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Thread: Full range speaker to 20Hz?

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    Full range speaker to 20Hz?

    Why is it that there is no Harman products (full range speakers) that are designed to go flat to 20Hz (3db down at 20Hz anechoic)

    I understand that a 3 cu ft speaker designed to go flat to 20Hz would have a low sensitivity (maybe 84 db). I also understand that JBL (Harman group) has a reputation for high sensitivity systems. And people have the option to utilize a sub woofer for low frequency extension.

    With all of that said, why is it that there is no products (full range speakers) that are designed to go flat to 20Hz?

    The only 2 possible answers that came to mind is:
    1. There isn’t much demand for this type of product
    2. It is extremely difficult to engineer

    Any thoughts why it is difficult to find such a product? I am assuming that it would be attractive to at least some people.

    PS: I am referring to a consumer type passive speaker (speakers with no internal amp, no DSP etc). I also realize that “in room response” of many speakers will measure down to 20Hz but I am looking for anechoic response to 20Hz.

    PSS: If it would be more appropriate for me to post this in a different forum (sub group) let me know. I am a newbie

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    Administrator Mr. Widget's Avatar
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    Welcome newbie and you picked a perfect place to post.

    I recently measured some passive subs with true flat to 20Hz bass. These units are about 100 cu ft each with four 12" or 15" drivers per cabinet and are in a transmission line configuration. The speakers were built into a client's home permanently built under a pair of staircases in their Great Room. I was testing them to see if they were worth keeping... they definitely were!

    I have never met another speaker that actually was flat to 20Hz without some form of EQ. I realize these speakers are not a full range system, but I mention them because it gives you an idea of what is required to produce true 20Hz response and have some level of usable output.


    Also, I imagine in most cases a speaker that is truly anechoically flat (a 4 pi measurement) to 20Hz would be very bass heavy in a normal 2 pi setting.


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    Quote Originally Posted by Mr. Widget View Post
    Welcome newbie and you picked a perfect place to post.

    I recently measured some passive subs with true flat to 20Hz bass. These units are about 100 cu ft each with four 12" or 15" drivers per cabinet and are in a transmission line configuration. The speakers were built into a client's home permanently built under a pair of staircases in their Great Room. I was testing them to see if they were worth keeping... they definitely were!

    I have never met another speaker that actually was flat to 20Hz without some form of EQ. I realize these speakers are not a full range system, but I mention them because it gives you an idea of what is required to produce true 20Hz response and have some level of usable output.


    Also, I imagine in most cases a speaker that is truly anechoically flat (a 4 pi measurement) to 20Hz would be very bass heavy in a normal 2 pi setting.


    Widget
    I am sorry because I wasn't sure if I should "Reply With Quote" or "Reply to Thread" Newbie

    If you don't mind me asking, what was the estimated sensitivity of that 100 cu ft system? Did the woofers have identical crossovers or did they have low pass filters at different frequencies (helper woofers)?

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    Administrator Mr. Widget's Avatar
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    I didn’t take any measurements that would give me an accurate sensitivity since these will be in a multi amp system, it really doesn’t matter. If I had to guess I would say probably 90dB 1watt/meter per driver. I measured all 8 woofers independently.

    The existing networks were discarded as we will be using new amps with built in DSP. The woofers are wired as two identical pairs of paralleled drivers, they are all running full range and will require two amplification channels per woofer cabinet.

    Due to the natural filtering of the front loaded transmission line they roll off naturally above about 200Hz.


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    Quote Originally Posted by Mr. Widget View Post
    Welcome newbie and you picked a perfect place to post.

    I recently measured some passive subs with true flat to 20Hz bass. These units are about 100 cu ft each with four 12" or 15" drivers per cabinet and are in a transmission line configuration. The speakers were built into a client's home permanently built under a pair of staircases in their Great Room. I was testing them to see if they were worth keeping... they definitely were!

    I have never met another speaker that actually was flat to 20Hz without some form of EQ. I realize these speakers are not a full range system, but I mention them because it gives you an idea of what is required to produce true 20Hz response and have some level of usable output.


    Also, I imagine in most cases a speaker that is truly anechoically flat (a 4 pi measurement) to 20Hz would be very bass heavy in a normal 2 pi setting.


    Widget
    In regards to your comment about a system that measures flat in a 4pi environment then listening to it in 2 pi setting:

    I think that it can potentially sound very nice. Obviously if the frequencies between 100Hz to 300Hz are exaggerated, they will sound very boomy. But if the frequencies between 20hz to 60hz are accentuated, it could be a desirable effect. I would maybe depend on the size and acoustics of the room. Some recording studios are mixing with monitors that measure flat down to 20Hz (4pi) like JBL M2 and PMC BB7 as an example. I have listened to systems with nice powered subs that were correctly integrated measuring flat to 20hz that sounded good. Maybe other people would not agree with me on that point but that is my experience.

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    Quote Originally Posted by Mr. Widget View Post
    I didn’t take any measurements that would give me an accurate sensitivity since these will be in a multi amp system, it really doesn’t matter. If I had to guess I would say probably 90dB 1watt/meter per driver. I measured all 8 woofers independently.

    The existing networks were discarded as we will be using new amps with built in DSP. The woofers are wired as two identical pairs of paralleled drivers, they are all running full range and will require two amplification channels per woofer cabinet.

    Due to the natural filtering of the front loaded transmission line they roll off naturally above about 200Hz.


    Widget
    That sounds like a very fun project. Were you able to get any ground plane measurements using an LMS?

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    Quote Originally Posted by Steve C 2020 View Post
    That sounds like a very fun project. Were you able to get any ground plane measurements using an LMS?
    Maybe if you built them in the house, it would have been impossible to get GP measurements before installing them. It is not easy to put a 100 cu ft box on a hand truck and move it around. lol.

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Steve C 2020 View Post
    Maybe if you built them in the house, it would have been impossible to get GP measurements before installing them. It is not easy to put a 100 cu ft box on a hand truck and move it around. lol.


    Yes, I couldn’t even see the drivers, much less move the beasts. Several walls and a built in safe would have to be moved to get to them!


    I have never performed a ground plane measurement. Not to discount their usefulness, but I have found close mic measurements during a system design project or spatially averaging 8-9 measurements of a finished system are easy and give me the info I need.


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    Senior Member HCSGuy's Avatar
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    Years ago, I used to sell Definitive Technology speakers, which were known for putting subwoofers into everything - tower speakers with a powered sub in the bottom, even some of their center speakers had a subwoofer. While these don’t strictly fit your definition, as they got close to 20hz only by being powered and EQ’d, they were full range towers. However, it was very rare that we got good bass and good imaging with the speakers in the same place. Telling someone who just dropped $3k on powered towers that you think they should buy an additional subwoofer it not usually appreciated, but was often the case. I think 20hz towers are rare just because 40hz towers with an additional really good subwoofer or two are usually easier to get to sound good.
    That the internet contains a blog documenting your life does not constitute proof that your existence is valid. Sorry.

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by HCSGuy View Post
    However, it was very rare that we got good bass and good imaging with the speakers in the same place. Telling someone who just dropped $3k on powered towers that you think they should buy an additional subwoofer it not usually appreciated, but was often the case.
    In the 2 channel world adding subs is usually frowned upon, but yes most of us have rooms that are a real challenge.

    Even in the better purpose built home theaters that I work on we have significant acoustic modeling and testing... which we use to locate subs. Typically we are also using 4 or more subs ideally located in corners or mid walls room dependent and very separate from the other speakers!


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    Quote Originally Posted by Mr. Widget View Post


    Yes, I couldn’t even see the drivers, much less move the beasts. Several walls and a built in safe would have to be moved to get to them!


    I have never performed a ground plane measurement. Not to discount their usefulness, but I have found close mic measurements during a system design project or spatially averaging 8-9 measurements of a finished system are easy and give me the info I need.


    Widget
    WOW! That sounds like a very complex installation. I cant imagine designing 100 cu ft TL cabinet.
    I thought that a GP measurement is more accurate for determining what the speaker sounds like in the listening position (for people who don't have access to a Anechoic chamber) but maybe that is not true. I was under the impression that JBL engineers often use that method for there low frequency measurements. It also seems hard to measure the sensitivity with close miking.

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    Quote Originally Posted by HCSGuy View Post
    Years ago, I used to sell Definitive Technology speakers, which were known for putting subwoofers into everything - tower speakers with a powered sub in the bottom, even some of their center speakers had a subwoofer. While these don’t strictly fit your definition, as they got close to 20hz only by being powered and EQ’d, they were full range towers. However, it was very rare that we got good bass and good imaging with the speakers in the same place. Telling someone who just dropped $3k on powered towers that you think they should buy an additional subwoofer it not usually appreciated, but was often the case. I think 20hz towers are rare just because 40hz towers with an additional really good subwoofer or two are usually easier to get to sound good.
    You make a good point. sometimes it is nice to be able to locate the subs in a different spot than the full range speakers and typically use an active EQ at 80 Hz. It is more flexible and you have more control over the low frequency volume. With that said, do you think there would be any advantage to a 4 cu ft speaker (for example) that was + - 1.5db 20 - 20Khz? You wouldn't need to be concerned with things like if the phase of the sub was in sink with the FR speakers and other integration issues.

    I didn't understand your comment "it was very rare that we got good bass and good imaging with the speakers in the same place" Maybe you were talking about placing the FR speakers and the subwoofer in close proximity to each other.

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    Quote Originally Posted by Steve C 2020 View Post
    I didn't understand your comment "it was very rare that we got good bass and good imaging with the speakers in the same place"
    He is talking about speaker placement. When you set up the speakers for ideal imaging in the room, relative to the listening position, room boundaries, reflections etc., you may find that the low frequency room modes or nulls may not be fall where you like. If you move subs around in the room separately to the main speakers you have greater flexibility and can get the best bass and imaging.


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    Quote Originally Posted by Steve C 2020 View Post
    WOW! That sounds like a very complex installation. I cant imagine designing 100 cu ft TL cabinet.
    I thought that a GP measurement is more accurate for determining what the speaker sounds like in the listening position (for people who don't have access to a Anechoic chamber) but maybe that is not true. I was under the impression that JBL engineers often use that method for there low frequency measurements. It also seems hard to measure the sensitivity with close miking.
    It was a very advanced custom install system with 3' ribbons on four walls with 12" infinite baffle helper woofers mounted in the floor directly below each ribbon and the pair of massive subs.

    Unfortunately I never got to hear it. The system was already in need of repair/replacement by the time our client bought the house. Luckily after testing the subs, I was able to establish that while someone had mis-wired part of it, they were still quite good.

    Regarding ground plane measurements, they are a very good way to measure bass, but they must be made outdoors or in a very large room. You do not want any additional planes beyond the one you are using.

    Regarding measuring sensitivity, I have never found measuring sensitivity particularly important. Relative sensitivity is usually quickly established and that is all I have ever needed to know. I guess if I was a speaker manufacturer, I would bother to measure the drive voltage and calculate the sensitivity, but I am not.


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    Quote Originally Posted by Mr. Widget View Post
    In the 2 channel world adding subs is usually frowned upon, but yes most of us have rooms that are a real challenge.

    Even in the better purpose built home theaters that I work on we have significant acoustic modeling and testing... which we use to locate subs. Typically we are also using 4 or more subs ideally located in corners or mid walls room dependent and very separate from the other speakers!


    Widget
    Yes I think that a full range tower speaker would be more popular in the 2 channel world. I noticed that the Definitive technology DEMAND D17 is -3db 43 Hz and they have aluminum tweeters. Do you think they have the sound quality of a good HIFI tower speaker? I wonder what a nice pair of tower speakers (like Revel Salon 2 -3db at 23Hz) would sound like in a listening room running 2 channel. I am guessing that the Salon speakers have a max SPL of 105db @ 23Hz. Do you think they would sound as good as a sat / sub combo? I think that you are probably right about placing the low frequency drivers in the corner of the room but I still would like to do an A - B comparison. What do you think?

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