html . |
|
|
| Vivek |
Maybe I should just try a sealed isobaric first. Will that work?
And if I am going the isobaric way, should the speakers be connected in phase or out of phase? |
|
|
| AndrewT |
| quote: | Originally posted by GM
is it fed from a LFE channel and at the same nominal impedance during a movie or.....? |
Hi Gm,
I used a 24dB/oct crossover. Cascaded Butterworth 2pole giving a 4pole Linkwitz Reilly (Bessel) characteristic for both the low pass and the high pass filters. No processor or LFE was used.
I used 150Hz as the cross over to limit the LF signal being sent to the tiny 5inch drivers in the main speakers.
I was measuring averages of around 1 to 2Vac into the mains and between 20mV and 200mV into the bass amplifiers. Both amps were +28dB gain and all the speakers were 8ohm. The mains are 88dB/W/m and the Bass drivers are about 89dB/W/m but they are close coupled (in one 300L box) giving an extra 3dB from the pair.
This test was a mix of mostly music and one film sound track. |
|
|
| Vivek |
Hi guys,
Here is some interesting news. I bought a cheap MOSFET amplifier (about $17) which claims to have an output of 70+70W RMS and hooked it to my subs. I also connected a loudspeaker and DC protection circiuit and played an MP3 CD from the player. Guess what? The sound is so loud I got the scare of my life when it started playing. And that too with the volume just very little from zero. I used a +/-30V supply. What does this tell us?
The amp |
|
|
| zobsky |
| quote: | Originally posted by Vivek
Maybe I should just try a sealed isobaric first. Will that work?
And if I am going the isobaric way, should the speakers be connected in phase or out of phase? |
I don't know if isobaric sealed will get you much of anything over regular sealed. The main reason for using isobaric is to halve the Vas and this reduce the required enclosure size. I suggested isobaric ported to reduce the large size of the suggested ported enclosure.
I suggest you download WinISD Pro, enter the T/S parameters for your drivers and play around.
If you don't want to cut up your existing enclosure while experimenting, you can mount the drivers isobarically, remove the terminal cup and temporarily rig a port there (may need to mount a flange to the port to ensure a good fit), and run the interior cabinet wires through the port to the outside.
Not sure what your MOSFET experiments mean. Maybe the required input sensitivity is much higher than your earlier amplifiers. Make sure you aren't clipping . If it solves your issues, all the better. |
|
|
| Vivek |
| I have both WinISD and Speaker Workshop with me. I will try stuff out. Before that I will try the isobaric ported. |
|
|
| Driver_King |
| I hate clipping!:mad: |
|
|
|
