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Goals with designing a sub for HT duties only.


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#1 of 17 OFFLINE   Jones_Rush

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Posted January 25 2001 - 08:16 AM

I am in the process of gathering information about my first DIY subwoofer project. There is something I want to understand about HT-only subs: Are there any benefits for an HT sub to be: tight, fast, precise, have good transient response, low group dealy and good frequency response. all of these factors define a good musical sub, are there any need for them in HT ? My dealer told me that a sub which is meant to be used only for HT duties should have these 2 charastaristics: 1) being able to play in the highest SPL's. 2) being able to reproduce the lowest frequencies. except for these two factors, my dealer told me that all the other factors, which make a lot of difference in music reproduction, make almost no difference at all with movies. my dealer has no reason not to be honest with me, since he know that I am going to build the sub myself. Can I trust him on this ?

#2 of 17 OFFLINE   Greg Monfort

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Posted January 25 2001 - 06:59 PM

Only if the sub is used exclusively as a LFE, and the mains/center/surrounds don't need any bass management, IOW it's pure BS for all but a very few, very serious HTs. GM ------------------ Loud is beautiful, if it's clean
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#3 of 17 OFFLINE   Jones_Rush

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Posted January 26 2001 - 01:51 AM

Well, I will need bass management for the center speaker (only goes doen to 60hz) and for the surounds (the actual surround speakers go very low but the decoder can only see them as small). Why is that a problem ?

#4 of 17 OFFLINE   Tom Vodhanel

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Posted January 26 2001 - 06:53 AM

>>>I am in the process of gathering information about my first DIY subwoofer project. There is something I want to understand about HT-only subs: Are there any benefits for an HT sub to be: tight, fast, precise, have good transient response, low group dealy and good frequency response.<<< I think they'd be some major benefits. Film bass isn't limited to atomic bomb blasts. There's a lot of detailed bass *lines* in their too. >>> all of these factors define a good musical sub, are there any need for them in HT ?<<< Yes. >>>My dealer told me that a sub which is meant to be used only for HT duties should have these 2 charastaristics: 1) being able to play in the highest SPL's. 2) being able to reproduce the lowest frequencies. except for these two factors, my dealer told me that all the other factors, which make a lot of difference in music reproduction, make almost no difference at all with movies. my dealer has no reason not to be honest with me, since he know that I am going to build the sub myself. Can I trust him on this ?<<< Ask your dealer which subwoofer's he may have heard that fall into each arena? Which are the *musical* subs, and which are the *HT-only* subs not having adequate... "tight, fast, precise, have good transient response, low group dealy and good frequency response" There's no reason a subwoofer that sounds great with music cannot sound great with film---and vice-versa. TV

#5 of 17 OFFLINE   Jack Gilvey

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Posted January 26 2001 - 07:49 AM

[quote]

Are there any benefits for an HT sub to be:
tight, fast, precise, have good transient response, low group dealy and good frequency response. all of these factors define a good musical sub, are there any need for them in HT ?

[quote]

A subwoofer is either going to accurately reproduce an input signal or it's not. Whether that's a T-rex footstep, or The Ox's Danelectro solo in "my Generation", I want to hear what was put into the recording.
Having said that, and to get to the heart of your question, I think that those qualities you mention above are less critical to enjoyment of home theater than music. Within reason,of course. I think the main reason for this is that we have no reference against which to judge much of we hear in a home theater environment ("wait a second, that's not what a helicopter plunging into a building sounds like ,this sucks!"). A cheap but capable sub, while not being quite exemplary in any area, can still add quite a bit to a HT, and really muck up music.
Of course, as Tom said, you don't have to trade extension for quality when building your own. Only when choosing a commercial sub on the cheap would I sacrifice one for the other.

I could be wrong,though.


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#6 of 17 OFFLINE   Jones_Rush

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Posted January 26 2001 - 11:29 AM

"Of course, as Tom said, you don't have to trade extension for quality when building your own. Only when choosing a commercial sub on the cheap would I sacrifice one for the other." Jack, Since I have a small room I am forced to use a sub with a sealed enclouse (If I want to get accurate,tight... bass). getting high SPL's and low frequencies from such a sub while still maintaining some of the benefits of a musical sub can only be done by using MONSTROUS enclosures. a sealed 300 liter sub (like some people here suggested) may sound very good in my small room for HT & music, the only problem is, I don't have space in that room for such a huge sub, 90 liter is the biggest I can go, and with that size, I can't get true HT performance. By using a vented 90 liter sub, I can reach frequencies of 16hz -3db in my small room, great for HT, the only problem is, the sound will NOT be : tight, fast, precise, have good transient response, low group dealy and good frequency response (due to limitations of the small room).

#7 of 17 ONLINE   Patrick Sun

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Posted January 26 2001 - 11:55 AM

Well, design a plug to plug up the port when you play music. Problem solved. Posted Image


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#8 of 17 OFFLINE   Jack Gilvey

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Posted January 26 2001 - 12:39 PM

[quote]

Since I have a small room I am forced to use a sub with a sealed enclouse (If I want to get accurate,tight... bass)...By using a vented 90 liter sub, I can reach frequencies of 16hz -3db in my small room, great for HT, the only problem is, the sound will NOT be : tight, fast, precise, have good transient response, low group dealy and good frequency response (due to limitations of the small room).


[quote]
I'm not really following you here as regards your room negatively affecting all of those parameters of a sub. Some room gain,yes. Do you mean that the small room is limiting your enclosure size?
There was no mention of a size restriction in your original post, or what driver you plan on using. If the 90l restriction is the primary consideration,why not try an isobaric design? You'd have to buy 2 drivers, but you'd then effectively have a 180 liter enclosure to play with. I think there have been some low-Q vented designs posted that would fit.
It sounds as if you've already concluded that a 90l good ht/good music sub is impossible. In that case,you'll have to choose between your sealed "tightness" or vented extension. If you can cross it over low enough, I'd take the extension.


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#9 of 17 OFFLINE   Jones_Rush

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Posted January 26 2001 - 06:05 PM

"It sounds as if you've already concluded that a 90l good ht/good music sub is impossible." No, I haven't concluded anything yet, I'm just following the explanations which I had been given so far. If people here tell me that I need a 260-300 liter enclosures for a sealed sub to sound good for HT in my small room, then the only thing I can do is to think that 90 liter won't suffice. If a 90 liter sealed can sound good in my room then I will be VERY happy, but if not, will it be possible to create a port then ? won't it be too late ? I mean with the enclosure being already glued and all...

#10 of 17 OFFLINE   Jack Gilvey

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Posted January 26 2001 - 08:07 PM

Well, you stated that 1) a 90l sealed sub won't give "true ht performance" and 2) a 90l vented sub will not be tight,fast,etc. I took that to be your conclusion, since they were your statements.
Please address the questions I posed in my last post so maybe we can find you a good design. To that end, what driver are these "people" suggesting you use in this "260-300 liter" enclosure? An Avatar Shiva in a 90 liter box will give a very good Q of 0.6 with extremely low GD and phase shift.
It will roll-off the deep bass compared to a comparably sized vented sub,though.
Have you read much on this, or at least downloaded a design program to see how it works? Try this . Play with it a bit, and see how box sizes and driver parameters affect the final design. It will make these exchanges much more productive for you.

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#11 of 17 OFFLINE   Greg Monfort

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Posted January 26 2001 - 10:29 PM

>Well, I will need bass management for the center speaker (only goes doen to 60hz) and for the surounds (the actual surround speakers go very low but the decoder can only see them as small). Why is that a problem ? ==== The LFE channel is supposed to only have simulated special effects when all the speakers are set to Large. When any are set to Small, then the LF music, etc. content is routed to the LFE channel too. As JG noted, it's not likely that you're going to be able to discern whether a concussive blast made on a synthesizer is derived from C-4, dynamite, exploding gas tanks, or some recording engr's vivid imagination, so a strictly LFE sub just needs to play loud and deep (high distortion can even enhance it some), but if it has to reproduce the LF BW of the music soundtrack, etc., too..... I don't know about you, but for me the quality of the music, etc., sountrack comes first, with the strictly LFE effects available secondary, though in the last few years drivers have become available at bargain basement prices that do a credible job of both. ==== >By using a vented 90 liter sub, I can reach frequencies of 16hz -3db in my small room, great for HT, the only problem is, the sound will NOT be : tight, fast, precise, have good transient response, low group dealy and good frequency response (due to limitations of the small room). ==== If you get -3dB/16Hz in-room/90L vented or sealed, it's because it's playing fairly low on average, with some EQ, as in quietly WRT HT levels. ==== >If a 90 liter sealed can sound good in my room then I will be VERY happy, but if not, will it be possible to create a port then ? won't it be too late ? I mean with the enclosure being already glued and all... ==== Of the sub drivers I compared, there's little difference between sealed/vented in 90L, so it's probably not worth the effort to vent. GM ------------------ Loud is beautiful, if it's clean
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#12 of 17 OFFLINE   Jones_Rush

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Posted January 27 2001 - 08:44 AM

"I don't know about you, but for me the quality of the music, etc., sountrack comes first, with the strictly LFE effects available secondary," Well, according to my measures, my main speakers can go down to 28hz -3db in my room (they have 5.5" woofers), 28hz is low enough, I don't think that there are many songs in the world with lower then 28hz information (I listen mainly to mainstream music). So, a sub can't really add anything to my music, that's why I'm considering it purely for HT.

#13 of 17 OFFLINE   Stan Marcewicz

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Posted January 27 2001 - 09:19 AM

>>>Well, according to my measures, my main speakers can go down to 28hz -3db in my room<<< A speaker's "extension" is often considered to be the point where the bass reaches half power or -3 dB below the (presumably linear) higher freqs. The trouble is that you can measure this at any SPL you want more or less. So you can get 3 inch woofers to put out 20 Hz at useless, inaudible levels for example. BTW the audibility threshold for 20 Hz is around 78 dB if memory serves. Is the 28 Hz reproduced cleanly and at a useful SPL? Don't forget that if you send 28 Hz to a speaker and then measure the SPL that this will also include any noise or distorion as part of the SPL. Since it can't discriminate. Some advantages to subs: 1) Gaining bass extension and clean output. 2) Freeing up your mains to handle "easier" higher freqs with additional headroom. Less distortion and strain at a given listening level. Especially if the woof extends well into the midrange. 3)Additional placement options. It is not often that the best location for bass exactly coincides with the best location for imaging. A huge point. Since yo can find the individual best loactions. And have a wider sweet spot in some cases. (more seating positions with high quality sound). 4) Director's or Producer's intent - HT or Music mixed with a sub in the studio might be best reproduced with a sub rather than downmixed. 5) If you find that different XO, level, bass magt options are better for certain program material, a good remote with a macro can get you set up with one button push. 6) Other stuff I forgot about. Stan

#14 of 17 OFFLINE   Jack Gilvey

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Posted January 27 2001 - 11:29 AM

[quote]

Well, according to my measures, my main speakers can go down to 28hz -3db in my room (they have 5.5" woofers),

[quote]
Very nice! What speakers are they, and how did you "measure" them?

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#15 of 17 OFFLINE   Jones_Rush

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Posted January 27 2001 - 01:15 PM

I used a Radio-Shack SPL meter, and played frequency tones from my computer (using a tone generator program) and from my DVD using a special cd (I used two SPL meters, both from radio shack, in order to make sure the readings were authentic + I used the correction numbers to compensate for the SPL meter anomalies). I think most of you never heard about my speakers, they are from a small Thai company named "nOrh", It's their marble 9.0 version which use the Revelator drivers from ScanSpeak. They play very nice tunes for small cash. (actually I don't own the speakers yet, I used my friend's ones for measuring, I will get mine next week, hopefully...)

#16 of 17 OFFLINE   Jack Gilvey

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Posted January 27 2001 - 02:12 PM

Actually, I have heard things about them. Very good things,in fact.

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#17 of 17 OFFLINE   Greg Monfort

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Posted January 27 2001 - 02:33 PM

Yes, unless you listen to organ or electronic music, the lowest fundamental is the piano and double bassoon's 27.5Hz, though there are subharmonics down into the single digits. Saying that there's nothing worth reproducing below the music's fundamentals is like saying there's no need to reproduce the upper harmonics beyond ~10kHz IMO. Of course if the medium, such as vinyl, doesn't have any information below ~25Hz, then it's moot. Posted Image CD/DVDs OTOH, often have much lower musical content.

Anyway, since 5.5" drivers don't have sufficient Vd to generate HT SPL levels in the lower octaves, especially with low distortion, the sub has to take up the slack.

GM


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